KR20250012518A - Method and apparatus for transmitting and receiving synchronization signal block and system information - Google Patents

Abstract

A method and device for transmitting and receiving SSB and SI are disclosed. The method of a terminal includes a step of receiving on-demand SSB transmission configuration information from a first base station to which the terminal is connected, and a step of receiving on-demand SSB from a second base station based on the on-demand SSB transmission configuration information, wherein the on-demand SSB transmission configuration information includes at least one of capability information of the second base station, on-demand SSB resource information, the number of on-demand SSB transmissions, on-demand SSB transmission instructions, or CSI configuration information.

Description

{METHOD AND APPARATUS FOR TRANSMITTING AND RECEIVING SYNCHRONIZATION SIGNAL BLOCK AND SYSTEM INFORMATION}

The present disclosure relates to communication technology, and more particularly, to technology for transmitting and receiving on demand SSB (synchronization signal block) and SI (system information).

In order to process the rapidly increasing wireless data, a communication system (e.g., a new radio (NR) communication system) using a higher frequency band (e.g., a frequency band higher than 6 GHz) than the frequency band (e.g., a frequency band lower than 6 GHz) of the LTE (long term evolution) communication system (or LTE-A communication system) is being considered. The NR communication system can support not only the frequency band higher than 6 GHz but also the frequency band lower than 6 GHz, and can support various communication services and scenarios compared to the LTE communication system. In addition, the requirements of the NR communication system may include eMBB (enhanced Mobile BroadBand), URLLC (Ultra Reliable Low Latency Communication), mMTC (massive Machine Type Communication), etc.

Meanwhile, the base station may periodically transmit SSB (synchronization signal block). The terminal may receive SSB from the base station and perform an initial access procedure (e.g., synchronization procedure) based on the SSB. Due to the periodic SSB transmission, the energy consumption of the base station may increase. A method of transmitting SSB to reduce the energy consumption of the base station may be required.

The purpose of the present disclosure to solve the above problems is to provide a method and device for transmitting and receiving SSB (synchronization signal block) and SI (system information).

A method of a terminal according to embodiments of the present disclosure for achieving the above object comprises the steps of: receiving on-demand SSB transmission configuration information from a first base station to which the terminal is connected; and receiving an on-demand SSB from a second base station based on the on-demand SSB transmission configuration information, wherein the on-demand SSB transmission configuration information includes at least one of capability information of the second base station, on-demand SSB resource information, the number of on-demand SSB transmissions, an on-demand SSB transmission instruction, or CSI configuration information.

The above capability information may include at least one of a cell ID of the second base station, a system bandwidth, numerology, a number of beams, or antenna configuration.

The on-demand SSB resource information may include at least one of time resource information for on-demand SSB transmission, frequency resource information for the on-demand SSB transmission, period information of the on-demand SSB transmission, information on when actual transmission of the on-demand SSB starts, or information on when actual transmission of the on-demand SSB ends.

The above time resource information may include at least one of an SFN, a half radio frame indicator, a subframe index, a slot index, or information about an actually transmitted SSB.

The above frequency resource information may include at least one of information about a synchronization raster or information about an ARFCN.

The above-mentioned on-demand SSB transmission instruction may be information indicating activation of the second base station.

The above CSI setting information may include resource information for reporting CSI generated based on the measurement results of the on-demand SSB.

The above-mentioned on-demand SSB can be a cell-defined SSB or a non-cell-defined SSB.

The above on-demand SSB can be received at frequency locations other than the synchronous raster.

If the on-demand SSB is a cell-defined SSB, the on-demand SSB may include a first barring indicator, and the first barring indicator may be used to block a legacy terminal from accessing the second base station.

If the terminal is a terminal capable of receiving the on-demand SSB, the terminal may ignore the first barring indicator included in the on-demand SSB, and the terminal may determine whether to barge the second base station based on the second barring indicator included in the RMSI received from the second base station.

According to embodiments of the present disclosure for achieving the above object, a method of a first base station includes a step of generating on-demand SSB transmission configuration information including at least one of capability information of a second base station, on-demand SSB resource information, the number of on-demand SSB transmissions, on-demand SSB transmission instructions, or CSI configuration information, and a step of transmitting the on-demand SSB transmission configuration information to a terminal, wherein an on-demand SSB based on the on-demand SSB transmission configuration information is transmitted from the second base station to the terminal.

The above capability information may include at least one of a cell ID of the second base station, a system bandwidth, numerology, a number of beams, or antenna configuration.

The on-demand SSB resource information may include at least one of time resource information for on-demand SSB transmission, frequency resource information for the on-demand SSB transmission, period information of the on-demand SSB transmission, information on when actual transmission of the on-demand SSB starts, or information on when actual transmission of the on-demand SSB ends.

If the on-demand SSB is a cell-defined SSB, the on-demand SSB may include a first barring indicator, and the first barring indicator may be used to block a legacy terminal from accessing the second base station.

The method of the first base station may further include, if a synchronization procedure between the terminal and the second base station is not completed, a step of generating modified on-demand SSB transmission configuration information, a step of transmitting the modified on-demand SSB transmission configuration information to the second base station, and a step of transmitting the modified on-demand SSB transmission configuration information to the terminal, wherein the on-demand SSB based on the modified on-demand SSB transmission configuration information may be retransmitted from the second base station to the terminal.

According to embodiments of the present disclosure for achieving the above object, a method of a second base station includes the steps of receiving on-demand SSB transmission configuration information from a first base station, and transmitting an on-demand SSB to a terminal based on the on-demand SSB transmission configuration information, wherein the on-demand SSB transmission configuration information includes at least one of capability information of the second base station, on-demand SSB resource information, the number of on-demand SSB transmissions, an on-demand SSB transmission instruction, or CSI configuration information.

The above capability information may include at least one of a cell ID of the second base station, a system bandwidth, numerology, a number of beams, or antenna configuration.

The on-demand SSB resource information may include at least one of time resource information for on-demand SSB transmission, frequency resource information for the on-demand SSB transmission, period information of the on-demand SSB transmission, information on when actual transmission of the on-demand SSB starts, or information on when actual transmission of the on-demand SSB ends.

The method of the second base station includes the steps of receiving modified on-demand SSB transmission configuration information from the first base station when a synchronization procedure between the terminal and the second base station is not completed, and the steps of retransmitting the on-demand SSB to the terminal based on the modified on-demand SSB transmission configuration information.

According to the present disclosure, a macro base station can generate on-demand SSB (synchronization signal block) transmission configuration information, and can transmit the on-demand SSB transmission configuration information to a small cell and/or a terminal. The small cell can transmit an on-demand SSB to the terminal based on the on-demand SSB transmission configuration information. The terminal can receive the on-demand SSB from the small cell based on the on-demand SSB transmission configuration information. According to the above operation, since the SSB (e.g., the on-demand SSB) can be transmitted upon the request of the terminal, the signaling overhead of the SSB transmission and the energy consumption due to the SSB transmission can be reduced. Therefore, the performance of the communication system can be improved.

Figure 1 is a conceptual diagram illustrating embodiments of a communication system.
FIG. 2 is a block diagram illustrating embodiments of communication nodes constituting a communication system.
Figure 3 is a conceptual diagram illustrating embodiments of a type 1 frame structure.
Figure 4 is a conceptual diagram illustrating embodiments of a type 2 frame structure.
FIG. 5 is a conceptual diagram illustrating embodiments of a first transmission method of an SS/PBCH block in a communication system.
Figure 6 is a conceptual diagram illustrating embodiments of SS/PBCH blocks in a communication system.
FIG. 7 is a conceptual diagram illustrating embodiments of a second transmission method of an SS/PBCH block in a communication system.
Figure 8 is a conceptual diagram illustrating embodiments of SSB burst settings.
Figure 9a is a conceptual diagram illustrating RMSI CORESET mapping pattern #1 in a communication system.
Figure 9b is a conceptual diagram illustrating RMSI CORESET mapping pattern #2 in a communication system.
Figure 9c is a conceptual diagram illustrating RMSI CORESET mapping pattern #3 in a communication system.
Figure 10 is a conceptual diagram illustrating examples of slot configurations in which PSFCH is set.
Figure 11 is a conceptual diagram illustrating embodiments of PSFCH for ACK/NACK transmission.
FIG. 12 is a conceptual diagram illustrating embodiments of a method for multiplexing control channels and data channels in sidelink communication.
Figure 13 is a conceptual diagram illustrating embodiments of resource selection operations.
Figure 14 is a conceptual diagram illustrating embodiments of resource re-selection operations.
Figure 15 is a conceptual diagram illustrating deployment scenarios of a communication system.
Figures 16a and 16b are conceptual diagrams illustrating SSB transmission of a small cell at preset time intervals (e.g., transmission periods).
Figures 17a, 17b, and 17c are conceptual diagrams illustrating SSB transmission of a small cell in flexible time intervals (e.g., flexible transmission periods).
Figure 18 is a flowchart illustrating embodiments of a transmission method of on-demand SSB.
Figure 19 is a conceptual diagram illustrating embodiments of S-SSB transmission and C-WUS transmission.

The present disclosure may have various modifications and various embodiments, and specific embodiments are illustrated in the drawings and described in detail. However, this is not intended to limit the present disclosure to specific embodiments, but should be understood to include all modifications, equivalents, or substitutes included in the spirit and technical scope of the present disclosure.

The terms first, second, etc. may be used to describe various components, but the components should not be limited by the terms. The terms are only used to distinguish one component from another. For example, without departing from the scope of the present disclosure, the first component could be referred to as the second component, and similarly, the second component could also be referred to as the first component. The term "and/or" includes any combination of a plurality of related listed items or any item among a plurality of related listed items.

In embodiments of the present disclosure, “at least one of A and B” can mean “at least one of A or B” or “at least one of combinations of one or more of A and B.” Furthermore, in embodiments of the present disclosure, “at least one of A and B” can mean “at least one of A or B” or “at least one of combinations of one or more of A and B.”

When it is said that a component is "connected" or "connected" to another component, it should be understood that it may be directly connected or connected to that other component, but that there may be other components in between. On the other hand, when it is said that a component is "directly connected" or "directly connected" to another component, it should be understood that there are no other components in between.

The terminology used in this disclosure is only used to describe specific embodiments and is not intended to be limiting of the present disclosure. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this disclosure, it should be understood that the terms "comprises" or "has" and the like are intended to specify that a feature, number, step, operation, component, part or combination thereof described in the specification is present, but do not exclude in advance the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts or combinations thereof.

Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Terms defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning they have in the context of the relevant art, and will not be interpreted in an idealized or overly formal sense unless expressly defined in this disclosure.

Hereinafter, with reference to the attached drawings, preferred embodiments of the present disclosure will be described in more detail. In order to facilitate an overall understanding in describing the present disclosure, the same reference numerals are used for the same components in the drawings, and redundant descriptions of the same components are omitted.

A communication system to which embodiments according to the present disclosure are applied will be described. The communication system may be a 4G communication system (e.g., a long-term evolution (LTE) communication system, LTE-A communication system), a 5G communication system (e.g., a new radio (NR) communication system), a 6G communication system, etc. The 4G communication system can support communication in a frequency band of 6 GHz or less, and the 5G communication system can support communication in a frequency band of 6 GHz or more as well as a frequency band of 6 GHz or less. The communication system to which embodiments according to the present disclosure are applied is not limited to the contents described below, and the embodiments according to the present disclosure can be applied to various communication systems. Here, the communication system may be used with the same meaning as a communication network, and "LTE" may indicate a "4G communication system", an "LTE communication system", or an "LTE-A communication system", and "NR" may indicate a "5G communication system" or an "NR communication system".

In an embodiment, "an operation (e.g., a transmission operation) is set to a communication node" may mean that "setting information for the operation (e.g., an information element, a parameter)" and/or "information instructing performance of the operation" are signaled to the communication node. In other words, "an operation (e.g., a transmission operation) is set to a communication node" may mean that the communication node receives "setting information for the operation (e.g., an information element, a parameter)" and/or "information instructing performance of the operation." "An information element (e.g., a parameter) is set to a communication node" may mean "the information element is signaled to the communication node (e.g., the communication node receives the information element)." The signaling may be at least one of system information (SI) signaling (e.g., transmission of system information block (SIB) and/or master information block (MIB)), RRC signaling (e.g., transmission of RRC parameters and/or higher layer parameters), MAC control element (CE) signaling, or PHY signaling (e.g., transmission of downlink control information (DCI), uplink control information (UCI), and/or sidelink control information (SCI)).

In the present disclosure, the transmission point in time may mean the transmission start point in time or the transmission end point in time, and the reception point in time may mean the reception start point in time or the reception end point in time. The time point may mean time. In other words, the time point and time may be used with the same meaning.

In the present disclosure, even if a method (e.g., transmitting or receiving a signal) performed by a first communication node among communication nodes is described, a second communication node corresponding thereto can perform a method (e.g., receiving or transmitting a signal) corresponding to the method performed by the first communication node. For example, if an operation of a terminal is described, a base station corresponding to the terminal can perform an operation corresponding to the operation of the terminal. Conversely, if an operation of a base station is described, a terminal corresponding to the base station can perform an operation corresponding to the operation of the base station. In addition, if an operation of a first terminal is described, a second terminal corresponding to the first terminal can perform an operation corresponding to the operation of the first terminal. Conversely, if an operation of a second terminal is described, a first terminal corresponding to the second terminal can perform an operation corresponding to the operation of the second terminal.

Figure 1 is a conceptual diagram illustrating embodiments of a communication system.

Referring to FIG. 1, the communication system (100) may include a plurality of communication nodes (110-1, 110-2, 110-3, 120-1, 120-2, 130-1, 130-2, 130-3, 130-4, 130-5, 130-6). In addition, the communication system (100) may further include a core network (e.g., a serving-gateway (S-GW), a packet data network (PDN)-gateway (P-GW), a mobility management entity (MME)). If the communication system (100) is a 5G communication system (e.g., a new radio (NR) system), the core network may include an access and mobility management function (AMF), a user plane function (UPF), a session management function (SMF), etc.

A plurality of communication nodes (110 to 130) can support a communication protocol specified in a 3rd generation partnership project (3GPP) standard (e.g., LTE communication protocol, LTE-A communication protocol, NR communication protocol, etc.). The plurality of communication nodes (110 to 130) may support CDMA (code division multiple access) technology, WCDMA (wideband CDMA) technology, TDMA (time division multiple access) technology, FDMA (frequency division multiple access) technology, OFDM (orthogonal frequency division multiplexing) technology, Filtered OFDM technology, CP (cyclic prefix)-OFDM technology, DFT-s-OFDM (discrete Fourier transform-spread-OFDM) technology, OFDMA (orthogonal frequency division multiple access) technology, SC (single carrier)-FDMA technology, NOMA (non-orthogonal multiple access) technology, GFDM (generalized frequency division multiplexing) technology, FBMC (filter bank multi-carrier) technology, UFMC (universal filtered multi-carrier) technology, SDMA (space division multiple access) technology, etc. Each of the plurality of communication nodes may have the following structure.

FIG. 2 is a block diagram illustrating embodiments of communication nodes constituting a communication system.

Referring to FIG. 2, a communication node (200) may include at least one processor (210), a memory (220), and a transceiver device (230) that is connected to a network and performs communication. In addition, the communication node (200) may further include an input interface device (240), an output interface device (250), a storage device (260), etc. Each component included in the communication node (200) may be connected by a bus (270) and may communicate with each other.

However, each component included in the communication node (200) may be connected through an individual interface or individual bus centered around the processor (210), rather than a common bus (270). For example, the processor (210) may be connected to at least one of the memory (220), the transceiver (230), the input interface device (240), the output interface device (250), and the storage device (260) through a dedicated interface.

The processor (210) can execute a program command stored in at least one of the memory (220) and the storage device (260). The processor (210) may mean a central processing unit (CPU), a graphics processing unit (GPU), or a dedicated processor on which methods according to embodiments of the present disclosure are performed. Each of the memory (220) and the storage device (260) may be configured with at least one of a volatile storage medium and a nonvolatile storage medium. For example, the memory (220) may be configured with at least one of a read only memory (ROM) and a random access memory (RAM).

Referring again to FIG. 1, the communication system (100) may include a plurality of base stations (110-1, 110-2, 110-3, 120-1, 120-2) and a plurality of terminals (130-1, 130-2, 130-3, 130-4, 130-5, 130-6). Each of the first base station (110-1), the second base station (110-2), and the third base station (110-3) may form a macro cell. Each of the fourth base station (120-1) and the fifth base station (120-2) may form a small cell. The fourth base station (120-1), the third terminal (130-3), and the fourth terminal (130-4) may be within the cell coverage of the first base station (110-1). The second terminal (130-2), the fourth terminal (130-4), and the fifth terminal (130-5) may be within the cell coverage of the second base station (110-2). The fifth base station (120-2), the fourth terminal (130-4), the fifth terminal (130-5), and the sixth terminal (130-6) may be within the cell coverage of the third base station (110-3). The first terminal (130-1) may be within the cell coverage of the fourth base station (120-1). The sixth terminal (130-6) may be within the cell coverage of the fifth base station (120-2).

Here, each of the plurality of base stations (110-1, 110-2, 110-3, 120-1, 120-2) may be referred to as a NodeB (NB), an evolved NodeB (eNB), a gNB, an advanced base station (ABS), a high reliability-base station (HR-BS), a base transceiver station (BTS), a radio base station, a radio transceiver, an access point, an access node, a radio access station (RAS), a mobile multihop relay-base station (MMR-BS), a relay station (RS), an advanced relay station (ARS), a high reliability-relay station (HR-RS), a home NodeB (HNB), a home eNodeB (HeNB), a road side unit (RSU), a radio remote head (RRH), a transmission point (TP), a transmission and reception point (TRP), etc.

Each of the plurality of terminals (130-1, 130-2, 130-3, 130-4, 130-5, 130-6) may be referred to as a user equipment (UE), terminal equipment (TE), advanced mobile station (AMS), high reliability-mobile station (HR-MS), terminal, access terminal, mobile terminal, station, subscriber station, mobile station, portable subscriber station, node, device, OBU (on board unit), etc.

Meanwhile, each of the plurality of base stations (110-1, 110-2, 110-3, 120-1, 120-2) may operate in a different frequency band or may operate in the same frequency band. Each of the plurality of base stations (110-1, 110-2, 110-3, 120-1, 120-2) may be connected to each other via an ideal backhaul link or a non-ideal backhaul link, and may exchange information with each other via the ideal backhaul link or the non-ideal backhaul link. Each of the plurality of base stations (110-1, 110-2, 110-3, 120-1, 120-2) may be connected to a core network via an ideal backhaul link or a non-ideal backhaul link. Each of the plurality of base stations (110-1, 110-2, 110-3, 120-1, 120-2) can transmit a signal received from the core network to the corresponding terminal (130-1, 130-2, 130-3, 130-4, 130-5, 130-6), and can transmit a signal received from the corresponding terminal (130-1, 130-2, 130-3, 130-4, 130-5, 130-6) to the core network.

In addition, each of the plurality of base stations (110-1, 110-2, 110-3, 120-1, 120-2) may support MIMO transmission (e.g., single user (SU)-MIMO, multi user (MU)-MIMO, massive MIMO, etc.), coordinated multipoint (CoMP) transmission, carrier aggregation (CA) transmission, transmission in an unlicensed band, device to device communication (D2D) (or, proximity services (ProSe)), Internet of Things (IoT) communication, dual connectivity (DC), etc. Here, each of the plurality of terminals (130-1, 130-2, 130-3, 130-4, 130-5, 130-6) can perform an operation corresponding to the base station (110-1, 110-2, 110-3, 120-1, 120-2) and an operation supported by the base station (110-1, 110-2, 110-3, 120-1, 120-2). For example, the second base station (110-2) can transmit a signal to the fourth terminal (130-4) based on the SU-MIMO scheme, and the fourth terminal (130-4) can receive a signal from the second base station (110-2) by the SU-MIMO scheme. Alternatively, the second base station (110-2) can transmit signals to the fourth terminal (130-4) and the fifth terminal (130-5) based on the MU-MIMO method, and each of the fourth terminal (130-4) and the fifth terminal (130-5) can receive signals from the second base station (110-2) by the MU-MIMO method.

Each of the first base station (110-1), the second base station (110-2), and the third base station (110-3) can transmit a signal to the fourth terminal (130-4) based on the CoMP scheme, and the fourth terminal (130-4) can receive a signal from the first base station (110-1), the second base station (110-2), and the third base station (110-3) based on the CoMP scheme. Each of the plurality of base stations (110-1, 110-2, 110-3, 120-1, 120-2) can transmit and receive a signal with terminals (130-1, 130-2, 130-3, 130-4, 130-5, 130-6) within its cell coverage based on the CA scheme. Each of the first base station (110-1), the second base station (110-2), and the third base station (110-3) can control D2D between the fourth terminal (130-4) and the fifth terminal (130-5), and each of the fourth terminal (130-4) and the fifth terminal (130-5) can perform D2D under the control of the second base station (110-2) and the third base station (110-3).

Meanwhile, the communication system can support three types of frame structures. The Type 1 frame structure can be applied to an FDD (frequency division duplex) communication system, the Type 2 frame structure can be applied to a TDD (time division duplex) communication system, and the Type 3 frame structure can be applied to an unlicensed band-based communication system (e.g., a LAA (licensed assisted access) communication system).

Figure 3 is a conceptual diagram illustrating embodiments of a type 1 frame structure.

Referring to FIG. 3, a radio frame (300) may include 10 subframes, and a subframe may include 2 slots. Accordingly, the radio frame (300) may include 20 slots (e.g., slot #0, slot #1, slot #2, slot #3, ..., slot #18, slot #19). The length (T _f ) of the radio frame (300) may be 10 ms (milliseconds), the subframe length may be 1 ms, and the slot length (T _slot ) may be 0.5 ms. Here, T _s may indicate a sampling time and may be 1/30,720,000s (second).

A slot can be composed of a plurality of OFDM symbols in the time domain and a plurality of resource blocks (RBs) in the frequency domain. A resource block can be composed of a plurality of subcarriers in the frequency domain. The number of OFDM symbols constituting a slot can vary depending on the configuration of a cyclic prefix (CP). The CP can be classified into a normal CP and an extended CP. When a normal CP is used, a slot can be composed of 7 OFDM symbols, in which case a subframe can be composed of 14 OFDM symbols. When an extended CP is used, a slot can be composed of 6 OFDM symbols, in which case a subframe can be composed of 12 OFDM symbols.

Figure 4 is a conceptual diagram illustrating embodiments of a type 2 frame structure.

Referring to FIG. 4, a radio frame (400) may include two half frames, and a half frame may include five subframes. Therefore, a radio frame (400) may include ten subframes. The length (T _f ) of the radio frame (400) may be 10 ms. The length of a half frame may be 5 ms. The subframe length may be 1 ms. Here, T _s may be 1/30,720,000s.

The radio frame (400) may include a downlink subframe, an uplink subframe, and a special subframe. Each of the downlink subframe and the uplink subframe may include two slots. The slot length (T _slot ) may be 0.5 ms. Among the subframes included in the radio frame (400), each of subframe #1 and subframe #6 may be a special subframe. For example, when the downlink-uplink switching period is 5 ms, the radio frame (400) may include two special subframes. Alternatively, when the downlink-uplink switching period is 10 ms, the radio frame (400) may include one special subframe. The special subframe may include a downlink pilot time slot (DwPTS), a guard period (GP), and an uplink pilot time slot (UpPTS).

The downlink pilot time slot can be regarded as a downlink period and can be used for cell search of the terminal, acquisition of time and frequency synchronization, channel estimation, etc. The guard period can be used to solve an interference problem of uplink data transmission caused by a downlink data reception delay. In addition, the guard period can include a time required for switching from a downlink data reception operation to an uplink data transmission operation. The uplink pilot time slot can be used for uplink channel estimation, acquisition of time and frequency synchronization, etc. Transmission of a physical random access channel (PRACH) or a sounding reference signal (SRS) can be performed in the uplink pilot time slot.

The length of each of the downlink pilot time slot, guard interval, and uplink pilot time slot included in the special subframe can be variably adjusted as needed. In addition, the number and location of each of the downlink subframe, uplink subframe, and special subframe included in the radio frame (400) can be changed as needed.

In a communication system, a transmission time interval (TTI) may be a basic time unit for transmitting encoded data through a physical layer. A short TTI may be used to support low-latency requirements in the communication system. The length of the short TTI may be less than 1 ms. A conventional TTI having a length of 1 ms may be referred to as a base TTI or a regular TTI. In other words, the base TTI may consist of one subframe. In order to support transmission of the base TTI unit, signals and channels may be set on a subframe basis. For example, a cell-specific reference signal (CRS), a physical downlink control channel (PDCCH), a physical downlink shared channel (PDSCH), a physical uplink control channel (PUCCH), a physical uplink shared channel (PUSCH), etc. may exist in each subframe.

On the other hand, synchronization signals (e.g., primary synchronization signal (PSS), secondary synchronization signal (SSS)) can exist every 5 subframes, and physical broadcast channel (PBCH) can exist every 10 subframes. In addition, radio frames can be distinguished by a system frame number (SFN), and the SFN can be used to define transmission of a signal whose transmission period is longer than one radio frame (e.g., a paging signal, a reference signal for channel estimation, a signal indicating channel state information, etc.). The period of the SFN can be 1024.

In an LTE system, a PBCH may be a physical layer channel used for transmitting system information (e.g., a master information block (MIB)). The PBCH may be transmitted every 10 subframes. In other words, a transmission period of the PBCH may be 10 ms, and the PBCH may be transmitted once in a radio frame. The same MIB may be transmitted during four consecutive radio frames, and the MIB may be changed according to the situation of the LTE system after four consecutive radio frames. The transmission period of the same MIB may be referred to as a "PBCH TTI", and a PBCH TTI may be 40 ms. In other words, the MIB may be changed every PBCH TTI.

MIB can be composed of 40 bits. Among the 40 bits composing the MIB, 3 bits can be used to indicate the system bandwidth, 3 bits can be used to indicate PHICH (physical hybrid ARQ (automatic repeat request) indicator channel) related information, 8 bits can be used to indicate SFN, 10 bits can be set as reserved bits, and 16 bits can be used for CRC (cyclic redundancy check).

An SFN distinguishing a radio frame can be composed of a total of 10 bits (B9 to B0), and among the 10 bits, 8 most significant bits (B9 to B2) can be indicated by a PBCH (e.g., MIB). The 8 MSB bits (B9 to B2) of an SFN indicated by a PBCH (e.g., MIB) can be the same during four consecutive radio frames (e.g., PBCH TTI). The 2 least significant bits (LSB) bits (B1 to B0) of an SFN can be changed during four consecutive radio frames (e.g., PBCH TTI) and may not be explicitly indicated by the PBCH (e.g., MIB). The LSB 2 bits (B1 to B0) of SFN can be implicitly indicated by a scrambling sequence for PBCH (hereinafter referred to as “PBCH scrambling sequence”).

A gold sequence initialized with a cell ID as a PBCH scrambling sequence can be used, and the PBCH scrambling sequence can be initialized every four consecutive radio frames (e.g., PBCH TTI) according to mod(SFN,4). A PBCH transmitted in a radio frame corresponding to an SFN in which the LSB 2 bits (B1 to B0) are set to "00" can be scrambled by the gold sequence initialized with the cell ID. Thereafter, the gold sequences generated according to mod(SFN,4) can be used to scramble the PBCH transmitted in the radio frames in which the LSB 2 bits (B1 to B0) of the SFN are "01", "10", and "11".

Therefore, a terminal that acquires a cell ID during the initial cell search process can implicitly find out the values of the LSB 2 bits (B1 to B0) of an SFN (e.g., "00", "01", "10", "11") through the PBCH scrambling sequence during the decoding process of the PBCH (e.g., MIB). Based on the PBCH scrambling sequence, the terminal can use the LSB 2 bits (B1 to B0) of the SFN identified and the MSB 8 bits (B9 to B2) of the SFN indicated by the PBCH (e.g., MIB) to identify the SFN (e.g., the entire bits (B9 to B0) of the SFN).

Meanwhile, the communication system can support not only high transmission rates but also technical requirements for various service scenarios. For example, the communication system can support high transmission rates (enhanced Mobile BroadBand; eMBB), short transmission delay times (Ultra Reliable Low Latency Communication; URLLC), and massive terminal connectivity (massive Machine Type Communication; mMTC).

The subcarrier spacing of a communication system (e.g., an OFDM-based communication system) can be determined based on carrier frequency offset (CFO), etc. CFO can be caused by Doppler effect, phase drift, etc., and can increase in proportion to the operating frequency. Therefore, in order to prevent performance degradation of the communication system due to CFO, the subcarrier spacing can increase in proportion to the operating frequency. On the other hand, CP overhead can increase as the subcarrier spacing increases. Therefore, the subcarrier spacing can be set based on channel characteristics according to frequency band, RF (radio frequency) characteristics, etc.

The communication system can support the numerology defined in Table 1 below.

For example, the subcarrier spacing of a communication system can be set to 15 kHz, 30 kHz, 60 kHz, or 120 kHz. The subcarrier spacing of an LTE system can be 15 kHz, and the subcarrier spacing of an NR system can be 1, 2, 4, or 8 times the existing subcarrier spacing of 15 kHz. When the subcarrier spacing increases in units of an exponential multiple of 2 of the existing subcarrier spacing, the frame structure can be easily designed.

The communication system may support FR2 as well as FR1. FR2 may be classified into FR2-1 and FR2-2. FR1 may be a frequency band of 6 GHz or less, FR2-1 may be a band of 24.25 to 52.6 GHz, and FR2-2 may be a band of 52.6 to 71 GHz. In an embodiment, FR2 may be a frequency band including FR2-1, FR2-2, or FR2-1 and FR2-2. The subcarrier spacing available for data transmission in each of FR1, FR2-1, and FR2-2 may be defined as shown in Table 2 below. The subcarrier spacing available for SSB (synchronization signal block) transmission in each of FR1, FR2-1, and FR2-2 may be defined as shown in Table 3 below. The subcarrier spacing available for RACH (random access channel) transmission (e.g., Msg1 or Msg-A) in each of FR1, FR2-1, and FR2-2 can be defined as shown in Table 4 below.

A communication system can support a wide frequency band (for example, hundreds of MHz to tens of GHz). Since the diffraction characteristics and reflection characteristics of radio waves are not good in a high frequency band, propagation loss (for example, path loss, reflection loss, etc.) in a high frequency band may be greater than propagation loss in a low frequency band. Therefore, the cell coverage of a communication system supporting a high frequency band may be smaller than that of a communication system supporting a low frequency band. To solve this problem, a beamforming method based on a plurality of antenna elements may be used to increase cell coverage in a communication system supporting a high frequency band.

Beamforming schemes may include digital beamforming schemes, analog beamforming schemes, hybrid beamforming schemes, etc. In a communication system using a digital beamforming scheme, beamforming gain can be obtained by using a plurality of RF paths based on a digital precoder or codebook. In a communication system using an analog beamforming scheme, beamforming gain can be obtained by using an analog RF device (e.g., a phase shifter, a power amplifier (PA), a variable gain amplifier (VGA), etc.) and an antenna array.

Since an expensive digital to analog converter (DAC) or analog to digital converter (ADC) and transceiver units corresponding to the number of antenna elements are required for the digital beamforming method, the complexity of antenna implementation may increase to increase the beamforming gain. In a communication system using an analog beamforming method, since multiple antenna elements are connected to one transceiver unit through a phase shifter, the complexity of antenna implementation may not increase significantly even when the beamforming gain is increased. However, the beamforming performance of a communication system using an analog beamforming method may be lower than that of a communication system using a digital beamforming method. In addition, since the phase shifter in a communication system using an analog beamforming method is controlled in the time domain, frequency resources may not be used efficiently. Therefore, a hybrid beamforming method, which is a combination of a digital method and an analog method, may be used.

When cell coverage is increased by using a beamforming scheme, not only the control channel and data channel of each terminal, but also the common control channel and common signal (e.g., reference signal, synchronization signal) for all terminals belonging to the cell coverage can be transmitted based on the beamforming scheme. In this case, the common control channel and common signal for all terminals belonging to the cell coverage can be transmitted based on a beam sweeping scheme.

In addition, in the NR system, a SS/PBCH (synchronization block/physical broadcast channel) block can also be transmitted in a beam sweeping manner. The SS/PBCH block can be composed of a PSS, an SSS, a PBCH, etc., and the PSS, SSS, and PBCH within the SS/PBCH block can be configured in a TDM (time division multiplexing) manner. In an embodiment, the SS/PBCH block can be referred to as SSB. One SS/PBCH block can be transmitted using N consecutive OFDM symbols. Here, N can be an integer greater than or equal to 4. The base station can periodically transmit the SS/PBCH block, and the terminal can obtain frequency/time synchronization, cell ID, system information, etc. based on the SS/PBCH block received from the base station. The SS/PBCH block can be transmitted as follows.

FIG. 5 is a conceptual diagram illustrating embodiments of a first transmission method of an SS/PBCH block in a communication system.

Referring to FIG. 5, one or more SS/PBCH blocks in an SS/PBCH block burst set may be transmitted in a beam sweeping manner. A maximum of L SS/PBCH blocks may be transmitted in one SS/PBCH block burst set. L may be an integer greater than or equal to 2 and may be defined in the 3GPP standard. L may vary depending on a system frequency domain. SS/PBCH blocks may be positioned consecutively or distributedly in an SS/PBCH block burst set. Consecutive SS/PBCH blocks may be referred to as an "SS/PBCH block burst" or an "SSB burst." An SS/PBCH block burst set may be repeated periodically, and system information (e.g., MIB) transmitted through the PBCH of SS/PBCH blocks in an SS/PBCH block burst set may be the same. SS/PBCH block index, SS/PBCH block burst index, OFDM symbol index, slot index, etc. can be explicitly or implicitly indicated by PBCH.

Figure 6 is a conceptual diagram illustrating embodiments of SS/PBCH blocks in a communication system.

Referring to FIG. 6, the arrangement order within the SS/PBCH block may be "PSS → PBCH → SSS → PBCH". Within the SS/PBCH block, the PSS, SSS, and PBCH may be configured in a TDM manner. In a symbol where the SSS is located, the PBCH may be arranged in higher frequency resources than the SSS and lower frequency resources than the SSS. When the maximum number of SS/PBCH blocks is 8 in a frequency band lower than 6 GHz, the index of the SS/PBCH block may be identified based on a demodulation reference signal (DMRS) (hereinafter referred to as "PBCH DMRS") used for demodulation of the PBCH. When the maximum number of SS/PBCH blocks is 64 in a frequency band higher than 6 GHz, among the 6 bits indicating the index of the SS/PBCH block, the 3 LSB bits may be identified based on the PBCH DMRS, and the remaining 3 MSB bits may be identified based on the PBCH payload.

The maximum system bandwidth supportable in the NR system may be 400 MHz. The size of the maximum bandwidth supportable by the terminal may vary depending on the capability of the terminal. Therefore, the terminal may perform an initial access procedure (e.g., an initial connection procedure) using a portion of the system bandwidth of the NR system supporting a wideband. In order to support the access procedure of terminals supporting bandwidths of various sizes, the SS/PBCH blocks may be multiplexed along the frequency axis within the system bandwidth of the NR system supporting a wideband. In this case, the SS/PBCH blocks may be transmitted as follows.

FIG. 7 is a conceptual diagram illustrating embodiments of a second transmission method of an SS/PBCH block in a communication system.

Referring to FIG. 7, a wideband component carrier (CC) may include multiple bandwidth parts (BWPs). For example, a wideband CC may include four BWPs. A base station may transmit an SS/PBCH block in each of BWPs #0 to 3 belonging to the wideband CC. A terminal may receive an SS/PBCH block in one or more BWPs among BWPs #0 to 3, and may perform an initial access procedure using the received SS/PBCH block.

After detecting an SS/PBCH block, the terminal can obtain system information (e.g., RMSI (remaining minimum system information)) and perform a cell access procedure based on the system information. The RMSI can be transmitted through a PDSCH scheduled by a PDCCH. Configuration information of a CORESET (control resource set) on which a PDCCH including scheduling information of a PDSCH on which RMSI is transmitted can be transmitted through a PBCH in an SS/PBCH block. A plurality of SS/PBCH blocks can be transmitted in the entire system bandwidth, and one or more SS/PBCH blocks among the plurality of SS/PBCH blocks can be SS/PBCH blocks associated with RMSI. The remaining SS/PBCH blocks may not be associated with RMSI. An SS/PBCH block associated with RMSI can be defined as a "cell defining SS/PBCH block". The terminal can perform a cell search procedure and an initial access procedure using the cell defining SS/PBCH block. SS/PBCH blocks that are not associated with RMSI may be used for synchronization procedures and/or measurement procedures in the corresponding BWP. A BWP in which an SS/PBCH block is transmitted may be confined to one or more BWPs within a wide bandwidth.

The location where SSB is transmitted in the time domain can be defined differently depending on the subcarrier spacing (SCS) and the L value. In the embodiments, SCS can mean a subcarrier size. SSB can be transmitted in some symbols within a slot, and a short UL transmission (e.g., UCI (Uplink control information) transmission) can be performed in the remaining symbols that are not used for SSB transmission within a slot. When SSB is transmitted in a radio resource to which a large SCS (e.g., 120 kHz SCS or 240 kHz SCS) is applied, a gap can be set in the middle of consecutive slots including SSB to enable long UL transmission (e.g., transmission of URLLC traffic) at least every 1 ms.

Figure 8 is a conceptual diagram illustrating embodiments of SSB burst settings.

Referring to FIG. 8, in a transmission procedure of SSBs (e.g., SSB burst) in a radio resource to which 120 kHz SCS is applied, the base station can transmit SSBs in 8 consecutive slots. In a transmission procedure of SSBs in a radio resource to which 240 kHz SCS is applied, the base station can transmit SSBs in 16 consecutive slots. A gap for UL transmission in a radio resource to which 120 kHz SCS or 240 kHz SCS is applied can be set.

RMSI can be obtained by performing "an operation of obtaining configuration information of CORESET from an SS/PBCH block (e.g., PBCH) → an operation of detecting PDCCH based on the configuration information of CORESET → an operation of obtaining scheduling information of PDSCH from PDCCH → an operation of receiving RMSI via PDSCH." The transmission resource of PDCCH can be set by the configuration information of CORESET. The RMSI CORESET mapping pattern can be defined as follows. The RMSI CORESET can be a CORESET used for transmitting and receiving RMSI.

FIG. 9a is a conceptual diagram illustrating RMSI CORESET mapping pattern #1 in a communication system, FIG. 9b is a conceptual diagram illustrating RMSI CORESET mapping pattern #2 in a communication system, and FIG. 9c is a conceptual diagram illustrating RMSI CORESET mapping pattern #3 in a communication system.

Referring to FIGS. 9A to 9C, one RMSI CORESET mapping pattern among the RMSI CORESET mapping patterns #1 to 3 can be used, and detailed settings can be completed according to one RMSI CORESET mapping pattern. In the RMSI CORESET mapping pattern #1, the SS/PBCH block, the CORESET (e.g., RMSI CORESET), and the PDSCH (e.g., RMSI PDSCH) can be set in a TDM manner. The RMSI PDSCH can mean a PDSCH on which RMSI is transmitted. In the RMSI CORESET mapping pattern #2, the CORESET (e.g., RMSI CORESET) and the PDSCH (e.g., RMSI PDSCH) can be set in a TDM manner, and the PDSCH (e.g., RMSI PDSCH) can be set in a SS/PBCH block and an FDM (frequency division multiplexing) manner. In RMSI CORESET mapping pattern #3, CORESET (e.g., RMSI CORESET) and PDSCH (e.g., RMSI PDSCH) can be configured in TDM manner, and CORESET (e.g., RMSI CORESET) and PDSCH (e.g., RMSI PDSCH) can be configured in SS/PBCH block and FDM manner.

In frequency bands below 6 GHz, only RMSI CORESET mapping pattern #1 can be used. In frequency bands above 6 GHz, all of RMSI CORESET mapping patterns #1, #2, and #3 can be used. The numerology of SS/PBCH block can be different from the numerology of "RMSI CORESET and RMSI PDSCH". Here, the numerology can be subcarrier spacing. Any combination of numerologies in RMSI CORESET mapping pattern #1 can be used. Any combination of "SS/PBCH block, RMSI CORESET/PDSCH = 120 kHz, 60 kHz or 240 kHz, 120 kHz" can be used in RMSI CORESET mapping pattern #2. In RMSI CORESET mapping pattern #3, the combination of "SS/PBCH block, RMSI CORESET/PDSCH = 120kHz, 120kHz" can be used.

According to the combination of the numerology of the SS/PBCH block and the numerology of the RMSI CORESET/PDSCH, one RMSI CORESET mapping pattern may be selected from the RMSI CORESET mapping patterns #1-3. The configuration information of the RMSI CORESET may include tables A and B. Table A may indicate the number of RBs (resource blocks) of the RMSI CORESET, the number of symbols of the RMSI CORESET, and the offset between the RB of the SS/PBCH block (e.g., a start RB or an end RB) and the RB of the RMSI CORESET (e.g., a start RB or an end RB). Table B may indicate the number of search space sets per slot, the offset of the RMSI CORESET, and the OFDM symbol index in each of the RMSI CORESET mapping patterns. Table B may indicate information for configuring a monitoring occasion of the RMSI PDCCH. Each of Table A and Table B may consist of multiple tables. For example, Table A may include Tables 13-1 to 13-8 as specified in TS 38.213, and Table B may include Tables 13-9 to 13-13 as specified in TS 38.213. The size of each of Table A and Table B may be 4 bits.

In the NR system, PDSCH can be mapped to the time domain according to PDSCH mapping type A or B. PDSCH mapping type A and B can be defined as shown in Table 5 below.

Type A (e.g., PDSCH mapping type A) may be slot-based transmission. When Type A is used, the position of the start symbol of the PDSCH may be set to one of {0, 1, 2, 3}. When Type A and a normal CP are used, the number of symbols constituting the PDSCH (e.g., the duration of the PDSCH) may be set to one of 3 to 14 within the symbol boundary. Type B (e.g., PDSCH mapping type B) may be non slot-based transmission. When Type B is used, the position of the start symbol of the PDSCH may be set to one of 0 to 12. When Type B and a normal CP are used, the number of symbols constituting the PDSCH (e.g., the duration of the PDSCH) may be set to one of {2, 4, 7} within the symbol boundary. A DMRS (hereinafter referred to as “PDSCH DMRS”) for demodulating a PDSCH (e.g., data) may be determined based on an ID indicating a PDSCH mapping type (e.g., Type A, Type B) and a length. The ID may be defined differently depending on the PDSCH mapping type.

Meanwhile, NR-U (unlicensed) is being discussed in the NR standardization meeting. NR-U system can increase network capacity by improving the utilization of limited frequency resources. NR-U system can support operation in unlicensed bands (e.g., unlicensed spectrum).

In the NR-U system, a terminal can determine whether a signal is transmitted from a base station based on a DRS (Discovery Reference Signal) received from the base station, similarly to a general NR system. In an NR-U system in the SA (Stand-Alone) mode, a terminal can obtain synchronization and/or system information based on the DRS. In the NR-U system, the DRS can be transmitted according to the regulations of the unlicensed band (e.g., transmission band, transmission power, transmission time, etc.). For example, according to the OCB (Occupied Channel Bandwidth) regulations, a signal can be configured and/or transmitted so as to occupy 80% of the total channel bandwidth (e.g., 20 MHz).

In the NR-U system, a communication node (e.g., a base station, a terminal) may perform LBT (Listen Before Talk) before transmitting a signal and/or channel for coexistence with other systems. The signal may be a synchronization signal, a reference signal (e.g., DRS, DMRS, CSI (channel state information)-RS, PT (phase tracking)-RS, SRS (sounding reference signal)), etc. The channel may be a downlink channel, an uplink channel, a sidelink channel, etc. In embodiments, the signal may mean a "signal", a "channel", or "signal and channel". The LBT may be an operation to check whether a signal is transmitted by another communication node. If it is determined by the LBT that there is no transmission signal (e.g., if the LBT succeeds), the communication node may transmit a signal in an unlicensed band. If it is determined by the LBT that there is a transmission signal (e.g., if the LBT fails), the communication node may not transmit a signal in the unlicensed band. A communication node can perform LBT according to various categories before transmitting a signal. The category of LBT can vary depending on the type of transmitted signal.

Meanwhile, NR V2X (vehicular to everything) communication technology is being discussed at the NR standardization meeting. NR V2X communication technology can be a technology that supports communication between vehicles, communication between vehicles and infrastructure, and communication between vehicles and pedestrians based on D2D (device to device) communication technology. Technologies for reducing power consumption and improving reliability for NR V2X communication are being discussed.

NR V2X communication (e.g., sidelink communication) can be performed according to three transmission methods (e.g., unicast, broadcast, and groupcast). When the unicast method is used, a PC5-RRC connection can be established between a first terminal (e.g., a transmitting terminal that transmits data) and a second terminal (e.g., a receiving terminal that receives data), and the PC5-RRC connection can mean a logical connection for a pair between a source ID of the first terminal and a destination ID of the second terminal. The first terminal can transmit data (e.g., sidelink data) to the second terminal. When the broadcast method is used, the first terminal can transmit data to all terminals. When the groupcast method is used, the first terminal can transmit data to a group (e.g., a groupcast group) composed of a plurality of terminals. In SL communication (e.g., SL-U (unlicensed) communication), a transmitting terminal may mean a terminal that transmits data, and a receiving terminal may mean a terminal that receives data. SL-U communication may mean SL communication in an unlicensed band.

When a unicast scheme is used, the second terminal can transmit feedback information (e.g., ACK (acknowledgement) or NACK (negative ACK)) for data received from the first terminal to the first terminal. In the embodiments below, the feedback information may be referred to as "HARQ-ACK", "feedback signal", "PSFCH (physical sidelink feedback channel) signal", etc. When ACK is received from the second terminal, the first terminal can determine that the data has been successfully received at the second terminal. When NACK is received from the second terminal, the first terminal can determine that the second terminal has failed to receive the data. In this case, the first terminal can transmit additional information to the second terminal based on a HARQ (hybrid automatic repeat request) scheme. Alternatively, the first terminal can improve the reception probability of the data at the second terminal by retransmitting the same data to the second terminal.

When the broadcast method is used, the procedure for transmitting feedback information about the data may not be performed. For example, the system information may be transmitted in the broadcast method, and the terminal may not transmit feedback information about the system information to the base station. Therefore, the base station may not know whether the system information has been successfully received by the terminal. To solve this problem, the base station may periodically broadcast the system information.

When the groupcast method is used, the procedure for transmitting feedback information about data may not be performed. For example, necessary information may be transmitted periodically in the groupcast method without the procedure for transmitting feedback information. However, when the target and/or number of terminals participating in communication based on the groupcast method are limited, and the data transmitted in the groupcast method is data that must be received within a preset time (e.g., data sensitive to delay), the procedure for transmitting feedback information may also be required in the groupcast sidelink communication. The groupcast sidelink communication may mean sidelink communication performed in the groupcast method. When the procedure for transmitting feedback information is performed in the groupcast sidelink communication, data can be transmitted and received efficiently and stably.

In groupcast sidelink communication, two HARQ-ACK feedback schemes (e.g., a procedure for transmitting feedback information) may be supported. "If there are many receiving terminals in a sidelink group and service scenario 1 is supported", some receiving terminals belonging to a specific range within the sidelink group may transmit NACK through PSFCH when data reception fails. This scheme may be "groupcast HARQ-ACK feedback option 1". In service scenario 1, some receiving terminals belonging to a specific range may be allowed to receive in a best-effort manner instead of all receiving terminals within the sidelink group. Service scenario 1 may be an extended sensor scenario in which some receiving terminals belonging to a specific range need to receive the same sensor information from a transmitting terminal. In embodiments, a transmitting terminal may mean a terminal transmitting data, and a receiving terminal may mean a terminal receiving data.

"If the number of receiving terminals in a sidelink group is limited and service scenario 2 is supported", each of all receiving terminals belonging to the sidelink group can individually report HARQ-ACK for data through a separate PSFCH. This method may be "Groupcast HARQ-ACK feedback option 2". Since PSFCH resources are sufficient in service scenario 2, the transmitting terminal can monitor HARQ-ACK feedback of all receiving terminals belonging to the sidelink group, and reception of data can be guaranteed for all receiving terminals belonging to the sidelink group.

As with broadcast sidelink communication, data can be transmitted and received without HARQ-ACK feedback procedure in unicast sidelink communication and groupcast sidelink communication. In this case, to increase the probability of data reception, the transmitting terminal can retransmit data a preset number of times.

In all transmission modes (e.g., unicast transmission, groupcast transmission, broadcast transmission), whether to apply the HARQ-ACK feedback procedure can be fixedly or semi-fixedly configured to the terminal(s) through signaling (e.g., signaling of system information, PC5-RRC signaling, UE-specific RRC signaling, signaling of control information). In sidelink communication, HARQ-ACK feedback information can be transmitted in PSFCH. If PSSCH reception is successful, the receiving terminal can transmit ACK for PSSCH (e.g., data) in PSFCH. If PSSCH reception fails, the receiving terminal can transmit NACK for PSSCH (e.g., data) in PSFCH. PSFCH can be a channel for reporting ACK/NACK information (e.g., HARQ-ACK feedback) to the transmitting terminal. A resource region (e.g., PSFCH resource region) for PSFCH transmission (e.g., transmission of HARQ-ACK feedback) within a specific resource pool can be preset. The PSFCH (e.g., PSFCH resource, PSFH resource region) can be configured periodically. A PSFCH period for the PSFCH resource can be k slots (e.g., logical SL (sidelink) slots). k can be a natural number. For example, k can be 1, 2, or 4.

Figure 10 is a conceptual diagram illustrating examples of slot configurations in which PSFCH is set.

Referring to Fig. 10, within a slot (e.g., SL slot), a PSFCH (e.g., HARQ-ACK feedback) may be repeatedly transmitted in two symbols (e.g., two OFDM symbols). The first of the two symbols in which the PSFCH is transmitted may be used for AGC (automatic gain control) purposes for adjusting the correct PSFCH receive power level.

The PSFCH can be transmitted within a frequency resource region preset by system information. In this case, the frequency resource region for PSFCH transmission can be indicated (e.g., signaled) in the form of a bitmap within a resource pool. The receiving terminal can implicitly select a location of the frequency resource region for PSFCH transmission based on a slot and subchannel index in which the PSSCH is received. The receiving terminal can check the number of PSFCH resources that can be multiplexed based on a resource block (RB) and a cyclic shift of a PSFCH sequence within the frequency resource region. The receiving terminal can implicitly select a PSFCH index for the PSFCH resource(s) based on a source ID (identifier) and a member ID. The source ID can be a physical layer source ID. The source ID can be an ID of a transmitting terminal that transmitted the PSSCH.

Member ID can be used in Groupcast HARQ-ACK feedback option 2. When Groupcast HARQ-ACK feedback option 2 is applied, each receiving terminal in the group can individually transmit HARQ-ACK feedback for SL data through a separate PSFCH (e.g., PSFCH resource). In other cases than the above embodiment, the member ID can be set to 0.

Figure 11 is a conceptual diagram illustrating embodiments of PSFCH for ACK/NACK transmission.

Referring to FIG. 11, the transmission time of the PSFCH may be the first slot (e.g., the PSFCH slot) in which PSFCH transmission is possible after a preset time (e.g., sl-MinTimeGapPSFCH ) from the reception time of the PSSCH. The PSFCH slot may be a slot in which PSFCH transmission is possible and/or a slot in which a PSFCH is set. sl-MinTimeGapPSFCH may be set by considering "the time to process the PSSCH after reception of the PSSCH" and "the time to prepare ACK/NACK (e.g., HARQ-ACK feedback) depending on whether the reception of the PSSCH is successful or not." sl-MinTimeGapPSFCH may be set to 2 or 3 slots. The terminal (e.g., the receiving terminal) may transmit the PSFCH in slot #n+12, which is a slot in which PSFCH transmission is possible after sl-MinTimeGapPSFCH (e.g., 3 slots) from the reception time of the PSSCH. n may be an integer greater than or equal to 0. In the present disclosure, the reception time point may mean the reception start time point and/or the reception end time point, and the transmission time point may mean the transmission start time point and/or the transmission end time point. The time point may mean time and/or duration.

In a receiving terminal, data reliability can be improved by appropriately controlling the power of the transmitting terminal according to the transmission environment. Interference to other terminals can be mitigated by appropriately controlling the power of the transmitting terminal. Energy efficiency can be improved by reducing unnecessary transmission power. Power control methods can be classified into an open-loop power control method and a closed-loop power control method. In the open-loop power control method, the transmitting terminal can determine the transmission power by considering the set and measured environment, etc. In the closed-loop power control method, the transmitting terminal can determine the transmission power based on a transmit power control (TPC) command received from the receiving terminal.

Predicting the received signal strength at a receiving terminal can be difficult due to various causes including multipath fading channels, interference, etc. Therefore, the receiving terminal can adjust the received power level (e.g., received power range) by performing an automatic gain control (AGC) operation to prevent quantization error of the received signal and maintain an appropriate received power. In a communication system, the terminal can perform the AGC operation using a reference signal received from a base station. However, in sidelink communication (e.g., V2X communication), the reference signal may not be transmitted from the base station. In other words, communication between terminals can be performed without a base station in sidelink communication. Therefore, performing the AGC operation in sidelink communication can be difficult. In sidelink communication, a transmitting terminal can first transmit a signal (e.g., a reference signal) to a receiving terminal before transmitting data, and the receiving terminal can adjust the received power range (e.g., received power level) by performing an AGC operation based on the signal received from the transmitting terminal. Thereafter, the transmitting terminal can transmit sidelink data to the receiving terminal. The signal used for AGC operation may be a duplicated signal for a signal to be transmitted later or a signal preset between terminals.

The time interval required for AGC operation may be 15 μs. When the subcarrier spacing is 15 kHz in an NR system, the time interval (e.g., length) of one symbol (e.g., OFDM symbol) may be 66.7 μs. When the subcarrier spacing is 30 kHz in an NR system, the time interval of one symbol (e.g., OFDM symbol) may be 33.3 μs. In the embodiments below, a symbol may mean an OFDM symbol. In other words, the time interval of one symbol may be twice or more than the time interval required for AGC operation.

For sidelink communication, transmission of a data channel for data transmission and a control channel including scheduling information for data resource allocation may be required. In sidelink communication, the data channel may be a Physical Sidelink Shared CHannel (PSSCH) and the control channel may be a Physical Sidelink Control CHannel (PSCCH). The data channel and the control channel may be multiplexed in a resource domain (e.g., time and frequency resource domain).

FIG. 12 is a conceptual diagram illustrating embodiments of a method for multiplexing control channels and data channels in sidelink communication.

Referring to FIG. 12, sidelink communication may support Option 1A, Option 1B, Option 2, and Option 3. When Option 1A and/or Option 1B is supported, the control channel and data channels may be multiplexed in the time domain. When Option 2 is supported, the control channel and data channels may be multiplexed in the frequency domain. When Option 3 is supported, the control channel and data channels may be multiplexed in the time and frequency domains. Sidelink communication may support Option 3 by default.

In sidelink communication (e.g., NR-V2X sidelink communication), a basic unit of resource configuration may be a subchannel. A subchannel may be defined by time and frequency resources. For example, a subchannel may be composed of a plurality of symbols (e.g., OFDM symbols) in the time domain and a plurality of resource blocks (RBs) in the frequency domain. A subchannel may be referred to as an RB set. Within a subchannel, data channels and control channels may be multiplexed based on Option 3.

In sidelink communication (e.g., NR-V2X sidelink communication), transmission resources can be allocated based on Mode 1 or Mode 2. When Mode 1 is used, a base station can allocate sidelink resources for data transmission to a transmitting terminal within a resource pool, and the transmitting terminal can transmit data to a receiving terminal using the sidelink resources allocated by the base station. Here, the transmitting terminal can be a terminal that transmits data in the sidelink communication, and the receiving terminal can be a terminal that receives data in the sidelink communication.

When Mode 2 is used, a transmitting terminal can autonomously select a sidelink resource to be used for data transmission by performing a resource sensing operation (e.g., a resource sensing procedure) and/or a resource selection operation (e.g., a resource selection procedure) within a resource pool. The base station can configure a resource pool for Mode 1 and a resource pool for Mode 2 to the terminal(s). The resource pool for Mode 1 can be configured independently from the resource pool for Mode 2. Alternatively, a common resource pool can be configured for Mode 1 and Mode 2.

When mode 1 is used, the base station can schedule resources used for sidelink data transmission to the transmitting terminal, and the transmitting terminal can transmit the sidelink data to the receiving terminal using the resources scheduled by the base station. Therefore, resource collision between the terminals can be prevented. When mode 2 is used, the transmitting terminal can select an arbitrary resource by performing a resource sensing operation and/or a resource selection operation, and can transmit the sidelink data using the selected arbitrary resource. Since the above-described procedure is performed based on the individual resource sensing operation and/or resource selection operation of each transmitting terminal, a collision between the selected resources may occur.

Figure 13 is a conceptual diagram illustrating embodiments of resource selection operations.

Referring to FIG. 13, a terminal (e.g., a transmitting terminal) can perform a resource sensing operation within a sensing window, and can perform a resource selection operation on sensed resource(s) (e.g., candidate resource(s)) within a selection window. When the resource selection operation is triggered at n, the terminal can select suitable resource(s) within the selection window (e.g., an interval from n+T ₁ to n+ _{T 2} ) based on the sensing result (e.g., resource(s) sensed by the resource sensing operation) within the sensing window (e.g., an interval from nT ₀ to nT proc, ₀ ).

The terminal may exclude candidate resource(s) that do not satisfy the condition within the selection window based on the result of the resource sensing operation. In other words, the terminal may determine the remaining candidate resources by excluding unsuitable candidate resource(s) from the entire candidate resources. If the ratio of the remaining candidate resources among the entire resources within the selection window is less than the reference ratio, the terminal may relax the condition for excluding the candidate resource(s). For example, the terminal may increase the RSRP (reference signal received power) threshold, which is the condition for excluding the candidate resource(s), by 3 dB. Thereafter, the terminal may perform the resource selection operation again. The reference ratio may be preset to one of 20%, 35%, or 50% according to the priority. If the ratio of the remaining candidate resources is greater than or equal to the reference ratio, the terminal may randomly select the final resource(s) to be used for SL transmission among the remaining candidate resources. The terminal may perform SL transmission using the final resource(s).

Figure 14 is a conceptual diagram illustrating embodiments of resource re-selection operations.

Referring to FIG. 14, the terminal may perform a resource re-selection operation after the resource selection operation, considering aperiodic data transmission, etc. The terminal may perform a resource re-selection operation by additionally considering the sensing result before the actual SL transmission (mT ₃ ) after performing the operations illustrated in FIG. 13. The resource re-selection operation may be performed within a re-selection window. The terminal may additionally determine the suitability of the resource(s) reserved in m. If the resource(s) reserved in m are determined to be suitable, the terminal may perform SL transmission using the reserved resource(s). If the resource reserved in m is determined to be not suitable, the terminal may re-select resource(s) for SL transmission, and perform SL transmission using the re-selected resource(s).

In case an independent SL carrier is not set in SL communication, some of the UL resources may be set as SL resources by the setting procedure of the SL resource pool. A bitmap may be repeatedly applied to the remaining slot(s) except for the slot(s) in which at least X UL symbols are not set among the slots in a specific period and the slot(s) in which S(sidelink)-SSB is transmitted. X may be a natural number. The bitmap may indicate the slot(s) used as the SL resource. For example, the slot(s) corresponding to the bit(s) set to 1 among the bits in the bitmap may be used as the SL resource.

"When 15kHz SCS(subcarrier spacing) is applied and X or more UL symbols are configured in all slots" can be assumed. "When there are 10240 available slots in a DFN(direct frame number), a transmission period of S-SSB is 160ms, and there are 2 slots used for S-SSB transmission in each transmission period of S-SSB", the number of slots used for S-SSB transmission in the DFN can be 128. A bitmap for configuring SL time resources can include 10 bits. When the bitmap (for example, a bitmap including 10 bits) is repeatedly applied to the remaining 10112 slots excluding the 128 slots used for S-SSB transmission out of the 10240 slots, there can be 2 slots (for example, reserved slots) to which the bitmap is not applied. It may be necessary to exclude the 2 reserved slots. Excluding two spare slots from the 10112 slots, 10110 slots can remain. The above bitmap (e.g., a bitmap including 10 bits) can be repeatedly applied to the 10110 slots 1011 times. "If the bitmap is 1111000000 and the slot corresponding to the bit set to 1 is used as an SL resource", 4044 slots in the DFN can be set as SL resources. In other words, 4044 slots out of 10240 slots can be used for SL communication by setting the SL resource pool.

A sidelink communication system supporting Rel-16 can be designed for terminals that do not have significant constraints on battery capacity (e.g., terminals mounted on automobiles, vehicle UEs (V-UEs)). Therefore, the issue of power saving in resource sensing/selection operations of the terminals may not be greatly considered. In a sidelink communication system supporting Rel-17, power saving methods will be needed for sidelink communication with terminals that have constraints on battery capacity (e.g., terminals carried by pedestrians, terminals mounted on bicycles, terminals mounted on motorcycles, pedestrian UEs (P-UEs)). In the present disclosure, a V-UE may mean a terminal that does not have significant constraints on battery capacity, a P-UE may mean a terminal that has constraints on battery capacity, and a "resource sensing/selection operation" may include a "resource sensing operation and/or a resource selection operation." The resource sensing operation may mean a partial sensing operation or a full sensing operation. The resource selection operation may mean a random selection operation. Additionally, in the present disclosure, “operation of a terminal” may be interpreted as “operation of a V-UE” and/or “operation of a P-UE.”

In order to save power in LTE V2X, partial sensing operation and/or random selection operation may be introduced. If partial sensing operation is supported, the terminal may perform resource sensing operation in some sections instead of the entire section within the sensing window, and select resources based on the results of the partial sensing operation. According to this operation, the power consumption of the terminal may be reduced.

In Rel-14 LTE V2X, only periodic data transmission and reception operations may be possible. In Rel-14 LTE V2X, a terminal may randomly select candidate slots considering a preset minimum number in a resource selection interval (e.g., a selection window), and perform a partial sensing operation considering a period of k×100ms. k may be signaled by a bitmap (e.g., a bitmap including 10 bits). k may be determined according to the position of the bitmap (e.g., a bit included in the bitmap). For example, 10 bits included in the bitmap may correspond to 1 to 10 from MSB, and the period may be determined based on a value corresponding to a bit set to 1. The value corresponding to the bit set to 1 may be k.

If the MSB in the bitmap is set to 1, k can be 1. In this case, the terminal can perform the partial sensing operation considering a period of 100 ms (= 1 × 100 ms). If the bit following the MSB in the bitmap is set to 1, k can be 2. In this case, the terminal can perform the partial sensing operation considering a period of 200 ms (= 2 × 100 ms). If the LSB in the bitmap is set to 1, k can be 10. In this case, the terminal can perform the partial sensing operation considering a period of 1000 ms (= 10 × 100 ms).

In Rel-14 LTE V2X, the period (e.g., the period of partial sensing operation) can be set to 20ms or 50ms. The 20ms period or 50ms period may not be supported in the resource pool for P-UE. In addition to the periods {0, 100ms, 200ms, ..., 1000ms}, a short period may be supported in the NR communication system. The short period may be {1ms, 2ms, ..., 99ms}. Up to 16 periods can be selected from the resource pool, and the selected periods can be preset in the terminal. The terminal can perform the resource sensing operation and/or the resource (re)selection operation using one or more of the configured periods. If the random selection operation is supported, the terminal can randomly select a resource without performing the resource sensing operation. Alternatively, the random selection operation can be performed together with the resource sensing operation. For example, a terminal can determine a resource by performing a resource sensing operation, and select a resource(s) by performing a random selection operation within the determined resources.

In LTE V2X supporting Rel-14, a resource pool capable of performing a partial sensing operation and/or a random selection operation can be configured independently from a resource pool capable of performing a complete sensing operation. A resource pool capable of performing a random selection operation, a resource pool capable of performing a partial sensing operation, and a resource pool capable of performing both a random selection operation and a partial sensing operation can be configured independently. In other words, a random selection operation, a partial sensing operation, or "both a random selection operation and a partial sensing operation" can be configured in each resource pool. When both a random selection operation and a partial sensing operation are configured in a resource pool, a terminal can select one operation from the random selection operation and the partial sensing operation, select a resource by performing the selected operation, and perform sidelink communication using the selected resource.

In LTE V2X supporting Rel-14, SL data can be transmitted periodically based on a broadcast method. In an NR communication system, SL data can be transmitted based on at least one of a broadcast method, a multicast method, a groupcast method, or a unicast method. In addition, in an NR communication system, SL data can be transmitted periodically or aperiodically. A transmitting terminal can transmit SL data to a receiving terminal, and the receiving terminal can transmit HARQ-ACK feedback (e.g., ACK or NACK) for the SL data to the transmitting terminal through a PSFCH. In the present disclosure, a transmitting terminal may mean a terminal transmitting SL data, and a receiving terminal may mean a terminal receiving the SL data.

A terminal with reduced capability (hereinafter referred to as a "RedCap terminal") can operate in a specific usage environment. The capability of the RedCap terminal may be lower than the capability of a new radio (NR) normal terminal, and may be higher than the capabilities of each of an LTE-MTC (machine type communication) terminal, an NB (narrow band)-IoT (internet of things) terminal, and an LPWA (Low Power Wide Area) terminal. For example, there may be a terminal requiring "high data rate and low latency conditions" (e.g., a surveillance camera) and/or a terminal requiring "low data rate, high latency conditions, and high reliability" (e.g., a wearable device). To support the above-mentioned terminals, the maximum carrier bandwidth in FR1 may be reduced from 100 MHz to 20 MHz, and the maximum carrier bandwidth in FR2 may be reduced from 400 MHz to 100 MHz. The number of receive antennas of the Redcap terminal may be smaller than the number of receive antennas of the NR general terminal. When the carrier bandwidth and the number of receive antennas are reduced, the reception performance of the RedCap terminal may be reduced, and thus the coverage of the RedCap terminal may be reduced.

A communication system (e.g., an NR system) may operate at a frequency band higher than the 52.6 GHz frequency band. As the frequency band in which the communication system operates increases, frequency offset error and phase noise may increase. For robust operation in such an environment, the use of a large SCS may be required. In the FR2 band, 60 kHz SCS and/or 120 kHz SCS may be supported, and additionally, 480 kHz SCS and/or 960 kHz SCS may be supported. In addition, "Physical Layer Signal and Channel Design" and "Physical Layer Procedures" according to the new SCS may be required. With respect to the initial access procedure, 120 kHz SSB and/or 240 kHz SSB may be supported in the FR2 band, and additionally, 480 kHz SSB and/or 960 kHz SSB may be supported. Here, 120kHz SSB may mean SSB transmitted in a radio resource to which 120kHz SCS is applied, and 240kHz SSB may mean SSB transmitted in a radio resource to which 240kHz SCS is applied. To support new SCS, an "initial BWP setup method" and an "SSB burst aggregation pattern" may be required.

The communication system may support network energy saving (NES) technology. For the NES technology, technology in the time domain, technology in the frequency domain, technology in the space domain, and/or technology in the power domain may be required. In the time domain, the technology may include SSB-less SCell (secondary cell) operation and/or cell DTX/DRX (discontinuous transmission/discontinuous reception) operation. For supporting the NES technology, on demand SSB transmission technology and on demand SI (system information) transmission technology may be required.

When there is a lot of downlink data to be transmitted to a terminal, when resources for transmitting a lot of downlink data are requested from the terminal, and when access to an additional small cell (e.g., SCell) is required due to other needs, SSB transmission in the small cell may be requested by a macro base station (e.g., a macro cell, a PCell (primary cell)). In the present disclosure, a macro base station may mean a base station (e.g., a cell) that is not a small cell. In other words, a macro base station may be a term used to distinguish it from a small cell, and a macro base station may be a term that collectively refers to base stations (e.g., cells) that are not small cells. A small cell may mean a cell (e.g., a base station) that is not a macro base station. In other words, a small cell may be a term used to distinguish it from a macro base station, and a small cell may be a term that collectively refers to cells (e.g., base stations) that are not macro base stations.

The operation and/or configuration of the macro base station may be performed identically or similarly by the small cell. Alternatively, the operation and/or configuration of the small cell may be performed identically or similarly by the macro base station. The base station may mean the macro base station and/or the small cell. In other words, the operation/configuration of the base station may be interpreted as the operation/configuration of the macro base station, the operation/configuration of the small cell, or "the operation/configuration of the macro base station and the small cell" depending on the context. The macro base station may be referred to as a first base station (e.g., a first cell), and the small cell may be referred to as a second base station (e.g., a second cell). Alternatively, the macro base station may be referred to as a second base station (e.g., a second cell), and the small cell may be referred to as a first base station (e.g., a first cell).

When the terminal is required to access a small cell due to the terminal's needs, the terminal can request SSB transmission of the small cell through the macro base station. The small cell can transmit SSB at the request of the macro base station and/or the terminal. The SSB transmitted at the request of the base station and/or the terminal may be an on-demand SSB. The terminal can perform an access procedure for the small cell based on the SSB received from the small cell. While the terminal is accessed to the small cell, the base station (e.g., the macro base station) associated with the small cell may not transmit SSB for energy saving. In the above situation, while the terminal performs communication (e.g., transmitting and receiving operation of a signal and/or channel) without SSB, the terminal can request SSB transmission for downlink resynchronization. The small cell can transmit SSB at the request of the macro base station and/or the terminal. The terminal can perform a synchronization procedure based on the SSB received from the small cell. At this time, the terminal can request the macro base station to transmit SSB of the small cell through an uplink signal and/or channel (e.g., PRACH, PUCCH, PUSCH, SRS, etc.). The macro base station can receive the SSB transmission request from the terminal and transmit the SSB transmission request to the small cell through a backhaul. The small cell can receive the SSB transmission request and transmit the SSB based on the SSB transmission request.

Alternatively, the terminal may request SSB transmission of the small cell via an uplink signal and/or channel (e.g., PRACH, PUCCH, PUSCH, SRS, etc.). The uplink signal and/or channel requesting SSB transmission may be transmitted to the macro base station, and the macro base station may transfer information requesting SSB transmission to the small cell, and the small cell may receive the uplink signal and/or channel requesting SSB transmission from the macro base station, and the small cell may transmit the SSB according to the request. Alternatively, the uplink signal and/or channel requesting SSB transmission may be directly transmitted from the terminal to the small cell, and the small cell may transmit the SSB according to the request of the terminal.

When a terminal requests SSB transmission, a trigger signal for the SSB transmission request may be separate indication information included in an uplink signal and/or a channel. For example, in a PRACH requesting SSB transmission, the PRACH preamble may be indication information that is explicit information requesting SSB transmission. A BSR (buffer status report) transmitted in a PUSCH requesting SSB transmission may be implicit indication information requesting SSB transmission. In other words, the SSB transmission request may be indicated by explicit and/or implicit methods.

Alternatively, the UE can request SSB transmission using the SCell activation/deactivation indicator. The SCell activation/deactivation indicator is an indicator used to inform the UE of activation or deactivation of the SCell, but in a similar way, the UE can request SSB transmission by reporting (e.g., transmitting) the SCell activation/deactivation indicator to the base station. For example, the SCell activation indicator can be used to request SSB transmission. For requesting SSB transmission to a small cell, the UE must be within the area (e.g., coverage) of the small cell. The macro base station and the small cell can be connected by the X2 interface, and coordination between the macro base station and the small cell can be possible based on the connection.

Figure 15 is a conceptual diagram illustrating deployment scenarios of a communication system.

Referring to FIG. 15, a macro base station (e.g., a first base station, a first cell) may mainly operate in a frequency range below 6 GHz and may cover a wide area. A small cell (e.g., a second base station, a second cell) may mainly operate in a frequency range above 6 GHz and may cover a smaller area compared to the macro base station. The small cell may have a wide system bandwidth and may transmit and receive a large amount of data using the wide system bandwidth. An interface may be established between the macro base station and the small cell, and mutual cooperation between the macro base station and the small cell may be possible based on the interface. A terminal may be able to access the macro base station and the small cell simultaneously. In the deployment scenario illustrated in FIG. 15, a procedure for transmitting an aperiodic on-demand SSB of a small cell according to a request of a macro base station, a small cell, and/or a terminal may be performed as follows.

1. Request for transmission of terminal-related information required for SSB transmission of small cells

In a situation where a terminal is connected to a macro base station and maintains a connection, it may be necessary for the terminal to additionally connect to a small cell. In this case, for time and/or frequency synchronization of the terminal with respect to the small cell, the small cell may transmit SSB. At this time, the macro base station may request the terminal to report terminal-related information (e.g., UE capability-related information) necessary for SSB transmission of the small cell. The terminal-related information may be as follows. The terminal may report terminal-related information (e.g., one or more pieces of information belonging to information set 1 below) to the macro base station upon a request from the macro base station. The macro base station may receive terminal-related information from the terminal. The macro base station may transmit the terminal-related information to the small cell. The small cell may receive terminal-related information from the macro base station. Information set 1 may include at least one of 1-A information or 1-B information. Information set 1 may include other information in addition to 1-A information and 1-B information.

<Information set 1>

- 1-A Information: Number of receiving beams of the terminal

- 1-B Information: Information related to the SSB transmission period (e.g., SSB transmission cycle).

The 1-A information may be information required to determine the number of SSB transmissions so that the terminal can see the SSBs transmitted in a beam sweeping manner through all reception beams of the terminal. The 1-A information may be replaced with the number of SSB transmissions requested by the terminal regardless of the number of reception beams of the terminal. In other words, the 1-A information may be the number of SSB transmission periods (e.g., SSB transmission periods) indicating how many cycles a plurality of SSBs transmitted in a specific period are transmitted through beam sweeping. The terminal may report the 1-A information to the macro base station.

The terminal can report appropriate 1-B information (e.g., information on SSB transmission intervals, information on SSB transmission periods) according to the processing power of the terminal. The terminal can select one SSB transmission interval among selectable SSB transmission intervals (e.g., candidate SSB transmission intervals, candidate SSB transmission periods) and report the selected one SSB transmission interval. In the present disclosure, an SSB transmission interval can mean an SSB transmission period (e.g., an interval according to an SSB transmission period). In other words, an SSB transmission interval can be interpreted as an SSB transmission period depending on the context.

The terminal may report the terminal-related information (e.g., 1-A information and/or 1-B information) together with the SSB transmission trigger information to the macro base station via an uplink channel (e.g., PUCCH and/or PUSCH). Alternatively, the terminal may report the terminal-related information (e.g., 1-A information and/or 1-B information) to the macro base station via an uplink channel (e.g., PUCCH and/or PUSCH) separately from the SSB transmission trigger information. The terminal-related information may be reported in an initial stage when the terminal accesses the macro base station. Alternatively, when the terminal needs to access a small cell, the macro base station may request the terminal to report the terminal-related information, and the terminal may report the terminal-related information based on the request. The macro base station may request the terminal to report the terminal-related information via signaling (e.g., UE-specific RRC signaling, MAC CE signaling, DCI signaling).

2. The macro base station can complete SSB transmission configuration based on terminal-related information, transmit SSB transmission configuration information to the terminal, and instruct the small cell to perform SSB transmission according to the SSB transmission configuration information.

The macro base station can set the environment related to the SSB transmission of the small cell based on the terminal-related information received from the terminal. In other words, the macro base station can complete the SSB transmission configuration based on the terminal-related information received from the terminal. The macro base station can transmit the SSB transmission configuration information to the small cell. The small cell can receive the SSB transmission configuration information from the macro base station.

Alternatively, the macro base station can set the environment related to the SSB transmission of the small cell without receiving terminal-related information from the terminal. In other words, the macro base station can complete the SSB transmission configuration based on the information that the macro base station has. The macro base station can transmit the SSB transmission configuration information to the small cell. The small cell can receive the SSB transmission configuration information from the macro base station.

Alternatively, the small cell may receive terminal related information from the macro base station, and may set an environment related to SSB transmission based on the terminal related information. The macro base station and/or the small cell may set the number of SSB transmission intervals (e.g., the number of SSB burst sets) on which beam sweeping is performed based on 1-A information. The macro base station and/or the small cell may set a period of the SSB transmission interval based on 1-B information. The macro base station and/or the small cell may complete the environment setting for SSB transmission based on the terminal related information (e.g., UE capability information), and may transmit the following information (e.g., one or more pieces of information belonging to information set 2 below) to the terminal. The terminal may receive one or more pieces of information belonging to information set 2 from the macro base station and/or the small cell. Information set 2 can include at least one of 2-A information, 2-B information, 2-C information, 2-D information, 2-E information, 2-F information, 2-G information, 2-H information, or 2-I information. Information set 2 can also include other information in addition to 2-A information and 2-I information. Information set 2 can be SSB transmission configuration information (e.g., on-demand SSB transmission configuration information). Information set 2 can be SSB transmission configuration information for SCell activation (e.g., on-demand SSB transmission configuration information). Information set 2 can be information about a small cell.

<Information set 2>

- 2-A Information: Capability information of small cell(s) including at least one of cell ID (identify), system bandwidth, numerology, or antenna configuration.

- 2-B information: Beam sweeping information including at least one of the number of beams (e.g., the number of SSBs and/or the number of SSBs actually transmitted) or the order of the beams.

- 2-C Information: Timing information (e.g. timing offset)

- 2-D information: starting position of SSB transmission (e.g. SFN, half radio frame indicator, subframe index, slot index, and/or indication of whether the macro base station and small cell are tightly synchronized)

- 2-E Information: Time resources (e.g., time period, transmission cycle) and/or frequency resources for SSB transmission.

- 2-F information: Number of SSB transmissions (e.g. number of SSB subframes and/or number of SSB burst sets based on number of beams of the UE)

- 2-G Information: RACH resources (if required)

- 2-H Information: SSB transmission instructions (e.g. SCell activation/deactivation)

- 2-I Information: CSI configuration information (e.g., resource(s) for CSI reporting)

2-A information may be information about neighboring small cells that the terminal can access. 2-A information may include at least one of a cell ID, a system bandwidth, numerology used in a cell (e.g., a small cell), or antenna configuration. 2-A information may include information about the overall system of the small cell.

The 2-B information may be beam sweeping information. The 2-B information may include at least one of the number of beams transmitting SSBs, the number of SSBs, or the beam sweeping order. The 2-B information may include information about the SSBs actually transmitted and/or beam sweeping information.

The 2-C information may include timing-related information. The timing-related information may include a timing offset between the macro base station and the small cell, a transmission time of on-demand SSB activation information (e.g., transmission time), and/or a start time (e.g., start time) of actual on-demand SSB transmission. The terminal may easily perform synchronization work between the terminal and the small cell based on the timing-related information (e.g., 2-C information).

The 2-D information may indicate a starting point from which an actual SSB is transmitted in the small cell. The 2-D information may include at least one of an SFN, a half radio frame indicator, a subframe index, a slot index, or a half frame indicator. The 2-D information may include information indicating whether the macro base station and the small cell are synchronized. If the macro base station and the small cell are indicated (e.g., signaled) as being synchronized, the location information (e.g., SFN, subframe index, slot index) of the SSB transmitted by the small cell may be identical to the location information (e.g., SFN, half radio frame indicator, subframe index, slot index) of the SSB transmitted by the macro base station. Alternatively, if the macro base station and the small cell are indicated (e.g., signaled) as being synchronized, the terminal may derive the location information (e.g., SFN, subframe index, slot index) of the SSB transmitted by the small cell by considering a numerology ratio between the small cell and the macro base station. If the macro base station and the small cell are indicated (e.g., signaled) to be out of sync, the terminal can determine the location of the SSB transmitted by the small cell by performing an exhaustive search.

Alternatively, the small cell may transmit SSB from the earliest SSB transmission time point based on the time point at which the SSB transmission instruction (e.g., SSB transmission request) is received from the macro base station. The transmittable position(s) of SSB (e.g., SSB transmission candidate time point(s), SSB transmission occasion(s)) may be preset (e.g., defined) for each SSB transmission period. The small cell may perform SSB transmission from the earliest SSB transmission position (e.g., the earliest SSB transmission possible position) according to the SSB transmission period from the time point at which the SSB transmission instruction is received.

The 2-E information may be information of time resources (e.g., time interval, transmission period) and/or frequency resources on which SSB is transmitted. In other words, the 2-E information may include time resource information and/or frequency resource information. The information of time resources (e.g., time interval, transmission period) may indicate a period on which SSB is transmitted. If the 1-B information reported by the terminal is valid, the macro base station may determine the SSB transmission period (e.g., time resources (e.g., time interval, transmission period) on which SSB is transmitted) based on the 1-B information. In order to reduce access latency when the terminal newly accesses the small cell, a short SSB transmission period may be selected. In other words, in order to reduce access latency for the small cell, a short SSB transmission period may be set. An SSB transmission period for continuously performing time synchronization, frequency synchronization, and/or measurement for the small cell after the terminal accesses the small cell may be set to an appropriate value considering the situation (e.g., mobility) of the terminal. Information on the SSB transmission period may be transmitted to the terminal via signaling (e.g., SI signaling, UE-specific RRC signaling). Information on the SSB transmission period may be signaled to the terminal from the macro base station and/or the small cell. If the terminal does not report 1-B information, the small cell may transmit SSB based on a default SSB transmission period (e.g., a default SSB transmission period).

There may be multiple SSB transmittable locations (e.g., multiple SSB transmission candidate frequencies) in the frequency domain. The frequency resource information may be information about one or more frequency resources (e.g., one or more frequency locations) among the frequency resources (e.g., frequency locations) where actual SSBs are transmitted. The frequency resource information may include information about an SSB synchronization raster and/or information about an Absolute Radio Frequency Channel Number (ARFCN). SSB transmission other than for initial access may be possible at a frequency location other than the SSB synchronization raster (e.g., a frequency location corresponding to the ARFCN value). In this case, the UE may regard an SSB received at a frequency location corresponding to the ARFCN value as a non-cell-defining SSB rather than a cell-defining SSB. In other words, an on-demand SSB may be transmitted at a frequency location other than the SSB synchronization raster. An on-demand SSB received at a frequency location other than the SSB synchronization raster may be a non-cell-defining SSB.

Alternatively, the SSB may be transmitted via the SSB synchronization raster, but the PBCH information included in the SSB may indicate that there is no RMSI associated with the SSB. If the PBCH information included in the SSB received via the SSB synchronization raster indicates that there is no RMSI associated with the SSB, the UE may regard the SSB as a non-cell defined SSB. The above operation (e.g., the interpretation operation of the SSB) may be preset.

A MIB (e.g., a MIB included in a cell-defined SSB) may include a barring indicator. The size of the barring indicator may be 1 bit. SSB transmission other than SSB transmission for initial access may be indicated by the barring indicator. For example, a barring indicator set to a first value (e.g., 0) may indicate that an SSB including the barring indicator is an SSB for initial access. A barring indicator set to a second value (e.g., 1) may indicate that an SSB including the barring indicator is an SSB other than an SSB for initial access. In this case, a terminal capable of on-demand SSB reception may receive RMSI regardless of the value of the barring indicator included in the MIB (or regardless of whether the MIB includes the barring indicator), and may determine whether to barre an SSB (e.g., a small cell) based on an indicator (e.g., a 1-bit indicator, a barring indicator) included in the RMSI. In other words, a terminal capable of on-demand SSB reception can determine whether to access a small cell based on the barring indicator included in RMSI instead of the barring indicator included in MIB. RMSI can be received from a small cell. The barring indicator can be used to block legacy terminals from accessing a small cell.

The 2-F information may be information indicating the number of transmission sections for the SSB when the small cell transmits the SSB in a beam sweeping manner. The macro base station may check the number of reception beams of the terminal based on the 1-A information, check all reception beams based on the number of reception beams of the terminal, and set the 2-F information (e.g., the number of SSB transmissions) so that the SSB can be received in all reception beams. Alternatively, the macro base station may set the 2-F information based on a value requested by the terminal through the 1-A information.

Alternatively, a range for the number of SSB transmissions (e.g., a range for the number of SSB subframes, a range for the number of SSB burst sets) can be preset (e.g., fixed), and the base station (e.g., the macro base station and/or the small cell) can set the number of SSB transmissions to a specific value within the preset range. In other words, the base station (e.g., the macro base station and/or the small cell) can implementally determine the number of SSB transmissions within the preset range. The 2-F information can be information about an interruption point (e.g., an end point) of the SSB transmission that is associated with 2-D information (e.g., a start position (e.g., a start time) of the SSB transmission) rather than the number of SSB transmission intervals (e.g., SSB transmission periods). Alternatively, if the number of SSB transmission intervals and/or the time point for stopping SSB transmissions is not separately configured (e.g., signaled), the started SSB transmissions may continue to be performed until the base station (e.g., macro base station and/or small cell) stops transmission.

After a base station (e.g., a macro base station and/or a small cell) completes SSB transmission setup, the base station can notify a terminal of an instruction for the small cell to perform actual SSB transmission. The instruction for the small cell to perform actual SSB transmission can be delivered to the terminal via the macro base station. Alternatively, the instruction for the small cell to perform actual SSB transmission can be directly delivered to the terminal via the small cell. The SSB transmission setup information (e.g., on-demand SSB transmission setup information) can implicitly indicate that the small cell performs actual SSB transmission. The terminal can implicitly confirm that the small cell performs actual SSB transmission (e.g., on-demand SSB transmission) based on the SSB transmission setup information received from the base station.

Alternatively, the base station can explicitly indicate that the small cell performs on-demand SSB transmission (e.g., actual SSB transmission) using a separate indicator. For example, the base station can indicate to the UE that the small cell performs (e.g., starts) on-demand SSB transmission via a separate PDCCH, etc. The base station can indicate to the UE that the small cell performs on-demand SSB transmission via a SCell activation/deactivation indicator over MAC CE. If the SCell activation/deactivation indicator delivered to the UE indicates activation of a SCell corresponding to a small cell transmitting on-demand SSB (e.g., a non-macro base station), the UE can determine that SSB transmission is started in the small cell. The UE can determine that the small cell starts SSB transmission at the earliest SSB transmission occasion after the time of reception of the indicator (e.g., a separate indicator, the SCell activation/deactivation indicator). Alternatively, the terminal may receive the above indicator (e.g., a separate indicator, SCell activation/deactivation indicator) and determine that the small cell starts SSB transmission at the earliest SSB transmission occasion after transmission of feedback (e.g., ACK/NACK) for the indicator.

After downlink synchronization for a small cell is completed, the base station can transmit 2-G information including information on resources required for RACH transmission for uplink synchronization, etc., to the terminal. The terminal can receive the 2-G information from the base station. The RACH resource information may be information on CBRA (contention based random access) resources and/or CFRA (contention free random access) resources. The RACH resource information may be information on specific RACH resources allocated only to the terminal. When a specific RACH resource (e.g., a CFRA resource) is allocated to the terminal, the terminal can perform a CFRA procedure. When the CFRA procedure is performed, an additional terminal identification procedure and/or contention resolution procedure may be omitted. When there are a plurality of candidate small cells (e.g., accessible small cells), the terminal can access a specific small cell based on the information on the plurality of candidate small cells, and can perform an RA procedure using the RACH resource of the specific small cell. By performing the RA procedure, the terminal can inform the terminal of the small cell to which it has actually accessed among multiple candidate small cells.

After a terminal completes access to a small cell, there may be information (e.g., CSI reporting information) that the terminal needs to report to the small cell. In this case, the small cell may inform the terminal of uplink resource information for reporting by the terminal. Based on the above procedure, after a terminal completes access to a small cell, the terminal can report information (e.g., CSI reporting information) to the small cell using uplink resources set by the small cell without performing a separate resource allocation procedure.

Information set 2 may include other information in addition to the 2-A information to the 2-I information. Information set 2 may include some information from the 2-A information to the 2-I information. Information set 2 may be information about one small cell to which the terminal can connect (e.g., one adjacent small cell) or information about a plurality of candidate small cells (e.g., candidate small cells to which the terminal can connect). The macro base station may request SSB transmission to the small cell based on information set 2 (e.g., at least one information from the 2-A information to the 2-I information). At this time, the essential information that the macro base station should inform the small cell may be all or part of the 2-A information to the 2-I information. The essential information that the macro base station should inform the small cell may include other information in addition to the 2-A information to the 2-I information. The small cell may perform actual SSB transmission based on the information received from the macro base station (e.g., information set 2). Depending on the time resources (e.g., time interval, transmission period)/frequency resources available for SSB transmission, various forms of SSB transmission may be possible.

Figures 16a and 16b are conceptual diagrams illustrating SSB transmission of a small cell at preset time intervals (e.g., transmission periods).

Referring to FIGS. 16A and 16B , time resources that can be SSB transmitted can be preset. Accordingly, setting and/or transmission of time resource information (e.g., time resource(s), time interval, transmission period) among 2-E information may not be necessary. The small cell can transmit SSB based on 2-F information (e.g., number of SSB transmissions) set by the macro base station. When the above method is used, since there is no need to separately set/transmit time resource information (e.g., time resource(s), time interval, transmission period) for SSB transmission, signaling overhead of information for SSB transmission can be reduced, and a communication system (e.g., SSB transmission procedure) can be simply implemented. Instead of the number of SSB transmission intervals (e.g., SSB transmission periods), the stop time (e.g., end time) of SSB transmission linked to the start time of SSB transmission among 2-D information can be set, and information on the stop time of SSB transmission can be signaled to the terminal. In this case, the SSB transmission can be performed in the interval from the start time of the SSB transmission to the stop time of the SSB transmission. Or, if the number of SSB transmission intervals and/or the stop time of the SSB transmission are not configured/signaled, the started SSB transmissions can be performed continuously until the base station stops transmission. Alternatively, the time resource (e.g., time interval, transmission period) can be flexibly allocated, and the SSB transmission can be dynamically configured based on the flexible time resource (e.g., time interval, transmission period).

Figures 17a, 17b, and 17c are conceptual diagrams illustrating SSB transmission of a small cell in flexible time intervals (e.g., flexible transmission periods).

Referring to FIGS. 17a, 17b, and 17c, flexible time resources (e.g., time intervals, transmission periods) for SSB transmission can be set. In this case, additional signaling for the SSB transmission period is required, but the SSB transmission period can be set flexibly. The SSB transmission periods can be set differently according to the capabilities of each terminal. Therefore, the synchronization procedure (e.g., synchronization procedure for a small cell) can be performed quickly. When a hypothesis test is required for the synchronization procedure, a terminal having sufficient processing power can quickly complete the synchronization procedure based on a short SSB transmission period, as in the embodiment of FIG. 17c. A terminal having insufficient processing power can perform the synchronization procedure based on a long SSB transmission period, as in the embodiment of FIG. 17b, in order to secure sufficient processing time for the hypothesis test.

The macro base station can set the SSB transmission period (e.g., 2-E information) based on the 1-B information reported from the terminal. Or, the macro base station can use the 1-B information reported from the terminal as 2-F information. In this case, as with the SSB transmission based on the 2-F information, the SSB transmission can be performed based on the setting and/or signaling of the number of SSB transmission sections and/or the time point of stopping the SSB transmission. After the SSB transmission section and/or the time point of stopping the SSB transmission, the SSB transmission can be stopped (e.g., terminated).

Alternatively, after the SSB transmission interval and/or the interruption point of the SSB transmission, the SSB transmission may be performed based on a different SSB transmission period. In other words, after the SSB transmission interval and/or the interruption point of the SSB transmission, the SSB transmission period may be changed, and the SSB transmission may be performed based on the changed SSB transmission period. The different SSB transmission period (e.g., the changed SSB transmission period) may be a default SSB transmission period (e.g., 20 ms). The default SSB transmission period may be used in the initial access procedure. Alternatively, the different SSB transmission period (e.g., the changed SSB transmission period) may be a separately configured SSB transmission period. It may be desirable that the different SSB transmission period (e.g., the changed SSB transmission period) be set to a value greater than a previous SSB transmission period. If the number of separate SSB transmission periods and/or separate interruption points of the SSB transmission are not configured and/or signaled, the started SSB transmission may be continuously performed until the base station stops the SSB transmission.

Although there is one frequency resource for SSB transmission in the embodiments of FIGS. 17a, 17b, and 17c, the embodiments of the present disclosure can also be applied to a case where there are multiple frequency resources for SSB transmission. In this case, additional information may be required to indicate the frequency resource(s) for SSB transmission.

3. After the synchronization procedure (e.g., the synchronization procedure for the small cell) is completed, the terminal can report information on whether the synchronization procedure is completed to the macro base station and/or the small cell.

The terminal can complete a synchronization procedure based on the SSB(s) received from the small cell. After the synchronization procedure is completed, the terminal can report (e.g., transmit) information about the completed synchronization procedure to the macro base station and/or the small cell. For example, the terminal can transmit the following information set 3 to the macro base station and/or the small cell. The macro base station and/or the small cell can receive the information set 3 from the terminal. The information set 3 can include at least one of 3-A information, 3-B information, 3-C information, or 3-D information. The information set 3 can also include other information in addition to the 3-A information and the 3-D information.

<Information set 3>

- 3-A Information: Synchronization completion message (e.g. success or failure)

- 3-B information: optimal M beam(s) (e.g. optimal beam index, optimal transmit beam index), where M is a natural number.

- 3-C information: optimal receiving beam (e.g. optimal receiving beam index)

- 3-D information: Link quality corresponding to the optimal beam index

After the synchronization procedure is completed, the terminal can report information on whether the synchronization is completed (e.g., 3-A information) to the base station (e.g., the macro base station and/or the small cell). The 3-A information may be information indicating whether the synchronization procedure is successful. If 3-B information, 3-C information, and/or 3-D information are reported to the base station, the base station may determine that the synchronization procedure is completed based on the reported information. In this case, the terminal may omit transmission of the 3-A information. In the synchronization procedure, the terminal can find an optimal beam pair. The optimal beam pair may include an optimal transmit beam and an optimal receive beam.

When SSB is transmitted in a beam sweeping manner (e.g., when SSB is transmitted through different beams in the time domain), the terminal can measure the reception quality (e.g., RSRP, signal to noise ratio (SNR), signal to interference plus noise ratio (SINR)) for each SSB, and find an optimal beam pair based on the measured reception quality (e.g., measured link quality). The terminal can inform the base station of the information on the optimal beam pair by reporting 3-B information and/or 3-C information.

The 3-B information may be information about the optimal transmission beam of the small cell. The 3-B information may be information about the optimal M transmission beams. M may be a natural number. The optimal M transmission beams may be M transmission beams having good quality among all transmission beams of the small cell. The optimal M transmission beam indices may be included in the 3-B information in the order of quality.

3-C information may be information about the optimal receiving beam(s) of the terminal. Since 3-C information is information required by the terminal, 3-C information may not be reported to the base station. By reporting 3-D information, the terminal can inform the base station of the link quality (e.g., RSRP, SNR, SINR) for the optimal beam pair.

All or part of the information included in Information Set 3 may include a rank indicator (RI), a precoding matrix indicator (PMI), and/or a layer indicator (LI). The reporting procedure for Information Set 3 may be the same as or similar to the CSI reporting procedure. The method of transmitting Information Set 3 (e.g., information belonging to Information Set 3) may vary depending on the reporting target and/or reporting method.

- Transmission method 1: The terminal transmits information set 3 to the macro base station via PUCCH and/or PUSCH.

The terminal can transmit information set 3 to the macro base station via PUCCH and/or PUSCH. The macro base station can receive information set 3 from the terminal and transmit the information set 3 to the small cell via an interface between the macro base station and the small cell. The small cell can receive information set 3 from the macro base station.

- Transmission method 2: The terminal transmits information set 3 to the small cell via RACH and/or SRS.

The terminal can transmit information set 3 to the small cell via RACH and/or SRS. The RACH and/or SRS can be used to transmit some information belonging to information set 3. The small cell can receive information set 3 from the terminal and transmit the information set 3 to the macro base station via an interface between the small cell and the macro base station. The macro base station can receive information set 3 from the small cell.

- Transmission method 3: The terminal transmits information set 3 to the macro base station via PUCCH and/or PUSCH, and transmits information set 3 to the small cell via RACH and/or SRS.

The terminal can transmit information set 3 to the macro base station via PUCCH and/or PUSCH, and can transmit information set 3 to the small cell via RACH and/or SRS. Each of the macro base station and the small cell can receive information set 3 from the terminal. The information transmitted to each of the macro base station and the small cell may be some information belonging to information set 3.

- Transmission method 4: The terminal transmits information set 3 to the small cell via PUCCH and/or PUSCH.

The terminal can complete a synchronization procedure based on the SSB received from the small cell. After the synchronization procedure is completed, the terminal can receive reporting configuration information from the macro base station and/or the small cell. The terminal can transmit information set 3 to the small cell through PUCCH and/or PUSCH based on the reporting configuration information. The small cell can receive information set 3 from the terminal. The reporting configuration information may include information required for transmission of information set 3. For example, the reporting configuration information may include resource information for PUCCH and/or PUSCH. The information transmitted to the small cell may be some information belonging to information set 3.

The reporting procedure for Information Set 3 may be identical or similar to the CSI reporting procedure. If the reporting procedure for Information Set 3 is identical or similar to the CSI reporting procedure, it may be desirable to use Transmission Method 4.

4. Whether to perform the SSB retransmission procedure can be determined based on whether the synchronization procedure is completed. Modified SSB transmission configuration information can be set as needed.

Even after the SSB transmission set by the macro base station is completed, if the synchronization procedure (e.g., the synchronization procedure between the terminal and the small cell) is not completed, the macro base station can determine whether to perform the SSB retransmission procedure. The macro base station can determine whether the synchronization procedure is completed based on a synchronization completion message reported from the terminal. The macro base station can determine whether the synchronization procedure is completed based on information indicated by the synchronization completion message (e.g., success or failure). Alternatively, the macro base station can determine whether the synchronization procedure is completed based on whether the synchronization completion message is received. Alternatively, the macro base station can determine whether the synchronization procedure is completed based on whether a PUCCH, a PUSCH, a RACH, and/or an SRS including information set 3 is received. Alternatively, the macro base station can determine whether the synchronization procedure is completed based on transmission of information set 3 via the PUCCH, the PUSCH, the RACH, and/or the SRS.

The SSB transmission of the small cell can be triggered. When the terminal goes out of the coverage of the small cell, the SSB transmission of the small cell may not be necessary. In this situation, the small cell may stop the SSB transmission. Until the SSB transmission is stopped (e.g., terminated) due to the occurrence of a specific situation, the small cell may continue to perform the SSB transmission. If the synchronization procedure for the small cell is not completed, the terminal may transmit a synchronization failure (fail) message to the base station. If the synchronization failure message is received from the terminal, the base station may determine that the synchronization procedure is not completed. The synchronization failure message may be a synchronization completion message indicating a failure. The base station may determine whether the synchronization procedure is completed based on whether the PUCCH, the PUSCH, the RACH, and/or the SRS including the information set 3 are received. For example, if the reception of the PUCCH, the PUSCH, the RACH, and/or the SRS including the information set 3 fails, the base station may determine that the synchronization procedure is not completed.

If the synchronization procedure is not completed and/or a synchronization failure message is received, the macro base station may instruct (e.g., request) SSB retransmission to the small cell. To instruct SSB retransmission, the macro base station may transmit the following information set 4 to the small cell. In addition, the macro base station may transmit the following information set 4 to the terminal. The information set 4 may include at least one of the 4-A information or the 4-B information. The information set 4 may include other information in addition to the 4-A information and/or the 4-B information. The information set 4 may be modified on-demand SSB transmission configuration information.

<Information set 4>

- 4-A Information: SSB Retransmission Instruction

- 4-B Information: Reset information including the number of increased SSB transmissions, modified interval, modified period, etc. Reset information is used for modified transmission of the synchronization signal.

The 4-A information may be information indicating SSB retransmission. The 4-B information may be SSB retransmission configuration information. The 4-B information may include at least one of 2-A information, 2-B information, 2-C information, 2-D information, 2-E information, 2-F information, or 2-G information (e.g., at least one piece of information requiring update). In order to ensure reliable and stable synchronization in the SSB retransmission procedure, it may be desirable to increase the number of SSB transmissions. The number of SSB transmissions may be indicated by the 2-F information.

The SSB transmission can be continuously performed without determining whether or not to perform the SSB retransmission procedure. In other words, the SSB transmission can be continuously performed before the reception of the synchronization completion message or before the synchronization procedure is determined to be completed. If the SSB transmission is configured and/or instructed by the macro base station, the small cell can continuously perform the SSB transmission until the synchronization procedure is determined to be completed. The SSB transmission of the small cell can be performed according to a preset SSB transmission cycle. In the SSB transmission procedure of the terminal, some of the SSB transmission configuration information (e.g., 2-D information and/or 2-F information) may not be necessary. When the synchronization completion message is directly received from the terminal or when the synchronization completion message of the terminal is received from the macro base station, the small cell can determine that the synchronization procedure of the terminal is completed. Alternatively, the small cell can determine that the synchronization procedure of the terminal is completed based on another method.

If a specific number or more of SSBs are transmitted according to an SSB transmission period based on SSB transmission configuration information, or if an SSB is transmitted during a specific time interval based on the SSB transmission configuration information, the SSB transmission period can be changed, and the SSB transmission can be continuously performed based on the changed SSB transmission period. The SSB transmission procedure can be performed without the need to determine whether to retransmit an SSB. The changed SSB transmission period (e.g., a different SSB transmission period) can be a default SSB transmission period (e.g., 20 ms). The default SSB transmission period can be used in the initial access procedure. Alternatively, the different SSB transmission period (e.g., the changed SSB transmission period) can be a separately set SSB transmission period. It may be desirable that the different SSB transmission period (e.g., the changed SSB transmission period) is set to a value greater than a previous SSB transmission period. The on-demand SSB transmission configuration information can include one or more SSB transmission periods, and the different SSB transmission period can be one SSB transmission period among the one or more SSB transmission periods.

Figure 18 is a flowchart illustrating embodiments of a transmission method of on-demand SSB.

Referring to FIG. 18, the macro base station may mean the first base station, and the small cell may mean the second base station. Alternatively, the macro base station may mean the first cell, and the small cell may mean the second cell. The small cell may transmit SSB based on a request of the terminal and/or the macro base station. The terminal may transmit a signal for triggering on-demand SSB transmission to the macro base station (S1801). The macro base station may determine that the on-demand SSB transmission is triggered based on a signal received from the terminal. Alternatively, the on-demand SSB transmission may be triggered by the macro base station. In this case, S1801 may be omitted. When SSB transmission of the small cell is required (e.g., when on-demand SSB transmission is triggered), the macro base station may transmit a signal requesting provision of information set 1 to the terminal (S1802). The terminal may determine that provision of information set 1 is requested based on a signal received from the macro base station. The terminal can generate information set 1 and transmit (e.g., report) information set 1 to the macro base station (S1803). The macro base station can receive information set 1 from the terminal and confirm information included in information set 1.

In the initial connection procedure between the terminal and the macro base station, the terminal may report information set 1 to the macro base station. In the above situation, if the need for SSB transmission is raised by the macro base station, if the need for SSB transmission is raised by the terminal, or if a signal triggering on-demand SSB transmission is received from the terminal, S1802 and S1803 may be omitted.

The macro base station can generate information set 2 based on information set 1 received from the terminal. The macro base station can transmit information set 2 to the terminal (S1804). The terminal can receive information set 2 from the macro base station and check information included in information set 2. The macro base station can transmit information set 2 to the small cell (S1805). The small cell can receive information set 2 from the macro base station and check information included in information set 2.

The small cell can determine that SSB transmission is required based on information set 2. In other words, the small cell can determine that on-demand SSB transmission is triggered based on information set 2. The small cell can transmit an SSB to the terminal based on information set 2 (S1806). The terminal can receive the SSB from the small cell and perform a synchronization procedure based on the SSB. The terminal can generate an information set 3 including a result for the synchronization procedure. The terminal can transmit the information set 3 to the macro base station (S1807).

The macro base station can receive information set 3 from the terminal. The macro base station can determine whether the synchronization procedure is successful based on the information included in the information set 3. The macro base station can determine whether to perform the SSB retransmission procedure based on the information included in the information set 3. The macro base station can transmit the information set 3 of the terminal to the small cell (S1808). The small cell can receive information set 3 from the macro base station. The small cell can determine whether the synchronization procedure is successful based on the information included in the information set 3. The small cell can determine whether to perform the SSB retransmission procedure based on the information included in the information set 3. In the embodiment of FIG. 18, information set 3 can be reported and/or transmitted based on transmission method 1. Information set 3 can be reported and/or transmitted based on transmission method 2, transmission method 3, or transmission method 4 instead of transmission method 1.

If it is determined that SSB transmission is required in the small cell without reporting information set 1, the macro base station can transmit information set 2 to the small cell. Information set 2 can be preset in the macro base station. The small cell can receive information set 2 from the macro base station, and perform SSB transmission based on the information included in the information set 2. Alternatively, if it is determined that SSB transmission is required in the small cell, the macro base station can transmit a signaling message triggering SSB transmission to the small cell without transmitting information set 2. The small cell can receive the signaling message from the macro base station, determine that SSB transmission is triggered based on the signaling message, and perform SSB transmission. The SSB transmission can be performed based on information set 2 (e.g., information corresponding to information set 2). Information set 2 (e.g., information corresponding to information set 2) can be preset in the small cell.

The information set transmitted in each step of the embodiment of FIG. 18 may include all or part of the information of the information set proposed in the present disclosure. The on-demand SSB transmission may be performed in not only the small cell but also other base stations and/or other cells depending on the configuration of the macro base station. The embodiment of FIG. 18 (e.g., the on-demand SSB transmission procedure) may be applied to all types of base stations constituting a primary cell and a secondary cell. The macro cell may be a PCell (primary cell) or a PSCell (primary secondary cell). The small cell may be a SCell (secondary cell). The SSB may be an SSB including a PSS, an SSS, and a PBCH. The SSB may be an SSB including a PSS and an SSS without a PBCH. The SSB may be an SSB including only an SSS. The SSB may include a PSS having a sequence different from an existing sequence (e.g., a new sequence). An SSB may include an SSS having a different sequence than the existing sequence (e.g., a new sequence).

In a different way from S1801, the UE may directly transmit a signaling message to the small cell for triggering SSB transmission. The signaling message (e.g., a signal) for triggering SSB transmission may be transmitted via an uplink signal and/or channel (e.g., RACH, SRS, PUCCH, PUSCH). Information on the uplink signal and/or channel for transmission of the signaling message for triggering SSB transmission may be configured (e.g., indicated) by signaling of the macro base station (e.g., UE-specific RRC, MAC CE, DCI (e.g., common DCI)).

The small cell can receive a signaling message from a terminal, determine that SSB transmission is triggered based on the signaling message, and perform SSB transmission. The small cell can start SSB transmission based on all or part of information belonging to information set 2 (e.g., preset information set 2). Among the points in time at which SSB transmission is possible, the small cell can start SSB transmission at the earliest SSB transmission point in time after the processing time for a signaling message for triggering SSB transmission. The transmission point in time of an uplink signal and/or channel for triggering SSB transmission can be inferred based on a downlink synchronization signal. Since it is before the SSB transmission of the small cell starts, the transmission point in time of an uplink signal and/or channel for the small cell can be inferred based on the SSB transmitted from the macro base station.

Alternatively, the uplink transmission configuration information received from the macro base station may include information related to a transmission time of an uplink signal and/or channel for the small cell. The terminal may confirm (e.g., infer) a transmission time of an uplink signal and/or channel for the small cell based on the uplink transmission configuration information received from the macro base station (e.g., information for transmission of an uplink signal and/or channel), and transmit an uplink signal and/or channel for triggering SSB transmission to the small cell at the transmission time.

In an environment where a primary cell and a secondary cell are configured, a secondary cell performing NSA (non stand-alone) operation can support an on-demand SSB transmission function. In addition, a cell performing SA (stand-alone) operation can also support an on-demand SSB transmission function. Since a base station performing SA operation cannot receive SSB transmission configuration information from other base stations in advance, the SSB transmission configuration information can be configured in advance. If there is no terminal within the coverage of the base station or if there is no terminal requiring SSB reception, the base station may not perform SSB transmission to reduce energy consumption. If a terminal newly enters the coverage of the base station or if a terminal within the coverage of the base station requires SSB reception for initial access, the terminal can request SSB transmission to the base station, and the base station can transmit SSB according to the request of the terminal. At this time, the terminal can transmit a C-WUS (cell-wakeup signal) for SSB transmission request to the base station.

In an activated SCell, a UE can initiate a beam failure recovery procedure due to a beam failure. In this case, since the UE can make a more appropriate judgment than the BS, it can request a suitable SSB beam to the BS or report an unsuitable SSB beam to the BS. The SSB beam may be a beam used for SSB transmission. In this scenario, the delay time of the beam failure recovery procedure based on on-demand SSB may be less than the delay time of the beam failure recovery procedure based on periodic SSB. If the configured SCell is not activated, the BS may be overloaded by unknown uplink (UL) traffic (e.g., MAC CE for reporting buffer status). Activation of the SCell may be required to offload the UL traffic. In other words, the UE may request activation of the SCell to offload the UL traffic.

The UE can trigger on-demand SSB transmission for SCell activation. For fast SCell activation, the procedure for triggering on-demand SSB transmission may be more efficient than "the procedure in which the UE reports its uplink buffer status to the base station, and the base station triggers SCell activation based on the uplink buffer status of the UE". In other words, if the UE does not receive a signal (e.g., data) from the base station for a long time on an activated SCell, the UE may lose synchronization with the base station. In such a situation, the UE needs to receive multiple sets of SSB bursts for resynchronization. For fast SCell resynchronization, using on-demand SSB may be more efficient than using conventional SSB with long periodicity. In this case, to trigger the on-demand SSB transmission, the UE may transmit C-WUS.

At the time when a terminal transmits C-WUS to a base station, the terminal may not be synchronized with the base station. In this case, since the base station cannot predict the time when the terminal transmits C-WUS, continuous monitoring of the C-WUS of the terminal may be required. Energy consumption of the base station may increase due to the monitoring operation of the C-WUS. Considering resource efficiency, the C-WUS may be transmitted according to a preset cycle. In other words, C-WUS transmission may not always be possible. In order for the base station to predict the time when the terminal transmits the C-WUS, a synchronization procedure between the terminal and the base station may be required before C-WUS transmission. It may be desirable for the base station to transmit a separate SSB (e.g., S(simplified)-SSB) for the synchronization procedure between the terminal and the base station instead of the existing SSB (e.g., N(normal)-SSB, SSB).

A base station supporting a transmission/reception operation using multiple beams can derive a reception beam based on a transmission beam. A terminal supporting a transmission/reception operation using multiple beams can derive a transmission beam based on a reception beam. The base station can transmit an S-SSB in a beam sweeping manner. The terminal can receive an S-SSB from the base station and derive a transmission beam for C-WUS transmission based on the S-SSB. A transmittable time point of the C-WUS can be set according to a specific offset based on the S-SSB. Alternatively, the transmittable time point of the C-WUS can be set to the earliest time point after a specific time point in consideration of a processing time of the received S-SSB.

The base station can transmit the S-SSB for the synchronization procedure instead of the N-SSB. In this case, the S-SSB can be composed of only the PSS or SSS of the N-SSB. Or, the S-SSB can be composed of a new type of sequence. It may be desirable to set the transmission period of the S-SSB longer than the transmission period of the N-SSB (e.g., 20 ms) in terms of energy saving. It may be desirable to set the transmission resources of the S-SSB so as not to overlap with the transmission resources of the N-SSB. The terminal can perform a synchronization procedure (e.g., a downlink synchronization procedure) with the base station based on the S-SSB, and derive a suitable transmission beam for C-WUS transmission based on the S-SSB. After deriving the transmission beam, the terminal can predict a transmittable time point of the C-WUS based on the synchronization between the terminal and the base station, and transmit the C-WUS to the base station using the derived transmission beam at the predicted transmittable time point.

The transmittable point in time of C-WUS may vary depending on the additionally received S-SSB. If the reception of S-SSB is successful, the terminal can transmit C-WUS at the point in time associated with the S-SSB. To support the above operation, the association between the transmittable points of S-SSB and C-WUS may be set in advance. Although the uplink synchronization procedure between the base station and the terminal is not performed, the base station can predict the transmission point of C-WUS of the terminal according to the downlink synchronization. Therefore, the base station can perform a monitoring operation for C-WUS at the predicted transmission point in time. In this case, energy consumption can be reduced compared to the continuous monitoring operation for C-WUS.

Figure 19 is a conceptual diagram illustrating embodiments of S-SSB transmission and C-WUS transmission.

Referring to FIG. 19, a base station can transmit an S-SSB. A transmission period of the S-SSB can be longer than a transmission period of an N-SSB (e.g., SSB). The SSB illustrated in FIG. 19 can mean an N-SSB. A terminal can receive an S-SSB from a base station, and determine a transmission time (e.g., a transmittable time) of a C-WUS based on the S-SSB. The terminal can transmit the C-WUS to the base station at the determined transmission time. The base station can receive the C-WUS from the terminal, and transmit the N-SSB to the terminal. The terminal can receive the N-SSB from the base station. The C-WUS can trigger the N-SSB transmission. The N-SSB transmission can be an on-demand SSB transmission.

The N-SSB transmission period can be set to 20ms. The S-SSB transmission period for obtaining synchronization required for C-WUS transmission can be set to 60ms. The terminal can obtain synchronization based on the S-SSB, and request N-SSB transmission by transmitting C-WUS based on the synchronization. After the C-WUS is received from the terminal, the base station can transmit the N-SSB. In other words, when the C-WUS is received from the terminal, the base station can determine that N-SSB transmission is requested, and transmit the N-SSB based on the determination.

The S-SSB transmission period can be longer than the N-SSB transmission period, and the structure of the S-SSB can be simpler than the structure of the N-SSB. In this case, the signaling overhead and/or energy consumption for the S-SSB transmission can be reduced. The embodiment of FIG. 19 can be applied to both the FDD system and the TDD system regardless of the duplex mode.

If C-WUS is received from the terminal, the base station can transmit the same N-SSB as the existing SSB. The terminal can receive the N-SSB from the base station and perform the initial access procedure based on the N-SSB. If a PRACH (e.g., Msg1) is received from the terminal performing the initial access procedure based on the N-SSB, the base station can stop the N-SSB transmission. If the CBRA method is used, the possibility that the terminal transmits the same PRACH may be high. Therefore, the base station can stop the N-SSB transmission after Msg3 is received from the terminal. Alternatively, the base station can stop the N-SSB transmission after feedback information (e.g., ACK or NACK) for Msg4 is received from the terminal.

If the base station receives specific signals and/or channels (e.g., feedback information for PRACH, Msg3, Msg4) from the terminal after transmitting the N-SSB at the request of the terminal, the base station may stop the N-SSB transmission. If the specific signals and/or channels are not received from the terminal, the base station may continue to perform the N-SSB transmission. In this case, the effect of reducing energy consumption may be minimal.

If the base station does not receive a specific signal and/or channel from the terminal after a specific time or a specific period from the time of transmitting the on-demand SSB (e.g., N-SSB), the base station may stop the on-demand SSB transmission. The specific time and/or the specific period may be preset. Considering the beam sweeping operation, the SSB burst may be composed of a plurality of adjacent N-SSBs. Since the SSB burst is transmitted during one period, the number of transmissions of the SSB bursts (e.g., the number of SSB bursts) may be set instead of the specific time and/or the specific period.

Embodiments of the present disclosure can be applied to SSB transmission upon request of a terminal. Embodiments of the present disclosure can also be applied to transmission of system information (e.g., SIB1) having a one-to-one mapping relationship with SSB. In other words, SSB and SIB1 mapped to the SSB can be transmitted based on a request of a terminal. When transmission of SSB is stopped, transmission of SIB1 mapped to the SSB can also be stopped.

C-WUS can be an existing uplink signal and/or channel (e.g., PUCCH, PUSCH, SRS, RACH). C-WUS can be a new signal and/or channel, and the new signal and/or channel can be configured with a new sequence. RA procedure can support CBRA mode and/or CFRA mode. Therefore, C-WUS can be transmitted based on CBRA mode or CFRA mode. C-WUS can be transmitted through PUCCH and/or PUSCH. In this case, request information for SSB transmission for each of a plurality of SCells can be set as a bitmap, and the bitmap can be included in C-WUS.

The operation of the method according to an embodiment of the present disclosure can be implemented as a computer-readable program or code on a computer-readable recording medium. The computer-readable recording medium includes all kinds of recording devices that store information that can be read by a computer system. In addition, the computer-readable recording medium can be distributed over network-connected computer systems so that the computer-readable program or code can be stored and executed in a distributed manner.

Additionally, the computer-readable recording medium may include hardware devices specifically configured to store and execute program instructions, such as ROM, RAM, flash memory, etc. The program instructions may include not only machine language codes generated by a compiler, but also high-level language codes that can be executed by the computer using an interpreter, etc.

While some aspects of the present disclosure have been described in the context of an apparatus, that may also represent a description of a corresponding method, wherein a block or device corresponds to a method step or a feature of a method step. Similarly, aspects described in the context of a method may also be described as a feature of a corresponding block or item or a corresponding device. Some or all of the method steps may be performed by (or using) a hardware device, such as, for example, a microprocessor, a programmable computer or an electronic circuit. In some embodiments, at least one or more of the most significant method steps may be performed by such a device.

In embodiments, a programmable logic device (e.g., a field-programmable gate array) may be used to perform some or all of the functions of the methods described herein. In embodiments, a field-programmable gate array may operate in conjunction with a microprocessor to perform one of the methods described herein. In general, the methods are preferably performed by some hardware device.

Although the present disclosure has been described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various modifications and changes may be made to the present disclosure without departing from the spirit and scope of the present disclosure as set forth in the claims below.

Claims (20)

As a terminal method,
A step of receiving on-demand SSB (synchronization signal block) transmission setting information from a first base station to which the terminal is connected; and
A step of receiving an on-demand SSB from a second base station based on the on-demand SSB transmission setting information is included.
The above-described on-demand SSB transmission configuration information includes at least one of capability information of the second base station, on-demand SSB resource information, the number of on-demand SSB transmissions, on-demand SSB transmission instructions, or CSI (channel state information) configuration information.
Terminal method. In claim 1,
The above capability information includes at least one of a cell ID (identifier), a system bandwidth, a numerology, a number of beams, or an antenna configuration of the second base station.
Terminal method. In claim 1,
The on-demand SSB resource information includes at least one of time resource information for on-demand SSB transmission, frequency resource information for the on-demand SSB transmission, period information of the on-demand SSB transmission, information on when actual transmission of the on-demand SSB starts, or information on when actual transmission of the on-demand SSB ends.
Terminal method. In claim 3,
The above time resource information includes at least one of a system frame number (SFN), a half radio frame indicator, a subframe index, a slot index, or information about an SSB actually transmitted.
Terminal method. In claim 3,
The above frequency resource information includes at least one of information about a synchronization raster or information about an Absolute Radio Frequency Channel Number (ARFCN).
Terminal method. In claim 1,
The above on-demand SSB transmission instruction is information that instructs the activation of the second base station.
Terminal method. In claim 1,
The above CSI setting information includes resource information for reporting CSI generated based on the measurement results of the on-demand SSB.
Terminal method. In claim 1,
The above-mentioned on-demand SSB is a cell defining SSB or a non-cell defining SSB.
Terminal method. In claim 1,
The above-mentioned on-demand SSB is received at a frequency location other than the synchronization raster.
Terminal method. In claim 1,
If the on-demand SSB is a cell-defined SSB, the on-demand SSB includes a first barring indicator, and the first barring indicator is used to block a legacy terminal from accessing the second base station.
Terminal method. In claim 10,
If the terminal is a terminal capable of receiving the on-demand SSB, the terminal ignores the first barring indicator included in the on-demand SSB, and the terminal determines whether to barge the second base station based on the second barring indicator included in the RMSI (remaining minimum system information) received from the second base station.
Terminal method. As a method of the first base station,
A step for generating on-demand SSB (synchronization signal block) transmission configuration information including at least one of capability information of a second base station, on-demand SSB resource information, the number of on-demand SSB transmissions, on-demand SSB transmission instructions, or channel state information (CSI) configuration information; and
A step of transmitting the above-mentioned on-demand SSB transmission setting information to a terminal is included.
On-demand SSB based on the above-mentioned on-demand SSB transmission setting information is transmitted from the second base station to the terminal.
Method of the first base station. In claim 12,
The above capability information includes at least one of a cell ID (identifier), a system bandwidth, a numerology, a number of beams, or an antenna configuration of the second base station.
Method of the first base station. In claim 12,
The on-demand SSB resource information includes at least one of time resource information for on-demand SSB transmission, frequency resource information for the on-demand SSB transmission, period information of the on-demand SSB transmission, information on when actual transmission of the on-demand SSB starts, or information on when actual transmission of the on-demand SSB ends.
Method of the first base station. In claim 12,
If the on-demand SSB is a cell defining SSB, the on-demand SSB includes a first barring indicator, and the first barring indicator is used to block a legacy terminal from accessing the second base station.
Method of the first base station. In claim 12,
A step of generating modified on-demand SSB transmission setting information when the synchronization procedure between the terminal and the second base station is not completed;
A step of transmitting the modified on-demand SSB transmission setting information to the second base station; and
Further comprising a step of transmitting the above modified on-demand SSB transmission setting information to the terminal,
The on-demand SSB based on the above modified on-demand SSB transmission setting information is retransmitted from the second base station to the terminal.
Method of the first base station. As a method of the second base station,
A step of receiving on-demand SSB (synchronization signal block) transmission setting information from a first base station; and
A step of transmitting an on-demand SSB to a terminal based on the on-demand SSB transmission setting information is included.
The above-described on-demand SSB transmission configuration information includes at least one of capability information of the second base station, on-demand SSB resource information, the number of on-demand SSB transmissions, on-demand SSB transmission instructions, or CSI (channel state information) configuration information.
Method of the second base station. In claim 17,
The above capability information includes at least one of a cell ID (identifier), a system bandwidth, a numerology, a number of beams, or an antenna configuration of the second base station.
Method of the second base station. In claim 17,
The on-demand SSB resource information includes at least one of time resource information for on-demand SSB transmission, frequency resource information for the on-demand SSB transmission, period information of the on-demand SSB transmission, information on when actual transmission of the on-demand SSB starts, or information on when actual transmission of the on-demand SSB ends.
Method of the second base station. In claim 17,
If the synchronization procedure between the terminal and the second base station is not completed, a step of receiving modified on-demand SSB transmission setting information from the first base station; and
Comprising a step of retransmitting the on-demand SSB to the terminal based on the modified on-demand SSB transmission setting information.
Method of the second base station.

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