WO2018135672A1 - Method for estimating difference in inter-symbol phase rotations in wireless communication system, and apparatus therefor - Google Patents

Abstract

Disclosed is a method for estimating the difference in inter-symbol phase rotations in a wireless communication system. The method, which is carried out by a terminal, comprises the steps of: receiving, from a base station, control data associated with the transmission of a signal utilized in estimating the difference in inter-symbol phase rotations; receiving from the base station, by means of a particular resource, a first signal utilized in estimating the phase rotations; estimating the difference in inter-symbol phase rotations by means of the received first signal; receiving from the base station, by means of a symbol following the transmission symbol of the first signal, a second signal utilized for estimating the phase rotations; estimating the difference in inter-symbol phase rotations by means of the received second signal; and decoding the received signal in consideration of the difference in phase rotations estimated by means of the second signal.

Description

Method and apparatus for estimating phase rotation difference between symbols in wireless communication system

The present disclosure relates to a wireless communication system, and more particularly, to a method and apparatus for estimating a phase rotation difference between symbols in a wireless communication system.

Mobile communication systems have been developed to provide voice services while ensuring user activity. However, the mobile communication system has expanded not only voice but also data service.As a result of the explosive increase in traffic, a shortage of resources and users are demanding higher speed services, a more advanced mobile communication system is required. have.

The requirements of the next generation of mobile communication systems will be able to accommodate the explosive data traffic, dramatically increase the data rate per user, greatly increase the number of connected devices, very low end-to-end latency, and high energy efficiency. It should be possible. Dual connectivity, Massive Multiple Input Multiple Output (MIMO), In-band Full Duplex, Non-Orthogonal Multiple Access (NOMA), Super Various technologies such as wideband support and device networking have been studied.

An object of the present specification is to provide a method of estimating a phase rotation difference between symbols using a PCRS and / or a data symbol.

In addition, the present specification provides a PCRS structure that can reduce the performance degradation that may occur by estimating a phase rotation difference between symbols using a PCRS and a data symbol when a large Caro Frequency Offset (CFO) occurs. For the purpose of providing it.

The technical problems to be achieved in the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned above will be clearly understood by those skilled in the art from the following description. Could be.

In the present specification, a method for estimating a phase rotation difference between symbols in a wireless communication system, and the method performed by the terminal is a signal of the signal used for estimating the phase rotation difference between the symbols Receiving control information related to transmission from a base station; Receiving a first signal used for phase rotation estimation from the base station through a specific resource, wherein the specific resource is set to a symbol after a symbol for transmitting a demodulation reference signal (DMRS) in a time domain and a specific index in a frequency domain Is set to at least one frequency tone corresponding to; Estimating a phase rotation difference between a transmission symbol of the first signal and a symbol immediately before the transmission symbol of the first signal using the received first signal; Receiving a second signal from the base station, the second signal being used for phase rotation estimation through a symbol after the transmission symbol of the first signal; Estimating a phase rotation difference between the transmission symbol of the second signal and the transmission symbol of the first signal using the received second signal; And decoding the received signal in consideration of the phase rotation difference estimated through the second signal.

In addition, in the present specification, the estimation of the phase rotation difference between the transmission symbol of the second signal and the transmission symbol of the first signal may reflect the phase rotation difference between symbols estimated using the received first signal. .

In the present specification, the first signal is characterized in that it is a phase rotation compensation reference signal (PCRS).

Also, in the present specification, a symbol in which the second signal is transmitted is a data symbol, and a data symbol in which the second signal is transmitted has a data symbol and a modulation order in which the second signal is not transmitted. It is characterized in that it is set differently.

In addition, in the present specification, the phase rotation difference estimation range using the second signal is determined according to the modulation order of the second signal.

Also, in the present specification, the first signal is used when it is out of a range of a phase rotation difference that can be estimated as the second signal.

The control information may include at least one of information indicating whether the first signal is transmitted or information indicating whether the second signal is transmitted.

In the present specification, the control information is received from the base station through Downlink Control Information (DCI) or Radio Resource Control (RRC) signaling.

Also, in the present specification, the number of transmission symbols of the first signal is one or two, and when the number of transmission symbols of the first signal is two, the transmission symbols of the first signal are continuous symbols. It is done.

In addition, the number of the specific index in the present specification is characterized in that two.

In addition, the present disclosure provides a terminal for estimating a phase rotation difference between symbols in a wireless communication system, the terminal comprising: a radio frequency (RF) unit for transmitting and receiving a radio signal; And a processor for controlling the RF unit, the processor receiving, from a base station, control information related to transmission of a signal used for estimating a phase rotation difference between symbols; A first signal used for phase rotation estimation is received from the base station through a specific resource, and the specific resource is set in a symbol after a symbol in which a demodulation reference signal (DMRS) is transmitted in a time domain, and at a specific index in a frequency domain. Set to a corresponding at least one frequency tone; Estimate a phase rotation difference between a transmission symbol of the first signal and a symbol immediately preceding the transmission symbol of the first signal using the received first signal; Receive from the base station a second signal used for phase rotation estimation via a symbol after the transmission symbol of the first signal; Estimating a phase rotation difference between the transmission symbol of the second signal and the transmission symbol of the first signal using the received second signal; And decoding the received signal in consideration of the phase rotation difference estimated through the second signal.

In the present specification, when a large Carrie Frequency Offset (CFO) occurs, the difference in phase rotation may be estimated by using PCRS, and then the phase rotation difference between symbols may be estimated using data symbols. There is an effect that can reduce.

The effects obtainable in the present invention are not limited to the above-mentioned effects, and other effects not mentioned will be clearly understood by those skilled in the art from the following description. .

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, included as part of the detailed description in order to provide a thorough understanding of the present invention, provide embodiments of the present invention and together with the description, describe the technical features of the present invention.

1 illustrates a structure of a radio frame in a wireless communication system to which the present invention can be applied.

2 is a diagram illustrating a resource grid for one downlink slot in a wireless communication system to which the present invention can be applied.

3 shows a structure of a downlink subframe in a wireless communication system to which the present invention can be applied.

4 shows a structure of an uplink subframe in a wireless communication system to which the present invention can be applied.

5 illustrates a reference signal pattern mapped to a downlink resource block pair in a wireless communication system to which the present invention can be applied.

6 is a diagram illustrating an example of a power spectral density of an oscillator.

7 illustrates an example of a PCRS arrangement for performing phase rotation estimation.

8 is a diagram illustrating an example of data symbol arrangement for phase rotation estimation.

9 is a diagram illustrating an example of estimating a phase rotation difference between symbols using BPSK symbols of contiguous OFDM symbols.

10 is a diagram illustrating an example of PCRS and data symbol arrangement for estimating phase rotation proposed in the present specification.

FIG. 11 is a diagram illustrating an example of a phase rotation estimation range that may be estimated between two OFDM symbols.

12 is a diagram illustrating a method of estimating a phase rotation difference by using a concatenated reference signal proposed in the specification.

FIG. 13 is a diagram illustrating an example of deriving a temporary phase difference value between two symbols by calculating a conjugation product of a third symbol and a fourth symbol proposed in the present specification.

14 is a diagram illustrating an example of a method of estimating a phase rotation difference in an environment in which a large CFO is proposed in the present specification.

15 is a flowchart illustrating an example of a method of decoding a received signal by estimating a phase rotation difference between symbols proposed in the present specification.

16 illustrates a block diagram of a wireless communication device to which the present invention can be applied.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. The detailed description, which will be given below with reference to the accompanying drawings, is intended to explain exemplary embodiments of the present invention and is not intended to represent the only embodiments in which the present invention may be practiced. The following detailed description includes specific details in order to provide a thorough understanding of the present invention. However, one of ordinary skill in the art appreciates that the present invention may be practiced without these specific details.

In some instances, well-known structures and devices may be omitted or shown in block diagram form centering on the core functions of the structures and devices in order to avoid obscuring the concepts of the present invention.

In this specification, a base station has a meaning as a terminal node of a network that directly communicates with a terminal. The specific operation described as performed by the base station in this document may be performed by an upper node of the base station in some cases. That is, it is obvious that various operations performed for communication with a terminal in a network composed of a plurality of network nodes including a base station may be performed by the base station or other network nodes other than the base station. A 'base station (BS)' may be replaced by terms such as a fixed station, a Node B, an evolved-NodeB (eNB), a base transceiver system (BTS), an access point (AP), and the like. . In addition, a 'terminal' may be fixed or mobile, and may include a user equipment (UE), a mobile station (MS), a user terminal (UT), a mobile subscriber station (MSS), a subscriber station (SS), and an AMS ( Advanced Mobile Station (WT), Wireless Terminal (WT), Machine-Type Communication (MTC) Device, Machine-to-Machine (M2M) Device, Device-to-Device (D2D) Device, etc.

Hereinafter, downlink (DL) means communication from a base station to a terminal, and uplink (UL) means communication from a terminal to a base station. In downlink, a transmitter may be part of a base station, and a receiver may be part of a terminal. In uplink, a transmitter may be part of a terminal and a receiver may be part of a base station.

Specific terms used in the following description are provided to help the understanding of the present invention, and the use of such specific terms may be changed to other forms without departing from the technical spirit of the present invention.

The following techniques are code division multiple access (CDMA), frequency division multiple access (FDMA), time division multiple access (TDMA), orthogonal frequency division multiple access (OFDMA), single carrier frequency division multiple access (SC-FDMA), and NOMA It can be used in various radio access systems such as non-orthogonal multiple access. CDMA may be implemented by a radio technology such as universal terrestrial radio access (UTRA) or CDMA2000. TDMA may be implemented with wireless technologies such as global system for mobile communications (GSM) / general packet radio service (GPRS) / enhanced data rates for GSM evolution (EDGE). OFDMA may be implemented in a wireless technology such as IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, evolved UTRA (E-UTRA). UTRA is part of a universal mobile telecommunications system (UMTS). 3rd generation partnership project (3GPP) long term evolution (LTE) is a part of evolved UMTS (E-UMTS) using E-UTRA, and employs OFDMA in downlink and SC-FDMA in uplink. LTE-A (advanced) is the evolution of 3GPP LTE.

Embodiments of the present invention may be supported by standard documents disclosed in at least one of the wireless access systems IEEE 802, 3GPP and 3GPP2. That is, steps or parts which are not described to clearly reveal the technical spirit of the present invention among the embodiments of the present invention may be supported by the above documents. In addition, all terms disclosed in the present document can be described by the above standard document.

For clarity, the following description focuses on 3GPP LTE / LTE-A, but the technical features of the present invention are not limited thereto.

General wireless communication system to which the present invention can be applied

1 illustrates a structure of a radio frame in a wireless communication system to which the present invention can be applied.

3GPP LTE / LTE-A supports a type 1 radio frame structure applicable to frequency division duplex (FDD) and a type 2 radio frame structure applicable to time division duplex (TDD).

In FIG. 1, the size of the radio frame in the time domain is expressed as a multiple of a time unit of T_s = 1 / (15000 * 2048). Downlink and uplink transmission consists of a radio frame having a period of T_f = 307200 * T_s = 10ms.

1A illustrates the structure of a type 1 radio frame. Type 1 radio frames may be applied to both full duplex and half duplex FDD.

A radio frame consists of 10 subframes. One radio frame is composed of 20 slots having a length of T_slot = 15360 * T_s = 0.5ms, and each slot is assigned an index of 0 to 19. One subframe consists of two consecutive slots in the time domain, and subframe i consists of slot 2i and slot 2i + 1. The time taken to transmit one subframe is called a transmission time interval (TTI). For example, one subframe may have a length of 1 ms and one slot may have a length of 0.5 ms.

In FDD, uplink transmission and downlink transmission are distinguished in the frequency domain. While there is no restriction on full-duplex FDD, the terminal cannot simultaneously transmit and receive in half-duplex FDD operation.

One slot includes a plurality of orthogonal frequency division multiplexing (OFDM) symbols in the time domain and a plurality of resource blocks (RBs) in the frequency domain. Since 3GPP LTE uses OFDMA in downlink, the OFDM symbol is for representing one symbol period. The OFDM symbol may be referred to as one SC-FDMA symbol or symbol period. A resource block is a resource allocation unit and includes a plurality of consecutive subcarriers in one slot.

FIG. 1B illustrates a frame structure type 2. FIG.

Type 2 radio frames consist of two half frames each 153600 * T_s = 5 ms in length. Each half frame consists of five subframes of 30720 * T_s = 1ms in length.

In a type 2 frame structure of a TDD system, an uplink-downlink configuration is a rule indicating whether uplink and downlink are allocated (or reserved) for all subframes.

Table 1 shows an uplink-downlink configuration.

Referring to Table 1, for each subframe of a radio frame, 'D' represents a subframe for downlink transmission, 'U' represents a subframe for uplink transmission, and 'S' represents a downlink pilot. A special subframe consisting of three fields: a time slot, a guard period (GP), and an uplink pilot time slot (UpPTS).

DwPTS is used for initial cell search, synchronization or channel estimation at the terminal. UpPTS is used for channel estimation at the base station and synchronization of uplink transmission of the terminal. GP is a section for removing interference caused in the uplink due to the multipath delay of the downlink signal between the uplink and the downlink.

Each subframe i is composed of slots 2i and slots 2i + 1 each having a length of T_slot = 15360 * T_s = 0.5ms.

The uplink-downlink configuration can be classified into seven types, and the location and / or number of downlink subframes, special subframes, and uplink subframes are different for each configuration.

The time point when the downlink is changed from the uplink or the time point when the uplink is switched to the downlink is called a switching point. Switch-point periodicity refers to a period in which an uplink subframe and a downlink subframe are repeatedly switched in the same manner, and both 5ms or 10ms are supported. In case of having a period of 5ms downlink-uplink switching time, the special subframe S exists every half-frame, and in case of having a period of 5ms downlink-uplink switching time, it exists only in the first half-frame.

In all configurations, subframes 0 and 5 and DwPTS are sections for downlink transmission only. The subframe immediately following the UpPTS and the subframe subframe is always an interval for uplink transmission.

The uplink-downlink configuration may be known to both the base station and the terminal as system information. When the uplink-downlink configuration information is changed, the base station may notify the terminal of the change of the uplink-downlink allocation state of the radio frame by transmitting only an index of the configuration information. In addition, the configuration information is a kind of downlink control information, which may be transmitted through a physical downlink control channel (PDCCH) like other scheduling information, and is commonly transmitted to all terminals in a cell through a broadcast channel as broadcast information. May be

Table 2 shows the configuration of the special subframe (length of DwPTS / GP / UpPTS).

The structure of a radio frame according to the example of FIG. 1 is just one example, and the number of subcarriers included in the radio frame or the number of slots included in the subframe and the number of OFDM symbols included in the slot may vary. Can be.

2 is a diagram illustrating a resource grid for one downlink slot in a wireless communication system to which the present invention can be applied.

Referring to FIG. 2, one downlink slot includes a plurality of OFDM symbols in the time domain. Here, one downlink slot includes seven OFDM symbols, and one resource block includes 12 subcarriers in a frequency domain, but is not limited thereto.

Each element on the resource grid is a resource element, and one resource block (RB) includes 12 × 7 resource elements. The number N ^ DL of resource blocks included in the downlink slot depends on the downlink transmission bandwidth.

The structure of the uplink slot may be the same as the structure of the downlink slot.

3 shows a structure of a downlink subframe in a wireless communication system to which the present invention can be applied.

Referring to FIG. 3, up to three OFDM symbols in the first slot in a subframe are control regions to which control channels are allocated, and the remaining OFDM symbols are data regions to which PDSCH (Physical Downlink Shared Channel) is allocated. data region). An example of a downlink control channel used in 3GPP LTE includes a physical control format indicator channel (PCFICH), a physical downlink control channel (PDCCH), a physical hybrid-ARQ indicator channel (PHICH), and the like.

The PCFICH is transmitted in the first OFDM symbol of a subframe and carries information about the number of OFDM symbols (ie, the size of the control region) used for transmission of control channels within the subframe. The PHICH is a response channel for the uplink and carries an ACK (Acknowledgement) / NACK (Not-Acknowledgement) signal for a hybrid automatic repeat request (HARQ). Control information transmitted through the PDCCH is called downlink control information (DCI). The downlink control information includes uplink resource allocation information, downlink resource allocation information or an uplink transmission (Tx) power control command for a certain terminal group.

The PDCCH is a resource allocation and transmission format of DL-SCH (Downlink Shared Channel) (also referred to as a downlink grant), resource allocation information of UL-SCH (Uplink Shared Channel) (also called an uplink grant), and PCH ( Paging information in paging channel, system information in DL-SCH, resource allocation for upper-layer control message such as random access response transmitted in PDSCH, arbitrary terminal It may carry a set of transmission power control commands for the individual terminals in the group, activation of Voice over IP (VoIP), and the like. The plurality of PDCCHs may be transmitted in the control region, and the terminal may monitor the plurality of PDCCHs. The PDCCH consists of a set of one or a plurality of consecutive CCEs. CCE is a logical allocation unit used to provide a PDCCH with a coding rate according to the state of a radio channel. The CCE corresponds to a plurality of resource element groups. The format of the PDCCH and the number of available bits of the PDCCH are determined according to the association between the number of CCEs and the coding rate provided by the CCEs.

The base station determines the PDCCH format according to the DCI to be transmitted to the terminal, and attaches a CRC (Cyclic Redundancy Check) to the control information. The CRC is masked with a unique identifier (referred to as RNTI (Radio Network Temporary Identifier)) according to the owner or purpose of the PDCCH. If the PDCCH for a specific terminal, a unique identifier of the terminal, for example, a C-RNTI (Cell-RNTI) may be masked to the CRC. Alternatively, if the PDCCH is for a paging message, a paging indication identifier, for example, P-RNTI (P-RNTI) may be masked to the CRC. If the system information, more specifically, the PDCCH for the system information block (SIB), the system information identifier and the system information RNTI (SI-RNTI) may be masked to the CRC. In order to indicate a random access response that is a response to the transmission of the random access preamble of the UE, a random access-RNTI (RA-RNTI) may be masked to the CRC.

Enhanced PDCCH (EPDCCH) carries UE-specific signaling. The EPDCCH is located in a physical resource block (PRB) that is UE-specifically configured. In other words, as described above, the PDCCH may be transmitted in up to three OFDM symbols in the first slot in the subframe, but the EPDCCH may be transmitted in a resource region other than the PDCCH. The start time (ie, symbol) of the EPDCCH in the subframe may be configured in the terminal through higher layer signaling (eg, RRC signaling, etc.).

EPDCCH is a transport format associated with the DL-SCH, resource allocation and HARQ information, a transport format associated with the UL-SCH, resource allocation and HARQ information, resource allocation associated with Side-link Shared Channel (SL-SCH) and Physical Sidelink Control Channel (PSCCH) Can carry information, etc. Multiple EPDCCHs may be supported and the UE may monitor a set of EPCCHs.

The EPDCCH may be transmitted using one or more consecutive enhanced CCEs (ECCEs), and the number of ECCEs per single EPDCCH may be determined for each EPDCCH format.

Each ECCE may be composed of a plurality of enhanced resource element groups (EREGs). EREG is used to define the mapping of ECCE to RE. There are 16 EREGs per PRB pair. Except for REs carrying DMRS within each pair of PRBs, all REs are numbered 0 through 15 in order of increasing frequency followed by time increments.

The terminal may monitor the plurality of EPDCCHs. For example, one or two EPDCCH sets in one PRB pair in which the UE monitors EPDCCH transmission may be configured.

By combining different numbers of ECCEs, different coding rates for the EPCCH may be realized. The EPCCH may use localized transmission or distributed transmission, so that the mapping of ECCE to the RE in the PRB may be different.

4 shows a structure of an uplink subframe in a wireless communication system to which the present invention can be applied.

Referring to FIG. 4, an uplink subframe may be divided into a control region and a data region in the frequency domain. A physical uplink control channel (PUCCH) carrying uplink control information is allocated to the control region. The data region is allocated a Physical Uplink Shared Channel (PUSCH) that carries user data. In order to maintain a single carrier characteristic, one UE does not simultaneously transmit a PUCCH and a PUSCH.

A PUCCH for one UE is allocated a resource block (RB) pair in a subframe. RBs belonging to the RB pair occupy different subcarriers in each of the two slots. This RB pair allocated to the PUCCH is said to be frequency hopping at the slot boundary (slot boundary).

Reference signal ( RS : Reference Signal)

Since data is transmitted over a wireless channel in a wireless communication system, the signal may be distorted during transmission. In order to correctly receive the distorted signal at the receiving end, the distortion of the received signal must be corrected using the channel information. In order to detect channel information, a signal transmission method known to both a transmitting side and a receiving side and a method of detecting channel information using a distorted degree when a signal is transmitted through a channel are mainly used. The above-mentioned signal is called a pilot signal or a reference signal (RS).

In addition, in recent years, when transmitting a packet in most mobile communication systems, a method of improving transmission / reception data efficiency by adopting a multiplexing antenna and a multiplexing antenna is avoided from using one transmitting antenna and one receiving antenna. use. When transmitting and receiving data using multiple input / output antennas, a channel state between a transmitting antenna and a receiving antenna must be detected in order to receive a signal accurately. Therefore, each transmit antenna must have a separate reference signal.

In a mobile communication system, RS can be classified into two types according to its purpose. There are RSs for channel information acquisition and RSs used for data demodulation. Since the former has a purpose for the UE to acquire channel information on the downlink, it should be transmitted over a wide band, and a UE that does not receive downlink data in a specific subframe should be able to receive and measure its RS. It is also used for measurements such as handover. The latter is an RS that the base station sends along with the corresponding resource when the base station transmits the downlink, and the UE can estimate the channel by receiving the RS, and thus can demodulate the data. This RS should be transmitted in the area where data is transmitted.

The downlink reference signal is one common reference signal (CRS: common RS) for acquiring information on channel states shared by all terminals in a cell, measurement of handover, etc. and a dedicated reference used for data demodulation only for a specific terminal. There is a dedicated RS. Such reference signals may be used to provide information for demodulation and channel measurement. That is, DRS is used only for data demodulation and CRS is used for both purposes of channel information acquisition and data demodulation.

The receiving side (i.e., the terminal) measures the channel state from the CRS and transmits an indicator related to the channel quality such as the channel quality indicator (CQI), precoding matrix index (PMI) and / or rank indicator (RI). Feedback to the base station). CRS is also referred to as cell-specific RS. On the other hand, a reference signal related to feedback of channel state information (CSI) may be defined as CSI-RS.

The DRS may be transmitted through resource elements when data demodulation on the PDSCH is needed. The UE may receive the presence or absence of a DRS through a higher layer and is valid only when a corresponding PDSCH is mapped. The DRS may be referred to as a UE-specific RS or a demodulation RS (DMRS).

5 illustrates a reference signal pattern mapped to a downlink resource block pair in a wireless communication system to which the present invention can be applied.

Referring to FIG. 5, a downlink resource block pair may be represented by 12 subcarriers in one subframe × frequency domain in a time domain in a unit in which a reference signal is mapped. That is, one resource block pair on the time axis (x-axis) has a length of 14 OFDM symbols in case of normal cyclic prefix (normal CP) (in case of FIG. 9 (a)), and an extended cyclic prefix ( extended CP: Extended Cyclic Prefix) has a length of 12 OFDM symbols (in case of FIG. 9 (b)). The resource elements (REs) described as '0', '1', '2' and '3' in the resource block grid are determined by the CRS of the antenna port indexes '0', '1', '2' and '3', respectively. The location of the resource element described as 'D' means the location of the DRS.

Hereinafter, the CRS will be described in more detail. The CRS is used to estimate a channel of a physical antenna and is distributed in the entire frequency band as a reference signal that can be commonly received to all terminals located in a cell. That is, this CRS is a cell-specific signal and is transmitted every subframe for the wideband. In addition, the CRS may be used for channel quality information (CSI) and data demodulation.

CRS is defined in various formats depending on the antenna arrangement at the transmitting side (base station). In a 3GPP LTE system (eg, Release-8), RS for up to four antenna ports is transmitted according to the number of transmit antennas of a base station. The downlink signal transmitting side has three types of antenna arrangements such as a single transmit antenna, two transmit antennas, and four transmit antennas. For example, if the number of transmitting antennas of the base station is two, CRSs for antenna ports 0 and 1 are transmitted, and if four, CRSs for antenna ports 0 to 3 are transmitted.

If the base station uses a single transmit antenna, the reference signal for the single antenna port is arranged.

When the base station uses two transmit antennas, the reference signals for the two transmit antenna ports are arranged using time division multiplexing (TDM) and / or FDM frequency division multiplexing (FDM) scheme. That is, the reference signals for the two antenna ports are assigned different time resources and / or different frequency resources so that each is distinguished.

In addition, when the base station uses four transmit antennas, reference signals for the four transmit antenna ports are arranged using the TDM and / or FDM scheme. The channel information measured by the receiving side (terminal) of the downlink signal may be transmitted by a single transmit antenna, transmit diversity, closed-loop spatial multiplexing, open-loop spatial multiplexing, or It may be used to demodulate data transmitted using a transmission scheme such as a multi-user MIMO.

When a multiple input / output antenna is supported, when a reference signal is transmitted from a specific antenna port, the reference signal is transmitted to a location of resource elements specified according to a pattern of the reference signal, and the location of resource elements specified for another antenna port. Is not sent to. That is, reference signals between different antennas do not overlap each other.

The rules for mapping CRSs to resource blocks are defined as follows.

In Equation 1, k and l represent a subcarrier index and a symbol index, respectively, and p represents an antenna port.

Denotes the number of OFDM symbols in one downlink slot,

Represents the number of radio resources allocated to the downlink.

Represents the slot index,

Represents a cell ID. mod stands for modulo operation. The position of the reference signal is in the frequency domain

It depends on the value.

Since is dependent on the cell ID, the position of the reference signal has various frequency shift values according to the cell.

More specifically, the position of the CRS may be shifted in the frequency domain according to the cell in order to improve channel estimation performance through the CRS. For example, when reference signals are located at intervals of three subcarriers, reference signals in one cell are allocated to the 3k th subcarrier, and reference signals in another cell are allocated to the 3k + 1 th subcarrier. In terms of one antenna port, the reference signals are arranged at six resource element intervals in the frequency domain, and are separated at three resource element intervals from the reference signal allocated to another antenna port.

In the time domain, reference signals are arranged at constant intervals starting from symbol index 0 of each slot. The time interval is defined differently depending on the cyclic prefix length. In the case of the normal cyclic prefix, the reference signal is located at symbol indexes 0 and 4 of the slot, and in the case of the extended cyclic prefix, the reference signal is located at symbol indexes 0 and 3 of the slot. The reference signal for the antenna port having the maximum value of two antenna ports is defined in one OFDM symbol. Thus, for four transmit antenna transmissions, the reference signals for reference signal antenna ports 0 and 1 are located at symbol indices 0 and 4 ( symbol indices 0 and 3 for extended cyclic prefix) of slots, The reference signal for is located at symbol index 1 of the slot. The positions in the frequency domain of the reference signal for antenna ports 2 and 3 are swapped with each other in the second slot.

In more detail with respect to DRS, DRS is used to demodulate data. Precoding weights used for a specific terminal in multiple I / O antenna transmission are used without change to estimate the corresponding channel by combining with the transmission channel transmitted from each transmission antenna when the terminal receives the reference signal.

The 3GPP LTE system (eg, Release-8) supports up to four transmit antennas and a DRS for rank 1 beamforming is defined. The DRS for rank 1 beamforming also indicates a reference signal for antenna port index 5.

The rules for mapping DRS to resource blocks are defined as follows. Equation 2 shows a case of a general cyclic transpose, and Equation 3 shows a case of an extended cyclic transpose.

In Equations 2 and 3, k and l represent subcarrier indexes and symbol indexes, respectively, and p represents an antenna port.

Denotes the resource block size in the frequency domain and is expressed as the number of subcarriers. n _PRB represents the number of physical resource blocks.

Denotes a frequency band of a resource block for PDSCH transmission. ns represents the slot index,

Represents a cell ID. mod stands for modulo operation. The position of the reference signal is in the frequency domain

It depends on the value.

Since is dependent on the cell ID, the position of the reference signal has various frequency shift values according to the cell.

LTE system evolution In the advanced LTE-A system, it should be designed to support up to eight transmit antennas in the downlink of the base station. Therefore, RS for up to eight transmit antennas must also be supported. Since the downlink RS in the LTE system defines only RSs for up to four antenna ports, when the base station has four or more up to eight downlink transmit antennas in the LTE-A system, RSs for these antenna ports are additionally defined. Must be designed. RS for up to eight transmit antenna ports must be designed for both the RS for channel measurement and the RS for data demodulation described above.

One of the important considerations in designing the LTE-A system is backward compatibility, i.e., the LTE terminal must work well in the LTE-A system, and the system must also support it. From an RS transmission point of view, an RS for an additional up to eight transmit antenna ports should be additionally defined in the time-frequency domain in which CRS defined in LTE is transmitted every subframe over the entire band. In the LTE-A system, when RS patterns of up to eight transmit antennas are added to all bands in every subframe in the same manner as the CRS of the existing LTE, the RS overhead becomes excessively large.

Therefore, the newly designed RS in LTE-A system is divided into two categories, RS for channel measurement purpose for selecting MCS, PMI, etc. (CSI-RS: Channel State Information-RS, Channel State Indication-RS, etc.) And RS (Data Demodulation-RS) for demodulation of data transmitted through eight transmit antennas.

CSI-RS for the purpose of channel measurement has a feature that is designed for channel measurement-oriented purposes, unlike the conventional CRS is used for data demodulation at the same time as the channel measurement, handover, and the like. Of course, this may also be used for the purpose of measuring handover and the like. Since the CSI-RS is transmitted only for the purpose of obtaining channel state information, unlike the CRS, the CSI-RS does not need to be transmitted every subframe. In order to reduce the overhead of the CSI-RS, the CSI-RS is transmitted intermittently on the time axis.

The DM-RS is transmitted to the UE scheduled in the corresponding time-frequency domain for data demodulation. That is, the DM-RS of a specific UE is transmitted only in a region where the UE is scheduled, that is, a time-frequency region in which data is received.

In the LTE-A system, the eNB should transmit CSI-RS for all antenna ports. Transmitting CSI-RS for each subframe for up to 8 transmit antenna ports has a disadvantage in that the overhead is too large. Therefore, the CSI-RS is not transmitted every subframe but is transmitted intermittently on the time axis. Can be reduced. That is, the CSI-RS may be periodically transmitted with an integer multiple of one subframe or may be transmitted in a specific transmission pattern. At this time, the period or pattern in which the CSI-RS is transmitted may be set by the eNB.

In order to measure the CSI-RS, the UE must transmit the CSI-RS index of the CSI-RS for each CSI-RS antenna port of the cell to which it belongs, and the CSI-RS resource element (RE) time-frequency position within the transmitted subframe. , And information about the CSI-RS sequence.

 In the LTE-A system, the eNB should transmit CSI-RS for up to eight antenna ports, respectively. Resources used for CSI-RS transmission of different antenna ports should be orthogonal to each other. When an eNB transmits CSI-RSs for different antenna ports, the CSI-RSs for each antenna port may be mapped to different REs so that these resources may be orthogonally allocated in the FDM / TDM manner. Alternatively, the CSI-RSs for different antenna ports may be transmitted in a CDM scheme that maps to orthogonal codes.

When the eNB informs its cell UE of the information about the CSI-RS, it is necessary to first inform the information about the time-frequency to which the CSI-RS for each antenna port is mapped. Specifically, the subframe numbers through which the CSI-RS is transmitted, or the period during which the CSI-RS is transmitted, the subframe offset through which the CSI-RS is transmitted, and the OFDM symbol number where the CSI-RS RE of a specific antenna is transmitted, and the frequency interval (spacing), the RE offset or shift value in the frequency axis.

Phase Compensation Reference Signal Signal: PCRS )

Hereinafter, the PCRS will be described in detail.

DL PCRS  step

If the UE detects an xPDCCH with DCI format B1 or B2 in subframe n intended for it, the UE receives DL PCRS at the PCRS antenna port indicated in the DCI at the corresponding subframe.

UL PCRS  step

If the UE detects an xPDCCH with DCI format A1 or A2 in subframe n intended for it, then the UE is the same one as the assigned DM-RS antenna port indicated in DCI except the conditions (condition 1 and condition 2) below. Alternatively, two PCRS antenna ports are used to transmit UL PCRS in subframe n + 4 + m + 1.

Condition 1: If the Dual PCRS field of the detected DCI is set to '1' and the number of DM-RS ports assigned to the xPUSCH is '1', then the UE assigns the assigned DM-RS antenna port indicated in the DCI. And UL PCRS in subframe n + 4 + m + 1 using the same PCRS port as the additional PCRS antenna port having the same subcarrier location as the particular PCRS antenna port.

Condition 2: The relative transmit power ratio of PCRS and xPUSCH is determined by the transmission scheme defined by Table 3 below.

Table 3 shows an example of the relative transmit power ratio of PCRS and xPUSCH on a given layer.

Transmission scheme	Relative Transmit Power Ratio
Single-layer transmission	3 dB
Two-layer transmission	6 dB

Hereinafter, the PCRS will be described in more detail.

The PCRS associated with the xPUSCH is transmitted at (1) antenna port (p) p∈ {40,41,42,43}, and (2) present and only compensates for phase noise if the xPUSCH transmission is associated with the corresponding antenna port. Is a valid criterion for (3) is transmitted only on the physical resource blocks and symbols to which the corresponding xPUSCH is mapped.

sequence  Sequence generation

For any antenna port of p ∈ {40, 41, 42, 43}, the reference signal sequence r (m) is defined as in Equation 4 below.

A pseudo-random sequence c (i) is defined by a gold sequence of length-31, and a pseudo random sequence generator is initialized at the beginning of each subframe, as shown in equation (5).

The quantity (i = 0, 1) is given by

-

, if

If no value for is provided by the upper layer.

-

,

If any value for is provided by a higher layer.

The value of is zero unless otherwise specified. for xPUSCH transmission,

Is given by the DCI format associated with the xPUSCH transmission.

Resource element Mapping (Mapping to resource elements)

For antenna port p∈ {40,41,42,43}, the frequency domain index allocated for the corresponding xPUSCH transmission

In the physical resource block having a, part of the reference signal sequence r (m)

Complex-value modulation symbol for the corresponding xPUSCH symbols in the subframe according to

Is mapped to.

Starting Physical Resource Block Index at xPUSCH Physical Resource Allocation

And the number of xPUSCH physical resource blocks

For, the resource element (k, l ') for one subframe is given by Equation 6 below.

In Equation 6, m '= 0,1,2, ...,

L 'represents a symbol index in one subframe,

Denotes the last symbol index of the xPUSCH for a given subframe.

The resource element (k, l ') used for transmission of UE specific PCRS from one UE on any antenna port in set S is not used for transmission of xPUSCH on any antenna port in the same subframe. .

Where S is {40}, {41} and {42}.

Carrier Frequency Offset Offset: CFO ) effect

Baseband signals transmitted by the transmitting end (e.g., base station) are shifted to the passband by the carrier frequency generated by the oscillator, and signals transmitted through the carrier frequency are transmitted by the same carrier frequency by the same carrier frequency at the receiving end (e.g., terminal). Is converted to.

In this case, the signal received by the receiver may include distortion associated with the carrier.

As one example of such distortion, there may be a distortion phenomenon caused by the difference between the carrier frequency of the transmitter and the carrier frequency of the receiver.

The reason for such carrier frequency offset is that the oscillators used at the transmitter and the receiver are not the same or the Doppler frequency transition occurs as the terminal moves.

Here, the Doppler frequency is proportional to the moving speed and the carrier frequency of the terminal and is defined as in Equation 7 below.

In Equation 7,

Denotes the carrier frequency, the Doppler frequency, the movement speed of the terminal, and the speed of light, respectively.

In addition, the normalized carrier frequency offset ε is defined as in Equation 8 below.

In Equation 8,

Denotes a carrier frequency offset normalized to a carrier frequency offset, a subcarrier spacing, and a subcarrier spacing in order.

If there is a carrier frequency offset, the received signal in the time domain is the result of multiplying the transmitted signal by the phase rotation, and the received signal in the frequency domain is the result of shifting the transmitted signal in the frequency domain.

In this case, all other subcarrier (s) are affected, resulting in inter-carrier-interference (ICI).

That is, when a decimal carrier frequency offset occurs, the received signal in the frequency domain is expressed by Equation 9 below.

Equation 9 shows a received signal having a CFO in the frequency domain.

In Equation 9,

Denote subcarrier index, symbol index, FFT size, received signal, transmitted signal, frequency response, ICI due to CFO, and white noise in order.

As defined in Equation 9, when the carrier frequency offset exists, the amplitude and phase of the k-th subcarrier are distorted, and it can be seen that interference by adjacent subcarriers occurs.

In this case, when there is a carrier frequency offset, interference by an adjacent subcarrier may be given by Equation 10 below.

Equation 10 represents the ICI caused by the CFO.

Phase Noise Effect

As previously discussed, the baseband signal transmitted by the transmitter is shifted to the passband by the carrier frequency generated by the oscillator, and the signal transmitted through the carrier frequency is converted into the baseband signal by the same carrier frequency at the receiver.

Here, the signal received by the receiver may include distortion associated with the carrier wave.

As an example of such a distortion phenomenon, phase noise generated due to unstable characteristics of an oscillator used in a transmitter and a receiver may be mentioned.

This phase noise refers to the frequency fluctuating with time around the carrier frequency.

This phase noise is a random process with zero mean and is modeled as a Wiener process and affects the OFDM system.

In addition, as shown in FIG. 6 below, the phase noise tends to increase as the frequency of the carrier increases.

This phase noise tends to be characterized by a power spectral density with the same oscillator.

6 is a diagram illustrating an example of a power spectral density of an oscillator.

As such, the distortion of the signal due to the phase noise appears in the form of a common phase error (CPE) and inter-carrier interference (ICI) in an OFDM system.

Equation 11 below shows the effect of the phase noise on the received signal of the OFDM system. That is, Equation 11 represents a received signal having phase noise in the frequency domain.

In Equation 11,

Indicates the subcarrier index, symbol index, FFT size, received signal, transmitted signal, frequency response, common phase error due to phase noise, inter-carrier interference due to phase noise, white noise, and phase rotation due to phase noise, respectively. .

Hereinafter, a method of estimating a phase rotation difference between symbols proposed in the present specification will be described in detail with reference to related drawings.

Specifically, in order to prevent performance degradation that may occur when estimating phase rotation using a data symbol in an environment in which a large carrier frequency offset (CFO) occurs, PCRS and / or Alternatively, the present invention provides a method of correctly decoding a received signal by estimating a phase rotation difference between symbols using a data symbol.

Phase rotation difference estimation methods may include (1) a method using PCRS (method 1), (2) a method using data symbols (method 2), (3) a method using simultaneously PCRS and data symbols (method 3), and the like. have.

Method 1, namely, a phase rotation estimation method using PCRS, is a method of transmitting PCRS on at least one frequency tone (or subcarrier) of all symbol (s) except for a symbol on which DL CCH and DMRS are transmitted.

Method 2, namely, a phase rotation estimation method using a data symbol, is a method of transmitting a data symbol through at least one frequency tone (or subcarrier) of all symbol (s) except for a symbol on which DL CCH and DMRS are transmitted.

Method 3, namely, a phase rotation estimation method using a PCRS and data symbol, transmits a PCRS and data symbol on at least one frequency tone (or subcarrier) of all symbol (s) except for a symbol on which DL CCH and DMRS are transmitted. to be.

When estimating the phase rotation of a symbol through the data symbol, a modulation order of a data symbol (hereinafter, referred to as a 'first data symbol' for convenience) is used as a data symbol for transmitting only data. Hereinafter, for convenience, the 'second data symbol' may be defined differently from the modulation order.

Here, the modulation order of the first data symbol may be set lower than the modulation order of the second data symbol.

Method 1: PCRS Phase rotation Compensation RS Phase rotation estimation using

7 illustrates an example of a PCRS arrangement for performing phase rotation estimation.

In the case of FIG. 7, it is assumed that a reference signal is transmitted in all OFDM symbols for phase rotation estimation.

Referring to FIG. 7, the DL CCH (Control Channel) 710 is transmitted through two symbols (symbol index 0 and symbol index 1), and data is stored in the next symbol (symbol index 2) of the symbol on which the DL CCH is transmitted. A reference signal (DMRS) 720 for demodulation of a symbol is transmitted.

The PCRS 730 may be transmitted through a subcarrier index 6 and a subcarrier index 18 in a frequency domain through a fourth symbol (symbol index 3) in a time domain and a 14th symbol (symbol index 13).

Such PCRS transmission can compensate for distortion such as CPE or CFO occurring in the high frequency band.

As shown in FIG. 7, when the PCRS is transmitted in all symbols except for the symbols in which the DL CCH and the DMRS are transmitted, phase rotation estimation can be performed in the entire range using the characteristics of the RS.

However, there is a disadvantage that the number of symbols that can transmit data is reduced due to the increase of the RS transmission symbol.

Method 2: data Data symbol  Phase rotation estimation method using

In the high frequency band (for example, 6GHz or more), the influence of phase noise is increased, so it is necessary to compensate for damage or distortion of the signal due to phase noise.

As a method of compensating for such signal distortion, there is a method of compensating for a common phase error (CPE) value that can be viewed as an average value in one OFDM symbol.

However, this method does not eliminate the interference due to ICI.

However, since the technique for compensating the ICI requires high complexity, a method of overcoming impairment due to phase noise by compensating CPE in consideration of complexity and performance may be sufficiently feasible. have.

Here, since the CPE has the same value for all subcarriers in one OFDM symbol, it is possible to estimate the CPE using a properly arranged reference signal.

A specific example thereof will be described above with reference to Salpin 7.

8 is a diagram illustrating an example of data symbol arrangement for phase rotation estimation.

As shown in FIG. 8, the DL CCH 810 is transmitted through two symbols (symbol 0, symbol 1), and the next symbol (symbol 2) of the symbol on which the DL CCH is transmitted is used for demodulation of data symbols. Reference signal (RS) 820 is transmitted.

In addition, phase rotation estimation is performed through the fourth symbol (symbol index 3) to the fourteenth symbol (symbol index 13) in the time domain and the seventh subcarrier (subcarrier index 6) and the nineteenth subcarrier (subcarrier index 18) in the frequency domain. It can be seen that the data symbol for the first data symbol 830 is transmitted.

As shown in FIG. 8, a method of estimating a phase rotation (or a difference in phase rotation between symbols) using data symbols can reduce overhead for RS transmission and can additionally transmit data through RS transmission resources. That has the advantage.

However, the phase rotation estimation method using the data symbol has a disadvantage in that the phase rotation estimation range is limited according to the modulation order of the data symbol.

Therefore, in an environment where a large CFO may occur, performance degradation may occur when the phase rotation is estimated using a data symbol.

The phase rotation estimation method using data symbols will be described in more detail.

Equation 12 below represents an equation for a received signal considering the influence of phase noise of a receiver in an OFDM system.

In Equation 12,

Respectively denotes OFDM symbol index, sample index, subcarrier index, phase rotation due to phase noise, white noise, transmission signal, frequency response, cyclic convolution operation, and IDFT operation.

Equation 12 shows that phase noise is added to each sample of the received signal due to phase noise of the signal in the time domain.

Based on Equation 12, the received signal in the frequency domain may be defined as Equation 13 below.

In Equation 13,

In each order, FFT size, received signal, transmitted signal, common phase error due to phase noise, and inter-carrier interference due to phase noise are shown.

Excluding distortion due to ICI and white noise in Equation 13, impairment due to phase noise may be assumed to be represented by phase rotation of constellation of a received signal in units of OFDM symbols.

In this case, contiguous (or adjacent) data symbols can be used to estimate phase rotation caused by phase noise.

9 is a diagram illustrating an example of estimating a phase rotation difference between symbols using BPSK symbols of contiguous OFDM symbols.

The left figure of FIG. 9 is shown in quadrants 1 and 4 when the concatenated BPSK symbols are the same symbol (X _l (k) = X _{l + 1} (k)), and the right figure of FIG. 9 shows symbols having different BPSK symbols ( In the case of X _l (k) ≠ X _{l + 1} (k)), the constellation is present in the second and third quadrants.

That is, the receiver can estimate the phase difference between two OFDM symbols through two concatenated data symbols.

In this case, when the BPSK symbol is used, the estimation range of the phase rotation is equal to -90 ° to + 90 °.

If phase rotation occurs out of the range, the phase rotation estimation performance of the receiver becomes worse.

Here, when a high modulation order is used as the modulation order of the data symbol transmitted for the phase rotation estimation, the estimation range of the phase rotation using the data symbol becomes smaller.

For example, in the case of using the QPSK symbol, the phase rotation estimation range has -45 ° to + 45 °.

Method 3: PCRS  Rotation Estimation Method Using Data and Data Symbol

Next, a method of estimating phase rotation using PCRS and data symbols will be described in order to prevent performance degradation that may occur when the phase rotation is estimated using data symbols.

That is, in the method 3, two or more concatenated OFDM symbols (or one OFDM symbol) located on the same frequency tone (or subcarrier) as shown in FIG. PCRS), and any data symbol having the same modulation order is transmitted to the remaining OFDM symbol (s) of the same frequency tone.

Here, the modulation order of the data symbol to be transmitted for phase rotation estimation is set differently from the modulation order of the data symbol to transmit data.

As described above, the method of estimating phase rotation between symbols using data symbols has a limited estimation range according to the modulation order of data symbols.

Therefore, since the degradation of the phase rotation estimation performance may occur in a large CFO environment, Method 3, that is, the phase rotation estimation method using the PCRS and the data symbol, performs the first and second steps below.

First, the receiver detects a CFO that is out of a phase rotation range that can be estimated using a data symbol using a reference signal (eg, PCRS) transmitted through the structure as shown in FIG. 10.

Second, the receiver additionally compensates for phase rotation through a data symbol for the first phase, that is, the range of phase rotation estimation compensated through PCRS.

That is, when the CFO occurs outside the range where the phase rotation can be estimated using the data symbol, the estimation of the phase rotation using the data symbol may have a large difference from the actual value.

As illustrated, the receiving end may first detect the CFO value using a reference signal (eg, PCRS) that has no limit on the phase rotation estimation range, and then compensate the detected CFO value in the phase rotation estimation using the data symbol.

That is, when the receiver compensates for the CFO value first when estimating the phase rotation using the data symbol, the influence of the CFO is removed to estimate the CPE value having a small estimated range.

10 is a diagram illustrating an example of PCRS and data symbol arrangement for estimating phase rotation proposed in the present specification.

That is, FIG. 10 illustrates that a reference signal is disposed or allocated to a specific region of a data symbol to compensate for the occurrence of a large CFO in the structure of estimating phase rotation using the data symbol of FIG. 8.

Referring to FIG. 10, a reference signal (PCRS) 1010 is disposed in a symbol (symbol index 3) after a DMRS transmission symbol, and data symbols 1020 for phase rotation estimation are disposed in the symbols after the PCRS transmission symbol. can see.

The arrangement structure of FIG. 10 is merely an example, and the PCRS may be arranged in two symbols, three symbols, four symbols, etc. after the DMRS transmission symbol.

Hereinafter, method 3, ie, a method of compensating a large CFO using the PCRS estimation result will be described in more detail.

As shown, Method 3 performs (1) primarily compensate for phase rotation over a large CFO via the PCRS transmitted as shown in FIG. 10, and (2) equally places on the frequency tone (or subcarrier) to which the PCRS is transmitted. The CPE is secondarily compensated using the data rotation estimation phase symbol.

Here, the modulation order of the data symbol located on the frequency tone to which the PCRS is transmitted, that is, the data symbol for phase rotation estimation, is preferably set differently from the modulation order of the data symbol located on a frequency tone different from the frequency tone to which the PCRS is transmitted. .

As illustrated, when the receiver estimates a phase difference between two OFDM symbols using a data symbol, the phase rotation estimation range may be limited according to a modulation order applied to the data symbol.

Therefore, when the phase difference between two OFDM symbols increases due to the occurrence of a large CFO, when the phase difference is outside the estimated range of phase rotation that can be estimated using the data symbol, the receiver may estimate an incorrect phase rotation value. Can be.

FIG. 11 is a diagram illustrating an example of a phase rotation estimation range that may be estimated between two OFDM symbols.

As shown in FIG. 11, when an error occurs in a phase rotation estimation value using a data symbol due to a large CFO, the receiving end first compensates for a large range of phase difference using a PCRS.

Thereafter, the receiving end may prevent an error on the CPE by additionally estimating the phase rotation by using a data symbol in the estimated range compensated by the PCRS.

Hereinafter, an example of a method of estimating a phase rotation difference between two OFDM symbols using a PCRS and a data symbol will be described.

The following description will refer to FIG. 10.

Step 1: Phase Difference Estimation Using Reference Signals of Second Symbol (symbol index 3) and Third Symbol (symbol index 4)

12 is a diagram illustrating a method of estimating a phase rotation difference by using a concatenated reference signal proposed in the specification.

In Figure 12,

Denotes an effective channel estimated for the k-th subcarrier of the l-th OFDM symbol.

Step 2: Estimation of Phase Rotation Difference Using Data Symbol of 3rd Symbol (symbol index 4) and 4th Symbol (symbol index 5)

Step 2-1: Calculate the conjugation product of the third symbol and the fourth symbol

FIG. 13 is a diagram illustrating an example of deriving a temporary phase difference value between two symbols by calculating a conjugation product of a third symbol and a fourth symbol.

Step 2-2: Compensate the estimated value obtained through the procedure of Step 1 (estimated phase difference value using the reference signal of the second and third symbols) on the result of Step 2-1.

14 is a diagram illustrating an example of a method of estimating a phase rotation difference in an environment in which a large CFO is proposed in the present specification.

That is, FIG. 14 illustrates a method of estimating a phase rotation difference value in an environment in which a large CFO is generated by compensating an estimated value obtained through PCRS to a phase rotation difference value estimated through data symbols.

In the Step 1 and Step 2 procedures, the exclusion of distortion due to phase noise

Denotes a frequency response according to a wireless environment.

In this case, for different OFDM symbols

Are assumed to be the same.

The method of estimating the phase rotation difference through the method 3 is the same as that of steps 1 and 2 for all symbols after the fifth symbol, and first compensates for the phase difference estimated from the previous symbol, and then phase difference within the estimated range. Of course, it is possible to compensate for the overall phase rotation by estimating.

Whether to use PCRS and / or data symbols for phase rotation estimation

The phase rotation estimation method using salping, PCRS and / or data symbols may be selectively performed using only PCRS, using only data symbols, and simultaneously using PCRS and data symbols.

To this end, the transmitter may transmit information on whether to use a PCRS and / or data symbol for phase rotation estimation to the receiver.

Specifically, the base station may be on / off information or / and large for transmission of data symbols for phase rotation estimation through downlink control information (DCI) or radio resource control (RRC) signaling. On / Off information on the transmission of the reference signal for CFO compensation may be transmitted to the terminal.

Here, the on of the transmission of the data symbol means that the phase rotation estimation is performed through the data symbol, and the off of the transmission of the data symbol may be interpreted vice versa.

In addition, the meaning of On for RS transmission indicates that phase rotation estimation is performed through PCRS, and the meaning of Off for PCRS transmission may be interpreted vice versa.

That is, the terminal is a phase proposed in this specification in consideration of data symbol for phase rotation estimation transmitted through the base station and / or on or off information (or data symbol and / or PCRS usage information) for transmission of the PCRS The rotation estimation method can be performed.

As with salpin, phase rotation results in greater performance degradation in high MCS situations than in low Modulation and Coding Schemes.

Therefore, for efficient system operation to prevent performance degradation due to phase rotation, transmission of data symbols used for phase rotation compensation may define On or Off differently according to MCS.

In this case, the base station may transmit information on whether to transmit the phase rotation estimation data symbol (or the first data symbol) to the terminal using DCI or RRC signaling.

Here, the data symbol for phase rotation estimation may use a value different from the modulation order of the data symbol not used for phase rotation estimation.

In addition, when transmitting a reference signal in all cases for large CFO compensation, the number of data symbols that can be transmitted can be reduced by that amount.

Accordingly, the base station determines whether to use the RS for phase rotation estimation through DCI or RRC signaling so that the reference signal for phase rotation estimation can be transmitted only when the CFO is large to prevent the number of data symbols to be transmitted. Can be sent to

The following shows an example of a method for performing the phase rotation estimation proposed herein.

First, a base station transmits a data symbol for estimating phase rotation due to phase noise and carrier frequency offset (CFO) and / or a reference signal (or PCRS) for large CFO compensation through DCI or RRC signaling. Whether or not to transmit to the terminal.

The PCRS may be located in the third symbol or the third and fourth symbols in the structure of FIG. 10.

When the PCRS is located in the third symbol, the phase rotation difference is estimated with the DMRS located in the second symbol. When the PCRS is located in the third and fourth symbols, the phase rotation difference using the RS is the third symbol. And estimate using the PCRS transmitted in the fourth and fourth symbols.

Here, the modulation order of the phase rotation estimation data symbol (first data symbol) preferably has a modulation order different from that of the data symbol (second data symbol) transmitted through the DL-SCH.

In the following description, it is assumed that the PCRS is transmitted in the third symbol (symbol index 4).

That is, the UE may define a reception operation differently depending on whether a reference signal for phase rotation estimation (eg, PCRS) is transmitted in the third symbol or not.

Whether the PCRS is transmitted may be transmitted from the base station to the terminal through DCI or RRC signaling.

First, when the PCRS is transmitted in the third symbol, it looks at the reception operation of the terminal.

When the terminal receives the PCRS transmitted from the base station, the phase of each OFDM symbol relative to the effective channel of the second symbol (DMRS transmission symbol) through the salping step 2 (step 2-1 and step 2-2) procedure Estimate the rotation difference value.

The terminal estimates the effective channel value in each OFDM symbol by reflecting the estimated phase rotation value of each OFDM symbol in the effective channel of the second OFDM symbol.

Thereafter, the terminal compensates the channel for the received signal of each OFDM symbol by using the estimated effective channel, and then receives a transmission bit (transmitted by the transmitter) by performing a demodulation process on the received symbol that compensates for the channel. .

Next, when the PCRS is not transmitted in the third symbol, looks at the reception operation of the terminal.

If the PCRS is not transmitted in the third OFDM symbol, the salping step 2-2 procedure is not performed.

That is, when the PCRS is not transmitted in the third symbol, it is assumed that the value estimated in the step 2-1 procedure, that is, the phase rotation result value estimated using the data symbol as the phase rotation difference value between OFDM symbols.

In this case, the phase rotation value of each OFDM symbol is also estimated by using the procedure of Step 2-1, compared to the effective channel of the second OFDM symbol, and reflected in the effective channel of the second OFDM symbol to determine the effective channel value in each OFDM symbol. Estimate.

The terminal performs a channel compensation process on the received signal of each OFDM symbol using an effective channel estimated from each OFDM symbol, and performs a demodulation process on the received symbol that compensates the channel (transmitted by the transmitter). Receive the transmit bit.

15 is a flowchart illustrating an example of a method of decoding a received signal by estimating a phase rotation difference between symbols proposed in the present specification.

First, the terminal receives control information related to transmission of a signal used for estimating a phase rotation difference between symbols from a base station (S1510).

Thereafter, the terminal receives a first signal used for phase rotation estimation from the base station through a specific resource (S1520).

Here, the specific resource may be set to a symbol after a symbol for transmitting a demodulation reference signal (DMRS) in the time domain and may be set to at least one frequency tone corresponding to the specific index in the frequency domain.

The first signal represents a phase rotation compensation reference signal (PCRS).

The control information includes at least one of information indicating whether the first signal is transmitted or information indicating whether the second signal will be described later.

In addition, the control information is received from the base station through Downlink Control Information (DCI) or Radio Resource Control (RRC) signaling.

The number of transmission symbols of the first signal is one or two, and when the number of transmission symbols of the first signal is two, the transmission symbols of the first signal are consecutive symbols.

In addition, the number of specific indexes in the frequency domain of the specific resource is two.

Thereafter, the terminal estimates a phase rotation difference between symbols using the received first signal, that is, between a transmission symbol of the first signal and a symbol immediately preceding the transmission symbol of the first signal (S1530).

Thereafter, the terminal receives a second signal used for phase rotation estimation from the base station through a symbol after the transmission symbol of the first signal (S1540).

Thereafter, the terminal estimates a phase rotation difference between symbols using the received second signal, that is, between a transmission symbol of the second signal and a transmission symbol of the first signal (S1550).

The symbol on which the second signal is transmitted is a data symbol, and the data symbol on which the second signal is transmitted has a modulation order different from that of the data symbol on which the second signal is not transmitted.

In addition, the phase rotation difference estimation range using the second signal is determined according to the modulation order of the second signal.

Here, the estimation of the phase rotation difference between the transmission symbol of the second signal and the transmission symbol of the first signal is performed by reflecting the phase rotation difference between symbols estimated using the received first signal.

Thereafter, the terminal decodes the received signal in consideration of the phase rotation difference estimated through the second signal (S1560).

Further, the first signal is used when it is out of a range of phase rotation difference that can be estimated as the second signal.

In FIG. 15, the steps of S1530 and S1540 may be performed sequentially or may be performed in a reversed order.

General apparatus to which the present invention can be applied

16 illustrates a block diagram of a wireless communication device according to an embodiment of the present invention.

Referring to FIG. 16, a wireless communication system includes a base station 1610 and a plurality of terminals 1620 located in an area of a base station 1610.

The base station 1610 includes a processor 1611, a memory 1612, and a radio frequency unit 1613. The processor 1611 implements the functions, processes, and / or methods proposed in FIGS. 1 to 15. Layers of the air interface protocol may be implemented by the processor 1611. The memory 1612 is connected to the processor 1611 and stores various information for driving the processor 1611. The RF unit 1613 is connected to the processor 1611 and transmits and / or receives a radio signal.

The terminal 1620 includes a processor 1621, a memory 1622, and an RF unit 1623. The processor 1621 implements the functions, processes, and / or methods proposed in FIGS. 1 to 15. Layers of the air interface protocol may be implemented by the processor 1621. The memory 1622 is connected to the processor 1621 and stores various information for driving the processor 1621. The RF unit 1623 is connected to the processor 1621 and transmits and / or receives a radio signal.

The memories 1612 and 1622 may be inside or outside the processors 1611 and 1621 and may be connected to the processors 1611 and 1621 by various well-known means.

In addition, the base station 1610 and / or the terminal 1620 may have a single antenna or multiple antennas.

The embodiments described above are the components and features of the present invention are combined in a predetermined form. Each component or feature is to be considered optional unless stated otherwise. Each component or feature may be embodied in a form that is not combined with other components or features. It is also possible to combine some of the components and / or features to form an embodiment of the invention. The order of the operations described in the embodiments of the present invention may be changed. Some components or features of one embodiment may be included in another embodiment or may be replaced with corresponding components or features of another embodiment. It is obvious that the claims may be combined to form an embodiment by combining claims that do not have an explicit citation relationship in the claims or as new claims by post-application correction.

Embodiments according to the present invention may be implemented by various means, for example, hardware, firmware, software, or a combination thereof. In the case of a hardware implementation, an embodiment of the present invention may include one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), FPGAs ( field programmable gate arrays), processors, controllers, microcontrollers, microprocessors, and the like.

In the case of implementation by firmware or software, an embodiment of the present invention may be implemented in the form of a module, procedure, function, etc. that performs the functions or operations described above. The software code may be stored in memory and driven by the processor. The memory may be located inside or outside the processor, and may exchange data with the processor by various known means.

It will be apparent to those skilled in the art that the present invention may be embodied in other specific forms without departing from the essential features of the present invention. Accordingly, the above detailed description should not be construed as limiting in all aspects and should be considered as illustrative. The scope of the invention should be determined by reasonable interpretation of the appended claims, and all changes within the equivalent scope of the invention are included in the scope of the invention.

Although the present invention has been described with reference to examples applied to 3GPP systems and 5G systems, it is possible to apply to various wireless communication systems.

Claims (11)

1. In the method for estimating the phase rotation difference between symbols in a wireless communication system, the method performed by the terminal,

   Receiving control information related to transmission of a signal used for estimating a phase rotation difference between symbols from a base station;

   Receiving from the base station a first signal used for phase rotation estimation via a particular resource,

   The specific resource is set to a symbol after a symbol to which a Demodulation Reference Signal (DMRS) is transmitted in the time domain, and is set to at least one frequency tone corresponding to a specific index in the frequency domain;

   Estimating a phase rotation difference between a transmission symbol of the first signal and a symbol immediately before the transmission symbol of the first signal using the received first signal;

   Receiving a second signal from the base station, the second signal being used for phase rotation estimation through a symbol after the transmission symbol of the first signal;

   Estimating a phase rotation difference between the transmission symbol of the second signal and the transmission symbol of the first signal using the received second signal; And

   And decoding the received signal in consideration of the phase rotation difference estimated through the second signal.
2. The method of claim 1,

   And estimating a phase rotation difference between the transmission symbol of the second signal and the transmission symbol of the first signal reflects a phase rotation difference between symbols estimated using the received first signal.
3. The method of claim 1,

   And wherein the first signal is a phase rotation compensation reference signal (PCRS).
4. The method of claim 3, wherein

   The symbol to which the second signal is transmitted is a data symbol,

   And a data order in which the second signal is transmitted is different from a data symbol in which the second signal is not transmitted and a modulation order.
5. The method of claim 1,

   The range of phase rotation difference estimation using the second signal is determined according to the modulation order of the second signal.
6. The method of claim 5,

   And wherein the first signal is used when it is out of a range of phase rotation difference that can be estimated as the second signal.
7. The method of claim 1,

   The control information may include at least one of information indicating whether the first signal is transmitted or information indicating whether the second signal is transmitted.
8. The method of claim 7, wherein

   The control information is received from the base station via Downlink Control Information (DCI) or Radio Resource Control (RRC) signaling.
9. The method of claim 1,

   The number of transmission symbols of the first signal is one or two,

   If the number of transmission symbols of the first signal is two, the transmission symbol of the first signal is a continuous symbol.
10. The method of claim 1,

    And the number of the specific indexes is two.
11. A terminal for estimating a phase rotation difference between symbols in a wireless communication system,

    An RF unit for transmitting and receiving radio signals; And

    A processor for controlling the RF unit, wherein the processor,

    Receive control information related to transmission of a signal used for estimating a phase rotation difference between symbols from a base station;

    Receiving a first signal from the base station used for phase rotation estimation through a specific resource,

    The specific resource is set to a symbol after a symbol to which a Demodulation Reference Signal (DMRS) is transmitted in the time domain, and is set to at least one frequency tone corresponding to a specific index in the frequency domain;

    Estimate a phase rotation difference between a transmission symbol of the first signal and a symbol immediately preceding the transmission symbol of the first signal using the received first signal;

    Receive from the base station a second signal used for phase rotation estimation via a symbol after the transmission symbol of the first signal;

    Estimating a phase rotation difference between the transmission symbol of the second signal and the transmission symbol of the first signal using the received second signal; And

    And controlling to decode the received signal in consideration of the phase rotation difference estimated through the second signal.

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