CN116998124A - Enhanced side-chain communication in cellular communication networks - Google Patents

Abstract

According to an example aspect of the invention, there is provided an apparatus comprising: means for receiving, by a receiving user equipment, first side chain control information from a transmitting user equipment, wherein the first side chain control information originates from the transmitting user equipment; means for determining, by a receiving user equipment, whether second side-chain control information is to be transmitted, wherein said second side-chain control information is an adapted retransmission version of said first side-chain control information; means for selecting, by the receiving user equipment, resources for transmitting said second side chain control information upon a positive determination; and means for transmitting, by the receiving user equipment, the second side-chain control information on the selected resource.

Description

Enhanced side-chain communication in cellular communication networks

Technical Field

Various example embodiments relate generally to cellular communication networks and, more particularly, to side-chain communications in such networks.

Background

The side chains SL are direct communication links between user equipments UEs in the cellular communication network and the UEs can communicate via the SL without going through the base station BS. Communication over SL may be enabled in various cellular communication networks, such as cellular communication networks operating according to 5G radio access technology. The 5G radio access technology may also be referred to as a new radio NR access technology. The third generation partnership project 3GPP has developed a standard of 5G/NR and some of the subject matter in the 3GPP discussion is related to SL communication. In light of the discussion, there is a need to provide improved methods, apparatus and computer programs related to the use of SL. Such improvements may also be used in other cellular communication networks.

Disclosure of Invention

According to some aspects, the subject matter of the independent claims is provided. Some example embodiments are defined in the dependent claims.

The scope of protection sought for the various exemplary embodiments of the present invention is as set forth in the independent claims. Example embodiments and features (if any) described in this specification that do not fall within the scope of the independent claims are to be construed as examples of various example embodiments that facilitate an understanding of the invention.

According to a first aspect of the present invention, there is provided an apparatus comprising means for receiving, by a receiving user equipment, first side chain control information from a transmitting user equipment, wherein the first side chain control information originates from the transmitting user equipment; means for determining, by a receiving user equipment, whether second side-chain control information is to be transmitted, wherein said second side-chain control information is an adapted retransmission version of said first side-chain control information; means for selecting, by the receiving user equipment, resources for transmitting said second side chain control information upon a positive determination; and means for transmitting, by the receiving user equipment, the second side-chain control information on the selected resource. The apparatus of the first aspect may comprise a receiving user equipment or a control device configured to control its functions (possibly when installed therein).

Example embodiments of the first aspect may include at least one feature or any combination of the following features in the following bulleted list:

the means for selecting resources for transmitting the second side chain control information comprises selecting based on at least one of: a mapping rule to be used for deriving a resource for transmitting the second side chain control information from the resource on which the first side chain control information is received; resources indicated by the transmitting user equipment; resources indicated by another user equipment or a network entity controlling side-chain communication; or user equipment

An autonomous resource allocation scheme;

means for determining whether the above second side chain control information is to be sent based on at least one of: receiving a configuration of the user equipment, wherein the configuration is received from the transmitting user equipment or from a network entity controlling the side-chain communication; an instruction in the first side chain control information; interference on at least one reserved resource indicated in the first sidelink control information; or at least one guard indicated in the first side chain control information

A conflict on the reserved resource;

the second side chain control information indicates the same security as the first side chain control information

At least some of the time-keeping resources;

adapting said second side-chain control information to generate an adapted retransmission version of said first side-chain control information such that said second side-chain control information indicates to a transmitting user equipment that at least one reserved resource indicated in said second side-chain control information will affect the transmission differently than the original side-chain control information received by the transmitting user equipment

A component of a sensing result of the user equipment;

means for adapting the information field of the above-mentioned second side chain control information by performing at least one of: adapting an information field related to time resource assignment according to a time interval between the second side chain control information and at least one reserved resource of the first side chain control information; merging a plurality of first side chain control information; or adapting a priority field to indicate that the second side chain control information is the first side chain control

Retransmission of the information;

the adapted retransmission version of the first side chain control information is indicated by at least one of a resource on which the second side chain control information is sent, an explicit indication, or a priority information field in the second side chain control information.

According to a second aspect of the present invention, there is provided an apparatus comprising means for transmitting, by a transmitting user equipment, first side chain control information to a receiving user equipment; means for receiving second side chain control information from a receiving user equipment in response to the transmitting. And means for detecting that the second side chain control information is an adapted retransmission version of the first side chain control information. The apparatus may comprise a transmitting user equipment or a control device configured to control its functions (possibly when installed therein).

Example embodiments of the second aspect may include at least one feature or any combination of the following features in the following bulleted list:

means for detecting that said second side chain control information indicates at least one reserved resource to be used for original side chain control received by the transmitting user equipment

The information affects the sensing result of the transmitting user equipment differently;

detecting that the second side-chain control information is an adapted retransmission version of the first side-chain control information based on at least one of a resource on which the second side-chain control information is received, an explicit indication, or a priority information field in the second side-chain control information;

The second side chain control information indicates at least some of the same reserved time resources as the first side chain control information.

According to a third aspect of the present invention there is provided a first method comprising: receiving, by a receiving user equipment, first side chain control information from a transmitting user equipment, wherein the first side chain control information originates from the transmitting user equipment; determining, by a receiving user equipment, whether second side-chain control information is to be transmitted, wherein said second side-chain control information is an adapted retransmission version of said first side-chain control information; selecting, by the receiving user equipment, a resource for transmitting the second side-chain control information upon a positive determination; and transmitting, by the receiving user equipment, the second side-chain control information on the selected resource. The first method may be performed by the receiving user equipment or a control device configured to control its functions (possibly when installed therein).

According to a fourth aspect of the present invention there is provided a second method comprising: transmitting, by a transmitting user equipment, first side chain control information to a receiving user equipment; receiving second side chain control information from the receiving user equipment in response to the transmitting; and detecting that the second side chain control information is an adapted retransmission version of the first side chain control information. The second method may be performed by the transmitting user equipment or a control device configured to control its functions (possibly when installed therein).

According to a fifth aspect of the present invention, there is provided an apparatus comprising at least one processing core, at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processing core, cause the apparatus at least to perform: receiving, by a receiving user equipment, first side chain control information from a transmitting user equipment, wherein the first side chain control information originates from the transmitting user equipment; determining, by a receiving user equipment, whether second side-chain control information is to be transmitted, wherein said second side-chain control information is an adapted retransmission version of said first side-chain control information; selecting, by the receiving user equipment, a resource for transmitting the second side-chain control information upon a positive determination; and transmitting, by the receiving user equipment, the second side-chain control information on the selected resource. The apparatus may comprise a receiving user device or a control device configured to control its functions (possibly when installed therein).

According to a sixth aspect of the present invention, there is provided an apparatus comprising at least one processing core, at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processing core, cause the apparatus at least to perform: transmitting, by a transmitting user equipment, first side chain control information to a receiving user equipment; receiving second side chain control information from the receiving user equipment in response to the transmitting; and detecting that the second side chain control information is an adapted retransmission version of the first side chain control information. The apparatus may comprise a transmitting user equipment or a control device configured to control its functions (possibly when installed therein).

According to a seventh aspect of the present invention, there is provided a non-transitory computer readable medium having stored thereon a set of computer readable instructions, which when executed by at least one processor, cause an apparatus to perform at least a first method or a second method. According to an eighth aspect of the present invention there is provided a computer program comprising instructions which, when executed by an apparatus, cause the apparatus to perform the first method or the second method.

Drawings

FIG. 1 illustrates an example of a communication network in accordance with at least some example embodiments;

fig. 2 illustrates a signaling diagram in accordance with at least some example embodiments;

FIG. 3 illustrates an example apparatus capable of supporting at least some example embodiments;

FIG. 4 shows a flow chart of a first method in accordance with at least some example embodiments; and

fig. 5 shows a flow chart of a second method in accordance with at least some example embodiments.

Detailed Description

Fig. 1 illustrates an example of a communication network in accordance with at least some example embodiments. According to the example scenario of fig. 1, there may be a cellular communication network comprising three user equipments UE configured to communicate using side-chain SL communication. The cellular communication network of fig. 1 includes a SL transmit Tx UE 110, a SL receive Rx UE 112, a third SL UE 114, a base station BS120, and a core network 130.SL Tx UE 110 may be referred to as a transmitting UE that transmits, for example, side chain control information, SCI, and/or SL data. SL Rx UE 112 may be referred to as a receiving UE that receives SCI and/or SL data. The SCI transmitted by SL Tx UE 110 may be referred to as a first SCI, and upon receipt of the first SCI, SL Rx UE 112 may then decide to transmit a second SCI, where the second SCI is an adapted retransmission version of the first SCI, i.e., a retransmission SCI.

SL Tx UE 110 and SL Rx UE 112 may be connected to each other over air interface 105. Similarly, the SL Rx UE 112 and the third SL UE 114 may also be connected to each other via the air interface 105, but there may not be a direct connection between the SL Tx UE 110 and the third SL UE 114. At least one of SL Tx UE 110, SL Rx UE 112, and third SL UE 114 may be further connected to BS120 or some other BS via air interface 115, but in the case of SL communication, such connection(s) is not mandatory.

UEs 110, 112, and 114 may include, for example, smartphones, cellular phones, machine-to-machine M2M nodes, machine-type communication MTC nodes, internet of things IoT nodes, automotive telemetry units, laptops, tablets, or virtually any kind of suitable wireless terminal. BS120 may be a network entity that configures some or all of the control information for UEs 110, 112, and 114 and allocates at least some of the resources. In some example embodiments, BS120 may be considered a serving node for at least one of SL Tx UE 110 and SL Rx UE 112.

The air interface 105 between UEs 110, 112 and 114 may be configured according to the radio access technology RAT that the UEs 110, 112, 114 are configured to support. Similarly, for example, the air interface 115 between the SL Rx UE 112 and the BS120 may be configured according to the RAT that the SL Rx UE 112 and the BS120 are configured to support. Examples of cellular RATs include long term evolution, LTE, new radio, NR, (also known as fifth generation 5G) radio access technology and multewire. For example, cellular RATs may be standardized by the third generation partnership project 3 GPP. Thus, UEs 110, 112 and 114 and BS120 may be configured to operate in accordance with 3GPP standards.

BS120 may connect with core network 130 directly via wired interface 125 or via at least one intermediate node. The core network 130, in turn, may be coupled via an interface 135 with another network (not shown in fig. 1) via which connections with other networks may be obtained, for example via the global internetwork. BS120 may connect with core network 130 or with another core network directly or via at least one intermediate node.

Example embodiments relate to using SL-based UE-to-UE communication between UEs 110, 112, and 114. SL refers to a direct communication link between UEs 110, 112 and 114 in a cellular communication network, and UEs may communicate via SL without going through BS120. That is, in some embodiments, SL Tx UE 110 may be referred to as a first device-to-device, D2D, UE and SL Rx UE 112 may be referred to as a second D2D UE.

SL communication may be performed by the PC5 based on the principles of sender-oriented one-to-many broadcast/multicast communication and/or one-to-one unicast communication, e.g. as described in 3gpp TS 36.300 for LTE and 3gpp TS38.300 for NR. There may be two resource allocation modes, referred to as mode 1 and mode 2, which are designated for SL transmissions, e.g., for NR SL. Mode 1 may be based on using scheduling resources or grants from a serving BS, such as BS120. Mode 2 may be based on autonomous allocation or selection of resources by a transmitting UE (such as SL Tx UE 110) from a pre-configured pool of transmission resources. The resource selection in mode 2 may be based on, for example, a simple random selection or a selection based on sensing. When using sensing-based resource selection, at least some example embodiments may be used to specifically address the issues related to resource selection in mode 2. However, this does not prevent the use of some example embodiments in other resource allocation/selection schemes, such as resource selection based on random and/or partial sensing.

In the case of mode 2 resource allocation, some problems may impair the reliability of SL communication, such as persistent collisions, hidden node problems, exposed node problems, and half-duplex problems. The above problems may be caused, at least in part, by the fact that: the resource allocation in mode 2 based on sensing may be based on resource reservation information received in SCI transmitted by, for example, SL Tx UE 110. For example, as shown in fig. 1, since the distance between the SL Tx UE 110 and the third SL UE 114 is large, the third SL UE 114 may be regarded as a hidden node from the perspective of the SL Tx UE 110 (i.e., the transmission UE of SL communication between the SL Tx UE 110 and the SL Rx UE 112). Therefore, the third SL UE 114 may not be able to detect the SCI transmitted by the SL Tx UE 110. If the third SL UE 114 would allocate mode 2 resources based on sensing for its own SL transmission, it may select at least a portion of the same resources as the SL Tx UE 110 used to send SL data to the SL Rx UE 112 for transmission to the SL Rx UE 112 and/or another SL Rx UE. In this case, the transmission of the third SL UE 114 may interfere with the reception of the SL data transmission of the SL Tx UE 110 at the SL Rx UE 112.

As another example, SL Tx UE 110 and third UE 114 may have persistent collisions on their selected resources such that SL Tx UE 110 and third SL UE 114 may not be able to detect collisions themselves due to the large distance between SL Tx client 110 and third UE 114. Alternatively or additionally, due to the half duplex capability of the SL Tx UE 110 and the third SL UE 114, i.e., if the SL Tx UE 110 and the third SL UE 114 would not be able to detect/receive while transmitting such that the persistent collision cannot be identified with the sensing procedure performed by the SL Tx UE 110 and the third SL UE 114, the SL Tx UE 110 and the third SL UE 114 may have the persistent collision on the resources they select.

Thus, example embodiments of the present invention enhance SL communication by enabling SL Rx UE 112 to retransmit SCIs transmitted by SL Tx UE 110 and originating from SL Tx UE 110, at least for SL mode 2 resource allocation that may be compromised by problems such as hidden node problems, persistent collisions, and half-duplex constraints. SL Rx UE 112 may be allowed to transmit an adapted retransmission version of the SCI of SL Tx UE 110 to indicate at least one resource reserved by SL Tx UE 110 for SL communication, wherein the at least one reserved resource is indicated by SL Tx client 110 in the SCI and by SL Rx UE 112 in the adapted retransmission version of the SCI. Thus, the third SL UE 114 may be able to detect/monitor the resources reserved by the SL Tx UE 110. Then, the third SL UE 114 may avoid selecting overlapping resources for its own SL transmissions in time and/or frequency. Note that monitoring of neighboring SCIs at the received SL Rx UE 112 for SL communication, and the SL Tx UE 110 and/or the third SL UE 114 for sensing to select mode 2 resources for SL transmission may be an essential feature of SL operation. Transmission of the adapted retransmission version of the SCI reuses the existing SCI transmission mechanism, which has less standardization impact. Thus, this will not cause significantly more processing and protocol overhead than an alternative where SL Rx UE 112 uses higher layer signaling rather than SCI to detect and notify resource handling conflicts between SL Tx UE 110 and third UE 114.

The retransmission of SCI may be further improved by considering when and how the SL Rx UE 112 transmits the adapted retransmission version of SCI. On the one hand, the adapted retransmission version of the SCI and the resource reservation information therein should be in the form of the SCI so that it can be considered as a normal SCI during the sensing of the third SL UE 114, in particular in order to support backward compatibility, e.g. if the third UE 114 is to be a SL UE implemented according to the 3GPP rel-16 specification. On the other hand, due to half duplex constraints of SL Tx UE 110 and/or SL Rx UE 112, the adapted retransmission version of SCI may not be sent by SL Rx UE 112, such that the transmission will overlap with reserved resources indicated by the original SCI transmission of SL Tx UE 110, at least in the time domain. Accordingly, SL Rx UE 112 may determine appropriate resources in the time and frequency domains for transmitting the adapted retransmission version of the SCI of SL Tx UE 110.

Alternatively or additionally, the retransmission of SCI may be further improved by considering how the SL Tx UE 110 determines whether the received SCI is an adapted retransmission version of its own transmitted SCI or a normal SCI from other UEs in the vicinity, since the SL Tx UE 110 does not take its own retransmission SCI into account during its sensing. For example, 3GPP rel-17 mode 2 resource allocation can be enhanced to support random or partial sensing based resource (re) selection for power saving. For shared resource pools for random and/or partial sensing and/or full sensing, it becomes more important to distinguish between retransmission SCIs and normal SCIs, as a fully sensed-based UE may be triggered to reselect or preempt its reserved resource(s) more aggressively than specified in Rel-16, e.g., if the reserved resource(s) conflict with the UE's resource reservation using a random and/or partial sensing-based resource selection mechanism. Thus, it becomes more beneficial to enable SL Tx UE 110 to distinguish between retransmission SCIs to avoid triggering unnecessary resource preemption or re-evaluation/reselection.

Furthermore, some example embodiments of the present invention allow SL Rx UE 112 to first determine whether an adapted retransmission version of the SCI originating from SL Tx UE 110 will be transmitted. In some example embodiments, SL Rx UE 112 may also select resources for retransmitting the adapted retransmission version of the SCI from SL Tx UE 110, e.g., in the frequency and/or time domain. In some example embodiments, SL Rx UE 112 may adapt the information field in the adapted retransmission version of the SCI according to the original SCI received from SL Tx UE 110 to indicate to SL Tx UE 110 that the resource reservation in the adapted retransmission version of the SCI is to be excluded from the sensing results of SL Tx 110. In some example embodiments, SL Rx UE 112 may adapt the information field in the adapted retransmission version of the SCI such that at least a portion of the reserved resources indicated in the adapted retransmission version of the SCI and the original SCI are the same. In general, the original SCI may also be referred to as a conventional SCI, as the original SCI is not an adapted retransmission version of another SCI.

SL Rx UE 112 may send the adapted retransmission version of the SCI and upon reception SL Tx UE 110 may detect that the resource reservation in the adapted retransmission version of the SCI will be excluded from the sensing result. For example, SL Tx UE 110 may detect that the adapted retransmission version of the SCI is a retransmission of the SCI that originated from itself, and based thereon determine that the resource reservation indicated in the adapted retransmission version of the SCI is to be excluded from its sensing results (e.g., for sensing-based mode 2 resource selection/reselection).

Fig. 2 illustrates a signaling diagram in accordance with at least some example embodiments. Referring to fig. 1, on the vertical axis, SL Tx UE 110 and SL Rx UE 112 are disposed from left to right. The time proceeds from top to bottom.

In step 210, under at least some conditions, SL Rx UE 112 may be configured to retransmit the SCI originating from SL Tx UE 110. SL Tx UE 110 and/or SL Rx UE 112 may be configured with triggers for activation/deactivation of the configuration. SL Rx UE 112 may be configured to retransmit the SCI originating from SL Tx UE 110 during SL unicast connection setup/modification using, for example, SL radio resource control, RRC, signaling between SL Tx UE 110 and SL Rx UE 112. In some example embodiments, SL Rx UE 112 may be configured to retransmit SCI of all SL transmissions of the target SL unicast. Alternatively, the SL Rx UE 112 may be configured to retransmit SCI for a particular SL transmission corresponding to, for example, SL traffic with a particular priority, SL traffic on a particular logical channel, PC5 radio conditions such as RSRP and/or CBR, etc.

In the case of SL multicast or broadcast, the configuration may be provided by a serving network (such as BS 120) for SL UEs within network coverage involving SL multicast and broadcast using broadcast or dedicated RRC signaling, or by pre-configuration for SL UEs outside network coverage. The network configuration or pre-configuration may enable all SL multicast or broadcast UEs with Rel-17 capabilities of the feature to activate the feature, or it may implement the feature for a particular SL multicast or broadcast with particular e.g. QoS, priority requirements and/or PC5 radio conditions (e.g. RSRP and/or CBR). Alternatively or additionally, the configuration may be enabled by the SL multicast or broadcast Tx UE 110 to include an explicit indication in the original SCI sent from the SL Tx UE. The explicit indication bit may be one of reserved bits in the Rel-16 SCI format.

The configuration procedure and corresponding configuration information may be different depending on the SCI retransmission resource determination options. For example, in the case of SCI retransmission resources mapped from the original SCI transmission resources or allocated by SL Tx UE 110, the feature activation/deactivation configuration may be triggered by SL Tx UE 110 and configured to SL Rx UE 112 using SL RRC signaling or indicated using an explicit indication in the original SCI transmission. If SCI retransmission resources are selected by SL Rx UE 112, SL Rx UE 112 may determine whether or not a retransmission of the SCI from Tx UE 110 is needed based on, for example, triggers of serving network configuration and QoS of the SL traffic, and radio channel conditions such as reference signal received power RSRP, monitored resource collision/contradiction, and/or channel busy rate.

If the SL Rx UE 112 is configured to determine whether to send an adapted retransmission version of the SCI based on the detected interference or resource reservation collision, then the interference threshold may be configured to the SL Rx UE 112, and different thresholds may be configured for different QoS, radio conditions (e.g., RSRP) between the SL Tx UE 112 and the SL Rx UE, and/or channel busy rate, etc.

In step 220, SL Tx UE 110 may select resources for SL transmission. For example, using mode 2 resource allocation, SL Tx UE 110 may select SL resources from the mode 2 resource pool for SL transmission (e.g., SL transmission to SL Rx UE 112). After the mode 2 resource selection described above, SL Tx UE 110 may generate an SCI including an indication of the selected resources to indicate the resources reserved for the current and future SL transmissions of SL Tx UE 110. The SCI generated by SL Tx UE 110 may be referred to as the original SCI, i.e., the first SCI, originating from SL Tx UE 110. In step 230, SL Tx UE 110 may transmit the first level SCI on a control channel (such as a physical side-chain control channel PSCCH) and the second level SCI and SL data/transport block on a shared channel (such as a physical side-chain shared channel PSSCH).

After receiving the SCI, in step 240, SL Rx UE 112 may determine whether the SCI originating from SL Tx UE 110 is to be retransmitted. That is, SL Rx UE 112 may determine whether an adapted retransmission version of the received SCI (i.e., the second SCI) is to be sent, e.g., based on the configuration from SL Tx UE 110 at step 210 (e.g., using SL RRC signaling) and/or the SL transmission at step 230 (e.g., using an explicit retransmission indication in the original SCI (i.e., the first SCI)). In some example embodiments, SL Rx UE 112 may be configured by a Tx UE or a serving network (such as BS 120), or as a pre-configuration, configured to transmit an adapted retransmission version of the received SCI. For example, SL Rx UE 112 may be configured to transmit an adapted retransmission version of all SCIs originating from SL Tx UE 110. Thus, based on the configuration of SL Rx UE 112, such as the identity of SL Tx UE 110, or the destination identity of the SL transmission from SL Tx UE 110 (e.g., the SL multicast destination L2 identity), SL Rx UE 112 may determine that an adapted retransmission version of the SCI is to be sent. Alternatively, SL Rx UE 112 may be configured to retransmit SCI from SL Tx UE 110 that satisfies some configuration conditions.

Alternatively, SL Rx UE 112 may determine whether to source the retransmission of the SCI from SL Tx UE 110 based on interference or collision with reserved resources indicated in the original SCI. For example, SL Rx UE 112 may determine whether interference to at least a portion of the reserved resources is above a configured threshold. If SL Rx UE 112 detects high interference or collision to reserved resources, SL Rx UE 112 may determine that an adapted retransmission version of the SCI needs to be sent and the adapted retransmission version of the SCI may be adapted to indicate interference/collision to SL Tx UE 110 and/or third SL UE 114.

In step 250, sl Rx UE 112 may select at least one resource for transmitting the adapted retransmission version of the original SCI based on, for example, a mapping rule, an inter-user equipment resource allocation procedure, or using a mode 2 allocation scheme. SL Rx UE 112 may select at least one resource after detecting/receiving the original SCI from SL Tx UE 110, e.g., if a retransmission of the original SCI is configured. The selected resources may be indicated by SL Tx UE 110, by another UE, or by a network entity controlling SL communication, such as BS 120. SL Tx UE 110 may indicate the resources to select in the original SCI or through other signaling such as MAC or RRC signaling.

For example, at least one resource used by SL Rx UE 112 to transmit the adapted retransmission version of the original SCI originating from SL Tx UE 110 may be mapped from the resource used for transmission of the original SCI. Mapping rules may be preconfigured for SL Rx UE 112 by standard specifications, serving network, or SL Tx UE 110. Alternatively, the mapping rules may be configured during configuration at step 210. Thus, the at least one resource used by SL Rx UE 112 to transmit the adapted retransmission version of the original SCI may indicate that the at least one reserved resource indicated in the adapted retransmission version of the SCI is to be excluded from the sensing result of SL Tx UE 110. As one example, in this case, SL Tx UE 110 does not consider at least one reserved resource indicated in the adapted retransmission version of SCI as reserved by SL Rx UE 112 during the sensing of SL Tx UE 110.

The mapping rules may be specified in the time domain, e.g., with a certain time offset from the transmission of the original SCI, or in both the time domain and the frequency domain, e.g., with a specific time offset and subchannel offset from the transmission of the original SCI. Alternatively or additionally, the at least one resource may comprise special symbol(s) for transmission of the adapted retransmission version of the SCI, which special symbol(s) may be configured, e.g., with/by a resource pool configuration or resource mapping rule. In some example embodiments, the special symbol(s) may be different from the symbol used to carry any original SCI. In this way, the adapted retransmission version of the SCI can be identified by a special symbol.

SL Tx UE 110 may also consider mapping rules when selecting resources (such as mode 2 resources). For example, SL Tx UE 110 may select mode 2 resources where mapping resources for transmitting the adapted retransmission version of the SCI are also available and do not collide or overlap with other SL transmissions, depending on the sensing result, making the process more efficient.

Alternatively, at least one resource used by SL Rx UE 112 to transmit the adapted retransmission version may be assigned by SL Tx UE 110 using an inter-UE resource allocation procedure, where SL Tx UE 110 may instruct SL Rx UE 112 to transmit the resource of the adapted retransmission version of the SCI. Thus, the resources used by SL Rx UE 112 to retransmit the SCI may actually be assigned by SL Tx UE 110. In this case, the transmission of the adapted retransmission version may be individually enabled for each SCI by SL Tx UE 110 by providing resources for the transmission of the adapted retransmission version of the SCI. In one example, the transmission at step 230 and/or some other step may include/indicate such resources allocated by SL Tx UE 110 for transmitting the adapted retransmission version of the SCI by SL Rx UE 112.

If at least one resource for transmission of an adapted retransmission version of the SCI is allocated by SL Tx UE 110 using inter-UE resource allocation, the first level SCI carried in the corresponding PSCCH resource may carry resource reservation information while the corresponding PSSCH resource may be used to transmit the second level SCI and data information to at least SL Tx UE 110. In this case, due to inter-UE resource allocation, transmission to the first stage SCI of SL Tx UE 110 may be skipped, as SL Tx UE 110 may already indicate the configuration to SL Rx UE 112 during the inter-UE resource configuration procedure.

In some example embodiments, SL Rx UE 112 may select at least one resource for transmission of the adapted retransmission version of the original SCI based not only on the sensing result but also on reserved resources indicated in the original SCI. For example, SL Rx UE 112 may select at least one resource for transmission of the adapted retransmission version of the original SCI at a particular time interval/offset (e.g., corresponding to at least one of SCI processing time and resource preemption/re-evaluation/reselection processing time) before the time of the next reserved resource(s) indicated in the original SCI. If SL Rx UE 112 correctly receives the SL transmission in the first transmission from SL Tx UE 110 and the reserved resources indicated in the original SCI are only used for the SL HARQ retransmission, then SL Rx UE 112 may use the next reserved resources indicated in the original SCI to send an adapted retransmission version of the original SCI that at least indicates the reserved resources for the SL HARQ retransmission, since SL Tx UE 112 may not use the next reserved resources for the SL HARQ retransmission after receiving the HARQ ACK feedback from the SL Tx UE.

In some example embodiments, at least one resource used by the SL Rx UE 112 to transmit the adapted retransmission version may be selected by the SL Rx UE 112 using a normal mode 2 resource allocation scheme, such as based on full sensing, based on partial sensing, and/or random resource selection scheme(s). In some embodiments, the mode 2 resource allocation scheme may be applied with additional considerations, e.g., SL Rx UE 112 may consider at least the reserved resources of SL Tx UE 110 indicated in the received SCI at least in the time domain to determine/select at least one resource for transmission of the adapted retransmission version of the original SCI to ensure that transmission of the adapted retransmission version occurs before the time/slot of the next reserved resources of SL Tx UE 110.

In some example embodiments, the at least one resource for transmission of the adapted retransmission version of the original SCI may comprise only PSCCH resources, or also PSSCH resources for transmission of second level or even SL data of the SCI. The inclusion of only PSCCH resources may require a new SL resource pool structure to allow decoupling of PSCCH transmissions from PSSCH transmissions. If PSSCH resources for transmission of second level of SCI or even SL data are included, the existing SL resource pool structure of PSCCH and associated PSCCH resources coupled in the same TTI as specified in 3GPP Rel-16 can be reused. In this case, the PSSCH resources associated with the PSCCH resources used for the transmission of the adapted retransmission version of the original SCI may be used to send second level SCI and/or SL data originating from SL Rx UE 112 for its own SL transmission.

In step 260, SL Rx UE 112 may adapt the original SCI to generate an adapted retransmission version of the SCI such that the adapted retransmission version of the SCI indicates to SL Tx UE 110: at least one reserved resource indicated in the adapted retransmission version of SCI will be excluded from the sensing result of SL Tx UE 110. For example, at least one resource on which the adapted retransmission version of the SCI is transmitted and/or at least one resource indicated by the adapted retransmission version of the SCI may indicate to the SL Tx UE 110 that resource reservations in the adapted retransmission version of the SCI are to be excluded from the above-described sensing results. Alternatively or additionally, the adapted retransmission version of SCI may be adapted to include an explicit indication to SL Tx UE 110 that resource reservation in the adapted retransmission version of SCI is to be excluded from the above-described sensing results. In some example embodiments, the priority field of the adapted retransmission version of SCI may be adapted to indicate to SL Tx UE 110 that resource reservation in the adapted retransmission version of SCI is to be excluded from the above-described sensing results. That is, the original SCI (i.e., the first SCI) may be adapted to generate an adapted retransmission version of the SCI (i.e., the second SCI) to affect the sensing results of the SL Tx UE 110 in a different manner (compared to the original (non-retransmitted) SCI that the SL Tx 110 receives or is about to receive from other UEs).

In some example embodiments, combinations of indications may also be utilized. For example, by using at least one resource and priority field, reliability may be improved without additional overhead. Reliability may be further enhanced by adding an explicit indication over at least one resource and priority field.

Furthermore, in some example embodiments, SL Rx UE 112 may adapt the information field in the adapted retransmission version of the original SCI according to the original SCI such that at least a portion of the reserved resources indicated in the adapted retransmission version of the SCI and the original SCI are the same. The adaptation may include at least an update time resource assignment field to reflect an updated time interval between the adapted retransmission version of the SCI and the next reserved resource.

Alternatively or additionally, the adapting may comprise merging multiple SCIs originating from the same or different SL Tx UEs into one adapted retransmission version of the multiple SCIs and reserved resources. If SL Rx UE 112 has several SL unicast connections with multiple SL Tx UEs 110 and receives multiple SCIs to retransmit, the adapted retransmission version of the SCI may be adapted to have one combined SCI retransmission. A combination of SCIs may be possible, for example, if each of the SL Tx UEs 110 reserves only one additional resource in the frequency resource assignment field, while the higher layer parameter SL-MaxNumPerReserve is configured to 3, which means that two additional resource reservations may be provided in the SCI. In this case, SL Rx UE 110 may combine the reserved resources of at least two original SCIs into one adapted retransmission version of the SCI. The merging of the multiple original SCIs may also take into account priority fields and/or reserved resources (e.g., subchannels) of the multiple original SCIs. For example, the merging may be performed only when the priority fields of the plurality of original SCIs are the same. Alternatively, if consecutive sub-channels in reserved resources of the plurality of original SCIs are reserved, combining may be performed.

In some example embodiments, the adapting may include setting a value for one or more fields of the adapted retransmission version of the SCI, the value being used to explicitly indicate that the adapted retransmission version is a retransmission SCI, which may be coupled or decoupled from resources used for retransmission of the original SCI.

In some example embodiments, the adapting may include updating a priority indication in a priority field of the SCI format and/or setting a corresponding transmit power for transmitting the adapted retransmission version of the SCI. The updated priority indication may be used, for example, to trigger resource preemption or reselection from SL Tx UE 110, or to avoid triggering unnecessary reselection/preemption of reserved resources from SL Tx UE 110.

In step 270, the sl Rx UE 112 may send the adapted retransmission version of the SCI. After receiving any SCI, SL Tx UE 110 may need to determine whether the received SCI is from another SL UE in the vicinity or whether the received SCI is a retransmitted version of its own SCI.

In step 280, sl Tx UE 110 may detect that the SCI received in step 270 is an adapted retransmission version of the SCI, e.g., to determine whether to exclude the received SCI from its sensing process. SL Tx UE 110 may handle both types of SCIs (normal SCI and retransmission SCI) differently for its sensing process. Normal SCI from other SL UEs may be considered as input to the sensing procedure for SL resource selection, while retransmission SCI may be excluded from the sensing procedure. However, if the resources used to retransmit the SCI also have associated PSSCH resources, and a portion of the resources of the PSSCH are actually used by the SL Rx UE 112 to transmit its own SL data, the portion of the PSSCH resources associated with the retransmitting SCI may not be excluded from the sensing process. In some example embodiments, in the case of an implicit indication of a retransmission SCI using a changed priority indication, the SL Tx UE 110 may be implicitly informed with an increased or decreased priority indication in the adapted retransmission version of the SCI to exclude the retransmission SCI from its sensing process.

The detection may be based on at least one resource on which an adapted retransmission version of the SCI is received if the at least one resource is mapped/derived from the resource used for transmission of the original SCI or allocated by SL Tx UE 110 through inter-UE coordination/resource allocation. Alternatively or additionally, the above detection may be based on an explicit indication, e.g. if the adapted retransmission version of the SCI comprises one or more of the reserved bits in the SCI format. For example, reserved bits in the second stage SCI format field or reserved bits at the end of the first stage SCI may be used. In some example embodiments, the detecting may be based on the priority indication if the priority indication in the adapted retransmission version of the SCI has changed compared to the priority indication of the original SCI. That is, SL Tx UE 110 may implicitly detect that the SCI received at step 270 is an adapted retransmission version of the SCI, because the priority information field in the adapted retransmission version of the SCI indicates a different priority than in the original SCI, such that the sensing procedure performed by SL Tx UE 110 is affected. The detection may also be based on a combination of at least two indications, if any, in order to improve reliability.

For a change in priority indication in the adapted retransmission version of the SCI, the SL Rx UE 112 may determine whether to decrease or increase the priority indication compared to the priority indication of the original SCI. For example, if SL Rx UE 112 detects conflicting resources reserved for lower priority SL traffic from another SL UE in proximity, SL Rx UE 112 may determine to lower the priority indication in the adapted retransmission version of the SCI as compared to the priority indication of the original SCI. In this way, SL Tx UE 112 may consider conflicting resource reservations received from SCIs of other UEs for SL traffic with lower priority, which may then not trigger SL Tx UE 110 to preempt or reselect its reserved resources. The adapted retransmission version of the SCI may prevent other SL UEs in the vicinity from selecting the same resources, even with a reduced priority indication. However, if there is a resource conflict between the SL Tx UE 110 in question and other SL Tx UEs in the vicinity, and the priority of traffic of the other SL Tx UEs is lower than the priority of SCI from the SL Tx UE 110 in question but higher than or equal to the reduced priority indicated by the adapted retransmission version of SCI, the reduced priority in the adapted retransmission version of SCI may also affect the sensing of the other SL UEs in the vicinity, thereby missing preemption.

In another example, if SL Rx UE 112 detects that conflicting resources from another SL UE in proximity are reserved for higher priority SL traffic, SL Rx UE 112 may determine to increase the priority in retransmission SCI. In this way, SL Tx UE 110 may consider conflicting resource reservations received from SCIs of other UEs to be for SL traffic with higher priority and thus be triggered to preempt or reselect resources to avoid resource reservation conflicts with other SL UEs in the vicinity of SL Rx UE 112.

Since priority-based resource preemption or reselection triggers may also be related to the RSRP of the received SCI, the transmit power of the retransmission SCI may be controlled such that its measured RSRP level at the SL Tx UE 110 may or may not trigger resource preemption or re-evaluation/reselection of the SL Tx UE 110, depending on whether interference/resource collision comes from a SL UE with a higher or lower priority.

In general, the exemplary embodiments of this invention may be applied to SL unicast, as well as to SL multicast or broadcast using the configuration of step 210. Since there may be multiple SL Rx UEs in SL multicast or broadcast, the retransmission efficiency of SCI may be controlled by: for example, when a SL multicast/broadcast Rx UE detects a retransmission SCI, it will not retransmit the SCI.

In some example embodiments, the existing SL resource pool structure and SCI format may be reused, and legacy SCI transport mechanisms with no change in SCI format may be used. This enables legacy SL UEs to detect reserved resources in the adapted retransmission version of SCI as normal SCI to achieve backward compatibility and enhance sensing-based mode 2 resource allocation for new or legacy UEs.

Alternatively, it may be desirable to support new SL resource pool structures, e.g., decoupled PSCCH and PSSCH transmissions, and/or pure PSCCH transmissions without associated PSSCH transmissions, the enhancement of mode 2 resource allocation based on sensing may not be applicable to legacy UEs. In some example embodiments, it may be ensured that legacy UEs are not affected to reduce their resource allocation performance.

The retransmission SCI may be applied to only the first stage SCI on the PSCCH, or may be applied to both the first stage SCI and the second stage SCI. In view of backward compatibility, the legacy UE may receive only the first-stage SCI of the retransmission, or both.

FIG. 3 illustrates an example apparatus capable of supporting at least some example embodiments. Illustrated is a device 300, which device 300 may include, for example, SL Tx UE 110 or SL Rx UE 112, or a device that may control its functions when installed therein. The processor 310 is included in the device 300, and the processor 310 may include, for example, a single-core processor including one processing core or a multi-core processor including more than one processing core. The processor 310 may generally include a control device. Processor 310 may include more than one processor. The processor 310 may be a control device. The processor 310 may include at least one application specific integrated circuit ASIC. The processor 310 may include at least one field programmable gate array FPGA. The processor 310 may include at least one Qualcomm Snapdragon and/or Intel Atom processor. The processor 310 may include, for example, a Cortex-A8 processing core manufactured by ARM holders or a Steamroller processing core manufactured by Advanced Micro Devices Corporation. Processor 310 may be means for performing method steps in device 300, such as determining, causing transmission, and causing reception. Processor 310 may be configured, at least in part, by computer instructions, to perform actions.

The processor may include circuitry or be constructed as one or more circuits configured to perform the stages of the method according to example embodiments described herein. As used herein, the term "circuitry" may refer to one or more or all of the following: (a) Hardware-only circuit implementations, such as implementations in analog and/or digital circuitry only, and (b) combinations of hardware circuitry and software, such as where applicable: (i) A combination of analog and/or digital hardware circuit(s) and software/firmware, and (ii) any portion of hardware processor(s) (including digital signal processor (s)) having software, and memory(s) that work together to cause a device (such as a network function) to perform various functions, and (c) a hardware circuit(s) and/or processor(s), such as microprocessor(s) or a portion of microprocessor(s), that require software (e.g., firmware) to operate, but software may not be present when software is not required to operate.

This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this disclosure, the term circuitry also encompasses hardware-only circuits or processors (or multiple processors) or a portion of a hardware circuit or processor and its attendant software and/or firmware implementations. For example and if applicable to the particular claim elements, the term circuitry also encompasses a baseband integrated circuit or processor integrated circuit for a mobile device, or a similar integrated circuit in a server, a cellular network device, or other computing or network device.

The device 300 may include a memory 320. Memory 320 may include random access memory and/or persistent memory. Memory 320 may include at least one RAM chip. Memory 320 may include, for example, solid-state, magnetic, optical, and/or holographic memory. Memory 320 may be at least partially accessible by processor 310. Memory 320 may be at least partially included in processor 310. Memory 320 may be a means for storing information. Memory 320 may include computer instructions that processor 310 is configured to execute. When computer instructions configured to cause processor 310 to perform certain actions are stored in memory 320, and device 300 is generally configured to run under the direction of processor 310 using computer instructions from memory 320, processor 310 and/or at least one processing core thereof may be considered to be configured to perform the specific actions described above. Memory 320 may be at least partially included in processor 310. Memory 320 may be at least partially external to device 300, but accessible by device 300.

The device 300 may include a transmitter 330. The device 300 may include a receiver 340. The transmitter 330 and the receiver 340 may be configured to transmit and receive information, respectively, according to at least one cellular or non-cellular standard. The transmitter 330 may include more than one transmitter. The receiver 340 may include more than one receiver. The transmitter 330 and/or the receiver 340 may be configured to operate in accordance with, for example, global system for mobile communications GSM, wideband code division multiple access WCDMA, long term evolution LTE, and/or 5G/NR standards.

The device 300 may comprise a near field communication NFC transceiver 350. The NFC transceiver 350 may support at least one NFC technology, such as Bluetooth, wibree or similar technology.

The device 300 may include a user interface UI 360.UI 360 may include at least one of a display, a keyboard, a touch screen, a vibrator arranged to signal the user by causing device 300 to vibrate. The user may be able to operate the device 300 via the UI 360, for example, to accept an incoming phone call, initiate a phone call or video call, browse the internet, manage digital files stored in the memory 320 or on a cloud accessible via the transmitter 330 and receiver 340 or via the NFC transceiver 350, and/or play a game.

The device 300 may include or be arranged to accept a user identity module 370. The user identity module 370 may comprise, for example, a subscriber identity module, SIM, card that is mountable in the device 300. User identity module 370 may include information identifying a subscription of a user of device 300. User identity module 370 may include cryptographic information that may be used to verify the identity of a user of device 300 and/or facilitate encryption of transmitted information and billing a user of device 300 for communications effectuated via device 300.

The processor 310 may be provided with a transmitter arranged to output information from the processor 310 to other devices comprised in the device 300 via electrical conductors inside the device 300. Such transmitters may comprise a serial bus transmitter arranged to output information to the memory 320 for storage in the memory 320, for example via at least one electrical lead. Instead of a serial bus, the transmitter may comprise a parallel bus transmitter. Likewise, the processor 310 may comprise a receiver arranged to receive information in the processor 310 from other devices comprised in the device 300 via electrical leads internal to the device 300. Such a receiver may comprise a serial bus receiver arranged to receive information from the receiver 340, for example via at least one electrical lead, for processing in the processor 310. As an alternative to a serial bus, the receiver may comprise a parallel bus receiver.

Device 300 may include other devices not shown in fig. 3. For example, where the device 300 comprises a smart phone, it may comprise at least one digital camera. Some devices 300 may include a rear camera that may be used for digital photography and a front camera for video telephony. The device 300 may comprise a fingerprint sensor arranged to authenticate, at least in part, a user of the device 300. In some embodiments, device 300 lacks at least one of the devices described above. For example, some devices 300 may lack NFC transceiver 350 and/or user identity module 370.

Processor 310, memory 320, transmitter 330, receiver 340, NFC transceiver 350, UI 360, and/or user identity module 370 may be interconnected in a number of different ways by electrical leads internal to device 300. For example, each of the above devices may be separately connected to a main bus internal to device 300 to allow the devices to exchange information. However, as will be appreciated by those skilled in the art, this is merely one example, and various ways of interconnecting at least two of the above-described devices may be selected according to embodiments without departing from the scope of the embodiments.

Fig. 4 is a flow chart of a first method in accordance with at least some example embodiments. The stages of the first method shown may be performed by the SL Rx UE 112 or a device controlling its functions (possibly when installed therein).

The first method may include: in step 410, first side chain control information is received by a receiving user equipment (SL Rx UE 112) from a transmitting user equipment (SL Tx UE 110), wherein the first side chain control information originates from the transmitting user equipment (SL Tx UE 110). The first method may further include: at step 420, it is determined by the receiving user equipment (SL Rx UE 112) whether second side-chain control information is to be transmitted, wherein said second side-chain control information is an adapted retransmission version of said first side-chain control information. Furthermore, the first method may include: in step 430, resources for transmitting the above second side chain control information are selected by the receiving user equipment (SL Rx UE 112) upon a positive determination. Finally, the first method may include: in step 440, the second side chain control information is transmitted by the receiving user equipment (SL Rx UE 112) on the selected resources.

Fig. 5 is a flow chart of a second method in accordance with at least some example embodiments. The stages of the second method shown may be performed by SL Tx UE 110 or a device controlling its functions (possibly when installed therein). The second method may include: in step 510, first side chain control information is transmitted by a transmitting user equipment (SL Tx UE 110) to a receiving user equipment (SL Rx UE 112). The second method may further include: in step 520, second side chain control information is received from the receiving user equipment (SL Rx UE 112) in response to the transmitting. Finally, the second method may include: in step 530, it is detected that the second side chain control information is an adapted retransmission version of the first side chain control information.

It is to be understood that the disclosed example embodiments are not limited to the specific structures, process steps, or materials disclosed herein, but extend to equivalents thereof as recognized by one of ordinary skill in the relevant arts. It is also to be understood that the terminology employed herein is for the purpose of describing particular example embodiments only and is not intended to be limiting.

In this specification, a reference to one example embodiment or example embodiment means that a particular feature, structure, or characteristic described in connection with the example embodiment is included in at least one example embodiment. Thus, the appearances of the phrase "in one example embodiment" or "in an example embodiment" in various places throughout this specification are not necessarily all referring to the same example embodiment. Where a term such as about or substantially is used to refer to a value, the exact value is also disclosed.

As used herein, a plurality of items, structural elements, constituent elements, and/or materials may be presented in a common list for convenience. However, these lists should be understood as though each member of the list is individually identified as a separate and unique member. Thus, any individual member of such a list should not be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. Further, various example embodiments and examples, as well as alternatives to their various components, may be referenced herein. It should be understood that such example embodiments, examples, and alternatives should not be construed as virtually equivalent to one another, but rather as independent and autonomous representations.

In example embodiments, an apparatus comprising, for example, SL Tx UE 110 or SL Rx UE 112 may further comprise means for performing the above example embodiments, and any combination thereof. The apparatus may be an apparatus of a cellular communication network, such as a 5G network, and include means for operating in the cellular communication network.

In one example embodiment, a computer program comprises instructions that when executed by a computer cause the computer to perform a method according to the example embodiments described above, and any combination thereof. In example embodiments, a computer program product embodied on a non-transitory computer readable medium may be configured to control a processor to perform a process including the example embodiments described above and any combination thereof.

In an example embodiment, an apparatus comprising, for example, SL Tx UE 110 or SL Rx UE 112, may further comprise at least one processor and at least one memory including computer program code, wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to perform at least the above example embodiments and any combination thereof. The apparatus may be an apparatus of a cellular communication network, such as a 5G network, and is configured to operate in the cellular communication network.

Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more example embodiments. In the previous descriptions, examples of specific details, such as lengths, widths, shapes, etc., are provided to provide a thorough understanding of example embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention may be practiced without one or more of the specific details, or with other methods, components, materials, and so forth. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.

While the foregoing illustrates the principles of example embodiments in one or more specific applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of embodiments can be made without departing from the principles and concepts of the invention. Accordingly, the invention is not intended to be limited except as by the following claims.

The verbs "comprise" and "include" as used in this document are used as open limits and neither exclude nor require the presence of unrecited features. The features recited in the dependent claims are freely combinable with each other unless explicitly stated otherwise. Furthermore, it should be understood that the use of "a" or "an" (i.e., in the singular) throughout this document does not exclude a plurality.

"at least one of A or B" in this document means A, or B, or both A and B.

INDUSTRIAL APPLICABILITY

At least some example embodiments find industrial application in cellular communication networks (such as 5G networks) and possibly in other cellular communication networks in the future.

List of abbreviations

3GPP: third generation partnership project

BS: base station

CBR: channel busy ratio

GSM: global mobile communication system

IoT: internet of things

LTE: long term evolution

M2M: machine-to-machine

NFC: near field communication

NR: new radio

PSCCH: physical side chain control channel

PSSCH: physical side chain shared channel

RAT: radio access technology

RRC: radio resource control

RSRP: reference signal received power

QoS: quality of service

SCI: side chain control information

SL: side chain

UE: user equipment

UI: user interface

WCDMA: wideband code division multiple access

WiMAX: worldwide interoperability for microwave access WLAN: wireless local area network

List of reference numerals

105、115	Air interface
		110	SL Tx UE
112	SL Rx UE
		114	Third SL UE
120	BS
		125、135	Wired interface
130	Core network
		210-280	The steps in FIG. 2
300-370	The structure of the device of FIG. 3
		410-440	Stages of the method in FIG. 4
510-530	Stages of the method in FIG. 5

Claims (14)

1. An apparatus, comprising:

-means for receiving, by a receiving user equipment, first side chain control information from a transmitting user equipment, wherein the first side chain control information originates from the transmitting user equipment;

-means for determining, by the receiving user equipment, whether to send second side-chain control information, wherein the second side-chain control information is an adapted retransmission version of the first side-chain control information;

-means for selecting, by the receiving user equipment, resources for transmitting the second side-chain control information upon a positive determination; and

-means for transmitting, by the receiving user equipment, the second side-chain control information on the selected resources.

2. The apparatus of claim 1, further comprising:

-means for determining whether to send the second side chain control information based on at least one of:

a configuration of the receiving user equipment, wherein the configuration is received from the transmitting user equipment or from a network entity controlling side-chain communication;

an indication in the first side chain control information;

interference on at least one reserved resource indicated in the first sidelink control information; or alternatively

A collision on the at least one reserved resource indicated in the first side chain control information.

3. The apparatus of claim 1 or claim 2, wherein the means for selecting the resource for transmitting the second side chain control information comprises selecting based on at least one of:

mapping rules to be used for deriving said resources for transmitting said second side chain control information from the resources on which said first side chain control information is received,

resources indicated by the transmitting user equipment,

-resources indicated by another user equipment, or a network entity controlling side-chain communication, or

-a user equipment autonomous resource allocation scheme.

4. The apparatus of any of the preceding claims, wherein the second side chain control information indicates at least some of the same reserved time resources as the first side chain control information.

5. The apparatus of any of the preceding claims, further comprising:

-means for adapting the second side-chain control information to generate the adapted retransmission version of the first side-chain control information such that the second side-chain control information indicates to the transmitting user equipment: the at least one reserved resource indicated in the second side-chain control information will affect the means of the sensing result of the transmitting user equipment differently than the original side-chain control information received by the transmitting user equipment.

6. The apparatus of any of the preceding claims, further comprising:

-means for adapting an information field of the second side chain control information by performing at least one of:

adapting the information field related to time resource assignment according to a time interval between the second side chain control information and at least one reserved resource of the first side chain control information;

Merging a plurality of first side chain control information; or alternatively

A priority field is adapted to indicate that the second side chain control information is a retransmission of the first side chain control information.

7. The apparatus according to any of the preceding claims, wherein the adapted retransmission version of the first side chain control information is indicated by at least one of: the resource on which the second side-chain control information is sent, an explicit indication, or a priority information field in the second side-chain control information.

8. An apparatus, comprising:

-means for transmitting, by a transmitting user equipment, first side chain control information to a receiving user equipment;

-means for receiving second side chain control information from said receiving user equipment in response to said transmitting; and

-means for detecting that the second side chain control information is an adapted retransmission version of the first side chain control information.

9. The apparatus of claim 8, further comprising:

-means for detecting that the second side-chain control information indicates at least one reserved resource that will affect the sensing result of the transmitting user equipment differently from the original side-chain control information received by the transmitting user equipment.

10. The apparatus of claim 8 or claim 9, wherein detecting that the second side-chain control information is an adapted retransmission version of the first side-chain control information is based on at least one of: the resource on which the second side-chain control information is received, an explicit indication, or a priority information field in the second side-chain control information.

11. The apparatus of any of claims 8 to 10, wherein the second side chain control information indicates at least some of the same reserved time resources as the first side chain control information.

12. A method, comprising:

-receiving, by a receiving user equipment, first side chain control information from a transmitting user equipment, wherein the first side chain control information originates from the transmitting user equipment;

-determining, by the receiving user equipment, whether to send second side-chain control information, wherein the second side-chain control information is an adapted retransmission version of the first side-chain control information;

-upon a positive determination, selecting, by the receiving user equipment, a resource for transmitting the second side-chain control information; and

-transmitting, by the receiving user equipment, the second side-chain control information on the selected resources.

13. A method, comprising:

-transmitting, by a transmitting user equipment, first side chain control information to a receiving user equipment;

-receiving second side chain control information from the receiving user equipment in response to the transmitting; and

-detecting that the second side chain control information is an adapted retransmission version of the first side chain control information.

14. A computer program configured to perform the method of claim 12 or claim 13.