EP4305792A1

EP4305792A1 - Enhanced sidelink communications in cellular communication networks

Info

Publication number: EP4305792A1
Application number: EP22709986.8A
Authority: EP
Inventors: Ling Yu; Vinh Van Phan; Lianghai JI
Original assignee: Nokia Technologies Oy
Current assignee: Nokia Technologies Oy
Priority date: 2021-03-08
Filing date: 2022-02-15
Publication date: 2024-01-17
Also published as: CN116998124A; WO2022189097A1

Abstract

According to an example aspect of the present invention, there is provided an apparatus comprising means for receiving, by a receiving user equipment, first sidelink control information from a transmitting user equipment, wherein said first sidelink control information is originated from the transmitting user equipment, means for determining, by the receiving user equipment, whether to transmit second sidelink control information, wherein said second sidelink control information is an adapted retransmission version of said first sidelink control information, means for selecting upon positive determination, by the receiving user equipment, a resource for transmitting said second sidelink control information and means for transmitting, by the receiving user equipment, said second sidelink control information on the selected resource.

Description

ENHANCED SIDELINE COMMUNICATIONS IN CELLULAR COMMUNICATION

NETWORKS

FIELD

[0001] Various example embodiments relate in general to cellular communication networks and more specifically, to sidelink communications in such networks.

BACKGROUND

[0002] Sidelink, SL, is a direct communication link between User Equipment, UEs, in a cellular communication network and UEs can communicate via a SL without going through a Base Station, BS. Communication over the SL may be enabled in various cellular communication networks, such as in cellular communication networks operating according to 5G radio access technology. 5G radio access technology may also be referred to as new radio, NR, access technology. 3rd generation partnership project, 3GPP, develops standards for 5G/NR and some topics in the 3GPP discussions are related to SL communications. According to the discussions there is a need to provide improved methods, apparatuses and computer programs related to the use of SL. Such improvements may be exploited in other cellular communication networks as well.

SUMMARY

[0003] According to some aspects, there is provided the subject-matter of the independent claims. Some example embodiments are defined in the dependent claims.

[0004] The scope of protection sought for various example embodiments of the invention is set out by the independent claims. The example embodiments and features, if any, described in this specification that do not fall under the scope of the independent claims are to be interpreted as examples useful for understanding various example embodiments of the invention.

[0005] According to a first aspect of the present invention, there is provided an apparatus, comprising means for receiving, by a receiving user equipment, first sidelink control information from a transmitting user equipment, wherein said first sidelink control information is originated from the transmitting user equipment, means for determining, by the receiving user equipment, whether to transmit second sidelink control information, wherein said second sidelink control information is an adapted retransmission version of said first sidelink control information, means for selecting upon positive determination, by the receiving user equipment, a resource for transmitting said second sidelink control information and means for transmitting, by the receiving user equipment, said second sidelink control information on the selected resource. The apparatus of the first aspect may comprise the receiving user equipment, or a control device configured to control the functioning thereof, possibly when installed therein.

[0006] Example embodiments of the first aspect may comprise at least one feature 14from the following bulleted list or any combination of the following features:

• said means for selecting the resource for transmitting said second sidelink control information comprises selecting based on at least one of: a mapping rule, to be used to derive the resource for transmitting said second sidelink control information from a resource on which said first sidelink control information is received, a resource indicated by the transmitting user equipment, a resource indicated by another user equipment or a network entity controlling sidelink communication, or a user equipment autonomous resource allocation scheme;

• means for determining whether to transmit said second sidelink 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 sidelink communication; an indication in said first sidelink control information; interference on at least one reserved resource indicated in said first sidelink control information; or conflict on the at least one reserved resource indicated in said first sidelink control information;

• said second sidelink control information indicates at least some of the same reserved time resources as said first sidelink control information;

• means for adapting said second sidelink control information to generate the adapted retransmission version of said first sidelink control information such that said second sidelink control information indicates to the transmitting user equipment that the at least one reserved resource indicated in said second sidelink control information is to impact a sensing result of the transmitting user equipment differently from original sidelink control information the transmitting user equipment received; • means for adapting an information field of said second sidelink control information by performing at least one of: adapting the information field related to a time resource assignment according to a time interval between said second sidelink control information and at least one reserved resource of said first sidelink control information; consolidating multiple first sidelink control information; or adapting a priority field to indicate that said second sidelink control information is a retransmission of said first sidelink control information;

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

[0007] According to a second aspect of the present invention, there is provided an apparatus, comprising means for transmitting, by a transmitting user equipment, first sidelink control information to a receiving user equipment, means for receiving from the receiving user equipment, responsive to said transmission, second sidelink control information and means for detecting that said second sidelink control information is an adapted retransmission version of said first sidelink control information. The apparatus may comprise the transmitting user equipment, or a control device configured to control the functioning thereof, possibly when installed therein.

[0008] Example embodiments of the second aspect may comprise at least one feature from the following bulleted list or any combination of the following features:

• means for detecting that said second sidelink control information indicates at least one reserved resource which is to impact a sensing result of the transmitting user equipment differently from original sidelink control information the transmitting user equipment received;

• it is detected that said second sidelink control information is an adapted retransmission version of said first sidelink control information based on at least one of a resource on which said second sidelink control information is received, an explicit indication, or a priority information field in said second sidelink control information

• said second sidelink control information indicates at least some of the same reserved time resources as said first sidelink control information. [0009] According to a third aspect of the present invention, there is provided a first method, comprising receiving, by a receiving user equipment, first sidelink control information from a transmitting user equipment, wherein said first sidelink control information is originated from the transmitting user equipment, determining, by the receiving user equipment, whether to transmit second sidelink control information, wherein said second sidelink control information is an adapted retransmission version of said first sidelink control information, selecting upon positive determination, by the receiving user equipment, a resource for transmitting said second sidelink control information and transmitting, by the receiving user equipment, said second sidelink control information on the selected resource. The first method may be performed by the receiving user equipment, or a control device configured to control the functioning thereof, possibly when installed therein.

[0010] According to a fourth aspect of the present invention, there is provided a second method, comprising transmitting, by a transmitting user equipment, first sidelink control information to a receiving user equipment, receiving from the receiving user equipment, responsive to said transmission, second sidelink control information and detecting that said second sidelink control information is an adapted retransmission version of said first sidelink control information. The second method may be performed by the transmitting user equipment, or a control device configured to control the functioning thereof, possibly when installed therein.

[0011] 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 being configured to, with the at least one processing core, cause the apparatus at least to perform, receive, by a receiving user equipment, first sidelink control information from a transmitting user equipment, wherein said first sidelink control information is originated from the transmitting user equipment, determine, by the receiving user equipment, whether to transmit second sidelink control information, wherein said second sidelink control information is an adapted retransmission version of said first sidelink control information, select upon positive determination, by the receiving user equipment, a resource for transmitting said second sidelink control information and transmit, by the receiving user equipment, said second sidelink control information on the selected resource. The apparatus may comprise the receiving user equipment, or a control device configured to control the functioning thereof, possibly when installed therein.

[0012] 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 being configured to, with the at least one processing core, cause the apparatus at least to perform, transmit, by a transmitting user equipment, first sidelink control information to a receiving user equipment, receive from the receiving user equipment, responsive to said transmission, second sidelink control information and detect that said second sidelink control information is an adapted retransmission version of said first sidelink control information. The apparatus may comprise a transmitting user equipment, or a control device configured to control the functioning thereof, possibly when installed therein.

[0013] 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 that, when executed by at least one processor, cause an apparatus to at least perform the first or the second method. According to an eighth aspect of the present invention, there is provided a computer program comprising instructions which, when the program is executed by an apparatus, cause the apparatus to carry out the first or the second method.

BRIEF DESCRIPTION OF THE DRAWINGS [0014] FIGURE 1 illustrates an example of a communication network in accordance with at least some example embodiments; [0015] FIGURE 2 illustrates a signalling graph in accordance with at least some example embodiments;

[0016] FIGURE 3 illustrates an example apparatus capable of supporting at least some example embodiments;

[0017] FIGURE 4 illustrates a flow graph of a first method in accordance with at least some example embodiments; and [0018] FIGURE 5 illustrates a flow graph of a second method in accordance with at least some example embodiments.

EXAMPLE EMBODIMENTS [0019] FIGURE 1 illustrates an example of a communication network in accordance with at least some example embodiments. According to the example scenario of FIGURE 1, there may be a cellular communication network which comprises three User Equipments, UEs, configured to communicate using Sidelink, SL, communications. The cellular communication network of FIGURE 1 comprises SL Transmit, Tx, UE 110, SL Receive, Rx, UE 112, third SL UE 114, Base Station, BS, 120 and core network 130. SL Tx UE 110 may be referred to as a transmitting UE, which transmits for example Sidelink Control Information, SCI, and/or SL data. SL Rx UE 112 may be referred to as a receiving UE, which receives the SCI, and/or SL data. The SCI transmitted by SL Tx UE 110 may be referred to as a first SCI and upon receiving the first SCI, SL Rx UE 112 may then decide to transmit a second SCI, wherein the second SCI is an adapted retransmission version of the first SCI, i.e., a retransmitted SCI.

[0020] SL Tx UE 110 and SL Rx UE 112 may be connected to each other via air interface 105. Similarly, SL Rx UE 112 and third SL UE 114 may be connected to each other via air interface 105 as well but there may be no direct connection between SL Tx UE 110 and 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 BS 120, or some other BS, via air interface 115, but such connection(s) are not mandatory in case of SL communications.

[0021] UEs 110, 112 and 114 may comprise, for example, a smartphone, a cellular phone, a Machine-to-Machine, M2M, node, Machine-Type Communications, MTC, node, an Internet of Things, IoT, node, a car telemetry unit, a laptop computer, a tablet computer or, indeed, any kind of suitable wireless terminal. BS 120 may be a network entity that configures some or all control information and allocates at least some resources for UEs 110, 112 and 114. In some example embodiments, BS 120 may be considered as a serving node for at least one of SL Tx UE 110 and SL Rx UE 112. [0022] Air interface 105 between UEs 110, 112 and 114 may be configured in accordance with a Radio Access Technology, RAT, which UEs 110, 112 and 114 are configured to support. Similarly, air interface 115 between for example SL Rx UE 112 and BS 120 may be configured in accordance with a RAT which SL Rx UE 112 and BS 120 are configured to support. Examples of cellular RATs include Long Term Evolution, LTE, New Radio, NR, which may also be known as fifth generation, 5G, radio access technology and MulteFire. A cellular RAT may be standardized by the 3^rd Generation Partnership Project, 3 GPP, for example. Hence, UEs 110, 112 and 114, and BS 120 as well, may be configured to operate according to the 3 GPP standards.

[0023] BS 120 may be connected, directly or via at least one intermediate node, with core network 130 via wired interface 125. Core network 130 may be, in turn, coupled via interface 135 with another network (not shown in FIGURE 1), via which connectivity to further networks may be obtained, for example via a worldwide interconnection network. BS 120 may be connected, directly or via at least one intermediate node, with core network 130 or with another core network.

[0024] Example embodiments are related to using SL based UE-to-UE communication between UEs 110, 112 and 114. A SL refers to a direct communication link between UEs 110, 112 and 114 in a cellular communication network and UEs can communicate via the SL without going through BS 120. 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.

[0025] SL communications may be performed over PC5 for example, as described for example in 3GPP TS 36.300 for LTE and 3GPP TS 38.300 for NR, based on a principle of a transmitter oriented one-to-many broadcast/groupcast communication and/or one-to-one unicast communication. There may be two modes of resource allocation, referred to as Mode 1 and Mode 2, specified for a SL transmission, e.g. for NR SL. Mode 1 may be based on using scheduled resources or grants from a serving BS, such as BS 120. Mode 2 may be based on autonomous allocation or selection of resources from a preconfigured transmit resource pool by a transmitting UE, such as SL Tx UE 110. Resource selection in Mode 2 may be based on, e.g. a simple random selection or sensing-based selection. At least some example embodiments may be used to specifically address issues related to resource selection in Mode 2 when sensing-based resource selection is used. However, it does not prevent from using some example embodiments in other resource allocation/selection schemes, e.g. random and/or partial sensing based resource selection. [0026] Several issues may impair the reliability of SL communication in case of Mode 2 resource allocation, such as persistent collisions, the hidden node issue, the exposed node issue and the half-duplex issue. The above issues may be at least partially caused by the fact that resource allocation in sensing-based Mode 2 may be based on resource reservation information received in a SCI, transmitted by SL Tx UE 110 for example. For instance, as illustrated in FIGURE 1, due to a large distance between SL Tx UE 110 and third SL UE 114, third SL UE 114 may be considered as a hidden node from the perspective of SL Tx UE 110, i.e., the transmitting UE of SL communication between SL Tx UE 110 and SL Rx UE 112. Third SL UE 114 may thus not be able to detect the SCI transmitted by SL Tx UE 110. If third SL UE 114 uses sensing-based Mode 2 resource allocation for its own SL transmission, it may select at least part of the same resources for transmission to SL Rx UE 112 and/or another SL Rx UE as SL Tx UE 110 uses for transmitting SL data to SL Rx UE 112. In such a case, the transmission of third SL UE 114 may interfere reception of SL data transmission of SL Tx UE 110 at SL Rx UE 112.

[0027] 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 the collision by themselves, due to a large distance between SL Tx UE 110 and third UE 114. Alternatively, or in addition, SL Tx UE 110 and third UE 114 may have persistent collisions on their selected resources due to half-duplexing capabilities of SL Tx UE 110 and third SL UE 114, i.e., if SL Tx UE 110 and third SL UE 114 would not be able to detect/receive while transmitting so that the persistent collisions cannot be identified with the sensing procedure performed by SL Tx UE 110 and third SL UE 114.

[0028] Example embodiments of the present invention therefore enhance SL communication by making it possible for SL Rx UE 112 to retransmit the SCI, transmitted by and originated from SL Tx UE 110, at least for SL Mode 2 resource allocation which may be impaired by issues, like a hidden node problem, persistent collisions and half-duplex constraint, etc. 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 UE 110 in the SCI and by SL Rx UE 112 in the adapted retransmission version of the SCI as well. Thus, third SL UE 114 may be able to detect/monitor the resources reserved by SL Tx UE 110. Third SL UE 114 may then avoid selecting overlapping resources, in time and/or frequency, for its own SL transmission. It is noted that monitoring of SCIs in proximity may be an essential feature for SL operation, at both SL Rx UE 112 for reception of SL communications and SL Tx UE 110 and/or third SL UE 114 for sensing to select Mode 2 resources for SL transmission. Transmission of the adapted retransmission version of the SCI reuses the existing SCI transmission mechanism with less standardization impact. Therefore it would not cause notably more processing and protocol overhead comparing with the alternative that SL Rx UE 112 detects and notifies resource processing conflicts between SL Tx UE 110 and third UE 114 using higher-layer signalling instead of the SCI.

[0029] Retransmission of the SCI may be further improved by considering when and how SL Rx UE 112 transmits the adapted retransmission version of the SCI. On one hand, the adapted retransmission version of the SCI, and resource reservation information therein, should be in the form of an SCI so that it can be taken into account in the sensing procedure of third SL UE 114 as a normal SCI, especially to support backward compatibility, e.g., if third UE 114 would be a SL UE implemented according to 3 GPP rel-16 specifications. On the other hand, the adapted retransmission version of the SCI may not be transmitted by SL Rx UE 112 so that the transmission would overlap at least in time domain with a reserved resource indicated by the original SCI transmission of SL Tx UE 110 due to half-duplex constraints of SL Tx UE 110 and/or SL Rx UE 112. Therefore, SL Rx UE 112 may determine suitable resources in time and frequency domain for transmitting the adapted retransmission version of the SCI of SL Tx UE 110.

[0030] Alternatively, or in addition, retransmission of the SCI may be further improved by considering how SL Tx UE 110 determines whether a received SCI is the adapted retransmission version of the SCI transmitted by itself or a normal SCI from other UEs in proximity, because SL Tx UE 110 should not take retransmitted SCIs of its own into account in its sensing procedure. For instance, 3 GPP rel-17 the Mode 2 resource allocation may be enhanced to support random or partial sensing-based resource (re-) selection for power saving. With a shared resource pool for random and/or partial sensing and/or full sensing, distinguishing the retransmitted SCI and a normal SCI becomes more important as a full sensing-based UE may be triggered to reselect or pre-empty its reserved resource(s) more aggressively than what is specified in Rel-16, e.g. if the reserved resource(s) collide with a resource reservation by a UE with random and/or partial sensing based resource selection mechanism. Thus, it becomes more beneficial to make it possible for SL Tx UE 110 to distinguish the retransmitted SCIs to avoid triggering unnecessary resource pre emption or re-evaluation/re-selection. [0031] Moreover, some example embodiments of the present invention make it possible for SL Rx UE 112 to first determine whether to transmit the adapted retransmission version of the SCI originated from SL Tx UE 110, or not. In some example embodiments, SL Rx UE 112 may also select resources, e.g., in frequency and/or time domain, for retransmitting the adapted retransmission version of the SCI originated from SL Tx UE 110. In some example embodiments, SL Rx UE 112 may adapt an 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 resource reservation in the adapted retransmission version of the SCI is to be excluded from 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 so that at least part of the reserved resources indicated in the adapted retransmission version of the SCI and the original SCI are the same. In general, original SCI may be referred to as regular SCI as well, because the original SCI is not an adapted retransmission version of another SCI.

[0032] SL Rx UE 112 may transmit the adapted retransmission version of the SCI and upon reception, SL Tx UE 110 may detect that resource reservation in the adapted retransmission version of the SCI is to be excluded from sensing results. For instance, SL Tx UE 110 may detect that the adapted retransmission version of the SCI is a retransmission of the SCI originated from it and based on that determine to exclude resource reservation indicated in the adapted retransmission version of the SCI from its sensing results, e.g., for sensing based mode 2 resource selection/re-selection.

[0033] FIGURE 2 illustrates a signalling graph in accordance with at least some example embodiments. With reference to FIGURE 1, on the vertical axes are disposed, from the left to the right, SL Tx UE 110 and SL Rx UE 112. Time advances from the top towards the bottom.

[0034] At step 210, SL Rx UE 112 may be configured to retransmit SCIs originated from SL Tx UE 110, at least under some conditions. 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 SCIs originated from SL Tx UE 110 during SL unicast connection establishment/modification using, e.g., SL Radio Resource Control, RRC, signalling between SL Tx UE 110 and SL Rx UE 112. In some example embodiments, SL Rx UE 112 may be configured to retransmit SCIs for all SL transmissions of a targeted SL unicast. Alternatively, SL Rx UE 112 may be configured to retransmit SCIs for a specific SL transmission corresponding to, e.g., SL traffic with specific priority, SL traffic on a specific logical channel, the PC5 radio condition such as RSRP and/or CBR, etc.

[0035] In case of SL groupcast or broadcast, the configuration may be provided by a serving network, such as BS 120, using broadcasted or dedicated RRC signalling for SL groupcast or broadcast involved SL UEs in network coverage or by pre-configuration for SL UEs out-of-network coverage. The network configuration or pre-configuration may enable all SL groupcast or broadcast UEs with Rel-17 capability of the feature to activate the feature or it may enable the feature for a specific SL groupcast or broadcast with certain e.g. QoS, priority requirement, and/or the PC5 radio condition, e.g., RSRP and/or CBR. Alternatively, or in addition, the configuration may be enabled by SL groupcast or broadcast Tx UE 110 to include one explicit indication in the original SCI transmitted from SL Tx UE. The explicit indication bit may be one of the reserved bits in Rel-16 SCI format.

[0036] Depending on different SCI re-transmission resource determination options, the configuration procedure and the corresponding configuration information may be different. For instance, in case of a SCI retransmission resource mapped from original SCI transmission resource 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 either SL RRC signalling or indicated using explicit indication in original SCI transmission. If the SCI retransmission resource is selected by SL Rx UE 112, SL Rx UE 112 may determine whether retransmission of the SCI originated from Tx UE 110 is needed or not based on, e.g., serving network configured triggers and the QoS of SL traffic as well as radio channel conditions such as Reference Signal Receive Power, RSRP, monitored resource confliction/collision, and/or channel busy ratio etc.

[0037] If SL Rx UE 112 is configured to determine whether to transmit the adapted retransmission version of the SCI based on detected interference or resource reservation confliction, the interference threshold may be configured to SL Rx UE 112 and different thresholds may be configured for different QoS, radio conditions (e.g. RSRP) between SL Tx UE 112 and SL Rx UE and/or channel busy ratio etc.

[0038] At step 220, SL Tx UE 110 may select resources for an SL transmission. For instance, using Mode 2 resource allocation, SL Tx UE 110 may select SL resources from mode 2 resource pool for the SL transmission, e.g., to SL Rx UE 112. Upon said Mode 2 resource selection, SL Tx UE 110 may generate an SCI comprising an indication about the selected resources to indicate reserved resources 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 an original SCI, i.e., first SCI, originated from SL Tx UE 110. At step 230, SL Tx UE 110 may transmit the 1^st stage SCI over a control channel, such as a Physical Sidelink Control Channel, PSCCH, and the 2^nd stage SCI and SL data/transport block over a shared channel, such as a Physical Sidelink Shared Channel, PSSCH.

[0039] Upon receiving the SCI, SL Rx UE 112 may determine, at step 240, whether to retransmit the SCI originated from SL Tx UE 110 or not. That is to say, SL Rx UE 112 may determine whether to transmit an adapted retransmission version of the received SCI, i.e., a second SCI, for example based on the configuration from SL Tx UE 110 at step 210 using e.g. SL RRC signalling and/or SL transmission at step 230 using e.g. explicit retransmission indication in the original SCI, i.e. first SCI. In some example embodiments, SL Rx UE 112 may be configured by either Tx UE or a serving network, such as BS 120, or as a pre-configuration, to transmit the adapted retransmission version of the received SCI. For instance, SL Rx UE 112 may be configured to transmit adapted retransmission versions of all SCIs originated from SL Tx UE 110. Thus, SL Rx UE 112 may determine that the adapted retransmission version of the SCI is to be transmitted based on a configuration of SL Rx UE 112, like an identity of SL Tx UE 110 or a destination identity (e.g. SL groupcast destination L2 identity) of SL transmission from SL Tx UE 110. Alternatively, SL Rx UE 112 may be configured to retransmit SCIs from SL Tx UE 110 that fulfil some configured conditions.

[0040] Alternatively, SL Rx UE 112 may determine whether to retransmit the SCI originated from SL Tx UE 110 based on interference or confliction on the reserved resources indicated in the original SCI. For instance, SL Rx UE 112 may determine whether interference on at least part of the reserved resources is higher than a configured threshold or not. If SL Rx UE 112 detects high interference or confliction on the reserved resources, SL Rx UE 112 may determine that the adapted retransmission version of the SCI needs to be transmitted and the adapted retransmission version of the SCI may be adapted to indicate interference/confliction to SL Tx UE 110 and/or third SL UE 114.

[0041] At step 250, SL Rx UE 112 may select at least one resource for transmitting the adapted retransmission version of the original SCI based on, e.g., a mapping rule, an inter-user equipment resource allocation procedure or using a Mode 2 allocation scheme. SL Rx UE 112 may select the at least one resource upon detecting/receiving the original SCI from SL Tx UE 110, e.g., if retransmission of the original SCI is configured. The selected resource may be indicated by SL Tx UE 110, by another UE or a network entity controlling SL communication, such as BS 120. SL Tx UE 110 may indicate the resource to be selected in the original SCI or by other signalling, such as MAC or RRC signalling.

[0042] For instance, the at least one resource used by SL Rx UE 112 to transmit the adapted retransmission version of the original SCI, originated from SL Tx UE 110, may be mapped from the resource used for transmission of the original SCI. The mapping rule may pre-configured for SL Rx UE 112, either by a standard specification, the serving network or SL Tx UE 110. Alternatively, the mapping rule may be configured during the 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 at least one reserved resource indicated in the adapted retransmission version of the SCI is to be excluded from sensing results of SL Tx UE 110. As one example, in this case, SL Tx UE 110 does not consider the at least one reserved resource indicated in the adapted retransmission version of the SCI as being reserved by SL Rx UE 112 in the sensing procedure of SL Tx UE 110.

[0043] The mapping rule may be specified in time domain, e.g., with a certain time offset from the transmission of the original SCI, or specified in both time and frequency domain, e.g., with a certain time offset and subchannel offset from the transmission of the original SCI. Alternatively, or in addition, the at least one resource may comprise special symbol(s) which may be configured, e.g., with/by a resource pool configuration or the resource mapping rule, for transmission of the adapted retransmission version of the SCI. In some example embodiments, the special symbol(s) may be different from symbols used for carrying any original SCIs. In this way, the adapted retransmission version of the SCI can be identified by the special symbol(s).

[0044] The mapping rule may be considered by SL Tx UE 110 as well when it selects resources, such as Mode 2 resources. For instance, SL Tx UE 110 may select the Mode 2 resources where the mapped resource for transmitting the adapted retransmission version of the SCI is also available according to a sensing result and does not collide or ovelap with other SL transmissions, thereby making the process more efficient. [0045] Alternatively, the 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, wherein SL Tx UE 110 may indicate a resource for SL Rx UE 112 for transmitting the adapted retransmission version of the SCI. Thus, the resource used by SL Rx UE 112 for retransmitting the SCI may be actually assigned by the SL Tx UE 110. In such a case, transmission of the adapted retransmission version may be enabled for each SCI individually by SL Tx UE 110 by providing resources for transmission of the adapted retransmission version of the SCI. In one example, transmission at step 230 and/or at some other step may contain/indicate such a resource allocated by SL Tx UE 110 for transmission of the adapted retransmission version of the SCI by SL Rx UE 112.

[0046] If the at least one resource for transmission of the adapted retransmission version of the SCI is allocated by SL Tx UE 110 using inter-UE resource allocation, a 1st stage SCI carried in a corresponding PSCCH resource may carry resource reservation information while a corresponding PSSCH resource may be used to transmit a 2nd stage SCI and data information towards at least SL Tx UE 110. In such a case, due to the inter-UE resource allocation, transmission of the 1st stage SCI towards SL Tx UE 110 may be skipped since SL Tx UE 110 may have indicated the configuration to SL Rx UE 112 during the inter- UE resource allocation procedure.

[0047] In some example embodiments, SL Rx UE 112 may select the at least one resource for transmission of the adapted retransmission version of the original SCI not only based on sensing results but also based on the reserved resources that are indicated in the original SCI. For instance, SL Rx UE 112 may select the at least one resources for transmission of the adapted retransmission version of the original SCI for transmission with a certain time gap/offset (e.g. corresponding to at least one of the SCI processing time and the resource pre-emption/re-evaluation/reselection processing time) before a time instance of a next reserved resource(s) indicated in the original SCI. If SL Rx UE 112 has received a SL transmission correctly in a first transmission from SL Tx UE 110 and the reserved resources indicated in the original SCI are used for SL HARQ retransmission only, SL Rx UE 112 may use the next reserved resources indicated in the original SCI to transmit the adapted retransmission version of the original SCI indicating at least the reserved resources for SL HARQ retransmission as SL Tx UE 112 may not use the next reserved resources for SL HARQ retransmission after receiving HARQ ACK feedback from SL Rx UE. [0048] In some example embodiments, the at least one resource used by SL Rx UE 112 to transmit the adapted retransmission version may be selected by SL Rx UE 112 using normal Mode 2 resource allocation scheme, like full sensing-based, partial sensing-based and/or random resource selection scheme(s). In some embodiments, Mode 2 resource allocation scheme may be applied with additional considerations, e.g., SL Rx UE 112 may take the reserved resources of at least SL Tx UE 110, indicated in the received SCI, at least in time domain into account to determine/select the at least one resource for transmission of the adapted retransmission version of the original SCI, to ensure that transmission of the adapted retransmission version takes place before the time instance/slot of next reserved resources by SL Tx UE 110.

[0049] In some example embodiments, the at least one resource for transmission of the adapted retransmission version of the original SCI may only include PSCCH resources or also include PSSCH resources for transmission of a 2nd stage of SCI or even SL data. Inclusion of PSCCH resources only may require a new SL resource pool structure to allow decoupling of a PSCCH transmission from a PSSCH transmission. If PSSCH resources for transmission of the 2nd stage of the SCI or even SL data are included, an existing SL resource pool structure of PSCCH and associated PSSCH resources coupled in the same TTI as specified in 3GPP Rel-16 may be reused. In such a case, a PSSCH resource associated with a PSCCH resource for transmission of the adapted retransmission version of the original SCI may be used to transmit the 2nd stage SCI and/or SL data originated from SL Rx UE 112 for its own SL transmission.

[0050] At step 260, SL Rx UE 112 may adapt the original SCI to generate the adapted retransmission version of the SCI such that the adapted retransmission version of the SCI indicates to SL Tx UE 110 that at least one reserved resource indicated in the adapted retransmission version of the SCI is to be excluded from sensing results of SL Tx UE 110. For instance, the at least one resource on which the adapted retransmission version of the SCI is transmitted and/or the at least one resource indicated by the adapted retransmission version of the SCI may indicate to SL Tx UE 110 that resource reservation in the adapted retransmission version of the SCI is to be excluded from said sensing results. Alternatively, or in addition, the adapted retransmission version of the SCI may be adapted to comprise an explicit indication which indicates to SL Tx UE 110 that resource reservation in the adapted retransmission version of the SCI is to be excluded from said sensing results. In some example embodiments, a priority field of the adapted retransmission version of the SCI may be adapted to indicate to SL Tx UE 110 that resource reservation in the adapted retransmission version of the SCI is to be excluded from said sensing results. That is to say, the original SCI, i.e., the first SCI, may be adapted to generate the adapted retransmission version of the SCI, i.e., the second SCI, to impact a sensing result of SL Tx UE 110 differently compared to original (not retransmitted) SCI received, or to be received, by SL Tx 110 from other UEs.

[0051] In some example embodiments, combinations of the indications may be exploited as well. For example, reliability may be improved without additional overhead by using the at least one resource and the priority field. Reliability may be further enhanced by adding the explicit indication on top of the at least one resource and the priority field.

[0052] Moreover, in some example embodiments, SL Rx UE 112 may adapt an information field in the adapted retransmission version of the original SCI according to the original SCI so that at least part of the reserved resources indicated in the adapted retransmission version of the SCI and the original SCI are the same. Said adaptation may include at least updating a time resource assignment field to reflect the updated time interval between the adapted retransmission version of the SCI and next reserved resources.

[0053] Alternatively, or in addition, said adaptation may comprise consolidation of multiple SCIs originated from same or different SL Tx UEs into one adapted retransmission version of said multiple SCIs and the reserved resources. If SL Rx UE 112 has several SL unicast connections with multiple SL Tx UEs 110 and receives multiple SCIs to be retransmitted, the adapted retransmission version of the SCI may be adapted to have one consolidated SCI retransmission. The consolidation of multiple SCIs may be possible, e.g., if each of SL Tx UEs 110 only reserved one additional resource in a frequency resource assignment field while the higher layer parameter si -MaxNumPerRe serve is configured to 3, meaning that two additional resource reservations may be provided in a SCI. In such a case, SL Rx UE 110 may consolidate the reserved resources of at least two original SCIs into one adapted retransmission version of the SCIs. The consolidation of multiple original SCIs may also take into account a priority field and/or the reserved resources (e.g., the subchannels) of the multiple original SCIs. For instance, only if the priority fields of multiple original SCIs are the same, the consolidation may be performed. Alternatively, if the consecutive subchannels are reserved in the reserved resources of multiple original SCIs, the consolidation may be performed. [0054] In some example embodiments, said adaptation may comprise setting value(s) for one or more field(s) of the adapted retransmission version of the SCI to indicate explicitly that the adapted retransmission version is a retransmitted SCI which may be coupled with or decoupled from the resources used for retransmitting the original SCI.

[0055] In some example embodiments, said adaptation may comprise updating a priority indication in a priority field of a SCI format and/or setting a corresponding transmission power for transmitting the adapted retransmission version of the SCI. The updated priority indication may be used, e.g., to either trigger a resource pre-emption or reselection from SL Tx UE 110 or to avoid triggering unnecessary reselection/pre-emption of reserved resources from SL Tx UE 110.

[0056] At step 270, SL Rx UE 112 may transmit the adapted retransmission version of the SCI. Upon receiving any SCI, SL Tx UE 110 may need to determine whether the received SCI is from another SL UE in proximity or the received SCI is a retransmitted version of its own SCI.

[0057] At step 280, SL Tx UE 110 may detect that the SCI received at step 270 is the adapted retransmission version of the SCI, e.g., to determine whether to exclude a received SCI from its sensing procedure or not. SL Tx UE 110 may treat the two types of SCIs (normal SCI and retransmitted SCI) in different way for its sensing procedure. The normal SCIs from other SL UEs may be taken into account as an input to the sensing procedure for SL resource selection while the retransmitted SCI may be excluded from the sensing procedure. However, if the resource used for the retransmitted SCI has also associated PSSCH resources and the part of PSSCH resources are actually used by SL Rx UE 112 to transmit its own SL data, then the part of the PSSCH resources associated with the retransmitted SCI may not be excluded from sensing procedure. In some example embodiments, with implicit indication of retransmitted SCI using the changed priority indication, SL Tx UE 110 may be informed about whether to exclude the retransmitted SCI from its sensing procedure implicitly with increased or decreased priority indication in the adapted retransmission version of the SCI.

[0058] Said detection may be based on the at least one resource on which the adapted retransmission version of the SCI is received if the at least one resource is mapped/derived from the resources used for transmission of the original SCI or allocated by SL Tx UE 110 by inter-UE coordination/resource allocation. Alternatively, or in addition, said detection may be based on an explicit indication, e.g., if the adapted retransmission version of the SCI comprises one or multiple bits of reserved bits in the SCI format. For instance, reserved bits in the 2nd-stage SCI format field or the reserved bits at the end of the 1^st stage SCI may be used. In some example embodiments, said detection may be based on a priority indication if the priority indication in the adapted retransmission version of the SCI has been changed compared to a priority indication of the original SCI. That is to say, SL Tx UE 110 may implicitly detect that the SCI received at step 270 is the adapted retransmission version of the SCI as a priority information field in the adapted retransmission version of the SCI indicates the different priority compared to a priority information in the original SCI so that the sensing procedure performed by SL Tx UE 110 is impacted. To improve reliability, said detection may be based on a combination of at least two of the indications as well, if present.

[0059] For a change of the priority indication in in the adapted retransmission version of the SCI, SL Rx UE 112 may determine to either reduce or increase the priority indication compared to the priority indication of the original SCI. For example, if SL Rx UE 112 detects the conflicted resources reserved from another SL UE in proximity for lower priority SL traffic, SL Rx UE 112 may determine to reduce the priority indication in the adapted retransmission version of the SCI compared to the priority indication of the original SCI. In such a way, SL Tx UE 112 may consider the conflicted resource reservation received from SCIs of other UEs for SL traffic with lower priority, which then may not trigger SL Tx UE 110 to pre-empty or reselect its reserved resources. The adapted retransmission version of the SCI even with reduced priority indication may prevent other SL UEs in proximity to select the same resources. However, the reduced priority in the adapted retransmission version of the SCI may also impact sensing of other SL UEs in proximity to have missed pre-emption if there is resource confliction between SL Tx UE 110 in question and other SL Tx UEs in proximity and the priority of other SL Tx UE’s traffic is lower than the priority of the SCI from SL Tx UE 110 in question but higher or equal to the reduced priority indicated by the adapted retransmission version of the SCI.

[0060] In another example, if SL Rx UE 112 detects the conflicted resource reservation from another SL UE in proximity for higher priority SL traffic, SL Rx UE 112 may determine to increase the priority in the retransmitted SCI. In this way, SL Tx UE 110 may consider the conflicted resource reservation received from SCI of other UEs is for SL traffic with higher priority, thus is triggered to pre-empty or reselect the resources to avoid resource reservation confliction with other SL UE in proximity of SL Rx UE 112. [0061] As priority based triggering of resource pre-emption or reselection may also be related to the RSRP of the received SCI, the transmission power of the retransmitted SCI may be controlled such that its RSRP level measured at SL Tx UE 110 may or may not trigger the resource pre-emption or re-evaulati on/re-selection of SL Tx UE 110 depending on whether interference/resource confliction is coming from SL UEs with higher or lower priority.

[0062] In general, example embodiments of the present invention may be applied for SL unicast and also SL groupcast or broadcast using the configuration at step 210. As there may be multiple SL Rx UEs in SL groupcast or broadcast, efficiency of retransmission of SCIs may be controlled by, e.g., when one SL groupcast/broadcast Rx UE detects the retransmitted SCI, it will not re-transmit the SCI anymore.

[0063] In some example embodiments, existing SL resource pool structures and SCI formats may be reused and the legacy SCI transmission mechanism without any change of SCI format may be used. This enables the legacy SL UEs to detect the reserved resources in the adapted retransmission version of the SCI as the normal SCI to enable backward compatibility and enhance the sensing-based Mode 2 resource allocation for either new or legacy UEs.

[0064] Alternatively, a new SL resource pool structure may need to be supported for, e.g., decoupled PSCCH and PSSCH transmissions, and/or pure PSCCH transmission without an associated PSSCH transmission, the enhancement for sensing based mode 2 resource allocation may not be applied for legacy UEs. In some example embodiments, it may be ensured that there is no impact on legacy UEs to degrade its resource allocation performance.

[0065] The retransmitted SCI may be applied only for 1st stage SCI over PSCCH or may be applied for both 1st and 2nd stage SCI. Considering backward compatibility, the legacy UE may receive the retransmitted 1st stage SCI only or receive both.

[0066] FIGURE 3 illustrates an example apparatus capable of supporting at least some example embodiments. Illustrated is device 300, which may comprise, for example, SL Tx UE 110 or SL Rx UE 112, or a device controlling functioning thereof, possibly when installed therein. Comprised in device 300 is processor 310, which may comprise, for example, a single- or multi-core processor wherein a single-core processor comprises one processing core and a multi-core processor comprises more than one processing core. Processor 310 may comprise, in general, a control device. Processor 310 may comprise more than one processor. Processor 310 may be a control device. Processor 310 may comprise at least one Application-Specific Integrated Circuit, ASIC. Processor 310 may comprise at least one Field-Programmable Gate Array, FPGA. Processor 310 may comprise at least one Qualcomm Snapdragon and/or Intel Atom processor. Processor 310 may comprise, for example, a Cortex-A8 processing core manufactured by ARM Holdings or a Steamroller processing core produced by Advanced Micro Devices Corporation. Processor 310 may be means for performing method steps in device 300, such as determining, causing transmitting and causing receiving. Processor 310 may be configured, at least in part by computer instructions, to perform actions.

[0067] A processor may comprise circuitry, or be constituted as circuitry or circuitries, the circuitry or circuitries being configured to perform phases of methods in accordance with example embodiments described herein. As used in this application, the term “circuitry” may refer to one or more or all of the following: (a) hardware-only circuit implementations, such as implementations in only analog and/or digital circuitry, and (b) combinations of hardware circuits and software, such as, as applicable: (i) a combination of analog and/or digital hardware circuit(s) with software/firmware and (ii) any portions of hardware processor(s) with software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a network function, to perform various functions) and (c) hardware circuit(s) and or processor(s), such as a microprocessor s) or a portion of a microprocessor(s), that requires software (e.g., firmware) for operation, but the software may not be present when it is not needed for operation.

[0068] 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 application, the term circuitry also covers an implementation of merely a hardware circuit or processor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and/or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in server, a cellular network device, or other computing or network device. [0069] Device 300 may comprise memory 320. Memory 320 may comprise random- access memory and/or permanent memory. Memory 320 may comprise at least one RAM chip. Memory 320 may comprise solid-state, magnetic, optical and/or holographic memory, for example. Memory 320 may be at least in part accessible to processor 310. Memory 320 may be at least in part comprised in processor 310. Memory 320 may be means for storing information. Memory 320 may comprise 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 overall is configured to run under the direction of processor 310 using computer instructions from memory 320, processor 310 and/or its at least one processing core may be considered to be configured to perform said certain actions. Memory 320 may be at least in part comprised in processor 310. Memory 320 may be at least in part external to device 300 but accessible to device 300.

[0070] Device 300 may comprise a transmitter 330. Device 300 may comprise a receiver 340. Transmitter 330 and receiver 340 may be configured to transmit and receive, respectively, information in accordance with at least one cellular or non-cellular standard. Transmitter 330 may comprise more than one transmitter. Receiver 340 may comprise more than one receiver. Transmitter 330 and/or receiver 340 may be configured to operate in accordance with Global System for Mobile communication, GSM, Wideband Code Division Multiple Access, WCDMA, Long Term Evolution, LTE, and/or 5G/NR standards, for example.

[0071] Device 300 may comprise a Near-Field Communication, NFC, transceiver 350. NFC transceiver 350 may support at least one NFC technology, such as Bluetooth, Wibree or similar technologies.

[0072] Device 300 may comprise User Interface, UI, 360. UI 360 may comprise at least one of a display, a keyboard, a touchscreen, a vibrator arranged to signal to a user by causing device 300 to vibrate, a speaker and a microphone. A user may be able to operate device 300 via UI 360, for example to accept incoming telephone calls, to originate telephone calls or video calls, to browse the Internet, to manage digital files stored in memory 320 or on a cloud accessible via transmitter 330 and receiver 340, or via NFC transceiver 350, and/or to play games.

[0073] Device 300 may comprise or be arranged to accept a user identity module 370. User identity module 370 may comprise, for example, a Subscriber Identity Module, SIM, card installable in device 300. A user identity module 370 may comprise information identifying a subscription of a user of device 300. A user identity module 370 may comprise cryptographic information usable to verify the identity of a user of device 300 and/or to facilitate encryption of communicated information and billing of the user of device 300 for communication effected via device 300.

[0074] Processor 310 may be furnished with a transmitter arranged to output information from processor 310, via electrical leads internal to device 300, to other devices comprised in device 300. Such a transmitter may comprise a serial bus transmitter arranged to, for example, output information via at least one electrical lead to memory 320 for storage therein. Alternatively to a serial bus, the transmitter may comprise a parallel bus transmitter. Likewise processor 310 may comprise a receiver arranged to receive information in processor 310, via electrical leads internal to device 300, from other devices comprised in device 300. Such a receiver may comprise a serial bus receiver arranged to, for example, receive information via at least one electrical lead from receiver 340 for processing in processor 310. Alternatively to a serial bus, the receiver may comprise a parallel bus receiver.

[0075] Device 300 may comprise further devices not illustrated in FIGURE 3. For example, where device 300 comprises a smartphone, it may comprise at least one digital camera. Some devices 300 may comprise a back-facing camera and a front-facing camera, wherein the back-facing camera may be intended for digital photography and the front- facing camera for video telephony. Device 300 may comprise a fingerprint sensor arranged to authenticate, at least in part, a user of device 300. In some embodiments, device 300 lacks at least one device described above. For example, some devices 300 may lack a NFC transceiver 350 and/or user identity module 370.

[0076] Processor 310, memory 320, transmitter 330, receiver 340, NFC transceiver 350, UI 360 and/or user identity module 370 may be interconnected by electrical leads internal to device 300 in a multitude of different ways. For example, each of the aforementioned devices may be separately connected to a master bus internal to device 300, to allow for the devices to exchange information. However, as the skilled person will appreciate, this is only one example and depending on the embodiment various ways of interconnecting at least two of the aforementioned devices may be selected without departing from the scope of the embodiments. [0077] FIGURE 4 is a flow graph of a first method in accordance with at least some example embodiments. The phases of the illustrated first method may be performed by SL Rx UE 112 or a device controlling functioning thereof, possibly when installed therein.

[0078] The first method may comprise, at step 410, receiving, by a receiving user equipment (SL Rx UE 112), first sidelink control information from a transmitting user equipment (SL Tx UE 110), wherein said first sidelink control information is originated from the transmitting user equipment (SL Tx UE 110). The first method may also comprise, at step 420, determining, by the receiving user equipment (SL Rx UE 112), whether to transmit second sidelink control information, wherein said second sidelink control information is an adapted retransmission version of said first sidelink control information. Moreover, the first method may comprise, at step 430, selecting upon positive determination, by the receiving user equipment (SL Rx UE 112), a resource for transmitting said second sidelink control information. Finally, the first method may comprise, at step 440, transmitting, by the receiving user equipment (SL Rx UE 112), said second sidelink control information on the selected resource.

[0079] FIGURE 5 is a flow graph of a second method in accordance with at least some example embodiments. The phases of the illustrated second method may be performed by SL Tx UE 110 or a device controlling functioning thereof, possibly when installed therein.

The second method may comprise, at step 510, transmitting, by a transmitting user equipment (SL Tx UE 110), first sidelink control information to a receiving user equipment (SL Rx UE 112). The second method may also comprise, at step 520, receiving from the receiving user equipment (SL Rx UE 112), responsive to said transmission, second sidelink control information. Finally, the second method may comprise, at step 530, detecting that said second sidelink control information is an adapted retransmission version of said first sidelink control information.

[0080] It is to be understood that the example embodiments disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular example embodiments only and is not intended to be limiting. [0081] Reference throughout this specification to one example embodiment or an 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, appearances of the phrases “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 reference is made to a numerical value using a term such as, for example, about or substantially, the exact numerical value is also disclosed.

[0082] As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should 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. In addition, various example embodiments and examples may be referred to herein along with alternatives for the various components thereof. It is understood that such example embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations.

[0083] In an example embodiment, an apparatus, comprising for example SL Tx UE 110 or SL Rx UE 112, may further comprise means for carrying out the example embodiments described above and any combination thereof. The apparatus may be an apparatus of a cellular communication network, such as a 5G network, and comprise means for operating in the cellular communication network.

[0084] In an example embodiment, a computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out a method in accordance with the example embodiments described above and any combination thereof. In an example embodiment, a computer program product, embodied on a non- transitory computer readable medium, may be configured to control a processor to perform a process comprising the example embodiments described above and any combination thereof.

[0085] 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 at least to perform the example embodiments described above and any combination thereof. The apparatus may be an apparatus of a cellular communication network, such as a 5G network, and configured to operate in the cellular communication network.

[0086] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more example embodiments. In the preceding description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., 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, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.

[0087] While the forgoing examples are illustrative of the principles of the example embodiments in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation may be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.

[0088] The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of “a” or “an”, that is, a singular form, throughout this document does not exclude a plurality.

[0089] The expression “at least one of A or B” in this document means A, or B, or both A and B.

INDUSTRIAL APPLICABILITY

[0090] 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 as well. ACRONYMS LIST

3GPP 3rd Generation Partnership Project

BS Base Station

CBR Channel Busy Ratio

GSM Global System for Mobile communication

IoT Internet of Things

LTE Long-Term Evolution

M2M Machine-to-Machine

NFC Near-Field Communication

NR New Radio

PSCCH Physical Sidelink Control Channel

PSSCH Physical Sidelink Shared Channel

RAT Radio Access Technology

RRC Radio Resource Control

RSRP Reference Signal Receive Power

QoS Quality of Service

SCI Sidelink Control Information

SL Sidelink

UE User Equipment

UI User Interface

WCDMA Wideband Code Division Multiple Access WiMAX Worldwide Interoperability for Microwave Access WLAN Wireless Local Area Network

REFERENCE SIGNS LIST

Claims

CLAIMS:

1. An apparatus, comprising:

- means for receiving, by a receiving user equipment, first sidelink control information from a transmitting user equipment, wherein said first sidelink control information is originated from the transmitting user equipment;

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

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

- means for transmitting, by the receiving user equipment, said second sidelink control information on the selected resource.

2. The apparatus according to claim 1, further comprising:

- means for determining whether to transmit said second sidelink 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 sidelink communication; an indication in said first sidelink control information; interference on at least one reserved resource indicated in said first sidelink control information; or conflict on the at least one reserved resource indicated in said first sidelink control information.

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

- a mapping rule, to be used to derive the resource for transmitting said second sidelink control information from a resource on which said first sidelink control information is received,

- a resource indicated by the transmitting user equipment, - a resource indicated by another user equipment or a network entity controlling sidelink communication, or

- a user equipment autonomous resource allocation scheme.

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

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

- means for adapting said second sidelink control information to generate the adapted retransmission version of said first sidelink control information such that said second sidelink control information indicates to the transmitting user equipment that the at least one reserved resource indicated in said second sidelink control information is to impact a sensing result of the transmitting user equipment differently from original sidelink control information the transmitting user equipment received.

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

- means for adapting an information field of said second sidelink control information by performing at least one of: adapting the information field related to a time resource assignment according to a time interval between said second sidelink control information and at least one reserved resource of said first sidelink control information; consolidating multiple first sidelink control information; or adapting a priority field to indicate that said second sidelink control information is a retransmission of said first sidelink control information.

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

8. An apparatus, comprising:

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

- means for receiving from the receiving user equipment, responsive to said transmission, second sidelink control information; and

- means for detecting that said second sidelink control information is an adapted retransmission version of said first sidelink control information.

9. The apparatus according to claim 8, further comprising:

- means for detecting that said second sidelink control information indicates at least one reserved resource which is to impact a sensing result of the transmitting user equipment differently from original sidelink control information the transmitting user equipment received.

10. The apparatus according to claim 8 or claim 9, wherein it is detected that said second sidelink control information is an adapted retransmission version of said first sidelink control information based on at least one of: a resource on which said second sidelink control information is received, an explicit indication, or a priority information field in said second sidelink control information.

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

12. A method comprising:

- receiving, by a receiving user equipment, first sidelink control information from a transmitting user equipment, wherein said first sidelink control information is originated from the transmitting user equipment;

- determining, by the receiving user equipment, whether to transmit second sidelink control information, wherein said second sidelink control information is an adapted retransmission version of said first sidelink control information;

- selecting upon positive determination, by the receiving user equipment, a resource for transmitting said second sidelink control information; and transmitting, by the receiving user equipment, said second sidelink control information on the selected resource.

13. A method comprising:

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

- receiving from the receiving user equipment, responsive to said transmission, second sidelink control information; and

- detecting that said second sidelink control information is an adapted retransmission version of said first sidelink control information.

14. A computer program configured to perform a method according to claim 12 or claim 13.