Carrier aggregation in sidelink communications

Abstract

The method includes transmitting one or more packets on one or more carriers of a plurality of carriers to be used for sidelink carrier aggregation; determining at least one of receiving an acknowledgment (ACK) from each of one or more target receiving user equipments (UEs) or not receiving a negative acknowledgment (NACK) on at least one of the one or more carriers of the plurality of carriers; and canceling one or more remaining transmissions or retransmissions for the one or more packets scheduled on the one or more carriers of the plurality of carriers in response to determining at least one of receiving an ACK from the at least one of the one or more target receiving UEs or not receiving a NACK on at least one of the one or more carriers of the plurality of carriers.

Description

[Technical Field]

[0001] Cross-reference to related patent applications This application claims priority to U.S. Provisional Application No. 63 / 377,572, filed September 29, 2022, entitled "CARRIER AGGREGATION IN SIDELINK COMMUNICATION," which is incorporated by reference herein in its entirety.

[0002] Apparatus and methods consistent with the present disclosure relate generally to communications, and more particularly to methods, systems, and devices for carrier aggregation in sidelink communications. [Background technology]

[0003] Carrier aggregation can enable increased throughput and / or improved reliability in sidelink communications. To improve reliability, a transmitting user equipment (UE) in sidelink communications can transmit the same transport block on each of multiple aggregated carriers. The transmitting UE may need to transmit the transport block in a unicast or groupcast manner, typically accompanied by an acknowledgement (ACK) or negative acknowledgement (NACK) signal from the receiving UEs. Therefore, for unicast or groupcast, the transmitting UE continues to retransmit the transport block even if communication on at least one of the sidelink carriers is successful, until the transmitting UE confirms that it has received ACKs or no NACKs from all target receiving UEs on all sidelink carriers on which the same transport block was transmitted. This minimizes spectral efficiency in sidelink carrier aggregation. Improved systems and methods for sidelink carrier aggregation for unicast or groupcast are desired.

[0004] The resource selection procedure for 3GPP (registered trademark) Release 16 / 17 5G New Radio (NR) vehicle-to-everything (V2X) PC5 Mode 2 is specified in 3GPP (registered trademark) Technical Specifications (TS) 38.213, TS 38.214, and TS 38.321. For resource selection, a UE performs channel sensing within a sensing window and collects resource reservation information of other UEs based on sidelink control information (SCI) decoding to identify candidate resources within a selection window T (T = [T1, T2]). First, the UE excludes some time slots from the selection window due to unmonitored resources within the sensing window that the UE cannot sense through its own transmissions (i.e., half-duplex constrained). The UE then further excludes resources reserved by other UEs from the selection window if the corresponding sidelink-reference signal received power (SL-RSRP) exceeds a (pre-)configured SL-RSRP exclusion threshold. After resource exclusion, the number of candidate resources is at least X% of the total number of resources in the selection window. Otherwise, the UE increases the SL-RSRP exclusion threshold by 3 dB until it obtains at least X% of resources, where X is (pre-)configured from {20, 35, 50}%. Finally, the UE randomly selects a resource among the candidate resources in the selection window. The selected frequency resource is used for subsequent transmissions (i.e., semi-persistent). Transmissions can be used multiple times at fixed time intervals for semi-persistent scheduling (SPS) or only once (i.e., one-shot transmission (OST)). The UE can also retransmit packets multiple times with or without feedback from the receiving UE to improve reliability (i.e., hybrid automatic repeat request (HARQ) retransmissions).

[0005] To obtain information for the UE to perform detection and receive packets from other UEs, the UE first decodes the SCI. In Release 16, as defined in 3GPP TS38.212, there are two types of SCI: the first-stage SCI (SCI format 1-A) and the second-stage SCI (SCI format 2-A or 2-B). The first-stage SCI carries resource reservation information for future transmissions, as well as information about resource allocation and modulation and coding scheme (MCS) for the physical sidelink shared channel (PSSCH), demodulation reference signal (DMRS) pattern, and second-stage SCI format. The second-stage SCI carries control information for HARQ procedures, source / destination IDs, distance-based groupcast (UE zone identification (ID) and communication range requirements), and so on. Based on the resource reservation included in the first stage SCI, each UE avoids using time / frequency resources reserved by other UEs when performing resource (re)selection.

[0006] Release 17 5G NR-V2X PC5 Mode 2 introduces inter-UE coordination (IUC), in which a first UE (UE-A) sends coordination information about resources to a second UE (UE-B), which uses this information for its resource (re)selection. Two schemes for inter-UE coordination are supported:

[0007] IUC scheme 1: UE-A can provide UE-B with an indication of resources that should preferably be included or excluded in UE-B's (re)selected resources. When including given resources, UE-B can rely on these resources alone, at least if it does not support sensing / resource exclusion, or it can combine these resources with resources identified by its own sensing procedure before making the final selection. The indication from UE-A to UE-B is sent in the medium access control (MAC) control element (CE) and / or in the second stage SCI.

[0008] IUC scheme 2: UE-A can provide an indication to UE-B that resources reserved for UE-B's transmission (which may or may not be to UE-A) are or should be subject to conflict with a transmission from another UE. UE-B then reselects new resources to replace them. The indication from UE-A to UE-B is sent on the physical sidelink feedback channel (PSFCH). Summary of the Invention

[0009] According to some embodiments of the present disclosure, a method for carrier aggregation in sidelink communications is provided, the method comprising: transmitting, by a first UE, one or more packets on one or more carriers of a plurality of carriers to be used for sidelink carrier aggregation; and receiving an ACK from each of one or more target receiving UEs or one or more of the plurality of carriers. and canceling, by the first UE, one or more remaining transmissions or retransmissions for one or more packets scheduled on one or more carriers of the plurality of carriers in response to determining at least one of receiving an ACK from at least one of the one or more target receiving UEs or not receiving a NACK on at least one of the one or more carriers of the plurality of carriers.

[0010] According to some embodiments of the present disclosure, a first UE is provided, the first UE including: a memory storing instructions; and a processor configured to execute the instructions stored in the memory to: transmit one or more packets on one or more carriers of a plurality of carriers to be used for sidelink carrier aggregation, determine at least one of receiving an ACK from each of one or more target receiving UEs or not receiving a NACK on at least one of the one or more carriers of the plurality of carriers, and cancel one or more remaining transmissions or retransmissions for one or more packets scheduled on one or more carriers of the plurality of carriers in response to determining at least one of receiving an ACK from at least one of the one or more target receiving UEs or not receiving a NACK on at least one of the one or more carriers of the plurality of carriers.

[0011] According to some embodiments of the present disclosure, a non-transitory computer-readable medium storing instructions executable by one or more processors of a first UE for performing a method is provided, the method including: transmitting, by the first UE, one or more packets on one or more carriers of a plurality of carriers to be used for sidelink carrier aggregation; determining, by the first UE, at least one of receiving an ACK from each of one or more target receiving UEs or not receiving a NACK on at least one of the one or more carriers of the plurality of carriers; and canceling, by the first UE, one or more remaining transmissions or retransmissions for the one or more packets scheduled on one or more carriers of the plurality of carriers in response to determining at least one of receiving an ACK from at least one of the one or more target receiving UEs or not receiving a NACK on at least one of the one or more carriers of the plurality of carriers. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a flowchart illustrating a method for resource selection during sidelink communication, consistent with some embodiments of the present disclosure. [Figure 2] 2 is a schematic diagram illustrating a resource candidate determination procedure according to the method of FIG. 1, consistent with some embodiments of the present disclosure. [Figure 3] 1 is a flowchart illustrating a method for resource selection during sidelink communication, consistent with some embodiments of the present disclosure. [Figure 4A] 4 is a schematic diagram illustrating a resource candidate determination procedure according to the method of FIG. 3, consistent with some embodiments of the present disclosure. [Figure 4B]4 is a table illustrating a correspondence between sub-carrier spacing (SCS) and subsets of resources according to the method of FIG. 3, consistent with some embodiments of the present disclosure. [Figure 5] FIG. 1 is a schematic diagram illustrating an example procedure for sidelink carrier aggregation, consistent with some embodiments of the present disclosure. [Figure 6] FIG. 10 is a schematic diagram illustrating another example procedure for sidelink carrier aggregation, consistent with some embodiments of the present disclosure. [Figure 7] 1 is a flowchart illustrating a method for sidelink carrier aggregation, consistent with some embodiments of the present disclosure. [Figure 8] 1 is a block diagram of a UE consistent with some embodiments of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0013] Reference will now be made in detail to exemplary embodiments, examples of which are illustrated in the accompanying drawings. The following description refers to the accompanying drawings, in which like numbers in different drawings represent the same or similar elements unless otherwise expressed. The implementations described in the following description of exemplary embodiments do not represent all implementations consistent with the present disclosure. Instead, the implementations are merely examples of systems, apparatus, and methods consistent with aspects related to the present disclosure, as recited in the appended claims.

[0014] FIG. 1 is a flowchart illustrating a method 100 (referred to as the "first method" in this disclosure) for resource selection during sidelink communication, and FIG. 2 is a schematic diagram illustrating a resource candidate determination procedure according to the first method, consistent with some embodiments of the present disclosure. Method 100 may be performed by a UE during sidelink communication. For example, method 100 may be performed by a vehicle during V2X communication. Method 100 may be performed in a mode (referred to as the "first mode" in this disclosure) employing discrete Fourier transform spread orthogonal frequency division multiplexing (DFT-s-OFDM) for the sidelink at the physical (PHY) layer. An example of the first mode is 3GPP Release 14 / 15 Long Term Evolution (LTE) V2X PC5 Mode 4.

[0015] As shown in FIG. 2, in the first mode, the time-frequency radio resources are divided into subframes in the time domain and subchannels in the frequency domain. In one embodiment, the first mode may support only 15 kHz subcarrier spacing. Each subframe may be 1 ms long and consist of 14 DFT-s-OFDM symbols. Each subchannel may consist of a number of consecutive physical resource blocks (PRBs), each occupying 180 kHz and consisting of 12 subcarriers with a 15 kHz SCS. The size of the subchannel (i.e., the number of PRBs per subchannel) may be configurable or pre-configurable. To handle high Doppler caused by high relative speeds in vehicular scenarios, the density of the DMRS used for frequency offset compensation and channel estimation may be set to 4 per subframe. Each UE can broadcast data (e.g., transport blocks (TBs)) in the PSSCH and SCI in the physical sidelink control channel (PSCCH). The PSCCH can occupy two consecutive PRBs. The number of PRBs for the PSSCH may be configurable or pre-configurable. The SCI format includes information for decoding the corresponding TB in the PSSCH, which can facilitate autonomous resource selection by the UE. As shown in Figure 2, the resource reservation interval can be set to one of allowed values ​​(e.g., 20, 50, 100, 200, 300...1000 ms). The PSCCH and the corresponding PSSCH can be transmitted in the same subframe in adjacent or non-adjacent PRBs in the frequency domain.

[0016] Referring to FIG. 1, a method 100 includes a step 102 of performing channel sensing (e.g., background sensing or other type of sensing, either full or partial sensing). For example, as shown in Figure 2, for resource selection, a UE may perform channel sensing within a sensing window (e.g., 1000 ms) to collect resource reservation information of another UE. The sensing window may be any duration depending on the implementation of the UE.

[0017] Referring back to FIG. 1 , the method 100 includes step 104 of collecting resource reservation information and corresponding SL-RSRPs of other UEs and measuring a sidelink received signal strength indicator (S-RSSI). For example, the UE may collect the resource reservation information and corresponding SL-RSRPs of other UEs. The UE may also measure the S-RSSI using the received sidelink signals. The UE may decode the received SCI included in the received sidelink signals to identify candidate resources within a selection window T (e.g., T = [T1, T2], where T1 ≦ 4 ms and 20 ≦ T2 ≦ 100 ms), as shown in FIG. 2 . The selection of the T1 and T2 values ​​depends on the UE implementation.

[0018] The method 100 includes step 106 of determining candidate resources by excluding occupied, reserved, and / or unmonitored resources and based on the average S-RSSI ranking. For example, as shown in FIG. 2, when resource selection or reselection is triggered, the UE may exclude some subframes from the selection window. The excluded subframes may be resources that are not monitored within the detection window. The UE may not be able to detect these resources, for example, due to its own transmission (e.g., half-duplex constraints). The UE may further exclude resources occupied or reserved by other UEs from the selection window if the corresponding SL-RSRP exceeds a configured or preconfigured SL-RSRP exclusion threshold. After the resource exclusion, the number of candidate resources may be at least 20% of the total number of resources in the selection window. Otherwise, the UE may increase the SL-RSRP exclusion threshold, for example, by 3 dB, until the candidate resources reach at least 20% of all resources. The UE may further calculate the corresponding S-RSSI for each subchannel resource as a linear average over the S-RSSI of the resources monitored at a specific interval (e.g., the average interval is 100 ms for a resource reservation interval of 100 ms or more). The UE may determine, for example, 20% of the best resources in terms of the lowest average S-RSSI as candidate resources among all resources within the selection window. The UE may use the 20% of resources with the lowest average S-RSSI based on the S-RSSI ranking as candidate resources.

[0019] The method 100 includes a step 108 of selecting a resource among the candidate resources. The selection of a resource among the candidate resources may be a random selection. For example, as shown in FIG. 2, the UE may select a single-subframe resource among the candidate single-subframe resources in a uniformly random manner. The selected frequency resource may be used for subsequent transmissions multiple times at fixed time intervals (this scheme is referred to as SPS in this disclosure) or only once (this scheme is referred to as OST in this disclosure).

[0020] The method 100 includes a step 110 of transmitting a packet based on the SPS or OST. The packet can be an initial or a retransmitted packet. For example, the UE can transmit the initial packet using selected resources. As another example, the UE can retransmit the packet at most one time without feedback from the receiving UE to improve the reliability of the transmission (this is referred to as "blind HARQ retransmission" in 3GPP and this disclosure). After transmission, the method continues with the step You can start again from step 102.

[0021] FIG. 3 is a flowchart illustrating a method 300 for resource selection during sidelink communication (referred to as the "second method" in this disclosure). FIG. 4A is a schematic diagram illustrating a resource candidate determination procedure according to the second method. FIG. 4B is a table illustrating a correspondence between subcarrier spacings (SCSs) and resource subsets according to the second method, consistent with some embodiments of the present disclosure. Method 300 may be performed by a UE during sidelink communication. For example, method 300 may be performed by a vehicle during V2X communication. Method 300 may be performed in a mode employing orthogonal frequency division multiplexing (OFDM) at the PHY layer for sidelink communication (referred to as the "second mode" in this disclosure). An example of the second mode is 3GPP Release 16 / 17 5G NR-V2X PC5 Mode 2.

[0022] As shown in Figure 4A, in the second mode, the time-frequency radio resource is divided into slots in the time domain and subchannels in the frequency domain. In one embodiment, the second mode is a 15 2 μ A subcarrier spacing (SCS) of 15, 30, and 60 kHz (i.e., μ∈{0,1,2}) may be supported for frequencies below 6 GHz, while SCSs of 60, 120, and 240 kHz (i.e., μ∈{2,3,4}) may be supported for frequencies above 6 GHz. Each slot is ½ μ ms long and consists of 14 OFDM symbols. Each subchannel can consist of a number of consecutive PRBs, each PRB having a length of 180 2 μ occupies 15.2 kHz μ The PSFCH consists of 12 subcarriers with an SCS of 1 kHz. The size of the subchannel (i.e., the number of PRBs per subchannel) is configurable or pre-configurable. Multiple DMRS density options (2 to 4 DMRS symbols per slot) are supported to support multiple SCSs and different Doppler spreads. Each UE can transmit the first stage SCI and data (TB) on the PSCCH and the second stage SCI on the PSSCH. HARQ feedback (e.g., ACK / NACK, or NACK only) can be transmitted on the PSFCH.

[0023] FIG. 4B illustrates a schematic diagram of an SCS and a detection and selection window (T SL proc,0 and T SL proc,1 ) parameters. For example, when the SCS is 15 kHz, as shown in the second and third columns of Figure 4B, T SL proc,0 corresponds to 1 ms, and T SL proc,1corresponds to 3 ms. As another example, when the SCS is 30 kHz, T SL proc,0 corresponds to 0.5 ms, and T SL proc,1 corresponds to 2.5 ms.

[0024] 3, the method 300 includes step 302 of performing channel sensing (e.g., background sensing or other types of sensing, either full or partial). For example, as shown in FIG. 4A, the UE may perform a sensing window T sensing (For example, T sensing =[T0,T SL proc,0 ], where T0=100 or 1100 ms, and T SL proc,0 Channel sensing can be performed within a 100 ms sensing window (shown in FIG. 4B). Channel sensing with a 100 ms sensing window may be for aperiodic traffic, while channel sensing with an 1100 ms sensing window may be for periodic traffic.

[0025] The method 300 includes collecting resource reservation information of another UE and measuring the corresponding SL-RSRP 304. For example, as shown in FIG. 4A, the UE may receive a detection win To perform channel sensing and identify candidate resources within a UE, the UE can collect resource reservation information of another UE based on SCI decoding. In one embodiment, the UE first decodes the SCI to perform channel sensing and obtain information for receiving packets of other UEs. As defined in the 3GPP specifications, SCI decoding can include two stages: a first-stage SCI (SCI format 1-A) and a second-stage SCI (SCI format 2-A or 2-B). The first-stage SCI can carry resource reservation information for future transmissions, information about resource allocation, an MCS for PSSCH, a DMRS pattern, and a second-stage SCI format. The second-stage SCI can carry control information for HARQ procedures, source / destination IDs, information about distance-based groupcast (e.g., the UE's zone ID and coverage requirements), and the like. Based on the resource reservation information included in the first-stage SCI, the UE can avoid using time and / or frequency resources reserved by other UEs when the UE performs resource selection or reselection.

[0026] The method 300 can support UE-to-UE coordination, in which a first UE (UE-A) sends coordination information about resources to a second UE (UE-B), and the UE-B utilizes this information for its resource selection or reselection. In some embodiments, the UE can support a first UE-to-UE coordination scheme. In the first UE-to-UE coordination scheme, the UE can receive an indication of resources from another UE that are preferably included or excluded from the UE's selected or reselected resources. In one embodiment, when the indication of resources indicates inclusion of certain resources, the UE can rely solely on these resources if the indication does not support sensing and / or resource exclusion. In one embodiment, the UE can also combine the indication of resources with resources identified by its own sensing procedure before making a final selection. The UE can receive a MAC address from another UE. The UE may receive the indication via the CE and / or the second stage SCI. In some embodiments, the UE may support a second UE-to-UE coordination scheme. In the second UE-to-UE coordination scheme, the UE may receive an indication that resources reserved for the UE's transmission are or should be subject to conflict with a transmission from another UE. In this case, the UE may reselect new resources. The UE may receive the indication via the PSFCH. The UE may use a mapping table that defines a mapping rule between PSSCH allocations (slots and subchannels) and PSFCH resources. Using the mapping table, the UE (and the transmitting UE) can determine the PSSCH allocations (slots and subchannels) to which information in the PSFCH resources refers. When more than one subchannel is reserved in the PSSCH, multiple PSFCH resources may be used. The mapping table may be predefined, preconfigured in the UE, or configured by a network node.

[0027] The method 300 includes determining 306 candidate resources by filtering out resources that are occupied, reserved, and / or not monitored. For example, the UE may select candidate resources within a selection window T (e.g., T=[T1, T2], where 0≦T1≦T2). SL proc,1 ms and T SL proc,1 4B, where T2 may be set based on the remaining packet delay budget). The UE may be unable to detect the unmonitored slots within the detection window due to, for example, its own transmission (e.g., half-duplex constraints). The UE may further exclude resources occupied or reserved by other UEs from the selection window if the corresponding SL-RSRP exceeds a configured or preconfigured SL-RSRP exclusion threshold. After resource exclusion, the number of candidate resources may be at least X% of the total number of resources in the selection window. Otherwise, the UE may continue to exclude resources until at least X% of the resources are acquired. For example, the SL-RSRP exclusion threshold may be increased by 3 dB, where X may be configured or pre-configured from {20, 35, 50}%.

[0028] The method 300 includes a step 308 of selecting a resource from the candidate resources. The selection may be random. For example, as shown in FIG. 4A, the UE may select a resource from the candidate resources within a selection window. The selected frequency resource may be used multiple times at fixed time intervals for SPS or only once for OST.

[0029] The method 300 includes checking resource availability based on re-evaluation and / or preemption of the selected resource 310. This step may be performed for late-arriving packets (e.g., aperiodic packets) after resource selection and before packet transmission.

[0030] Method 300 includes step 312 of determining whether resource reselection is necessary. If it is determined that resource reselection is necessary, the method may repeat from step 304. On the other hand, if it is determined that resource reselection is not necessary, the method may proceed with step 314 of transmitting a packet based on the SPS or OST. The packet may be an initial packet or a retransmitted packet. The UE may also retransmit the packet multiple times (e.g., HARQ retransmission) with or without feedback from the receiving UE to improve the reliability of the transmission. After step 314, the method repeats from step 302.

[0031] At least some embodiments of the present disclosure are directed to carrier aggregation in sidelink communications, supporting the first mode described above with reference to Figures 1-2 and / or the second mode described above with reference to Figures 3 and 4A-4B. Carrier aggregation is desirable in sidelink communications because it enables high-throughput and reliable communications. While the first mode described above can only support broadcast, the second mode described above can support broadcast, unicast, and groupcast with HARQ feedback.

[0032] FIG. 5 is a schematic diagram illustrating an example sidelink carrier aggregation scheme consistent with some embodiments of the present disclosure. Referring to FIG. 5, a UE 502 in a first sidelink communication implements carrier aggregation to achieve high throughput and improved reliability. The UE 502 may be a transmitting (Tx) UE in the first sidelink communication. For example, to improve throughput, the UE 502 may transmit multiple Medium Access Control Protocol Data Units (MAC PDUs) on multiple sidelink carriers. To improve reliability, the UE 502 may implement Packet Data Convergence Protocol (PDCP) overlapping, in which the same PDCP packet is transmitted on multiple sidelink carriers. For example, as shown in FIG. 5, the UE 502 uses an aggregation of three sidelink carriers, namely, Carrier 1, Carrier 2, and Carrier 3, to transmit data (e.g., a transport block). The first sidelink communication may support the second mode described above. For example, the first sidelink communication may be an NR sidelink communication. The UE 502 may transmit the same PDCP packet or transport block on each of the three carriers to improve reliability.

[0033] The UE 502 can select or reselect three sidelink carriers for transmission based on the measured channel busy ratio (CBR) per sidelink carrier. For example, the UE 502 may consider multiple sidelink carriers as candidate sidelink carriers if the measured CBR of each of the multiple sidelink carriers is below a CBR threshold. The CBR threshold may be configured by a network node or preconfigured in the UE 502. The CBR threshold may be associated with a priority of the sidelink transmission. The UE 502 may select three sidelink carriers from the multiple candidate sidelink carriers in order of increasing CBR from the lowest CBR. The UE 502 may determine the number of sidelink carriers to be aggregated (e.g., three) based on the UE capabilities. The UE 502 may independently select resources on each sidelink carrier based on the detection and resource selection procedure. The UE 502 may use the selected sidelink carriers at least until carrier reselection is triggered.

[0034] Unicast or groupcast is typically associated with ACK / NACK feedback. For example, a transmitting UE transmitting data via unicast or groupcast option 2 typically involves ACK feedback from one or more receiving UEs, while a transmitting UE transmitting data via groupcast option 1 typically involves NACK feedback. If the transmitting UE receives neither ACK nor NACK feedback from one or more receiving UEs, the transmitting UE retransmits the same data to one or more receiving UEs until the transmitting UE receives ACK / NACK feedback, even if communication on at least one of the sidelink carriers is successful. For example, as shown in FIG. 5, carrier 1 is for unicast, and UE 502 receives an ACK after the first retransmission, indicating that communication on at least carrier 1 was successful. However, UE 502 continues to perform retransmissions on carrier 2 and carrier 3 until UE 502 receives an ACK or no NACK on carrier 2 and carrier 3 (the retransmissions on carriers 2 and 3 occur after receiving an ACK on carrier 1). This causes unnecessary transmissions or retransmissions, thus reducing spectral efficiency. At least some embodiments of the present disclosure solve the above-mentioned problems in sidelink carrier aggregation for unicast and groupcast.

[0035] FIG. 6 is a schematic diagram illustrating another example procedure for sidelink carrier aggregation consistent with some embodiments of the present disclosure. Referring to FIG. 6, a UE 602 in a first sidelink communication uses carrier aggregation to achieve high throughput and / or improved reliability. The UE 602 may be a Tx UE in the first sidelink communication. Similar to the UE 502 in FIG. 5, the UE 602 uses an aggregation of three sidelink carriers, namely, Carrier 1, Carrier 2, and Carrier 3, to transmit a transport block. The UE can select Carriers 1-3 based on the procedure described with respect to FIG. 5. For brevity, the carrier selection procedure is omitted here. The first sidelink communication can support the second mode described above. For example, the first sidelink communication may be an NR sidelink communication. The UE can transmit the same transport block on each of the three sidelink carriers to improve reliability.

[0036] Instead of continuously transmitting or retransmitting the same transport block (as in Figure 5), in Figure 6 the UE 602 can cancel remaining transmissions or retransmissions for the same transport block on all three sidelink carriers if the UE 602 determines that communication on at least one of the three sidelink carriers has been successful. To this end, the UE 602 can use MAC-level packet duplication instead of PDCP packet duplication so that the MAC layer recognizes that packets transmitted over multiple sidelink carriers contain the same TB. For example, As shown, carrier 3 is for unicast and the UE receives an ACK after the initial transmission indicating successful communication on at least carrier 3. In this case, the UE cancels the initial transmission on carrier 2 and all retransmissions on carriers 1 through 3.

[0037] In this manner, the disclosed method can minimize unnecessary transmissions and / or retransmissions and therefore improve spectral efficiency in sidelink carrier aggregation for unicast and groupcast.

[0038] Although the above examples in this disclosure relate to carrier aggregation of three sidelink carriers, application of the disclosed methods is not so limited. The number of aggregated carriers can be any number depending on the capabilities of the UE. The methods described in this disclosure can be applied to any sidelink communication (or radio access technology (RAT)), such as sidelink communication of a future generation (sixth generation (6G), seventh generation (7G), or any future generation). The methods described in this disclosure can also be applied to other systems, such as carrier aggregation in systems conforming to IEEE standards.

[0039] 7 is a flowchart illustrating a method 700 for sidelink carrier aggregation consistent with some embodiments of the present disclosure. The method 700 may be performed by a UE engaged in sidelink communication, such as the UE 602 of FIG. 6.

[0040] The method 700 includes a step 702 of transmitting, by a first UE, one or more packets on one or more carriers of a plurality of carriers to be used for sidelink carrier aggregation. For example, the first UE, such as UE 602 of FIG. 6, may transmit a packet on one or more carriers of the plurality of carriers. The plurality of carriers form a carrier aggregation. In some embodiments, the first UE may transmit the same packet on each of the plurality of carriers to improve reliability. The one or more packets may be signals or data (e.g., transport blocks). For example, in one embodiment, the one or more packets are one or more transport blocks at the MAC layer. The plurality of carriers may be carriers for the same RAT or carriers for different RATs.

[0041] In some embodiments, the first UE may select one or more carriers among a plurality of carriers on which one or more packets are to be transmitted. The first UE may select one or more carriers among a plurality of carriers on which one or more packets are to be transmitted based on at least one of (a) a priority of each of the one or more carriers, (b) a traffic load of each of the one or more carriers, or (c) a number of unsuccessful receptions in X slots on each of the one or more carriers, where X is a natural number. The value of X may be configured by a network node or preconfigured in the first UE.

[0042] In some embodiments, the first UE may further adjust the number of selected one or more carriers among the plurality of carriers on which one or more packets will be transmitted. For example, the first UE may dynamically adjust the number of selected one or more carriers among the plurality of carriers on which one or more packets will be transmitted based on whether a metric calculated from a CBR associated with a candidate carrier among the plurality of carriers is greater than a first threshold. The first threshold may be configured by the network node or may be preconfigured in the first UE. As another ... number of unsuccessful receptions on one or more carriers is greater than a second threshold. The first UE may dynamically adjust the number of selected one or more carriers among the plurality of carriers over which one or more packets are to be transmitted based on whether the second threshold is greater than the first threshold. The second threshold may be configured by the network node or may be preconfigured in the first UE. The second threshold may depend on the priority of each of the one or more carriers and a CBR associated with each of the one or more carriers. The metric calculated from the CBRs associated with the candidate carriers may include at least one of a maximum CBR of the candidate carriers, a minimum CBR of the candidate carriers, an average CBR of the candidate carriers, or a median CBR of the candidate carriers.

[0043] In some embodiments, the first UE may further exclude at least one carrier from the candidate carriers in response to determining that the number of unsuccessful receptions in the X slots on each of the one or more carriers is greater than a threshold value, which may be configured by the network node or pre-configured in the first UE.

[0044] The method 700 includes step 704 of determining, by the first UE, at least one of receiving an ACK from each of the one or more target receiving UEs or not receiving a NACK on at least one of one or more carriers of the plurality of carriers. The ACK and NACK may be HARQ feedback signals. The ACK or NACK may be received by the first UE via a PSFCH. In some embodiments, the first UE may determine at least one of receiving an ACK from each of the one or more target receiving UEs or not receiving a NACK on at least one of one or more carriers of the plurality of carriers in one or more HARQ feedback occasions or before a sidelink timer expires. The sidelink timer may be configured by the network node or pre-configured in the first UE.

[0045] The method 700 includes canceling 706, by the first UE, one or more remaining transmissions or retransmissions for one or more packets scheduled on one or more carriers in response to determining at least one of receiving an ACK from at least one of the one or more target receiving UEs or not receiving a NACK on at least one of the one or more carriers of the plurality of carriers. In some embodiments, the first UE may cancel one or more remaining transmissions or retransmissions for one or more packets on one or more carriers of the plurality of carriers in response to determining receiving an ACK from each of the one or more target receiving UEs on one or more particular carriers of the plurality of carriers. The one or more particular carriers may be configured by the network node or pre-configured in the first UE.

[0046] In some embodiments, the first UE may cancel one or more remaining transmissions or retransmissions for one or more packets on one or more particular carriers of the plurality of carriers in response to determining not receiving a NACK on one or more particular carriers of the plurality of carriers, The one or more particular carriers may be configured by the network node or may be pre-configured in the first UE.

[0047] In some embodiments, the first UE may cancel one or more remaining transmissions or retransmissions for one or more packets on one or more carriers of the plurality of carriers in response to (a) determining receipt of an ACK from each of the one or more target receiving UEs on one or more particular carriers of the plurality of carriers, or (b) determining non-receipt of a NACK on one or more particular carriers of the plurality of carriers. The one or more particular carriers may be selected by the network node. The first UE may select one or more particular carriers based on at least one of (a) a highest CBR level associated with one or more carriers of the plurality of carriers, (b) a maximum sidelink reference signal received power (RSRP) level associated with one or more carriers of the plurality of carriers, or (c) a pre-selected, configured, or pre-configured anchor carrier.

[0048] In some embodiments, the first UE may cancel one or more remaining transmissions or retransmissions for one or more packets on one or more first carriers of the plurality of carriers in response to receiving an ACK or determining a non-receipt of a NACK from at least one of the one or more target receiving UEs on one or more second carriers different from the one or more first carriers of the plurality of carriers. The one or more second carriers may be configured by the network or pre-configured in the first UE. In some embodiments, the first UE may cancel one or more remaining transmissions or retransmissions for one or more packets on one or more first carriers of the plurality of carriers in response to determining a non-receipt of a NACK on one or more second carriers different from the one or more first carriers of the plurality of carriers.

[0049] In some embodiments, the first UE may cancel one or more remaining transmissions or retransmissions for one or more packets on one or more carriers of the plurality of carriers in response to determining receipt of an ACK from at least one particular target recipient UE among the one or more target recipient UEs, The at least one particular target recipient UE may be configured by the network node or pre-configured at the first UE.

[0050] In some embodiments, the first UE may cancel one or more remaining transmissions or retransmissions for one or more packets on one or more carriers of the multiple carriers in response to determining receipt of ACKs from a specific number of UEs from among the one or more target receiving UEs. The specific number may be configured by a network node or preconfigured in the first UE. In some embodiments, the first UE may cancel one or more remaining transmissions or retransmissions for one or more packets on one or more carriers of the multiple carriers in response to determining receipt of some NACKs on at least one of the multiple carriers. The number of NACKs may be configured by the network node or preconfigured in the first UE.

[0051] In some embodiments, the first UE may cancel one or more remaining transmissions or retransmissions for one or more packets on one or more carriers of the plurality of carriers in response to (a) determining receipt of an ACK from each of the one or more target receiving UEs, or (b) determining non-receipt of a NACK on one or more carriers of the plurality of carriers.

[0052] In some embodiments, the first UE may utilize resources associated with the canceled transmission or retransmission for other purposes, e.g., the first UE may use resources associated with one or more canceled remaining transmissions or retransmissions for the packet to schedule transmission of one or more other packets to one or more other target receiving UEs.

[0053] In some embodiments, the first UE is the second UE among the one or more target recipient UEs. In response to determining that an ACK has been received or a NACK has not been received from a number of target receiving UEs, do not reserve resources for one or more retransmissions for one or more packets on one or more carriers of the plurality of carriers. The first number may be greater than a threshold number. The threshold number may be configured by the network node or preconfigured in the first UE. The threshold number may be determined by a priority of each of the one or more carriers or by a CBR associated with each of the one or more carriers. The threshold number may also be determined by a priority of each of the one or more carriers and a CBR associated with each of the one or more carriers.

[0054] In some embodiments, the first UE can dynamically switch between groupcast and unicast based on the number of one or more target receiving UEs that unsuccessfully receive on one or more carriers of the plurality of carriers. For example, when the first UE performs groupcast, the first UE can switch from groupcast to unicast in response to determining that the number of one or more target receiving UEs that unsuccessfully receive is less than a threshold. The threshold may be configured by the network node or may be preconfigured in the first UE. The first UE can further perform link adaptation on each of the one or more unicast links. For example, the first UE can perform MCS adjustment on the one or more unicast links. The first UE can also apply different block error rate (BLER) targets for packet duplication or for transport block transmissions to each of the one or more unicast links. The first UE can further cancel one or more remaining transmissions or retransmissions for the packet in response to determining that the number of NACKs corresponds to a BLER higher than the carrier's initial BLER target.

[0055] In some embodiments, one or more carriers of the plurality of carriers may be a first set of carriers for a packet transmission for which HARQ feedback is enabled. In this case, the first UE may perform one or more blind retransmissions of one or more packets using a second set of carriers of the plurality of carriers. The second set of carriers may be different from the first set of carriers. The first UE may further stop the one or more blind retransmissions in response to determining receipt of an ACK on at least one of the first set of carriers. The first UE may perform packet transmission using the first set of carriers, and the one or more blind retransmissions using the second set of carriers are performed via a PSSCH.

[0056] In some embodiments, one or more carriers of the plurality of carriers may be licensed carriers for packet transmissions for which HARQ feedback is enabled. In this case, the first UE may perform one or more blind retransmissions of one or more packets using one or more unlicensed carriers. The first UE may further stop the one or more blind retransmissions in response to determining receipt of an ACK on at least one of the licensed carriers. The first UE may perform packet transmissions on the licensed carrier and one or more blind retransmissions on one or more unlicensed carriers via the PSSCH.

[0057] In some embodiments, the first UE may transmit one or more indications for cancellation of one or more previously indicated resource reservations on one or more carriers of the plurality of carriers. The first UE may transmit one of more indications via at least one of a PSCCH, a PSSCH, a PSFCH, a MAC CE, or a higher layer, such as a network layer, a transport layer, or an application layer.

[0058] FIG. 8 is a block diagram of a UE 800 consistent with some embodiments of the present disclosure. The UE 800 may support the first and / or second modes described above. The UE 800 may be mounted to a moving vehicle or a fixed location. The UE 800 may take any form, including, but not limited to, a vehicle, a vehicle-mounted component, a roadside unit, a laptop computer, a wireless terminal including a mobile phone, a wireless handheld device, or a wireless personal device, or any other form. Referring to FIG. 8, the UE 800 may include an antenna 802 that may be used for transmitting or receiving electromagnetic signals to or from a base station or another UE. The antenna 802 may include one or more antenna elements and may enable different input / output antenna configurations, such as a multiple-input multiple-output (MIMO) configuration, a multiple-input single-output (MISO) configuration, and a single-input multiple-output (SIMO) configuration. In some embodiments, the antenna 802 may include a large number (e.g., tens or hundreds) of antenna elements and may enable multi-antenna functions such as beamforming. In some embodiments, the antenna 802 is a single antenna.

[0059] The UE 800 may include a transceiver 804 coupled to the antenna 802. The transceiver 804 may be a wireless transceiver in the UE 800 and may communicate bidirectionally with a base station or other UEs. For example, the transceiver 804 may receive / transmit wireless signals to / from a base station via downlink / uplink communication. The transceiver 804 may also receive / transmit wireless signals to / from another UE or a roadside unit via sidelink communication. The transceiver 804 may include a modem for modulating packets and providing the modulated packets to the antenna 802 for transmission, and for demodulating packets received from the antenna 802.

[0060] The UE 800 may include memory 806. The memory 806 may be any type of computer-readable storage medium, including volatile or non-volatile memory devices, or a combination thereof. Computer-readable storage media include, but are not limited to, non-transitory computer storage media. Non-transitory storage media may be accessed by a general-purpose or special-purpose computer. Examples of non-transitory storage media include, but are not limited to, portable computer diskettes, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM), electrically erasable programmable ROM (EEPROM), digital versatile disks (DVDs), flash memory, compact disk (CD) ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, etc. The non-transitory medium may be used to carry or store desired program code means (e.g., instructions and / or data structures) and may be accessed by a general-purpose or special-purpose computer or a general-purpose or special-purpose processor. In some examples, the software / program code may be transmitted from a remote source (e.g., a website, a server, etc.) using coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave. In such examples, coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are within the definition of media. Combinations of the above examples are also within the scope of computer-readable media.

[0061] The memory 806 may store information regarding the identity of the UE 800, as well as signals and / or data received by the antenna 802. The memory 806 may also store processed signals and / or data. The memory 806 may also store computer-readable program instructions, mathematical models, and algorithms used in signal processing at the receiver 804 and calculations at the processor 808. The memory 806 may further store computer-readable program instructions for execution by the processor 808 to operate the UE 800 to perform various functions described in this disclosure. In some examples, the memory 806 may include a basic input / output system (BIOS), which may control basic hardware or software operations, such as interaction with peripheral components or devices. In some embodiments, the memory 806 includes both an LTE sidelink module and an NR sidelink module. In some embodiments, the memory 806 includes only an NR sidelink module. In some embodiments, the memory 806 includes only an LTE sidelink module.

[0062] The computer-readable program instructions of the present disclosure may be assembler instructions, instruction set architecture (ISA) instructions, machine language instructions, machine-dependent instructions, microcode, firmware instructions, state-setting data, or source or object code written in any combination of one or more programming languages, including object-oriented programming languages ​​and conventional procedural programming languages. The computer-readable program instructions may execute entirely on a computing device as a standalone software package, or partially on a first computing device and partially on a second computing device that is remote from the first computing device. In the latter scenario, the second, remote computing device may be connected to the first computing device through any type of network, including a local area network (LAN) or a wide area network (WAN).

[0063] The UE 800 may include a processor 808, which may include hardware devices having processing capabilities. The processor 808 may include at least one of a general-purpose processor, a digital signal processor (DSP), a central processing unit (CPU), a microcontroller, an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), a programmable logic device, a discrete gate or transistor logic component, a discrete hardware component, or another programmable logic device. Examples of general-purpose processors include, but are not limited to, a microprocessor, any conventional processor, controller, microcontroller, or state machine. In some embodiments, the processor 808 may be implemented using a combination of devices (e.g., a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration). The processor 808 may receive downlink or sidelink signals from the transceiver 804 and further process the signals. The processor 808 may also receive data packets from the transceiver 804 and further process the packets. In some embodiments, the processor 808 may be configured to operate the memory using a memory controller. In some embodiments, the memory controller may be integrated into the processor 808. The processor 808 may be configured to execute computer-readable instructions stored in a memory (e.g., memory 806) to cause the UE 800 to perform various functions.

[0064] The UE800 is a global positioning system (GPS) The GPS 810 may include a GPS (Global Positioning System) 810. The GPS 810 may be used to enable location-based services or other services based on the geographic location of the UE 800 and / or synchronization between UEs. The GPS 810 receives Global Navigation Satellite System (GNSS) signals from a single satellite or multiple satellite signals via the antenna 802 and provides the geographic location of the UE 800 (e.g., the coordinates of the UE 800). In some embodiments, the UE 800 does not include a GPS 810.

[0065] The UE 800 may include input / output (I / O) devices 812 that may be used to communicate the results of signal processing and calculations to a user or another device. The I / O devices 812 may include a user interface, including a display and an input device for sending user commands to the processor 808. The display may be configured to display the status of signal reception in the UE 800, data stored in the memory 806, the status of signal processing, and the results of calculations. The display may include, but is not limited to, a cathode ray tube (CRT), a liquid crystal display (LCD), a light-emitting diode (LED), a gas plasma display, a touchscreen, or other image projection devices for displaying information to a user. The input devices may be any type of computer hardware equipment used to receive data and control signals from a user. The input devices may include, but are not limited to, a keyboard, a mouse, a scanner, a digital camera, a joystick, a trackball, cursor direction keys, a touchscreen monitor, or an audio / video commander.

[0066] The UE 800 may further include a mechanical interface 814, such as an electrical bus, that connects the transceiver 804, memory 806, processor 808, GPS 810, and I / O devices 812.

[0067] In some embodiments, the UE 800 may be configured or programmed to perform carrier aggregation during sidelink communication. The processor 808 may be configured or programmed to execute instructions stored in the memory 806 to: transmit one or more packets on one or more carriers of the plurality of carriers to be used for sidelink carrier aggregation; determine at least one of receiving an ACK from each of one or more target receiving UEs or not receiving a NACK on at least one of the one or more carriers of the plurality of carriers; and cancel one or more remaining transmissions or retransmissions for one or more packets scheduled on one or more carriers of the plurality of carriers in response to determining at least one of receiving an ACK from at least one of the one or more target receiving UEs or not receiving a NACK on at least one of the one or more carriers of the plurality of carriers.

[0068] As used in this disclosure, the use of the term "or" in a list of items indicates an inclusive list. A list of items may be prefaced with a phrase such as "at least one of" or "one or more of." For example, a list of at least one of A, B, or C includes A or B or C or AB (i.e., A and B), or AC or BC or ABC (i.e., A and B and C). Also, as used in this disclosure, prefaced a list of conditions with the phrase "based on" should not be construed as "based only on" the set of conditions, but rather as "based at least in part on" the set of conditions. For example, a conclusion stated as "based on condition A" could be based on both condition A and condition B without departing from the scope of this disclosure.

[0069] As used herein, the terms "comprise," "include," or "contain" are used interchangeably, can have the same meaning, and are to be interpreted in an inclusive and broad manner. The terms "comprise," "include," or "contain" can be used before a list of elements to indicate that at least all of the listed elements in the list are present, but that other elements not in the list may also be present. For example, if A comprises B and C, If A is a symmetrical pair, then both {B,C} and {B,C,D} are within the range of A.

[0070] The present disclosure, along with the accompanying drawings, describes illustrative configurations that are not representative of all examples that may be implemented or of all configurations within the scope of the present disclosure. The term "exemplary" should not be interpreted as "preferred" or "advantageous over other examples," but rather as "illustration, instance, or example." By reading this disclosure, including the description of the embodiments and figures, those skilled in the art will recognize that the technology disclosed herein may be implemented using alternative embodiments. Those skilled in the art will recognize that the embodiments, or specific features of the embodiments, described herein may be combined to arrive at still other embodiments for practicing the technology described in the present disclosure. Thus, the present disclosure is not limited to the examples and designs described herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

[0071] The flowcharts and block diagrams in the figures illustrate example architecture, functionality, and operation of possible implementations of systems, methods, and devices according to various embodiments. It should be noted that in some alternative implementations, the functions noted in the blocks may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending on the functionality involved. Likewise, additional steps may be included in such methods, and certain steps may be omitted or combined, in methods consistent with various embodiments.

[0072] It is understood that the described embodiments are not mutually exclusive, and that elements, components, materials, or steps described in connection with one illustrative embodiment may be combined with or removed from other embodiments in any suitable manner to achieve desired design objectives.

[0073] References herein to "some embodiments" or "some exemplary embodiments" mean that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment. The appearances of the phrases "one embodiment," "some embodiments," or "another embodiment" in various places in this disclosure do not necessarily all refer to the same embodiments, nor do separate or alternative embodiments necessarily exclude other embodiments from one another.

[0074] Additionally, the articles "a" and "an," as used in this disclosure and the appended claims, should generally be construed to mean "one or more," unless otherwise specified or unless it is clear from the context that the singular form is intended.

[0075] Unless expressly stated otherwise, each numerical value and range should be interpreted as an approximation, such as by the word "about" or "approximately" preceding the value or range value.

[0076] Although elements in the following method claims, if any, are recited in a particular order, these elements are not necessarily intended to be limited to being performed in this particular order, unless the recitation of a claim otherwise suggests a particular order for performing some or all of these elements.

[0077] Certain features of the present disclosure, which are, for clarity, described in the context of separate embodiments, may also be incorporated into a single embodiment. It is understood that various features herein may be provided in combination in any of the embodiments. Conversely, various features herein that are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination, or as appropriate in any other described embodiment herein. Particular features described in the context of various embodiments are not essential features of those embodiments, unless noted as such.

[0078] It will be further understood that various changes, substitutions, and variations in the details, materials, and arrangements of parts described and illustrated to explain the nature of the described embodiments may be made by those skilled in the art without departing from the scope of the present disclosure, and it is therefore intended that the following claims encompass all such alternatives, modifications, and variations as fall within the scope of the claims.

[0079] Supplementary Note 1: A method for carrier aggregation in sidelink communications, comprising: transmitting, by a first user equipment (UE), one or more packets on one or more carriers of a plurality of carriers to be used for sidelink carrier aggregation; determining, by the first UE, at least one of receiving an acknowledgment (ACK) from each of the one or more target recipient UEs or not receiving a negative acknowledgment (NACK) on at least one of the one or more carriers of the plurality of carriers; and canceling, by the first UE, one or more remaining transmissions or retransmissions for one or more packets scheduled on one or more carriers of the plurality of carriers in response to determining at least one of: receiving an ACK from at least one of the one or more target receiving UEs; or not receiving a NACK on at least one of the one or more carriers of the plurality of carriers.

[0080] Appendix 2: The method of Appendix 1, wherein the ACK and NACK are hybrid automatic repeat request (HARQ) feedback signals.

[0081] Attachment 3: The method of attachment 1, wherein the one or more packets are one or more transport blocks at a medium access control (MAC) layer.

[0082] Supplementary Note 4: Cancelling one or more remaining transmissions or retransmissions for one or more packets canceling, by the first UE, one or more remaining transmissions or retransmissions for one or more packets on one or more particular carriers of the plurality of carriers in response to determining receipt of an ACK from each of the one or more target receiving UEs on one or more particular carriers of the plurality of carriers, wherein the one or more particular carriers are configured or pre-configured. 2. The method of claim 1, further comprising:

[0083] Appendix 5: Cancelling one or more remaining transmissions or retransmissions for one or more packets and canceling, by the first UE, one or more remaining transmissions or retransmissions for one or more packets on one or more carriers of the plurality of carriers in response to determining non-receipt of a NACK on one or more particular carriers of the plurality of carriers, wherein the one or more particular carriers are configured or pre-configured. 2. The method of claim 1, further comprising:

[0084] Supplementary Note 6: Cancelling one or more remaining transmissions or retransmissions for one or more packets (a) determining receipt of an ACK from each of one or more target receiving UEs on one or more particular carriers of the plurality of carriers, the one or more particular carriers being configured or pre-configured; or (b) determining non-receipt of a NACK on one or more particular carriers of the plurality of carriers; and canceling, by the first UE, one or more remaining transmissions or retransmissions for the one or more packets on one or more carriers of the plurality of carriers in response to the 2. The method of claim 1, further comprising:

[0085] Appendix 7: (a) a maximum channel busy ratio (CBR) level associated with one or more carriers of the plurality of carriers; (b) a maximum sidelink reference signal received power (RSRP) level associated with one or more carriers of the plurality of carriers; or (c) Preselected or preconfigured anchor carriers selecting, by the first UE, one or more particular carriers based on at least one of 7. The method of claim 6, further comprising:

[0086] Appendix 8: Cancelling one or more remaining transmissions or retransmissions for one or more packets (a) determining receipt of an ACK or non-reception of a NACK from at least one of the one or more target receiving UEs on one or more second carriers different from the one or more first carriers of the plurality of carriers, the one or more second carriers being configured or pre-configured; or (b) determining non-receipt of a NACK on one or more second carriers different from the one or more first carriers of the plurality of carriers; and canceling, by the first UE, one or more remaining transmissions or retransmissions for one or more packets on one or more first carriers of the plurality of carriers in response to the 2. The method of claim 1, further comprising:

[0087] Supplementary Note 9: Cancelling one or more remaining transmissions or retransmissions for one or more packets canceling, by the first UE, one or more remaining transmissions or retransmissions for one or more packets on one or more carriers of the plurality of carriers in response to determining receipt of an ACK from at least one specific target recipient UE among the one or more target recipient UEs, wherein the at least one specific target recipient UE is configured or pre-configured. 2. The method of claim 1, further comprising:

[0088] Supplementary Note 10: Cancelling one or more remaining transmissions or retransmissions for one or more packets (a) determining receipt of ACKs from a specific number of UEs from among one or more target receiving UEs, the specific number being configured or pre-configured; or (b) receiving some NACKs on at least one of the plurality of carriers; Determining whether the number of NACKs received is configured or pre-configured and canceling, by the first UE, one or more remaining transmissions or retransmissions for the one or more packets on one or more carriers of the plurality of carriers in response to the 2. The method of claim 1, further comprising:

[0089] Supplementary Note 11: Cancelling one or more remaining transmissions or retransmissions for one or more packets (a) determining receipt of an ACK from each of one or more target receiving UEs; or (b) determining non-receipt of a NACK on one or more of the plurality of carriers; and canceling, by the first UE, one or more remaining transmissions or retransmissions for the one or more packets on one or more carriers of the plurality of carriers in response to the 2. The method of claim 1, further comprising:

[0090] Supplementary Note 12: Scheduling, by the first UE, the transmission of one or more other packets to one or more other target receiving UEs using resources associated with the canceled one or more remaining transmissions or retransmissions for the one or more packets. 2. The method of claim 1, further comprising:

[0091] Supplementary Note 13: Cancelling one or more remaining transmissions or retransmissions for one or more packets and not reserving resources for one or more retransmissions for one or more packets on one or more carriers of the plurality of carriers in response to determining receipt of an ACK or non-reception of a NACK from a first number of target recipient UEs among the one or more target recipient UEs, the first number being greater than a threshold number, the threshold number being configured or pre-configured. 2. The method of claim 1, further comprising:

[0092] Appendix 14: The method of Appendix 13, wherein the threshold number depends on at least one of: a priority of each of the one or more carriers; or a CBR associated with each of the one or more carriers.

[0093] Supplementary Note 15: Selecting, by the first UE, one or more carriers among a plurality of carriers on which one or more packets will be transmitted. 2. The method of claim 1, further comprising:

[0094] Supplementary Note 16: One or more carriers among a plurality of carriers on which one or more packets will be transmitted are (a) the respective priorities of one or more carriers; (b) the traffic load of each of one or more carriers; or (c) the number of unsuccessful receptions in X slots on each of one or more carriers; 16. The method of claim 15, wherein X is configured or pre-configured and X is a natural number.

[0095] Supplementary Note 17: One or more packets will be transmitted on one of a plurality of carriers. adjusting, by the first UE, the number of one or more selected carriers; 17. The method of claim 16, further comprising:

[0096] Supplementary Note 18: The number of one or more carriers selected from the plurality of carriers on which one or more packets will be transmitted is (a) whether a metric calculated from a CBR associated with a candidate carrier among a plurality of carriers is greater than a configured or preconfigured first threshold; or (b) whether the number of unsuccessful receptions on one or more carriers is greater than a configured or preconfigured second threshold; 18. The method of claim 17, wherein the dynamic adjustment is based on at least one of:

[0097] 19. The method of claim 18, wherein the metric calculated from the CBRs associated with the candidate carriers comprises at least one of a maximum CBR of the candidate carriers, a minimum CBR of the candidate carriers, an average CBR of the candidate carriers, or a median CBR of the candidate carriers.

[0098] 20. The method of claim 18, wherein the configured or pre-configured second threshold depends on a priority of each of the one or more carriers and a CBR associated with each of the one or more carriers.

[0099] 21. Excluding, by the first UE, at least one carrier from the candidate carriers in response to determining that the number of unsuccessful receptions in the X slots on each of the one or more carriers is greater than a threshold, the threshold being configured or pre-configured. 19. The method of claim 18, further comprising:

[0100] Supplementary Note 22: Dynamically switching by the first UE between groupcast and unicast based on the number of one or more target receiving UEs that unsuccessfully receive on one or more carriers of the plurality of carriers. 2. The method of claim 1, further comprising:

[0101] Supplementary Note 23: A first UE performs groupcast, and the method comprises: switching from groupcast to unicast in response to determining that the number of one or more target recipient UEs that received unsuccessfully is less than a threshold; and performing link adaptation on each of the one or more unicast links; 23. The method of claim 22, further comprising:

[0102] APPENDIX 24: Performing link adaptation on each of one or more unicast links Applying a different Block Error Rate (BLER) target to each of one or more unicast links 24. The method of claim 23, further comprising:

[0103] 25. Cancelling one or more remaining transmissions or retransmissions for one or more packets in response to determining that the number of NACKs corresponds to a BLER higher than the carrier's initial BLER target. 25. The method of claim 24, further comprising:

[0104] Supplementary Note 26: The method of Supplementary Note 1, wherein the ACK or NACK is received by the first UE via a physical sidelink feedback channel (PSFCH).

[0105] Supplementary Note 27: One or more carriers of the plurality of carriers are a first set of carriers for one or more packet transmissions for which HARQ feedback is enabled, and the method comprises: performing one or more blind retransmissions of the one or more packets using a second set of carriers of the plurality of carriers, the second set of carriers being different from the first set of carriers; stopping the one or more blind retransmissions in response to determining receipt of the ACK on at least one of the first set of carriers; 3. The method of claim 2, further comprising:

[0106] Supplementary Note 28: The method of Supplementary Note 27, wherein the one or more packet transmissions using a first set of carriers and one or more blind retransmissions using a second set of carriers are performed via a physical sidelink shared channel (PSSCH).

[0107] Supplementary Note 29: One or more carriers of the plurality of carriers are licensed carriers for one or more packet transmissions for which HARQ feedback is enabled, and the method comprises: performing one or more blind retransmissions of one or more packets using one or more unlicensed carriers; and stopping the one or more blind retransmissions in response to determining receipt of the ACK at at least one of the licensed carriers. 3. The method of claim 2, further comprising:

[0108] Supplementary Note 30: The method of Supplementary Note 29, wherein the one or more packet transmissions on the licensed carrier and the one or more blind retransmissions on the one or more unlicensed carriers are performed via a PSSCH.

[0109] Supplementary Note 31: Cancelling one or more remaining transmissions or retransmissions for one or more packets 2. The method of claim 1, further comprising: transmitting one or more instructions for cancellation of one or more previously indicated resource reservations on one or more carriers of the plurality of carriers, wherein one of the more instructions is transmitted via at least one of a Physical Sidelink Control Channel (PSCCH), a Physical Sidelink Shared Channel (PSSCH), a Physical Sidelink Feedback Channel (PSFCH), a Medium Access Control (MAC) Control Element (CE), or a higher layer.

[0110] Supplementary Note 32: Determining at least one of receiving an ACK from each of one or more target recipient UEs or not receiving a NACK on at least one of one or more carriers of the plurality of carriers; determining, by the first UE, at least one of receiving an ACK from each of the one or more target receiving UEs or not receiving a NACK on at least one of the one or more carriers of the plurality of carriers before the sidelink timer expires; 29. The method of claim 29, further comprising:

[0111] Supplementary Note 33: A first user equipment (UE) for sidelink communication, comprising: a memory for storing instructions; 1. A processor, comprising: Multiple carriers to be used for sidelink carrier aggregation transmitting one or more packets on one or more of the carriers; determining at least one of receiving an acknowledgment (ACK) from each of the one or more target recipient UEs or not receiving a negative acknowledgment (NACK) on at least one of the one or more carriers of the plurality of carriers; and canceling one or more remaining transmissions or retransmissions for one or more packets scheduled on one or more carriers of the plurality of carriers in response to determining at least one of receiving an ACK from at least one of the one or more target recipient UEs or not receiving a NACK on at least one of the one or more carriers of the plurality of carriers. a processor configured to execute instructions stored in a memory to perform the a first UE comprising:

[0112] Appendix 34: The first UE of Appendix 33, wherein the ACK and NACK are hybrid automatic repeat request (HARQ) feedback signals.

[0113] Supplementary Note 35: The first UE of Supplementary Note 33, wherein the one or more packets are one or more transport blocks at a Medium Access Control (MAC) layer.

[0114] Addendum 36: In canceling one or more remaining transmissions or retransmissions for one or more packets, the processor: canceling one or more remaining transmissions or retransmissions for one or more packets on one or more carriers of the plurality of carriers in response to determining receipt of an ACK from each of the one or more target receiving UEs on one or more particular carriers of the plurality of carriers, wherein the one or more particular carriers are configured or pre-configured. 34. The first UE of Claim 33, further configured to execute instructions stored in the memory for:

[0115] Addendum 37: In canceling one or more remaining transmissions or retransmissions for one or more packets, the processor: and canceling one or more remaining transmissions or retransmissions for one or more packets on one or more carriers of the plurality of carriers in response to determining non-receipt of a NACK on one or more particular carriers of the plurality of carriers, the one or more particular carriers being configured or pre-configured. 34. The first UE of Claim 33, further configured to execute instructions stored in the memory for:

[0116] Addendum 38: In canceling one or more remaining transmissions or retransmissions for one or more packets, the processor: (a) determining receipt of an ACK from each of one or more target receiving UEs on one or more particular carriers of the plurality of carriers, the one or more particular carriers being configured or pre-configured; or (b) determining non-receipt of a NACK on one or more particular carriers of the plurality of carriers; and canceling one or more remaining transmissions or retransmissions for one or more packets on one or more carriers of the plurality of carriers in response to the 34. The first UE of Claim 33, further configured to execute instructions stored in the memory for:

[0117] Appendix 39: The processor: (a) a maximum channel busy ratio (CBR) level associated with one or more carriers of the plurality of carriers; (b) a maximum sidelink reference signal received power (RSRP) level associated with one or more carriers of the plurality of carriers; or (c) Preselected or preconfigured anchor carriers 39. The first UE of Claim 38, further configured to execute instructions stored in the memory for selecting one or more particular carriers based on at least one of:

[0118] Addendum 40: In canceling one or more remaining transmissions or retransmissions for one or more packets, the processor: (a) determining receipt of an ACK or non-reception of a NACK from at least one of the one or more target receiving UEs on one or more second carriers different from the one or more first carriers of the plurality of carriers, the one or more second carriers being configured or pre-configured; or (b) determining non-receipt of a NACK on one or more second carriers different from the one or more first carriers of the plurality of carriers; and canceling one or more remaining transmissions or retransmissions for one or more packets on one or more first carriers of the plurality of carriers in response to the 34. The first UE of Claim 33, further configured to execute instructions stored in the memory for:

[0119] Addendum 41: In canceling one or more remaining transmissions or retransmissions for one or more packets, the processor: canceling one or more remaining transmissions or retransmissions for one or more packets on one or more carriers of the plurality of carriers in response to determining receipt of an ACK from at least one particular target recipient UE among the one or more target recipient UEs, where the at least one particular target recipient UE is configured or pre-configured; 34. The first UE of Claim 33, further configured to execute instructions stored in the memory for:

[0120] Addendum 42: In canceling one or more remaining transmissions or retransmissions for one or more packets, the processor: (a) determining receipt of ACKs from a specific number of UEs from among one or more target receiving UEs, the specific number being configured or pre-configured; or (b) determining receipt of a number of NACKs on at least one of the plurality of carriers, the number of NACKs received being configured or pre-configured; and canceling one or more remaining transmissions or retransmissions for one or more packets on one or more carriers of the plurality of carriers in response to the 34. The first UE of Claim 33, further configured to execute instructions stored in the memory for:

[0121] Addendum 43: In canceling one or more remaining transmissions or retransmissions for one or more packets, the processor: (a) determining receipt of an ACK from each of one or more target receiving UEs; or (b) determining non-receipt of a NACK on one or more of the plurality of carriers; and canceling one or more remaining transmissions or retransmissions for one or more packets on one or more carriers of the plurality of carriers in response to the 34. The first UE of Claim 33, further configured to execute instructions stored in the memory for:

[0122] Appendix 44: The processor: scheduling transmission of one or more other packets to one or more other target receiving UEs using resources associated with the canceled one or more remaining transmissions or retransmissions for the one or more packets; 34. The first UE of Claim 33, further configured to execute instructions stored in the memory for:

[0123] Addendum 45: In canceling one or more remaining transmissions or retransmissions for one or more packets, the processor: and not reserving resources for one or more retransmissions for one or more packets on one or more carriers of the plurality of carriers in response to determining receipt of an ACK or non-reception of a NACK from a first number of target recipient UEs among the one or more target recipient UEs, the first number being greater than a threshold number, the threshold number being configured or pre-configured. 34. The first UE of Claim 33, further configured to execute instructions stored in the memory for:

[0124] Supplementary Note 46: The first UE of Supplementary Note 45, wherein the threshold number depends on at least one of: a priority of each of the one or more carriers; or a CBR associated with each of the one or more carriers.

[0125] Appendix 47: The processor: Selecting one or more carriers from the plurality of carriers over which one or more packets will be transmitted. 34. The first UE of Claim 33, further configured to execute instructions stored in the memory for:

[0126] Supplementary Note 48: One or more carriers among a plurality of carriers on which one or more packets will be transmitted are (a) the respective priorities of one or more carriers; (b) the traffic load of each of one or more carriers; or (c) the number of unsuccessful receptions in X slots on each of one or more carriers; 48. The first UE of claim 47, wherein X is configured or pre-configured, and X is a natural number.

[0127] Appendix 49: The processor: adjusting the number of one or more selected carriers among the plurality of carriers over which one or more packets will be transmitted; 49. The first UE of Claim 48, further configured to execute instructions stored in the memory for:

[0128] Supplementary Note 50: The number of one or more carriers selected from a plurality of carriers on which one or more packets will be transmitted is (a) A memory capacity calculated from a CBR associated with a candidate carrier among a plurality of carriers. whether the trick is greater than a configured or preconfigured first threshold, or (b) whether the number of unsuccessful receptions on one or more carriers is greater than a configured or preconfigured second threshold; 49. The first UE of claim 49, wherein the first UE is dynamically adjusted based on at least one of:

[0129] Attachment 51: The first UE of attachment 50, wherein the metric calculated from the CBRs associated with the candidate carriers comprises at least one of a maximum CBR of the candidate carriers, a minimum CBR of the candidate carriers, an average CBR of the candidate carriers, or a median CBR of the candidate carriers.

[0130] Appendix 52: The first UE of Appendix 50, wherein the configured or pre-configured second threshold depends on a priority of each of the one or more carriers and a CBR associated with each of the one or more carriers.

[0131] Appendix 53: The processor: removing at least one carrier from the candidate carriers in response to determining that the number of unsuccessful receptions in the X slots on each of the one or more carriers is greater than a threshold, the threshold being configured or preconfigured. 51. The first UE of Claim 50, further configured to execute instructions stored in the memory for:

[0132] Appendix 54: The processor: Dynamically switching between groupcast and unicast based on the number of one or more target receiving UEs that are unsuccessfully received on one or more of the plurality of carriers. 34. The first UE of Claim 33, further configured to execute instructions stored in the memory for:

[0133] Supplementary Note 55: The first UE performs groupcast, and the processor: switching from groupcast to unicast in response to determining that the number of one or more target recipient UEs that received unsuccessfully is less than a threshold; and performing link adaptation on each of the one or more unicast links; 55. The first UE of Claim 54, further configured to execute instructions stored in the memory for:

[0134] Attachment 56: In performing link adaptation for each of the one or more unicast links, the processor: Applying a different Block Error Rate (BLER) target to each of one or more unicast links 56. The first UE of Claim 55, further configured to execute instructions stored in the memory for:

[0135] Appendix 57: The processor: canceling one or more remaining transmissions or retransmissions for one or more packets in response to determining that the number of NACKs corresponds to a BLER that is higher than an initial BLER target for the carrier. 57. The first UE of Claim 56, further configured to execute instructions stored in the memory for:

[0136] Supplementary Note 58: ACK or NACK is transmitted via the physical sidelink feedback channel (PS 34. The first UE of claim 33, wherein the first UE receives the first FCH via the FCH.

[0137] Supplementary Note 59: One or more carriers of the plurality of carriers are a first set of carriers for one or more packet transmissions for which HARQ feedback is enabled, and the processor: performing one or more blind retransmissions of the one or more packets using a second set of carriers of the plurality of carriers, the second set of carriers being different from the first set of carriers; stopping the one or more blind retransmissions in response to determining receipt of the ACK on at least one of the first set of carriers; 35. The first UE of Claim 34, further configured to execute instructions stored in the memory for:

[0138] Supplementary Note 60: The first UE of Supplementary Note 59, wherein the one or more packet transmissions using the first set of carriers and the one or more blind retransmissions using the second set of carriers are performed via a physical sidelink shared channel (PSSCH).

[0139] Supplementary Note 61: One or more carriers of the plurality of carriers are licensed carriers for one or more packet transmissions for which HARQ feedback is enabled, and the processor: performing one or more blind retransmissions of one or more packets using one or more unlicensed carriers; and stopping the one or more blind retransmissions in response to determining receipt of the ACK at at least one of the licensed carriers. 35. The first UE of Claim 34, further configured to execute instructions stored in the memory for:

[0140] Supplementary Note 62: The first UE of Supplementary Note 61, wherein the one or more packet transmissions on the licensed carrier and the one or more blind retransmissions on the one or more unlicensed carriers are performed via PSSCH.

[0141] Addendum 63: In canceling one or more remaining transmissions or retransmissions for one or more packets, the processor: transmitting one or more instructions for cancellation of one or more previously indicated resource reservations on one or more carriers of the plurality of carriers, wherein one of the more instructions is transmitted via at least one of a Physical Sidelink Control Channel (PSCCH), a Physical Sidelink Shared Channel (PSSCH), a Physical Sidelink Feedback Channel (PSFCH), a Medium Access Control (MAC) Control Element (CE), or a higher layer. 34. The first UE of Claim 33, further configured to execute instructions stored in the memory for:

[0142] Supplementary Note 64: In determining at least one of receiving an ACK from each of the one or more target recipient UEs or not receiving a NACK on at least one of the one or more carriers of the plurality of carriers, the processor: determining at least one of receiving an ACK from each of the one or more target receiving UEs or not receiving a NACK on at least one of the one or more carriers of the plurality of carriers before the sidelink timer expires; 34. The method of claim 33, further configured to execute instructions stored in the memory for performing First UE.

[0143] Supplementary Note 65: A non-transitory computer-readable medium storing instructions executable by one or more processors of a first user equipment (UE) for sidelink communication for implementing a method, the method comprising: transmitting, by the first UE, one or more packets on one or more carriers of a plurality of carriers to be used for sidelink carrier aggregation; determining, by the first UE, at least one of receiving an acknowledgment (ACK) from each of the one or more target recipient UEs or not receiving a negative acknowledgment (NACK) on at least one of the one or more carriers of the plurality of carriers; and canceling, by the first UE, one or more remaining transmissions or retransmissions for one or more packets scheduled on one or more carriers of the plurality of carriers in response to determining at least one of: receiving an ACK from at least one of the one or more target receiving UEs; or not receiving a NACK on at least one of the one or more carriers of the plurality of carriers.

Claims

1. 1. A method for carrier aggregation in sidelink communication, comprising: transmitting, by a first user equipment (UE), one or more packets on one or more carriers of a plurality of carriers to be used for sidelink carrier aggregation; determining, by the first UE, at least one of receiving an acknowledgement (ACK) from each of one or more target receiving UEs or not receiving a negative acknowledgement (NACK) on at least one of the one or more carriers of the plurality of carriers; canceling, by the first UE, one or more remaining transmissions or retransmissions for the one or more packets scheduled on the one or more carriers in response to determining at least one of receiving the ACK from at least one of the one or more target receiving UEs or not receiving the NACK on the at least one of the one or more carriers of the multiple carriers; A method comprising:

2. 2. The method of claim 1, wherein the ACK and the NACK are hybrid automatic repeat request (HARQ) feedback signals.

3. The method of claim 1 , wherein the one or more packets are one or more transport blocks at a medium access control (MAC) layer.

4. canceling the one or more remaining transmissions or retransmissions for the one or more packets; canceling, by the first UE, the one or more remaining transmissions or retransmissions for the one or more packets on the one or more carriers of the plurality of carriers in response to determining receipt of the ACK from each of the one or more target receiving UEs on one or more particular carriers of the plurality of carriers, wherein the one or more particular carriers are configured or pre-configured. The method of claim 1 further comprising:

5. canceling the one or more remaining transmissions or retransmissions for the one or more packets; canceling, by the first UE, the one or more remaining transmissions or retransmissions for the one or more packets on the one or more carriers of the plurality of carriers in response to determining not receiving the NACK on one or more particular carriers of the plurality of carriers, wherein the one or more particular carriers are configured or pre-configured. The method of claim 1 further comprising:

6. canceling the one or more remaining transmissions or retransmissions for the one or more packets; (a) determining receipt of the ACK from each of the one or more target receiving UEs on one or more particular carriers of the plurality of carriers, the one or more particular carriers being configured or pre-configured; or (b) determining non-receipt of the NACK on the one or more particular carriers of the plurality of carriers; and canceling, by the first UE, the one or more remaining transmissions or retransmissions for the one or more packets on the one or more carriers of the plurality of carriers in response to the The method of claim 1 further comprising:

7. canceling the one or more remaining transmissions or retransmissions for the one or more packets; (a) determining receipt of the ACK or non-receipt of the NACK from the at least one of the one or more target receiving UEs on one or more second carriers different from one or more first carriers of the plurality of carriers, the one or more second carriers being configured or pre-configured; or (b) determining non-receipt of the NACK on the one or more second carriers different from the one or more first carriers of the plurality of carriers; and canceling, by the first UE, the one or more remaining transmissions or retransmissions for the one or more packets on the one or more first carriers of the plurality of carriers in response to the canceling. The method of claim 1 further comprising:

8. canceling the one or more remaining transmissions or retransmissions for the one or more packets; canceling, by the first UE, the one or more remaining transmissions or retransmissions for the one or more packets on the one or more carriers of the plurality of carriers in response to determining receipt of the ACK from at least one specific target receiving UE among the one or more target receiving UEs, wherein the at least one specific target receiving UE is configured or pre-configured. The method of claim 1 further comprising:

9. canceling the one or more remaining transmissions or retransmissions for the one or more packets; (a) determining receipt of the ACK from a specific number of UEs from among the one or more target receiving UEs, the specific number being configured or pre-configured; or (b) determining receipt of some of the NACKs on at least one of the plurality of carriers, the number of receipts of the NACKs being configured or pre-configured; and canceling, by the first UE, the one or more remaining transmissions or retransmissions for the one or more packets on the one or more carriers of the plurality of carriers in response to the The method of claim 1 further comprising:

10. canceling the one or more remaining transmissions or retransmissions for the one or more packets; (a) determining receipt of the ACK from each of the one or more target receiving UEs; or (b) determining non-receipt of the NACK on the one or more carriers of the plurality of carriers; and canceling, by the first UE, the one or more remaining transmissions or retransmissions for the one or more packets on the one or more carriers of the plurality of carriers in response to the The method of claim 1 further comprising:

11. the canceled one or more remaining packets for the one or more packets scheduling, by the first UE, the transmission of one or more other packets to one or more other target receiving UEs using resources associated with the transmission or retransmission; The method of claim 1 further comprising:

12. canceling the one or more remaining transmissions or retransmissions for the one or more packets; and in response to receiving the ACK or determining that the NACK has not been received from a first number of target receiving UEs among the one or more target receiving UEs, not reserving resources for the one or more retransmissions for the one or more packets on the one or more carriers of the plurality of carriers, the first number being greater than a threshold number, the threshold number being configured or pre-configured. The method of claim 1 further comprising:

13. selecting, by the first UE, the one or more carriers among the plurality of carriers over which the one or more packets will be transmitted; The method of claim 1 further comprising:

14. dynamically switching by the first UE between groupcast and unicast based on a number of the one or more target receiving UEs that unsuccessfully receive on the one or more carriers of the plurality of carriers. The method of claim 1 further comprising:

15. 2. The method of claim 1, wherein the ACK or the NACK is received by the first UE via a physical sidelink feedback channel (PSFCH).

16. canceling the one or more remaining transmissions or retransmissions for the one or more packets; transmitting one or more indications for cancellation of one or more previously indicated resource reservations on the one or more carriers of the plurality of carriers, wherein the one of the more indications is transmitted via at least one of a Physical Sidelink Control Channel (PSCCH), a Physical Sidelink Shared Channel (PSSCH), a Physical Sidelink Feedback Channel (PSFCH), a Medium Access Control (MAC) Control Element (CE), or a higher layer. The method of claim 1 further comprising:

17. A first user equipment (UE) for sidelink communication, comprising: a memory for storing instructions; 1. A processor, comprising: transmitting one or more packets on one or more carriers of a plurality of carriers to be used for sidelink carrier aggregation; determining at least one of receiving an acknowledgement (ACK) from each of one or more target receiving UEs or not receiving a negative acknowledgement (NACK) on at least one of the one or more carriers of the plurality of carriers; and in response to determining at least one of receiving the ACK from at least one of the one or more target receiving UEs or not receiving the NACK on the at least one of the one or more carriers of the plurality of carriers, canceling one or more remaining transmissions or retransmissions for the one or more packets scheduled on the one or more carriers of the plurality of carriers. To cancel a processor configured to execute the instructions stored in the memory to perform a first UE comprising:

18. The first UE of claim 17, wherein the ACK and the NACK are hybrid automatic repeat request (HARQ) feedback signals.

19. 18. The first UE of claim 17, wherein the one or more packets are one or more transport blocks at a medium access control (MAC) layer.

20. 1. A non-transitory computer-readable medium storing instructions executable by one or more processors of a first user equipment (UE) for sidelink communication to implement a method, the method comprising: transmitting, by the first UE, one or more packets on one or more carriers of a plurality of carriers to be used for sidelink carrier aggregation; determining, by the first UE, at least one of receiving an acknowledgement (ACK) from each of one or more target receiving UEs or not receiving a negative acknowledgement (NACK) on at least one of the one or more carriers of the plurality of carriers; canceling, by the first UE, one or more remaining transmissions or retransmissions for the one or more packets scheduled on the one or more carriers in response to determining at least one of receiving the ACK from at least one of the one or more target receiving UEs or not receiving the NACK on the at least one of the one or more carriers of the multiple carriers; 1. A non-transitory computer-readable medium comprising:

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