Carrier aggregation in sidelink communications

Abstract

Methods, apparatuses, and systems for sidelink carrier aggregation are disclosed. The method comprises 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 receiver user equipments (UEs), or not receiving a negative acknowledgement (NACK) on at least one of the one or more of the plurality of carriers; and responsive to the determination of at least one of the following, and canceling one or more remaining transmissions or retransmissions for the one or more packets scheduled on the one or more of the plurality of carriers: receiving an ACK from at least one of the one or more target recipient UEs, or the NACK is not received on the at least one carrier of the one or more carriers of the plurality of carriers.

Description

Cross - reference to Related Patent Applications

[0001] This application claims the benefit of U.S. Provisional Application No. 63 / 377,572, entitled "CARRIER AGGREGATION IN SIDELINK COMMUNICATION", filed on September 29, 2022, the entire content of which is incorporated herein by reference. Technical Field

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

[0003] Carrier aggregation can allow for increased throughput and / or improved reliability in sidelink communication. To improve reliability, a transmitting user equipment (UE) in sidelink communication may 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, which typically involves an acknowledgement (ACK) signal or a negative acknowledgement (NACK) signal from the receiving UE. Thus, for unicast or groupcast, the transmitting UE keeps re - transmitting the transport block until it receives an ACK or determines that there is no NACK from all target receiving UEs on all sidelink carriers on which the same transport block is transmitted, even if the communication on at least one of these sidelink carriers is successful. This minimizes the spectral efficiency in sidelink carrier aggregation. Improved systems and methods for sidelink carrier aggregation for unicast or groupcast are desired.

[0004] The 3rd Generation Partnership Project (3GPP) Technical Specifications (TS) 38.213, TS 38.214, and TS 38.321 specify the resource selection procedures for 3GPP Release 16 / 17 5G New Radio (NR) Vehicle - to - Everything (V2X) PC5 mode 2. For resource selection, the UE performs channel sensing in a sensing window and collects resource reservation information of other UEs based on sidelink control information (SCI) decoding to identify the selection window T (T = [T 1 ,T 2Candidate resources in []. First, the UE excludes some time slots from the selection window due to unmonitored resources in the sensing window that the UE cannot sense due to its own transmission (i.e., half-duplex constraint). Then, if the corresponding Sidelink-Reference Signal Received Power (SL-RSRP) exceeds the (pre)-configured SL-RSRP exclusion threshold, the UE also excludes resources reserved by other UEs from the selection window. After resource exclusion, the number of candidate resources should be 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 at least X% of the resource positions are obtained, 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 can be used multiple times at fixed time intervals for subsequent transmissions (i.e., Semi-Persistent Scheduling (SPS)) or only once (i.e., One-Shot Transmission (OST)). In addition, the UE can retransmit the packet multiple times (i.e., Hybrid Automatic Repeat Request (HARQ) retransmission) with or without feedback from the receiving UE to improve reliability.

[0005] For the UE to perform sensing and obtain information to receive packets from other UEs, the UE first decodes the SCI. In Release 16, there is a first-stage SCI (SCI format 1-A) and a second-stage SCI (SCI format 2-A or 2-B) as defined in 3GPP TS 38.212. The first-stage SCI carries resource reservation information for future transmissions, as well as information related to resource allocation and modulation and coding scheme (MCS) for the Physical Sidelink Shared Channel (PSSCH), Demodulation Reference Signal (DMRS) pattern, second-stage SCI format, etc. The second-stage SCI carries control information for the HARQ process, source / destination ID, information for distance-based groupcast (area identification (ID) of the UE and communication range requirements), etc. Based on the resource reservation included in the first-stage SCI, each UE avoids using the time / frequency resources reserved by other UEs when it performs resource (re)selection.

[0006] In Release 17 5G NR-V2X PC5 mode 2, Inter-UE Coordination (IUC) is introduced. In this Inter-UE Coordination, the first UE (UE-A) sends coordination information related to resources to the second UE (UE-B), and UE-B uses this information for its resource (re)selection. The following two Inter-UE Coordination schemes are supported:

[0007] IUC Scheme 1: UE-A can provide an indication of resources that are preferably included in or preferably excluded from the (re)selected resources of UE-B. When resources are given to be included, before making a final selection, UE-B can rely only on these resources (at least if it does not support sensing / resource exclusion), or can combine them with the resources identified through its own sensing process. The indication from UE-A to UE-B is sent in the Medium Access Control (MAC) Control Element (CE) and / or the second-phase SCI.

[0008] IUC Scheme 2: UE-A can provide an indication that the resources reserved for the transmission of UE-B (which may or may not be a transmission to UE-A) will be or may be in conflict with the transmissions from other UEs. Then, UE-B reselects new resources to replace them. The indication from UE-A to UE-B is sent in 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 communication is provided. The method includes: transmitting, by a first UE, one or more packets on one or more of a plurality of carriers to be used for sidelink carrier aggregation; determining, by the first UE, at least one of the following: receiving an ACK from each of 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; and canceling, by the first UE, in response to the determination of at least one of the following, one or more remaining transmissions or retransmissions of the one or more packets scheduled on the one or more carriers of the plurality of carriers: receiving an ACK from at least one of the one or more target recipient UEs or not receiving a NACK on the 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 includes: a memory that stores instructions; and a processor configured to execute the instructions stored in the memory to: transmit one or more packets on one or more of a plurality of carriers to be used for sidelink carrier aggregation; determine at least one of the following: receiving an ACK from each of 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; and in response to the determination of at least one of the following, cancel one or more remaining transmissions or retransmissions of the one or more packets scheduled on the one or more carriers of the plurality of carriers: receiving an ACK from at least one of the one or more target recipient UEs, or not receiving a NACK on the 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 is provided that stores instructions executable by one or more processors of a first UE to perform a method. The method includes: transmitting, by the first UE, one or more packets on one or more of a plurality of carriers to be used for sidelink carrier aggregation; determining, by the first UE, at least one of the following: receiving an ACK from each of 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; and canceling, by the first UE, in response to the determination of at least one of the following, one or more remaining transmissions or retransmissions of the one or more packets scheduled on the one or more carriers of the plurality of carriers: receiving an ACK from at least one of the one or more target recipient UEs, or not receiving a NACK on the at least one of the one or more carriers of the plurality of carriers. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 Figure 1 is a flowchart showing a method for resource selection in sidelink communication in accordance with some embodiments of the present disclosure.

[0013] Figure 2 Figure 2 is a schematic diagram showing a resource candidate determination process of a method in accordance with some embodiments of the present disclosure according to Figure 1 the method.

[0014] Figure 3 Figure 3 is a flowchart showing a method for resource selection in sidelink communication in accordance with some embodiments of the present disclosure. ​​​​​​

[0015] Figure 4A Figure 4A is a schematic diagram showing a resource candidate determination process according to a method of Figure 3 in accordance with some embodiments of the present disclosure.

[0016] Figure 4B Figure 4B is a table showing the correspondence between sub-carrier spacing (SCS) and a resource subset according to a method of Figure 3 in accordance with some embodiments of the present disclosure.

[0017] Figure 5 Figure 5 is a schematic diagram showing an exemplary process for sidelink carrier aggregation in accordance with some embodiments of the present disclosure.

[0018] Figure 6 Figure 6 is a schematic diagram showing another exemplary process for sidelink carrier aggregation in accordance with some embodiments of the present disclosure.

[0019] Figure 7 Figure 7 is a flowchart showing a method for sidelink carrier aggregation in accordance with some embodiments of the present disclosure.

[0020] Figure 8 Figure 8 shows a block diagram of a UE in accordance with some embodiments of the present disclosure. DETAILED DESCRIPTION

[0021] Reference will now be made in detail to the exemplary embodiments, examples of which are illustrated in the accompanying drawings. In the following description, reference is made to the accompanying drawings, in which like numerals in different drawings represent the same or similar elements unless otherwise indicated. The implementations set forth in the following description of the exemplary embodiments do not represent all implementations in accordance with the present disclosure. On the contrary, they are merely examples of systems, apparatuses, and methods in accordance with aspects related to the present disclosure as recited in the appended claims.

[0022] Figure 1 is a flowchart showing Method 100 (referred to as the "first method" in the present disclosure) for resource selection in sidelink communication; and Figure 2 ​​​​​​​​​​​​FIG. is a schematic diagram showing a resource candidate determination process according to a first method in accordance with some embodiments of the present disclosure. Method 100 may be performed by a UE in sidelink communication. For example, method 100 may be performed by a vehicle in V2X communication. Method 100 may be performed in a mode that employs Discrete Fourier Transform Spread Orthogonal Frequency Division Multiplexing (DFT-s-OFDM) (referred to as the "first mode" in the present disclosure) 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.

[0023] As Figure 2 shown, 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 a 15 kHz subcarrier spacing. Each subframe may be 1 ms in length and may consist of 14 DFT-s-OFDM symbols. Each subchannel may consist of a plurality of consecutive Physical Resource Blocks (PRBs), where each PRB occupies 180 kHz and consists 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 cope with the high Doppler caused by the high relative speed in the vehicle scenario, the density of the DMRS for frequency offset compensation and channel estimation may be set to four per subframe. Each UE may broadcast data (e.g., a Transport Block (TB)) in the PSSCH and an SCI in the Physical Sidelink Control Channel (PSCCH). The PSCCH may occupy two consecutive PRBs. The number of PRBs of the PSSCH may be configurable or pre-configurable. The SCI format may contain information to decode the corresponding TB in the PSSCH and facilitate UE autonomous resource selection. As Figure 2 shown, the resource reservation interval may be set to one of the allowed values (e.g., 20 ms, 50 ms, 100 ms, 200 ms, 300 ms... 1000 ms). The PSCCH and the corresponding PSSCH may be transmitted in the same subframe in adjacent or non-adjacent PRBs in the frequency domain.

[0024] See Figure 1, Method 100 includes: Step 102, performing channel sensing (e.g., background sensing or any other type of full sensing or partial sensing). For example, as shown in Figure 2 , for resource selection, the UE can perform channel sensing in a sensing window (e.g., 1000 ms) to collect resource reservation information of other UEs. Depending on the implementation of the UE, the sensing window can be of any time length.

[0025] Returning to Figure 1 , Method 100 includes: Step 104, collecting resource reservation information of other UEs and the corresponding SL-RSRP, and measuring the sidelink received signal strength indicator (S-RSSI). For example, the UE can collect resource reservation information of other UEs and the corresponding SL-RSRP. The UE can also use the received sidelink signal to measure S-RSSI. The UE can decode the received SCI included in the received sidelink signal to identify candidate resources in the selection window T (e.g., T = [T 1 , T 2 , where T 1 ≤ 4 ms, and 20 ms ≤ T 2 ≤ 100 ms), as shown in Figure 2 . The selection of T 1 and T 2 values depends on the implementation of the UE.

[0026] Method 100 includes: Step 106, determining candidate resources by excluding occupied, reserved, and / or unmonitored resources based on the average S-RSSI ranking. For example, as shown in Figure 2As shown, once resource selection or reselection is triggered, the UE can exclude some subframes from the selection window. The excluded subframes can be unmonitored resources in the sensing window. For example, due to the UE's own transmission (e.g., half-duplex constraint), the UE may not be able to sense these resources. If the corresponding SL-RSRP exceeds the configured or pre-configured SL-RSRP exclusion threshold, the UE can also exclude resources occupied or reserved by other UEs from the selection window. After resource exclusion, the number of candidate resources can be at least 20% of the total number of resources in the selection window. Otherwise, the UE can increase the SL-RSRP exclusion threshold by, for example, 3 dB until the candidate resources reach at least 20% of the total resources. The UE can also calculate the corresponding S-RSSI for each subchannel resource as a linear average of the S-RSSI of the monitored resources with a certain interval (e.g., for a resource reservation interval greater than or equal to 100 ms, the average interval is 100 ms). For example, the UE can determine the 20% best resources based on the lowest average S-RSSI as candidate resources among the total resources in the selection window. The UE can use the 20% of the resources with the lowest average S-RSSI as candidate resources based on the S-RSSI sorting.

[0027] Method 100 includes: step 108, selecting a resource among the candidate resources. The selection of a resource among the candidate resources can be a random selection. For example, as Figure 2 shown, the UE can select a single subframe resource in a consistent random manner among the candidate single subframe resources. The selected frequency resource can be used multiple times at fixed time intervals for subsequent transmissions (this solution is referred to as SPS in this disclosure) or only once (this solution is referred to as OST in this disclosure).

[0028] Method 100 includes: step 110, transmitting a packet based on SPS or OST. The packet can be an initial packet or can also be a retransmitted packet. For example, the UE can use the selected resources to transmit an initial packet. Again, for example, the UE can retransmit the packet at most once without feedback from the receiving UE to improve the transmission reliability (this is referred to as "blind HARQ retransmission" in 3GPP and in this disclosure). After transmission, the method can start again from step 102.

[0029] Figure 3 is a flowchart showing method 300 (referred to as the "second method" in this disclosure) for resource selection in sidelink communication; Figure 4A is a schematic diagram showing the resource candidate determination process according to the second method; and Figure 4BIt is a table showing the correspondence between the sub-carrier spacing (SCS) according to a second method and a subset of resources in accordance with some embodiments of the present disclosure. Method 300 may be performed by a UE in sidelink communication. For example, Method 300 may be performed by a vehicle in V2X communication. Method 300 may be performed in a mode that employs orthogonal frequency division multiplexing (OFDM) (referred to as the "second mode" in the present disclosure) for sidelink communication at the PHY layer. An example of the second mode is 3GPP Release 16 / 17 5G NR-V2X PC5 mode 2.

[0030] As Figure 4A shown, in the second mode, the time-frequency radio resources are divided into time slots in the time domain and sub-channels in the frequency domain. In one embodiment, the second mode may support a sub-carrier spacing (SCS) of 15·2 μ kHz, where μ is the OFDM numeral, μ ∈ {0, 1, 2, 3, 4}. For sub-6 GHz frequencies, SCSs of 15 kHz, 30 kHz, and 60 kHz (i.e., μ ∈ {0, 1, 2}) may be supported, while for frequencies above 6 GHz, SCSs of 60 kHz, 120 kHz, and 240 kHz (i.e., μ ∈ {2, 3, 4}) may be supported. Each time slot is 1 / 2 μ ms in length and consists of 14 OFDM symbols. Each sub-channel may be composed of a plurality of consecutive PRBs, where each PRB occupies 180·2 μ kHz and consists of 12 sub-carriers with a 15·2 μ kHz SCS. The size of the sub-channel (i.e., the number of PRBs per sub-channel) is configurable or pre-configurable. To support multiple SCSs and different Doppler spreads, multiple DMRS density options (2 to 4 DMRS symbols per time slot) are supported. Each UE may transmit the first-stage SCI and data (TB) in the PSCCH, and the second-stage SCI in the PSSCH. HARQ feedback (e.g., ACK / NACK, or only NACK) may be transmitted in the PSFCH.

[0031] Figure 4B shows the correspondence between the SCS and the parameters of the sensing window and the selection window (T SL proc,0 and T SL proc,1 ) in accordance with some embodiments of the present disclosure. For example, when the SCS is 15 kHz, as Figure 4B shown in the second and third columns of SLproc,0 corresponds to 1 ms, while T SL proc,1 corresponds to 3 ms. For another example, when the SCS is 30 kHz, T SL proc,0 corresponds to 0.5 ms, while T SL proc,1 corresponds to 2.5 ms.

[0032] Return to refer to Figure 3 , method 300 includes: step 302, perform channel sensing (e.g., background sensing or any other type of full sensing or partial sensing). For example, as Figure 4A shown in sensing (e.g., T sensing =[T 0 , T SL proc,0 , where T 0 =100 ms or 1100 ms, and T SL proc,0 given in Figure 4B ), perform channel sensing to collect resource reservation information of other UEs. Channel sensing with a sensing window of 100 ms can be used for non-periodic services, while channel sensing with a sensing window of 1100 ms can be used for periodic services.

[0033] Method 300 includes: step 304, collect resource reservation information of other UEs, and measure the corresponding SL-RSRP. For example, as Figure 4A shown in

[0034] Method 300 may support inter-UE coordination, in which a first UE (UE-A) sends coordination information related to resources to a second UE (UE-B), and UE-B uses this information for its resource selection or reselection. In some embodiments, a UE may support a first inter-UE coordination scheme. In the first inter-UE coordination scheme, a UE may receive from other UEs an indication of resources that are preferably to be included in or preferably to be excluded from the resources selected or reselected by the UE. In one embodiment, when the indication of a resource indicates inclusion of a given resource, if the indication does not support sensing and / or resource exclusion, the UE may rely only on these resources. In one embodiment, before making a final selection, the UE may also combine the indication of the resources with the resources identified through its own sensing procedure. The UE may receive the indication via a MAC CE and / or a phase 2 SCI. In some embodiments, a UE may support a second inter-UE coordination scheme. In the second inter-UE coordination scheme, a UE may receive an indication that the resources reserved for the UE's transmission will or may conflict with a transmission from another UE. In this case, the UE may reselect new resources. The UE may receive the indication via a PSFCH. The UE may use a mapping table that defines a mapping rule between a PSSCH allocation (time slot and subchannel) and a PSFCH resource. Using the mapping table, the UE (and the transmitting UE) may determine the PSSCH allocation ((one or more) time slots and (one or more) subchannels) referred to by the information in the PSFCH resource. When more than one subchannel is reserved in the PSSCH, multiple PSFCH resources may be used. The mapping table may be predefined, preconfigured at the UE, or configured by a network node.

[0035] Method 300 includes: step 306 of determining candidate resources by excluding occupied, reserved, and / or unmonitored resources. For example, a UE may select from a selection window T (e.g., T = [T 1 , T 2 , where 0 ms ≤ T 1 ≤ T SL proc,1 ms, T SL proc,1 as given in Figure 4B and T 2exclude unmonitored time slots from those that can be set based on the remaining packet delay budget). The UE may be unable to sense unmonitored time slots in the sensing window due to, for example, its own transmissions (e.g., half-duplex constraint). If the corresponding SL-RSRP exceeds a configured or pre-configured SL-RSRP exclusion threshold, the UE may also exclude resources occupied or reserved by other UEs from the selection window. After resource exclusion, the number of candidate resources can be at least X% of the total number of resources in the selection window. Otherwise, the UE may increase the SL-RSRP exclusion threshold by, for example, 3 dB until at least X% of the resources are obtained, where X can be configured or pre-configured from {20, 35, 50}%.

[0036] Method 300 includes: step 308, select a resource among the candidate resources. The selection can be a random selection. For example, as Figure 4A shown, the UE may select a resource among the candidate resources in the selection window. The selected frequency resource can be used multiple times at fixed time intervals for SPS or only once for OST.

[0037] Method 300 includes: step 310, check resource availability based on re-evaluation and / or preemption of the selected resource. This step can be performed on later-arriving packets (e.g., non-periodic packets) after resource selection and before packet transmission.

[0038] Method 300 includes: step 312, determine whether resource reselection is needed. If it is determined that resource reselection is needed, the method may repeat from step 304. On the other hand, if it is determined that resource reselection is not needed, the method may continue with: step 314, transmit a packet based on SPS or OST. The packet can 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.

[0039] At least some embodiments of the present disclosure relate to supporting carrier aggregation in sidelink communication for the first mode described above with respect to Figures 1 to 2 and / or the second mode described above with respect to Figure 3 、 Figures 4A to 4B . Carrier aggregation is desired in sidelink communication because it allows for high throughput and reliable communication. The first mode described above may support only broadcasting, while the second mode described above may support broadcasting, unicasting, and groupcasting with HARQ feedback.

[0040] Figure 5 is a schematic diagram showing an exemplary sidelink carrier aggregation in accordance with some embodiments of the present disclosure. Refer to Figure 5, the UE 502 in the first sidelink communication implements carrier aggregation to achieve high throughput and improved reliability. The UE 502 can be a transmitting (Tx) UE in the first sidelink communication. For example, to increase throughput, the UE 502 can transmit multiple Media Access Control Protocol Data Units (MAC PDUs) on multiple sidelink carriers. To improve reliability, the UE 502 can support Packet Data Convergence Protocol (PDCP) duplication, where the same PDCP packet is transmitted on multiple sidelink carriers. For example, as Figure 5 shown, the UE 502 uses the aggregation of three sidelink carriers (i.e., carrier 1, carrier 2, and carrier 3) to transmit data (e.g., transport blocks). The first sidelink communication can support the second mode described above. For example, the first sidelink communication can be an NR sidelink communication. The UE 502 can transmit the same PDCP packet or transport block on each of the three carriers to improve reliability.

[0041] The UE 502 can select or reselect the three sidelink carriers for transmission based on the measured Channel Busy Ratio (CBR) of each sidelink carrier. For example, if the measured CBR of each sidelink carrier among multiple sidelink carriers is below the CBR threshold, the UE 502 can consider the multiple sidelink carriers as candidate sidelink carriers. The CBR threshold can be configured by a network node or pre-configured at the UE 502. The CBR threshold can be associated with the priority of sidelink transmission. The UE 502 can select three sidelink carriers among the multiple candidate sidelink carriers in ascending order of CBR starting from the lowest CBR. The UE 502 can determine the number of sidelink carriers to be aggregated (e.g., three) based on UE capabilities. The UE 502 can independently select resources on each sidelink carrier based on a sensing and resource selection process. The UE 502 can use the selected sidelink carriers at least until a carrier reselection is triggered.

[0042] Unicast or multicast is typically associated with ACK / NACK feedback. For example, a transmitting UE that transmits data via unicast or multicast option 2 typically involves ACK feedback from one or more receiving UEs, and a transmitting UE that transmits data via multicast option 1 typically involves NACK feedback. If the transmitting UE does not receive ACK or NACK feedback from the one or more receiving UEs, the transmitting UE retransmits the same data to the one or more receiving UEs until the transmitting UE receives ACK / NACK feedback, even if the communication on at least one of these sidelink carriers is successful. For example, as Figure 5 shown, carrier 1 is used for unicast, and UE 502 receives an ACK after the first retransmission, which indicates that the communication on at least carrier 1 is successful. However, UE 502 keeps performing retransmissions on carrier 2 and carrier 3 (the retransmissions on carrier 2 and carrier 3 occur after the ACK on carrier 1 is received) until UE 502 receives an ACK or does not receive a NACK on carrier 2 and carrier 3. This results in unnecessary transmissions or retransmissions and thus reduces the spectral efficiency. At least some embodiments of the present disclosure address the above problems in sidelink carrier aggregation for unicast and multicast.

[0043] Figure 6 is a schematic diagram showing another exemplary process for sidelink carrier aggregation in accordance with some embodiments of the present disclosure. Referring to Figure 6 , the UE 602 in the first sidelink communication uses carrier aggregation to achieve high throughput and / or improved reliability. The UE 602 can be a Tx UE in the first sidelink communication. Similar to Figure 5 the UE 502, the UE 602 uses the aggregation of three sidelink carriers (i.e., carrier 1, carrier 2, and carrier 3) to transmit a transport block. The UE can select carrier 1 to carrier 3 based on the process described with respect to Figure 5 . For the sake of brevity, the process of carrier selection is omitted here. The first sidelink communication can support the second mode described above. For example, the first sidelink communication can be an NR sidelink communication. The UE can transmit the same transport block on each of the three sidelink carriers to improve reliability.

[0044] Instead of continuously transmitting or retransmitting the same transport block (which is the case in Figure 5 ), in Figure 6In [the above example], if UE 602 determines that the communication on at least one of the three sidelink carriers is successful, UE 602 may cancel the remaining transmissions or retransmissions on all sidelink carriers for the same transport block. To this end, UE 602 may use MAC layer packet duplication instead of PDCP packet duplication, so that the MAC layer knows that the packets transmitted on multiple sidelink carriers include the same TB. For example, as Figure 6 shown, carrier 3 is used for unicast, and the UE receives an ACK after the initial transmission, which indicates that the communication on at least carrier 3 is successful. In this case, UE cancels the initial transmission on carrier 2 and all retransmissions on carriers 1 to 3.

[0045] In this way, the disclosed method can minimize unnecessary transmissions and / or retransmissions, and thus improve the spectral efficiency in sidelink carrier aggregation for unicast and multicast.

[0046] Although the above examples in this disclosure relate to the aggregation of three sidelink carriers, the application of the disclosed method is not limited thereto. Depending on UE capabilities, the number of aggregated carriers can be any number. The method described in this disclosure can be applied to any sidelink communication (or radio access technology (RAT)), for example, future generation (sixth generation (6G), seventh generation (7G), or any future generation) sidelink communication. The method described in this disclosure can also be applied to other systems, such as carrier aggregation in systems compliant with IEEE standards.

[0047] Figure 7 is a flowchart of a method 700 for sidelink carrier aggregation according to some embodiments of this disclosure. Method 700 may be executed by a UE in sidelink communication, such as Figure 6 UE 602.

[0048] Method 700 includes: step 702, a first UE transmits one or more packets on one or more of a plurality of carriers to be used for sidelink carrier aggregation. For example, the first UE (such as Figure 6 UE 602) may transmit one or more packets on one or more of the plurality of carriers. The plurality of carriers form a carrier aggregation. In some embodiments, the first UE may transmit the same one or more packets 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 in the MAC layer. The plurality of carriers may be a plurality of carriers for the same RAT or a plurality of carriers for different RATs.

[0049] In some embodiments, the first UE may select one or more of the plurality of carriers on which to transmit the one or more packets. The first UE may select one or more of the plurality of carriers on which to transmit the one or more packets based on at least one of the following: (a) the priority of each of the one or more carriers; (b) the traffic load of each of the one or more carriers; or (c) the number of unsuccessful receptions in X time 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 pre-configured at the first UE.

[0050] In some embodiments, the first UE may also adjust the number of the selected one or more carriers of the plurality of carriers on which to transmit the one or more packets. For example, the first UE may dynamically adjust the number of the selected one or more carriers of the plurality of carriers on which to transmit the one or more packets based on whether a metric calculated according to the CBR associated with a candidate carrier of the plurality of carriers is greater than a first threshold. The first threshold may be configured by a network node or pre-configured at the first UE. As another example, the first UE may dynamically adjust the number of the selected one or more carriers of the plurality of carriers on which to transmit the one or more packets based on whether the number of unsuccessful receptions on the one or more carriers is greater than a second threshold. The second threshold may be configured by a network node or pre-configured at the first UE. The second threshold may be a function of the CBR associated with each of the one or more carriers and the priority of each of the one or more carriers. The metric calculated according to the CBR associated with a candidate carrier may include at least one of the following: the maximum value of the CBR of the candidate carrier, the minimum value of the CBR of the candidate carrier, the average value of the CBR of the candidate carrier, or the median value of the CBR of the candidate carrier.

[0051] In some embodiments, the first UE may also exclude at least one carrier from the candidate carriers in response to determining that the number of unsuccessful receptions in X time slots on each of the one or more carriers is greater than a threshold. The threshold may be configured by a network node or pre-configured at the first UE.

[0052] Method 700 includes: step 704, where a first UE determines at least one of the following: receiving an ACK from each of one or more target recipient UEs, or not receiving a NACK on at least one of the one or more carriers among the multiple carriers. The ACK and NACK can be HARQ feedback signals. The ACK or NACK can be received by the first UE on the PSFCH. In some embodiments, the first UE may determine at least one of the following: receiving an ACK from each of one or more target recipient UEs at one or more HARQ feedback opportunities or before the sidelink timer expires, or not receiving a NACK on at least one of the one or more carriers among the multiple carriers. The sidelink timer can be configured by a network node or pre-configured at the first UE.

[0053] Method 700 includes: step 706, where the first UE cancels one or more remaining transmissions or retransmissions of one or more packets scheduled on the one or more carriers among the multiple carriers in response to the determination of at least one of the following: receiving an ACK from at least one of the one or more target recipient UEs, or not receiving a NACK on the at least one of the one or more carriers among the multiple carriers. In some embodiments, the first UE may cancel one or more remaining transmissions or retransmissions of one or more packets on the one or more carriers among the multiple carriers in response to determining that an ACK is received from each of the one or more target recipient UEs on one or more specific carriers among the multiple carriers. The one or more specific carriers can be configured by a network node or pre-configured at the first UE.

[0054] In some embodiments, the first UE may cancel one or more remaining transmissions or retransmissions of one or more packets on the one or more carriers among the multiple carriers in response to determining that a NACK is not received on one or more specific carriers among the multiple carriers. The one or more specific carriers can be configured by a network node or pre-configured at the first UE.

[0055] In some embodiments, the first UE may cancel one or more remaining transmissions or retransmissions of one or more packets on one or more of the plurality of carriers in response to (a) determining that an ACK is received from each of one or more target recipient UEs on one or more specific carriers among the plurality of carriers, or (b) determining that a NACK is not received on one or more specific carriers among the plurality of carriers. The one or more specific carriers may be configured by a network node or pre-configured at the first UE. The first UE may select the one or more specific carriers based on at least one of the following: (a) the highest CBR level associated with one or more of the plurality of carriers; (b) the highest sidelink reference signal received power (RSRP) level associated with one or more of the plurality of carriers; or (c) a pre-selected, configured, or pre-configured anchor carrier.

[0056] In some embodiments, the first UE may cancel one or more remaining transmissions or retransmissions of one or more packets on one or more of the first carriers among the plurality of carriers in response to determining that an ACK is received or a NACK is not received from at least one of the one or more target recipient UEs on one or more second carriers different from one or more of the first carriers among the plurality of carriers. The one or more second carriers may be configured by the network or pre-configured at the first UE. In some embodiments, the first UE may cancel one or more remaining transmissions or retransmissions of one or more packets on one or more of the first carriers among the plurality of carriers in response to determining that a NACK is not received on one or more of the second carriers different from one or more of the first carriers among the plurality of carriers.

[0057] In some embodiments, the first UE may cancel one or more remaining transmissions or retransmissions of one or more packets on one or more of the plurality of carriers in response to determining that an ACK is received from at least one specific target recipient UE among the one or more target recipient UEs. The at least one specific target recipient UE may be configured by a network node or pre-configured at the first UE.

[0058] In some embodiments, the first UE may cancel one or more remaining transmissions or retransmissions of the one or more packets on one or more of the plurality of carriers in response to determining that ACKs have been received from a specific number of UEs among the one or more target recipient UEs. The specific number may be configured by a network node or preconfigured at the first UE. In some embodiments, the first UE may cancel one or more remaining transmissions or retransmissions of the one or more packets on one or more of the plurality of carriers in response to determining that a certain amount of NACKs have been received on at least one of the plurality of carriers. The amount may be configured by a network node or preconfigured at the first UE.

[0059] In some embodiments, the first UE may cancel one or more remaining transmissions or retransmissions of the one or more packets on one or more of the plurality of carriers in response to: (a) determining that ACKs have been received from each of the one or more target recipient UEs; or (b) determining that no NACKs have been received on one or more of the plurality of carriers.

[0060] In some embodiments, the first UE may utilize the resources associated with the cancelled transmission or retransmission for other purposes. For example, the first UE may use the resources associated with the one or more remaining transmissions or retransmissions of the packet that were cancelled to schedule the transmission of one or more other packets to one or more other target recipient UEs.

[0061] In some embodiments, the first UE, in response to determining that ACKs have been received or no NACKs have been received from a first number of target recipient UEs among the one or more target recipient UEs, does not reserve resources for one or more retransmissions of the one or more packets on one or more of the plurality of carriers. The first number may be greater than a threshold number. The threshold number may be configured by a network node or preconfigured at the first UE. The threshold number may be a function of the priority of each of the one or more carriers, or a function of the CBR associated with each of the one or more carriers. The threshold number may also be a function of the CBR associated with each of the one or more carriers and the priority of each of the one or more carriers.

[0062] In some embodiments, the first UE may dynamically switch between multicast and unicast based on the number of unsuccessful receptions among the one or more target recipient UEs on the one or more carriers among the plurality of carriers. For example, when the first UE performs multicast, the first UE may switch from multicast to unicast in response to determining that the number of unsuccessful receptions among the one or more target recipient UEs is less than a threshold. The threshold may be configured by a network node or pre-configured at the first UE. The first UE may also perform link adaptation for each of the one or more unicast links. For example, the first UE may perform MCS adjustment on the one or more unicast links. The first UE may also apply different Block Error Rate (BLER) targets for each of the one or more unicast links for packet duplication or for transport block transmission. The first UE may also cancel the one or more remaining transmissions or retransmissions for a packet in response to determining that a number of NACKs corresponds to a BLER higher than the initial BLER target of a carrier.

[0063] In some embodiments, the one or more carriers among the plurality of carriers may be a first set of carriers for (one or more) packet transmissions enabled with HARQ feedback. In this case, the first UE may use a second set of carriers among the plurality of carriers to perform one or more blind retransmissions of the one or more packets. The second set of carriers may be different from the first set of carriers. The first UE may also stop the one or more blind retransmissions in response to determining that an ACK is received on at least one of the carriers in the first set of carriers. The first UE may perform (one or more) packet transmissions using the first set of carriers and the one or more blind retransmissions using the second set of carriers on the PSSCH.

[0064] In some embodiments, the one or more carriers among the plurality of carriers may be licensed carriers for (one or more) packet transmissions enabled with HARQ feedback. In this case, the first UE may use one or more unlicensed carriers to perform one or more blind retransmissions of the one or more packets. The first UE may also stop the one or more blind retransmissions in response to determining that an ACK is received on at least one of the licensed carriers. The first UE may perform (one or more) packet transmissions on the licensed carriers and the one or more blind retransmissions on the one or more unlicensed carriers on the PSSCH.

[0065] In some embodiments, a first UE may transmit one or more indications regarding cancellation of one or more resource reservations that have been indicated on one or more of the plurality of carriers. The first UE may transmit the one or more indications on at least one of the following: PSCCH, PSSCH, PSFCH, MAC CE, or a higher layer such as a network layer or a transport layer or an application layer.

[0066] Figure 8 A block diagram of a UE 800 in accordance with some embodiments of the present disclosure is shown. The UE 800 may support the first mode and / or the second mode described above. The UE 800 may be installed in a mobile vehicle or in a fixed location. The UE 800 may take any form, including but not limited to, a vehicle, a component installed in a vehicle, a roadside unit, a laptop computer, a wireless terminal including a cellular phone, a wireless handheld device, or a wireless personal device, or any other form. Referring to Figure 8 , the UE 800 may include an antenna 802 that may be used to transmit electromagnetic signals to or receive electromagnetic signals from a base station or other UE. The antenna 802 may include one or more antenna elements and may enable different input / output antenna configurations, e.g., 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 plurality (e.g., dozens or hundreds) of antenna elements and may enable multi-antenna functions such as beamforming. In some embodiments, the antenna 802 is a single antenna.

[0067] The UE 800 may include a transceiver 804 coupled to the antenna 802. The transceiver 804 may be a wireless transceiver at the UE 800 and may communicate bidirectionally with a base station or other UE. For example, the transceiver 804 may receive / transmit wireless signals from / to a base station via downlink / uplink communication. The transceiver 804 may also receive / transmit wireless signals from / to other UE or roadside unit via sidelink communication. The transceiver 804 may include a modem that is used to modulate packets and provide the modulated packets to the antenna 802 for transmission, and to demodulate packets received from the antenna 802.

[0068] The UE 800 may include a 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 or special-purpose computer. Examples of non-transitory storage media include, but are not limited to, portable computer floppy disks, hard disks, random access memory (RAM), erasable programmable read-only memory (EPROM), read-only memory (ROM), electrically erasable programmable ROM (EEPROM), digital versatile disk (DVD), flash memory, compact disk (CD) ROM, or other optical disk storage, magnetic disk storage, or other magnetic storage devices, etc. Non-transitory media 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 or special-purpose computer, or a general or special-purpose processor. In some examples, software / program code may be transmitted from a remote source (e.g., a website, a server, etc.) using coaxial cables, fiber optic cables, twisted pairs, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave. In such examples, coaxial cables, fiber optic cables, twisted pairs, DSL, or wireless technologies such as infrared, radio, and microwave are within the scope defined by the medium. Combinations of the above examples are also within the scope of computer-readable media.

[0069] The memory 806 may store information related to the identification of the UE 800 and the signals and / or data received by the antenna 802. The memory 806 may also store post-processed signals and / or data. The memory 806 may also store computer-readable program instructions, mathematical models, and algorithms used in signal processing in the receiver 804 and calculations in the processor 808. The memory 806 may also store computer-readable program instructions for execution by the processor 808 to operate the UE 800 to perform the various functions described in this disclosure. In some examples, the memory 806 may include a Basic Input / Output System (BIOS) that may control basic hardware or software operations, such as interactions 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 the NR sidelink module. In some embodiments, the memory 806 includes only the LTE sidelink module.

[0070] The computer-readable program instructions of this disclosure may be assembly instructions, Instruction-Set-Architecture (ISA) instructions, machine instructions, machine-related instructions, microcode, firmware instructions, state-setting data, or source code or object code written in any combination of one or more programming languages, including object-oriented programming languages and traditional procedural programming languages. The computer-readable program instructions may be executed entirely on a computing device as a stand-alone software package, or partially on a first computing device and partially on a second computing device remote from the first computing device. In the latter scenario, the remote second 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).

[0071] The UE 800 may include a processor 808, which may include a hardware device with 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, discrete gate or transistor logic components, discrete hardware components, or other programmable logic devices. Examples of general-purpose processors include, but are not limited to, microprocessors, any conventional processor, a controller, a microcontroller, or a 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 combination with a DSP core, or any other such configuration). The processor 808 may receive a downlink signal or a sidelink signal from the transceiver 804 and further process the signal. The processor 808 may also receive data packets from the transceiver 804 and further process these 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., the memory 806) to cause the UE 800 to perform various functions.

[0072] The UE 800 may include a global positioning system (GPS) 810. The GPS 810 may be used to enable location-based services or other services based on the geographical location of the UE 800, and / or synchronization between UEs. The GPS 810 may receive global navigation satellite system (GNSS) signals from a single satellite or multiple satellite signals via the antenna 802 and provide the geographical location of the UE 800 (e.g., the coordinates of the UE 800). In some embodiments, the UE 800 does not include the GPS 810.

[0073] The UE 800 may include an Input / Output (I / O) device 812, which may be used to communicate the results of signal processing and computing to the user or other devices. The I / O device 812 may include a user interface, which includes a display and an input device for transmitting user commands to the processor 808. The display may be configured to display the status of signal reception at the UE 800, the data stored at the memory 806, the status of signal processing, and the results of computing, etc. 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 plasma gas display, a touch screen, or other image projection devices for displaying information to the user. The input device may be any type of computer hardware device for receiving data and control signals from the user. The input device may include, but is not limited to, a keyboard, a mouse, a scanner, a digital camera, a joystick, a trackball, cursor direction keys, a touch screen monitor, or an audio / video commander, etc.

[0074] The UE 800 may further include a machine interface 814, such as an electrical bus connecting the transceiver 804, the memory 806, the processor 808, the GPS 810, and the I / O device 812.

[0075] In some embodiments, the UE 800 may be configured or programmed to perform carrier aggregation in sidelink communication. The processor 808 may be configured or programmed to execute the instructions stored in the memory 806 to: transmit one or more packets on one or more of a plurality of carriers to be used for sidelink carrier aggregation; determine at least one of the following: receive an ACK from each of one or more target receiving UEs, or not receive a NACK on at least one of the one or more carriers among the plurality of carriers; and in response to the determination of at least one of the following, cancel one or more remaining transmissions or retransmissions of the one or more packets scheduled on the one or more carriers among the plurality of carriers: receive an ACK from at least one of the one or more target receiving UEs, or not receive a NACK on the at least one of the one or more carriers among the plurality of carriers.

[0076] As used in this disclosure, the use of the term "or" in a list of items indicates an inclusive list. The list of items may be prefaced with phrases such as "at least one" or "one or more". 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). Further, as used in this disclosure, prefacing a list of conditions with the phrase "based on" should not be construed as "based solely on" the set of conditions, but rather should be construed as "based at least in part on" the set of conditions. For example, a result described as "based on condition A" may be based on both condition A and condition B without departing from the scope of this disclosure.

[0077] In this specification, the terms "comprise", "contain" or "include" may be used interchangeably and have the same meaning, and are construed as inclusive and open-ended. The terms "comprise", "contain" or "include" may be used before a list of elements and indicate that at least all of the listed elements within the list are present, but other elements not in the list may also be present. For example, if A comprises B and C, then {B, C} and {B, C, D} are both within the scope of A.

[0078] In conjunction with the accompanying drawings, this disclosure describes example configurations that do not represent all examples that can be implemented or all configurations within the scope of this disclosure. The term "exemplary" should not be construed as "preferred" or "advantageous compared to other examples", but rather should be construed as "illustrative, instance or example". By reading this disclosure, including the description of the embodiments and the drawings, those of ordinary skill in the art will understand that alternative embodiments can be used to implement the technologies disclosed herein. Those skilled in the art will appreciate that the embodiments described herein or certain features of the embodiments can be combined to obtain other embodiments for practicing the technologies described in this disclosure. Therefore, this disclosure is not limited to the examples and designs described herein, but rather should be accorded the broadest scope consistent with the principles and novel features disclosed herein.

[0079] The flowcharts and block diagrams in the figures illustrate examples of the 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 marked in the blocks may occur out of the order marked in the figures. For example, depending on the functions involved, two consecutive blocks shown may actually be executed substantially simultaneously, or these blocks may sometimes be executed in the reverse order. Similarly, in methods consistent with various embodiments, such methods may include additional steps, and certain steps may be omitted or combined.

[0080] It should be understood that the described embodiments are not mutually exclusive, and elements, components, materials, or steps described in connection with one exemplary embodiment can be combined with other embodiments in a suitable manner or eliminated from other embodiments to achieve the desired design objective.

[0081] References herein to "some embodiments" or "some exemplary embodiments" mean that the particular features, structures, or characteristics described in connection with the embodiments can be included in at least one embodiment. The appearances of the phrases "one embodiment", "some embodiments", or "another embodiment" throughout this disclosure are not necessarily all referring to the same embodiment, nor are they necessarily separate or alternative embodiments that are mutually exclusive of other embodiments.

[0082] Furthermore, the articles "a" and "an" used in this disclosure and the appended claims should generally be construed to mean "one or more", unless otherwise specified or clearly indicated to be in the singular form according to the context.

[0083] Unless otherwise clearly stated, each numerical value and range should be interpreted as approximate, just as if the word "about" or "substantially" had preceded the value of the numerical value or range.

[0084] Although the elements (if any) in the following method claims are recited in a particular order, these elements are not necessarily intended to be implemented in that particular order unless the claim recitation otherwise implies a particular order for implementing some or all of these elements.

[0085] It should be understood that certain features of the present disclosure described in the context of separate embodiments for clarity can also be provided in combination in a single embodiment. Conversely, the various features described in the context of a single embodiment for brevity can also be provided separately, or in any suitable sub-combination, or appropriately in any other described embodiment of this specification. Certain features described in the context of various embodiments are not essential features of these embodiments unless otherwise stated.

[0086] It will be further understood that those skilled in the art can make various modifications, substitutions, and changes to the details, materials, and arrangements of the components described and illustrated for the purpose of explaining the nature of the described embodiments without departing from the scope. Accordingly, the appended claims cover all such substitutions, modifications, and changes that fall within the aspects of the claims.

[0087] Clause 1: A method for carrier aggregation in sidelink communication, the method comprising: Transmitting, by a first user equipment (UE), one or more packets on one or more carriers among a plurality of carriers to be used for sidelink carrier aggregation; The first UE determines at least one of the following: receiving an acknowledgement (ACK) from each of one or more target recipient UEs, or not receiving a negative acknowledgement (NACK) on at least one of the one or more carriers among the multiple carriers; and The first UE cancels one or more remaining transmissions or retransmissions of the one or more packets scheduled on the one or more carriers among the multiple carriers in response to the determination of at least one of the following: receiving the ACK from at least one of the one or more target recipient UEs, or not receiving the NACK on at least one of the one or more carriers among the multiple carriers.

[0088] Clause 2: The method according to clause 1, wherein the ACK and the NACK are hybrid automatic repeat request (HARQ) feedback signals.

[0089] Clause 3: The method according to clause 1, wherein the one or more packets are one or more transport blocks in a media access control (MAC) layer.

[0090] Clause 4: The method according to clause 1, wherein cancelling the one or more remaining transmissions or retransmissions of the one or more packets further comprises: The first UE cancels the one or more remaining transmissions or retransmissions of the one or more packets on the one or more carriers among the multiple carriers in response to determining that the ACK is received from each of the one or more target recipient UEs on one or more specific carriers among the multiple carriers, and the one or more specific carriers are configured or pre-configured.

[0091] Clause 5: The method according to clause 1, wherein cancelling the one or more remaining transmissions or retransmissions of the one or more packets further comprises: The first UE cancels the one or more remaining transmissions or retransmissions of the one or more packets on the one or more carriers among the multiple carriers in response to determining that the NACK is not received on one or more specific carriers among the multiple carriers, and the one or more specific carriers are configured or pre-configured.

[0092] Clause 6: The method according to clause 1, wherein cancelling the one or more remaining transmissions or retransmissions of the one or more packets further comprises: The first UE cancels the one or more remaining transmissions or retransmissions for the one or more packets on the one or more carriers in response to the following: (a) Determining that the ACK has been received from each of the one or more target recipient UEs on one or more specific carriers among the multiple carriers, where the one or more specific carriers are configured or pre-configured; or (b) Determining that the NACK has not been received on the one or more specific carriers among the multiple carriers.

[0093] Clause 7: The method according to Clause 6 further includes: The first UE selects the one or more specific carriers based on at least one of the following: (a) The highest channel busy ratio (CBR) level associated with one or more of the multiple carriers; (b) The highest sidelink reference signal received power (RSRP) level associated with one or more of the multiple carriers; or (c) A pre-selected or pre-configured anchor carrier.

[0094] Clause 8: The method according to Clause 1, wherein canceling the one or more remaining transmissions or retransmissions for the one or more packets further includes: The first UE cancels the one or more remaining transmissions or retransmissions for the one or more packets on one or more first carriers among the multiple carriers in response to the following: (a) Determining that the ACK has been received or the NACK has not been received from the at least one of the one or more target recipient UEs on one or more second carriers different from the one or more first carriers among the multiple carriers, where the one or more second carriers are configured or pre-configured; or (b) Determining that the NACK has not been received on the one or more second carriers different from the one or more first carriers among the multiple carriers.

[0095] Clause 9: The method according to Clause 1, wherein canceling the one or more remaining transmissions or retransmissions for the one or more packets further includes: The first UE cancels the one or more remaining transmissions or retransmissions of the one or more packets on the one or more carriers in response to determining that the ACK has been received from at least one specific target recipient UE among the one or more target recipient UEs, where the at least one specific target recipient UE is configured or preconfigured.

[0096] Clause 10: The method according to Clause 1, wherein canceling the one or more remaining transmissions or retransmissions of the one or more packets further comprises: The first UE cancels the one or more remaining transmissions or retransmissions of the one or more packets on the one or more carriers in response to: (a) determining that the ACK has been received from a specific number of UEs among the one or more target recipient UEs, where the specific number is configured or preconfigured; or (b) determining that a certain amount of the NACK has been received on at least one of the one or more carriers, where the amount is configured or preconfigured.

[0097] Clause 11: The method according to Clause 1, wherein canceling the one or more remaining transmissions or retransmissions of the one or more packets further comprises: The first UE cancels the one or more remaining transmissions or retransmissions of the one or more packets on the one or more carriers in response to: (a) determining that the ACK has been received from each target recipient UE among the one or more target recipient UEs; or (b) determining that the NACK has not been received on the one or more carriers.

[0098] Clause 12: The method according to Clause 1 further comprises: The first UE uses the resources associated with the one or more remaining transmissions or retransmissions of the one or more packets that are canceled to schedule the transmission of one or more other packets to one or more other target recipient UEs.

[0099] Clause 13: The method according to Clause 1, wherein canceling the one or more remaining transmissions or retransmissions of the one or more packets further comprises: In response to determining that the ACK has been received or the NACK has not been received from a first number of target recipient UEs among the one or more target recipient UEs, without reserving resources for one or more retransmissions of the one or more packets on the one or more carriers among the plurality of carriers, the first number being greater than a threshold number, and the threshold number being configured or pre-configured.

[0100] Clause 14: The method according to clause 13, wherein the threshold number is a function of at least one of: the priority of each of the one or more carriers, or the CBR associated with each of the one or more carriers.

[0101] Clause 15: The method according to clause 1, further comprising: The first UE selects the one or more carriers among the plurality of carriers on which to transmit the one or more packets.

[0102] Clause 16: The method according to clause 15, wherein the one or more carriers among the plurality of carriers on which to transmit the one or more packets are selected based on at least one of: (a) the priority of each of the one or more carriers; (b) the traffic load of each of the one or more carriers; or (c) the number of unsuccessful receptions in X time slots on each of the one or more carriers, the X being configured or pre-configured, wherein the X is a natural number.

[0103] Clause 17: The method according to clause 16, further comprising: The first UE adjusts the number of the selected one or more carriers among the plurality of carriers on which to transmit the one or more packets.

[0104] Clause 18: The method according to clause 17, wherein the number of the selected one or more carriers among the plurality of carriers on which to transmit the one or more packets is dynamically adjusted based on at least one of: (a) whether a metric calculated according to the CBR associated with a candidate carrier among the plurality of carriers is greater than a first threshold, the first threshold being configured or pre-configured; or (b) whether the number of unsuccessful receptions on the one or more carriers is greater than a second threshold, the second threshold being configured or pre-configured.

[0105] Clause 19: The method according to Clause 18, wherein the metric calculated according to the CBR associated with the candidate carrier includes at least one of the following: the maximum value of the CBR of the candidate carrier, the minimum value of the CBR of the candidate carrier, the average value of the CBR of the candidate carrier, or the median of the CBR of the candidate carrier.

[0106] Clause 20: The method according to Clause 18, wherein the configured or pre-configured second threshold is a function of the priority of each of the one or more carriers and the CBR associated with each of the one or more carriers.

[0107] Clause 21: The method according to Clause 18, further comprising: The first UE excludes at least one carrier from the candidate carriers in response to determining that the number of unsuccessful receptions in the X time slots on each of the one or more carriers is greater than a threshold, where the threshold is configured or pre-configured.

[0108] Clause 22: The method according to Clause 1, further comprising: The first UE dynamically switches between multicast and unicast based on the number of unsuccessful receptions among the one or more target receiving UEs on the one or more carriers among the plurality of carriers.

[0109] Clause 23: The method according to Clause 22, wherein the first UE performs the multicast, and the method further comprises: Switching from the multicast to the unicast in response to determining that the number of unsuccessful receptions among the one or more target receiving UEs is less than a threshold; and Performing link adaptation for each of the one or more unicast links.

[0110] Clause 24: The method according to Clause 23, wherein performing the link adaptation for each of the one or more unicast links further comprises: Applying different block error ratio (BLER) targets for each of the one or more unicast links.

[0111] Clause 25: The method according to Clause 24, further comprising: Canceling the one or more remaining transmissions or retransmissions for the one or more packets in response to determining that a number of NACKs correspond to a BLER higher than the initial BLER target of the carrier.

[0112] Clause 26: The method according to Clause 1, wherein the ACK or the NACK is received by the first UE on a Physical Sidelink Feedback Channel (PSFCH).

[0113] Clause 27: The method according to Clause 2, wherein the one or more carriers among the plurality of carriers are a first set of carriers for the one or more packet transmissions for which HARQ feedback is enabled, and the method further comprises: performing one or more blind retransmissions of the one or more packets using a second set of carriers among the plurality of carriers, the second set of carriers being different from the first set of carriers; and stopping the one or more blind retransmissions in response to determining that the ACK is received on at least one of the carriers in the first set of carriers.

[0114] Clause 28: The method according to Clause 27, 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 on a Physical Sidelink Shared Channel (PSSCH).

[0115] Clause 29: The method according to Clause 2, wherein the one or more carriers among the plurality of carriers are licensed carriers for the one or more packet transmissions for which HARQ feedback is enabled, and the method further comprises: performing one or more blind retransmissions of the one or more packets using one or more unlicensed carriers; and stopping the one or more blind retransmissions in response to determining that the ACK is received on at least one of the licensed carriers.

[0116] Clause 30: The method according to Clause 29, wherein the one or more packet transmissions on the licensed carriers and the one or more blind retransmissions on the one or more unlicensed carriers are performed on the PSSCH.

[0117] Clause 31: The method according to Clause 1, wherein canceling the one or more remaining transmissions or retransmissions for the one or more packets further comprises: transmitting one or more indications of cancellation of one or more resource reservations indicated on the one or more carriers among the plurality of carriers, wherein the one or more indications are transmitted on at least one of the following: Physical Sidelink Control Channel (PSCCH), Physical Sidelink Shared Channel (PSSCH), Physical Sidelink Feedback Channel (PSFCH), Medium Access Control (MAC) Control Element (CE), or higher layer.

[0118] Clause 32: The method according to Clause 29, wherein determining at least one of the following: receiving an ACK from each of one or more target recipient UEs, or not receiving a NACK on at least one of the one or more carriers among the plurality of carriers, further includes: The first UE determines at least one of the following: receiving an ACK from each of one or more target recipient UEs before a sidelink timer expires, or not receiving a NACK on at least one of the one or more carriers among the plurality of carriers.

[0119] Clause 33: A first user equipment (UE) for sidelink communication, the first UE comprising: a memory that stores instructions; and a processor configured to execute the instructions stored in the memory to: transmit one or more packets on one or more carriers among a plurality of carriers to be used for sidelink carrier aggregation; determine at least one of the following: receiving an acknowledgment (ACK) from each of one or more target recipient UEs, or not receiving a negative acknowledgment (NACK) on at least one of the one or more carriers among the plurality of carriers; and in response to determining at least one of the following, canceling one or more remaining transmissions or retransmissions of the one or more packets scheduled on the one or more carriers among the plurality of carriers: receiving the ACK from at least one of the one or more target recipient UEs, or not receiving the NACK on at least one of the one or more carriers among the plurality of carriers.

[0120] Clause 34: The first UE according to Clause 33, wherein the ACK and the NACK are hybrid automatic repeat request (HARQ) feedback signals.

[0121] Clause 35: The first UE according to Clause 33, wherein the one or more packets are one or more transport blocks in a media access control (MAC) layer.

[0122] Clause 36: The first UE according to Clause 33, wherein in canceling the one or more remaining transmissions or retransmissions of the one or more packets, the processor is further configured to execute the instructions stored in the memory to: In response to determining that the ACK has been received from each of the one or more target recipient UEs on one or more specific carriers among the multiple carriers, canceling the one or more remaining transmissions or retransmissions of the one or more packets on the one or more carriers among the multiple carriers, where the one or more specific carriers are configured or preconfigured.

[0123] Clause 37: The first UE according to Clause 33, wherein, in canceling the one or more remaining transmissions or retransmissions of the one or more packets, the processor is further configured to execute the instructions stored in the memory to: In response to determining that the NACK has not been received on one or more specific carriers among the multiple carriers, canceling the one or more remaining transmissions or retransmissions of the one or more packets on the one or more carriers among the multiple carriers, where the one or more specific carriers are configured or preconfigured.

[0124] Clause 38: The first UE according to Clause 33, wherein, in canceling the one or more remaining transmissions or retransmissions of the one or more packets, the processor is further configured to execute the instructions stored in the memory to: In response to the following, canceling the one or more remaining transmissions or retransmissions of the one or more packets on the one or more carriers among the multiple carriers: (a) Determining that the ACK has been received from each of the one or more target recipient UEs on one or more specific carriers among the multiple carriers, where the one or more specific carriers are configured or preconfigured; or (b) Determining that the NACK has not been received on the one or more specific carriers among the multiple carriers.

[0125] Clause 39: The first UE according to Clause 38, wherein the processor is further configured to execute the instructions stored in the memory to: Select the one or more specific carriers based on at least one of the following: (a) The highest channel busy ratio (CBR) level associated with the one or more carriers among the multiple carriers; (b) The highest sidelink reference signal received power (RSRP) level associated with the one or more carriers among the multiple carriers; or (c) A preselected or preconfigured anchor carrier.

[0126] Clause 40: The first UE according to Clause 33, wherein, in canceling the one or more remaining transmissions or retransmissions for the one or more packets, the processor is further configured to execute instructions stored in the memory to: Cancel the one or more remaining transmissions or retransmissions for the one or more packets on one or more first carriers among the plurality of carriers in response to: (a) Determining that the ACK is received or the NACK is not received from at least one of the one or more target recipient UEs on one or more second carriers different from the one or more first carriers among the plurality of carriers, the one or more second carriers being configured or pre-configured; or (b) Determining that the NACK is not received on the one or more second carriers different from the one or more first carriers among the plurality of carriers.

[0127] Clause 41: The first UE according to Clause 33, wherein, in canceling the one or more remaining transmissions or retransmissions for the one or more packets, the processor is further configured to execute instructions stored in the memory to: Cancel the one or more remaining transmissions or retransmissions for the one or more packets on the one or more carriers among the plurality of carriers in response to determining that the ACK is received from at least one specific target recipient UE among the one or more target recipient UEs, the at least one specific target recipient UE being configured or pre-configured.

[0128] Clause 42: The first UE according to Clause 33, wherein, in canceling the one or more remaining transmissions or retransmissions for the one or more packets, the processor is further configured to execute instructions stored in the memory to: Cancel the one or more remaining transmissions or retransmissions for the one or more packets on the one or more carriers among the plurality of carriers in response to: (a) Determining that the ACK is received from a specific number of UEs among the one or more target recipient UEs, the specific number being configured or pre-configured; or (b) Determining that a certain amount of the NACK is received on at least one of the plurality of carriers, the amount being configured or pre-configured.

[0129] Clause 43: The first UE according to Clause 33, wherein, in canceling the one or more remaining transmissions or retransmissions for the one or more packets, the processor is further configured to execute instructions stored in the memory to: In response to the following, canceling one or more remaining transmissions or retransmissions of the one or more packets on the one or more carriers among the plurality of carriers: (a) Determining that the ACK has been received from each of the one or more target recipient UEs; or (b) Determining that the NACK has not been received on the one or more carriers among the plurality of carriers.

[0130] Clause 44: The first UE according to Clause 33, wherein the processor is further configured to execute instructions stored in the memory to: Use resources associated with the one or more remaining transmissions or retransmissions of the one or more packets that are canceled to schedule the transmission of one or more other packets to one or more other target recipient UEs.

[0131] Clause 45: The first UE according to Clause 33, wherein in canceling the one or more remaining transmissions or retransmissions of the one or more packets, the processor is further configured to execute instructions stored in the memory to: In response to determining that the ACK has been received or the NACK has not been received from a first number of target recipient UEs among the one or more target recipient UEs, not reserve resources for the one or more retransmissions of the one or more packets on the one or more carriers among the plurality of carriers, the first number being greater than a threshold number, and the threshold number being configured or preconfigured.

[0132] Clause 46: The first UE according to Clause 45, wherein the threshold number is a function of at least one of the following: the priority of each of the one or more carriers, or the CBR associated with each of the one or more carriers.

[0133] Clause 47: The first UE according to Clause 33, wherein the processor is further configured to execute instructions stored in the memory to: Select the one or more carriers among the plurality of carriers on which to transmit the one or more packets.

[0134] Clause 48: The first UE according to Clause 47, wherein the one or more carriers among the plurality of carriers on which to transmit the one or more packets are selected based on at least one of the following: (a) The priority of each of the one or more carriers; (b) The traffic load of each of the one or more carriers; or (c) The number of unsuccessful receptions in X time slots on each of the one or more carriers, where X is configured or pre-configured, and where X is a natural number. Clause 49: The first UE according to Clause 48, wherein the processor is further configured to execute instructions stored in the memory to: Adjust the number of the one or more selected carriers among the plurality of carriers on which the one or more packets are to be transmitted.

[0135] Clause 50: The first UE according to Clause 49, wherein the number of the one or more selected carriers among the plurality of carriers on which the one or more packets are to be transmitted is dynamically adjusted based on at least one of the following: (a) Whether a metric calculated based on the CBR associated with a candidate carrier among the plurality of carriers is greater than a first threshold, where the first threshold is configured or pre-configured; or (b) Whether the number of unsuccessful receptions on the one or more carriers is greater than a second threshold, where the second threshold is configured or pre-configured.

[0136] Clause 51: The first UE according to Clause 50, wherein the metric calculated based on the CBR associated with the candidate carrier includes at least one of the following: the maximum value of the CBR of the candidate carrier, the minimum value of the CBR of the candidate carrier, the average value of the CBR of the candidate carrier, or the median value of the CBR of the candidate carrier.

[0137] Clause 52: The first UE according to Clause 50, wherein the configured or pre-configured second threshold is a function of the priority of each of the one or more carriers and the CBR associated with each of the one or more carriers.

[0138] Clause 53: The first UE according to Clause 50, wherein the processor is further configured to execute instructions stored in the memory to: In response to determining that the number of unsuccessful receptions in the X time slots on each of the one or more carriers is greater than a threshold, exclude at least one carrier from the candidate carriers, where the threshold is configured or pre-configured.

[0139] Clause 54: The first UE according to Clause 33, wherein the processor is further configured to execute instructions stored in the memory to: Dynamically switch between multicast and unicast based on the number of unsuccessful receptions among the one or more target receiving UEs on the one or more carriers among the plurality of carriers.

[0140] Clause 55: The first UE according to Clause 54, wherein the first UE performs the multicast, and the processor is further configured to execute instructions stored in the memory to: In response to determining that the number of unsuccessful receptions among the one or more target recipient UEs is less than a threshold, switch from the multicast to the unicast; and Perform link adaptation for each unicast link among the one or more unicast links.

[0141] Clause 56: The first UE according to Clause 55, wherein, in performing the link adaptation for each unicast link among the one or more unicast links, the processor is further configured to execute instructions stored in the memory to: Apply different block error ratio (BLER) targets for each unicast link among the one or more unicast links.

[0142] Clause 57: The first UE according to Clause 56, wherein the processor is further configured to execute instructions stored in the memory to: In response to determining that a number of NACKs correspond to a BLER higher than an initial BLER target of a carrier, cancel the one or more remaining transmissions or retransmissions for the one or more packets.

[0143] Clause 58: The first UE according to Clause 33, wherein the ACK or the NACK is received by the first UE on a physical sidelink feedback channel (PSFCH).

[0144] Clause 59: The first UE according to Clause 34, wherein one or more of the plurality of carriers are a first set of carriers for one or more packet transmissions with HARQ feedback enabled, and the processor is further configured to execute instructions stored in the memory to: Perform one or more blind retransmissions of the one or more packets using a second set of carriers among the plurality of carriers, the second set of carriers being different from the first set of carriers; and In response to determining that the ACK is received on at least one of the carriers in the first set of carriers, stop the one or more blind retransmissions.

[0145] Clause 60: The first UE according to Clause 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 on a physical sidelink shared channel (PSSCH).

[0146] Clause 61: The first UE according to Clause 34, wherein one or more of the plurality of carriers are licensed carriers for one or more packet transmissions for which HARQ feedback is enabled, and the processor is further configured to execute instructions stored in the memory to: perform one or more blind retransmissions of the one or more packets using one or more unlicensed carriers; and stop the one or more blind retransmissions in response to determining that the ACK has been received on at least one of the licensed carriers.

[0147] Clause 62: The first UE according to Clause 61, wherein the one or more packet transmissions on the licensed carriers and the one or more blind retransmissions on the one or more unlicensed carriers are performed on the PSSCH.

[0148] Clause 63: The first UE according to Clause 33, wherein in canceling one or more remaining transmissions or retransmissions for the one or more packets, the processor is further configured to execute instructions stored in the memory to: transmit one or more indications of cancellation of one or more resource reservations indicated on one or more of the plurality of carriers, wherein the one or more indications are transmitted on at least one of the following: Physical Sidelink Control Channel (PSCCH), Physical Sidelink Shared Channel (PSSCH), Physical Sidelink Feedback Channel (PSFCH), Medium Access Control (MAC) Control Element (CE), or higher layers.

[0149] Clause 64: The first UE according to Clause 33, wherein in determining at least one of the following: receiving an ACK from each of one or more target recipient UEs, or not receiving a NACK on at least one of the one or more of the plurality of carriers, the processor is further configured to execute instructions stored in the memory to: determine at least one of the following: receiving an ACK from each of one or more target recipient UEs before a sidelink timer expires, or not receiving a NACK on at least one of the one or more of the plurality of carriers.

[0150] Clause 65: A non-transitory computer-readable medium storing instructions executable by one or more processors of a first user equipment (UE) for sidelink communication to perform a method, the method comprising: Transmit, by the first UE, one or more packets on one or more of a plurality of carriers to be used for sidelink carrier aggregation; Determine, by the first UE, at least one of the following: 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 Cancel, by the first UE, in response to determination of at least one of the following, one or more remaining transmissions or retransmissions of the one or more packets scheduled on the one or more carriers of the plurality of carriers: 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.

Claims

1. A method for carrier aggregation in sidelink communication, the method comprising: transmitting, by a first user equipment (UE), one or more packets on one or more carriers among a plurality of carriers to be used for sidelink carrier aggregation; determining, by the first UE, at least one of the following: 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 among the plurality of carriers; and canceling, by the first UE, in response to the determination of at least one of the following, one or more remaining transmissions or retransmissions of the one or more packets scheduled on the one or more carriers among the plurality of carriers: 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 among the plurality of carriers.

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

3. The method according to claim 1, wherein the one or more packets are one or more transport blocks in a media access control (MAC) layer.

4. The method according to claim 1, wherein canceling the one or more remaining transmissions or retransmissions of the one or more packets further comprises: canceling, by the first UE, in response to determining that the ACK is received from each of the one or more target receiving UEs on one or more specific carriers among the plurality of carriers, the one or more remaining transmissions or retransmissions of the one or more packets on the one or more carriers among the plurality of carriers, the one or more specific carriers being configured or pre-configured.

5. The method according to claim 1, wherein canceling the one or more remaining transmissions or retransmissions of the one or more packets further comprises: canceling, by the first UE, in response to determining that the NACK is not received on one or more specific carriers among the plurality of carriers, the one or more remaining transmissions or retransmissions of the one or more packets on the one or more carriers among the plurality of carriers, the one or more specific carriers being configured or pre-configured.

6. The method according to claim 1, wherein canceling the one or more remaining transmissions or retransmissions of the one or more packets further comprises: canceling, by the first UE, in response to the following item, the one or more remaining transmissions or retransmissions of the one or more packets on the one or more carriers among the plurality of carriers: (a) determining that the ACK is received from each of the one or more target receiving UEs on one or more specific carriers among the plurality of carriers, the one or more specific carriers being configured or pre-configured; or (b) Determine that the NACK is not received on the one or more specific carriers among the multiple carriers.

7. The method according to claim 1, wherein, canceling the one or more remaining transmissions or retransmissions for the one or more packets further includes: the first UE cancels the one or more remaining transmissions or retransmissions for the one or more packets on one or more first carriers among the multiple carriers in response to: (a) determining that the ACK is received or the NACK is not received 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 among the multiple carriers, and the one or more second carriers are configured or preconfigured; or (b) determining that the NACK is not received on the one or more second carriers different from the one or more first carriers among the multiple carriers.

8. The method according to claim 1, wherein, canceling the one or more remaining transmissions or retransmissions for the one or more packets further includes: the first UE cancels the one or more remaining transmissions or retransmissions for the one or more packets on the one or more carriers among the multiple carriers in response to determining that the ACK is received from at least one specific target receiving UE among the one or more target receiving UEs, and the at least one specific target receiving UE is configured or preconfigured.

9. The method according to claim 1, wherein, canceling the one or more remaining transmissions or retransmissions for the one or more packets further includes: the first UE cancels the one or more remaining transmissions or retransmissions for the one or more packets on the one or more carriers among the multiple carriers in response to: (a) determining that the ACK is received from a specific number of UEs among the one or more target receiving UEs, and the specific number is configured or preconfigured; or (b) determining that a certain amount of the NACK is received on at least one of the multiple carriers, and the amount is configured or preconfigured.

10. The method according to claim 1, wherein, canceling the one or more remaining transmissions or retransmissions for the one or more packets further includes: the first UE cancels the one or more remaining transmissions or retransmissions for the one or more packets on the one or more carriers among the multiple carriers in response to: (a) determining that the ACK is received from each of the one or more target receiving UEs; or (b) determining that the NACK is not received on the one or more carriers among the multiple carriers.

11. The method according to claim 1, further includes: The first UE uses resources associated with the one or more remaining transmissions or retransmissions of the cancelled one or more packets to schedule the transmission of one or more other packets to one or more other target recipient UEs.

12. The method according to claim 1, wherein, cancelling the one or more remaining transmissions or retransmissions of the one or more packets further includes: in response to determining that an ACK has been received or an NACK has not been received from a first quantity of target recipient UEs among the one or more target recipient UEs, not reserving resources for the one or more retransmissions of the one or more packets on the one or more carriers among the plurality of carriers, the first quantity being greater than a threshold quantity, and the threshold quantity being configured or preconfigured.

13. The method according to claim 1, further including: the first UE selects the one or more carriers among the plurality of carriers on which to transmit the one or more packets.

14. The method according to claim 1, further including: the first UE dynamically switches between multicast and unicast based on the number of unsuccessful receptions among the one or more target recipient UEs on the one or more carriers among the plurality of carriers.

15. The method according to claim 1, wherein, the ACK or the NACK is received by the first UE on a Physical Sidelink Feedback Channel (PSFCH).

16. The method according to claim 1, wherein, cancelling the one or more remaining transmissions or retransmissions of the one or more packets further includes: transmitting one or more indications of cancellation of one or more resource reservations indicated on the one or more carriers among the plurality of carriers, wherein the one or more indications are transmitted on at least one of: Physical Sidelink Control Channel (PSCCH), Physical Sidelink Shared Channel (PSSCH), Physical Sidelink Feedback Channel (PSFCH), Medium Access Control (MAC) Control Element (CE), or higher layer.

17. A first User Equipment (UE) for sidelink communication, the first UE comprises: 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 among a plurality of carriers to be used for sidelink carrier aggregation; determine at least one of: receiving an acknowledgement (ACK) from each of one or more target recipient UEs, or not receiving a negative acknowledgement (NACK) on at least one of the one or more carriers among the plurality of carriers; and Canceling one or more remaining transmissions or retransmissions of the one or more packets scheduled on the one or more carriers among the plurality of carriers in response to a determination of at least one of: receiving the ACK from at least one of the one or more target recipient UEs, or not receiving the NACK on at least one of the one or more carriers among the plurality of carriers.

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

19. The first UE according to claim 17, wherein, the one or more packets are one or more transport blocks in the media access control (MAC) layer.

20. A non-transitory computer-readable medium storing instructions executable by one or more processors of a first user equipment (UE) for sidelink communication to perform a method, the method comprising: transmitting, by the first UE, one or more packets on one or more carriers among 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 among the plurality of carriers; and canceling, by the first UE, one or more remaining transmissions or retransmissions of the one or more packets scheduled on the one or more carriers among the plurality of carriers in response to a determination of at least one of: receiving the ACK from at least one of the one or more target recipient UEs, or not receiving the NACK on at least one of the one or more carriers among the plurality of carriers.

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