WO2023147704A1

WO2023147704A1 - Methods and apparatus for sidelink communications on unlicensed frequency bands

Info

Publication number: WO2023147704A1
Application number: PCT/CN2022/075404
Authority: WO
Inventors: Junqiang CHENG; Tao Chen; Min LEI
Original assignee: Mediatek Singapore Pte. Ltd.
Priority date: 2022-02-07
Filing date: 2022-02-07
Publication date: 2023-08-10
Also published as: CN116567835A

Abstract

This disclosure describes methods and apparatus for sidelink communications on unlicensed frequency bands. Each sidelink UE performs independent and asynchronous sensing and (re-) selection/reservation mechanism on the unlicensed frequency bands to (re-) select/reserve resources for the traffic (re-) transmission. Then, the sidelink UE performs LBT before every (re-) selected/reserved resource to achieve fair coexistence with other wireless communication systems operated on the unlicensed frequency bands. If the LBT is successful, the sidelink UE can transmit traffic on the resource. If the LBT is failed, the sidelink UE cannot transmit traffic on the resource, and it should move to the next (re-) selected/reserved resource and perform LBT. In order to improve the channel access probability on unlicensed spectrum, for sidelink UE, the number of (re-) selected/reserved resources, and/or the maximum number of resources can be (re-) selected/reserved, and/or the maximum number of (re-) selected/reserved resources can be indicated in the 1 ^st-stage SCI, and/or the actual LBT trigger time can be dynamically indicated/configured according to the LBT failure probability and/or channel loading status information and/or channel congestion control information of the unlicensed spectrum. Besides, if the LBT before the initially (re-) selected/reserved resources is failed, the sidelink UE can be dynamically configured with a new selection window to (re-) select/reserve new candidate resources with the limit of traffic PDB.

Description

METHODS AND APPARATUS FOR SIDELINK COMMUNICATIONS ON UNLICENSED FREQUENCY BANDS

FIELD

The invention discussed below relates generally to wireless communication systems, and more particularly, the methods and apparatus for sidelink communications on unlicensed frequency bands in a wireless communication system.

BACKGROUND

Sidelink communication is originally introduced in 3GPP Release 12 to enable direct transmission between two user equipments (UEs) , which is also known as the device-to-device (D2D) communications. Then with the development of 3GPP normative works, the scenarios of sidelink are extended to UE-to-network relay, public safety, vehicle-to-everything (V2X) communications and so on. The critical role of sidelink in long term evolution (LTE) and also the new radio (NR) has made it an inevitable remedy to support diverse use cases of future wireless communications.

On the other hand, to meet the increased demands of wireless data traffic, the utilization of unlicensed frequency bands has drawn a lot of attention in wireless industry as a way to improve the capacity of future wireless communication systems, which further motivates the successful development of LTE licensed assisted access (LAA) and 5G NR unlicensed (NR-U) communications in 3GPP. Under this background, the utilization of unlicensed spectrum for sidelink communications is regarded as the most promising direction for further development of sidelink. However, for the reason that some radio access technologies (RATs) , such as NR-U communications, Wi-Fi, etc., have already operated in the unlicensed frequency bands, one of the most critical issues of allowing sidelink communications to operate in the unlicensed frequency bands is to ensure the fair and harmonious coexistence with other RATs.

Based on the above assumptions, the present disclosure gives the methods and apparatus for sidelink communications on unlicensed frequency bands (SL-U) that address the problem of fair coexistence among sidelink system and other wireless communication systems operated on unlicensed frequency bands.

SUMMARY

The following presents a simplified summary of one or more aspects in order to provide a basic understanding of such aspects. This summary is not an extensive overview of all contemplated aspects, and is intended to neither identify key or critical elements of all aspects nor delineate the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form as a prelude to the more detailed description that is presented later.

Various aspects of the present disclosure relate to methods and apparatus for sidelink communication on unlicensed frequency bands. Each sidelink UE may perform independent and asynchronous sensing and selection procedures on the unlicensed spectrum to select/reserve resources for the traffic (re-) transmission. It should be noted that the number of resources selected/reserved by sidelink UE, and/or the maximum number of resources can be selected/reserved by sidelink UE, and/or the maximum number of selected/reserved resources can be indicated in the 1 ^st-stage sidelink channel information (SCI) can be dynamically configured according to the channel traffic load or channel collision status, etc. Empowered by this scheme, the sidelink UEs can be granted more chances to access the unlicensed spectrum and combat the effect of potential listed-before-talk (LBT) failures. Then, the sidelink UEs perform LBT mechanism immediately before the reserved resources to achieve fair coexistence with other wireless communication system operated in the unlicensed frequency bands. If the LBT is successful, which indicates the reserved resource is idle, the sidelink UEs can transmit traffic on the resource. If the LBT is failed, which indicates the reserved resource is busy, the sidelink UEs cannot transmit traffic on that resource.

In an aspect of the disclosure, the sidelink UEs sense the channel resources on unlicensed frequency bands. During this procedure, the UEs decode the 1 ^st-stage SCI from other sidelink UEs to obtain the resource reservation information of other sidelink UEs. Besides, the sidelink UEs measure the sidelink reference signal received power (RSRP) of the transmissions on the unlicensed frequency bands. The RSRP can be measured by the demodulation reference signal (DMRS) of physical sidelink control channel (PSCCH) , and/or measured by the DMRS of physical sidelink shared channel (PSSCH) , which can be configured by the information element (IE) sl-RS-ForSensing from higher layer.

In another aspect of the disclosure, after the trigger of resource selection/reservation, the sidelink UE defines a selection window SW, where the sidelink UE selects the candidate resources for traffic transmission. During the selection window, the sidelink UE performs two steps to select resources. The first step excludes some candidate resources in the selection window. The excluded resources include, for example, the resources related to the half-duplex operation, the resources reserved by other sidelink UEs, etc. The later excluded resources can be determined based on the reservation information in the 1st-stage SCIs and the associated RSRP obtained from the sensing stage. After the first step, the second step in the selection procedure is randomly selecting N resources from the list of available resources after the first step.

In another aspect of the disclosure, after the resource selection procedures, the sidelink UE performs LBT immediately before every selected/reserved unlicensed resource. If the LBT is successful, which means the corresponding resource is idle, then the sidelink UE can transmit the traffic on that resource. If the LBT is failed, which means the corresponding resource is busy or occupied by other UEs, then the sidelink UE cannot transmit the traffic on that resource. Besides, the selected/reserved resources in the selection window can be continuous or discontinuous.

In another aspect of the disclosure, the number of resources selected/reserved by sidelink UE, and/or the maximum number of resources can be selected/reserved by sidelink UE, and/or the maximum number of selected/reserved resources can be indicated in the 1 ^st-stage sidelink channel information (SCI) , can be dynamically indicated and/or configured according to the LBT failure probability (e.g., derived/determined based on the ratio of the failure times over the total times for LBT sensing in the past X ms/slots, or the consecutive number of LBT failure times) and/or channel loading status information and/or channel congestion control information. With this scheme, sidelink UEs will have more chances to access the unlicensed channel. For example, during the selection window, if the LBT is successful, the sidelink UE can transmit the traffic on that resource. If the LBT is failed, the sidelink UE cannot transmit the traffic on that resource. However, with more potential resources are selected/reserved, i.e., overbooking, the sidelink UEs still have other chances to perform LBT successfully for the transmission of other selected/reserved resources. With the proposed scheme, the sidelink UE will have more chances to access the unlicensed spectrum, which improves the channel access probability in the unlicensed spectrum.

In another aspect of the disclosure, to further combat the potential LBT failure, the LBT trigger time can be indicated and/or configured dynamically according to the actual overbooking status, and/or the LBT failure probability, and/or the channel loading status information and/or the channel congestion control information. For example, when the actual resource overbooking number is smaller than the requirement, and/or the LBT failure probability is high, and/or the channel loading is high, the LBT can be triggered earlier than the original LBT required time. If the gap between the LBT successful position and the ideal resource position is larger than one symbol, the UE can execute the LBT self-defer mechanism. Then immediately before the ideal resource position, the UE can execute a relatively simpler LBT procedures to access the corresponding resource. If the gap is no more than one symbol, the UE can utilize the cyclic prefix (CP) extension to align the boundary between the LBT successful position and the ideal resource position. Empowered by this scheme, the UE can have more time and/or chances to try LBT, which further leads to an increased LBT success probability.

In another aspect of the disclosure, the position of the selection window can be dynamically indicated and/or configured according to the LBT failure probability within packet delay budget (PDB) . In particular, if the LBT before one selected/reserved resource is failed, the sidelink UE determines a new selection window SW′ with the last slot of SW′ before the PDB, then the sidelink UE can select/reserve a new resource in the new selection window SW′. It should be noted that the sidelink UE could have initially select/reserve N resource in the initial selection window. Therefore, if the sidelink UE detects that a subset of N _sub (0≤N _sub≤N) of the selected/reserved are not available anymore because of the LBT failure, then the sidelink UE will select N _sub new resources in the new selection window SW′ derived from PDB and UE processing capabilities.

In another aspect of the disclosure, if the LBT is used to initiate a channel occupancy time (COT) or the LBT is out of the COT, Type 1 LBT can be configured. If the LBT is used within an initiated/shared COT, the LBT type for UEs sharing the COT can be configured from Type 2A LBT, Type 2B LBT and Type 2C LBT.

In another aspect of the disclosure, the channel access priority class (CAPC) in Type 1 LBT can be mapping directly or indirectly from 5G quality of service (QoS) identifier (5QI) and/or PC5 QoS identifier (PQI) .

In another aspect of the disclosure, an apparatus for the sidelink communication on unlicensed frequency bands is provided. The apparatus includes at least a processor, and at least a memory communicatively coupled to the processor. The processor is configured to conduct the methods disclosed in the present invention.

To the accomplishment of the foregoing and related ends, the one or more aspects comprise the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed figures set forth in detail certain illustrative features of the one or more aspects. These features are indicative, however, of but a few of the various ways in which the principles of various aspects may be employed, and this description is intended to include all such aspects and their equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram illustrating a scheme for sidelink communications on unlicensed spectrum involving LBT, sensing and selection, in accordance with certain aspects of the present disclosure.

FIG. 2 is a flow diagram illustrating a resource selection mechanism for sidelink communications, in accordance with certain aspects of the present disclosure.

FIG. 3 illustrates an exemplary diagram of LBT type determination scheme, in accordance with certain aspects of the present disclosure.

FIG. 4 (a) illustrates an exemplary diagram with resolving mapping relation from 5QI to CAPC, in accordance with certain aspects of the present disclosure.

FIG. 4 (b) illustrates an exemplary diagram with resolving mapping relation from PQI to CAPC, in accordance with certain aspects of the present disclosure.

FIG. 4 (c) illustrates an exemplary diagram with resolving mapping relation from 5QI to PQI and then to CAPC, in accordance with certain aspects of the present disclosure.

FIG. 4 (d) illustrates an exemplary diagram with resolving mapping relation from PQI to 5QI and then to CAPC, in accordance with certain aspects of the present disclosure.

FIG. 5 illustrates a sidelink communication scheme on unlicensed spectrum with configurable number of selected/reserved resources, in accordance with certain aspects of the present disclosure.

FIG. 6 illustrates a sidelink communication scheme on unlicensed spectrum with configurable location of new selection window, in accordance with certain aspects of the present disclosure.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appended drawings is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In some instances, well known structures and components are shown in block diagram form in order to avoid obscuring such concepts.

Several aspects of telecommunication systems will now be presented with reference to various apparatus and methods. These apparatus and methods will be described in the following detailed description and illustrated in the accompanying drawings by various blocks, components, circuits, processes, algorithms, etc. (collectively referred to as “elements” ) . These elements may be implemented using electronic hardware, computer software, or any combination thereof. Whether such elements are implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system.

The described invention operates in the context of sidelink communications on unlicensed frequency bands. In general, sidelink communications refer to the direct communications between terminal nodes or UEs without the data going through the network. More specifically, sidelink communication is originally introduced in 3GPP Release 12 as the LTE D2D communication, i.e., direct communication between two devices. Next, in Release 13, the scope of sidelink transmission is evolved to support UE-to-network relay to extend the service range of an eNB, where the inter-coverage UE acts as the relay node between an eNB and an out-of-coverage UE. Then, with the sustainable development of 3GPP normative works, LTE V2X is developed in Release 14 and further enhanced in Release 15 as the eV2X. While it should be note that the aforementioned sidelink transmissions are all based on LTE, and only from Release 16, the sidelink is developed based on 5G NR interface, which is then further enhanced in Release 17. From the development of sidelink transmission, it is obvious that the critical role of sidelink in LTE and NR has made it an inevitable remedy to support diverse use cases of future wireless communications networks.

Resource allocation scheme is one of the most critical issues for sidelink transmission. In Release 16, two modes of resource allocation schemes are identified for NR sidelink. The first one is named in Mode 1, while the second is Mode 2. For Mode 1, the resource allocation is scheduled by the gNB using the Uu interface. This mode is only suitable for the sidelink UEs in network coverage. For Mode 2, the sidelink UE can autonomously select the resources from a (pre-) configured resource pool (s) based on the channel sensing mechanism over PC5 interface. In this case, the sidelink UEs can operate both under in-coverage and out-of-coverage. When a transmitting sidelink UE attempts to select/reserve resources with Mode 2, it should conduct the resource selection/reservation procedures, which mainly include two stages: resource sensing and resource selection/reservation. Generally, in sensing stage, in order to avoid causing interference to the existing sidelink transmissions operated by other sidelink UEs, the purpose of the sensing stage is to identify the candidate resources potentially available to be utilized for the sidelink transmission. Next, in selection stage, the sidelink UE can select the candidate resources used for transmission block (TB) transmission with the assistance of the sensing results.

With the development of wireless communication network, more and more devices are deployed in various use cases, which results in the very-high demand of the wireless capacity. Therefore, the utilization of unlicensed frequency bands has drawn a lot of attention in wireless industry as a way to improve the capacity of future wireless communication networks. Therefore, the utilization of unlicensed frequency bands for sidelink communications is regarded as the most promising direction for further development of sidelink.

For sidelink transmissions on unlicensed spectrum (SL-U) , one of the most critical issues is to ensure the fair coexistence with other RATs operated in unlicensed spectrum, such as NR-U and Wi-Fi, etc. To this end, the utilization of listen before talk/transmission (LBT) is mandated before a UE access to the unlicensed channel. In general, LBT is a spectrum sharing technology by which a device must perform the clear channel assessment (CCA) check before it starts a transmission. Empowered by the LBT mechanism, it is possible for multiple UEs to share a same channel, and the fair coexistence among different RATs can be guaranteed. Therefore, for SL-U, the combination design of sidelink sensing and LBT is a promising resource allocation scheme to guarantee the harmonious coexistence among sidelink and other wireless systems.

In this disclosure, a resource allocation or channel access scheme is proposed for SL-U to achieve fair coexistence with other wireless systems operated in the unlicensed frequency bands. In particular, a combination scheme of sidelink sensing, selection, and LBT is proposed for the resource allocation or channel access of SL-U UEs. Based on the sensing and selection mechanism of sidelink, the sidelink UE can select/reserve resources for the TB (re-) transmission, and avoid the collision with other sidelink UEs. Meanwhile, the LBT process before every selected/reserved resource proposed in this disclosure can guarantee the fair coexistence among SL-U and other RATs operated in the unlicensed spectrum, such as NR-U, Wi-Fi, etc.

In this disclosure, when a sidelink UE is not transmitting, it keeps sensing the unlicensed channel resources in order to identify the available candidate resources. During the sensing procedure, the sidelink UE decodes the 1 ^st-SCI form other sidelink UEs on the unlicensed channel. By decoding the 1 ^st-stage SCI, the sidelink UE can know the resources that have been reserved by other sidelink UEs for their TB initial transmission and re-transmission (s) . During the sensing procedure, the sidelink UE also measures the sidelink reference signal received power (RSRP) of the transmission from other sidelink UEs. The information element (IE) sl-RS-ForSensing from higher layer indicates whether the RSRP of PSCCH or RSRP of PSSCH is measured. This sensing information, including the 1 ^st-stage SCI and RSRP, is stored by the sidelink UE, and will be used in the following resource selection procedure.

An example of the methods for sidelink communications on unlicensed spectrum is described in Figure 1. A sidelink UE can (re-) select/reserve new resources when a new TB is generated, and/or the new TB does not fit in the previously selected/reserved resources, and/or the re-selection counter (RC) decreased to 0, etc. If the resource (re-) selection/reservation is triggered at slot n, the sidelink UE should first collect the sensing information in a certain period [n-T ₀, n-T _proc, 0] , where T ₀ is an integer defined in number of slot and equals to x ms (e.g., 1100ms or 100ms) , which is determined by the higher layer IE sl-SensingWindow. Besides, T _proc, 0 is the time required to complete the sensing procedure.

As described in Figure 1, after collecting the sensing information, the sidelink UE will select resources in a selection window (SW) defined by the range of [n+T ₁, n+T ₂] , where T ₁ is the processing time. The value of T ₂ is left to the UE implementation but should meet the range T _2, min≤T ₂≤PDB, where T _2, min depends on the priority of the TB and also the SCS. Besides, PDB is the packet delay budget (PDB) in slot, which indicates the transmission deadline, and the TB must be transmitted before it.

As described in Figure 2, during the resource selection procedure, the sidelink UE first excludes some candidate resources in the selection window. The exclusion resources can include the resources reserved by other sidelink UEs, which can be indicated by the reservation information in the 1 ^st-stage SCI. For this case, the resources are only excluded if the sidelink UE has measured an RSRP of the reserved resources is higher than a RSRP threshold, which is determined by the higher layer parameter sl-Thres-RSRP-List. After the exclusion process, the sidelink UE will check whether the percentage of the remaining candidate resources in the selection window meets the requirement, i.e., equal or larger than x%. If the requirement is not satisfied, the RSRP threshold can be increased by 3dB, and the process is repeated iteratively until the percentage of the remaining candidate resources in the selection window meets the requirement. The value of x depends on the priority of the TB and is indicated by the higher layer parameter SL-TxPercentageConfig. After the requirement is satisfied, the sidelink UE can randomly choose N resources used for transmission from the remaining available candidate resources in the selection window.

In this disclosure, to guarantee the fair coexistence among sidelink communication and other RATs operated in the unlicensed spectrum, as described in Figure 1, after the resource selection procedures, the sidelink UE should choose LBT type based on the (pre-) configuration and/or traffic type/QoS and then perform LBT mechanism for transmission of every selected/reserved resource. The determination of the LBT type is illustrated in Figure 3. As described in Figure 3, if the LBT is used to initiate a channel occupancy time (COT) or the LBT is out of the COT, Type 1 LBT can be configured. Besides, if the LBT is used within an initiated/shared COT, the LBT type can be (pre-) configured from Type 2A LBT, Type 2B LBT and Type 2C LBT.

If Type 1 LBT is (pre-) configured, the energy detection/sensing duration of the LBT, and/or the duration of the initiated/shared COT after successful LBT can be determined by the channel access priority class (CAPC) . In this disclosure, as described in Figure 4, the value of the CAPC can be determined according to the following principles. In general, the CAPC can be directly or indirectly mapped from the 5G quality of service (QoS) identifier (5QI) or the PC5 QoS identifier (PQI) of the traffic. For example, as described in Figure 4 (a) , the CAPC can be directly mapped from the 5QI of the traffic. Moreover, as described in Figure 4 (b) , the CAPC can be directly mapped from the PQI of the traffic that being transmitted. Moreover, as described in Figure 4 (c) , the 5QI of the traffic can be first mapped to PQI, and then the PQI can be mapped to CAPC. Moreover, as described in Figure 4 (d) , the PQI of the traffic is first mapped to 5QI, and then the 5QI is mapped to CAPC.

After the LBT operation the transmission of the resource selected/reserved by sidelink sensing and (re-) selection can be determined. As described in Figure 1, if LBT is successful, , the sidelink UE can utilize the corresponding selected/reserved resource to transmit TB. However, if LBT is failed, the sidelink UE cannot perform the transmission on the selected/reserved resource. Instead, it should wait for the next selected/reserved resource to perform the corresponding LBT for transmission. In this disclosure, the aforementioned process is iteratively repeated starting from the first selected/reserved resource to the last one.

As described in Figure 1, during the selection procedure, the sidelink UE selects N candidate resources within the selection window for the initial transmission of the TB and the following N-1 blind or HARQ re-transmissions. The value of N is left to the UE implementation but should meet the range N≤N _max, where N _max is (pre-) configured within the range 1≤N _max≤32, and/or can derived based on on the channel utilization or loading. Besides, the number of selected/reserved resource N should not be higher than the number of the available candidate resources.

During the resource (re-) selection/reservation procedure, the sidelink UE should also consider the size limitation of the 1 ^st-stage SCI. Particularly, the 1 ^st-stage SCI can only indicate the selected/reserved resources located within 32 slots, which constrains the maximum gap between two consecutive selected/reserved resources. Besides, the 1 ^st-stage SCI can only indicate a maximum number of N _SCI selected/reserved resources. The maximum number of N _SCI is (pre-) configured per resource pool, and can be equal to one of the numbers in a range from 2 to 20.

For the unlicensed spectrum with SL-U communication, there may be operations of the other wireless systems such as NR-U, Wi-Fi, etc. The LBT before the selected/reserved resource may fail, which means the corresponding transmission cannot be performed anymore. This case will affect the resource allocation scheme of SL-U. For example, the resource reservation information indicated in the 1 ^st-stage SCI may not be used for transmission. In other words, no transmission on the failed selected/reserved resource may mean that the sidelink UE cannot receive the corresponding SCI on that resource for sensing. In addition, the failure of the LBT may also lead to the resources that can be actually used for sidelink TB (re-) transmission are smaller than the original selected/reserved resource number N. In this case, the sidelink TB (re-) transmission may also fail due to insufficient resources.

In this disclosure, in order to combat the effect of the potential LBT failure, and guarantee the consecutive reservation information transmission, the maximum number of the selected/reserved resources indicated in the 1 ^st-stage SCI (i.e., N _SCI) , can be increased more than 3 or larger than the case without LBT operation. In general, N _SCI can be dynamically configured according to the channel traffic load, and/or the channel collision probability, etc. In particularly, with the increase of the channel traffic load, and/or the channel collision probability, etc., the value of N _SCI can be adjusted larger to combat the higher LBT failure probability. For example, if the channel traffic load, and/or the channel collision probability is higher than a threshold Th _i, the value of N _SCI can be configured as the corresponding value N _SCI, i, where 1≤i≤I _max and I _max represents the size of the N _SCI, i configuration set or the total number of resources for a packet.

For the case that more selected/reserved resources are indicated in 1 ^st-stage SCI, the time resource assignment field in the 1 ^st-stage SCI will be also increased. In general, if the increased bits are larger than a threshold Th _sci, they can be carried on the 1 ^st-stage SCI with a new format. If the increased bits are less than the threshold Th _sci, they can be carried on the 1 ^st-stage SCI with original format. For example, if the maximum number of selected/reserved resources indicated in the 1 ^st-stage SCI is configured larger than 4, the 1 ^st-stage SCI with a new format can be used. Otherwise, the 1 ^st-stage SCI with original format can be used.

In this disclosure, to avoid the number of the candidate selected/reserved resources can be used actually for TB (re-) transmission is insufficient due to the potential LBT failure, as described in Figure 5, a method is, for example, the value of the selected/reserved resources N can be configured larger than the original demand of the TB (re-) transmission, e.g., N _ori. Empowered by this principle, the SL-U UE can be configured to select/reserve more resources, which means the SL-U UE have more opportunities to execute LBT and (re-) transmit the TB. In general, the value of N can also be indicated/configured dynamically according to the LBT failure probability (e.g., derived/determined based on the ratio of the failure times over the total times for LBT sensing in the past X ms/slots, or the consecutive number of LBT failure times) and/or channel loading status information and/or channel congestion control information. For example, with the increase of the channel traffic load, and/or the channel collision probability, etc., N can be configured with a larger number to combat the higher LBT failure probability. If the channel traffic load, and/or the channel collision probability is higher than a threshold Th′ _i, the value of N can be configured as the corresponding value N _i, where 1≤i≤I′ _max and I′ _max represents the size of the N _i configuration set.

In addition, to avoid the number of the candidate selected/reserved resources can be used actually for TB (re-) transmission is insufficient due to the potential LBT failure, a method is, for example, the maximum number of the resources can be selected/reserved by the SL-U UE, i.e., N _max, can be configured within a new range

where the value of

can be configured larger than 32. In general, the value of

can also be configured dynamically according to the LBT failure probability (e.g., derived/determined based on the ratio of the failure times over the total times for LBT sensing in the past X ms/slots, or the consecutive number of LBT failure times) and/or channel loading status information and/or channel congestion control information. For example, with the increase of the channel traffic load, and/or the channel collision probability, etc.,

can be configured with a larger number to combat the higher LBT failure probability. For example, if the channel traffic load, and/or the channel collision probability is higher than a threshold Th″ _i, the value of

can be configured as the corresponding value N _max, i, where 1≤i≤I″ _max and I″ _max represents the size of the

configuration set.

In addition, to avoid the number of the candidate selected/reserved resources can be used actually for TB (re-) transmission is insufficient due to the potential LBT failure, a method is, for example, the initial selection window SW can be dynamically configured according to the LBT failure probability (e.g., derived/determined based on the ratio of the failure times over the total times for LBT sensing in the past X ms/slots, or the consecutive number of LBT failure times) and/or channel loading status information and/or channel congestion control information. In particular, an example is described in Figure 6, if the LBT before one initially selected/reserved resource is failed, the sidelink UE defines a new selection window SW′, and then the sidelink UE can select/reserve a new resource in the new selection window SW′. For example, denote n′ as the slot at which the LBT is failed, then the new selection window SW′ can start at slot n′+T′ ₁ and end at slot n′+T′ ₂ , where T′ ₁ is the processing time required by the sidelink UE to turn from LBT sensing to resource selection/reservation. Besides, T′ ₂ must be within the range T′ ₂≤PDB- (n′-n) , which guarantees the new resource selection/reservation in the new selection window can be terminated before the PDB requirement of the traffic. It should be noted that the sidelink UE could have initially selected/reserved N resources in the initial selection window SW. Therefore, the sidelink UE may detect that a subset of N _sub (0≤N _sub≤N) of the initially selected/reserved resources are not available anymore because of multiple LBT failures. In this case, the sidelink UE will select N _sub new resources in the new selection window SW′ with the limit of the PDB requirement.

In this disclosure, in order to combat the potential LBT failure, the LBT trigger time can be dynamically indicated/configured according to the actual resource overbooking number, and/or the LBT failure probability (e.g., derived/determined based on the ratio of the failure times over the total times for LBT sensing in the past X ms/slots, or the consecutive number of LBT failure times) , and/or the channel loading status information and/or channel congestion control information. For example, the potential sensing slot (e.g., 9 μs ) failure time can be assumed as n, which is related to the actual resource overbooking number, and/or the LBT failure probability, and/or the channel loading status information, etc. If the selected/reserved resource position is assumed as T, and the original LBT required time is assumed as ΔT ₁, then the original LBT trigger time is T-ΔT ₁. But with the proposed scheme, the actual LBT trigger time can be configured ΔT ₂ earlier than the original LBT trigger time, i.e., T-ΔT ₁-ΔT ₂, where ΔT ₂=n×T _d, and T _d is the defer duration in the conventional LBT procedures. Next, when the LBT is successful, and if the gap between the LBT successful position and the selected/reserved resource position is larger than one symbol, the UE should conduct the LBT self-defer mechanism. Then immediately before the selected/reserved resource position, the UE can execute a relatively simpler LBT to access the corresponding resource. If the gap is no more than one symbol, the UE can utilize the CP extension to align the boundary between the of LBT successful position and the selected/reserved resource position. Empowered by this scheme, the sidelink UE can have more time and/or chances to try LBT, which further leads to an increased success probability of LBT.

The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but is to be accorded the full scope consistent with the language claims, wherein reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more. ” The word “exemplary” is used herein to mean “serving as an example, instance, or illustration. ” Any aspect described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects. Unless specifically stated otherwise, the term “some” refers to one or more. Combinations such as “at least one of A, B, or C, ” “one or more of A, B, or C, ” “at least one of A, B, and C, ” “one or more of A, B, and C, ” and “A, B, C, or any combination thereof” include any combination of A, B, and/or C, and may include multiples of A, multiples of B, or multiples of C. Specifically, combinations such as “at least one of A, B, or C, ” “one or more of A, B, or C, ” “at least one of A, B, and C, ” “one or more of A, B, and C, ” and “A, B, C, or any combination thereof” may be A only, B only, C only, A and B, A and C, B and C, or A and B and C, where any such combinations may contain one or more member or members of A, B, or C. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. The words “module, ” “mechanism, ” “element, ” “device, ” and the like may not be a substitute for the word “means. ” As such, no claim element is to be construed as a means plus function unless the element is expressly recited using the phrase “means for. ”

While aspects of the present disclosure have been described in conjunction with the specific embodiments thereof that are proposed as examples, alternatives, modifications, and variations to the examples may be made. Accordingly, embodiments as set forth herein are intended to be illustrative and not limiting. There are changes that may be made without departing from the scope of the claims set forth below.

Claims

A method of wireless communication comprising:

Coexistence schemes for sidelink communication with other wireless communication systems operated on unlicensed frequency bands.
The method of claim 1, wherein a resource (re-) selection/reservation scheme includes sensing procedures of the unlicensed frequency bands to collect the information of the 1 ^st-stage SCI and RSRP of other sidelink UEs.
The method of claim 1, wherein a resource (re-) selection/reservation scheme includes the resource (re-) selection/reservation procedures in a selection window on the unlicensed frequency bands.
The method of claim 3, wherein the resource (re-) selection/reservation procedures in the selection window include the exclusion of the candidate resources that cannot be used, and then followed by a random resource (re-) selection/reservation mechanism.
The method of claim 1, wherein the (re-) selected/reserved resources can be continuous or discontinuous.
The method of claim 1, wherein a resource (re-) selection/reservation scheme includes LBT mechanisms before every (re-) selected/reserved resource to achieve fair coexistence with other wireless communication systems operated in the unlicensed frequency bands.
The method of claim 6, wherein if the LBT procedure before the (re-) selected/reserved resource is successful, the sidelink UE can transmit the traffic on the resource.
The method of claim 6, wherein if the LBT procedure before the (re-) selected/reserved resource is failed, the sidelink UE cannot transmit the traffic on the resource, and the sidelink UE should move to the next (re-) selected/reserved resource and perform LBT.
The method of claim 6, wherein if the LBT before the (re-) selected/reserved resource is used to initiate a COT or the LBT is out of the COT, the Type 1 LBT can be configured.
The method of claim 9, wherein the sensing duration of Type 1 LBT can be determined by the channel access priority class (CAPC) of the traffic that being transmitted.
The method of claim 9, wherein the COT duration after a successful Type 1 LBT can be determined by the CAPC of the traffic that being transmitted.
The method of claim 10 and claim 11, wherein the CAPC can be determined directly or indirectly by the 5G quality of service (QoS) identifier (5QI) of the traffic that being transmitted.
The method of claim 10 and claim 11, wherein the CAPC can be determined directly or indirectly by the PC5 QoS identifier (PQI) of the traffic that being transmitted.
The method of claim 6, wherein if the LBT before the (re-) selected/reserved resource is used within an initiated/shared COT, the LBT can be (pre) configured/indicated from Type 1 LBT, Type 2A LBT, Type 2B LBT, and Type 2C LBT.
The method of claim 14, the selection of Type 2A LBT, Type 2B LBT, and Type 2C LBT can be indicated/configured by the gap between two consecutive (re-) selected/reserved resources.
The method of claim 14, the selection of Type 1 LBT, Type 2A LBT, Type 2B LBT, and Type 2C LBT can be scheduled/configured/indicated by the COT initiator.
The method of claim 1, wherein the maximum number of (re-) selected/reserved resources indicated in the 1 ^st-stage SCI can be configured larger than 3 to combat the effect of the potential LBT failure, and guarantee the consecutive transmissions of the reservation information.
The method of claim 17, wherein the maximum number of (re-) selected/reserved resources indicated in the 1 ^st-stage SCI can be dynamically configured according to the LBT failure probability and/or channel loading status information and/or channel congestion control information, etc.
The method of claim 17, wherein if the maximum number of the (re-) selected/reserved resources indicated in the 1 ^st-stage SCI is configured larger than 4, the 1 ^st-stage SCI with a new format can be used. Otherwise, the 1 ^st-stage SCI with original format can be used.
The method of claim 1, wherein the number of (re-) selected/reserved resources can be configured more than the actually demand, i.e., overbooking, to combat the effect of the potential LBT failure, and grant sidelink UEs more chances to access the unlicensed frequency bands.
The method of claim 20, wherein the number of resources (re-) selected/reserved by sidelink UE can be dynamically configured according to the LBT failure probability and/or channel loading status information and/or channel congestion control information, etc.
The method of claim 1, wherein the maximum number of resources can be (re-) selected/reserved by sidelink UE can be (pre-) configured larger than 32 to combat the effect of the potential LBT failure, and grant sidelink UE more potential chances to access the unlicensed frequency bands.
The method of claim 22, wherein the maximum number of resources can be (re-) selected/reserved by sidelink UE can be dynamically configured according to the LBT failure probability and/or channel loading status information and/or channel congestion control information, etc.
The method of claim 1, wherein the trigger time of the LBT can be dynamically configured according to the LBT failure probability and/or channel loading status information and/or channel congestion control information, to combat the effect of the potential LBT failure, and grant sidelink UE more potential chances to access the unlicensed frequency bands.
The method of claim 1, wherein according to the LBT failure status before the initially (re-) selected/reserved resources, the sidelink UE can be dynamically configured with a new selection window to (re-) select/reserve new candidate resources.