Method, device, and computer-readable medium for communications

Abstract

The present disclosure relates to a method, a device, and a computer-readable medium for communication. A first device determines an expected time interval of a channel access procedure for a transmission on a first candidate resource in an initial set of candidate resources. According to a determination that the expected time interval overlaps with a transmission symbol of at least one reserved resource preceding the first candidate resource, the first device determines a first set of candidate resources for sidelink transmission by excluding the first candidate resource from the initial set.

Description

[Technical Field]

[0001] TECHNICAL FIELD Implementations of the present disclosure relate generally to the field of telecommunications, and more particularly to methods, devices, and computer-readable media for communication. [Background technology]

[0002] Some communication systems allow vehicle-to-everything (V2X) and device-to-device (D2D) communications to take place. V2X communications can be based on communication technologies such as sidelink communication technologies. To this end, sidelink resource pools and sidelink channels can be established for vehicles participating in such communications.

[0003] In V2X communication, there are two modes of resource allocation: In the first mode (hereinafter also referred to as NR V2X Mode 1 or Mode 1), one terminal device may conduct V2X communication with other terminal devices by using resources allocated by a network device; and in the second mode (hereinafter also referred to as NR V2X Mode 2 or Mode 2), one terminal device may conduct V2X communication with other terminal devices by using resources autonomously selected by the one terminal device in a resource pool. Summary of the Invention [Means for solving the problem]

[0004] Generally, example implementations of the present disclosure provide methods, devices, and computer-readable media for communication.

[0005] In a first aspect, a first device is provided, the first device comprising at least one processor and at least one memory containing computer program code configured by the at least one processor to cause the first device to: determine an expected time interval of a channel access procedure for transmission on a first candidate resource within an initial set of candidate resources; and, if the expected time interval overlaps with a transmission symbol of at least one reserved resource preceding the first candidate resource, determine a first set of candidate resources for sidelink transmission by excluding the first candidate resource from the initial set.

[0006] In a second aspect, a method is provided for implementation in a first device, the method including: determining, at the first device, an expected time interval of a channel access procedure for transmission on a first candidate resource within an initial set of candidate resources; and determining a first set of candidate resources for sidelink transmission by excluding the first candidate resource from the initial set according to a determination that the expected time interval overlaps with a transmission symbol of at least one reserved resource preceding the first candidate resource.

[0007] In a third aspect, an apparatus is provided, comprising: means for determining an expected time interval of a channel access procedure for transmission on a first candidate resource within an initial set of candidate resources; and means for determining a first set of candidate resources for sidelink transmission by excluding the first candidate resource from the initial set according to a determination that the expected time interval overlaps with a transmission symbol of at least one reserved resource preceding the first candidate resource.

[0008] In a fourth aspect, there is provided a non-transitory computer readable medium comprising program instructions for causing an apparatus to perform a method according to the second aspect.

[0009] It should be understood that the Summary section is not intended to identify key or essential features of implementations of the present disclosure, nor is it intended to be used to limit the scope of the present disclosure. Other features of the present disclosure will be readily apparent through the following description.

[0010] These and other objects, features, and advantages of the present disclosure will become more apparent through a more detailed description of several implementations of the present disclosure in the accompanying drawings. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 illustrates an example communication network in which implementations of the present disclosure may be practiced. [Figure 2] FIG. 10 illustrates an example of a CCA slot, according to some implementations of the present disclosure. [Figure 3] FIG. 1 illustrates an example of an initiating device obtaining a COT via LBT Type 1, according to some implementations of the present disclosure. [Figure 4] FIG. 10 illustrates an example of a contention window countdown procedure according to some implementations of the present disclosure. [Figure 5] FIG. 10 illustrates an example of a tolerance gap for enabling the LBT Type 2 transformation, according to some implementations of the present disclosure. [Figure 6] FIG. 10 illustrates an example of when a responding device must obtain a new COT, according to some implementations of the present disclosure. [Figure 7] FIG. 1 illustrates an example of NR SL resource allocation in Mode 2, in accordance with some implementations of the present disclosure. [Figure 8] 1 is a flowchart of a legacy SL resource allocation method. [Figure 9] 1 is a flowchart of a legacy method for forming a resource candidate set. [Figure 10] A diagram illustrating an example of an SL slot structure according to some implementations of the present disclosure. [Figure 11] 10A-10C illustrate examples of how other SL UEs may disrupt the contention window countdown procedure, according to some implementations of the present disclosure. [Figure 12] 1 is a flowchart of an example method according to some implementations of the present disclosure. [Figure 13] A diagram illustrating an example of SL resource selection according to some implementations of the present disclosure. [Figure 14] A diagram illustrating another example of SL resource selection according to some implementations of the present disclosure. [Figure 15] 1 is a flowchart of an example method according to some implementations of the present disclosure. [Figure 16] 1 illustrates an example of an RP with different configurations to facilitate LBT transmission of different CWSs. [Figure 17] FIG. 1 is a simplified block diagram of an apparatus suitable for implementing embodiments of the present disclosure. [Figure 18] 1 is a block diagram of an example computer-readable medium according to some implementations of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0012] Throughout the drawings, the same or similar reference numbers refer to the same or similar elements.

[0013] The principles of the present disclosure will now be described with reference to some exemplary implementations. It should be understood that these implementations are described for the purposes of illustration and to aid those skilled in the art in understanding and practicing the present disclosure, without implying any limitation on the scope of the present disclosure. The present disclosure described herein can be implemented in various ways other than those described below.

[0014] In the following description and claims, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.

[0015] In this disclosure, references such as "one embodiment," "one embodiment," "exemplary embodiment," and the like indicate that the described embodiment may include a particular feature, structure, or characteristic, but do not necessarily mean that every embodiment includes the particular feature, structure, or characteristic. Moreover, such phrases do not necessarily refer to the same embodiment. Furthermore, when a particular feature, structure, or characteristic is described in connection with one embodiment, it is contemplated that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other implementations, whether or not explicitly described.

[0016] Terms such as "first" and "second" may be used herein to describe various elements, but it is understood that these elements should not be limited to these terms. These terms are used only to distinguish one element from another. For example, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element, without departing from the scope of the example implementations. As used herein, the term "and / or" includes any and all combinations of one or more of the listed terms.

[0017] The terminology used herein is for the purpose of describing particular implementations only and is not intended to be limiting of example implementations. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms unless the context clearly indicates a different interpretation. It will be further understood that the terms "comprises," "comprising," "has," "having," "includes," and / or "including," as used herein, specify the presence of stated features, elements, and / or components, etc., but do not exclude the presence or addition of one or more other features, elements, components, and / or combinations thereof.

[0018] As used in this application, the term "circuitry" may refer to one or more or all of the following: (a) hardware-only circuit implementations (e.g., implementations using only analog and / or digital circuitry); and (b) A combination of hardware circuitry and software (as applicable): (i) Analog and / or digital hardware circuitry in combination with software / firmware; and (ii) any portion of hardware processors (including digital signal processors) with software, software, and memory that work together to cause a device, such as a mobile phone or server, to perform various functions; and (c) A hardware circuit and / or processor, such as a microprocessor or portion of a microprocessor, that requires software (e.g., firmware) to operate, but that does not require software when not necessary for operation.

[0019] This definition of circuit applies to all uses of the term in this application, including any claims. As another example, the term circuit as used in this application also encompasses implementations of simply a hardware circuit or processor (or processors), or portions of a hardware circuit or processor, and its (or their) accompanying software and / or firmware. The term circuit also encompasses, for example, and where applicable to certain claim elements, a baseband or processor integrated circuit for a mobile device, or a similar integrated circuit in a server, cellular network device, or other computing or network device.

[0020] As used herein, the term "communications network" refers to a network conforming to any suitable communications standard, such as Long Term Evolution (LTE), LTE-Advanced (LTE-A), Wideband Code Division Multiple Access (WCDMA), High-Speed ​​Packet Access (HSPA), Narrow Band Internet of Things (NB-IoT), etc. Furthermore, communications between terminal devices and network devices within a communications network may be conducted according to any suitable generation of communications protocol, including, but not limited to, first generation (1G), second generation (2G), 2.5G, 2.75G, third generation (3G), fourth generation (4G), 4.5G, future fifth generation (5G) communications protocols, and / or any other protocols now known or developed in the future. Implementations of the present disclosure may be applied to various communications systems. Given the rapid advances in communications, there will of course also be future types of communications technologies and systems in which the present disclosure may be embodied, and this should not be seen to limit the scope of the present disclosure to only the systems mentioned above.

[0021] As used herein, the term "network device" refers to a node in a communication network through which a terminal device accesses the network and receives services therefrom. Depending on the terminology and technology applied, a network device may refer to a base station (BS) or access point (AP), e.g., a Node B (NodeB or NB), evolved Node B (eNodeB or eNB), NR Next Generation Node B (gNB), a Remote Radio Unit (RRU), a Radio Header (RH), a Remote Radio Head (RRH), an Integrated Access and Backhaul (IAB) node, a relay, a femto, a pico, or other low-power node. A network device may be defined as part of a gNB, e.g., in a CU / DU split, in which case the network device is defined as a gNB-CU or a gNB-DU.

[0022] The term "terminal device" refers to any end device that may have wireless communication capabilities. By way of example and not limitation, a terminal device may also be referred to as a communication device, user equipment (UE), subscriber station (SS), portable subscriber station, mobile station (MS), or access terminal (AT). Terminal devices may include, without limitation, mobile phones, cellular phones, smartphones, voice over IP (VoIP) phones, wireless local loop phones, tablets, wearable terminal devices, personal digital assistants (PDAs), portable computers, desktop computers, image capture terminal devices such as digital cameras, gaming terminal devices, music storage and playback equipment, in-vehicle wireless terminal devices, wireless endpoints, mobile stations, laptop embedded equipment (LEE), laptop mounted equipment (LME), USB dongles, smart devices, wireless customer-premises equipment (CPE), Internet of Things (IoT) devices, watches or other wearables, head-mounted displays (HMD), vehicles, drones, medical devices and applications (e.g., remote surgery), industrial devices and applications (e.g., robots and / or other wireless devices operating in the context of industrial and / or automated processing chains), consumer electronic devices, devices operating on commercial and / or industrial wireless networks, and the like. In the following description, the terms "terminal device", "communication device", "terminal", "user equipment", and "UE" may be used interchangeably.

[0023] 1 shows a schematic diagram of an example communication network 100 in which implementations of the present disclosure may be practiced. As shown in FIG. 1, communication network 100 may include a first device 110, a second device 120, and a third device 130. Third device 130 may communicate with first device 110 and second device 120 via respective wireless communication channels.

[0024] In this example, for ease of discussion only, first device 110 and second device 120 are depicted as vehicles enabling V2X communication, and third device 130 is depicted as a network device serving devices 110 and 120. It should be understood that terminal device and network device are merely example implementations of first device 110, second device 120, and third device 130, respectively, without implying any limitation on the scope of the present application. Any other suitable implementations are also possible.

[0025] 1 is shown for illustrative purposes without implying any limitation to the present disclosure, and communication network 100 may include any suitable number of devices adapted to carry out implementations of the present disclosure.

[0026] Communications within communication network 100 may conform to any suitable standard, including, but not limited to, Global System for Mobile Communications (GSM), LTE, LTE Evolution, LTE Advanced (LTE-A), Wideband Code Division Multiple Access (WCDMA), Code Division Multiple Access (CDMA), GSM EDGE Radio Access Network (GERAN), Machine Type Communication (MTC), and the like. Furthermore, communications may occur according to any generation of communication protocols now known or developed in the future. Examples of communication protocols include, but are not limited to, first generation (1G), second generation (2G), 2.5G, 2.75G, third generation (3G), fourth generation (4G), 4.5G, and fifth generation (5G) communication protocols.

[0027] 1. Background of Unauthorized Operation In some implementations, communications within the communications network 100 may comprise sidelink (SL) communications. In sub-7 GHz unlicensed bands, coexistence of New Radio (NR) with other systems (e.g., IEEE 802.11) is ensured through a Listen Before Talking (LBT) channel access mechanism. According to this channel access mechanism, a user equipment (UE) intending to make an SL transmission must first successfully complete an LBT check before it can begin the same transmission. The LBT procedure may also be referred to as a Clear Channel Assessment (CCA) or channel access procedure.

[0028] To pass the LBT check, the UE must ensure that the channel is available for several consecutive CCA slots. In sub-7 GHz, these slots have a duration of 9 μs, as shown in Figure 2. Figure 2 shows that the CCA slots are of duration T sl = 9 μs, and energy sensing occurs during 4 μs. The UE determines that the channel is available in a CCA slot if the measured power (i.e., the energy collected during the CCA slot) is below a regulatory specified threshold, which may depend on the operating band and geographic region.

[0029] When a UE initiates communication (i.e., the UE acts as the initiating device), the UE must obtain the "right" to access the channel for a certain period of time, denoted in the regulations as Channel Occupancy Time (COT), by applying an "extended" LBT procedure, where the channel must be considered free for the entire duration of the Contention Window (CW). This "extended" LBT procedure is commonly known as LBT Type 1, as specified in TS 37.213. This procedure is shown in Figure 3.

[0030] Both the CW duration and the COT duration in Figure 3 depend on the Channel Access Priority Class (CAPC) associated with the UE's traffic, as shown in Table 1. Control plane traffic (such as PSCCH) is transmitted with p=1, and user plane traffic has p>1. Table 1 shows the details of LBT Type 1 for the Uu uplink (UL) case. It is noted that the LBT Type 1 parameters for the downlink (DL) case can also be adopted in principle in SL.

[0031] [Table 1]

[0032] Table 1 shows the CAPC for the UL. The contention window length in the CCA slot associated with each CAPC is the minimum (CW min,p ) and maximum value (CW max,p ) The duration of the COT is T ulm cot,p is given by

[0033] An example of the behavior during the contention window countdown procedure is shown in Figure 4. It should be noted that if the LBT check fails in any CCA slot during the countdown procedure, the countdown procedure will stop and will only resume if the channel is determined to be free (i.e., the LBT check is successful) during the defer time.

[0034] Specifically, Figure 4 shows examples of the LBT Type 1 contention window countdown procedure and how it can be perturbed. In example (a), neither the deferral time nor the countdown is perturbed (i.e., the channel is not detected as busy during the sensing slot). In example (b), the deferral time is perturbed (i.e., the channel is detected as busy during the deferral time sensing slot). In example (c), the contention window countdown is perturbed (i.e., the channel is detected as busy during the countdown sensing slot). In Figure 4, T d represents the postponement time, and T sl represents the CCA slot duration, and N represents the number of CCA slots required to be determined free before the contention window countdown is complete.

[0035] Upon successfully completing LBT Type 1, the transmitting UE (also called the initiating device) begins transmission and obtains a COT with a duration associated with the corresponding CAPC. The obtained COT remains valid even if the initiating device pauses its transmission, but the initiating device is still required to perform a "reduced" LBT procedure if it wants to make a new transmission (within the COT). This "reduced" LBT procedure is commonly known as LBT Type 2, with the following variations: - Type 2A (25 μs LBT) - for SL transmissions within the COT acquired by the initiating device (if the gap between two SL transmissions is ≥ 25 μs and for SL transmissions following another SL transmission), as shown in examples (c) and (f) of Figure 5. Type 2B (16 μs LBT) - for SL transmissions within the COT acquired by the initiating device, as shown in examples (b) and (e) of Figure 5 (can only be used for SL transmissions that follow another SL with a gap exactly equal to 16 μs) - Type 2C (without LBT) - can only be used for SL transmissions following another SL with a gap < 16 μs, as shown in examples (a) and (d) of Figure 5, and the allowed duration of an SL transmission is ≦ 584 μs.

[0036] Additionally, examples (a), (b), and (c) both illustrate the case where there is a gap between two transmissions from an initiating UE, while examples (d), (e), and (f) illustrate the case where there is a gap between two different transmissions from an initiating UE and its corresponding responding UE.

[0037] The initiating device may share its obtained COT with its intended receiver (also called the responding device). To do this, the initiating device must inform the responding device (e.g., via control signaling) about the duration of this COT. The responding device then uses this information to determine which type of LBT to apply when making a transmission where the intended receiver is the initiating device. If the responding device transmission is outside the range of the COT, the responding device will have to obtain a new COT using LBT Type 1 with the appropriate CAPC. This is explained with reference to Figure 6.

[0038] FIG. 6 shows an example of when a responding device must obtain a new COT. UE A obtains a new COT 605 using an LBT Type 1 procedure 610. UE A may transmit an SL transmission 620 to UE B on the PSCCH and / or PSSCH. In addition, UE A shares its obtained COT with UE B. UE B then uses this information to determine which type of LBT to apply when making a transmission where UE A is the intended receiver. To do this, UE A must inform UE B (e.g., via control signaling) about the duration of the COT 605. In this example, upon receiving the SL transmission 620, UE B performs an LBT Type 2 procedure 630 and transmits SL feedback information 640 to UE A on the PSFCH in response to the success of the LBT Type 2 procedure 630.

[0039] Because the transmission from UE B to UE C is outside the range of the COT 605, UE B must obtain a new COT 645 using an LBT Type 1 procedure 650 with the appropriate CAPC. UE B may transmit an SL transmission 660 to UE C on the PSCCH and / or PSSCH. In addition, UE B shares its obtained COT with UE C. UE C then uses this information to determine which type of LBT to apply when making a transmission where UE B is the intended receiver. To this end, UE B must inform UE C (e.g., via control signaling) about the duration of the COT 645. In this example, upon receiving the SL transmission 660, UE C performs an LBT Type 2 procedure 670 and, in response to the success of the LBT Type 2 procedure 670, transmits SL feedback information 680 to UE B on the PSFCH.

[0040] 2.NR-SL overview NR SL has been designed to facilitate user equipment (UE) communication with other nearby UEs through direct / SL communication. Two resource allocation modes are specified, one of which an SL transmitter (TX) UE (e.g., first device 110 or second device 120) is configured to perform NR SL transmissions. These modes are denoted NR SL Mode 1 and NR SL Mode 2. In Mode 1, the SL TX UE is assigned or scheduled with sidelink transmission resources by a network device (e.g., third device 130), and in Mode 2, the SL TX UE autonomously selects its SL transmission resources.

[0041] In Mode 1, the network device is responsible for SL resource allocation and the configuration and operation is similar to that on the Uu interface.

[0042] Figure 7 shows an example of NR SL resource allocation in Mode 2. In Mode 2, SL UEs autonomously perform resource selection using a sensing procedure. More specifically, an SL TX UE in NR SL Mode 2 first performs a sensing procedure through one or more configured SL transmission resource pools to gain knowledge of one or more resources reserved by at least one other nearby SL TX UE. Based on the knowledge gained from sensing, the SL TX UE may adaptively select at least one resource from the available SL resources. SL UEs need to decode sidelink control information (SCI) to perform sensing and obtain the information necessary to receive SL transmissions. In Release 16, SCIs related to data transmissions include first-phase SCIs and second-phase SCIs.

[0043] 2.1 NR SL Resource Allocation Mode 2 As mentioned above, in Mode 2, each UE autonomously selects resources by decoding the physical sidelink control channel (PSCCH) (or sidelink control information (SCI)) and performing RSRP measurements of at least one configured or pre-configured resource pool based on the procedure for the candidate resource pool during a sensing window interval.

[0044] Figure 8 shows a flowchart of a legacy SL resource allocation method 800. As shown in Figure 8, at block 810, the UE has data to transmit, so a sensing procedure for resource selection is initiated.

[0045] At block 820, the UE collects sensing information, including reserved resources and SL-RSRP measurements.

[0046] In block 830, the UE forms a candidate resource set.

[0047] In block 840, the UE selects Tx resources semi-persistently or up to a maximum reservation at start time "m".

[0048] In block 850, the UE continues decoding the PSCCHs of other UEs and re-evaluates its resource selection by measuring the corresponding PSSCH energies.

[0049] In block 860, the UE determines whether a resource reselection has been triggered (from the reevaluation).

[0050] If resource reselection has not been triggered, the UE begins transmission at block 870. If resource reselection has been triggered, method 800 proceeds to block 820.

[0051] In block 880, the UE determines whether resource reselection was triggered by reaching a maximum number of reservations.

[0052] If resource reselection is triggered by reaching the maximum number of reservations, the UE restarts method 800, and method 800 proceeds to block 820. If resource reselection is not triggered by reaching the maximum number of reservations, the UE continues to use the reservations, and method 800 proceeds to block 870.

[0053] In method 800, with respect to block 810, monitoring the resource pool and obtaining information to be used during the resource selection procedure may occur before the Tx UE knows it has a transmission to make. Additionally, with respect to block 830, the Tx UE may form a candidate resource set after obtaining sufficient information from monitoring the resource pool.

[0054] 9 shows a flowchart of a legacy method 900 for forming a resource candidate set. The method 900 occurs for resources in a candidate resource pool that are monitored during a detection window interval. During this detection window interval, the UE selects S of potential candidate resource slots that fall within a defined selection window period. A Collect the set of and filter out all resources / slots that satisfy at least one of the following: - the UE is not monitoring them during the sensing period (e.g. due to its own transmission or other activity, including DRX); and - The decoded SCI format 1-A is the pre-configured RSRP with the candidate slots reserved and the corresponding measured RSRP. threshold indicates that it is higher than

[0055] Specifically, as shown in FIG. 9, in block 910, the UE determines a selection window and threshold Set.

[0056] In block 920, the UE selects a candidate single slot resource set S A Initialize.

[0057] In block 930, the UE identifies the unmonitored resources as a set S A Exclude from.

[0058] In block 940, the UE receives the RSRP threshold The resources with RSRP greater than A Exclude from.

[0059] In block 950, the UE determines that the number of remaining slots is |XS A Determine whether |S| is greater than |, where X=0.2, 0.35, or 0.5. A | is Set S A Represents the initial total number of resources in

[0060] Number of remaining slots is |XS A If | is less than, the UE may, at block 960, threshold (i.e., RSRP threshold =RSRP threshold + step, where the step is now defined as 3 dB). The method 900 then proceeds to block 920.

[0061] Number of remaining slots is |XS AIf | is greater than |, the UE forwards the potential candidate slot to a higher order for final resource selection in block 970.

[0062] 2.2 SL physical layer structure The configuration of resources in the sidelink resource pool specifies the minimum information needed for an RX UE to be able to decode a transmission, including the number of subchannels, the number of PRBs per subchannel, the number of symbols in the PSCCH, which slots have a PSFCH, and other configuration aspects not relevant to this invention.

[0063] However, details of the actual sidelink transmission (i.e., payload) are provided in the PSCCH (first stage SCI) for each individual transmission, including, among other things, the time and frequency resources, the DMRS configuration of the PSSCH, the MCS, the PSFCH.

[0064] An example of an SL slot structure is shown in FIG. 10, which shows a slot with PSCCH / PSSCH in example (a) and a slot with PSCCH / PSSCH in example (b) where the last symbol is used for PSFCH.

[0065] Table 2 shows the PSSCH DMRS configurations based on the number of symbols used and the duration of the PSCCH.

[0066] [Table 2]

[0067] The PSCCH configuration (e.g., DMRS, MCS, number of symbols used) is part of the resource pool configuration. In addition, an indication of which slots have PSFCH symbols is also part of the resource pool configuration. However, the PSSCH configuration (e.g., number of symbols used, DMRS pattern, and MCS) is provided by the first stage SCI, which is the payload sent within the PSCCH, and follows the configuration shown in Table 2.

[0068] As explained in the background, for SL communications currently operating in SL mode 2, the UE determines a set of candidate single slot resources based on the received SCIs by checking which single slot resources are not reserved by other UEs and whether the RSRP associated with each of these SCIs is below a threshold. From that set of candidate single slot resources, the UE can then uniformly randomly select the required resources.

[0069] However, this resource selection procedure does not take into account that a UE must successfully complete an LBT procedure (LBT Type 1 or Type 2) before it can transmit within the selected resource. Furthermore, the successful completion of the LBT Type 1 procedure (i.e., the contention window countdown procedure) may be affected by the activity of other SL UEs and other WiFi devices.

[0070] FIG. 11 shows an example of how other SL UEs can disrupt the contention window countdown procedure associated with an SL UE's LBT Type 1 procedure. That is, upon sensing the resource pool, determining that a resource is free to use, and then selecting it for its transmission, the UE may be prevented from using the resource because the contention window countdown is not successfully completed (due to the disruption) within the start time of the selected resource. The impact is higher for UEs with high CAPC transmissions, which are generally associated with somewhat longer contention window durations. This disruption of the contention window countdown can be caused by the transmitting WiFi (or LTE LAA / NR-U) device and from SL transmissions occurring in slots preceding the slot of the selected resource. However, the disruption caused by the WiFi device is not known a priori, but does not apply to other SL transmissions, since the UE may become aware of both of these during the sensing procedure through normal monitoring of the resource pool. Furthermore, if the LBT contention window overlaps with the transmission symbols of another UE's reserved resource, there is a high probability of an LBT failure occurring during the contention window countdown, which may prevent the SL UE from successfully completing the final LBT check just before the start of the selected resource. In other words, neglecting the impact of the LBT procedure on the Mode 2 resource selection procedure will lead to very inefficient resource selection.

[0071] 11, it is assumed that resources 1110, 1112, and 1114 are detected as reserved by another UE, while resources 1120, 1122, and 1124 are detected as available candidate resources. Even if resources 1120, 1122, and 1124 are detected as free candidate resources, the UE may have problems if it selects them. Depending on the LBT contention window, the LBT procedure may fail because another UE has a reserved transmission immediately before resources 1120, 1122, and 1124.

[0072] NR-U supports multiple transmission start points through allocation of consecutive slots for transmission. In NR-U, the reserved adjacent allocations are for different transmission blocks (TBs) of the UE. However, in SL, the resource reservation is for one or more retransmissions of a TB, or for different TBs in the case of SPS allocations.

[0073] Implementations of the present disclosure provide a solution to SL resource selection to solve one or more of the above problems and other potential problems. According to the solution, when a device performs sensing-based resource selection, it knows that it will need to be able to complete a channel access procedure before transmitting, and it knows to take the associated channel access procedure duration (i.e., contention window countdown) into account when selecting a resource. More specifically, according to the solution, a first terminal device determines an expected time interval of a channel access procedure for transmission on a first candidate resource within an initial set of candidate resources. If the expected time interval overlaps with a transmission symbol of at least one reserved resource preceding the first candidate resource, the first terminal device excludes the first candidate resource from the initial set. The principles of the present disclosure will be described below with reference to Figures 12 to 17.

[0074] 12 shows a flowchart of an example method 1200 according to some implementations of the present disclosure. In some implementations, the method 1200 may be implemented in a device such as the device 110 or the device 120 as shown in FIG. 1. For purposes of discussion, the method 1200 will be described with reference to FIG. 1 as being performed by the first device 110, without loss of generality.

[0075] At block 1210, the first device 110 determines an expected time interval of a channel access procedure for transmission on a first candidate resource within the initial set of candidate resources.

[0076] At block 1220, the first device 110 determines whether the expected time interval overlaps with a transmission symbol of at least one reserved resource preceding the first candidate resource.

[0077] If the expected time interval overlaps with a transmission symbol of at least one reserved resource preceding the first candidate resource, the first device 110 determines a first set of candidate resources for sidelink transmission by excluding the first candidate resource from the initial set, at block 1230.

[0078] In some implementations, the at least one reserved resource may include a pre-configured number of reserved resources that precede the first candidate resource.

[0079] In some implementations, optionally, if the expected time interval does not overlap with the transmission symbols of at least one reserved resource preceding the first candidate resource, the first device 110 may determine a first set of candidate resources by including the first candidate resource in the first set at block 1240.

[0080] The method 1200 allows for the exclusion of all resources that are not available in any way due to the LBT Type 1 procedure not being successfully completed at the time the slot associated with the resource starts, thus avoiding the inefficient selection of unavailable resources.

[0081] In some implementations, the method 1200 may be performed for each candidate resource in the initial set.

[0082] 13 illustrates an example of SL resource selection according to some implementations of the present disclosure. In this example, resources 1310, 1312, 1314, 1316, and 1318 are reserved resources by the second device 120. The initial set of candidate resources includes resources 1320, 1322, 1324, and 1326, which are detected as free candidate resources.

[0083] In each of the reserved resources 1310, 1312, 1314, 1316, and 1318, the second device 120 may occupy symbols except for the final guard period (GP) symbol to make an SL transmission. Accordingly, the occupied symbols except for the final guard period (GP) symbol in each of the reserved resources 1310, 1312, 1314, 1316, and 1318 are also referred to as transmission symbols.

[0084] The first device 110 determines whether an expected time interval of a channel access procedure for transmission on the candidate resource 1320 overlaps with transmission symbols of the reserved resources 1310 and 1312 that precede the candidate resource 1320. If the expected time interval overlaps with transmission symbols of the reserved resources 1310 and 1312 that precede the candidate resource 1320, the first device 110 may exclude the candidate resource 1320 from its initial set of candidate resources. In this case, the first device 110 may include the candidate resource 1322 after the candidate resource 1320 in its initial set of candidate resources.

[0085] Similarly, the first device 110 determines whether the expected time interval of a channel access procedure for transmission on the candidate resource 1324 overlaps with the transmission symbols of the reserved resource 1316 that precede the candidate resource 1324. If the expected time interval overlaps with the transmission symbols of the reserved resource 1316 that precedes the candidate resource 1324, the first device 110 may exclude the candidate resource 1324 from its initial set of candidate resources. In this case, the first device 110 may include the candidate resource 1326 after the candidate resource 1324 in its initial set of candidate resources.

[0086] In some implementations, it is expected that for transmissions with high CAPC (i.e., lower priority traffic), the contention window countdown procedure will require several symbols (and in some extreme cases, several slots). Therefore, at least a completely empty slot may be required preceding the slot of the resource being evaluated, so that this resource is not excluded.

[0087] In some implementations, transmissions in slots following an empty slot may be limited to initial transmissions so that a Type 1 channel access procedure can occur within the unallocated slot time. In other words, the Type 1 channel access procedure requires one or more unoccupied slots before it can be finalized. In this case, resource exclusion may depend on whether the RSRP associated with the SCI indicated by the reserved transmission in the previous slot is higher than a configured RSRP threshold.

[0088] In some implementations, if the channel access procedure is a type 1 channel access procedure and the CAPC for the transmission is higher than a predefined value, the first device 110 may exclude a first candidate resource if there is a reserved resource that precedes the first candidate resource.

[0089] In some implementations, if the channel access procedure is a type 2 channel access procedure and the time interval is shorter than the guard period of at least one reserved resource, the first device 110 may include a first candidate resource in the first set if there is a reserved resource that precedes the first candidate resource.

[0090] In some implementations, a type 1 channel access procedure with a lower CAPC (high priority) is more likely to complete successfully within the guard symbol or period because the required channel access procedure time / duration is shorter. For example, CAPC-1 has a CW of up to seven CCA slots (i.e., 63 μs), which is less than the guard symbol length (approximately 71 μs) at 15 kHz subcarrier spacing. Similarly, for transmissions within a shared COT that can use a type 2 channel access procedure (occupying up to 25 μs), the channel access procedure can be successfully completed within the guard symbol. On the other hand, a type 1 channel access procedure with a higher CAPC (for low-priority transmissions or targeting a large COT size) cannot complete within the guard symbol because the CW of CAPC-3 starts at 15 CCA slots (135 μs).

[0091] In some implementations, the first device 110 that obtains the COT may also share the COT with other neighbor devices if they have reserved allocations following the slot allocated by the first device 110. The COT sharing information may be transmitted through the SCI or a similarly configured grant uplink control information (CG-UCI) from the NR-U.

[0092] In some implementations, for transmissions with low CAPC (i.e., high priority traffic) or within the COT, it is expected that the contention window countdown procedure may be contained within the guard period of the previous transmission, so that no resources are excluded in this case. In other words, the Type 1 channel access procedure may be finalized within the duration of the guard period (i.e., unoccupied symbols) of the previous allocation of reserved resources.

[0093] In some implementations, resource exclusion may also depend on whether the expected time interval of the channel access procedure and an additional time buffer (to account for potential disturbances due to WiFi device activity) overlap in time with a reserved transmission in a previous slot.

[0094] In some implementations, if the first device 110 is successful in the channel access procedure and obtains the COT, it may transmit in subsequent slots within the COT according to a type 2 channel access procedure. This means, for example, in FIG. 13, if candidate resource 1320 is reserved, candidate resource 1322 may also be reserved if needed by the first device 110, because if the channel access procedure is successful in transmitting in resource 1320, the COT may be used for transmission in subsequent resources.

[0095] In some implementations, the energy threshold E threshold may be used to estimate whether the energy level of other UE transmissions will cause LBT failure in a slot before the candidate resource. In such an implementation, the first device 110 may estimate the energy level of the sidelink transmission on the transmitted symbol. If the estimated energy level is higher than the energy threshold and the expected time interval overlaps with the transmitted symbol, the first device 110 may exclude the first candidate resource.

[0096] In some implementations, if the energy threshold is within a predetermined range, the first device 110 may determine whether the estimated energy level is higher than the energy threshold.

[0097] In some implementations, the first device 110 threshold In some implementations, the configuration may be used to disable some implementations of the present disclosure. For example, E threshold A high or inappropriate value of ≠ ...

[0098] The energy measurement may be based on RSSI or other energy-related measurements of other UE transmissions measured during the detection window, such as RSRP, carrier-to-interference ratio (CIR), signal-to-noise ratio (SNR), etc. Based on this, a combined energy estimate of previous transmissions on the candidate resource is calculated to determine whether the combined energy estimate satisfies an energy threshold E threshold If it is less than 1, the candidate resource is not excluded from selection. This is explained with reference to FIG.

[0099] 14 illustrates another example of SL resource selection according to some implementations of the present disclosure. In this example, the first device 110 estimates an energy level of a sidelink transmission on the transmission symbols of the reserved resources 1310 and 1312. If the estimated energy level is higher than an energy threshold and the expected time interval 1410 of the LBT procedure for transmission on the candidate resource 1320 overlaps with the transmission symbol, the first device 110 excludes the candidate resource 1320 from the initial set. On the other hand, if the estimated energy level is lower than the energy threshold and the expected time interval 1410 overlaps with the transmission symbol, the first device 110 may not exclude the candidate resource 1320 from the initial set.

[0100] 15 shows a flowchart of an example method 1500 according to some implementations of the present disclosure. Method 1500 may be considered an example implementation of method 1200. In some implementations, method 1500 may be implemented in a device such as device 110 or device 120 as shown in FIG. 1. For purposes of discussion, method 1500 will be described with reference to FIG. 1 as being performed by first device 110 without loss of generality.

[0101] In block 1510, the first device 110 determines a selection window and threshold Set.

[0102] At block 1530, the first device 110 selects a candidate single-slot resource set S A In the following, we initialize the set S A is also referred to as the initial set of candidate resources.

[0103] At block 1540, the first device 110 removes the unmonitored resources from the initial set.

[0104] At block 1550, the first device 110 threshold Remove from the initial set any resources that have an RSRP greater than .

[0105] In block 1210, the first device 110 determines an expected time interval of a channel access procedure for transmission on the first candidate resource. Block 1210 in Figure 15 is the same as block 1210 in Figure 12, and therefore details of block 1210 are omitted.

[0106] The first device 110 then determines whether the expected time interval overlaps with a transmission symbol of at least one reserved resource that precedes the first candidate resource, in block 1220. Block 1220 of Figure 15 is the same as block 1210 of Figure 12, and therefore details of block 1220 are omitted.

[0107] If the expected time interval overlaps with a transmission symbol of at least one reserved resource preceding the first candidate resource, the first device 110 estimates, at block 1520, an energy level of the sidelink transmission on a transmission symbol of at least one reserved resource preceding the first candidate resource in the initial set of candidate resources.

[0108] At block 1560, the first device 110 determines whether the estimated energy level is greater than an energy threshold.

[0109] If the estimated energy level is higher than the energy threshold, the first device 110 excludes the first candidate resource from the initial set at block 1570 .

[0110] At block 1580, the first device 110 determines whether the number of remaining resources is greater than 20% of the initial total number of resources in the initial set.

[0111] If the number of remaining resources is less than 20% of the initial total number of resources in the initial set, the first device 110 threshold The method 1500 then proceeds to block 1530.

[0112] If the number of remaining resources is greater than 20% of the initial total number of resources in the initial set, the first device 110 selects the last resource at block 1590 .

[0113] On the other hand, if the first device 110 determines in block 1220 that the expected time interval does not overlap with the transmission symbols of at least one reserved resource preceding the first candidate resource, or if the first device 110 determines in block 1560 that the estimated energy level is below an energy threshold, method 1500 may proceed to block 1580.

[0114] In some implementations, if there is no available resource in the first set of candidate resources whose time intervals for the channel access procedure do not overlap with the transmission symbols of the reserved resources, the first device 110 may do at least one of: determine a first set of candidate resources that includes the first candidate resource, extend the detection window, or increase the measurement threshold to find a candidate resource whose time intervals for the channel access procedure do not overlap with the transmission symbols of the reserved resources in the initial set.

[0115] In other words, after determining the candidate resource, if there is no available resource after an unoccupied slot that fits into the remaining duration of the channel access procedure (or a channel access procedure with a larger contention window size (CWS)), the first device 110 may decide to select the candidate resource (that would have been excluded) anyway, despite the risk of failure of the channel access procedure caused by other SL transmissions. Alternatively, the first device 110 can extend its sensing window and / or increase the SCI RSRP threshold to increase the chance of finding a more available resource option that gives enough time to finalize the channel access procedure.

[0116] In some implementations, the first device 110 may receive a configuration for at least one empty resource in the sidelink resource pool and exclude the at least one empty resource from the initial set of candidate resources.

[0117] In other words, in some implementations, a specific subset of slots may be excluded from being used for Mode 2 resource selection (e.g., according to a periodic configuration). That is, some slots may be configured to be empty using the parameter sl-TimeResource in 3GPP TS 38.331, for example, to facilitate LBT for larger CWSs. This configuration should be common for all SL devices. Empty slots may be excluded from any SL resource pool (RP), not just the resource pool (RP) that the first device 110 will use to reselect resources. The proposed implementation for reserving resources after empty slots may be limited to apply only to these configured slots, or alternatively, may be applicable to any slot detected as empty.

[0118] In some implementations, the first device 110 may receive a first configuration for a first sidelink resource pool (RP) having a first starting symbol and a first length of symbols. The first device 110 may also receive a second configuration for a second sidelink RP having a second starting symbol and a second length of symbols. The second starting symbol and second length are different from the first starting symbol and first length, respectively. The first device 110 may then select an initial set of candidate resources from one of the first and second sidelink RPs based on a priority of the sidelink transmission.

[0119] In other words, to facilitate transmission by LBT of different CWSs, a semi-static approach may be taken for different RPs with different configurations of start symbols (represented by sl-startSymbol) and symbol lengths (represented by sl-lengthSymbols) defined in SL. This semi-static approach may be taken especially for SL devices with high CAPC transmissions, which generally require a somewhat longer contention window duration. RPs with different start and length may be in different LBT bandwidths. This is explained with reference to Figure 16.

[0120] Figure 16 shows an example of RPs with different configurations to facilitate transmission by LBT of different CWSs. As shown in Figure 16, for a given SL BWP, one RP has a configuration of sl-startSymbol=0 and sl-lengthSymbols=14, and another RP has a configuration of sl-startSymbol=7 and sl-lengthSymbols=7. The selection of the Tx RP is based on the CAPC associated with the intended transmission; i.e., one of the RPs may be intended for high CAPC transmission and the other for low CAPC. Thus, the first device 110 may exclude from the RPs candidate resources that do not match the corresponding CAPC.

[0121] For example, as shown in Figure 16, for a lower CAPC transmission, the first device 110 may choose RP#0 if it can be guaranteed that the LBT will be finalized within the GUARD-symbol. For a higher CAPC transmission, the first device 110 may use RP#1, and the "white" symbol after the GUARD-symbol may be useful to finalize the long LBT required by the high CAPC transmission and to avoid LBT overlap with other SL-U terminal device transmissions. Two RPs (e.g., RP#0 and RP#1) are configured in different unlicensed channels so that transmissions on RP#0 do not affect the LBT for transmissions on RP#1.

[0122] In some example implementations, an apparatus (e.g., a device) capable of performing any of method 1200 may comprise means for performing each step of method 1200. The means may be implemented in any suitable manner. For example, the means may be implemented in a circuit or a software module.

[0123] In some example implementations, the apparatus comprises: means for determining an expected time interval of a channel access procedure for transmission on a first candidate resource within an initial set of candidate resources; and means for determining a first set of candidate resources for sidelink transmission by excluding the first candidate resource from the initial set according to a determination that the expected time interval overlaps with a transmission symbol of at least one reserved resource preceding the first candidate resource.

[0124] In some implementations, the apparatus further comprises means for estimating an energy level of the sidelink transmission over the transmitted symbol; and the means for eliminating the first candidate resource comprises: means for eliminating the first candidate resource according to a determination that the estimated energy level is higher than an energy threshold and the expected time interval overlaps with the transmitted symbol.

[0125] In some implementations, the apparatus further comprises means for: determining, in accordance with a determination that the energy threshold is within a predetermined range, whether the estimated energy level is higher than the energy threshold.

[0126] In some implementations, the apparatus further comprises means for, in accordance with a determination that there is no available resource in the first set of candidate resources whose time interval of the channel access procedure does not overlap with a transmission symbol of the reserved resource, doing at least one of the following: determining a first set of candidate resources that includes the first candidate resource; Expanding the detection window or increasing the measurement threshold to find candidate resources whose time intervals of channel access procedures do not overlap with the transmitted symbols of reserved resources in the initial set.

[0127] In some implementations, the apparatus further comprises: means for receiving a configuration for at least one empty resource in a sidelink resource pool; and means for excluding the at least one empty resource from the initial set of candidate resources.

[0128] In some implementations, the means for excluding the first candidate resource comprises: means for excluding the first candidate resource if there is a reserved resource preceding the first candidate resource when the channel access procedure is a type 1 channel access procedure and a Channel Access Priority Class (CAPC) for transmission is higher than a predefined value; and means for including the first candidate resource in the first set if there is a reserved resource preceding the first candidate resource when the channel access procedure is a type 2 channel access procedure and the time interval is shorter than a guard period of at least one reserved resource.

[0129] In some implementations, the apparatus further comprises: means for receiving a first configuration for a first sidelink resource pool having a first starting symbol and a first length of symbols; means for receiving a second configuration for a second sidelink resource pool having a second starting symbol and a second length of symbols, the second starting symbol and second length being different from the first starting symbol and first length, respectively; and means for selecting an initial set of candidate resources from one of the first and second sidelink resource pools based on a priority of the sidelink transmission.

[0130] In some implementations, the apparatus further comprises: means for excluding the first candidate resource from the initial set if the slot preceding the first candidate resource is empty and the channel access procedure is not a type 1 channel access procedure.

[0131] 17 is a simplified block diagram of a device 1700 suitable for implementing embodiments of the present disclosure. The device 1700 may be provided to implement a communications device, such as the first device 110 or the second device 120 as shown in FIG. 1. As shown, the device 1700 includes one or more processors 1710, one or more memories 1720 coupled to the processors 1710, and one or more communications modules 1740 coupled to the processors 1710.

[0132] The communication module 1740 is for two-way communication. The communication module 1740 has at least one antenna to facilitate communication. The communication interface may represent any interface necessary for communication with other network elements.

[0133] The processor 1710 can be of any type suitable for a local technology network: by way of non-limiting examples, it may include one or more of a general-purpose computer, a special-purpose computer, a microprocessor, a digital signal processor (DSP), and a processor based on a multi-core processor architecture. The device 1700 may have multiple processors, such as application-specific integrated circuits, that are slaved in time to a clock that synchronizes the main processor.

[0134] The memory 1720 may include one or more non-volatile memories and one or more volatile memories. Examples of non-volatile memories include, but are not limited to, read-only memory (ROM) 1724, electrically programmable read-only memory (EPROM), flash memory, hard disks, compact disks (CDs), digital video disks (DVDs), and other magnetic and / or optical storage. Examples of volatile memories include, but are not limited to, random access memory (RAM) 1722 and other volatile memories that do not persist through power-down durations.

[0135] The computer program 1730 includes computer-executable instructions that are executed by the associated processor 1710. The program 1730 may be stored in the ROM 1724. The processor 1710 may load the program 1730 into the RAM 1722 to perform any suitable operation or process.

[0136] Embodiments of the present disclosure may be implemented by a program 1730 such that the device 1700 may perform any process of the present disclosure, such as those discussed with reference to Figures 1 to 16. Embodiments of the present disclosure may also be implemented by hardware or a combination of software and hardware.

[0137] In some exemplary embodiments, the program 1730 may be tangibly contained in a computer-readable medium, which may be included in the device 1700 (such as in memory 1720) or other storage device accessible by the device 1700. The device 1700 may load the program 1730 from the computer-readable medium into RAM 1722 for execution. The computer-readable medium may include any type of tangible non-volatile storage, such as ROM, EPROM, flash memory, hard disk, CD, DVD, and the like. Figure 18 shows an example of a computer-readable medium 1800 in the form of a CD or DVD. The computer-readable medium has the program 1730 stored thereon.

[0138] In general, various embodiments of the present disclosure may be implemented in hardware or special purpose circuits, software, logic, or a combination thereof. Some aspects may be implemented in hardware, while other aspects may be implemented in firmware or software that may be executed by a controller, microprocessor, or other computing device. While various aspects of the embodiments of the present disclosure are shown and described as block diagrams, flowcharts, or using some other graphical representations, it should be understood that the blocks, apparatus, systems, techniques, or methods described herein may be implemented in, by way of non-limiting example, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing device, or some combination thereof.

[0139] The present disclosure also provides at least one computer program product tangibly stored on a non-transitory computer-readable storage medium. The computer program product includes computer-executable instructions, such as those included in program modules, that execute on a target device on a real or virtual processor to perform methods 1200 and 1500 as described above with reference to FIGS. 12 and 15. Generally, program modules include routines, programs, libraries, objects, classes, components, data structures, etc. that perform particular tasks or implement particular abstract data types. The functionality of the program modules may be combined or divided among program modules as desired in various embodiments. Machine-executable instructions for program modules may be executed in local or distributed devices. In distributed devices, program modules may be located in both local and remote storage media.

[0140] Program code for carrying out the methods of the present disclosure may be written in any combination of one or more programming languages. These program codes may be provided to a processor or controller of a general-purpose computer, a special-purpose computer, or other programmable data processing apparatus such that, when executed by the processor or controller, the functions / acts specified in the flowcharts and / or block diagrams are performed. The program code may run as a stand-alone software package, entirely on the machine, partially on the machine, partially on the machine and partially on a remote machine, or entirely on a remote machine or server.

[0141] In the context of the present disclosure, computer program code or associated data may be carried by any suitable carrier to enable a device, apparatus, or processor to perform the various processes and operations as described above. Examples of carriers include signals, computer-readable media, and the like.

[0142] The computer-readable medium may be a computer-readable signal medium or a computer-readable storage medium. The computer-readable medium may include, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination thereof. More specific examples of computer-readable storage media include an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination thereof.

[0143] Additionally, while operations are shown in a particular order, it should not be understood that such operations need to be performed in the particular order or sequence shown, or that all of the operations shown need to be performed, to achieve desired results. In some situations, multitasking and parallel processing may be advantageous. Similarly, while details of several specific implementations are included in the above discussion, these should not be construed as limitations on the scope of the disclosure, but rather as descriptions of features that may be unique to particular embodiments. Some features that are described in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment may also be implemented in multiple embodiments separately or in any suitable subcombination.

[0144] Although the present disclosure has been described in language specific to structural features and / or methodological acts, it should be understood that the present disclosure, as defined in the appended claims, is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.

Claims

1. determining, at the first device, an expected time interval of a channel access procedure for transmission on a first candidate resource within an initial set of candidate resources; determining a first set of candidate resources for sidelink transmission by excluding the first candidate resource from the initial set in accordance with a determination that the expected time interval overlaps with a time interval of a transmission symbol of at least one reserved resource of the second device preceding the first candidate resource; A method comprising:

2. Estimating an energy level of a sidelink transmission on a transmitted symbol further comprising Eliminating the first candidate resource includes: Eliminating the first candidate resource in accordance with a determination that the estimated energy level is higher than an energy threshold and the expected time interval overlaps with a time interval of a transmitted symbol of the second device. The method of claim 1 , comprising:

3. and determining whether the estimated energy level is greater than the energy threshold following a determination that the energy threshold is within a predetermined range. The method of claim 2 further comprising:

4. In response to determining that there is no available resource within the first set of candidate resources, the time interval of which does not overlap with the time interval of the transmission symbols of the reserved resource, determining a first set of candidate resources including a first candidate resource; Expanding the detection window, or increasing the measurement threshold to find candidate resources whose time intervals for channel access procedures do not overlap with the time intervals for transmission symbols of reserved resources in the initial set; The method of claim 1 , further comprising performing at least one of:

5. receiving a configuration for at least one empty resource in a sidelink resource pool; excluding at least one empty resource from the initial set of candidate resources; The method of claim 1 further comprising:

6. Eliminating the first candidate resource If the channel access procedure is a type 1 channel access procedure and a Channel Access Priority Class (CAPC) for transmission is higher than a predefined value, excluding a first candidate resource if there is a reserved resource preceding the first candidate resource; If the channel access procedure is a type 2 channel access procedure and the time interval is shorter than the guard period of at least one reserved resource, including the first candidate resource in the first set if there is a reserved resource preceding the first candidate resource; The method of claim 1 , comprising:

7. receiving a first configuration for a first sidelink resource pool having a first starting symbol and a first length in symbols; receiving a second configuration for a second sidelink resource pool having a second starting symbol and a second length of symbols, the second starting symbol and the second length being different from the first starting symbol and the first length, respectively; selecting an initial set of candidate resources from one of the first and second sidelink resource pools based on a priority of the sidelink transmission; The method of claim 1 further comprising:

8. If the slot preceding the first candidate resource is empty and the channel access procedure is not a type 1 channel access procedure, then excluding the first candidate resource from the initial set.

8. The method of claim 1, further comprising:

9. means for determining an expected time interval of a channel access procedure for transmission on a first candidate resource within an initial set of candidate resources; means for determining a first set of candidate resources for sidelink transmission by excluding a first candidate resource from the initial set according to a determination that the expected time interval overlaps with a time interval of a transmission symbol of at least one reserved resource of another device that precedes the first candidate resource; An apparatus comprising:

10. Means for estimating an energy level of a sidelink transmission on a transmitted symbol - Patent Application 20070122933 Furthermore, The means for eliminating a first candidate resource includes: means for eliminating the first candidate resource in accordance with a determination that the estimated energy level is higher than an energy threshold and the expected time interval overlaps with a time interval of a transmitted symbol of another device; The apparatus of claim 9, comprising:

11. means for determining whether the estimated energy level is greater than the energy threshold following a determination that the energy threshold is within a predetermined range; The apparatus of claim 10 further comprising:

12. In response to a determination that there are no available resources within the first set of candidate resources whose time intervals for the channel access procedure do not overlap with time intervals for transmission symbols of the reserved resources, determining a first set of candidate resources including a first candidate resource; Expanding the detection window, or increasing the measurement threshold to find candidate resources whose time intervals for channel access procedures do not overlap with the time intervals for transmission symbols of reserved resources in the initial set; The apparatus of claim 9 further comprising means for performing at least one of:

13. means for receiving a configuration for at least one empty resource in a sidelink resource pool; means for excluding at least one empty resource from the initial set of candidate resources; The apparatus of claim 9 further comprising:

14. The means for eliminating a first candidate resource comprises: means for excluding a first candidate resource if there is a reserved resource preceding the first candidate resource, when the channel access procedure is a type 1 channel access procedure and a Channel Access Priority Class (CAPC) for the transmission is higher than a predefined value; and means for including a first candidate resource in the first set if there is a reserved resource preceding the first candidate resource, if the channel access procedure is a type 2 channel access procedure and the time interval is shorter than a guard period of at least one reserved resource; The apparatus of claim 9, comprising:

15. means for receiving a first configuration for a first sidelink resource pool having a first starting symbol and a first length in symbols; means for receiving a second configuration for a second sidelink resource pool having a second starting symbol and a second length of symbols, the second starting symbol and the second length being different from the first starting symbol and the first length, respectively; and means for selecting an initial set of candidate resources from one of the first and second sidelink resource pools based on a priority of the sidelink transmission; The apparatus of claim 9 further comprising:

16. means for excluding a first candidate resource from the initial set if the slot preceding the first candidate resource is empty and the channel access procedure is not a type 1 channel access procedure; 16. The apparatus of claim 9, further comprising:

17. A computer-readable medium comprising program instructions that, when executed by an apparatus, cause the apparatus to: determining, at the first device, an expected time interval of a channel access procedure for transmission on a first candidate resource within an initial set of candidate resources; determining a first set of candidate resources for sidelink transmission by excluding the first candidate resource from the initial set according to a determination that the expected time interval overlaps with a time interval of a transmission symbol of at least one reserved resource of another device preceding the first candidate resource; and A computer-readable medium for causing

18. When executed by the device, the device: Estimating an energy level of a sidelink transmission on a transmitted symbol and further comprising program instructions to cause the Eliminating the first candidate resource includes: Eliminating the first candidate resource according to a determination that the estimated energy level is higher than an energy threshold and the expected time interval overlaps with a time interval of a transmitted symbol of another device.

20. The computer-readable medium of claim 17, comprising:

19. When executed by the device, the device: and determining whether the estimated energy level is greater than the energy threshold following a determination that the energy threshold is within a predetermined range.

20. The computer readable medium of claim 18, further comprising program instructions to:

20. When executed by the device, the device: In response to determining that there is no available resource within the first set of candidate resources, the time interval of which does not overlap with the time interval of the transmission symbols of the reserved resource, determining a first set of candidate resources including a first candidate resource; Expanding the detection window, or increasing the measurement threshold to find candidate resources whose time intervals for channel access procedures do not overlap with the time intervals for transmission symbols of reserved resources in the initial set; 20. The computer-readable medium of claim 17, further comprising program instructions that cause the computer to perform at least one of the following:

21. When executed by the device, the device: receiving a configuration for at least one empty resource in a sidelink resource pool; excluding at least one empty resource from the initial set of candidate resources; 20. The computer readable medium of claim 17, further comprising program instructions to:

22. Eliminating the first candidate resource If the channel access procedure is a type 1 channel access procedure and a Channel Access Priority Class (CAPC) for transmission is higher than a predefined value, excluding a first candidate resource if there is a reserved resource preceding the first candidate resource; If the channel access procedure is a type 2 channel access procedure and the time interval is shorter than the guard period of at least one reserved resource, including the first candidate resource in the first set if there is a reserved resource preceding the first candidate resource; 20. The computer-readable medium of claim 17, comprising:

23. When executed by the device, the device: receiving a first configuration for a first sidelink resource pool having a first starting symbol and a first length in symbols; receiving a second configuration for a second sidelink resource pool having a second starting symbol and a second length of symbols, the second starting symbol and the second length being different from the first starting symbol and the first length, respectively; selecting an initial set of candidate resources from one of the first and second sidelink resource pools based on a priority of the sidelink transmission; 20. The computer readable medium of claim 17, further comprising program instructions to:

24. When executed by the device, the device: If the slot preceding the first candidate resource is empty and the channel access procedure is not a type 1 channel access procedure, then excluding the first candidate resource from the initial set.

24. The computer readable medium of claim 17, further comprising program instructions to:

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