WO2022126600A1

WO2022126600A1 - Method and apparatus for sidelink transmission

Info

Publication number: WO2022126600A1
Application number: PCT/CN2020/137614
Authority: WO
Inventors: Jing HAN; Congchi ZHANG; Ran YUE; Lianhai WU; Haiming Wang
Original assignee: Lenovo (Beijing) Limited
Priority date: 2020-12-18
Filing date: 2020-12-18
Publication date: 2022-06-23

Abstract

The present application relates to a method and an apparatus for sidelink transmission. The method includes: transmitting or receiving an SCI to or from another user equipment, wherein the SCI includes a NDI and a HARQ feedback indicator; and determining whether to start an inactivity timer according to the NDI and the HARQ feedback indicator.

Description

METHOD AND APPARATUS FOR SIDELINK TRANSMISSION

TECHNICAL FIELD

Embodiments of the present application generally relate to wireless communication technology, especially to a method and an apparatus for sidelink transmission under 3GPP (3rd Generation Partnership Project) 5G new radio (NR) .

BACKGROUND

With network developments of 3rd Generation Partnership Project (3GPP) 5G New Radio (NR) , sidelink transmission between user equipment is developed. For power saving issue, timer-based discontinuous reception (DRX) scheme used for Uu interface between the user equipment and the base station is introduced for sidelink transmission between the user equipment. One of the timers used in the DRX scheme on Uu interface is inactivity timer. However, when the inactivity timer is introduced for sidelink transmission between the user equipment, mis-alignment issues among base station and the user equipment happen.

SUMMARY

Some embodiments of the present application provide a method performed by a user equipment (UE) for wireless communication. The method includes: transmitting a sidelink control information (SCI) to another user equipment, wherein the SCI includes a new data indicator (NDI) and a hybrid automatic repeat request (HARQ) feedback indicator; and determining whether to start an inactivity timer according to the NDI and the HARQ feedback indicator.

Some embodiments of the present application provide a method performed by a UE for wireless communication. The method includes: receiving a SCI from another user equipment, wherein the SCI includes a NDI and a HARQ feedback indicator; and determining whether to start an inactivity timer according to the NDI and the HARQ feedback indicator.

Some embodiments of the present application provide an apparatus. The apparatus includes: a non-transitory computer-readable medium having stored thereon computer-executable instructions; a receiving circuitry; a transmitting circuitry; and a processor coupled to the non-transitory computer-readable medium, the receiving circuitry and the transmitting circuitry, wherein the computer-executable instructions cause the processor to implement the abovementioned method for wireless communications.

The details of one or more examples are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to describe the manner in which advantages and features of the application can be obtained, a description of the application is rendered by reference to specific embodiments thereof, which are illustrated in the appended drawings. These drawings depict only example embodiments of the application and are not therefore to be considered limiting of its scope.

FIG. 1 illustrates a schematic diagram of a wireless communication system in accordance with some embodiments of the present application.

FIGS. 2A to 2C illustrate schematic diagrams of data transmissions in accordance with some embodiments of the present application.

FIG. 3 illustrates a schematic diagram of message transmission in accordance with some embodiments of the present application.

FIG. 4A to 4C illustrate schematic diagrams of message transmissions in accordance with some embodiments of the present application.

FIG. 5 illustrates a flow chart of a method for wireless communications according to an embodiment of the present disclosure.

FIGS. 6A to 6C illustrate flow charts of a method for wireless communications according to an embodiment of the present disclosure.

FIG. 7 illustrates a block diagram of an exemplary apparatus in accordance with some embodiments of the present application.

DETAILED DESCRIPTION

The detailed description of the appended drawings is intended as a description of preferred embodiments of the present application and is not intended to represent the only form in which the present application may be practiced. It should be understood that the same or equivalent functions may be accomplished by different embodiments that are intended to be encompassed within the spirit and scope of the present application.

Reference will now be made in detail to some embodiments of the present application, examples of which are illustrated in the accompanying drawings. Embodiments of the present application may be provided in a network architecture that adopts various service scenarios, for example but is not limited to, 3GPP 3G, long-term evolution (LTE) , LTE-Advanced (LTE-A) , 3GPP 4G, 3GPP 5G NR (new radio) , etc. It is contemplated that along with the 3GPP and related communication technology development, the terminologies recited in the present application may change, which should not affect the principle of the present application.

FIG. 1 illustrates a schematic diagram of a wireless communication system 100 in accordance with some embodiments of the present application. The wireless communication system 100 includes a user equipment (UE) 101, a UE 102 and a base station (BS) 103. Although a specific number of UEs 101, 102 and BS 103 are depicted in FIG. 1, it is contemplated that any number of UE, BS and core network (CN) may be included in the wireless communication system 100.

The BS 103 may be distributed over a geographic region. In certain embodiments of the present application, the BS 103 may also be referred to as an access point, an access terminal, a base, a base unit, a macro cell, a Node-B, an evolved Node B (eNB) , a gNB, a Home Node-B, a relay node, or a device, or described using other terminology used in the art. The BS 103 is generally part of a radio access network that may include one or more controllers communicably coupled to one or more corresponding BS (s) .

UEs 101 and 102 may include, for example, but is not limited to, computing devices, such as desktop computers, laptop computers, personal digital assistants (PDAs) , tablet computers, smart televisions (e.g., televisions connected to the Internet) , set-top boxes, game consoles, security systems (including security cameras) , vehicle on-board computers, network devices (e.g., routers, switches, and modems) , Internet of Thing (IoT) devices, or the like.

According to some embodiments of the present application, UEs 101 and 102 may include, for example, but is not limited to, a portable wireless communication device, a smart phone, a cellular telephone, a flip phone, a device having a subscriber identity module, a personal computer, a selective call receiver, a wireless sensor, a monitoring device, or any other device that is capable of sending and receiving communication signals on a wireless network.

In some embodiments of the present application, UEs 101 and 102 may include, for example, but is not limited to, wearable devices, such as smart watches, fitness bands, optical head-mounted displays, or the like. Moreover, UEs 101 and 102 may be referred to as a subscriber unit, a mobile, a mobile station, a user, a terminal, a mobile terminal, a wireless terminal, a fixed terminal, a subscriber station, a user terminal, or a device, or described using other terminology used in the art. UEs 101 and 102 may communicate with each other via sidelink transmission. The UE 101 and 102 may respectively communicate with the BS 103 via uplink communication signals.

The wireless communication system 100 is compatible with any type of network that is capable of sending and receiving wireless communication signals. For example, the wireless communication system 100 is compatible with a wireless communication network, a cellular telephone network, a time division multiple access (TDMA) -based network, a code division multiple access (CDMA) -based network, an orthogonal frequency division multiple access (OFDMA) -based network, an LTE network, a 3GPP-based network, a 3GPP 5G network, a satellite communications network, a high altitude platform network, and/or other communications networks.

According to existing agreements, timer-based discontinuous reception (DRX) scheme used for sidelink interface between UEs 101, 102 and BS 103 may be introduced for sidelink transmission between UEs 101 and 102 for power saving issues. The timers used in the DRX scheme on Uu interface include on-duration timer and inactivity timer. However, when the inactivity timer is introduced for sidelink transmission between UEs 101 and 102, mis-alignment issues among UEs 101, 102 and BS 103 may happen.

For example, referring to FIG. 2A, UE 101 may have transmissions T01 and T02 which are both within on-duration timer. UE 101 may start inactivity timer after transmission T01. In some cases (e.g., hidden node issue or half duplex transmission scheme) , UE 102 may not receive transmission T01 so that UE 102 may not start inactivity timer. When UE 102 received transmission T02, UE 102 may consider transmission T02 as a new transmission so that UE 102 may start inactivity timer. Therefore, UEs 101 and 102 may has misaligned active time, and UE 102 may still keep awake unnecessarily after inactivity timer of UE 101 expires.

For another example, referring to FIG. 2B, UE 101 may have transmissions T01 and T02 and transmission T01 is within on-duration timer. UE 101 may start inactivity timer after transmission T01 and transmission T02 may happen within inactivity timer. In some cases (e.g., hidden node issue or half duplex transmission scheme) , UE 102 may not receive transmission T01 so that UE 102 may not start inactivity timer. When on-duration timer expires after transmission T01 and before transmission T02, UE 102 may switch to DRX so that UE 102 may not receive transmission T02. Moreover, UE 102 may not receive all data transmission after on-duration timer expires. Therefore, UEs 101 and 102 may have misaligned active time, and packet loss problem may happen after on-duration timer of UE 102 expires.

For another example, referring to FIG. 2C, UE 101 may have transmissions T01 and T02 and transmission T01 is within on-duration timer. UE 101 and BS 103 may start inactivity timer after transmission T01 and transmission T02 may happen within inactivity timer. In some cases (e.g., hidden node issue or half duplex transmission scheme) , UE 102 may not receive transmission T01 so that UE 102 may not start inactivity timer. When on-duration timer expires after transmission T01 and before transmission T02, UE 102 may switch to DRX. However, BS 103 may not be informed of that UE 102 switches to DRX, and BS 103 may still schedule sidelink transmission so that UE 102 may miss the sidelink transmission.

Accordingly, in the present disclosure, to avoid mis-alignment issues of the inactivity timer among

UEs

101, 102 and BS 103, a timer alignment scheme may be introduced. More details on embodiments of the present disclosure will be further described hereinafter.

In particular,

UEs

101 and 102 may have established PC5 radio resource control (PC5-RRC) connection of sidelink transmission. Sidelink DRX configuration may be exchanged and aligned between

UEs

101 and 102, which means that

UEs

101 and 102 may have aligned understanding of an on-duration timer and an inactivity timer.

Then, inactivity timer for sidelink transmission may not start when: (1) transmitting UE (i.e., Tx UE) does not know status of receiving UE (i.e., Rx UE) , e.g., no hybrid automatic repeat request (HARQ) feedback is transmitted from Rx UE; or (2) only negative-acknowledgement (NACK) feedback is transmitted from Rx UE. Inactivity timer for sidelink transmission may start when sidelink control information (SCI) indicates that HARQ feedback function is enabled for this transmission and HARQ feedback information includes acknowledgement (ACK) or NACK.

FIG. 3 is a schematic diagram of message transmission in accordance with some embodiments of the present application. In detail, UE 101 (e.g., a transmitting UE, Tx UE) may transmit a SCI 101A to UE 102 (e.g., a receiving UE, Rx UE) . SCI 101A may include a new data indicator (NDI) 101A1 and an HARQ feedback indicator 101A2.

UE

101 and 102 may determine whether to start an inactivity timer used for sidelink transmission according to NDI 101A1 and HARQ feedback indicator 101A2.

In some embodiments,

UEs

101 and 102 may use unicast transmission mode for transport block (TB) (i.e., a cast type indicator of SCI 101A indicates 10 which means unicast transmission) . When UE 101 transmits a TB corresponding to SCI 101A to UE 102,

UEs

101 and 102 may check whether the TB is new data transmission by NDI 101A1. When NDI 101A1 is not toggled, which means that NDI 101A1 indicates that the TB is not new data transmission (i.e., NDI 101A1 is the same as a previous NDI for the same sidelink process between UEs 101 and 102) ,

UEs

101 and 102 may determine not to start the inactivity timer. When NDI 101A1 is toggled, which means that NDI 101A1 indicates that the TB is new data transmission (i.e., NDI 101A1 is not the same as a previous NDI for the same sidelink process between UEs 101 and 102) ,

UEs

101 and 102 may check whether HARQ feedback function is enabled by HARQ feedback indicator 101A2.

When HARQ feedback indicator 101A2 indicates a disablement of HARQ feedback function (i.e., HARQ feedback indicator 101A2 is set to 0 which indicates that the TB does not require HARQ feedback) ,

UEs

101 and 102 may determine not to start the inactivity timer. When HARQ feedback indicator 101A2 indicates an enablement of HARQ feedback function (i.e., HARQ feedback indicator 101A2 is set to 1 which indicates that the TB requires HARQ feedback) and a cast type indicator of SCI 101A indicates unicast (i.e., the cast type indicator is set to 10) ,

UEs

101 and 102 may determine to start the inactivity timer.

In some embodiments, when UE 101 transmits a TB corresponding to SCI 101A to UE 102,

UEs

101 and 102 may determine not to start the inactivity timer. When HARQ feedback indicator 101A2 indicates an enablement of HARQ feedback function (i.e., HARQ feedback indicator 101A2 is set to 1 which indicates that the TB requires HARQ feedback) and the cast type indicator of SCI 101A indicates groupcast with HARQ feedback information including only NACK (i.e., the cast type indicator is set to 11) ,

UEs

101 and 102 may determine not to start the inactivity timer. When HARQ feedback indicator 101A2 indicates an enablement of HARQ feedback function (i.e., HARQ feedback indicator 101A2 is set to 1 which indicates that the TB requires HARQ feedback) and the cast type indicator of SCI 101A indicates groupcast with HARQ feedback information including ACK and NACK (i.e., the cast type indicator is set to 01) ,

UEs

101 and 102 may determine to start the inactivity timer.

In some embodiments,

UEs

101 and 102 may use broadcast transmission mode for TB, (i.e., the cast type indicator of SCI 101A indicates 00 which means the broadcast transmission) . When UE 101 transmits a TB corresponding to SCI 101A to UE 102,

UEs

101 and 102 may determine not to start the inactivity timer.

As described above, when NDI 101A1 is not toggled, UEs 101 and 102 may determine not to start the inactivity timer. When NDI 101A1 is toggled, whether to start the inactivity timer may be determined by the rules of the following table:

In some implementations, the cast type indicator may include two bits and ‘00’ for broadcast type, ‘01’ for groupcast type HARQ feedback with ACK/NACK, ‘10’ for unicast type and ‘11’ for groupcast type HARQ feedback with only NACK.

In some embodiments, UE 101 may be capable of selecting a resource for data transmission between UEs 101 and 102 (i.e., UE 101 is under of sidelink transmission mode 2 which is UE autonomous resource selection mode) , the inactivity timer may start (i.e., NDI 101A1 is toggled, HARQ feedback indicator 101A2 is set to 1 which indicates that this TB requires HARQ feedback function) , and the cast type indicator may indicate unicast (i.e., the cast type indicator is set to 10) .

Then, after transmitting the TB, when UE 101 detects discontinuous transmission (DTX) status on corresponding HARQ feedback channel (i.e., UE 101 does not receive HARQ feedback from UE 102 on corresponding physical sidelink feedback channel (PSFCH) ) , UE 101 may determine that UE 102 does not start the corresponding inactivity timer. Therefore, UE 101 may restore the inactivity timer because UE 102 does not start the corresponding inactivity timer, and UE 101 may be triggered to determine an active time of UE102.

In some implementations, UE 101 may check whether an upcoming reserved resource is within the active time of UE 102. When the upcoming reserved resource is not within the active time of UE 102, UE 101 may trigger resource re-selection, and select new resource according to determined active time of UE 102. In some implementations, UE 101 may perform a resource reselection check, which output a result of whether the upcoming reserved resource is within the active time of UE 102. When the result is negative, UE 101 may trigger the resource reselection, and select new resource according to determined active time of UE 102.

In some embodiments, BS 103 may schedule data transmission between UEs 101 and 102 (i.e.,

UEs

101 and 102 are under of sidelink transmission mode 1 which the resources are scheduled by BS) , the inactivity timer may start (i.e., NDI 101A1 is toggled, HARQ feedback indicator 101A2 is set to 1 which indicates that this TB requires HARQ feedback function) , and the cast type indicator may indicate unicast (i.e., the cast type indicator is set to 10) .

Then, after transmitting the TB, when UE 101 detects DTX status on corresponding HARQ feedback channel (i.e. UE 101 does not receive HARQ feedback from UE 102 on corresponding PSFCH) , UE 101 may determine that UE 102 does not start inactivity timer. Therefore, UE 101 may restore the inactivity timer because UE 102 does not start the corresponding inactivity timer, and UE 101 may be triggered to determine an active time of UE102.

Referring to FIG. 4A, UE 101 may transmit an indicator 101B to BS103. In some implementations, indicator 101B may indicate to BS 103 that the inactivity timer of UE 102 does not start. For example, indicator 101B is 1 bit. When indicator 101B is set to 1, it means that UE 102 does not start the inactivity timer. Indicator 101B is carried in physical uplink control channel (PUCCH) that is configured by BS 103.

Referring to FIG. 4B, UE 101 may transmit an indicator 101C to BS103. In some implementations, indicator 101C may indicate to BS 103 the detection of DTX status on corresponding HARQ feedback channel. For example, indicator 101C is 1 bit. When indicator 101C is set to 1, it means that UE 101 detects DTX status on corresponding HARQ feedback channel. Indicator 101C is carried in PUCCH that is configured by BS 103.

Referring to FIG. 4C, after determining the active time of UE 102, UE 101 may transmit an indicator 101D to BS103. In some implementations, indicator 101D may request BS 103 to schedule a retransmission between

UEs

101 and 102 within the active time of UE 102. In some implementations, when BS 103 schedules another transmission between

UEs

101 and 102 and the another transmission is not within the active time determined by UE 101, UE 101 may transmit an indicator 101E to indicate to BS 103 that the scheduling is out of time and invalid.

FIG. 5 illustrates a flow chart of a method for wireless communications in accordance with some embodiments of the present application. Referring to FIG. 5, method 500 is performed by Tx UE (e.g., UE 101) and Rx UE (e.g., UE 102) in some embodiments of the present application.

In some embodiments, operation S501 is executed to transmit, by Tx UE, a SCI to Rx UE. The SCI may include an NDI and a HARQ feedback indicator. Operation S502 is executed to receive, by Rx UE, the SCI from Tx UE. Operations S503A and S503B are executed to determine, by Tx UE and Rx UE respectively, whether to start an inactivity timer according to the NDI and the HARQ feedback indicator.

FIGS. 6A to 6C illustrate flow charts of a method for wireless communications in accordance with some embodiments of the present application. Referring to FIGS. 6A to 6X, method 600 is performed by Tx UE (e.g., UE 101) , Rx UE (e.g., UE 102) and BS (e.g., BS 103) in some embodiments of the present application.

In some embodiments, operation S601 is executed to transmit, by Tx UE, a SCI to Rx UE. The SCI may include an NDI and a HARQ feedback indicator. Operation S602 is executed to receive, by Rx UE, the SCI from Tx UE. Operations S603 to S607 are executed to determine, by Tx UE and Rx UE respectively, whether to start an inactivity timer.

In detail, operation S603 is executed to determine, by Tx UE or Rx UE, whether the NDI of the SCI is toggled. When the NDI of the SCI is not toggled, which means that NDI indicates that the corresponding TB between Tx UE and Rx UE is not new data transmission (i.e., NDI is the same as a previous NDI for the same sidelink process between Tx UE and Rx UE) , operation S604 is executed not to start, by Tx UE or Rx UE, the inactivity timer.

When the NDI of the SCI is toggled, which means that NDI indicates that the corresponding TB between Tx UE and Rx UE is new data transmission (i.e., NDI is not the same as a previous NDI for the same sidelink process between Tx UE and Rx UE) , operation S605 is executed to determine, by Tx UE or Rx UE, whether HARQ feedback function is disabled or is the cast type broadcast. When HARQ feedback function is disabled (i.e., the HARQ feedback indicator indicates a disablement of HARQ feedback function) or the cast type is broadcast, operation S604 is executed.

When HARQ feedback function is enabled (i.e., the HARQ feedback indicator indicates an enablement of HARQ feedback function) and the cast type is not broadcast, operation S606 is executed to determine, by Tx UE or Rx UE, the cast type. When the cast type is: (1) unicast; or (2) groupcast with ACK/NACK of HARQ feedback function, operation S607 is executed to start, by Tx UE or Rx UE, the inactivity timer. When the cast type is groupcast with NACK of HARQ feedback function, operation S604 is executed.

In some embodiments, after Tx UE starts the inactivity timer, operation S608 is executed to detect, by Tx UE, DTX status on corresponding HARQ feedback channel or an active time corresponding to Rx UE. When Tx UE detects DTX status on corresponding HARQ feedback channel or the active time corresponding to Rx UE, operation S609 is executed to determine, by Tx UE, that Rx UE does not start the corresponding inactivity timer of Rx UE according to the detection of DTX. Operation S610 is executed to restore, by Tx UE, the inactivity timer.

In some embodiments, when data transmission between Tx UE and Rx UE is scheduled by a BS, operation S611 is executed to transmit, by Tx UE, an indicator to the BS. In some implementations, the indicator may indicate to the BS that the inactivity timer of Rx UE does not start. In some implementations, the indicator may indicate to the BS the detection of DTX status on corresponding HARQ feedback channel. In some implementations, the indicator may request the BS to schedule a retransmission between Tx UE and Rx UE within the active time of Rx UE.

When the BS schedules another transmission between Tx UE and Rx UE and the another transmission is not within the active time determined by Tx UE1, operation S612 is optionally executed to transmit, by Tx UE, another indicator to indicate to the BS that the scheduling is out of time and invalid.

In some embodiments, when data transmission between Tx UE and Rx UE is selected by Tx UE, operation S613 is executed to trigger, by Tx UE, a resource re-selection when an upcoming reserved resource for Rx UE is not within the active time.

FIG. 7 illustrates an example block diagram of an apparatus 7 according to an embodiment of the present disclosure.

As shown in FIG. 7, the apparatus 7 may include at least one non-transitory computer-readable medium (not illustrated in FIG. 7) , a receiving circuitry 71, a transmitting circuitry 73, and a processor 75 coupled to the non-transitory computer-readable medium (not illustrated in FIG. 7) , the receiving circuitry 71 and the transmitting circuitry 73. The apparatus 7 may be an UE.

Although in this figure, elements such as processor 75, transmitting circuitry 73, and receiving circuitry 71 are described in the singular, the plural is contemplated unless limitation to the singular is explicitly stated. In some embodiments of the present disclosure, the receiving circuitry 71 and the transmitting circuitry 73 are combined into a single device, such as a transceiver. In certain embodiments of the present disclosure, the apparatus 7 may further include an input device, a memory, and/or other components.

In some embodiments of the present disclosure, the non-transitory computer-readable medium may have stored thereon computer-executable instructions to cause a processor to implement the method with respect to the user equipment as described above. For example, the computer-executable instructions, when executed, cause the processor 7 interacting with receiving circuitry 71 and transmitting circuitry 73, so as to perform the operations with respect to UE depicted in FIGS. 1 to 4.

Those having ordinary skill in the art would understand that the operations of a method described in connection with the aspects disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, a hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. Additionally, in some aspects, the steps of a method may reside as one or any combination or set of codes and/or instructions on a non-transitory computer-readable medium, which may be incorporated into a computer program product.

While this disclosure has been described with specific embodiments thereof, it is evident that many alternatives, modifications, and variations may be apparent to those skilled in the art. For example, various components of the embodiments may be interchanged, added, or substituted in the other embodiments. Also, all of the elements of each figure are not necessary for operation of the disclosed embodiments. For example, one of ordinary skill in the art of the disclosed embodiments would be enabled to make and use the teachings of the disclosure by simply employing the elements of the independent claims. Accordingly, embodiments of the disclosure as set forth herein are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the disclosure.

In this document, the terms "includes" , "including" , or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by "a" , "an" , or the like does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that includes the element. Also, the term "another" is defined as at least a second or more. The term "having" and the like, as used herein, are defined as "including" .

In this document, the terms "comprises, " "comprising, " or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by "a, " "an, " or the like does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element. Also, the term "another" is defined as at least a second or more. The terms "including, " "having, " and the like, as used herein, are defined as "comprising. "

Claims

A method of a user equipment, comprising:

transmitting a sidelink control information (SCI) to another user equipment, wherein the SCI includes a new data indicator (NDI) and a hybrid automatic repeat request (HARQ) feedback indicator; and

determining whether to start an inactivity timer according to the NDI and the HARQ feedback indicator.
The method of Claim 1, wherein the step of determining whether to start the inactivity timer according to the NDI and the HARQ feedback indicator comprises:

determining not to start the inactivity timer when the NDI is the same as a previous NDI for the same sidelink process.
The method of Claim 1, wherein a cast type indicator of the SCI indicates unicast or groupcast with HARQ feedback information including acknowledgement (ACK) and negative-acknowledgement (NACK) , and the step of determining whether to start the inactivity timer according to the NDI and the HARQ feedback indicator comprises:

determining to start the inactivity timer when the NDI is not the same as a previous NDI for the same sidelink process and the HARQ feedback indicator indicates an enablement of HARQ feedback; and

determining not to start the inactivity timer when the NDI is the same as the previous NDI for the same sidelink process and the HARQ feedback indicator indicates a disablement of HARQ feedback.
The method of Claim 1, wherein a cast type indicator of the SCI indicates broadcast or groupcast with HARQ feedback information including negative-acknowledgement (NACK) , and the step of determining whether to start the inactivity timer according to the NDI and the HARQ feedback indicator comprises:

determining not to start the inactivity timer according to the NDI and the HARQ feedback indicator.
The method of Claim 1, wherein the inactivity timer starts, and the method comprises:

detecting discontinuous transmission (DTX) status or an active time corresponding to the another user equipment; and

restoring the inactivity timer.
The method of Claim 5, comprising:

determining that the another user equipment does not start a corresponding inactivity timer of the another user equipment according to the detection of DTX.
The method of Claim 6, wherein data transmission between the user equipment and the another user equipment is scheduled by a base station, and the method comprises:

transmitting an indicator to the base station, wherein the indicator indicates to the base station that the another user equipment does not start the corresponding inactivity timer or indicates to the base station the detection of the DTX.
The method of Claim 6, wherein data transmission between the user equipment and the another user equipment is scheduled by a base station, and the method comprises:

transmitting an indicator to a base station, wherein the indicator requests the base station to schedule a retransmission between the user equipment and the another user equipment within the active time.
The method of Claim 8, comprising:

transmitting another indicator to the base station, wherein the another indicator indicates the base station that the retransmission is invalid.
The method of Claim 5, wherein a resource for data transmission between the user equipment and the another user equipment is selected by the user equipment, and the method comprises:

triggering a resource re-selection when an upcoming reserved resource for the another user equipment is not within the active time.
A method of a user equipment, comprising:

receiving a sidelink control information (SCI) from another user equipment, wherein the SCI includes a new data indicator (NDI) and a hybrid automatic repeat request (HARQ) feedback indicator; and

determining whether to start an inactivity timer according to the NDI and the HARQ feedback indicator.
The method of Claim 11, wherein the step of determining whether to start the inactivity timer according to the NDI and the HARQ feedback indicator comprises:

determining not to start the inactivity timer when the NDI is the same as a previous NDI for the same sidelink process.
The method of Claim 11, wherein a cast type indicator of the SCI indicates unicast or groupcast with HARQ feedback information including acknowledgement (ACK) and negative-acknowledgement (NACK) , and the step of determining whether to start the inactivity timer according to the NDI and the HARQ feedback indicator comprises:

determining to start the inactivity timer when the NDI is not the same as a previous NDI for the same sidelink process and the HARQ feedback indicator indicates an enablement of HARQ feedback; and

determining not to start the inactivity timer when the NDI is the same as a previous NDI for the same sidelink process and the HARQ feedback indicator indicates a disablement of HARQ feedback.
The method of Claim 11, wherein a cast type indicator of the SCI indicates broadcast or groupcast with HARQ feedback information including negative-acknowledgement (NACK) , and the step of determining whether to start the inactivity timer according to the NDI and the HARQ feedback indicator comprises:

determining not to start the inactivity timer according to the NDI and the HARQ feedback indicator.
An apparatus, comprising:

a non-transitory computer-readable medium having stored thereon computer-executable instructions;

a receiving circuitry;

a transmitting circuitry; and

a processor coupled to the non-transitory computer-readable medium, the receiving circuitry and the transmitting circuitry;

wherein the computer-executable instructions cause the processor to implement the method of any of Claims 1-14.