Methods and apparatus for wireless communication

Abstract

Methods, apparatus and computer-readable medium are disclosed for wireless communication with a radio link control (RLC) entity in acknowledged mode (AM). A method comprises determining whether or not every RLC service data unit (SDU) previously submitted to a lower protocol layer in one or more RLC protocol data unit (PDU) is either positively acknowledged or has been indicated as discarded. The method comprises stopping a timer for retransmitting a poll at least based on a determination that every RLC SDU previously submitted to the lower protocol layer in the one or more RLC PDU is either positively acknowledged or has been indicated as discarded.

Description

[0001] METHODS AND APPARATUS FOR WIRELESS COMMUNICATION

[0002] TECHNICAL FIELD

[0003]

[0001] Various example embodiments relate generally to wireless communication technology, and more particularly, to methods and apparatus for wireless communication of radio link control (RLC) layer in acknowledged mode (AM).

[0004] BACKGROUND

[0005]

[0002] In a wireless interface protocol stack, radio link control (RLC) layer is arranged in a second layer, between packet data convergence protocol (PDCP) layer and medium access control (MAC) layer. At a transmitting side, RLC entity receives PDCP protocol data units (PDUs), i.e., RLC service data units (SDUs), from the PDCP layer and sends RLC PDUs to its peer RLC entity via the MAC and PHY layers. At a receiving side, RLC entity receives RLC PDUs from its peer RLC entity via the MAC and PHY layers and delivers PDCP PDUs (i.e., RLC SDUs) to the PDCP layer.

[0006]

[0003] In RLC AM, the initial transmission of each RLC SDU is performed in ascending order of RLC sequence numbers (SNs) and stored in a buffer to wait for an acknowledgement. Since RLC AM supports automatic repeat request (ARQ) for reliable transmission, an AM RLC entity at a receiving side would send RLC status PDUs to its peer AM RLC entity in order to provide positive and / or negative acknowledgements of RLC SDUs (or portions of them).

[0007]

[0004] In RLC AM, there are two mechanisms used to detect loss of an RLC data PDU at MAC. One mechanism is detection of missing data at the receiving side. When data with a higher RLC SN is received while data with a lower RLC SN remains unreceived, a timer t-Reassembly is started at the receiving side of an AM RLC entity. If the timer t-Reassembly expires before the missing data is received, a NACK for the missing data is sent in an RLC status PDU. To work, this mechanism requires the reception of the data with a higher RLC SN, so another mechanism is needed to detect a loss of the last data sent (for some time).

[0008]

[0005] When a last RLC data (i.e., RLC SDU or RLC SDU segment) queued for transmission is sent, it is sent with a polling bit requesting an RLC status PDU with an ACK or NACK for all the previous data (in terms of RLC SNs) up to and including the RLC Data PDU including the poll, and a timer t-PollRe transmit is started. If the timer t-PollRetransmit expires before ACK or NACK is received for the last RLC data, another poll is transmitted by retransmitting the last RLC data with a polling bit requesting an RLC status PDU, and t-PollRetransmit is started again, which continues until ACK or NACK is received for the last RLC data.

[0009]

[0006] This latter mechanism can be enhanced to reduce unnecessary retransmissions and status reporting.

[0010] SUMMARY

[0011]

[0007] This summary is provided to introduce simplified concepts of the present disclosure. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

[0008] According to a first aspect of the disclosure, there is provided an apparatus for wireless communication with radio link control (RLC) layer in acknowledged mode (AM). The apparatus comprises at least one processor, and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to determine whether or not every RLC service data unit (SDU) previously submitted to a lower protocol layer in one or more RLC protocol data unit (PDU) is either positively acknowledged or has been indicated as discarded. The apparatus is further caused to stop a timer for retransmitting a poll at least based on a determination that every RLC SDU previously submitted to the lower protocol layer in the one or more RLC PDU is either positively acknowledged or has been indicated as discarded.

[0012]

[0009] According to some embodiments, the apparatus may be further caused to make the determination by determining whether or not every RLC SDU with an RLC sequence number (SN) greater than or equal to an acknowledgement state variable, TX_Next_Ack, and less than a send state variable, TX Next, is either positively acknowledged or has been indicated as discarded.

[0013]

[0010] According to some embodiments, the apparatus may be further caused to receive a discard indication for one or more RLC SDUs from packet data convergence protocol (PDCP) layer; and trigger the determining in response to a reception of the discard indication.

[0014]

[0011] According to some embodiments, the apparatus may be further caused to determine sequence numbers (SNs) of RLC SDUs indicated as discarded based on the discard indication, and store the SNs of the RLC SDUs indicated as discarded.

[0015]

[0012] According to some embodiments, the apparatus may be further caused to receive from a peer RLC entity, an RLC status report which provides positive acknowledgements and / or negative acknowledgements of one or more RLC SDUs previously submitted to the lower protocol layer; and trigger the determining in response to a reception of the RLC status report.

[0016]

[0013] According to some embodiments, the apparatus may be further caused to stop the timer for retransmitting the poll, in case that it is determined that every RLC SDU previously submitted to the lower protocol layer in the one or more RLC PDU is either positively acknowledged or has been indicated as discarded.

[0017]

[0014] According to some embodiments, the apparatus may be further caused to determine whether or not a RLC transmitting window of the RLC entity is stalled; and keep the timer for retransmitting the poll running, in case that it is determined that a RLC transmitting window is stalled.

[0018]

[0015] According to some embodiments, the apparatus may be further caused to stop the timer for retransmitting the poll, in case that it is determined that a RLC transmitting window is not stalled, and every RLC SDU previously submitted to the lower protocol layer in the one or more RLC PDU is either positively acknowledged or has been indicated as discarded.

[0019]

[0016] According to some embodiments, the timer may be t-PollRe transmit.

[0020]

[0017] According to some embodiments, the RLC entity is in a base station or user equipment.

[0021]

[0018] According to a second aspect of the disclosure, there is provided a method for wireless communication with radio link control (RLC) layer in acknowledged mode (AM). The methodcomprises determining whether or not every RLC service data unit (SDU) previously submitted to a lower protocol layer in one or more RLC protocol data unit (PDU) is either positively acknowledged or has been indicated as discarded; and stopping a timer for retransmitting a poll at least based on a determination that every RLC SDU previously submitted to the lower protocol layer in the one or more RLC PDU is either positively acknowledged or has been indicated as discarded.

[0022]

[0019] According to a third aspect of the disclosure, there is provided an apparatus for wireless communication with radio link control (RLC) layer in acknowledged mode (AM). The apparatus comprising means for determining whether or not every RLC service data unit (SDU) previously submitted to a lower protocol layer in one or more RLC protocol data unit (PDU) is either positively acknowledged or has been indicated as discarded; and means for stopping a timer for retransmitting a poll at least based on a determination that every RLC SDU previously submitted to the lower protocol layer in the one or more RLC PDU is either positively acknowledged or has been indicated as discarded.

[0023]

[0020] According to a fourth aspect of the disclosure, there is provided a computer-readable medium having computer program codes embodied thereon which, when executed by a processor, cause the processor to perform any of the methods according to the second aspect of the disclosure.

[0024]

[0021] According to a fifth aspect of the disclosure, there is provided a computer program product comprising computer programs or instructions which, when executed by a processor, cause the processor to perform any of the methods according to the second aspect of the disclosure.

[0025]

[0022] It is to be understood that the summary section is not intended to identify key or essential features of embodiments 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 become easily comprehensible through the following description.

[0026] BRIEF DESCRIPTION OF THE DRAWINGS

[0027]

[0023] Some example embodiments will now be described with reference to the accompanying drawings in which:

[0028]

[0024] FIG. 1 shows an example of a communication network to which examples disclosed herein may be applied;

[0029]

[0025] FIG. 2 is a flow chart depicting a method performed at performed at a transmitting side of an AM RLC entity according to embodiments of the present disclosure;

[0030]

[0026] FIG. 3 illustrates an exemplary procedure of data transfer according to an embodiment of the present disclosure;

[0031]

[0027] FIG. 4 illustrates another exemplary procedure of data transfer according to an embodiment of the present disclosure;

[0032]

[0028] FIG. 5 is a flow chart depicting another method according to embodiments of the present disclosure;

[0029] FIG. 6 is a flow chart depicting yet another method according to embodiments of the present disclosure; and

[0033]

[0030] FIG. 7 is a block diagram showing an apparatus suitable for practicing some embodiments of the disclosure.

[0034] DETAILED DESCRIPTION

[0035]

[0031] The following embodiments are exemplary. Although the specification may refer to “an”, “one”, or “some” embodiment s) in several locations of the text, this does not necessarily mean that each reference is made to the same embodiment s), or that a particular feature only applies to a single embodiment. Single features of different embodiments may also be combined to provide other embodiments. Further, when a particular feature, structure, or characteristic is described in connection of an embodiment, it is within the knowledge of one skilled in the art to apply such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

[0036]

[0032] For the purposes of the present disclosure, the phrases “at least one of A or B”, “at least one of A and B”, and “A and / or B” means (A), (B), or (A and B). For the purposes of the present disclosure, the phrase “A, B, and / or C” means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B, and C).

[0037]

[0033] Embodiments described may be implemented in a communication network, such as any of the following radio access technologies (RATs): Universal Mobile Telecommunication System (UMTS, 3G) based on basic wideband-code division multiple access (W-CDMA), highspeed packet access (HSPA), Long Term Evolution (LTE), LTE-Advanced, and enhanced LTE (eLTE), 5G (also called NR), or any future RAT such as 6G.

[0038]

[0034] 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 skills in the art to which this disclosure belongs.

[0039]

[0035] As used herein, the term “network device” or “network node” refers to a node in a communication network via which user equipment may access the radio access network and / or which is capable of controlling radio communication and managing radio resources within a cell. The network node or network device may be referred to as a base station (BS), an access point (AP) or an access node. The network device may be, depending on the applied technology, for example, a node B (NodeB or NB), an evolved NodeB (eNodeB or eNB), an NR NB (also referred to as a gNB), a Remote Radio Unit (RRU), a radio head (RH), a remote radio head (RRH), a relay, an Integrated Access and Backhaul (IAB) node, a low power node, a nonterrestrial network (NTN) or non-ground network device such as a satellite network device, a low earth orbit (LEO) satellite and a geosynchronous earth or-bit (GEO) satellite, or an aircraft network device.

[0040]

[0036] Moreover, in connection of split radio access network (RAN), the network device may refer to a central unit (CU) of a base station and / or a distributed unit (DU) of a base station. An interface between CU and DU may be referred to as an Fl interface in NR. In the split RAN architecture, node operations may be carried out, at least partly, in the central / centralized unit,CU, (e.g. server, host or node) operationally coupled to the DU, (e.g. a radio head / node). One CU may control one or more DUs, acting at least as transmit / receive (Tx / Rx) nodes. In some embodiments, the DUs may comprise e.g. a radio link control (RLC), medium access control (MAC) layer and a physical (PHY) layer, whereas the CU may comprise the layers above RLC layer, such as a packet data convergence protocol (PDCP) layer, a radio resource control (RRC) and an internet protocol (IP) layers. Other functional splits are possible too. In practice, any processing task may be performed in either the CU or the DU and the boundary where the responsibility is shifted between the CU and the DU may depend on the applied implementation.

[0041]

[0037] The term “terminal device” refers to any end device that may be capable of wireless communication. By way of example, a terminal device may be referred to as a communication device, user equipment (UE), a Subscriber Station (SS), or a Mobile Station (MS). The terminal device may include a mobile phone, a cellular phone, a smart phone, voice over IP (VoIP) phones, wireless local loop phones a tablet, a wearable terminal device, a personal digital assistant (PDA), portable computers, desktop computer, image capture terminal devices such as digital cameras, gaming terminal devices, music storage and playback appliances, vehiclemounted wireless terminal devices, USB dongles, an Internet of Things (loT) device, a watch or other wearable, a head-mounted display (HMD), a vehicle, a drone, a medical device and applications (e.g., remote surgery), an industrial device and applications (e.g., a robot and / or other wireless devices operating in an industrial and / or an automated processing chain contexts), a consumer electronics device, a device operating on commercial and / or industrial wireless networks, and the like.

[0042]

[0038] As defined herein, a “computer-readable storage medium,” which refers to a non-transitory physical storage medium (e.g., volatile or non-volatile memory device), may be differentiated from a “computer-readable transmission medium,” which refers to an electromagnetic signal. Such a medium may take many forms, including, but not limited to a non-transitory computer-readable storage medium (e.g., non-volatile media, volatile media), and transmission media. Transmission media include, for example, coaxial cables, copper wire, fiber optic cables, and carrier waves that travel through space without wires or cables, such as acoustic waves and electromagnetic waves, including radio, optical and infrared waves. Signals include man-made transient variations in amplitude, frequency, phase, polarization or other physical properties transmitted through the transmission media. Examples of non-transitory computer-readable media include a magnetic computer readable medium (e.g., a floppy disk, hard disk, magnetic tape, any other magnetic medium), an optical computer readable medium (e.g., a compact disc read only memory (CD-ROM), a digital versatile disc (DVD), a Blu-Ray disc, or the like), a random access memory (RAM), a programmable read only memory (PROM), an erasable programmable read only memory (EPROM), a FLASH-EPROM, or any other non-transitory medium from which a computer may read. The term computer-readable storage medium is used herein to refer to any computer-readable medium except transmission media. However, it will be appreciated that where embodiments are described to use a computer-readable storage medium, other types of computer-readable mediums may be substituted for or used in addition to the computer-readable storage medium in alternative embodiments.

[0043]

[0039] FIG. 1 illustrates an example of a communication network to which examples disclosed herein may be applied. The communication network or a cellular communication network may comprise a network node 110 providing one or more cells, such as cell 100, and a network node 112 providing one or more other cells, such as cell 102. Each cell may be, e.g., a macro cell, a micro cell, femto, or a pico cell, for example. The cell may define a coverage area or a service area of the corresponding access node.

[0044]

[0040] The network node 110 may provide a user equipment (UE) 120 (one or more UEs) with wireless access to the communication network. The wireless access may comprise downlink (DL) communication from the network node to the UE 120 and uplink (UL) communication from the UE 120 to the network node. Examples of uplink channels comprise physical uplink control channel (PUCCH) for transmitting control information and physical uplink shared channel (PUSCH) for transmitting data towards the network. Examples of downlink channels comprise physical downlink control channel (PDCCH) for transmitting control information and physical downlink shared channel (PDSCH) for transmitting data towards the user equipment.

[0045]

[0041] There may be a plurality of UEs 120, 122 in the system. Each of them may be served by the same or by different network nodes 110, 112. UE may be configured with dual connectivity (DC), wherein the UE, e.g. UE 120, may be connected to multiple network nodes 110, 112. The UEs 120, 122 may communicate with each other, in case device-to-device (D2D) communication interface is established between them via a so-called sidelink (SL). Such D2D communications may be referred to as machine-to-machine, peer-to-peer (P2P) communications, or vehicle-to-vehicle (V2V), for example.

[0046]

[0042] In the case of multiple network nodes in the communication network, the network nodes may be connected to each other via an interface. LTE specifications call such an interface as X2 interface. An interface between an LTE node and a 5G node, or between two 5G nodes may be called Xn interface.

[0047]

[0043] The network nodes 110 and 112 may be further connected via another interface to a core network 116 of the communication network. The LTE specifications specify the core network as an evolved packet core (EPC), and the core network may comprise e.g. a mobility management entity (MME) and a gateway node. The MME may handle mobility of terminal devices in a tracking area encompassing a plurality of cells and handle signaling connections between the terminal devices and the core network. The gateway node may handle data routing in the core network and to / from the terminal devices. The 5G specifications specify the core network as a 5G core (5GC). The 5G core may comprise e.g. an access and mobility management function (AMF) and a user plane function / gateway (UPF) and other functions. The AMF may handle termination of non-access stratum (NAS) signaling, NAS ciphering and integrity protection, registration management, connection management, mobility management, access authentication and authorization, security context management. The UPF node may support packet routing and forwarding, packet inspection and quality of service (QoS) handling, for example.

[0044] The ongoing work for wireless communication technology has the following objective: RLC re-transmission related enhancements for operation of RLC AM with small packet delay budget. As part of this work, a mechanism of unnecessary retransmissions avoidance is introduced. In this mechanism, when a transmitting side of an RLC entity (also referred to TX RLC entity, hereinafter) receives a discard indication of a RLC SDU from a PDCP layer, the TX RLC entity considers the RLC SDU as an outdated RLC SDU. The TX RLC entity does not perform any transmission and retransmission of the RLC SDU or a segment of the RLC SDU.

[0048]

[0045] For example, this mechanism of unnecessary retransmissions avoidance may make the following modifications (which are underlined) for RLC specification, e.g., 3GPP TS 38.322:

[0049] 5.2.3 AM data transfer

[0050] 5.2.3.1 Transmit operations

[0051] 5.2.3.1.1 General

[0052] If stopReTxObsoleteSDU is set to enabled, when receiving a discard indication for an RLC SDU with SN = x from the upper layer (see TS 38,323 [4]), the transmitting side of an AM RLC entity shall stop transmission of the RLC SDU and stop retransmission in 5,3,2 (if any) and stop autonomous retransmission in 5,x,2 (if any).

[0053] 5.3.3.4 Exp i ry of t-PollRetransmit

[0054] Upon expiry of t-PollRe transmit, the transmitting side of an AM RLC entity shall:

[0055] - if both the transmission buffer and the retransmission buffer are empty (excluding transmitted RLC SDU or RLC SDU segment awaiting acknowledgements and excluding RLC SDUs or RLC SDU segments for which the transmission and retransmission are stopped); or

[0056] - if no new RLC SDU or RLC SDU segment can be transmitted (e.g. due to window stalling):

[0057] - consider the RLC SDU with the highest SN among the RLC SDUs submitted to lower layer for retransmission; or

[0058] - consider any RLC SDU which has not been positively acknowledged for retransmission.

[0059] - include a poll in an AMD PDU as described in clause 5.3.3.2.

[0060]

[0046] A TX AM RLC entity can poll its peer AM RLC entity in order to trigger STATUS reporting at the peer AM RLC entity. To include a poll in an AMD PDU, the TX AM RLC entity may set a poll bit (denoted as P field) of the AMD PDU to request an RLC status PDU. For example, the value of the poll bit may be set to “1” to indicate that an RLC status PDU is requested. Upon submission of an AMD PDU including a poll (e.g., a poll bit set to “1”) to lowerlayer, the TX AM RLC entity may start or restart a timer, e.g., t-PollRetransmit as defined in 3GPP TS 38.322 V18.2.0. When the peer AM RLC entity receives the poll, it may send an RLC status report to the TX AM RLC entity in order to provide positive and / or negative acknowledgements of RLC SDUs (or portions of them). If no RLC status report is received from the peer AM RLC entity upon expiry of the timer t-PollRe transmit, the TX AM RLC entity may retransmit a poll in an AMD PDU.

[0061]

[0047] As mentioned above, a TX AM RLC entity may receive a discard indication for an RLC SDU from a PDCP layer. For example, when a discard timer corresponding to a PDCP SDU expires, the PDCP layer would notify a TX AM RLC entity to discard the relevant RLC SDU in case that the corresponding PDCP PDU has already been sent to the TX AM RLC entity. If all RLC SDUs stored at the TX AM RLC entity have been either positively acknowledged or indicated as discarded by a PDCP layer when the timer t-PollRe transmit expires, it may be unnecessary to retransmit a poll in the first place. This is because on the one hand, in this situation, retransmitting a poll requires retransmitting an RLC SDU that has already been discarded by a PDCP layer, and on the other hand, the ACK / NACK feedback that remains missing at the time when t-PollRe transmit expired (which is why t-PollRe transmit expired) is no longer useful. In this regard, if a RLC SDU stored at the TX AM RLC entity may be negatively acknowledged by a status report (if any) in response to the retransmitted poll, the negative acknowledgment (e.g., a NACK) for this RLC SDU will not result in retransmission of the RLC SDU, because of the mechanism of unnecessary retransmissions avoidance mentioned above. If a RLC SDU stored at the TX AM RLC entity may be positively acknowledged by a status report (if any) in response to the retransmitted poll, the positive acknowledgment (e.g., an ACK) would progress an RLC transmitting window at the TX AM RLC entity to be on par with an RLC receiving window at the peer RLC entity. However, this is not urgent, and can be achieved if / when new data is received from a PDCP layer for transmission. As such, it may be unnecessary to retransmit a poll when the timer t-PollRe transmit expires, in case that all RLC SDUs stored at the TX AM RLC entity have been either positively acknowledged or indicated as discarded by a PDCP layer.

[0062]

[0048] Embodiments of the present disclosure are proposed to avoid such unnecessary polling possibly requiring unnecessary retransmission of an RLC SDU (via a RLC PDU including a poll bit set to “1” and the RLC SDU). Embodiments of the present disclosure proposes a new stopping condition for a timer used for retransmitting a poll, e.g., t-PollRe transmit for a TX AM RLC entity: when every RLC SDU previously submitted to a lower layer (e.g., MAC layer) in one or more RLC Data PDUs (e.g., RLC SDUs with an RLC SN up to and excluding TX Next) is either positively acknowledged or has been indicated as discarded by a PDCP layer, a TX AM RLC entity stops and resets t-PollRetransmit.

[0063]

[0049] TX Next is the RLC state variable storing a value of an SN to be assigned for the next newly generated AM data (AMD) PDU. It is initially set to 0, and is updated whenever the TX AM RLC entity constructs an AMD PDU with SN = TX Next and contains an RLC SDU or the last segment of a RLC SDU.

[0050] FIG. 2 is a flow chart depicting a method 200 performed at a transmitting side of an AM RLC entity (also referred to as TX AM RLC entity) according to embodiments of the present disclosure. In an example, the method may be performed at a terminal device (e.g., UE), or an apparatus for use in a terminal device, for uplink transmission. In another example, the method may be performed at a network node (e.g., gNB), or an apparatus for use in a network node, for downlink transmission.

[0064]

[0051] At step 210, a TX AM RLC entity determines whether a stopping condition for a timer for retransmitting a poll is fulfilled. In this regard, the TX AM RLC entity determines whether or not every RLC SDU previously submitted to a lower layer (e.g., MAC layer) in one or more RLC PDU is either positively acknowledged or has been indicated as discarded. Generally, the TX AM RLC entity would store these RLC SDUs after submitting them to the lower layer, so that these RLC SDUs can be retransmitted as necessary based on the reception of these RLC SDUs at a peer RLC entity.

[0065]

[0052] In an example, RLC SDUs or RLC SDU segments which are previously submitted to the lower layer and for which a positive acknowledgement has not been received, may be stored in a retransmission buffer. For example, the RLC SDUs or RLC SDU segments stored in the retransmission buffer may be waiting for acknowledgments from the peer RLC entity, or may be negatively acknowledged by the peer RLC entity, or may be indicated as discarded by a higher layer (e.g., PDCP layer).

[0066]

[0053] At step 220, the TX AM RLC entity stops a timer for retransmitting a poll at least based on a determination that every RLC SDU previously submitted to the lower layer (e.g., MAC layer) in the one or more RLC PDU is either positively acknowledged or has been indicated as discarded. In some examples, in case it is determined that every RLC SDU previously submitted to the lower layer (e.g., MAC layer) in the one or more RLC PDU is either positively acknowledged or has been indicated as discarded, the TX AM RLC entity stops the timer.

[0067]

[0054] The timer may have been started or re-started when a RLC SDU or a part of an RLC SDU was previously submitted to MAC layer in one of the one or more RLC PDU with a poll (e.g., a poll bit set to “1”). The determination may be made only if the timer is running. In an example, the timer may be t-PollRetransmit.

[0068]

[0055] In some examples, step 210 may be triggered in response to a reception of a discard indication for an RLC SDU from a higher protocol layer (e.g., PDCP). The discard indication may cause the TX RLC AM entity to stop any transmission and retransmission of the RLC SDU. For example, the TX RLC AM entity may determine one or more RLC SNs of the RLC SDUs indicated as discarded based on the discard indication, and then store the determined SNs of RLC SDUs indicated as discarded. When PDCP layer and RLC layer are co-located (such as in the UE), it is up to implementation what kind of reference to use for determining the RLC SDUs indicated as discarded. Any kind of internal identity (ID) number can be allocated and used for the determining. For downlink (DL) traffic, when PDCP layer and RLC layer are in CU and DU, respectively, separated by an interface Fl-U, as a part of a standardized frame format, the discard indication is included in discard-indication fields by using PDCP SNs. In this case, the DU needsto inspect these PDCP SNs from PDCP PDUs, so as to determine RLC SNs of the RLC SDUs discarded at PDCP.

[0069]

[0056] In some examples, step 210 may be triggered in response to a reception of an RLC status report from the peer RLC entity. The RLC status report may inform the TX AM RLC entity about RLC SDUs or segments of RLC SDUs that are received successfully (i.e., positively acknowledged), and RLC SDUs or segments of RLC SDUs that are detected to be lost by the peer RLC entity (i.e., negatively acknowledged). In some examples, the peer RLC entity may also positively aknowlegde RLC SDUs that it has found to be missing for an extended period of time.

[0070]

[0057] In some examples, although not shown in FIG.2, the TX AM RLC entity may further determine whether a RLC transmitting window is stalled, for considering an exception to the stopping condition for the timer. In this regard, when the RLC transmitting window is stalled, a maximum allowed difference between an SN (e.g., denoted as SN #X) of an RLC SDU to be transmitted and an SN (e.g., denoted as SN #Y, which may be smaller than #X) of an RLC SDU which has not been positively acknowledged, has been reached. In terms of RLC state variables and constants, when TX_Next = TX_Next_Ack + AM_Window_Size, the RLC transmitting window is stalled.

[0071]

[0058] TX Next Ack is a state variable with a value of an RLC SN of a next RLC SDU for which a positive acknowledgment is to be received in-sequence, and it serves as the lower edge of the RLC transmitting window. It is initially set to 0, and is updated whenever the TX AM RLC entity receives a positive acknowledgment for an RLC SDU with SN = TX_Next_Ack.

[0072]

[0059] AM Window Size is a constant used by both the transmitting side and the receiving side of each AM RLC entity. AM_Window_Size = 2048 when a 12 bit RLC SN is used, AM_Window_Size = 131072 when an 18 bit RLC SN is used.

[0073]

[0060] In case that the TX AM RLC entity determines that a RLC transmitting window is stalled, the TX AM RLC entity would not stop the timer even though every RLC SDU previously submitted to the lower layer (e.g., MAC layer) in the one or more RLC PDU is either positively acknowledged or has been indicated as discarded. In this case, it is necessary to let the timer expire to enable a retransmission of poll when no RLC status report is received from the peer RLC entity till expiry of the timer, so that a RLC status report may be received eventually, allowing the TX AM RLC entity to work towards having an RLC SDU with the lowest SN among RLC SDUs which have not yet been positively acknowledged being positively acknowledged.

[0074]

[0061] Below is a text proposal (where proposed new text is underlined) on top of a running change request to the RLC specification of 3GPP, incorporating also the exception for window stalling. For the purpose of this text proposal, it is assumed that the changes for the above-mentioned mechanism of unnecessary retransmissions avoidance have been accepted by the RLC specification of 3 GPP.5.2 Data transfer procedures

[0075] 5.2.3 AM data transfer

[0076] 5.2.3.1 Transmit operations

[0077] 5.2.3.1.1 General

[0078] The transmitting side of an AM RLC entity shall prioritize transmission of RLC control PDUs over AMD PDUs. The transmitting side of an AM RLC entity shall prioritize transmission of AMD PDUs containing previously transmitted RLC SDUs or RLC SDU segments over transmission of AMD PDUs containing not previously transmitted RLC SDUs or RLC SDU segments.

[0079] Editor’s Note: FFS the transmitting priority between AMD PDUs for ARQ and AMD PDUs for autonomous retransmission.

[0080] The transmitting side of an AM RLC entity shall maintain a transmitting window according to the state variable TX Next Ack as follows:

[0081] - a SN falls within the transmitting window if TX Next Ack <= SN < TX Next Ack + AM Window Size; - a SN falls outside of the transmitting window otherwise.

[0082] The transmitting side of an AM RLC entity shall not submit to lower layer any AMD PDU whose SN falls outside of the transmitting window.

[0083] For each RLC SDU received from the upper layer, the AM RLC entity shall:

[0084] - associate a SN with the RLC SDU equal to TX Next and construct an AMD PDU by setting the SN of the AMD PDU to TX Next;

[0085] - increment TX Next by one.

[0086] When submitting an AMD PDU that contains a segment of an RLC SDU, to lower layer, the transmitting side of an AM RLC entity shall:

[0087] - set the SN of the AMD PDU to the SN of the corresponding RLC SDU.

[0088] The transmitting side of an AM RLC entity can receive a positive acknowledgement (confirmation of successful reception by its peer AM RLC entity) for an RLC SDU by the following:

[0089] - STATU S PDU from its peer AM RLC entity.

[0090] When receiving a positive acknowledgement for an RLC SDU with SN = x, the transmitting side of an AM RLC entity shall:

[0091] - send an indication to the upper layers of successful delivery of the RLC SDU;

[0092] - set TX Next Ack equal to the SN of the RLC SDU with the smallest SN, whose SN falls within the range TX Next Ack <= SN <= TX Next and for which a positive acknowledgment has not been received yet. If stopReTxObsoleteSDU is set to enabled, when receiving a discard indication for an RLC SDU with SN = x from the upper layer (see TS 38.323 [4]), the transmitting side of an AM RLC entity shall:

[0093] - stop transmission of the RLC SDU and stop retransmission in 5.3.2 (if any) and stop autonomous retransmission in 5.X.2 (if any);

[0094] - if t-PollRetransmit is running, TX Next < TX Next Ack + AM Window Size, and for every RLC SDU whose SN falls within the range TX Next Ack <= SN < TX Next either a positive acknowledgement ina STATUS report from the receiving RLC AM entity or a discard indication from the upper layer (see TS 38.323 [4]) has been received:

[0095] - stop and reset t-PollRetransmit.

[0096] 5.3 ARQ procedures

[0097] 5.3.3 Polling

[0098] 5.3.3.3 Reception of a STATUS report

[0099] Upon reception of a STATUS report from the receiving RLC AM entity the transmitting side of an AM RLC entity shall:

[0100] - if the STATUS report comprises a positive or negative acknowledgement for the RLC SDU with sequence number equal to POLL SN; or

[0101] - if . stop / ?e7xOZ>.sv> / efe.S7)U is set to enabled, TX Next< TX Next Ack + AM Window Size, and for every RLC SDU whose SN falls within the range TX Next Ack <= SN < TX Next either a positive acknowledgement in a STATUS report from the receiving RLC AM entity or a discard indication from the upper layer (see TS 38.323 [4]) has been received:

[0102] - if t-PollRe transmit is running:

[0103] - stop and reset t-PollRe transmit.

[0104]

[0105]

[0062] In the above text proposal, the parameter “stopReTxObsoleteSDU” is a parameter used by the transmitting side of AM RLC entity to determine whether to stop RLC retransmission of obsolete or discarded RLC SDUs. If stopReTxObsoleteSDU is set to enabled, when receiving a discard indication for an RLC SDU with SN = x (“x” refers to any suitable value of a SN) from a higher protocol layer, a transmitting side of an AM RLC entity shall stop transmission of the RLC SDU and stop retransmission of the RLC SDU (if any) and stop autonomous retransmission (triggered by expiry of a retransmission timer for an SDU or segment of SDU) of the RLC SDU (if any).

[0106]

[0063] FIGs. 3 and 4 illustrate exemplary procedures of data transfer according to an embodiment of the present disclosure. In these procedures, a transmitting device (e.g., UE for uplink data transfer) transmits a sequence of RLC data PDUs to a receiving device (e.g., a gNB or a distributed unit of a gNB). For example, the transmitting device and the receiving device may be implemented as UE 120 and gNB 110 shown in FIG. 1, respectively.

[0107]

[0064] As shown in FIG. 3, UE 120 transmits a sequence of RLC data PDUs with RLC SNs 100 through 103 to gNB 110. In this regard, a TX AM RLC entity of UE 120 may submit a RLC AMD PDU with SN=100 to MAC layer at step 301. In an example, no poll is transmitted with this RLC AMD PDU. For example, the poll bit in the RLC AMD PDU may be set to “0”, to indicate that RLC status report is not requested. It is assumed that at this time instance, a next RLC SDU for which a positive acknowledgment is to be received in-sequence is this RLC AMD PDU with SN=100. That is, TX_Next_Ack = 100.

[0108]

[0065] Next to step 301, the TX AM RLC entity of UE 120 may submit the other RLC AMD PDUs with SNs=101, 102, and 103 to MAC layer at steps 302, 303 and 304, respectively. A pollmay be transmitted with the RLC AMD PDU with SN=102, at step 303. For example, the poll bit in the RLC AMD PDU may be set to “1”, to indicate that RLC status report is requested. Upon the transmission of the poll or upon submitting the RLC AMD PDUs with SN=102, a timer t-PollRe transmit is started or re-started, as shown at 310.

[0109]

[0066] At step 305, the UE 120 receives an RLC status report from the gNB 110. In this regard, the receiving side of AM RLC entity at gNB 110 may transmit the RLC status report to the TX AM RLC entity of UE 120, when it detects a reception failure of the RLC SDU with SN = 100. The RLC status PDU may include an Ack SN field indicating an SN of value 102 and a Nack_SN field indicating an SN of value 100. The Ack_SN field and Nack_SN field indicate that all RLC SDUs up to but not including the RLC SDU with SN = Ack_SN=102 have been successfully received, except for the RLC SDU with SN = Nack_SN=100. At that time, TX_Next_Ack is still 100.

[0110]

[0067] At step 306, the UE 120 obtains one or more discard indications indicating one or more RLC SDUs which are discarded at a higher protocol layer. In this regard, the TX AM RLC entity of UE 120 may receive discard indications from a PDCP layer of the UE 120. For example, the UE 120 may determine, e.g., at the PDCP layer, that a discard timer corresponding to a PDCP SDU expired and then the PDCP SDU is outdated and should be discarded. For example, this may be caused due to that the RLC data PDUs with SNs=100, 102, 103 are lost as shown at steps 301, 303, 304. Then PDCP layer may send discard indications to the TX AM RLC entity, and the TX AM RLC entity may be caused to stop transmissions of RLC SDUs which carry the PDCP SDUs discarded at the PDCP layer. The TX AM RLC entity may determine from the one or more discard indications, that transmissions of RLC SDUs with SNs 100, 102 and 103 should be stopped. At that time, TX_Next_Ack is still 100, and TX_Next is still 104.

[0111]

[0068] At step 307, the UE 120 determines that the stopping condition for the timer t-PollRetransmit is fulfilled, as all RLC SDUs with SNs falling within a range TX Next Ack (= 100) <= SN < TX_Next (=104) are either indicated as discarded or positively acknowledged. Then, at step 308, the UE 120 stops the running timer t-PollRe transmit. The timer t-PollRetransmit may be reset. As shown at 330, the timer t-PollRetransmit is stopped earlier than the originally scheduled expiration time (shown at 320). Meanwhile, this avoids unnecessary retransmission of a poll, and avoids unnecessary retransmission of RLC SDUs with SNs falling within a range 100 <= SN < 104.

[0112]

[0069] In FIG. 4, UE 120 transmits a sequence of RLC data PDUs with RLC SNs 100 through 103 to gNB 110. In this regard, a TX AM RLC entity of UE 120 may submit a RLC AMD PDU with SN=100 to MAC layer at step 401. For example, it may be assumed that at this time instance, a next RLC SDU for which a positive acknowledgment is to be received in-sequence is this RLC AMD PDU with SN=100. That is, TX_Next_Ack = 100.

[0113]

[0070] Next to step 401, the TX AM RLC entity of UE 120 may submit the other RLC AMD PDUs with SNs=101, 102, and 103 to MAC layer at steps 402, 403 and 404, respectively. A poll may be transmitted with the RLC AMD PDU with SN=102, at step 403. For example, the poll bit in the RLC AMD PDU may be set to “1”, to indicate that RLC status report is requested.Upon the transmission of the poll or upon submitting the RLC AMD PDUs with SN=102, a timer t-PollRe transmit is started or re-started, as shown at 410.

[0114]

[0071] At step 405, the UE 120 obtains one or more discard indications indicating one or more RLC SDUs which are discarded at a higher protocol layer. In this regard, the TX AM RLC entity of UE 120 may receive a discard indication from a PDCP layer of the UE 120. For example, the UE 120 may determine, e.g., at the PDCP layer, that a discard timer corresponding to a PDCP SDU expired, e.g., due to the loss of the RLC data PDU with SN=100 as shown at step 401. Then, PDCP layer may send a discard indication to the TX AM RLC entity. The TX AM RLC entity may determine from the discard indication that transmissions of the RLC SDU with SN=100 should be stopped. At that time, TX_Next_Ack is still 100, and TX_Next is 104.

[0115]

[0072] In response to the reception of the discard indication, the UE 120 may determine or check whether or not the stopping condition for the timer t-PollRe transmit is fulfilled at step 406. The UE 120 may determine that the stopping condition is not fulfilled, as the RLC SDUs with SNs = 101, 102, 103 are neither indicated as discarded or been positively acknowledged by the peer RLC entity of the gNB 110. Thus, the timer t-PollRe transmit is kept running. Information of SN of the RLC SDU indicated as discarded would be stored, for future determination for the stopping condition for the timer t-PollRetransmit.

[0116]

[0073] At step 407, the UE 120 receives an RLC status report from the gNB 110. In this regard, the TX AM RLC entity of UE 120 may receive an RLC status PDU which includes an ACK SN field indicating an SN of value 104 and an Nack_SN field indicating an SN of value 100. The Ack SN field and Nack SN field indicate that all RLC SDUs up to but not including the RLC SDU with SN = ACK_SN=104 have been successfully received by its peer AM RLC entity, except for the RLC SDU with SN = Nack_SN=100. At that time, TX_Next_Ack is still 100, and TX Next is 104.

[0117]

[0074] At step 408, the UE 120 determines that the stopping condition for the timer t-PollRetransmit is fulfilled, as a part of RLC SDUs with SNs falling within a range 100 <= SN < 104, namely RLC SDU with SN=100 is indicated as discarded, and the remaining part of RLC SDUs with SNs falling within the range 100 <= SN < 104, namely RLC SDUs with SNs=101, 102, and 103, have been positively acknowledged.

[0118]

[0075] Then, at step 409, the UE 120 stops the running timer t-PollRetransmit. The timer t-PollRetransmit may be reset. As shown at 430, the timer t-PollRetransmit is stopped earlier than the originally scheduled expiration time (shown at 420). Meanwhile, this avoids unnecessary retransmission of a poll, and avoids unnecessary retransmission of RLC SDU with SN=100.

[0119]

[0076] FIG. 5 is a flow chart depicting a method 500 according to embodiments of the present disclosure. In an example, the method may be performed at a terminal device (e.g., UE), or an apparatus for use in a terminal device, for uplink transmission at RLC layer. In another example, the method may be performed at a network node (e.g., gNB), or an apparatus for use in a network node, for downlink transmission at RLC layer.

[0120]

[0077] At step 520, an AM RLC entity (of a UE or gNB) receives a discard indication for an RLC SDU with SN=x from an upper protocol layer (e.g., PDCP layer), “x” is a value of the SNof the RLC SDU indicated as discarded. In some examples, the AM RLC entity may determine from the discard indication, an SN of an RLC SDU indicated as discarded.

[0121]

[0078] At step 530, in response to the reception of the discard indication, the AM RLC entity may determine whether or not the following three conditions are fulfilled:

[0122] • A parameter stopReTxObsoleteSDU is set to enabled,

[0123] • The timer t-PollRetransmit is running,

[0124] • TX_Next < TX_Next_Ack + AM_Window_Size, and

[0125] • For every RLC SDU whose SN falls within a range TX_Next_Ack <= SN < TX Next, either a positive acknowledgement in a status report from a peer RLC AM entity or a discard indication from the upper protocol layer has been received.

[0126]

[0079] At step 530, the AM RLC entity may stop and reset the timer t-PollRe transmit if the three conditions are fulfilled.

[0127]

[0080] The timer t-PollRe transmit may be started or restarted at an early time before step 520. For example, the AM RLC entity may submit an RLC PDU including a poll to a lower protocol layer (e.g., MAC layer). In this regard, a poll bit in the header of the RLC PDU may be set to request acknowledgement feedback, which may be positive acknowledgement or negative acknowledgement. Upon the submission of the RLC PDU including the poll, the AM RLC entity start or restart the timer t-PollRe transmit, as shown at step 510. The RLC PDU may also include an RLC SDU or a part of an RLC SDU whose SN falls within the range TX_Next_Ack <= SN < TX Next.

[0128]

[0081] FIG. 6 is a flow chart depicting a method 600 according to embodiments of the present disclosure. In an example, the method may be performed at a terminal device (e.g., UE), or an apparatus for use in a terminal device, for uplink transmission at RLC layer. In another example, the method may be performed at a network node (e.g., gNB), or an apparatus for use in a network node, for downlink transmission at RLC layer.

[0129]

[0082] At step 620, an AM RLC entity (of a UE for uplink transmission, or of a gNB for downlink transmission) receives an RLC status report from a peer RLC entity. In some examples, the RLC status report may comprise positive acknowledgements and / or negative acknowledgements of one or more RLC SDUs or segments of RLC SDUs previously transmitted from the AM RLC entity to the peer RLC entity.

[0130]

[0083] At step 630, in response to the reception of the status report, the AM RLC entity may determine whether or not the following three conditions are fulfilled:

[0131] • A parameter stopReTxObsoleteSDU is set to enabled,

[0132] • The timer t-PollRetransmit is running,

[0133] • TX_Next < TX_Next_Ack + AM_Window_Size, and

[0134] • For every RLC SDU whose SN falls within a range TX_Next_Ack <= SN < TX Next, either a positive acknowledgement in a status report from a peer RLC AM entity or a discard indication from the upper protocol layer has been received.

[0135]

[0084] At step 630, the AM RLC entity may stop and reset the timer t-PollRetransmit if the four conditions are fulfilled.

[0085] The timer t-PollRetransmit may be started or restarted at an early time before step 620. For example, the AM RLC entity may submit an RLC PDU including a poll to a lower protocol layer (e.g., MAC layer). In this regard, a poll bit in the header of the RLC PDU may be set to request acknowledgement feedback, which may be positive acknowledgement or negative acknowledgement. Upon the submission of the RLC PDU including the poll, the AM RLC entity start or restart the timer t-PollRe transmit, as shown at step 610. The RLC PDU may also include an RLC SDU or a part of an RLC SDU whose SN falls within the range TX_Next_Ack <= SN < TX Next.

[0136]

[0086] Embodiments herein may avoid unnecessary polling for acknowledgement feedback in AM RLC entity, which would also entail unnecessary retransmission of RLC data. The embodiments herein are not limited to the features and advantages mentioned above. A person skilled in the art will recognize additional features and advantages upon reading the following detailed description.

[0137]

[0087] FIG. 7 shows, by way of example, a block diagram of an apparatus 10, that may be embodied in / as the terminal device, or the network node. The apparatus 10 comprises, for example, at least one processor 12 and at least one memory 14 storing instructions 15 that, when executed by the at least one processor, cause the apparatus 10 at least to perform the method or methods as disclosed herein, and any of the embodiments thereof. In an example, the at least one memory and the instructions (e.g. a computer program code, software), are configured, with the at least one processor, to cause the apparatus 10 to perform the method or methods as disclosed herein, and any of the embodiments thereof.

[0138]

[0088] A processor 12 may comprise circuitry, or be constituted as circuitry or circuitries, the circuitry or circuitries being configured to perform phases of methods in accordance with example embodiments described herein. As used in this application, the term “circuitry” may refer to one or more or all of the following: (a) hardware-only circuit implementations, such as implementations in only analog and / or digital circuitry, and (b) combinations of hardware circuits and software, such as, as applicable: (i) a combination of analog and / or digital hardware circuit(s) with software / firmware and (ii) any portions of hardware processor(s) with software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a user equipment, to perform various functions) and (c) hardware circuit(s) and or processor(s), such as a microprocessor(s) or a portion of a microprocessor(s), that requires software (e.g., firmware) for operation, but the software may not be present when it is not needed for operation. This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely a hardware circuit or processor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and / or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in server, a cellular network device, or other computing or network device.

[0089] The memory 14 may be implemented using any suitable data storage technology. The memory may comprise a database for storing data. The memory 14 may be at least in part external to apparatus 10 but accessible to apparatus 10.

[0139]

[0090] The instructions 15 may be comprised in a computer readable medium or a non-transitory computer readable medium. A term non-transitory, as used herein, is a limitation of the medium itself (i.e. tangible, not a signal) as opposed to a limitation on data storage persistency (e.g. random access memory, RAM, vs. read only memory, ROM).

[0140]

[0091] For example, the apparatus 10 is a transmitting device, e.g., a base station or a terminal device. As another example, the apparatus is comprised in such a transmitting device, e.g. as a chipset configured to control the transmitting device. The apparatus 10 may be caused or configured to perform at least the method of FIGs. 2, 5, and 6, and / or any one or more of the embodiments described.

[0141]

[0092] The apparatus may comprise one or more entities of any of protocol layers, such as a MAC entity, an RRC entity, an RLC entity, a PDCP entity or a PHY entity. In some embodiments, the entity is configured to perform at least the method of FIGs. 2, 5, and 6, and / or any one or more of the embodiments described.

[0142]

[0093] The apparatus 10 comprises a radio interface 16. The radio interface 16 may provide the apparatus 10 with communication capabilities. The radio interface 16 may comprise a receiver configured to receive information in accordance with at least one cellular or non-cellular standard. The radio interface 16 may comprise a transmitter configured to transmit information in accordance with at least one cellular or non-cellular standard. The receiver may comprise more than one receiver. The transmitter may comprise more than one transmitter. The radio interface 16 may comprise a transceiver configured to receive and transmit information in accordance with at least one cellular or non-cellular standard. The transceiver may comprise more than one transceiver.

[0143]

[0094] The apparatus 10 may comprise a user interface 18 comprising, for example, at least one of a keypad, a microphone, a touch display, a display, a speaker, etc. The user interface 18 may be used to control the apparatus by the user. The user interface 18 may be external to the apparatus 10. For example, the apparatus 10 may be connected to another device, such as a computer, either via wireless or wired connection, and the apparatus 10 is controlled by the user via the computer.

[0144]

[0095] In an embodiment, at least some of the processes described herein may be carried out by an apparatus comprising means for carrying out at least some of the described processes. Means for performing method steps as disclosed herein may include software and / or hardware components of the apparatus 10. For example, the at least one processor 12, the memory 14, and the computer program code form means for carrying out the method or methods as disclosed herein, and any of the embodiments thereof. As used herein the term “means” is to be construed in singular form, i.e. referring to a single element, or in plural form, i.e. referring to a combination of single elements. Therefore, terminology “means for [performing A, B, C]”, is to be interpreted to cover an apparatus in which there is only one means for performing A, B and C,or where there are separate means for performing A, B and C, or partially or fully overlapping means for performing A, B, C. Further, terminology “means for performing A, means for performing B, means for performing C” is to be interpreted to cover an apparatus in which there is only one means for performing A, B and C, or where there are separate means for performing A, B and C, or partially or fully overlapping means for performing A, B, C.

[0145]

[0096] It should be appreciated that at least some aspects of the exemplary embodiments of the disclosures may be embodied in computer-executable instructions, such as in one or more program modules, executed by one or more computers or other devices. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types when executed by a processor in a computer or other device. The computer executable instructions may be stored on a computer readable medium, for example, non-transitory computer readable medium, such as a hard disk, optical disk, removable storage media, solid state memory, RAM, etc. As will be appreciated by one of skills in the art, the function of the program modules may be combined or distributed as desired in various embodiments. In addition, the function may be embodied in whole or in part in firmware or hardware equivalents such as integrated circuits, field programmable gate arrays (FPGA), and the like.

[0146]

[0097] Further, while operations are depicted in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Likewise, while several specific implementation details are contained in the above discussions, these should not be construed as limitations on the scope of the present disclosure, but rather as descriptions of features that may be specific to particular embodiments. Certain 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 sub-combination.

[0147]

[0098] Even though the invention has been described above with reference to an example according to the accompanying drawings, it is clear that the invention is not restricted thereto but may be modified in several ways within the scope of the appended claims. Therefore, all words and expressions should be interpreted broadly and they are intended to illustrate, not to restrict, the embodiment. It will be obvious to a person skilled in the art that, as technology advances, the inventive concept may be implemented in various ways. Further, it is clear to a person skilled in the art that the described embodiments may, but are not required to, be combined with other embodiments in various ways.

Claims

CLAIMS1. An apparatus for wireless communication with a radio link control (RLC) entity in acknowledged mode (AM), the apparatus comprising:at least one processor; andat least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to:determine whether or not every RLC service data unit (SDU) previously submitted to a lower protocol layer in one or more RLC protocol data unit (PDU) is either positively acknowledged or has been indicated as discarded; andstop a timer for retransmitting a poll at least based on a determination that every RLC SDU previously submitted to the lower protocol layer in the one or more RLC PDU is either positively acknowledged or has been indicated as discarded.

2. The apparatus according to claim 1, wherein the instructions, when executed by the at least one processor, further cause the apparatus to determine whether or not every RLC SDU previously submitted to the lower protocol layer in the one or more RLC PDU is either positively acknowledged or has been indicated as discarded by,determining whether or not every RLC SDU with an RLC sequence number (SN) greater than or equal to an acknowledgement state variable, TX Next Ack, and less than a send state variable, TX Next, is either positively acknowledged or has been indicated as discarded.

3. The apparatus according to claim 1 or 2, wherein the instructions, when executed by the at least one processor, further cause the apparatus to:receive a discard indication for one or more RLC SDUs from packet data convergence protocol (PDCP) layer; andtrigger the determining in response to a reception of the discard indication.

4. The apparatus according to claim 3, wherein the instructions, when executed by the at least one processor, further cause the apparatus to:determine sequence numbers (SNs) of RLC SDUs indicated as discarded according to the discard indication; andstore the SNs of the RLC SDUs indicated as discarded.

5. The apparatus according to any of claims 1 to 4, wherein the instructions, when executed by the at least one processor, further cause the apparatus to:receive from a peer RLC entity, an RLC status report which provides positive acknowledgements and / or negative acknowledgements of one or more RLC SDUs previously submitted to the lower protocol layer; andtrigger the determining in response to a reception of the RLC status report.

6. The apparatus according to any of claims 1 to 5, wherein the instructions, when executed by the at least one processor, further cause the apparatus to:stop the timer for retransmitting the poll, in case that it is determined that every RLC SDU previously submitted to the lower protocol layer in the one or more RLC PDU is either positively acknowledged or has been indicated as discarded.

7. The apparatus according to any of claims 1 to 5, wherein the instructions, when executed by the at least one processor, further cause the apparatus to:determine whether or not a RLC transmitting window of the RLC entity is stalled; and keep the timer for retransmitting the poll running, in case that it is determined that a RLC transmitting window is stalled.

8. The apparatus according to claim 7, wherein the instructions, when executed by the at least one processor, further cause the apparatus to:stop the timer for retransmitting the poll, in case that it is determined that a RLC transmitting window is not stalled, and every RLC SDU previously submitted to the lower protocol layer in the one or more RLC PDU is either positively acknowledged or has been indicated as discarded.

9. The apparatus according to any of claims 1 to 8, wherein the timer is t-PollRe transmit.

10. The apparatus according to any of claims 1 to 9, wherein the RLC entity is in a base station or user equipment.

11. A method for wireless communication with an RLC entity in acknowledged mode (AM), the method comprising:determining whether or not every radio link control (RLC) service data unit (SDU) previously submitted to a lower protocol layer in one or more RLC protocol data unit (PDU) is either positively acknowledged or has been indicated as discarded; andstopping a timer for retransmitting a poll at least based on a determination that every RLC SDU previously submitted to the lower protocol layer in the one or more RLC PDU is either positively acknowledged or has been indicated as discarded.

12. The method according to claim 11, wherein determining whether or not every RLC SDU previously submitted to the lower protocol layer in the one or more RLC PDU is either positively acknowledged or has been indicated as discarded comprises,determining whether or not every RLC SDU with an RLC sequence number (SN) greater than or equal to an acknowledgement state variable, TX Next Ack, and less than a send state variable, TX Next, is either positively acknowledged or has been indicated as discarded.

13. The method according to claim 11 or 12, further comprising,receiving a discard indication for one or more RLC SDUs from packet data convergence protocol (PDCP) layer; andtriggering the determining in response to a reception of the discard indication.

14. The method according to claim 13, further comprising:determining sequence numbers (SNs) of RLC SDUs indicated as discarded according to the discard indication; andstoring the SNs of the RLC SDUs indicated as discarded.

15. The method according to any of claims 11 to 14, wherein determining whether the missing of the one or more packets is to be skipped comprises,receiving from a peer RLC entity, an RLC status report which provides positive acknowledgements and / or negative acknowledgements of one or more RLC SDUs previously submitted to the lower protocol layer; andtriggering the determining in response to a reception of the RLC status report.

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