Retransmission timing

Abstract

Example embodiments of the present disclosure are directed to retransmission timing. A method comprises submitting, from a first apparatus at a higher-layer protocol, a protocol data unit (PDU) to a second apparatus at a lower-layer protocol, the first apparatus and the second apparatus being comprised in a first device; receiving, from the second apparatus, a local positive acknowledgement (ACK) for a payload of the PDU; and starting a retransmission timer for the payload based on receiving the local positive ACK.

Description

RETRANSMISSION TIMINGFIELD

[0001] Various example embodiments of the present disclosure generally relate to the field of telecommunication and in particular, to methods, devices, apparatuses and computer readable storage medium for retransmission timing.BACKGROUND

[0002] A communication network may serve as a facility that enables communications between two or more communication devices or provides communication devices access to a data network. A mobile or wireless communication network is one example of a communication network. The communication network may operate in accordance with standards such as those provided by Third Generation Partnership Project (3GPP) or European Telecommunications Standards Institute (ETSI). Examples of standards provided by 3 GPP are the so-called 3 GPP standards for cellular technology generations, such as 3GPP standards for 4G technology, 5G technology, 6G technology etc.SUMMARY

[0003] In a first aspect of the present disclosure, there is provided a first apparatus. The first apparatus comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the first apparatus to: submit, at a higher-layer protocol, a protocol data unit (PDU) to a second apparatus at a lower-layer protocol, the first apparatus and the second apparatus being comprised in a first device; receive, from the second apparatus, a local positive acknowledgement (ACK) for a payload of the PDU; and start a retransmission timer for the payload based on receiving the local positive ACK.

[0004] In a second aspect of the present disclosure, there is provided a second apparatus The second apparatus comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the second apparatus to: receive, at a lower-layer protocol, a protocol data unit (PDU) of a higher-layer protocol from a first apparatus at the higher-layer protocol, the first apparatus and the second apparatus being comprised in a first device; transmit a payload of the PDU to a second device different from the first device; and send, to the first apparatus, a local positiveacknowledgement (ACK) for the payload.

[0005] In a third aspect of the present disclosure, there is provided a first device. The first device comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the first device to: submit from a first apparatus at a higher-layer protocol, a protocol data unit (PDU) to a second apparatus at a lower-layer protocol, wherein the first device comprises the first apparatus and the second apparatus; receive, by the second apparatus at the lower -layer protocol, the protocol data unit (PDU) of the higher-layer protocol from the first apparatus at the higher-layer protocol; transmit, from the second apparatus, a payload of the PDU to a second device different from the first device; and send, from the second apparatus to the first apparatus, a local positive acknowledgement (ACK) for the payload; receive, by the first apparatus from the second apparatus, the local positive acknowledgement (ACK) for the payload; and start, by the first apparatus, a retransmission timer for the payload based on receiving the local positive ACK.

[0006] In a fourth aspect of the present disclosure, there is provided a method. The method comprises: submitting, from a first apparatus at a higher-layer protocol, a protocol data unit (PDU) to a second apparatus at a lower-layer protocol, the first apparatus and the second apparatus being comprised in a first device; receiving, from the second apparatus, a local positive acknowledgement (ACK) for a payload of the PDU; and starting a retransmission timer for the payload based on receiving the local positive ACK.

[0007] In a fifth aspect of the present disclosure, there is provided a method. The method comprises: receiving, by a second apparatus at a lower-layer protocol, a protocol data unit (PDU) of a higher-layer protocol from a first apparatus at the higher -layer protocol, the first apparatus and the second apparatus being comprised in a first device; transmitting a payload of the PDU to a second device different from the first device; and sending, to the first apparatus, a local positive acknowledgement (ACK) for the payload.

[0008] In a sixth aspect of the present disclosure, there is provided a method. The method comprises: submitting from a first apparatus at a higher-layer protocol, a protocol data unit (PDU) to a second apparatus at a lower-layer protocol, wherein the first device comprises the first apparatus and the second apparatus; receiving, by the second apparatus at the lower-layer protocol, the protocol data unit (PDU) of the higher -layer protocol from the first apparatus at the higher-layer protocol; transmitting, from the second apparatus, a payload of the PDU to a second device different from the first device; and sending, fromthe second apparatus to the first apparatus, a local positive acknowledgement (ACK) for the payload; receiving, by the first apparatus from the second apparatus, the local positive acknowledgement (ACK) for the payload; and starting, by the first apparatus, a retransmission timer for the payload based on receiving the local positive ACK.

[0009] In a seventh aspect of the present disclosure, there is provided a first apparatus. The first apparatus comprises means for submitting, at a higher-layer protocol, a protocol data unit (PDU) to a second apparatus at a lower-layer protocol, the first apparatus and the second apparatus being comprised in a first device; means for receiving, from the second apparatus, a local positive acknowledgement (ACK) for a payload of the PDU; and means for starting a retransmission timer for the payload based on receiving the local positive ACK.

[0010] In an eighth aspect of the present disclosure, there is provided a second apparatus. The second apparatus comprises means for receiving, at a lower-layer protocol, a protocol data unit (PDU) of a higher-layer protocol from a first apparatus at the higher -layer protocol, the first apparatus and the second apparatus being comprised in a first device; means for transmitting a payload of the PDU to a second device different from the first device; and means for sending, to the first apparatus, a local positive acknowledgement (ACK) for the payload.

[0011] In a ninth aspect of the present disclosure, there is provided a first device. The first device comprises means for submitting from a first apparatus at a higher-layer protocol, a protocol data unit (PDU) to a second apparatus at a lower-layer protocol, wherein the first device comprises the first apparatus and the second apparatus; means for receiving, by the second apparatus at the lower-layer protocol, the protocol data unit (PDU) of the higher-layer protocol from the first apparatus at the higher-layer protocol; means for transmitting, from the second apparatus, a payload of the PDU to a second device different from the first device; and means for sending, from the second apparatus to the first apparatus, a local positive acknowledgement (ACK) for the payload; means for receiving, by the first apparatus from the second apparatus, the local positive acknowledgement (ACK) for the payload; and means for starting, by the first apparatus, a retransmission timer for the payload based on receiving the local positive ACK.

[0012] In a tenth aspect of the present disclosure, there is provided a computer readable medium. The computer readable medium comprises instructions stored thereon for causing an apparatus to perform at least the method according to the fourth aspect and anyof the embodiments thereof.

[0013] In an eleventh aspect of the present disclosure, there is provided a computer readable medium. The computer readable medium comprises instructions stored thereon for causing an apparatus to perform at least the method according to the fifth aspect and any of the embodiments thereof.

[0014] In a twelfth aspect of the present disclosure, there is provided a computer readable medium. The computer readable medium comprises instructions stored thereon for causing an apparatus to perform at least the method according to the sixth aspect and any of the embodiments thereof.

[0015] 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.BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Some example embodiments will now be described with reference to the accompanying drawings, where:

[0017] FIG. 1 illustrates an example communication environment in which example embodiments of the present disclosure can be implemented;

[0018] FIG. 2 illustrates a signaling flow of an example process for retransmission timing based on a local positive acknowledgement in accordance with some example embodiments of the present disclosure;

[0019] FIG. 3 illustrates a signaling flow of an example process for retransmission timing based on a local positive acknowledgement from a medium access control (MAC) entity in accordance with some example embodiments of the present disclosure;

[0020] FIG. 4 illustrates a signaling flow of an example process for a retransmission with delay reduction in accordance with some example embodiments of the present disclosure;

[0021] FIG. 5 illustrates a flowchart of a method implemented at a first apparatus in accordance with some example embodiments of the present disclosure;

[0022] FIG. 6 illustrates a flowchart of a method implemented at a second apparatus in accordance with some example embodiments of the present disclosure;

[0023] FIG. 7 illustrates a flowchart of a method implemented at a first device in accordance with some example embodiments of the present disclosure;

[0024] FIG. 8 illustrates a flowchart of a method implemented at a radio link control (RLC) entity in accordance with some example embodiments of the present disclosure;

[0025] FIG. 9 illustrates a flowchart of a method implemented at a medium access control (MAC) entity in accordance with some example embodiments of the present disclosure;

[0026] FIG. 10 illustrates a flowchart of a method implemented at a user equipment in accordance with some example embodiments of the present disclosure;

[0027] FIG. 11 illustrates a simplified block diagram of a device that is suitable for implementing example embodiments of the present disclosure; and

[0028] FIG. 12 illustrates a block diagram of an example computer readable medium in accordance with some example embodiments of the present disclosure.

[0029] Throughout the drawings, the same or similar reference numerals represent the same or similar element.DETAILED DESCRIPTION

[0030] Principle of the present disclosure will now be described with reference to some example embodiments. It is to be understood that these embodiments are described only for the purpose of illustration and help those skilled in the art to understand and implement the present disclosure, without suggesting any limitation as to the scope of the disclosure. Embodiments described herein can be implemented in various manners other than the ones described below.

[0031] 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.

[0032] References in the present disclosure to “one embodiment,” “an embodiment,” “an example embodiment,” and the like indicate that the embodiment described may include a particular feature, structure, or characteristic, but it is not necessary that every embodiment includes the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it issubmitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

[0033] It shall be understood that although the terms “first,” “second,”..., etc. in front of noun(s) and the like may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another and they do not limit the order of the noun(s). For example, a first element could be termed a second element, and similarly, a second element could be termed a first element, without departing from the scope of example embodiments. As used herein, the term “and / or” includes any and all combinations of one or more of the listed terms.

[0034] As used herein, “at least one of the following: ” and “at least one of ” and similar wording, where the list of two or more elements are joined by “and” or “or”, mean at least any one of the elements, or at least any two or more of the elements, or at least all the elements.

[0035] As used herein, unless stated explicitly, performing a step “in response to A” does not indicate that the step is performed immediately after “A” occurs and one or more intervening steps may be included.

[0036] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises”, “comprising”, “has”, “having”, “includes” and / or “including”, when used herein, specify the presence of stated features, elements, and / or components etc., but do not preclude the presence or addition of one or more other features, elements, components and / or combinations thereof.

[0037] 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) withsoftware / 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 mobile phone or server, 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.

[0038] 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.

[0039] As used herein, the term “communication network” refers to a network following any suitable communication standards, such as New Radio (NR), Long Term Evolution (LTE), LTE-Advanced (LTE-A), Wideband Code Division Multiple Access (WCDMA), High-Speed Packet Access (HSPA), Narrow Band Internet of Things (NB-IoT) and so on. Furthermore, the communications between a terminal device and a network device in the communication network may be performed according to any suitable generation communication protocols, including, but not limited to, the first generation (1G), the second generation (2G), 2.5G, 2.75G, the third generation (3G), the fourth generation (4G), 4.5G, the fifth generation (5G), 5.5G, the sixth generation (6G) communication protocols, and / or any other protocols either currently known or to be developed in the future. Embodiments of the present disclosure may be applied in various communication systems. Given the rapid development in communications, there will of course also be future type communication technologies and systems with which the present disclosure may be embodied. It should not be seen as limiting the scope of the present disclosure to only the aforementioned system.

[0040] As used herein, the term “network device” refers to a node in a communication network via which a terminal device accesses the network and receives services therefrom. The network device may refer to a base station (BS) or an access point (AP), 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 header (RH), a remote radio head (RRH), a relay, an Integrated Access and Backhaul (IAB) node, a low power node such as a femto, a pico, a non-terrestrial network (NTN) or non-ground network device such as a satellite network device, a low earth orbit (LEO) satellite and a geosynchronous earth orbit (GEO) satellite, an aircraft network device, and so forth, depending on the applied terminology and technology. In some example embodiments, radio access network (RAN) split architecture comprises a Centralized Unit (CU) and a Distributed Unit (DU) at an IAB donor node. An IAB node comprises a Mobile Terminal (IAB -MT) part that behaves like a UE toward the parent node, and a DU part of an IAB node behaves like a base station toward the next-hop IAB node.

[0041] The term “terminal device” refers to any end device that may be capable of wireless communication. By way of example rather than limitation, a terminal device may also be referred to as a communication device, user equipment (UE), a Subscriber Station (SS), a Portable Subscriber Station, a Mobile Station (MS), or an Access Terminal (AT). The terminal device may include, but not limited to, 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, vehicle -mounted wireless terminal devices, wireless endpoints, mobile stations, laptop-embedded equipment (LEE), laptop -mounted equipment (LME), USB dongles, smart devices, wireless customer-premises equipment (CPE), 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. The terminal device may also correspond to a Mobile Termination (MT) part of an IAB node (e.g., a relay node). In the following description, the terms “terminal device”, “communication device”, “terminal”, “user equipment” and “UE” may be used interchangeably.

[0042] As used herein, the term “resource,” “transmission resource,” “resource block,” “physical resource block” (PRB), “uplink resource,” or “downlink resource” may refer to any resource for performing a communication, for example, a communication between a terminal device and a network device, such as a resource in time domain, a resource in frequency domain, a resource in space domain, a resource in code domain, or any other combination of the time, frequency, space and / or code domain resource enabling a communication, and the like. In the following, unless explicitly stated, a resource in both frequency domain and time domain will be used as an example of a transmission resource for describing some example embodiments of the present disclosure. It is noted that example embodiments of the present disclosure are equally applicable to other resources in other domains.

[0043] FIG. 1 illustrates an example communication environment 100 in which example embodiments of the present disclosure can be implemented. In the communication environment 100, a plurality of communication devices, including a terminal device 110 and a network device 120, can communicate with each other. In the example of FIG. 1, the terminal device 110 may be a UE and the network device 120 may be a base station serving the UE. The serving area of the network device 120 may be called a cell 102.

[0044] It is to be understood that the number of devices and their connections shown in FIG. 1 are only for the purpose of illustration without suggesting any limitation. The communication environment 100 may include any suitable number of devices configured to implementing example embodiments of the present disclosure. Although not shown, it would be appreciated that one or more additional devices may be located in the cell 102, and one or more additional cells may be deployed in the communication environment 100. It is noted that although illustrated as a base station, the network device 120 may be another device than a base station. Although illustrated as a UE, the terminal device 110 may be another device than a UE.

[0045] In the following, for the purpose of illustration, some example embodiments are described with the terminal device 110 operating as a UE and the network device 120 operating as abase station. However, in some example embodiments, operations described in connection with a terminal device may be implemented at a network device or other device, and operations described in connection with a network device may be implemented at a terminal device or other device.

[0046] In some example embodiments, a transmission direction from the network device120 to the terminal device 110 is referred to as a downlink (DL), while a transmission direction from the terminal device 110 to the network device 120 is referred to as an uplink (UL). In DL, the network device 120 is a transmitting (TX) device (or a transmitter) and the terminal device 110 is a receiving (RX) device (or a receiver). In UL, the terminal device 110 is a TX device (or a transmitter) and the network device 120 is a RX device (or a receiver).

[0047] Communications in the communication environment 100 may be implemented according to any proper communication protocol(s), comprising, but not limited to, cellular communication protocols, wireless local network communication protocols such as Institute for Electrical and Electronics Engineers (IEEE) 802.11 and the like, and / or any other protocols currently known or to be developed in the future. Moreover, the communication may utilize any proper wireless communication technology, comprising but not limited to: Code Division Multiple Access (CDMA), Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Frequency Division Duplex (FDD), Time Division Duplex (TDD), Multiple-Input Multiple-Output (MIMO), Orthogonal Frequency Division Multiple (OFDM), Discrete Fourier Transform spread OFDM (DFT-s-OFDM) and / or any other technologies currently known or to be developed in the future.

[0048] With the development of communication technologies, various mechanisms for controlling retransmission timing have been proposed. For example, in the 3GPP NR protocol stack, retransmissions based on feedback from a receiver may be applied at both a medium access control (MAC) layer in its Hybrid-automatic repeat request (HARQ) mechanism, and a radio link control (RLC) layer in its ARQ mechanism (in case RLC is configured with Acknowledged Mode (AM)). Various timers are also proposed for timely retransmissions. For example, upon expiry of a retransmission timer, a retransmission may be performed.

[0049] There may be a compromise between configurations of the retransmission timers and feedback-based retransmissions. For example, on the one hand, the duration of the retransmission timer may need to be shorter to reduce delays. On the other hand, if the retransmission timer expires quickly, retransmissions may be performed prematurely before reception of positive feedback from the receiver. This may become more complicated if feedback-based retransmissions and / or retransmission timers are configured at multiple protocol layers. For example, the duration of a retransmission timerconfigured at the higher-layer may need to be set longer to allow possible retransmissions at the lower-layer to avoid unnecessary retransmission from the higher-layer. However, the longer duration of the retransmission timer may cause more delays.

[0050] According to embodiments of the present disclosure, several solutions for retransmission timing are proposed. In one solution, a first apparatus submits, at a higher-layer protocol, a protocol data unit (PDU) to a second apparatus at a lower-layer protocol, and the first apparatus and the second apparatus are comprised in a first device. The first apparatus receives, from the second apparatus, a local positive acknowledgement (ACK) for a payload of the PDU, and starts a retransmission timer for the payload based on receiving the local positive ACK.

[0051] With this solution, a local positive ACK from the lower layer can be used as an indication to start the retransmission timer to achieve balance between the delay and capacity. For example, the local positive ACK may be referred to as an unreliable positive ACK or unreliable local positive ACK. It is proposed in the present disclosure that, in some cases the local positive ACK from the lower layer may be followed soon by a reliable positive ACK indicating that the PDU has been delivered to the peer higher layer of the receiving device. Thus, a relatively short duration may be set for the retransmission timer. It is expected that in most cases the retransmission timer may be stopped before expiry because of reception of the reliable positive ACK, thereby reducing unnecessary retransmissions at the higher-layer and reducing capacity loss from duplicated transmissions of the same missing data. If the local positive ACK is not followed by a reliable positive ACK at the higher layer, the retransmission timer may expire quickly due to the short duration, thereby reducing the delays. Due to the relatively short duration, the proposed retransmission timer based on the local ACK may be also referred to as a fast retransmission timer in the following.

[0052] In another solution, the MAC layer and RLC layer are specifically considered. A RLC entity submits, a RLC data PDU to a MAC entity. The RLC entity and the MAC entity are comprised in a first device. The RLC entity receives, from the MAC entity, a tentative local positive ACK for a payload of the RLC data PDU. In accordance with a determination that a condition is met, the RLC entity starts a fast retransmission timer for the payload based on receiving the tentative local positive ACK.

[0053] In this solution, the retransmission timer can be started based on the local positive ACK and the determination that the condition is met. Thus the retransmission timer canbe started in a suitable scenario where the condition can be satisfied.

[0054] Several solutions of the present disclosure have been briefly described. Principle and implementations of the present disclosure will be described in detail below with reference to the accompanying drawings. It will be appreciated that acts, steps, processes, and / or flowcharts illustrated in the drawings are only examples without suggesting any limitation. For example, the steps may be performed in any suitable manner. The steps as illustrated in one or more drawings may be selectively performed in an actual implementation. Moreover, example embodiments described with reference to the drawings may be implemented separately or combined in any suitable manner. For example, one or more example embodiments shown in a single drawing may be combined with one or more example embodiments shown in one or more other drawings.

[0055] FIG. 2 illustrates a signaling flow of an example process 200 for retransmission timing based on a local positive acknowledgement in accordance with some example embodiments of the present disclosure. As illustrated in FIG. 2, the process 200 involves a first device 201 and a second device 202 in communication.

[0056] For the purpose of discussion, the first device 201 may be an example of the terminal device 110 in FIG. 1 and the second device 202 may be an example of the network device 120 in FIG. 1. Alternatively, the first device 201 may be an example of the network device 120 in FIG. 1 and the second device 202 may be an example of the terminal device 110 in FIG. 1.

[0057] The first device 201 includes a first apparatus at a higher -layer protocol, i.e., a high layer apparatus 211 and a second apparatus at a lower-layer protocol, i.e., a low layer apparatus 215. The second device 202 includes a first apparatus at a higher-layer protocol, i.e., a high layer apparatus 221 and a second apparatus at a lower-layer protocol, i.e., a low layer apparatus 225.

[0058] The higher-layer protocol and the lower-layer protocol may refer to any suitable protocol layer in 5G, 6G or future generations. In some embodiments, in 3GPP NR protocol, an example of the higher layer may be the RLC layer and an example of the lower layer may be the MAC layer.

[0059] In the process 200, the high layer apparatus 211 submits 231 at a higher -layer protocol, a PDU to the low layer apparatus 215 at a lower-layer protocol. The low layer apparatus 215 receives 235 the PDU of the higher-layer protocol, and transmits 240 atleast a payload of the PDU (e.g. the whole PDU) to the second device 202 different from the first device 201. The low layer apparatus 215 may transmit the payload within a PDU of the lower-layer protocol to the second device 202.

[0060] The second device 202 may receive 245 the payload successfully or not. As an example, the low layer apparatus 225 may receive the PDU of the lower-layer protocol and deliver it to the high layer apparatus 221. As another example, the low layer apparatus 225 may not successfully receive the payload and may transmit feedback to the first device 201 (not shown in FIG. 2).

[0061] The low layer apparatus 215 sends 250, to the high layer apparatus 211, a local positive ACK for the payload. The high layer apparatus 211 receives 255 the local positive ACK for the payload and starts 260 a retransmission timer for the payload of the PDU of the higher-layer protocol based on receiving the local positive ACK. In some embodiments, the payload of the PDU may comprise a service data unit (SDU) or a segment of the SDU. In the following, the positive ACK may be also referred to as ACK in short.

[0062] As discussed above, by using the local ACK from the low layer as an indication to start the retransmission timer, the retransmission timer may be configured with a relatively short duration for waiting for a possible reliable ACK from the second device 202. It is expected that in most cases the high layer apparatus 211 would receive the reliable ACK from the second device 202 soon after receiving the local ACK from the low layer apparatus 215. However, if no feedback is received, upon expiry of the retransmission timer, the high layer apparatus 211 may retransmit the payload to the low layer apparatus 215. In some embodiments, the high layer apparatus 211 may retransmit the payload in the same PDU or a different PDU as in the previous submission of the PDU.

[0063] In some embodiments, the local positive ACK may indicate a tentative positive ACK from the low layer apparatus 215 of successful reception of the payload at the second device 202. The tentative positive ACK may be unreliable. For example, the low layer apparatus 215 may consider that the payload is successfully received by the second device 202 but in fact the payload is not successfully received by the second device 202. In other words, the local positive ACK is generated based on a decision of the low layer apparatus 215 and it may be correct or incorrect.

[0064] In some embodiments, the local positive ACK may be generated by the low layerapparatus 215 based on feedback received from the second device 202. In some embodiments, the local positive ACK may be associated with HARQ feedback. The low layer apparatus 215 may receive, from the second device 202, HARQ feedback associated with the payload, and generate the local positive ACK based on the HARQ feedback.

[0065] In some embodiments, the low layer apparatus 215 may decode the received HARQ feedback as a HARQ ACK associated with the payload, and generate the local positive ACK based on the HARQ ACK. The low layer apparatus 215 may determine the HARQ ACK based on correct decoding of the HARQ feedback or erroneous decoding of the HARQ feedback. In other words, the low layer apparatus 215 may generate the local positive ACK based on its decision on the received HARQ feedback.

[0066] The erroneous decoding of the HARQ feedback may occur in a case where HARQ feedback is not checksum-protected against errors. In this case, the low layer apparatus 215 may mis-interpret a transmitted request for a retransmission from the second device 202 as that no retransmission is needed, leading to loss of a MAC PDU.

[0067] In some embodiments, the feedback received from the second device 202 may comprise an indication that a HARQ process is not to perform a retransmission associated with the payload. The low layer apparatus 215 may receive the indication from the second device 202 and generate the local positive ACK based on the indication. For example, the low layer apparatus 215 may receive the indication by receiving a New-Data-Indicator (NDI) field via the physical layer.

[0068] In some embodiments, the low layer apparatus 215 may further receive, from the second device 202, a further positive ACK associated with the payload. The low layer apparatus 215 may deliver the further ACK to the high layer apparatus 211. The further positive ACK indicates successful reception of the payload at the higher-layer protocol of the second device. Compared to the local positive ACK, the further positive ACK from the second device 202 may be more reliable.

[0069] In some embodiments, the further positive ACK may be protected against an error by means of cyclic redundancy check (CRC) at a lower layer than the higher-layer protocol. In the example of the MAC layer and the RLC layer, the HARQ feedback may not be checksum-protected against errors but the RLC feedback (ACK or negative ACK) may be protected against errors by means of CRC at lower layers.

[0070] In some embodiments, the high layer apparatus 211 may receive this reliable ACKfrom the second device 202 before expiry the retransmission timer. In accordance with a determination that the further positive ACK is received before the retransmission timer expires, the high layer apparatus 211 may stop the retransmission timer.

[0071] In some embodiments, the high layer apparatus 211 may receive this reliable ACK from the second device 202 after expiry the retransmission timer. In accordance with a determination that the retransmission timer expires (before receiving the further positive ACK), the high layer apparatus 211 may retransmit the payload to the low layer apparatus 215.

[0072] In some embodiments, in accordance with the determination that the further positive ACK is received, the high layer apparatus 211 may discard the payload. The high layer apparatus 211 may discard the payload before or after the expiry of the retransmission timer.

[0073] In some embodiments, the low layer apparatus 215 may further receive, from the second device 202, a negative ACK (NACK) associated with the payload, and deliver the NACK to the high layer apparatus 211. The NACK indicates failed reception of the payload at the higher-layer protocol of the second device 202. Similar to the ACK from the second device 202, the NACK from the second device 202 may be more reliable than the local positive ACK generated by the low layer apparatus 215. For example, the RLC NACK may be checksum-protected.

[0074] The high layer apparatus 211 may decide to retransmit or not retransmit the payload (and decide to stop the retransmission timer or not) upon receiving the NACK from the second device 202. For example, the high layer apparatus 211 may be configured with an ACK only feature, i.e., it is configured to not retransmit based on a received NACK. In this case, the high layer apparatus 211 may decide to not retransmit upon receiving the NACK.

[0075] In some embodiments, in accordance with a determination that the NACK is received before the retransmission timer expires and the NACK triggers a retransmission associated with the payload, the high layer apparatus 211 may stop the retransmission timer. In addition, the high layer apparatus 211 may retransmit the payload.

[0076] With the process 200, a tentative (unreliable) local -ACK indication from a lower-layer protocol (e.g., MAC layer) for a PDU can be used at a higher-layer protocol (e.g., RLC layer) in determining whether and when to perform a retransmission of the PDU’spayload. The local positive ACK generated by the low layer apparatus 215 can be used as an indication that a reliable ACK from the receiving device may follow soon. As such, with the retransmission timer being started based on reception of the local ACK, a relatively short duration can be configured for the retransmission timer, thereby reducing the delays and unnecessary retransmissions.

[0077] FIG. 3 illustrates a signaling flow of an example process 300 for retransmission timing based on a local positive acknowledgement from a MAC entity in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the process 300 will be described with reference to the process 200 in FIG. 2.

[0078] As illustrated in FIG. 3, the first device 201 comprises an RLC entity 311 and a MAC entity 315. The RLC entity 311 may be an example of the high layer apparatus 211 and the MAC entity 315 may be an example of the low layer apparatus 215. The second device 202 comprises an RLC entity 321 and a MAC entity 325. The RLC entity 321 may be an example of the high layer apparatus 221 and the MAC entity 325 may be an example of the low layer apparatus 225. The process 300 may be deemed as a detailed example of the process 200.

[0079] In the process 300, the RLC entity 311 submits, a RLC data PDU to the MAC entity 315. The MAC entity 315 receives 335 the RLC data PDU, and transmits 340, to the second device 202, a MAC PDU comprising at least a payload of the RLC data PDU. The second device 202 may successfully receive 345 the MAC PDU or not.

[0080] The MAC entity 315 generates 348 a tentative local positive ACK for the payload based on feedback received from the second device 202 for the MAC PDU. The payload of the RLC data PDU may comprise an RLC SDU or a segment of the RLC SDU. In some embodiments, the tentative local positive ACK may indicate a tentative ACK from the MAC entity 315 of successful reception of the payload at a peer RLC entity of the second device 202, e.g., the RLC entity 321. The term “tentative local positive ACK” may be used interchangeably with the term “local positive ACK” as discussed with reference to FIG. 2.

[0081] In some embodiments, the MAC entity 315 may determine that the feedback from the second device 202 indicates a positive ACK for the MAC PDU. For example, the MAC entity 315 may correctly or erroneously decode the HARQ feedback as a HARQ ACK for the payload. Alternatively or in addition, the MAC entity 315 may determine that thefeedback indicates the positive ACK for the MAC PDU based on receiving from the second device 202 an indication that a HARQ process is not to perform a retransmission associated with the payload. In some examples, the MAC entity 315 may determine the positive ACK based on reception via the physical layer of an explicit HARQ ACK for a MAC PDU containing the RLC PDU or an NDI field indicating that a HARQ process is not to perform retransmission of a previously transmitted MAC PDU containing the RLC PDU.

[0082] In some embodiments, in accordance with a determination that the feedback is received from the second device 202 for a MAC PDU comprising payload (i.e., a MAC SDU) from a logical channel configured with a tentative local positive ACK feature, the MAC entity 315 may generate the tentative local positive ACK for the payload. That is, the MAC entity 315 may further determine whether the RLC entity 311 is configured or enabled to use / receive the tentative local positive ACK.

[0083] The MAC entity 315 sends 350, to the RLC entity 311, the tentative local positive ACK for the payload. The RLC entity 311 receives 355, from the MAC entity 315, the tentative local positive ACK for the payload. The RLC entity 311 further determines 358 whether a condition is met. In accordance with a determination that a condition is met, the RLC entity 311 starts 360 a fast retransmission timer for the payload based on receiving the tentative local positive ACK. Upon expiry of the fast retransmission timer, the RLC entity 311 may retransmit the payload to the MAC entity in the same RLC data PDU or a different RLC data PDU. Details of the condition will be described in the following.

[0084] As discussed above with reference to FIG. 2, in some embodiments, the MAC entity 315 may further receive, from the peer RLC entity, an RLC ACK for the payload, and deliver the RLC ACK to the RLC entity 311. The RLC entity 311 may receive the RLC ACK for the payload from the peer RLC entity 321 while the fast retransmission timer is running. In some examples, the RLC entity 311 may stop the fast retransmission timer based on receiving the RLC ACK.

[0085] In some embodiments, the MAC entity 315 may further receive, from the peer RLC entity 321, an RLC NACK for the payload, and deliver the RLC NACK to the RLC entity 311. The RLC entity 311 may receive the RLC NACK for the payload from the peer RLC entity 321 while the fast retransmission timer is running. In some examples, the RLC entity 311 may stop the fast retransmission timer based on receiving the RLC NACK.

[0086] In some embodiments, in accordance with the determination that the NACK is received before the fast retransmission timer expires and the NACK triggers the retransmission associated with the payload, the RLC entity 311 may retransmit the payload to the MAC entity 315.

[0087] In some embodiments, the RLC entity 311 may be further configured with one or more retransmission timers in addition to the fast retransmission timer as discussed above. The fast retransmission timer may be referred to as t-FastRetransmit in the following.

[0088] For example, the RLC entity 311 may be configured with an additional retransmission timer t-retransmit for autonomous retransmission. The RLC entity 311 may start this retransmission timer based on transmitting the RLC SDU. If an RLC ACK is received for the PDU’s payload, this retransmission timer may be stopped, and the payload may be discarded. If this retransmission timer expires for the PDU’s payload before it is RLC-ACKed, the RLC entity 311 may retransmit the payload. The payload may be (blindly) retransmitted (in an RLC Data PDU that may or may not differ from the previous PDU). To minimize autonomous retransmissions based on this retransmission timer t-retransmit, the network may send frequent ACKs, by introducing a possibility to configure the UE not to consider SDUs for retransmission based on received NACKs (to eradicate the problem of premature NACKs). This configuration may be also referred to as ACKOnlyOperation.

[0089] Alternatively or in addition, the RLC entity 311 may be configured with a poll retransmission timer. The RLC entity 311 may start this poll retransmission timer based on transmitting the RLC SDU. For example, if the RLC entity 311 is configured with RLC acknowledged mode (AM) defined in 3GPP standards, the poll retransmission timer t-PollRetransmit may be used for detection loss of an RLC data PDU at the MAC layer.

[0090] In some examples, when the last data queued for transmission is sent, it may be sent with a polling bit requesting a Status PDU with an ACK or NACK for all the previous data (in terms of RLC sequence numbers) up to and including the RLC Data PDU including the poll, and the poll retransmission timer t-PollRetransmit may be started. If the poll retransmission timer expires before an ACK or NACK is received for the last data, another poll may be transmitted and poll retransmission timer may be started again, which continues until an ACK or NACK is received for the last data. If a NACK is received, the timer t-PollRe transmit may be stopped and the retransmission may be performed.

[0091] The timer t-PollRetransmit may be used together with a reassembly timer t-Reassembly for detection and retransmission of missing data. When higher-numbered data is received while lower-numbered data remains unreceived, the timer t-Reassembly may be started. If the timer t-Reassembly expires before the missing data is received, a NACK for the missing data may be sent in an RLC Status PDU.

[0092] In configuring the duration of the timer t-PollRetransmit, the network may take into account that the polling is only responded to when a confident ACK or NACK can be sent for all the previous data. In a case where the RLC Data PDU preceding the PDU including the poll has been lost at MAC, reception of the PDU including the poll may start the timer t-Reassembly and it needs to expire before the polling is responded to.

[0093] Thus, configuring the durations of the RLC-AM timers governing its ARQ operation, e.g., t-Reassembly and t- PollRelransmil. and the retransmission timer t-r etransmit may require making a sacrifice on either the delay or capacity.

[0094] For example, to avoid sacrificing capacity, the duration of t-Reassembly may be set long enough to allow some maximum number of HARQ retransmissions of the missing data to take place (otherwise an RLC NACK can be sent prematurely); and the durations of t-PollRetransmit and t-retransmit may be greater than that of t-Reassembly (otherwise an RLC Data PDU can be retransmitted prematurely, without giving a proper chance to reception of RLC ACK). On the other hand, to reduce delays, these rules may be neglected, but that may come with the risk of duplicated transmissions of the same missing data, which wastes capacity.

[0095] With the solution of the present disclosure, the proposed retransmission timer t-FastRe transmit can be used as a faster retransmission timer compared to the t-PollRetransmit and t-retransmit. With the tentative local ACK from the MAC entity 315, the duration of the timer t-FastRe transmit may be set relatively shorter, because it is expected that in most cases the reliable RLC ACK may follow soon after the tentative local ACK, and if the RLC ACK is not received before expiry of the timer t-FastRetransmit, the payload may need to be retransmitted. Thus, the solution of the present disclosure can achieve a delay reduction. Details will be described below with reference to FIG. 4 in the following.

[0096] As discussed above, the RLC entity 311 starts 360 the fast retransmission timer t-FastRetransmit in accordance with a determination that a condition is met. The conditionmay be defined to further justify the following expectation, such that the fast retransmission timer and local ACK can be applied in suitable scenarios. The expectation may be that most likely the local positive ACK means that the RLC Data PDU has been delivered to the peer RLC entity and, correspondingly, a (reliable) RLC ACK for the PDU’s payload can be expected soon. The expectation may not always hold true for example because the HARQ feedback is not always reliable. However, even in this case, i.e., if the expected RLC ACK has not been received, the PDU’s payload can be retransmitted after a reasonable delay.

[0097] In some embodiments, the condition may comprise that the RLC entity 311 is configured not to retransmit based on a received RLC NACK from the peer RLC entity 321. For example, if the RLC entity 311 is configured with the ACKOnlyOperation, the RLC ACK may be transmitted frequently. Prompt sending of RLC ACKs may be allowed even for non-consecutive data without, in the process, requesting retransmission of the other data for which RLC ACK is not sent. In this case, setting the short duration for the fast retransmission timer t-FastRetransmit can be efficient and may not cause a large number of unnecessary transmissions.

[0098] In some embodiments, in addition to the above condition (e.g., ACKOnly Operation), the condition may comprise that a sequence number (SN) of the RLC SDU for which local ACK was received is between a SN of a next RLC SDU for which a positive acknowledgment is to be received in-sequence and the highest SN of RLC data PDUs submitted to the MAC layer. In other words, the RLC entity 311 may start the timer t-FastRetransmit when the two above conditions are met. In 3 GPP standards, the SN of a next RLC SDU for which a positive acknowledgment is to be received insequence may be maintained by the parameter TX Next Ack, and details of this will be omitted in this specification. With this additional condition, it can be ensured that the SDU for which local ACK was received still falls within the RLC entity’s active transmitting window.

[0099] In some embodiments, the condition may comprise that polled ACK or NACK feedback for the payload of the RLC data PDU is pending; and that the payload is the only data PDU payload for which an RLC ACK is pending. In other words, the local positive ACK may be generated for an RLC data PDU for whose payload polled ACK / NACK feedback is pending, and the payload is also the only Data-PDU payload for which an RLC ACK is pending. In this case, if the t-Reassembly is configured, it may not delay theresponse to the polling, such that the RLC ACK may be transmitted to the RLC entity 311 in a relatively short duration, which justifies the short duration of the timer t-FastRetransmit.

[0100] In some embodiments, the RLC entity 311 may be configured with the timer t-PollRetransmit associated with the polled ACK or NACK feedback. In this case, the condition may comprise that the timer t-PollRetransmit is running, implying that the polled ACK or NACK feedback for the payload of the RLC data PDU is pending. In some embodiments, the condition may comprise that the RLC data PDU is a single RLC data PDU for a radio resource control (RRC) measurement report. This may be considered as a specific scenario where the above condition can be met. That is, if the UE only has an RRC MeasurementReport to send on a signaling radio bearer, and it is transmitted within a single RLC Data PDU, the local positive ACK may be utilized for this RLC data PDU.

[0101] With reference to the process 300, the solution of the present disclosure is described in the context of RLC layer and MAC layer. In the present solution, RLC AM can be enabled to recover from a loss of a MAC PDU due to HARQ-feedback decoding error with a shorter delay, in the meantime, without risking capacity loss from duplicated transmissions of the same missing data. This can be achieved based on the expectation that tentative acknowledgment information available at the MAC layer, if correct, will shortly be confirmed by reliable acknowledgment information exchanged at the RLC layer.

[0102] FIG. 4 illustrates a signaling flow of an example process 400 for a retransmission with delay reduction in accordance with some example embodiments of the present disclosure. As illustrated in FIG. 4, the process 400 involves a first apparatus 401 and a second apparatus 402. The first apparatus 401 may be a UE and the second apparatus 402 may be a network device, or vice versa. The first apparatus 401 includes a first RLC AM entity (i.e., an RLC entity configured with the Acknowledged Mode), also referred to as first RLC entity in the following, and a first MAC entity. The second apparatus 402 includes a second RLC AM entity, also referred to as second RLC entity in the following, and a second MAC entity. The process 400 may be a detailed example of the process 200 or process 300, thus details of similar steps will be omitted in this specification.

[0103] In the process 400, at step 410, the network configures the UE with the tentative local ACK feature and the fast retransmission timer t-FastRetransmit. At step 411, the first RLC entity receives an RLC SDU from the upper layer. At step 412, the first RLC entity starts the t-retransmit for the SDU and / or the t-PollRetransmit. At step 413, thefirst RLC entity submits the SDU within an RLC data PDU. The first RLC entity may start the t-retransmit or the t-PollRetransmit based on transmitting the SDU by submitting the RLC data PDU to the first MAC entity.

[0104] As illustrated in FIG. 4, the first MAC entity transmits the RLC data PDU within a MAC PDU to the second apparatus 402. The second apparatus 402 may successfully receive the MAC PDU or not (the latter shown with a mark “x”). At step 414, the second MAC entity transmits feedback to the first MAC entity. In some examples, the feedback may indicate the first apparatus 401 to retransmit the payload of the MAC PDU.

[0105] At step 415, the first MAC entity may erroneously decode the feedback as “do not retransmit”. The first MAC entity may generate a tentative local positive ACK for the RLC data PDU based on the erroneous decoding of the feedback. At step 416, the first MAC entity sends the tentative local ACK to the first RLC entity. At step 417, based on receiving the local ACK, the first RLC entity starts the timer t-FastRetransmit for the RLC SDU. Although it is not shown, the first RLC entity may start the timer t-FastRetransmit after determining that a condition is met.

[0106] At step 418, the timer t-FastRetransmit expires for the SDU. Before this expiry of the timer t-FastRetransmit, an ACK or NACK may be received or not by the first RLC entity, as illustrated by hypothetical steps in FIG. 4. If no ACK is received before expiry of the timer t-FastRetransmit, at step 419, the first RLC entity may retransmit the RLC SDU to the second apparatus 402.

[0107] At step 420, the second MAC entity may request retransmission if failing to receive the payload, or deliver the received RLC data PDU to the second RLC entity.

[0108] At step 421, the t-retransmit for the SDU or the t-PollRetransmit expires. The expiry of t-retransmit represents a case where t-FastRetransmit is not applied. In a case where t-FastRetransmit is applied, t-retransmit may be stopped at step 417, which is not shown in the figure. Before this expiry, the first RLC entity may receive an RLC ACK or not. If no RLC ACK is received before the expiry, at step 422, the first RLC entity may retransmit the RLC SDU.

[0109] As can be seen from FIG. 4, without the timer t-FastRetransmit, i.e., without steps 416 to 418, if at step 415 the first MAC entity erroneously decodes the feedback, the first RLC entity may wait and retransmit the payload until the t-retransmit for the SDU or the t-PollRetransmit expires (if no RLC ACK or NACK is received before expiry). In contrast,if the timer t-FastRe transmit is configured for the RLC entity, due to the shorter duration of the timer t-FastRetransmit, the first RLC entity may retransmit the payload earlier so as to reduce delays.

[0110] FIG. 4 further illustrates some other examples with the hypothetical steps. As an example, if the second MAC entity successfully receives the MAC PDU comprising the RLC Data PDU from the first MAC entity, at step 430, the second MAC entity may deliver the RLC data PDU to the second RLC entity. At step 431, the second RLC entity may generate an RLC ACK for the RLC SDU within the RLC Data PDU. At step 432, the RLC ACK may be transmitted to the first apparatus 401 before the timer t-FastRetransmit expires. In this case, the first RLC entity may stop the timer t-FastRetransmit and discard the payload. The ACK of step 432 may be referred to as hypothetical ACK. If this hypothetical ACK is received by the first apparatus 401, it may be considered as a reliable ACK.[OHl] As another example, if at step 415, the first MAC entity correctly decodes the feedback as “Retransmit”, the first MAC entity may not generate the local ACK for the RLC SDU. At steps 440 to 442, the first MAC entity may perform several HARQ retransmissions to the second apparatus 402. At step 443, the second MAC entity may deliver the received RLC data PDU to the second RLC entity. At step 444, the second RLC entity may generate an RLC ACK for the RLC SDU. At step 445, the RLC ACK may be transmitted to the first apparatus 401 before the t-retransmit for the SDU or the t-P oil Retransmit expires, such that unnecessary retransmissions of the RLC SDU by the first RLC entity may be avoided. In this case, the timer t-FastRetransmit may be started only upon receiving feedback (not shown in the figure) for step 442 The ACK of step 445 may be referred to as hypothetical ACK. If this hypothetical ACK is received by the first apparatus 401, it may be considered as a reliable ACK.

[0112] According to the solutions of the present disclosure, potential changes to current 3GPP standards, e.g., NR RLC TS 38.322, NR RLC TS 38.321, are also proposed. Below are examples of the changes according to the present disclosure. The proposed changes are underlined for ease of reading.

[0113] Example 1. Text proposal to the NR RLC TS 38.322.5.2 Data transfer procedures5.2.3 AM data transfer5.2.3.1 Transmit operations5.2.3.1.1 GeneralThe 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.The transmitting side of an AM RLC entity shall maintain a transmitting window according to the state variable TX_Next_Ack as follows:- 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.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.For each RLC SDU received from the upper layer, the AM RLC entity shall:- 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;increment TX_Next by one.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:- set the SN of the AMD PDU to the SN of the corresponding RLC SDU.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:- STATUS PDU from its peer AM RLC entity.When receiving a positive acknowledgement for an RLC SDU with SN = x, the transmitting side of an AM RLC entity shall:send an indication to the upper layers of successful delivery of the RLC SDU;- 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.When receiving a positive acknowledgement for an RLC SDU or an RLC SDU segment, the transmitting side of an AM RLC entity shall:if t-F as tRe transmit is running for the acknowledged RLC SDU or RLC SDU segment:stop t- FastRetransmit for the acknowledged RLC SDU or RLC SDU segment.5.3 ARQ procedures5.3.1 GeneralARQ procedures are only performed by an AM RLC entity.5.3.2 RetransmissionThe transmitting side of an AM RLC entity not configured ( )n!y( )pe ration can receive anegative acknowledgement (notification of reception failure by its peer AM RLC entity) for an RLC SDU or an RLC SDU segment by the following:- STATUS PDU from its peer AM RLC entity.When receiving a negative acknowledgement for an RLC SDU or an RLC SDU segment by a STATUS PDU from its peer AM RLC entity, the transmitting side of the AM RLC entity shall:- if the SN of the corresponding RLC SDU falls within the range TX_Next_Ack <= SN < = the highest SN of the AMD PDU among the AMD PDUs submitted to lower layer:consider the RLC SDU or the RLC SDU segment for which a negative acknowledgement was received for retransmission^- if t-F as tRe transmit is running for the negatively acknowledged RLC SDU or RLC SDU segment:- stop t- FastRetransmit for the negatively acknowledged RLC SDU or RLC SDU segment. The transmitting side of an AM RLC entity configured with t-FastRetransmit can receive a tentative positive acknowledgement (tentative indication of successful reception by its peer AM RLC entity) for an RLC SDU or an RLC SDU segment by the following:local indication from lower layer.When receiving a tentative positive acknowledgement for byte segment numbers y to z of an RLC SDU with SN = x by a local indication from lower layer, the transmitting side of the AM RLC entity shall:if x <= POLL SN and t-P ollRetransmit is running and the byte segment numbers y to z are the only byte segments of any RLC SDU for which a positive acknowledgement in a received Status PDU is pending (implying that x = TX Next Ack); orif the AM RLC entity is configured with ACKOnlyOperatior.- if the SN of the corresponding RLC SDU falls within the range TX Next Ack <= SN < = the highest SN of the AMD PDU among the AMD PDUs submitted to lower layer:- start t- FastRetransmit for the tentatively acknowledged byte segments.When an RLC SDU or an RLC SDU segment is considered for retransmission, the transmitting side of the AM RLC entity shall:if the RLC SDU or RLC SDU segment is considered for retransmission for the first time :set the RETX_COUNT associated with the RLC SDU to zero.else, if it (the RLC SDU or the RLC SDU segment that is considered for retransmission) is not pending for retransmission already and the RETX_COUNT associated with the RLC SDU has not been incremented due to another negative acknowledgment in the same STATUS PDU:- increment the RETX_COUNT.if RETX_COUNT = maxRetxThreshold'.indicate to upper layers that max retransmission has been reached.When retransmitting an RLC SDU or an RLC SDU segment, the transmitting side of an AM RLC entity shall:if needed, segment the RLC SDU or the RLC SDU segment;form a new AMD PDU which will fit within the total size of AMD PDU(s) indicated by lower layer at the particular transmission opportunity;submit the new AMD PDU to lower layer.When forming a new AMD PDU, the transmitting side of an AM RLC entity shall:only map the original RLC SDU or RLC SDU segment to the Data field of the new AMD PDU; modify the header of the new AMD PDU in accordance with the description in clause 6.2.2.4; set the P field according to clause 5.3.3.5,3,2.x Expiry of t-FastRetransmitUpon expiry of t-FastRetransmit for an RLC SDU or an RLC SDU segment, the transmitting side of an

[0114] Example 2. Text proposal to the NR MAC TS 38.321.5.4 UL-SCH data transfer5.4.2 HARQ operation5.4.2.2 HARQ processEach HARQ process is associated with a HARQ buffer.New transmissions are performed on the resource and with the MCS indicated on PDCCH or indicated in the Random Access Response (i.e. MAC RAR or fallbackRAR), or signalled in RRC or determined as specified in clause 5.1 ,2a for MSGA payload. Retransmissions are performed on the resource and, if provided, with the MCS indicated on PDCCH, or on the same resource and with the same MCS as was used for last made transmission attempt within a bundle, or on stored configured uplink grant resources and stored MCS when cg-RetransmissionTimer or cg-SDT-RetransmissionTimer or cg- RRC-RetransmissionTimer is configured. If cg-RetransmissionTimer is configured, retransmissions with the same HARQ process may be performed on any configured grant configuration if the configured grant configurations have the same TBS. If cg-SDT-RetransmissionTimer is configured, retransmission for the initial CG-SDT transmission with the same HARQ process may be performed on any configured grant configuration if the configured grant configurations have the same TBS. When cg-RetransmissionTimer is configured and the HARQ entity obtains a MAC PDU to transmit and LBT failure indication is received from lower layer, the corresponding HARQ process is considered to be pending. For a configured uplink grant, configured with cg-RetransmissionTimer, each associated HARQ process is considered as not pending when:a transmission is performed on that HARQ process and LBT failure indication is not received from lower layers; orthe configured uplink grant is initialised and this HARQ process is not associated with another active configured uplink grant; orthe HARQ buffer for this HARQ process is flushed.If the HARQ entity requests a new transmission for a TB, the HARQ process shall:> store the MAC PDU in the associated HARQ buffer;> store the uplink grant received from the HARQ entity;> generate a transmission as described below.If the HARQ entity requests a retransmission for a TB, the HARQ process shall:1> store the uplink grant received from the HARQ entity;1> generate a transmission as described below.To generate a transmission for a TB, the HARQ process shall:1> if the MAC PDU was obtained from the Msg3 buffer; or1> if the MAC PDU was obtained from the MSGA buffer; or1> if there is no measurement gap at the time of the transmission and, in case of retransmission, the retransmission does not collide with a transmission for a MAC PDU obtained from the Msg3 buffer or the MSGA buffer:2> if there are neither NR sidelink transmission nor transmission of V2X sidelink communication at the time of the transmission; or2> if the transmission of the MAC PDU is prioritized over sidelink transmission or can be simultaneously performed with sidelink transmission:3> instruct the physical layer to generate a transmission according to the stored uplink grant.If a HARQ process receives downlink feedback information, the HARQ process shall:1> stop the cg-RetransmissionTimer, if running;1> if acknowledgement is indicated:2> stop the configuredGrantTimer, if runnings2> for all MAC SDUs in the acknowledged MAC PDU that were received from a logical channel configured with tentativeLocalACK, indicate a tentative acknowledgement to the upper layer of the logical channel from which the MAC SDU was received.If the configuredGrantTimer expires for a HARQ process, the HARQ process shall:1> stop the cg-RetransmissionTimer, if running;1> stop the cg-SDT-RetransmissionTimer, if running.1> stop the cg-RRC-RetransmissionTimer, if running;1> if a PDCCH addressed to the MAC entity's C-RNTI has not been received after initial transmission for the CG-SDT with CCCH message to which the configuredGrantTimer corresponds:2> indicate failure to perform SDT procedure to the upper layer.

[0115] FIG. 5 shows a flowchart of an example method 500 implemented at a firstapparatus in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 500 will be described from the perspective of the high layer apparatus 211 in FIG. 2 as an example of the first apparatus.

[0116] At block 510, the high layer apparatus 211 submits, at a higher-layer protocol, a protocol data unit (PDU) to a second apparatus at a lower-layer protocol, the first apparatus and the second apparatus being comprised in a first device.

[0117] At block 520, the high layer apparatus 211 receives, from the second apparatus, a local positive acknowledgement (ACK) for a payload of the PDU.

[0118] At block 530, the high layer apparatus 211 starts a retransmission timer for the payload based on receiving the local positive ACK.

[0119] In some example embodiments, the method 500 further comprises: upon expiry of the retransmission timer, retransmitting the payload to the second apparatus in the same PDU or a different PDU.

[0120] In some example embodiments, the local positive ACK indicates a tentative ACK from the second apparatus of successful reception of the payload at a second device different from the first device.

[0121] In some example embodiments, the method 500 further comprises: receiving, from the second device, a further positive ACK associated with the payload, the further positive ACK indicating successful reception of the payload at the higher -layer protocol of the second device.

[0122] In some example embodiments, the further positive ACK is protected against an error by means of cyclic redundancy check (CRC) at a lower layer than the higher-layer protocol.

[0123] In some example embodiments, the method 500 further comprises: in accordance with a determination that the retransmission timer expires before receiving the further positive ACK, retransmitting the payload to the second apparatus.

[0124] In some example embodiments, the method 500 further comprises: in accordance with a determination that the further positive ACK is received before the retransmission timer expires, stopping the retransmission timer.

[0125] In some example embodiments, the method 500 further comprises: in accordancewith the determination that the further positive ACK is received, discarding the payload.

[0126] In some example embodiments, the method 500 further comprises: receiving, from the second device, a negative ACK (NACK) associated with the payload, the NACK indicating failed reception of the payload at the higher-layer protocol of the second device.

[0127] In some example embodiments, the method 500 further comprises: in accordance with a determination that the NACK is received before the retransmission timer expires and the NACK triggers a retransmission associated with the payload, stopping the retransmission timer.

[0128] In some example embodiments, the method 500 further comprises: in accordance with the determination that the NACK is received before the retransmission timer expires and the NACK triggers the retransmission associated with the payload, retransmitting the payload to the second apparatus.

[0129] In some example embodiments, the payload of the PDU comprises a service data unit (SDU) or a segment of the SDU.

[0130] In some example embodiments, the local positive ACK is associated with hybrid automatic repeat request (HARQ) feedback.

[0131] FIG. 6 shows a flowchart of an example method 600 implemented at a second apparatus in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 600 will be described from the perspective of the low layer apparatus 215 in FIG. 2 as an example of the second apparatus.

[0132] At block 610, the low layer apparatus 215 receives, at a lower-layer protocol, a protocol data unit (PDU) of a higher-layer protocol from a first apparatus at the higher-layer protocol, the first apparatus and the second apparatus being comprised in a first device.

[0133] At block 620, the low layer apparatus 215 transmits a payload of the PDU to a second device different from the first device.

[0134] At block 630, the low layer apparatus 215 sends, to the first apparatus, a local positive acknowledgement (ACK) for the payload.

[0135] In some example embodiments, the local positive ACK indicates a tentative acknowledgement by the second apparatus of successful reception of the payload at thesecond device.

[0136] In some example embodiments, the method 600 further comprises: receiving, from the second device, hybrid automatic repeat request (HARQ) feedback associated with the payload; and generating the local positive ACK based on the HARQ feedback.

[0137] In some example embodiments, generating the local positive ACK based on the HARQ feedback comprises: decoding the HARQ feedback as a HARQ ACK associated with the payload; and generating the local positive ACK based on the HARQ ACK.

[0138] In some example embodiments, decoding the HARQ feedback as the HARQ ACK associated with the payload comprises: determining the HARQ ACK based on correct decoding of the HARQ feedback or erroneous decoding of the HARQ feedback.

[0139] In some example embodiments, the method 600 further comprises: receiving, from the second device, an indication that a HARQ process is not to perform a retransmission associated with the payload; and generating the local positive ACK based on the indication.

[0140] In some example embodiments, the method 600 further comprises: receiving, from the second device, a further positive ACK associated with the payload, the further positive ACK indicating successful reception of the payload at the higher -layer protocol of the second device; and delivering the further ACK to the first apparatus.

[0141] In some example embodiments, the method 600 further comprises: receiving, from the second device, a negative ACK (NACK) associated with the payload, the NACK indicating failed reception of the payload at the higher-layer protocol of the second device; and delivering the NACK to the first apparatus.

[0142] In some example embodiments, the payload of the PDU comprises a service data unit (SDU) or a segment of the SDU.

[0143] FIG. 7 shows a flowchart of an example method 700 implemented at a first device in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 700 will be described from the perspective of the first device 201 in FIG. 2.

[0144] At block 710, the first device 201 submits from a first apparatus at a higher-layer protocol, a protocol data unit (PDU) to a second apparatus at a lower-layer protocol, wherein the first device comprises the first apparatus and the second apparatus.

[0145] At block 720, the first device 201 receives, by the second apparatus at the lower-layer protocol, the protocol data unit (PDU) of the higher-layer protocol from the first apparatus at the higher-layer protocol.

[0146] At block 730, the first device 201 transmits, from the second apparatus, a payload of the PDU to a second device different from the first device.

[0147] At block 740, the first device 201 sends, from the second apparatus to the first apparatus, a local positive acknowledgement (ACK) for the payload.

[0148] At block 750, the first device 201 receives, by the first apparatus from the second apparatus, the local positive acknowledgement (ACK) for the payload.

[0149] At block 760, the first device 201 starts, by the first apparatus, a retransmission timer for the payload based on receiving the local positive ACK.

[0150] In some example embodiments, the first apparatus of the first device 201 may be an example of the high layer apparatus 211 described with reference to FIG. 5 and the second apparatus of the first device 201 may be an example of the low layer apparatus 215 described with reference to FIG. 6.

[0151] In some example embodiments, a first apparatus capable of performing any of the method 500 (for example, the high layer apparatus 211 in FIG. 2) may comprise means for performing the respective operations of the method 500, and any of the embodiments thereof. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The first apparatus may be implemented as or included in the high layer apparatus 211 in FIG. 2.

[0152] In some example embodiments, a second apparatus capable of performing any of the method 600 (for example, the low layer apparatus 215 in FIG. 2) may comprise means for performing the respective operations of the method 600 and any of the embodiments thereof. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The second apparatus may be implemented as or included in the low layer apparatus 215 in FIG. 2.

[0153] In some example embodiments, a first device capable of performing any of the method 700 (for example, the first device 201 in FIG. 2) may comprise means for performing the respective operations of the method 700 and any of the embodiments thereof. The means may be implemented in any suitable form. For example, the meansmay be implemented in a circuitry or software module. The first device may be implemented as or included in the first device 201 in FIG. 2.

[0154] FIG. 8 shows a flowchart of an example method 800 implemented at a radio link control (RLC) entity in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 800 will be described from the perspective of the radio link control (RLC) entity 311 in FIG. 3.

[0155] At block 810, the radio link control (RLC) entity 311 submits, a RLC data protocol data unit (PDU) to a medium access control (MAC) entity, the RLC entity and the MAC entity being comprised in a first device.

[0156] At block 820, the radio link control (RLC) entity 311 receives, from the MAC entity, a tentative local positive acknowledgement (ACK) for a payload of the RLC data PDU.

[0157] At block 830, in accordance with a determination that a condition is met, the radio link control (RLC) entity 311 starts a fast retransmission timer for the payload based on receiving the tentative local positive ACK.

[0158] In some example embodiments, the RLC entity is further caused to: upon expiry of the fast retransmission timer, retransmit the payload to the MAC entity in the same RLC data PDU or a different RLC data PDU.

[0159] In some example embodiments, the tentative local positive ACK indicates a tentative ACK from the MAC entity of successful reception of the payload at a peer RLC entity of a second device different from the first device.

[0160] In some example embodiments, the condition comprises: that the RLC entity is configured not to retransmit based on a received RLC negative ACK (NACK) from the peer RLC entity.

[0161] In some example embodiments, the condition comprises: that the RLC entity is configured not to retransmit based on a received RLC negative ACK (NACK) from the peer RLC entity; and that a sequence number (SN) of a service data unit (SDU) of the RLC data PDU is between a SN of a next RLC service data unit (SDU) for which a positive acknowledgment is to be received in-sequence and the highest SN of RLC data PDUs submitted to the MAC layer.

[0162] In some example embodiments, the condition comprises: that polled ACK orNACK feedback for the payload of the RLC data PDU is pending; and that the payload is the only data PDU payload for which an RLC ACK is pending.

[0163] In some example embodiments, the RLC entity is configured with a poll retransmission timer associated with the polled ACK or NACK feedback, and the condition further comprises that the poll retransmission timer is running.

[0164] In some example embodiments, the condition comprises: that the RLC data PDU is a single RLC data PDU for a radio resource control (RRC) measurement report.

[0165] In some example embodiments, the RLC entity is further caused to: receive an RLC ACK for the payload from the peer RLC entity while the fast retransmission timer is running; and stopping the fast retransmission timer based on receiving the RLC ACK.

[0166] In some example embodiments, the RLC entity is further caused to: receive an RLC NACK for the payload from the peer RLC entity while the fast retransmission timer is running; and stopping the fast retransmission timer based on receiving the RLC NACK.

[0167] In some example embodiments, the payload of the RLC data PDU comprises an RLC service data unit (SDU) or a segment of the RLC SDU.

[0168] In some example embodiments, the RLC entity is further caused to: start a retransmission timer or a poll retransmission timer based on transmitting the RLC SDU.

[0169] FIG. 9 shows a flowchart of an example method 900 implemented at a medium access control (MAC) entity in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 900 will be described from the perspective of the medium access control (MAC) entity 315 in FIG. 3.

[0170] At block 910, the MAC entity 315 receives, a radio link control (RLC) data protocol data unit (PDU) from an RLC entity, the RLC entity and the MAC entity being comprised in a first device.

[0171] At block 920, the MAC entity 315 transmits, to a second device different from the first device, a MAC PDU comprising a payload of the RLC data PDU.

[0172] At block 930, the MAC entity 315 generates a tentative local positive acknowledgement (ACK) for the payload based on feedback received from the second device for the MAC PDU.

[0173] At block 940, the MAC entity 315 sends, to the RLC entity, the tentative localpositive ACK for the payload.

[0174] In some example embodiments, the tentative local positive ACK indicates a tentative ACK from the MAC entity of successful reception of the payload at a peer RLC entity of the second device.

[0175] In some example embodiments, generating the tentative local positive ACK based on the feedback comprises: determining that the feedback indicates a positive ACK for the MAC PDU; and in accordance with a determination that, in the MAC PDU, a MAC SDU comprising the payload is received from a logical channel configured with a tentative local positive ACK feature, generating the tentative local positive ACK for the payload.

[0176] In some example embodiments, the feedback is hybrid automatic repeat request (HARQ) feedback for the payload, and determining that the feedback indicates the positive ACK for the MAC PDU comprises: decoding the HARQ feedback as a HARQ ACK for the payload.

[0177] In some example embodiments, decoding the HARQ feedback as the HARQ ACK for the payload comprises: determining the HARQ ACK based on correct decoding of the HARQ feedback or erroneous decoding of the HARQ feedback.

[0178] In some example embodiments, the feedback from the second device for the MAC PDU comprises: an indication that a HARQ process is not to perform a retransmission associated with the payload.

[0179] In some example embodiments, the MAC entity is further caused to: receive, from the peer RLC entity, an RLC ACK for the payload; and deliver the RLC ACK to the RLC entity.

[0180] In some example embodiments, the MAC entity is further caused to: receive, from the peer RLC entity, an RLC NACK for the payload; and deliver the RLC NACK to the RLC entity.

[0181] In some example embodiments, the payload of the RLC data PDU comprises an RLC service data unit (SDU) or a segment of the RLC SDU.

[0182] FIG. 10 shows a flowchart of an example method 1000 implemented at a user equipment in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 1000 will be described from the perspective of the first device 201 in FIG. 3.

[0183] At block 1010, the first device 201 submits, from a radio link control (RLC) entity, a RLC data protocol data unit (PDU) to a medium access control (MAC) entity, wherein the user equipment comprises the RLC entity and the MAC entity.

[0184] At block 1020, the first device 201 receives, by the MAC entity, the radio link control (RLC) data protocol data unit (PDU) from the RLC entity.

[0185] At block 1030, the first device 201 transmits, to a second device different from the user equipment, a MAC PDU comprising a payload of the RLC data PDU.

[0186] At block 1040, the first device 201 generates, by the MAC entity, a tentative local positive acknowledgement (ACK) for the payload based on feedback received from the second device for the MAC PDU.

[0187] At block 1050, the first device 201 sends, from the MAC entity to the RLC entity, the tentative local positive ACK for the payload.

[0188] At block 1060, the first device 201 receives, by the RLC entity from the MAC entity, the tentative local positive acknowledgement (ACK) for the payload of the RLC data PDU.

[0189] At block 1070, in accordance with a determination that a condition is met, the first device 201 starts by the RLC entity, a fast retransmission timer for the payload based on receiving the tentative local positive ACK.

[0190] In some example embodiments, a radio link control (RLC) entity capable of performing any of the method 800 (for example, the radio link control (RLC) entity 311 in FIG. 3) may comprise means for performing the respective operations of the method 800 and any of the embodiments thereof. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The radio link control (RLC) entity may be implemented as or included in the radio link control (RLC) entity 311 in FIG. 3.

[0191] In some example embodiments, a medium access control (MAC) entity capable of performing any of the method 900 (for example, the medium access control (MAC) entity 315 in FIG. 3) may comprise means for performing the respective operations of the method 900 and any of the embodiments thereof. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The medium access control (MAC) entity may be implemented as or included inthe medium access control (MAC) entity 315 in FIG. 3.

[0192] In some example embodiments, a user equipment capable of performing any of the method 1000 (for example, the first device 201 in FIG. 3) may comprise means for performing the respective operations of the method 1000 and any of the embodiments thereof. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The user equipment may be implemented as or included in the first device 201 in FIG. 3.

[0193] FIG. 11 is a simplified block diagram of a device 1100 that is suitable for implementing example embodiments of the present disclosure. The device 1100 may be provided to implement a communication device, for example, the terminal device 110 or the network device 120 as shown in FIG. 1. As shown, the device 1100 includes one or more processors 1110, one or more memories 1120 coupled to the processor 1110, and one or more communication modules 1140 coupled to the processor 1110.

[0194] The communication module 1140 is for bidirectional communications. The communication module 1140 has one or more communication interfaces to facilitate communication with one or more other modules or devices. The communication interfaces may represent any interface that is necessary for communication with other network elements. In some example embodiments, the communication module 1140 may include at least one antenna.

[0195] The processor 1110 may be of any type suitable to the local technical network and may include one or more of the following: general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on multicore processor architecture, as non-limiting examples. The device 1100 may have multiple processors, such as an application specific integrated circuit chip that is slaved in time to a clock which synchronizes the main processor.

[0196] The memory 1120 may include one or more non-volatile memories and one or more volatile memories. Examples of the non-volatile memories include, but are not limited to, a Read Only Memory (ROM) 1124, an electrically programmable read only memory (EPROM), a flash memory, a hard disk, a compact disc (CD), a digital video disk (DVD), an optical disk, a laser disk, and other magnetic storage and / or optical storage. Examples of the volatile memories include, but are not limited to, a random -access memory (RAM) 1122 and other volatile memories that will not last in the power-downduration.

[0197] A computer program 1130 includes computer executable instructions that are executed by the associated processor 1110. The instructions of the program 1130 may include instructions for performing operations / acts of some example embodiments of the present disclosure. The program 1130 may be stored in the memory, e.g., the ROM 1124. The processor 1110 may perform any suitable actions and processing by loading the program 1130 into the RAM 1122.

[0198] The example embodiments of the present disclosure may be implemented by means of the program 1130 so that the device 1100 may perform any process of the disclosure as discussed with reference to FIG. 2 to FIG. 10. The example embodiments of the present disclosure may also be implemented by hardware or by a combination of software and hardware.

[0199] In some example embodiments, the program 1130 may be tangibly contained in a computer readable medium which may be included in the device 1100 (such as in the memory 1120) or other storage devices that are accessible by the device 1100. The device 1100 may load the program 1130 from the computer readable medium to the RAM 1122 for execution. In some example embodiments, the computer readable medium may include any types of non -transitory storage medium, such as ROM, EPROM, a flash memory, a hard disk, CD, DVD, and the like. The 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., RAM vs. ROM).

[0200] FIG. 12 shows an example of the computer readable medium 1200 which may be in form of CD, DVD or other optical storage disk. The computer readable medium 1200 has the program 1130 stored thereon.

[0201] Generally, various embodiments of the present disclosure may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. Some aspects may be implemented in hardware, and other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device. Although various aspects of embodiments of the present disclosure are illustrated and described as block diagrams, flowcharts, or using some other pictorial representations, it is to be understood that the block, apparatus, system, technique or method described herein may be implemented in, as non-limiting examples, hardware,software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

[0202] Some example embodiments of the present disclosure also provide at least one computer program product tangibly stored on a computer readable medium, such as a non-transitory computer readable medium. The computer program product includes computerexecutable instructions, such as those included in program modules, being executed in a device on a target physical or virtual processor, to carry out any of the methods as described above. Generally, program modules include routines, programs, libraries, objects, classes, components, data structures, or the like that perform particular tasks or implement particular abstract data types. The functionality of the program modules may be combined or split between program modules as desired in various embodiments. Machine-executable instructions for program modules may be executed within a local or distributed device. In a distributed device, program modules may be located in both local and remote storage media.

[0203] Program code for carrying out methods of the present disclosure may be written in any combination of one or more programming languages. The program code may be provided to a processor or controller of a general -purpose computer, special purpose computer, or other programmable data processing apparatus, such that the program code, when executed by the processor or controller, cause the fun cti on s / op erations specified in the flowcharts and / or block diagrams to be implemented. The program code may execute entirely on a machine, partly on the machine, as a stand-alone software package, partly on the machine and partly on a remote machine or entirely on the remote machine or server.

[0204] In the context of the present disclosure, the computer program code or related data may be carried by any suitable carrier to enable the device, apparatus or processor to perform various processes and operations as described above. Examples of the carrier include a signal, computer readable medium, and the like.

[0205] The computer readable medium may be a computer readable signal medium or a computer readable storage medium. A computer readable medium may include but not limited to an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples of the computer readable storage medium would include an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random -access memory (RAM), a read-only memory (ROM), an erasable programmable read-onlymemory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

[0206] Further, although 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, although 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. Unless explicitly stated, certain features that are described in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, unless explicitly stated, various features that are described in the context of a single embodiment may also be implemented in a plurality of embodiments separately or in any suitable sub-combination.

[0207] Although the present disclosure has been described in languages specific to structural features and / or methodological acts, it is to be understood that the present disclosure defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.

Claims

42WHAT IS CLAIMED IS:

1. A first apparatus comprising:at least one processor; andat least one memory storing instructions that, when executed by the at least one processor, cause the first apparatus to:submit, at a higher-layer protocol, a protocol data unit (PDU) to a second apparatus at a lower-layer protocol, the first apparatus and the second apparatus being comprised in a first device;receive, from the second apparatus, a local positive acknowledgement (ACK) for a payload of the PDU; andstart a retransmission timer for the payload based on receiving the local positive ACK.

2. The first apparatus of claim 1, wherein the first apparatus is further caused to: upon expiry of the retransmission timer, retransmit the payload to the second apparatus in the same PDU or a different PDU.

3. The first apparatus of claim 1, wherein the local positive ACK indicates a tentative ACK from the second apparatus of successful reception of the payload at a second device different from the first device.

4. The first apparatus of claim 3, wherein the first apparatus is further caused to: receive, from the second device, a further positive ACK associated with the payload, the further positive ACK indicating successful reception of the payload at the higher-layer protocol of the second device.

5. The first apparatus of claim 4, wherein the further positive ACK is protected against an error by means of cyclic redundancy check (CRC) at a lower layer than the higher-layer protocol.

6. The first apparatus of claim 4 or 5, wherein the first apparatus is further caused to:in accordance with a determination that the retransmission timer expires before43receiving the further positive ACK, retransmit the payload to the second apparatus.

7. The first apparatus of claim 4 or 5, wherein the first apparatus is further caused to:in accordance with a determination that the further positive ACK is received before the retransmission timer expires, stop the retransmission timer.

8. The first apparatus of claim 7, wherein the first apparatus is further caused to: in accordance with the determination that the further positive ACK is received, discard the payload.

9. The first apparatus of claim 3, wherein the first apparatus is further caused to: receive, from the second device, a negative ACK (NACK) associated with the payload, the NACK indicating failed reception of the payload at the higher-layer protocol of the second device.

10. The first apparatus of claim 9, wherein the first apparatus is further caused to: in accordance with a determination that the NACK is received before the retransmission timer expires and the NACK triggers a retransmission associated with the payload, stop the retransmission timer.

11. The first apparatus of claim 10, wherein the first apparatus is further caused to: in accordance with the determination that the NACK is received before the retransmission timer expires and the NACK triggers the retransmission associated with the payload, retransmit the payload to the second apparatus.

12. The first apparatus of any of claims 1 to 11, wherein the payload of the PDU comprises a service data unit (SDU) or a segment of the SDU.

13. The first apparatus of any of claims 1 to 12, wherein the local positive ACK is associated with hybrid automatic repeat request (HARQ) feedback.

14. A second apparatus comprising:at least one processor; and44at least one memory storing instructions that, when executed by the at least one processor, cause the second apparatus to:receive, at a lower-layer protocol, a protocol data unit (PDU) of a higher-layer protocol from a first apparatus at the higher -layer protocol, the first apparatus and the second apparatus being comprised in a first device;transmit a payload of the PDU to a second device different from the first device; andsend, to the first apparatus, a local positive acknowledgement (ACK) for the payload.

15. The second apparatus of claim 14, wherein the local positive ACK indicates a tentative acknowledgement by the second apparatus of successful reception of the payload at the second device.

16. The second apparatus of claim 14 or 15, wherein the second apparatus is further caused to:receive, from the second device, hybrid automatic repeat request (HARQ) feedback associated with the payload; andgenerate the local positive ACK based on the HARQ feedback.

17. The second apparatus of claim 16, wherein generating the local positive ACK based on the HARQ feedback comprises:decoding the HARQ feedback as a HARQ ACK associated with the payload; and generating the local positive ACK based on the HARQ ACK.

18. The second apparatus of claim 17, wherein decoding the HARQ feedback as the HARQ ACK associated with the payload comprises:determining the HARQ ACK based on correct decoding of the HARQ feedback or erroneous decoding of the HARQ feedback.

19. The second apparatus of claim 14 or 15, wherein the second apparatus is further caused to:receive, from the second device, an indication that a HARQ process is not to perform a retransmission associated with the payload; andgenerate the local positive ACK based on the indication.

20. The second apparatus of claim 14 or 15, wherein the second apparatus is further caused to:receive, from the second device, a further positive ACK associated with the payload, the further positive ACK indicating successful reception of the payload at the higher-layer protocol of the second device; anddeliver the further ACK to the first apparatus.

21. The second apparatus of claim 14 or 15, wherein the second apparatus is further caused to:receive, from the second device, a negative ACK (NACK) associated with the payload, the NACK indicating failed reception of the payload at the higher-layer protocol of the second device; anddeliver the NACK to the first apparatus.

22. The second apparatus of any of claims 14 to 21, wherein the payload of the PDU comprises a service data unit (SDU) or a segment of the SDU.

23. A first device comprising:at least one processor; andat least one memory storing instructions that, when executed by the at least one processor, cause the first device to:submit from a first apparatus at a higher-layer protocol, a protocol data unit (PDU) to a second apparatus at a lower-layer protocol, wherein the first device comprises the first apparatus and the second apparatus;receive, by the second apparatus at the lower-layer protocol, the protocol data unit (PDU) of the higher-layer protocol from the first apparatus at the higher-layer protocol;transmit, from the second apparatus, a payload of the PDU to a second device different from the first device; andsend, from the second apparatus to the first apparatus, a local positive acknowledgement (ACK) for the payload;receive, by the first apparatus from the second apparatus, the local positiveacknowledgement (ACK) for the payload; andstart, by the first apparatus, a retransmission timer for the payload based on receiving the local positive ACK.

24. The first device of claim 23 comprising the first apparatus of any of the claims 2 to 13 and the second apparatus of any of the claims 15 to 22.

25. A method comprising:submitting, from a first apparatus at a higher-layer protocol, a protocol data unit (PDU) to a second apparatus at a lower-layer protocol, the first apparatus and the second apparatus being comprised in a first device;receiving, from the second apparatus, a local positive acknowledgement (ACK) for a payload of the PDU; andstarting a retransmission timer for the payload based on receiving the local positive ACK.

26. A method comprising:receiving, by a second apparatus at a lower-layer protocol, a protocol data unit (PDU) of a higher-layer protocol from a first apparatus at the higher -layer protocol, the first apparatus and the second apparatus being comprised in a first device;transmitting a payload of the PDU to a second device different from the first device; andsending, to the first apparatus, a local positive acknowledgement (ACK) for the payload.

27. A method comprising:submitting, by a first device, from a first apparatus at a higher-layer protocol, a protocol data unit (PDU) to a second apparatus at a lower -layer protocol, wherein the first device comprises the first apparatus and the second apparatus;receiving, by the second apparatus at the lower-layer protocol, the protocol data unit (PDU) of the higher-layer protocol from the first apparatus at the higher -layer protocol;transmitting, from the second apparatus, a payload of the PDU to a second device different from the first device; and47sending, from the second apparatus to the first apparatus, a local positive acknowledgement (ACK) for the payload;receiving, by the first apparatus from the second apparatus, the local positive acknowledgement (ACK) for the payload; andstarting, by the first apparatus, a retransmission timer for the payload based on receiving the local positive ACK.

28. A first apparatus comprising:means for submitting, at a higher-layer protocol, a protocol data unit (PDU) to a second apparatus at a lower-layer protocol, the first apparatus and the second apparatus being comprised in a first device;means for receiving, from the second apparatus, a local positive acknowledgement (ACK) for a payload of the PDU; andmeans for starting a retransmission timer for the payload based on receiving the local positive ACK.

29. A second apparatus comprising:means for receiving, at a lower-layer protocol, a protocol data unit (PDU) of a higher-layer protocol from a first apparatus at the higher-layer protocol, the first apparatus and the second apparatus being comprised in a first device;means for transmitting a payload of the PDU to a second device different from the first device; andmeans for sending, to the first apparatus, a local positive acknowledgement (ACK) for the payload.

30. A first device comprising:means for submitting from a first apparatus at a higher-layer protocol, a protocol data unit (PDU) to a second apparatus at a lower-layer protocol, wherein the first device comprises the first apparatus and the second apparatus;means for receiving, by the second apparatus at the lower-layer protocol, the protocol data unit (PDU) of the higher-layer protocol from the first apparatus at the higher-layer protocol;means for transmitting, from the second apparatus, a payload of the PDU to a second device different from the first device; andmeans for sending, from the second apparatus to the first apparatus, a local positive acknowledgement (ACK) for the payload;means for receiving, by the first apparatus from the second apparatus, the local positive acknowledgement (ACK) for the payload; andmeans for starting, by the first apparatus, a retransmission timer for the payload based on receiving the local positive ACK.

31. A computer readable medium comprising instructions stored thereon for causing an apparatus at least to perform the method of any one of claims 25 to 27.

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