Hybrid automatic repeat request (HARQ) feedback failures in a non-terrestrial network (NTN)

Abstract

This disclosure provides systems, methods, and apparatuses for a user equipment (UE) (102) to detect (160) an acknowledgement-to-nonacknowledgement (A2N) problem (140) in a non-terrestrial network (NTN. The UE receives a downlink (DL) transport block (TB) via the NTN and transmits a first hybrid automatic repeat request (HARQ) acknowledgement (ACK) based on decoding the DL TB. The UE receives subsequent DL TBs consecutively, where each subsequent DL TB does not have a new data indicator (NDI) toggled. The UE maintains a count of HARQ transmissions related to the first DL TB and indicates (180) an A2N problem from a lower layer (112) to an upper layer (118) based on the count exceeding a count threshold. In some implementations, the UE starts a timer when the count exceeds the count threshold and indicates the A2N problem when the timer expires.

Description

Docket No. 14730880600PCTHYBRID AUTOMATIC REPEAT REQUEST (HARQ) FEEDBACK FAIEURES IN A NON-TERRESTRIAL NETWORK (NTN)RELATED APPLICATION

[0001] This application claims the priority benefit of U.S. Provisional Patent Application Serial No. 63 / 870.723, filed August 26, 2025, and U.S. Provisional Patent Application Serial No. 63 / 755,992. filed February 07, 2025. both entitled “HYBRID AUTOMATIC REPEAT REQUEST (HARQ) FEEDBACK FAILURES IN A NON-TERRESTRIAL NETWORK (NTN),” the entire contents of which are hereby incorporated by reference herein.TECHNICAL FIELD

[0002] This disclosure relates generally to wireless communication, and some aspects relate to detecting and mitigating hybrid automatic repeat request (HARQ) feedback failures in a non-terrestrial network (NTN).BACKGROUND

[0003] This background description is provided for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.

[0004] A wireless communication sy stem includes one or more network entities (such as base stations) enabling communication for a mobile communication device (referred to as a user equipment (UE)). Network entities operate one or more cells and collectively form a radio access network (RAN). A RAN can be classified as a terrestrial network (TN) or a nonterrestrial network (NTN). An NTN refers to a network, or segment of networks, using radio frequency (RF) resources on board an NTN node, such as spaceborne vehicles or airborne vehicles. The discussion below refers to all such apparatuses as satellites or NTN nodes.

[0005] A UE can use an NTN to access a core network. An access stratum (AS) refers to the protocols between the UE and a RAN, while a non-access stratum (NAS) refers to the protocols between the UE and a core network. NAS messages travel between the UE and the core network via the RAN. In addition to a physical radio interface, the AS typically includes a media access control (MAC) layer, a radio link control (RLC) layer, and other layers, sometimes collectively referred to as a “layer 2” (or data link layer) in a protocol stack. Hybrid automatic repeat request (HARQ) is typically implemented in a MAC layer. HARQ isDocket No. 14730880600PCTa protocol used in wireless communication systems to enhance data transmission reliability. HARQ combines forward error correction with automatic repeat request (ARQ), allowing for both error correction and error detection with retransmission of data that experienced a decoding failure at the receiver. The HARQ process involves sending data packets with errorcorrecting codes and requesting retransmission only for packets that cannot be corrected. HARQ is implemented in the AS to ensure reliable radio transmission of messages between the UE and a network entity of the RAN.

[0006] After a UE establishes a radio connection with a RAN network entity, the UE performs a NAS attach procedure (sometimes also referred to as a network registration) with the core network. In an NTN, the NAS attach procedure can stall due to asymmetric uplink / downlink conditions at the UE. This occurs more frequently when the UE can receive downlink transmissions (including reference signals (RS)) but the UE uplink transmissions are blocked, for example, by temporary obstacles or inappropriate device orientation. Examples of temporary obstacles can include clouds, a flock of birds, w eather conditions, or buildings, among other examples. The UE can experience asymmetric uplink / downlink conditions for a variety of reasons, such as when the UE has a lower uplink transmission power compared to the higher downlink transmission power of the satellite. When a UE’s antennas are oriented away from the satellite, and beam steering cannot fully compensate for suboptimal antenna orientation, this powder imbalance can be exacerbated. The asymmetric uplink / downlink conditions can cause problems for a HARQ protocol because the HARQ protocol relies on HARQ feedback (acknowledgements) and / or retransmissions in the radio link between the UE and the satellite. In addition to normally higher delays for communication between the UE and the satellite, the HARQ protocol failure can add additional delay - potentially impacting a NAS attach procedure. The long attach delay is undesirable, particularly when the UE is trying to attach to a core network for sending an emergency / SOS message.BRIEF SUMMARY

[0007] The systems, methods, and apparatuses of this disclosure each have several innovative aspects, no single one of which is solely responsible for the desirable attributes disclosed herein.

[0008] One innovative aspect of the subject matter in this disclosure can be implemented as a method for wireless communication by a user equipment (UE). The method includes the UE receiving, from a non-terrestrial network (NTN) (such as a satellite), a first downlink (DL) transport block (TB). The UE transmits, to the satellite, a first hybrid automatic repeat requestDocket No. 14730880600PCT(HARQ) acknowledgement (ACK) based on decoding the first DL TB. The UE receives, from the satellite, subsequent DL TBs consecutively from the satellite in which each subsequent DL TB does not have a new data indicator (NDI) toggled. The UE maintains a count of HARQ transmissions related to the first DL TB. Based, at least in part, on the count exceeding a count threshold, the UE detects a persistent acknowledgement-to-nonacknowledgement (A2N) problem. In some aspects, the UE detects the A2N problem in a lower layer (such as a media access control (MAC) layer) and the lower layer provides an indication of the A2N problem to an upper layer (such as a non-access stratum (NAS) layer) of the UE.

[0009] Another innovative aspect of this disclosure can be implemented as a method for wireless communication by a UE. The method includes the UE starting a timer (ntn SilentTimer) when a count of HARQ retransmissions related to a same DL TB exceeds a count threshold. The UE detects the A2N problem when the timer (ntn_SilentTimer) expires.

[0010] Another innovative aspect of the subject matter described in this disclosure can be implemented as an apparatus that includes a communication unit and a processing system configured to control the communication unit to implement any one of the above-referenced methods.

[0011] Details of one or more implementations of the subject matter described in this disclosure are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages will become apparent from the description, the drawings, and the claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Like reference numbers and designations in the various drawings indicate like elements. Note that the relative dimensions of the figures may not be drawn to scale. To easily identify the discussion of any particular element or act, the most significant digit or digits in a reference number refer to the figure number in which that element is first introduced.

[0013] FIG. 1 is a system diagram illustrating an example wireless communication system in which a user equipment (UE) can detect an acknowledgement-to-nonacknowledgement (A2N) problem in a lower layer (e.g., a media access control (MAC) layer) communication via a non-terrestrial network (NTN).

[0014] FIG. 2 is a system diagram illustrating an example NTN infrastructure in a wireless communication system.Docket No. 14730880600PCT

[0015] FIG. 3 is a block diagram illustrating an example configuration of a UE using counters and a timer (e.g., ntn_SilentTimer) to detect a persistent hybrid automatic repeat request (HARQ) feedback failure.

[0016] FIG. 4 is a sequence diagram illustrating a conventional non-access stratum (NAS) attach procedure.

[0017] FIG. 5A is a sequence diagram illustrating a first scenario where a NAS attach procedure is delayed due to a HARQ feedback failure, such as a persistent A2N problem.

[0018] FIG. 5B is a sequence diagram illustrating a second scenario where a NAS attach procedure is delayed due to a HARQ feedback failure, such as a persistent A2N problem.

[0019] FIG.6 is a sequence diagram illustrating example operations for a UE using an NTN silent timer to detect an A2N problem.

[0020] FIG. 7 is a sequence diagram illustrating example operations for a UE using an NTN reception counter to detect an A2N problem.

[0021] FIG. 8 is a flow chart diagram illustrating example operations for a MAC layer of a UE to indicate an A2N problem.

[0022] FIG. 9 is a flow chart diagram illustrating example operations for a UE to detect an A2N problem.

[0023] FIG. 10A is a flow chart diagram illustrating example operations for a UE to detect an A2N problem based on decoding one or more DL TBs.

[0024] FIG. 10B is a flow chart diagram with changes related to FIG. 10A, and illustrating example operations of a timer for detecting an A2N problem.

[0025] FIG. 11A is a block diagram illustrating example operations in an example control plane protocol stack.

[0026] FIG. 11B is a block diagram illustrating example operations in an example user plane protocol stack.

[0027] FIG. 12 is a block diagram illustrating an example user equipment.

[0028] FIG. 13 is a block diagram illustrating an example wireless communication system with hardware features and communication interfaces.DETAILED DESCRIPTION

[0029] The following description is directed to certain implementations for the purpose of describing innovative aspects of this disclosure. However, a person having ordinary skill in the art will readily recognize that the teachings herein can be applied in a multitude ofDocket No. 14730880600PCTdifferent ways. Some examples in this disclosure are based on wireless communication according to the 3rd Generation Partnership Project (3GPP) wireless standards, such as the 4th generation (4G) Long Term Evolution (LTE) and 5th generation (5G) New Radio (NR) standards. However, the described implementations can be implemented in any device, system, or network capable of transmitting and receiving radio frequency signals according to any wireless communication standard, including Institute of Electrical and Electronics Engineers (IEEE) 802.11 or 802.16 standards, or other signals used within a wireless, cellular, or satellite network, such as a system utilizing 4G, 5G, 6th generation (6G), Wi-Fi, WiMAX, or future radio technology.

[0030] The 3GPP organization is extending wireless communication technologies to nonterrestrial networks (NTNs) using 5G NR technologies or LTE technologies tailored for the narrowband intemet-of-things (loT) (NB-IoT) or the enhanced machine type communication (eMTC) technologies. Communications in an NTN, particularly those utilizing satellites, can introduce significant signal propagation delays. To accommodate these operational conditions, various protocol timers, such as those associated with non-access-stratum (NAS) procedures, are often configured with extended durations. The 3 GPP technical specifications specify extended durations for many NAS timers related to communication via an NTN. The extended durations are generally suitable for routine NTN operations where connectivity might be intermittent. For example, a technical specification can define the durations of some NAS timers to several minutes which might be reasonable for non-urgent data. However, the extended durations of NAS timers can cause delays when a user equipment (UE) has timesensitive uplink data to transmit.

[0031] This disclosure provides systems, methods, and apparatuses for a UE to detect an A2N problem in a lower layer, such as a media access control (MAC) layer, and to provide an indication of the A2N problem to an upper layer such as a NAS layer. An example of a persistent HARQ protocol failure is the acknowledgement-to-nonacknowledgement (A2N) problem. Normally, a UE transmits a HARQ acknowledgement (ACK) (HARQ ACK) to a base station (BS) to acknowledge a downlink (DL) transmission. The BS normally would respond with a transport block (TB) having a new data indicator (ND1) toggled, thus confirming it has received the ACK. If the BS does not receive the ACK or the ACK is not properly processed, the BS transmits a DL TB with the NDI not toggled. In a normal HARQ protocol, the UE would retransmit the previous uplink (UL) ACK message in response to the NDI not-toggled indication. An A2N occurs when the UE transmits an ACK and receives the NDI not toggled. So, the UE retransmits the ACK. The cycle of ACK (from UE to BS) and NDI not toggled (from BS to UE) can repeat, causing a HARQ protocol failure referred to asDocket No. 14730880600PCTa persistent A2N problem. A persistent A2N (sometimes also referred to as a consistent A2N, or consecutive A2N) can cause excessive delay. A2N often occurs due to asymmetric uplink / downlink conditions, as described above.

[0032] A UE may perform a NAS procedure (such as a NAS attach, authentication, service request, or tracking area update) with a core network (CN) via a satellite in a NTN. Due to the distance between a UE and the satellite, there is a longer delay for communication in the access stratum (AS). NAS messaging, such as for an attach procedure, can take longer and the 3GPP has defined a longer timer duration for a timer (e.g.. T3410 timer) associated with the attach procedure via the NTN. The persistent A2N can cause the attach procedure to fail but a NAS layer of the UE might not detect the attach procedure failure until the T3410 timer expires. Because a UE might be performing the attach procedure for emergency communication (which is a common use case for satellite communication), it is undesirable to wait for the T3410 timer to expire when there is an A2N problem.

[0033] In some aspects, a lower layer of the UE (e.g., the UE's MAC layer) receives a first DL TB from a satellite of a non-terrestrial network. The UE transmits a first HARQ ACK to the satellite of the NTN based on decoding the first DL TB. In some implementations, the UE receives one or more subsequent DL TBs consecutively from the satellite, where each of the subsequent DL TBs do not have an NDI toggled. The UE maintains a count of HARQ transmissions related to the first DL TB. In several implementations, the UE indicates (or detects) an A2N problem based, at least in part, on the count of HARQ transmissions exceeding a count threshold (e.g., a first threshold or second threshold).

[0034] In some examples, the lower layer of the UE can provide an indication of the A2N problem to a higher layer (e.g., a radio link control (RLC) layer, a radio resource control (RRC) layer, or a NAS layer). In some implementations, the higher layer can declare a radio link failure (RLF) based on the indicated A2N problem. In some implementations, the NAS layer of the UE can stop or extend a timer (e.g., T3410 timer). Alternatively, or additionally, the NAS layer can reinitiate an attach procedure (e.g., a NAS attach request) without the UE having to wait for the full timer duration of the previous attach procedure. In some implementations, the UE can perform a new cell selection or PLMN search when the asymmetric UL / DL conditions are such that the existing NTN access will continue to produce a persistent A2N problem.

[0035] In some aspects, the UE detects the A2N problem based on a counter (such as a counter “NTN ACK COUNT”) to count the number of positive HARQ feedback that the UE has transmitted for a TB that has been successfully decoded / received (e.g.. a first counterDocket No. 14730880600PCT(NTN_ACK_COUNT)). If the counter exceeds a count threshold (e.g., a maximum value, such as an ”NTN_N(JM_A2N"). the UE's MAC layer can provide an indication of the A2N problem to an upper layer (e.g., the NAS layer, RLC layer, or RRC layer). For example, the count threshold can include a first threshold (NTN_NUM_A2N) (also referred to as a first count threshold (NTN_NUM_A2N)) associated with the counter (NTN ACK COUNT).

[0036] In some implementations, the lower layer of the UE does not immediately provide the indication to the upper layer. For example, the UE's MAC layer can start / restart a timer (such as an "ntn SilentTimer”) to track a silent period since transmitting the last ACK. In one example, upon the silent period exceeding a threshold duration, the UE's MAC layer provides the indication of the A2N problem to the UE's NAS layer. The threshold duration can be network-configured, user-configured, manufacturer-configured, or dynamically calculated, among other examples. In some implementations, the threshold duration can depend on channel conditions, UE movement, NTN radio access technology (RAT), or other parameters. Similarly, the count threshold (NTN_NUM_A2N) can be configured with a variety7of configurations and depend on various factors. As an example, the count threshold (NTN_NUM_A2N) can be configured to a 1, 2, 3, 5, or 10 count threshold, among other examples.

[0037] Another implementation for detecting the A2N problem is based on a count of a number of consecutive instances that the UE has successfully -decoded a same TB. A lower layer of the UE can maintain a count (such as an "‘NTN RECEPTION COUNT”) of the number of times the UE receives and successfully decodes the same TB pay load (e.g., a second counter (NTN RECEPTION COUNT)). Thus, the NTN RECEPTION COUNT increments based on receiving the same DL TB with NDI not toggled even though the UE is transmitting an ACK. When the NTN RECEPTION COUNT exceeds a count threshold (such as an “NTN_RECEPTION_MAX”), the lower layer can provide an indication of the A2N problem to an upper layer. For example, the count threshold can include a second threshold (NTN_RECEPTION_MAX) (also referred to as a second count threshold (NTN RECEPTION MAX)) associated with the counter (NTN ACK COUNT). The NTN_ACK_COUNT and NTN RECEPTION COUNT are example names for counters and the NTN_NUM_A2N and NTN_RECEPTION_MAX are example names for count thresholds, and other names can be given to either counter or count threshold, respectively.

[0038] Particular implementations of the subject matter described in this disclosure can be implemented to realize one or more of the following potential advantages. A UE attempting to get access to a core network can avoid longer delays that might otherwise occur for an A2N problem. By detecting the A2N problem without waiting for a timer (e.g., T3410 timer) toDocket No. 14730880600PCTexpire, the UE can more quickly take corrective action, such as declaring an RLF. restarting the NAS procedure, adjusting UL transmission power, or performing a cell (re)selection procedure.

[0039] Although the examples of this disclosure are based on an attach procedure, the example operations can apply to other types of NAS procedures, such as an authentication procedure, a service request procedure, a network registration procedure, a tracking area update procedure, or any NAS communication between a UE and a CN over an NTN access. For example, an example operation described below can replace an ATTACEI REQUEST and a T3410 timer with a SERVICE REQUEST and a T3416 timer, respectively.

[0040] In this disclosure, generally speaking, similar events in the drawings are labeled with reference numbers that have the same lower-order digits. For example, item 180 is similar to items 680, 880, and 1080. Where possible, the same reference numbers are used in multiple figures to represent the same concepts. For brevity, similar events are not discussed in detail in each instance, but the discussion of a certain event with reference to one figure also applies to similar events in other figures. In some instances, the descriptions of messages and features are abbreviated to focus on the differences among the features while omitting redundant explanation. Flowever, any of the variations or alternatives described for messages / blocks in one Figure also apply to messages / blocks having the same lower-order digits in another Figure.

[0041] FIG. 1 shows an example wireless communication system 100 in which a UE 102 can detect an A2N problem in a lower layer communication via an NTN and indicate the A2N problem to an upper layer. The example wireless communication system 100 shows the UE 102 accessing a core network (CN) 110 via an NTN, such as an NTN node 101. An NTN extends or augments the service capability of a wireless communication system. An NTN refers to a network, or segment of networks, using radio frequency (RF) resources on board an NTN node 101 (such as a spaceborne vehicle or an airborne vehicle). The NTN node 101 can belong to one of several types based on altitude, orbit, and beam footprint size. For example, FIG. 1 shows the NTN node 101 as a satellite 104. The satellite 104 can support a transparent or a regenerative (with on board processing) payload architecture (e.g., as described in FIG. 2). For a transparent pay load implementation, a satellite 104 can apply RF filtering and frequency conversion and amplification, and not change the waveform signal. For a regenerative payload implementation, a satellite 104 can apply RF filtering, frequency conversion and amplification, demodulation and decoding, routing, and coding / modulation.Docket No. 14730880600PCT

[0042] An NTN gateway 108 (sometimes also referred to as a “sat-gateway” or “GW”) communicatively couples the satellite 104 to ground components of the example wireless communication system 100 (such as a ground NTN BS 106', a CN 110, or other data network resources). In some deployments, the NTN node 101 (e.g., satellite 104) can perform some or all functions of a base station (shown as BS 106). The BS 106 can be included on-board the satellite 104 or can be partially or wholly located on the ground (shown as ground NTN BS 106'). In this disclosure, the term BS 106 can refer to either or both of the BS 106' on the ground (when present) or the BS 106 (when onboard the satellite 104). The satellite 104, the NTN gateway 108. and the BS 106 / 106' form part of a radio access network (RAN) (sometimes referred to as an NTN RAN). In some implementations, the radio access technology for the NTN RAN is based on 5G NR. In other aspects, the radio access technology7for the NTN RAN can use an Evolved Universal Terrestrial Radio Access (E-UTRA) air interface for 4G LTE, or another radio access technology such as NB-IoT, among other examples. Any number of RANs can be communicatively coupled to the CN 110. The CN 110 can be an evolved packet core (EPC), a 5G core (5GC), or a 6G core (6GC).

[0043] In this disclosure, the NTN node 101 can refer to the satellite 104, the BS 106 / 106', or collectively to the satellite 104 and the BS 106 / 106'. such that the phrases or reference numbers can be interchangeable. When the UE 102 is within a coverage area of the satellite 104, the UE 102 can establish a radio connection to the satellite 104 via an NTN cell (not shown). The NTN cell refers to a coverage area in which the satellite 104 operates as part of a radio network. The radio network can be associated with a footprint on the surface of the Earth or could be deployed in air, space, a spaceship, or other planetary objects. In terms of the satellite moving pattern, there are three types of service links (e.g., service link 103) that are supported in NTN:• Earth-fixed: provisioned by beam(s) continuously covering the same geographical areas all the time (e.g., the case of Geostationary Earth Orbit or Geosynchronous Orbit (GEO / GSO) satellites);• Quasi-Earth-fixed: provisioned by beam(s) covering one geographic area for a limited period and a different geographic area during another period (e.g.. the case of Low Earth Orbit or Medium Earth Orbit (LEO / MEO) satellites capable of using steerable beams); or • Earth-moving: provisioned by beam(s) whose coverage area slides over the Earth surface (e.g., the case of LEO / MEO satellites using fixed or non-steerable beams).

[0044] The radio connection between the UE 102 and the satellite 104 can also be referred to as service link 103. The satellite 104 communicates the UE traffic to the CN 110 via a feeder link 107 that communicatively couples the satellite 104 to the NTN gateway 108. TheDocket No. 14730880600PCTUE 102 can enter a radio resource connection (RRC) connected (RRC CONNECTED) state in the access stratum (AS) which includes the service link 103 and the feeder link 107. The UE can also enter an RRC idle (RRC IDLE) state refers to a state where the radio connection is released or not yet established. An RRC inactive (RRC INACTIVE) state refers to a state where the radio connection is suspended. The RRC states refer to the states of radio connections in the AS, where the NTN RAN provides AS connections. In order to access core network services, the UE 102 and the CN 110 communicate via NAS messages (such as UL NAS message 122 and DL NAS message 124). For example, the UE 102 can communicate a network registration request or other UL NAS messages 122 to the CN 110 via the NTN. The CN 110 determines whether to accept or reject the network registration based on user subscription information. The CN 110 provides the network registration accept / reject or other DL NAS messages 124 to the UE 102 via the NTN RAN. The UE 102 can include a lower layer (e.g., a MAC layer 112) and an upper layer (e.g., a NAS layer 118), as well as other protocol layers (not shown), for communicating with the BS or CN 110. The NAS layer 118 can transmit UL NAS messages 122 to (and receives DL NAS messages 124 from) a NAS entity 119 of the CN 110 via the BS. The MAC layer 112 can communicate with a MAC layer 116 of the BS (e.g., either the BS 106 onboard the satellite 104, if present, or the NTN BS 106'). Among other features, the MAC layer 112 can implement a HARQ protocol with the MAC layer 116. The HARQ protocol can include a HARQ feedback failure that occurs more frequently in an NTN compared to a terrestrial network (TN).

[0045] FIG. 1 shows an example NAS attach procedure 120 and persistent HARQ feedback failures that might be ongoing, failed, or unsuccessful (e.g., the unsuccessful UL L2 HARQ 145). In some aspects, a MAC layer 112 of a UE 102 might transmit a HARQ ACK (e.g., UL L2 HARQ 145) to a BS (e.g., the MAC layer 116 of the BS) to acknowledge a DL transmission (e.g., DL NAS message 124). The BS, however, may not receive the HARQ ACK 145 due to a temporary obstruction 113 that affects the service link 103 UL more than the DL. When the BS does not receive the ACK or the ACK is not properly processed, the BS might transmit a DL TB with the NDI not toggled (i.e., NDI not-toggled indication), signaling for the UE to retransmit the previous UL message. An A2N problem 140 occurs when a receiver (e.g., the MAC layer 112. sometimes referred to as UE layer 2 “UE L2?’) sends an acknowledgement of received data (e.g., upon received DL TB, transmits HARQ ACK based on decoding the DL TB) to a transmitter (e.g., the MAC layer 116, sometimes referred to as “Network L2”) that does not receive the acknowledgement of the received data. When the MAC layer 112 receives an NDI not toggled from the MAC layer 116 (e.g., via DL L2 HARQ 149) the UE 102 might retransmit the ACK. For example, the cycle of ACK (from UE 102 to BS) andDocket No. 14730880600PCTNDI not toggled (from BS to UE 102) can repeat, causing a persistent A2N problem 140 (also referred to as an A2N, A2N problem, persistent A2N, a consistent A2N, or consecutive A2N, among others) that can cause excessive delays.

[0046] The UE 102 can perform an NAS procedure with the CN 110 via the satellite 104 of the NTN node 101. Due to the distance between the UE 102 and the satellite 104, there is a longer delay for communication in the AS. For example, the NAS layer 118 of the UE 102 can implement a NAS attach procedure 120 (or other NAS messaging) to communicate with the NAS entity 119 of the CN 110 via the satellite 104, which can result in a longer (or extended) delay for the implemented NAS attach procedure 120. In some aspects, the NAS attach procedure 120 is normally delayed as the 3GPP has defined long timeout settings for NAS messaging when using NTN access (e.g., the 3GPP has defined a longer timer duration for a timer (such as T3410 timer) associated with an attach procedure (such as the NAS attach procedure 120). In some aspects, an A2N problem 140 can cause the attach procedure to fail but the attach procedure failure might not be detected by the NAS layer 118 until the T3410 timer expires. The duration of the T3410 timer can vary depending on the network's configuration and radio access technology (e.g., for NB-IoT, the T3410 timer duration is 255 seconds) arises. However, as a UE (e.g., UE 102) might be performing an attach procedure for emergency communication (which is a common use case for satellite communication), it is undesirable to wait for an T3410 timer to expire when a persistent A2N problem.

[0047] In some implementations, a temporary obstruction 113 (e.g., clouds, rain, flock of birds, etc.) can impact either the UL HARQ messages (e.g., as shown with the unsuccessful UL L2 HARQ 145) or DL HARQ messages between the MAC layer 112 and the MAC layer 116. As shown in FIG. 1, the MAC layer 112 can detect 160 an A2N problem and provide an indication 180 of the A2N problem to the NAS layer 118. For example, the MAC layer 112 can provide an early indication (such as the indication 180) to the NAS layer 118 (or other upper layers such as RLC layer or RRC layer) to indicate HARQ feedback failures (or radio link failures) based on the detected A2N problem 160. As such, due to an uplink transmission problem, the BS might act as if it had received a NACK even though the UE 102 transmitted an ACK. Thus, in some aspects, the BS might retransmit the same DL TB payload and the NDI not toggled. When the UE 102 receives a DL TB payload with the NDI not toggled, the UE 102 may send a new ACK message such as in the A2N problem 140 scenario. During such an A2N problem 140 scenario, the UE 102 might transmit a large number of ACK messages and only receive an NDI with an initial value (of NDI not toggled). In some implementations, after the UL L2 HARQ 145 resource grant for sending ACKs is depleted, the UE might no longer send ACKs.Docket No. 14730880600PCT

[0048] Although the temporary obstruction 113 tends to impact UL channels more than DL channels due to the asymmetric transmission power of the UE 102 compared to the satellite 104 and / or potential for misalignment of the UE beams relative to the satellite position, the temporary obstruction 113 can impact either UL or DL. Thus, the techniques of this disclosure can be applied in either direction. For consistency, the examples of this disclosure are based on a problem in which UL HARQ feedback messages (ACKs) are not received by the BS, but the HARQ messages are not limited and may include one or more of UL or DL messages, ACK or NACK messages, or the like.

[0049] Although shown as the same component, in some implementations, the UE 102 includes hardware that can implement the features of both the MAC layer 112 and the detect 160 as separate components (e.g., as shown with reference to FIG. 12). In other implementations, a first component (e.g., a PHY / MAC 1212 of a modem 1211 as shown in FIG. 12) can implement the MAC layer 112 and a second component (e.g., a consecutive HARQ feedback A2N detection module 1260 as shown in FIG. 12) can implement the detection 160 feature. The component(s) that implement the MAC layer 112 and / or the detect 160 can be part of a chip or other type of integrated circuit.

[0050] FIG. 2 is a system diagram illustrating an example NTN infrastructure 205 in an example wireless communication system 200. The example wireless communication system may use one Npe of NTN deployment with a payload architecture, which involves the NTN infrastructure 205. an NTN gateway 108, and a satellite 104 for extending the range of a Uu interface. The Uu interface refers to a link (such as a service link 103) between a UE 102 and a base station 106'. In some implementations, the satellite 104 implements a frequency conversion and an RF amplifier in both the uplink and downlink directions. In some implementations, the satellite 104 function is similar to that of an analogue RF repeater. As a result, the satellite 104 repeats the Uu radio interface from a feeder link 107 (between the NTN gateway 108 and the satellite 104) to the service link 103 (between the satellite 104 and the UE 102) in the downlink direction and vice versa in the uplink direction. Alternatively, the satellite 104 can carry a regenerative pay load and perform features of the base station 106’ using an on-board base station (such as base station 106 of FIG. 1), in which case the Uu radio interface is on the service link 103 and the feeder link 107 carries an Ng or SI interface between the base station 106 and the core network 110.

[0051] In some aspects, the feeder link 107 from the BS 106 to the NTN gateway 108 can be referred to as a satellite radio interface (SRI). For example, the SRI can be used as a transport link between the NTN gateway 108 and the satellite 104 to carry traffic for an Ng (or SI) interface. The NTN gateway 108 at one end of the SRI can serve as an intermediateDocket No. 14730880600PCTnode forwarding the Sl / Ng traffic to and from the CN 110. The CN 110 can implement a NAS (or HARQ) protocol for mobility, user subscription and / or access to a data network 210. In some aspects, the SRI on the feeder link 107 is the Uu interface, and the NTN gateway 108 supports all necessary functions to forward the signal of the Uu interface. The NTN gateway 108 can be collocated at the same site as the BS 106' location, or can be connected to the BS 106' at a distance via a wired link. It is also possible to connect more than one NTN gateway 108 to a BS 106'. In some implementations, different satellites may be connected to the same base station, via the same NTN gateway, or via different NTN gateways.

[0052] FIG. 3 is a block diagram 300 illustrating an example configuration of a UE 102 using counters and / or a timer to detect persistent HARQ feedback failures. The UE 102 can detect a persistent A2N problem using one or more of a count of HARQ transmissions 361, a count threshold 367, and / or a timer 370 (e.g., ntn_SilentTimer). The count of HARQ transmissions 361 can include one or more counters such as a first counter 362 (count (NTN ACK COUNT)) and a second counter 364 (count (NTN RECEPTION COUNT)). For example, to maintain the count of HARQ transmissions 361 related to a DL TB (e.g., a first DL TB), the UE 102 can use the first counter 362 and / or the second counter 364 and indicate the detected A2N problem based, at least in part, on the first counter 362 (or second counter 364) exceeding the count threshold 367 (e.g., the first or second thresholds), as described further with reference to FIG. 6 and FIG. 7, respectively.

[0053] The UE 102 can maintain the count of HARQ transmissions 361 by using the counter (NTN ACK COUNT) 362, which maintains a count of HARQ ACKs sent for the DL TB and the one or more subsequent DL TBs that do not have NDI toggled. For example, the counter (NTN_ACK_COUNT) 362 can track at least the first HARQ ACK and subsequent ACKs. In some implementations, the UE 102 can maintain the count of HARQ transmissions 361 by using the counter (NTN_RECEPTION_COUNT) 364, which maintains a count of consecutive subsequent DL TBs that do not have the NDI toggled. In some implementations, the UE 102 can use a timer 370 (such as a timer (ntn_SilentTimer)) to verify the A2N problem before providing an indication (e.g., indication 180) to an upper layer.

[0054] FIG. 4 is a sequence diagram 400 illustrating a conventional NAS attach procedure 421 involving a UE 102, a BS 106, and a CN 110. The UE 102 includes a MAC layer 112 and a NAS layer 118. The BS 106 includes a MAC layer 116. The CN 110 includes a NAS entity 119. The UE 102 communicates with the BS 106 via a satellite 104. In some aspects, the BS 106 or the satellite 104 can communicate with the CN 110 via an NTN gateway (such as the NTN gateway 108). The UE 102 establishes 404 a radio connection (such as a RRC connection) with the BS 106. The NAS layer 118 of the UE 102 begins (or initiates) 421 aDocket No. 14730880600PCTNAS attach procedure. The attach procedure can include various messages, such as an attach request 422, an authentication request 424, an authentication response 434, an attach accept 458, and an attach complete 492.

[0055] After initiating 421 the attach procedure, the NAS layer 118 communicates an attach request message 422 (e.g., the UL NAS message 122) to the NAS entity 119 of the CN 110. To communicate the attach request message 422, the NAS layer 118 passes the message to the MAC layer 112, which transmits the message via the RAN (e.g., satellite 104, and BS 106) to the NAS entity 119. Upon transmitting the attach request message 422, the NAS layer 118 starts 423 aT3410 timer. The T3410 timer supervises the attach procedure. If the T3410 timer expires before the NAS layer 118 receives an attach accept or attach reject message, the NAS layer 118 considers the attach procedure to have failed. In this example, the NAS layer 118 sets a duration of the T3410 timer (e.g., 255 seconds) associated with the NTN access (such as the satellite 104 access). Assuming the NAS layer 118 successfully receives an attach accept message 458 while the T3410 time is running, the NAS layer 118 stops the T3410 timer upon receiving the attach accept message 458. Although FIG. 4 does not illustrate the scenario, it is possible that the T3410 timer expires naturally when the NAS layer 118 does not receive the attach accept message 458 before expiration of the set duration (e.g.. 255 seconds). For example, if the T3410 timer expires before the NAS layer 118 receives the attach accept message 458, the NAS layer 118 considers the initiated attached procedure 421 to have failed and might reattempt a new attach procedure at that time.

[0056] Returning to the attach procedure, after sending the attach request 422, the UE 102 receives an authentication request message 424. The authentication request 424 is a NAS message that traverses the radio connection and MAC layer protocol between the MAC layer 112 and the MAC layer 116 of the BS 106. In the BS 106, the communication from the MAC layer 116 to the MAC layer 112 includes DL TBs that include all or part of the NAS message. As shown in FIG. 4, the MAC layer 112 can transmit an uplink L2 ACK message 425 (e.g., the UL L2 HARQ message 145) to the MAC layers 116 of the BS 106 to acknowledge the DL TB (not shown) that carries the authentication request 424. The UL L2 ACK message 425 is an example of a HARQ message to coordinate reliable delivery of messages at the MAC protocol layer. The BS 106 might respond with a DL TB 427 having an NDI toggled to confirm that the MAC layer 116 has received the UL L2 ACK message 425.

[0057] The CN 110 transmits the security mode command 436 to the UE 102. Similar to the NAS message for the authentication request 424, the security mode command 436 is a NAS message that is carried via one or more MAC layer transport blocks. FIG. 4 shows the securityDocket No. 14730880600PCTmode command 436 carried via DL TB 437. The MAC layer 112 of the UE 102 might transmit an uplink L2 ACK message 445 (e.g., an UL HARQ ACK message) to the MAC layer 116 of the BS 106 to acknowledge that the UE 102 has successfully decoded / received the DL TB 437. In some implementations, the BS 106 might transmit a DL TB 447 with the NDI toggled to confirm that the MAC layer 116 has received the UL L2 ACK 445.

[0058] Upon receiving the security mode command 436, the NAS layer 118 transmits a security mode complete message to the CN 110. After completing the security mode change, the CN 110 transmits the attach accept message 458. In some examples, assuming the NAS layer 118 successfully receives the attach accept message 458 (as described above), the NAS layer 118 might stop the T3410 timer upon receiving the attach accept message 458 and transmit the attach complete message 492 to the CN 110. According to such examples, upon the NAS layer 118 transmitting the attach complete message 492, the UE 102 might complete 494 the attach procedure.

[0059] Although shown as the BS 106 successfully received the ACK (shown as the L2 ACK message 445). if the BS 106 does not receive the ACK 445 or the ACK is not properly- processed, the BS 106 might transmit a DL TB (e.g., the DL TB 437) with the NDI not toggled. In a normal HARQ protocol, the UE 102 might retransmit the previous L2 ACK message in response to the NDI not-toggled indication such that the MAC layer 112 might detect HARQ feedback failures (such as the A2N problem 140) based on the persistently repeating cycle of ACK (from UE 102 to BS 106) and NDI not toggled (from BS 106 to UE 102) messages.

[0060] As further shown in FIG. 5A through FIG. 7 (with relation to FIG. 1 through FIG.4), examples of this disclosure describe the concepts illustrated above as an A2N problem in which the UE 102 can implement the MAC layer 112 to detect (or indicate) the A2N problem to its NAS layer 118 (or other upper layers of the UE 102) based, at least in part, on the satellite 104 retransmitting one or more DL TBs (e.g., the DL TB 437) with one or more NDIs not toggled in response to the UL HARQ ACK transmissions. For example, in such implementations, the satellite 104 of the BS 106 might be reacting as if the UE 102 transmitted UL NACK messages rather than UL ACK NAS messages.

[0061] In comparison to FIG. 4 (and FIG. 5A and FIG. 5B), FIG. 6 and FIG. 7 describe several example operations for the MAC layer 112 of the UE 102 to detect 160 (or indicate) the A2N problem 140 to enable the UE 102 to transmit an A2N problem indication 680 (such as the A2N problem 140) sooner than the scenarios of FIG. 4 through FIG. 5B. For brevity, the descriptions of FIG. 5A through FIG. 7 will omit descriptions of elements alreadyDocket No. 14730880600PCTdescribed with reference to FIG. 1 through FIG. 4. Instead, the descriptions of FIG. 5A through FIG. 7 will focus on the differences relative to those figures.

[0062] FIG. 5A is a sequence diagram 500A illustrating a scenario where a UE 102 in an NTN mode 520 initiates an attach procedure between the NAS layer 118 of the UE 102 and theNAS entity 119 of the CN 110, which is delayed due to an A2N problem 140 between the MAC layer 112 of the UE 102 and the MAC layer 116 of the BS 106. FIG. 5A is similar to the sequence diagram 400 of FIG. 4, and the description of the attach procedure is not repeated. The sequence diagram begins with events similar to those described in FIG. 4, including the UE 102 transmitting the attach request message 422 and starting 423 the T3410 timer. FIG. 5 A shows a scenario where UE 102 experiences a persistent A2N problem 140. The A2N problem 140 is shown as a series of consecutive HARQ failures: a first HARQ feedback failure 542A, a second HARQ feedback failure 542B, and a third HARQ feedback failure 542C. The HARQ feedback failures 542A-C are example names of A2N instances and other names can be given to the HARQ feedback failures.

[0063] Each of the A2N instances 542A - 542C can have a similar sequence, described with reference to the first HARQ feedback failure 542A for brevity. The MAC layer 112 transmits 541 an L2 ACK 545 to the BS 106. For any variety of reasons (such as communication failure, temporary obstruction, etc.) the L2 ACK 545 is not received 546 at the BS 106. Because the BS 106 does not receive the L2 ACK 545, the BS 106 may assume a transmission error and transmits to the UE 102 a DL TB 549 with the NDI not toggled. In some implementations, upon receiving the DL NDI not toggled, the UE 102 might proceed to retransmit the L2 ACK (which in turn might begin the second HARQ feedback failure 542B). The second HARQ feedback failure 542B and the third HARQ feedback failure 542C might follow the same pattern as the first HARQ feedback failure 542A. Because the HARQ process never successfully completes, the UE 102 does not receive an UL transmission grant 559 from the BS 106, and cannot complete the security mode transition.

[0064] The UE 102 and BS 106 might enter 581 a silent period during which no communication occurs because of the HARQ failures at the MAC layers. For example, if the BS 106 does not configure or grant any new UL transmission resources to the UE 102, the UE 102 cannot send any new UL transmissions (such as the security mode complete / rejection message 456) to the BS 106 and / or the CN 110 - and similarly both the BS 106 and CN 110 cannot transmit any new DL transmissions directed to the UE 1 2. As shown in FIG. 5 A, the UE 102 might wait 583 for the T3410 timer to expire 584 (e g., after the duration of 80s or 255s) before the UE 102 initiates a new attach request procedure 596.Docket No. 14730880600PCT

[0065] Although shown as the T3410 timer (e.g.. 255s). it is also noted that example operations over an NTN can have a NAS timeout value that can be higher because satellite communication normally has a higher propagation delay compared to a terrestrial network. For example, a NAS timer (e.g., T3410 timer) defines the amount of time that the UE 102 will wait before considering a NAS procedure to have failed and restarting / reissuing the NAS procedure. In aNB-IoT using the NTN, the T3410 timer is set to 255 seconds, however there is currently no defined timeout period for a repeated HARQ failure. As such, in some implementations, the MAC layer 112 of the UE 102 might adopt the same time period for a RRC inactivity timer (such as the RRC inactivity timer (80s) 523 shown in FIG. 5B). such as 80s as defined for a RRC connection setup timeout.

[0066] FIG. 5A shows the potential long delays (or timeout settings) in a NAS attach procedure when using NTN access (e g., as shown with the delayed NAS attach procedure 120 of FIG. 1). In such scenarios, these long (or extended) delays can impact the user experience of a UE such that when the UE does not receive an ATTACH ACCEPT or ATTACH REJECT response, absent the example operations described in this disclosure, the UE might wait around 255s (as shown with the T3410 timer of FIG. 5A) or 80s (as shown with the RRC inactivity timer (80s) 523 of FIG. 5B based on the data inactivity timer) for the respective timer to expire to initiate (or reissue) a new (or subsequent) attach request. The phrase “reissue” an attach request can mean sending a new attach request, such as for a new instance of the attach procedure or as a retransmission of a previous attach request for the existing attach procedure.

[0067] FIG. 5B is a sequence diagram 500B illustrating a second scenario with changes relative to FIG. 5A, where the NAS attach procedure is delayed due to the persistent A2N problem 140. FIG. 5B is similar to the sequence diagram 500A of FIG. 5A. and the description of the attach procedure is not repeated. In FIG. 5B, the UE 102 starts 423, 523 both the T3410 timer and the RRC inactivity timer (80s) after sending the attach request 422. Instead of the T3410 timer expiring, the UE 102 waits 585 for the RRC inactivity7timer to expire 586 before the UE 102 aborts 587 the connection and reissues the attach request 596. Although the RRC inactivity timer has a shorter duration (e.g., 80s) compared to the T3410 timer, the UE 102 might wait unnecessarily when the UE 102 experiences a persistent A2N problem that might be detected sooner using the techniques of this disclosure

[0068] FIG.6 is a sequence diagram 600 illustrating example operations for a UE 102 using an NTN silent timer 674B to detect an A2N problem 160 and provide an A2N problem indication 680 from the MAC layer 112 to the NAS layer 118. FIG. 6 is similar to the sequence diagrams 500A - 500B of FIG. 5A and FIG. 5B, and the description of the attach procedureDocket No. 14730880600PCTis not repeated. However, the sequence diagram 600 shows example operations of the UE 102 using a counter 663 (e.g., the counter (NTN ACK COUNT) 363 of FIG. 3) and a NTN silent timer 674B to detect 160 the A2N problem 160

[0069] In some implementations, the UE 102 counts the number of instances it sends an ACK for a same DL TB. Initially, the NTN_ACK_COUNT 663 might be equal to 0 and increments for each of the A2N instances 542A - 542C. For example, the UE 102 can implement the count (NTN_ACK_COUNT) 663 of HARQ ACKs (counting the HARQ ACKs sent for the first DL TB and the one or more subsequent DL TBs that do not have the NDI toggled) to count and track at least the first HARQ ACK (e.g., NTN_ACK_COUNT = 0) and any subsequent HARQ ACKs (e.g., NTN_ACK_COUNT = 1, 2, 3). When the count (NTN ACK COUNT) 663 exceeds a count threshold 674A (e.g., NTN_NUM_A2N, shown as NTN ACK COUNT > NTN_NUM_A2N), the MAC layer 112 starts 674B the the NTN silent timer (e.g., ntn_SilentTimer). After the ntn_SilentTimer expires 677, if the MAC layer 112 has not received a new' DL TB (not shown) with DL NDI toggled, the MAC layer 112 provides the A2N problem indication 680 to the NAS layer 118. Unlike the scenarios shown in FIG. 4 and FIGS. 5A - 5B in which the UE 102 waits for the T3410 timer and / or the RRC inactivity timer to expire before the UE 102 aborts 587 the connection and reissues the attach request, the example operations of this disclosure enable the UE 102 to detect 160 and provide 680 the indication of the detected A2N problem 140 and also abort 687 the connection and restart the attach request procedure - without having to wait for the expiration of the T3410 timer and / or the RRC inactivity’ timer that can otherwise cause longer and extend delays.

[0070] FIG. 7 is a sequence diagram 700 illustrating example operations for a UE 102 using an NTN reception counter 767 to detect an A2N problem 140 and provide an A2N problem indication 680. FIG. 7 is similar to the sequence diagram 600 of FIG. 6, and the description of the attach procedure is not repeated. However, the sequence diagram 700 shows example operations of the UE 102 using the counter (NTN_RECEPTION_COUNT) 767 (counting one or more consecutive subsequent DL TBs that do not have the NDI toggled) to detect 160 the A2N problem 140 and provide the A2N problem indication 680. For example, the UE 102 can implement the counter (NTN RECEPT1ON COUNT) of HARQ ACKs to count 763, 765 and track any of the consecutive subsequent DL TBs that do not have the NDI toggled. According to this scenario, when the NTN_RECEPTION_COUNT > NTN_RECEPTION_MAX 767 exceeds the count threshold (e.g., the second threshold (NTN RECEPTION MAX)) associated with the NTN RECEPTION COUNT, the UE 102 can provide the A2N problem indication 680 to the NAS layer 118 in response to the triggered (or satisfied) NTN reception counter 767.Docket No. 14730880600PCT

[0071] Similar to the example operations illustrated in FIG. 6. the example operations of this disclosure in FIG. 7 also enable the UE 102 to detect 160 the A2N problem, provide 680 the A2N problem indication 680, and abort 787 the connection and restart the attach request procedure earlier - without having to wait for timers that can otherwise cause longer and extend delays.

[0072] FIG. 8 is a flowchart diagram 800 illustrating example operations of a UE to detect an A2N problem via an NTN. The UE receives 837 a first DE TB at a lower layer from a satellite of an NTN. The UE transmits 845 a first HARQ ACK to the satellite of the NTN based on decoding of the first DL TB. The UE receives 849 subsequent DL TBs consecutively from the satellite of the NTN, where the subsequent DL TBs do not have a NDI toggled. The UE maintains 860 a count of HARQ transmissions related to the first DL TB. The UE indicates 880 an A2N problem to an upper layer from the lower layer based, at least in part, on the count of HARQ transmissions exceeding a count threshold. Some examples of operations to indicate (or detect) persistent A2N problems are illustrated (or described) in FIGs. 1-3, 6-9, 10A-B, and 11 A.

[0073] Modifications and variations may be made in light of the above disclosure. While the aspects of the disclosure have been described in terms of various examples, any combination of aspects from any of the examples is also possible. The following paragraphs describe additional features and options that can be combined with the previously described implementations.

[0074] In some implementations, the UE can start a timer (e.g., timer (ntn SilentTimer)) when the count of HARQ transmissions exceeds the count threshold and detects the A2N problem when the timer expires. Furthermore, when the UE maintains the count of HARQ transmissions, the UE can also maintain at least one or more of a first counter (NTN ACK COUNT) of HARQ ACKs sent for the first DL TB and the one or more subsequent DL TBs that do not have the NDI toggled, and / or a second counter (NTN_RECEPTION_COUNT) of consecutive subsequent DL TBs that do not have the NDI toggled. For example, the first counter (NTN_ACK_COUNT) of HARQ ACKs sent can track at least the first HARQ ACK and subsequent ACKs.

[0075] According to some aspects, the count threshold can include, for example, at least one or more of a first threshold (NTN_NUM_A2N) associated with the NTN_ACK_COUNT, a second threshold (NTN_RECEPTION_MAX) associated with the NTN RECEPTION COUNT, a threshold associated with both the NTN ACK COUNT and the NTN_RECEPTION_COUNT, and / or a threshold associated with one or more other NTN-Docket No. 14730880600PCTrelated counts, among other examples. In some implementations, the UE can implement the count threshold based on at least one of: a network-provided setting; a user-configured value; a manufacturer-configured value; channel conditions; NTN radio access technology; and / or UE movement. Furthermore, the UE can implement the lower layer as the MAC layer and the upper layer(s) as the NAS layer, the RLC layer, and / or the RRC layer.

[0076] FIG. 9 is a flowchart diagram 900 illustrating example operations of a UE to detect an A2N problem based, at least in part, on a count of HARQ ACK transmissions. The UE initiates 920 a NAS procedure with a CN via a NTN. For example, the UE 102 can initiate a NAS attach request (such as the attach request message 422 illustrated in FIG. 6) with a CN 110 via a satellite 104 of a NTN node 101. The UE detects 960 an A2N problem based, at least in part, on a count of HARQ ACK transmissions that are followed by receptions of a retransmitted DL TB. In other implementations, the UE can also detect 962 the A2N problem based on a timer (ntn_SilentTimer). Some examples of operations to detect the A2N problem based, at least in part, on the count of HARQ ACK transmissions and the timer (ntn SilentTimer) are illustrated (or described) in FIGs. 1-3, 6-9, 10A-B, and 11 A.

[0077] Modifications and variations may be made in light of the above disclosure. While the aspects of the disclosure have been described in terms of various examples, any combination of aspects from any of the examples is also possible. The following paragraphs describe additional features and options that can be combined with the previously described implementations.

[0078] In some implementations, the UE can detect whether a count exceeds a count threshold (e.g., a first threshold (NTN_NUM_A2N) or a second threshold (NTN RECEPTION MAX)). According to other aspects, the UE can implement the count as a reception count (NTN RECEPTION COUNT) of subsequent DL TBs received that do not have the NDI toggled. The reception count (NTN_RECEPTION_COUNT) can also tack at least a first DL TB that has the NDI toggled. In some implementations, the UE can implement the NAS procedure as at least one or more of an attach procedure, an authentication procedure, a service request procedure, and / or a tracking area update procedure, among other examples. Furthermore, in some aspects based on the detected A2N problem, the UE can implement the following example actions, where the at least one action includes, for example, any combination to: restart the NAS procedure, stop a timer associated with the NAS procedure, increase uplink transmission power perform a cell (re)selection procedure, or generate a UI indication.Docket No. 14730880600PCT

[0079] FIG. 10A is a flowchart diagram 1000a illustrating example operations for a UE to detect an A2N problem based on decoding a first DL TB and maintain a count of HARQ transmissions related to the first DL TB and subsequent DL TBs. The UE can receive 1024 a first DL TB that has NDI toggled from a satellite of a non-terrestrial network. In the flowchart, the UE can reset 1063 a count of HARQ transmissions related to the first DL TB (e.g., reset to “0” or '‘1”). For example, the count can be similar to the count of HARQ transmissions 361 of FIG. 3 that includes a first counter 362 and / or a second counter 364. After the count is reset, the UE transmits 1045 a HARQ ACK to the satellite based on decoding the first DL TB and receives 1049 a subsequent DL TB from the satellite.

[0080] Continuing with the flowchart, the UE checks 1059 if the subsequent DL TB has the NDI toggled. If the subsequent DL TB does not have an NDI toggled ("No" branch), the UE proceeds to update 1065 the count of HARQ transmissions related to the first DL TB (e.g., count = count + 1). If the subsequent DL TB does have an NDI toggled ("YES" branch), the UE proceeds to consider 1047 this subsequent DL TB as a success of the previous first DL TB and treat the subsequent DL TB as a new7first DL TB. After considering a new first DL TB. the UE can continue to reset 1063 the count of HARQ transmissions related to the new first DL TB.

[0081] Continuing with the flowchart, the UE checks 1067 if the count of HARQ transmissions exceeds a count threshold. Examples of the count threshold can include, for example, a first threshold (NTN NUM A2N) associated with a count (NTN ACK COUNT) or a second threshold (NTN_RECEPTION_MAX). If the count does not exceed the count threshold ("No" branch), the UE proceeds to maintain 1066 the count until the next (or subsequent) DL TB. If the count does exceed the count threshold ("YES" branch), the UE detects an A2N problem (such as the A2N problem 140). After the A2N problem is detected, the UE may proceed to reference A with relation to FIG. 10B to implement one or more example operations.

[0082] FIG. 10B is a flowchart diagram 1000b with changes related to FIG. 10A, and illustrating example operations for a UE to provide an indication of the detected A2N problem from a lower layer to an upper layer. Similar to FIG. 10A, the UE can detect an A2N problem after a count of HARQ transmissions exceeds a count threshold (omitted from FIG. 10A for brevity). After detecting 1060 the A2N problem with relation to FIG. 10A, the UE can proceed to reference A 1036 to start 1074 a timer (e.g., ntn_SilentTimer). FIGs. 3 and 6 illustrate a more detailed implementation of using a timer (ntn_SilentTimer), such as the timer (ntn SilentTimer) 370 illustrated in FIG. 3 and the ntn SilentTimer illustrated in FIG. 6.Docket No. 14730880600PCT

[0083] Continuing with the flowchart, the UE checks 1077 if the timer (ntn SilentTimer) is expired. If the timer (ntn_SilentTimer) is expired ("Yes" branch), the UE confirms 1078 the detection of the A2N problem. If the timer (ntn_SilentTimer) is not expired ("No" branch), the UE checks 1079 whether a new DL TB has been received. If the new DL TB has been received ("Yes" branch), the UE can proceed to reference B with relation to FIG. 10A to receive a subsequent DL TB from a satellite. If the new DL TB has not been received ("No" branch), the UE continues to check 1077 whether the timer (ntn_SilentTimer) is expired. After confirming 1078 the A2N problem, the UE can provide 1080 an indication of the detected A2N problem to an upper layer from a lower layer. For example, as shown in FIG. 1, the MAC layer 112 of the UE 102 can provide a notification 180 (or early notification) to the NAS layer 118 (or RLC / RRC layer) to indicate persistent HARQ feedback failures (or radio link failures) based on the detected A2N problem.

[0084] FIG. 11A is a block diagram of an example NTN control plane protocol stack 1100 A. The NTN control plane protocol stack 1100A shows the communication interfaces between a UE 102, a satellite 104, an NTN gateway 108, and a CN 110. The satellite 104 includes an onboard BS 106. The BS 106 can be either, or both, a network entity on the ground (such as BS 106') or a network entity partially or completely onboard the satellite 104 (such as the onboard BS 106). In some aspects, the BS 106 is a gNB, while, in other aspects, the BS can be an eNB. The diagram of the NTN control plane protocol stack 1100A shows the NR-Uu interface (e.g., via a service link, such as service link 103) between the satellite 104 (e.g., the BS 106) and the UE 102. The NR-Uu interface includes protocol layers such as the PDCP layer, MAC layer 112, RLC layer, and RRC layer. The Ng-C interface is between the BS 106 and the CN 110.

[0085] The NTN control plane protocol stack 1100A shows an N1 interface (e.g., the 3GPP standards, such as the 3GPP TS 24.501 version 18.4.0, refer to an N1 interface). The N1 interface is between the NAS layer 118 of the UE 102 and the NAS entity 119 (or NAS layer) of the CN 110. The N1 interface links the UE 102 and the AMF of the CN 110 via an access network. In FIG. 11A, the access network includes the NTN (such as the satellite 104 and BS 106) coupled by the NTN gateway 108. In normal operations, and in traditional implementations of regenerative satellite access, the satellite 104 does not participate in the N1 interface other than to relay communications through the lower layers of the protocol stacks of the NR-Uu and Ng-C interfaces. In some aspects, the satellite 104 can perform NAS procedures. For example, during the NAS procedures, the satellite 104 can maintain awareness of a NAS state 1130 between the NAS layer 118 and the NAS entity 119. The CN 110 can illustrate operations of an AMF of the 5GC or a MME of an EPC. For example, ifDocket No. 14730880600PCTthe radio access technology for the NTN RAN is E-UTRA or NB-IoT, the Ng-U interface can be referred to as an S 1 -MME interface. The Nr-Uu can be referred to as an LTE-Uu interface.

[0086] The protocol layers between the UE 102 and the BS 106 include the PHY layer (or sub-layer) that provides transport channels. The MAC layer 112 provides logical channels for the RLC layer. The RLC layer in turn provides data transfer services to the PDCP layer. The PDCP layer in turn can provide data transfer services to the RRC layer. For a 5GC, the protocol layers between the BS 106 and the CN 110 include a layer 1 (LI) sub-layer, a layer 2 (L2) sub-layer, an IP sub-layer, a SCTP sub-layer, and aNGAP layer.

[0087] Aspects of this disclosure are related to the NAS communications between the UE 102 and the CN 110 (such as a 5GC) via NTN access (such as the satellite 104 of the NTN node 101). Generally speaking, a NAS protocol manages the UE’s mobility, session, and control plane signaling between the UE 102 and the CN 110, transparent to any access network node (e.g., BS 106). In some aspects, the CN 110 implements various discrete control plane functions (shown as AMF or MME). The AMF and / or the SMF of the CN 110 can implement portions of the NAS layer (e g., the NAS entity 119). For example, the AMF can provide MM aspects of the NAS entity 119, while the SMF can provide SM aspects of the NAS layer. The UE 102 and the CN 110 (such as the CN's AMF) communicate with each other via the N 1 control interface. The N 1 control interface is a logical interface that traverses the Uu interface (Nr-Uu) and the Sl / NG interface (NG-C or N2 interface in a 5GC

[0088] FIG. 11B is a block diagram of an example NTN user plane protocol stack 1100B. The NTN user plane protocol stack 1100B includes the user data path between a UE 102 and a CN 110 (e.g., a UPF or SGW), relayed through satellite 104 and an NTN gateway 108. The NTN user plane protocol stack 1100B is similar to the NTN control plane protocol stack 1100A described with reference to FIG. 11 A. Some nomenclature differences between FIG.1 IB and FIG. 11 A include: the CN 110 can operate as a UPF or SGW and the Ng-C interface is labeled as an Ng-U interface, and the GW is labeled as the NTN GW. The NTN user plane protocol stack 1100B on the UE 102 includes several layers for processing user data, starting from the application-level protocol data unit (PDU) layer, followed by the SDAP layer, PDCP layer, RLC layer, MAC layer, and PHY layer. These layers facilitate communication over the NR-Uu interface with corresponding layers on the satellite 104. For example, user data, encapsulated as PDUs, is passed from the UE 102 through the lower protocol layers of the satellite 104 and the NTN gateway 108 to the CN 110.

[0089] The interface between the satellite 104 and the CN 110, via the NTN gateway 108, is the Ng-U interface. In a 5GC architecture, the BS 106 is a gNB, and the CN 110 representsDocket No. 14730880600PCTa UPF. If the NTN is based on an E-UTRA or NB-IoT radio access technology, the BS 106 is an eNB, and the CN 110 function can be performed by a SGW in an EPC. Tn some aspects, the NR-Uu interface may be referred to as the LTE-Uu interface, and the Ng-U interface may be referred to as the Sl-U interface. Furthermore, for NTN based on E-UTRA or NB-IoT, the SDAP layer may not be present in the protocol stack.

[0090] Aspects of this disclosure are related to the NAS and HARQ protocols and can be applied to either the 5GS or EPS. For avoidance of doubt, in this disclosure when referring to UL NAS messages (e.g.. UL NAS messages 122), the UL NAS message is communicated from the UE 102 to any of the NAS endpoints in the CN 110 (such as the AMF, MME, UPF, or SGW). DL NAS messages (e.g., DL NAS messages 124) are communicated to the UE 102 from any of the NAS endpoints in the CN 110 (such as the AMF, MME, UPF, or SGW).

[0091] FIG. 12 is a block diagram illustrating an example user equipment. Note that the depicted hardware configurations represent the processing components and communication components of a UE 1202 (such as the UE 102 described herein). The depicted hardware configurations may omit certain components well-understood to be frequently implemented in such electronic devices, such as displays, peripherals, power supplies, and the like.

[0092] The UE 1202 includes antennas 1211 A, a radio frequency front end (RF front end) 121 IB. and radio-frequency transceivers (e.g., an LTE transceiver 1203A and a 5G NR transceiver 1203B) for communicating with a network entity (such as an NTN node). The RF front end 121 IB includes one or more modems configured for the corresponding RAT(s) employed (for example, 3GPP 5GNR, one or more analog-to-digital converters (ADCs), one or more digital-to-analog converters (DACs), signal processors, and the like). In the example illustrated in FIG. 12, the RF front end 121 IB of the UE 1202 may couple or connect the LTE transceiver 1203 A, and the 5G NR transceiver 1203B to the antennas 1211 A to facilitate various types of wireless communication. The RF front end 121 IB operates, in effect, as a physical (PHY) transceiver interface to conduct and process signaling between the one or more processor(s) 1203C and antennas 1211 A so as to facilitate various types of wireless communication.

[0093] The antennas 1211 A of the UE 1202 may include an array of multiple antennas that may be tuned to one or more frequency bands associated with a corresponding RAT. The antennas 1211 A and the RF front end 121 IB may be tuned to, and / or be tunable to, one or more frequency bands defined by the 3 GPP LTE and 5G NR communication standards and implemented by the LTE transceiver 1203A, and / or the 5G NR transceiver 1203B. Additionally, the antennas 1211A, the RF front end 121 IB, the LTE transceiver 1203 A, and / orDocket No. 14730880600PCTthe 5GNR transceiver 1203B may be configured to support beamforming for the transmission and reception of communications with an NTN node (e.g., the BS 106 and satellite 104). By way of example and not limitation, the antennas 1211 A and the RF front end 121 IB may be implemented for operation in sub-gigahertz bands, sub-6 GHz bands, and / or above 6 GHz bands that are defined by the 3GPP LTE and 5GNR communication standards.

[0094] The UE 1202 also includes processor(s) 1203C and computer-readable storage media (CRM) 1203D. The processor(s) 1203C may include, for example, one or more central processing units, graphics processing units (GPUs), or other application-specific integrated circuits (ASIC), and the like. To illustrate, the processor(s) 1203C may include an application processor (AP) utilized by the UE 1202 to execute an operating system and various user-level software applications, as well as one or more processors utilized by modems (e.g., a modem 1211) or a baseband processor of the RF front end 121 IB.

[0095] CRM 1203D may include any suitable memory or storage device such as randomaccess memory (RAM), static RAM (SRAM), dynamic RAM (DRAM), non-volatile RAM (NVRAM), read-only memory (ROM), flash memory, solid-state drive (SSD) or other massstorage devices, and the like useable to store one or more sets of executable software instructions and associated data that manipulate the one or more processor(s) 1203C and other components of the UE 1202 to perform the various functions described herein and attributed to the UE 1202. The sets of executable software instructions include, for example, an operating system (OS) and various drivers (not shown), and various software applications (not shown), which are executable by processor(s) 1203C to enable user-plane communication, control-plane signaling, and user interaction with the UE 1202.

[0096] In some implementations, the UE 1202 can include a modem 1211, a HARQ consecutive HARQ feedback A2N detection module 1260, among other components (not shown). The consecutive HARQ feedback A2N detection module 1260 can communicate with the network using the modem 1211. The modem 1211 can include a receiver, transmitter, or other components for managing network communication. For example, the modem 1211 can implement a PHY / MAC layer 1212, an RRC layer 1214, and a NAS layer 1218 for communicating with the network, while the consecutive HARQ feedback A2N detection module 1260 can implement one or more protocol layers to detect A2N problems 140 in the lower layer (such as the PHY / MAC 1212) and indicate the detected A2N problems 140 to the upper layer(s) (such as the NAS 1218 and / or the RRC layers 1214). The UE 1202 can implement the NAS layer 1218 and the RRC layer 1214 using hardware and / or software -such as using a special-purpose processor or by a combination of a processor with computer readable instructions. The RRC layer 1214 can process communications from the lower layerDocket No. 14730880600PCT(such as the PHY / MAC 1212) and the upper layer (such as the NAS layer 1218). Although shown as separate components, in some implementations, the UE 1202 includes hardware that can implement the features of both the modem 1211 and the consecutive HARQ feedback A2N detection module 1260. The component(s) and / or feature(s) that implement the modem 1211 and / or the consecutive HARQ feedback A2N detection module 1260 can be part of a same chip or other single type of integrated circuit.

[0097] In accordance with some aspects of this disclosure, the MAC layer of the PHY / MAC 1212. the NAS layer 1218. and / or the consecutive HARQ feedback A2N detection module 1260 can also implement any of the example operations described in FIGs. 1-3, 6-9, 10A-B, and 11 A. For example, the MAC layer of the PHY / MAC 1212 and consecutive HARQ feedback A2N detection module 1260 can be implemented to detect a persistent A2N problem (e.g., A2N problem 140) using at least one or more of a counter of HARQ transmissions, a count (NTN ACK COUNT), a count (NTN RECEPTION COUNT), a count threshold, and a timer (e.g., ntn_SilentTimer).

[0098] FIG. 13 shows a block diagram of an example wireless communication system 1300 with hardware features and communication interfaces. The depicted hardware configurations may omit certain components well-understood to be frequently implemented in such electronic devices, such as displays, peripherals, power supplies, and the like. The wireless communication system 1300 includes the same elements as described with reference to FIG.1. including the UE 102, the BS 106, the satellite 104, and the CN 110. In some implementations, the UE 102 can support at least a 5G NR (or simply, “NR”) or E-UTRA air interface to communicate with the BS 106. The BS 106 connects to the CN 110 via an interface (e.g., SI or NG interface). The BS 106 can connect to other base stations (including the BS 106' or the BS 1314) via an interface (e.g., X2 or Xn interface) for interconnecting NG RAN nodes. In FIG. 13, the BS 1314 operates a TN cell 1317.

[0099] The BS 106 is equipped with processing hardware 1304 that can include a receiver 1305B configured to receive data in the uplink direction. The processing hardware 1304 can also include a transmitter 1305 A configured to transmit data in the downlink direction. The processing hardware can further include one or more general-purpose processor(s) 1305C (e.g., CPUs) and a non-transitory computer-readable memory (CRM) 1305D storing instructions that the one or more general-purpose processors execute. Additionally, or alternatively, the processing hardware 1304 can include special-purpose processing units. The processor 1305C may include, for example, one or more central processing units, graphics processing units (GPUs), or other application-specific integrated circuits (ASICs), and the like. CRM 1305D may include any suitable memory or storage device such as random-accessDocket No. 14730880600PCTmemory (RAM), static RAM (SRAM), dynamic RAM (DRAM), non-volatile RAM (NVRAM), read-only memory (ROM), or flash memory usable to store device data of the BS 106. The satellite 104 can include processing hardware 1306, such as a transmitter 1307 A, a receiver 1307B, a processor 1307C, and CRM 1307D (similar to components 1304, 1305A, 1305B. 1305C and 1305D of the BS 106). In some implementations, the components 1305A, 1305B, 1305C and 1305D can implement the components 1307A, 1307B, 1307C and 1307D. The BS 1314 can include generally similar components (not shown) as the processing hardware 1304.

[0100] The UE 102 is equipped with processing hardware 1302 that can include one or more general-purpose processors such as CPUs and non-transitory CRM 1303D storing machine-readable instructions executable on the one or more general-purpose processors, and / or special-purpose processing units. The processing hardware 1302 can also include a transmitter 1303 A configured to transmit data in the uplink direction. The processing hardware can further include a receiver 1303B configured to receive data in the downlink direction. The processing hardware 1302, in an example implementation, includes a processor 1303C to process data that the UE 102 will transmit in the uplink direction or process data received by UE 102 in the downlink direction. The processor(s) 1303C may include, for example, one or more central processing units, GPUs, or other ASICs, and the like. To illustrate, the processor(s) 1303C may include an AP utilized by the UE 102 to execute an operating system and various user-level software applications, as well as one or more processors utilized by modems or a baseband processor. The CRM 1303D may include any suitable memory or storage device such as RAM, SRAM, DRAM, NVRAM, ROM, flash memory, SSD, or other mass-storage devices, and the like useable to store one or more sets of executable software instructions and associated data that manipulate the one or more processor(s) 1303C and other components of the processing hardware 1302 to perform the various functions described herein and attributed to the UE 102. The sets of executable software instructions include, for example, an operating system (OS) and various drivers (not shown), and various software applications (not shown), which are executable by processor(s) 1303C to enable user-plane communication, control-plane signaling, and user interaction with the UE 102.

[0101] The CN 110 can be an EPC and / or a 5GC. Among other components, the EPC can include a serving gateway (SGW), a mobility management entity (MME), a home subscriber server (HSS), and a packet data network gateway (PGW). The SGW in general is configured to transfer user-plane packets related to audio calls, video calls, Internet traffic, etc., and the MME is configured to manage authentication, registration, paging, and other related functions. The PGW provides connectivity from the UE to one or more external packet dataDocket No. 14730880600PCTnetworks, e.g.. an internet network and / or an IP multimedia subsystem (IMS) network. The 5GC includes a user plane function (UPF), a unified data management (UDM), an access and mobility management function (AMF), and / or session management function (SMF). Generally speaking, the UPF is configured to transfer user-plane packets related to audio calls, video calls, Internet traffic, etc., the AMF is configured to manage authentication, registration, paging, and other related functions, and the SMF is configured to manage PDU sessions. The HSS and the UDM store and maintain subscription information regarding the UE 102. One or more processing elements (shown as processing hardware 1310) can implement the CN 110. The processing hardware 1310 can include a transmitter 1311 A, a receiver 131 IB, a processor 1311C, and a CRM 131 ID, similar to corresponding components described with reference to processing hardware 1302, 1306, and 1304.

[0102] The transmitters 1303A, 1307A, 1305A, and 1311A and receivers 1303B. 1307B, 1305B, and 131 IB are examples of a communication unit. Any of the processors 1303C, 1307C, 1305C, and 1311C can also be referred to as a processing system. Other examples of a communication unit and a processing system are possible, including some examples that are commonly used in a wireless communication system. The BS 106, UE 102, satellite 104. and CN 110 can include other components not illustrated in FIG. 13.

[0103] FIG. 1 through FIG. 13 and the operations described herein are examples meant to aid in understanding example implementations and should not be used to limit the potential implementations or limit the scope of the claims. Some implementations may perform additional operations, fewer operations, operations in parallel or in a different order, and some operations differently.

[0104] The detailed description above describes various example implementations. The following paragraphs describe additional features and options that can be combined with the previously described implementations to further enhance the detection and mitigation of A2N problems in NTN environments.

[0105] In some implementations, the threshold values for the counters (e g., NTN ACK COUNT and / or NTN RECEPTION COUNT) or the timer duration for the ntn SilentTimer can be configured by the network. For example, a base station can transmit these configuration parameters to the UE 102 via an RRC message. This networkbased configuration allows an operator to dynamically adjust the sensitivity and timing of the A2N detection mechanism based on network conditions, UE capabilities, or specific subscription details. Similarly, in some aspects, when the UE 102 receives another DL TB retransmission while the ntn_SilentTimer is already running, the MAC layer 112 can restartDocket No. 14730880600PCTthe ntn_SilentTimer. Restarting the timer ensures that the silent period is measured from the last known HARQ activity, providing a more accurate window to confirm a persistent A2N problem.

[0106] Furthermore, upon receiving a consistent A2N problem indication from a lower layer such as the MAC layer 112, an upper layer such as the RRC layer can determine that a RLF has occurred. For an NB-IoT UE operating in a non-terrestrial network, this lower-layer indication can serve as a trigger for the RRC layer to declare an RLF. This action can expedite the connection recovery’ process, as the UE 102 can then abort the current failed procedure and attempt to re-establish a connection or perform a cell reselection sooner than waiting for a NAS-level timer like T3410 to expire. This rapid response is particularly advantageous for time-sensitive communications, such as emergency messages, where prolonged delays are undesirable. This RLF declaration can also address potential interoperability issues where a network entity might incorrectly assume the UE is still in an RRC CONNECTED state after experiencing prolonged uplink failures.

[0107] In some aspects, when a UE is an NB-IoT UE and operating in a non-terrestrial network, the UE manages a counter of HARQ transmissions. For example, the UE increments a counter, such as NTN_RECEPTION_COUNT, by 1 for each consecutively’ received subsequent DL TB that does not have the NDI toggled. In another example, when the UE is an NB-IoT UE and operating in a non-terrestrial network, the MAC layer increments a counter, such as NTN ACK COUNT, by 1 for each HARQ ACK transmission.

[0108] In some implementations, the UE manages a timer (e.g, ntn SilentTimer) based on HARQ retransmissions. If the ntn SilentTimer is running and the MAC layer receives a subsequent DL TB corresponding to a retransmission, the MAC layer can restart the ntn_SilentTimer. This restart action ensures the timer accurately reflects the silent period since the last retransmission activity’. The network can configure the timer's threshold duration and the count thresholds (e.g, NTN RECEPTION MAX and NTN_NUM_A2N) and transmit them to the UE, for example, in an RRC message.

[0109] Upon receiving a consistent HARQ A2N problem indication from lower layers, such as the MAC layer, the UE takes specific actions. For example, the UE configures an RRC layer of the UE to consider that it has detected a radio link failure (RLF). This action is particularly applicable if the UE is an NB-IoT UE operating in a non-terrestrial network, where a consistent A2N indication from lower layers can serve as a trigger for an RLF declaration for the master cell group (MCG). Furthermore, upon receiving a consistent HARQ A2N problem indication from lower layers, the UE (specifically an NB-IoT UE in a non-Docket No. 14730880600PCTterrestrial network) forwards the indication to upper layers, such as the RRC layer. This forwarding ensures upper layers are promptly informed of persistent lower-layer communication problems, enabling faster recovery actions.

[0110] In some aspects, a computer-readable medium can store instructions which, when executed by a processor, causes the processor to perform any one of the above-mentioned functionalities. In some aspects, a system can implement means for implementing any one of the above-mentioned functionalities. In some aspects, an apparatus can implement one or more processors configured to perform one or more operations from any one of the above-mentioned functionalities or the following implementation options (enumerated as clauses for clarity).

[0111] Clause 1: A method of a lower layer of a user equipment (UE) (102), the method comprising: receiving, from a satellite (104) of a non-terrestrial network, a first downlink (DL) transport block (TB); transmitting, to the satellite, a first hybrid automatic repeat request (HARQ) acknowledgement (ACK) based on decoding the first DL TB; receiving, from the satellite, one or more subsequent DL TBs consecutively from the satellite, wherein each of the one or more subsequent DL TBs do not have a new data indicator (NDI) toggled; maintaining a count of HARQ transmissions related to the first DL TB; and detecting (160) a persistent acknowledgement-to-nonacknowledgement (A2N) problem (140) based, at least in part, on the count exceeding a count threshold.

[0112] Clause 2: The method of clause 1, wherein the detecting the A2N problem includes: starting a timer (NTN_SilentTimer) when the count exceeds the count threshold; and detecting the A2N problem when the timer expires.

[0113] Clause 3: The method of clause 1 or 2, wherein the maintaining the count of HARQ transmissions includes at least one of: maintaining a count (NTN_ACK_COUNT) of HARQ ACKs sent for the first DL TB and the one or more subsequent DL TBs that do not have the NDI toggled, wherein the count tracks at least the first HARQ ACK and subsequent ACKs; maintaining a count (NTN_ACK_COUNT) of HARQ ACKs sent for the one or more subsequent DL TBs that do not have the NDI toggled, wherein the count tracks the subsequent ACKs; maintaining a count (NTN_RECEPTION_COUNT) of consecutive DL TBs that include the first DL TB having the NDI toggled followed by the one or more subsequent DL TBs that do not have the NDI toggled; or maintaining a count (NTN RECEPTION COUNT) of consecutive subsequent DL TBs that do not have the NDI toggled.Docket No. 14730880600PCT

[0114] Clause 4: The method of clause 3, wherein the count threshold includes at least one of: a first threshold (NTN_NUM_A2N) associated with the NTN_ACK_COUNT; or a second threshold (NTN RECEPTION MAX) associated with the NTN RECEPTION COUNT.

[0115] Clause 5: The method of any one of clauses 1 to 4, wherein the count threshold is based on at least one of: a network-provided setting: a user-configured value; a manufacturer-configured value; channel conditions; NTN radio access technology; or UE movement.

[0116] Clause 6: The method of any one of clauses 1 to 5, wherein the lower layer is a media access control (MAC) layer, the method further comprising: providing an indication (180) of the A2N problem to an upper layer, wherein the upper layer includes at least one of a radio link control (RLC) layer, a radio resource control (RRC) layer, or non-access stratum (NAS) layer.

[0117] Clause 7: A method of a user equipment (UE) (102), the method comprising: initiating anon-access stratum (NAS) procedure with a core network (CN) via a satellite (104) of a non-terrestrial network; and detecting a persistent acknowledgement-to-nonacknowledgement (A2N) problem based, at least in part, on a count of hybrid automatic repeat request (HARQ) acknowledgement (ACK) transmissions that are followed by receptions of a retransmitted downlink (DL) transport block (TB).

[0118] Clause 8: The method of clause 7, wherein the detecting the A2N problem includes: detecting that the count exceeds a count threshold.

[0119] Clause 9: The method of clause 8, further comprising: starting a timer (NTN_SilentTimer) when the count exceeds the count threshold; and notifying an upper protocol layer of the A2N problem when the timer expires.

[0120] Clause 10: The method of any one of clauses 7 to 9, wherein the count (NTN ACK COUNT) tracks HARQ ACKs sent for the retransmitted DL TBs that do not have the NDI toggled; and wherein the count threshold includes a first threshold (NTN_NUM_A2N) associated with the NTN ACK COUNT.

[0121] Clause 11: The method of clause 10, wherein the count (NTN_ACK_COUNT) also tracks a first HARQ ACK sent for an initially transmitted DL TB.

[0122] Clause 12: The method of any one of clauses 7 to 9. wherein the (NTN RECEPTION COUNT) tracks consecutive DL TBs that do not have the NDI toggled; and wherein the count threshold includes a second threshold (NTN_RECEPTION_MAX) associated with the NTN RECEPTION COUNT.

[0123] Clause 13: The method of clause 12, wherein the count (NTN RECEPTION COUNT) also tracks a first DL TB that has the NDI toggled.Docket No. 14730880600PCT

[0124] Clause 14: The method of any one of clauses 8 to 13, wherein the count threshold is based on at least one of: a network-provided setting: a user-configured value; a manufacturer-configured value; channel conditions; NTN radio access technology; or UE movement.

[0125] Clause 15: The method of any one of clauses 7 to 14, wherein the NAS procedure is at least one of: an attach procedure: an authentication procedure; a service request procedure, or a tracking area update procedure.

[0126] Clause 16: The method of any one of clauses 7 to 15, further comprising: taking at least one action based on the detecting the A2N problem, the at least one action including any combination of: restarting the NAS procedure; stopping a timer associated with the NAS procedure; increasing uplink transmission power; performing a cell (re)selection procedure; or generating a user interface (UI) indication;

[0127] Clause 17: An apparatus for use in a user equipment (UE), comprising: a communication interface; and a processing system configured to control the communication interface to implement any one of the methods of any one of clauses 1 to 16.

[0128] The following additional considerations may apply to the foregoing and the following discussions. Generally speaking, description for one of the above figures can apply to another of the above figures. Any event or block described above can be optional. For example, an event or block with dashed lines can be optional. In some implementations, "message" is used and can be replaced by “information element (IE),” and vice versa. In some implementations, “IE” is used and can be replaced by “field,” and vice versa. In some implementations, “subband” can be replaced with “sub-band.” In some implementations, “configuration” can be replaced by “configurations” or “configuration parameters,” and vice versa. In some implementations, “some” means “one or more.” In some implementations, “at least one” means “one or more.” The “eNB” can be replaced by “base station,” “gNB,” “6G base station,” “evolved gNB,” or 6G gNB. “MME” can be replaced by AMF or evolved AMF or 6G AMF. “Core network (CN)” can be replaced by EPC. 5GC or 6GC.

[0129] Unless defined otherwise, technical and scientific terms used herein have the same meaning as is commonly understood by one of ordinary skill in the art to which this specification belongs. The terms “first,” “second.” and the like, as used herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. The use of terms “including,” “comprising” or “having” and variations thereof herein are meant to encompass the items listed thereafter and equivalents thereof as well as additional items. The terms “connected” and “coupled” are not restricted to physical or mechanical connections or couplings and can include electrical connections or couplings, whether directDocket No. 14730880600PCTor indirect. Furthermore, terms "circuit” and "circuitry” and "control unit” may include either a single component or a plurality of components, which are either active and / or passive and are connected or otherwise coupled together to provide the described function. In addition, the term operationally coupled as used herein includes wired coupling, wireless coupling, electrical coupling, magnetic coupling, radio communication, software based communication, or combinations thereof.

[0130] Some or all of the foregoing or the following implementations can be jointly combined or formed to be a new or another one implementation. The foregoing or the following techniques can be used to solve at least (but not limited to) the issue(s) or scenario(s) mentioned in this disclosure. Any two or more than two of the foregoing or the following paragraphs, (sub)-bullets, points, actions, or claims described in each method / technique / implementation may be combined logically, reasonably, and properly to form a specific method. Any sentence, paragraph, (sub)-bullet, point, action, or claim described in each of the foregoing or the following technique(s) / implementation(s) / concept(s) may be implemented independently and separately to form a specific method. Dependency, such as “based on.” “more specifically,” “where” or etc., in technique(s) / implementation(s) / concept(s) mentioned in this disclosure is just one possible implementation which would not restrict the specific method.

[0131] As used herein, the terms “user device”, “user equipment” (for example, UE 102), “wireless communication device”, “mobile communication device”, "communication device”, or “mobile device” refer to any one or all of cellular telephones, smartphones, portable computing devices, personal or mobile multi-media players, laptop computers, tablet computers, smartbooks, loT devices, palm-top computers, wireless electronic mail receivers, multimedia Internet enabled cellular telephones, wireless gaming controllers, display subsystems, driver assistance systems, vehicle controllers, vehicle system controllers, vehicle communication system, infotainment systems, vehicle telematics systems or subsystems, vehicle display systems or subsystems, vehicle data controllers, point-of-sale (POS) terminals, health monitoring devices, drones, cameras, media-streaming dongles or another personal media devices, wearable devices such as smartwatches, wireless hotspots, femtocells, broadband routers or other types of routers, and similar electronic devices which include a programmable processor and memory and circuitry configured to perform operations as described herein. Further, the user device, in some implementations, may be embedded in an electronic system such as the head unit of a vehicle or an advanced driver assistance system (ADAS). Still further, the user device can operate as an loT device or a mobile-internet device (MID). Depending on the type, the user device can include one or moreDocket No. 14730880600PCTgeneral-purpose processors, a computer-readable memory, a user interface, one or more network interfaces, one or more sensors, etc.

[0132] Certain techniques are described in this disclosure as including logic or a number of components or modules. Modules can be software modules (e.g., code, or machine-readable instructions stored on non-transitory machine-readable medium) or hardware modules. A hardware module is a tangible unit capable of performing certain operations and may be configured or arranged in a certain manner. A hardware module can comprise dedicated circuitry or logic that is permanently configured (e.g.. as a special-purpose processor, such as a field programmable gate array (FPGA) or an application-specific integrated circuit (ASIC), a digital signal processor (DSP), etc.) to perform certain operations. A hardware module may also comprise programmable logic or circuitry (e.g. , as encompassed within a general-purpose processor or other programmable processor) that is temporarily configured by software to perform certain operations. The decision to implement a hardware module in dedicated and permanently configured circuitry, or in temporarily configured circuitry (e.g., configured by software) may be driven by cost and time considerations.

[0133] When implemented in software, the techniques can be provided as part of the operating system, a library used by multiple applications, a particular software application, etc. The software can be executed by one or more general-purpose processors or one or more special-purpose processors.

[0134] As used herein, the terms ‘'component” and “module” are intended to be broadly construed as hardware, firmware, or a combination of hardware and software. As used herein, a processor is implemented in hardware, firmware, or a combination of hardware and software. As used herein, the phrase “based on” is intended to be broadly construed to mean ■‘based at least in part on.”

[0135] As used herein, a phrase referring to a list of items separated by “or” refers to any combination of those items, including single members. For example, “a, B. or c” is intended to cover the possibilities of: a only, B only, c only, a combination of a and B, a combination of a and c, a combination of B and c, and a combination of a and B and c.

[0136] In this disclosure, an expression of “X / Y” may include meaning of any of the following: '‘X or Y” or “X and Y” or “X and / or Y." An expression of “(A) B” or “B (A)” may include concept of “only B.” An expression of “(A) B” or “B (A)” may include the concept of “A+B” or “B+A.”Docket No. 14730880600PCT

[0137] In this disclosure, the term "can" indicates a capability, or alternatively indicates a possible implementation option. The term "may" indicates a permission or a possible implementation option.

[0138] Some aspects are described herein in connection with thresholds. As used herein, satisfying a threshold may refer to a value being greater than the threshold, greater than or equal to the threshold, less than the threshold, less than or equal to the threshold, equal to the threshold, not equal to the threshold, or the like.

[0139] The various illustrative components, logic, logical blocks, modules, circuits, operations and algorithm processes described in connection with the implementations disclosed herein may be implemented as electronic hardware, firmware, software, or combinations of hardware, firmware or software, including the structures disclosed in this specification and the structural equivalents thereof. The interchangeability of hardware, firmware and software has been described generally, in terms of functionality7, and illustrated in the various illustrative components, blocks, modules, circuits and processes described above. Whether such functionality is implemented in hardware, firmware or software depends upon the particular application and design constraints imposed on the overall system.

[0140] As described above, some aspects of the subject matter described in this specification can be implemented as software. For example, various functions of components disclosed herein, or various blocks or steps of a method, operation, process or algorithm disclosed herein can be implemented as one or more modules of one or more computer programs. Such computer programs can include non-transitory processor-executable or computer-executable instructions encoded on one or more tangible processor-readable or computer-readable storage media for execution by, or to control the operation of, a data processing apparatus including the components of the devices described herein. By way of example, and not limitation, such storage media may include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that may be used to store program code in the form of instructions or data structures. Combinations of the above should also be included within the scope of storage media.

[0141] Various modifications to the implementations described in this disclosure may be readily apparent to persons having ordinary skill in the art, and the generic principles defined herein may be applied to other implementations without departing from the scope of this disclosure. Thus, the claims are not intended to be limited to the implementations shown herein but are to be accorded the widest scope consistent with this disclosure, the principles and the novel features disclosed herein.Docket No. 14730880600PCT

[0142] Additionally, various features that are described in this specification in the context of separate implementations can also be implemented in combination in a single implementation. Conversely, various features that are described in the context of a single implementation can also be implemented in multiple implementations separately or in any suitable subcombination. As such, although features may be described above as acting in particular combinations, and even initially claimed as such, one or more features from a claimed combination can, in some implementations, be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.

[0143] The drawings may schematically depict one or more example processes in the form of a flowchart or flow diagram. However, other operations that are not depicted can be incorporated in the example processes that are schematically illustrated. For example, one or more additional operations can be performed before, after, simultaneously, or between any of the illustrated operations. In some circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the implementations described above should not be understood as requiring such separation in all implementations, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products. Additionally, other implementations are within the scope of the following claims. In some implementations, the actions recited in the claims can be performed in a different order and still achieve desirable results.

[0144] The foregoing disclosure provides illustration and description but is not intended to be exhaustive or to limit the aspects to the precise form disclosed. Modifications and variations may be made in light of the above disclosure or may be acquired from practice of the aspects. While the aspects of the disclosure have been described in terms of various examples, any combination of aspects from any of the examples is also within the scope of the disclosure. The examples in this disclosure are provided for pedagogical purposes.

Claims

1. Docket No. 14730880600PCTCLAIMSWhat is claimed is:

1. A method performed by a lower layer protocol (112) in a user equipment (UE) (102), the method comprising:receiving (837), from a satellite (104) of a non-terrestrial network (NTN), a first downlink (DL) transport block (TB) (437);transmitting (845), to the satellite, a first hybrid automatic repeat request (HARQ) acknowledgement (ACK) (545) based on decoding the first DL TB;receiving (849), from the satellite, one or more subsequent DL TBs consecutively from the satellite, wherein each of the one or more subsequent DL TBs does not have a new data indicator (NDI) toggled (549);maintaining (860) a count (361) of HARQ transmissions related to the first DL TB; andindicating (180, 680), to an upper layer (118), an acknowledgement-to-nonacknowledgement (A2N) problem (140) based, at least in part, on the count of HARQ transmissions exceeding a count threshold (367).

2. The method of claim 1, further comprising:starting a timer (370) (ntn_SilentTimer) when the count of HARQ transmissions exceeds the count threshold; andwherein the indicating the A2N problem occurs when the timer expires (677, 1077).

3. The method of claim 1 or 2, wherein the maintaining the count of HARQ transmissions includes at least one of:maintaining a first counter (362) (NTN_ACK_COUNT) of HARQ ACKs sent for the first DL TB and the one or more subsequent DL TBs that do not have the NDI toggled, wherein the first counter tracks at least the first HARQ ACK and subsequent ACKs; or maintaining a second counter (364) (NTN_RECEPTION_COUNT) of the one or more subsequent DL TBs that do not have the NDI toggled.

4. The method of claim 3, wherein the count threshold includes at least one of:a first threshold (NTN_NUM_A2N) associated with the NTN_ACK_COUNT; or a second threshold (NTN RECEPTION MAX) associated with the NTN RECEPTION COUNT.Docket No. 14730880600PCT5. The method of any one of claims 1 to 4, wherein the count threshold is based on at least one of:a network-provided setting;a user-configured value:a manufacturer-configured value;channel conditions;NTN radio access technology; orUE movement.

6. The method of any one of claims 1 to 5, wherein the lower layer (112) is a media access control (MAC) layer, and wherein the upper layer (118) includes at least one of a radio link control (RLC) layer, a radio resource control (RRC) layer, or non-access stratum (NAS) layer.

7. A method of a user equipment (UE) (102), the method comprising:initiating (920) anon-access stratum (NAS) procedure with a core network (CN) via a satellite (104) of anon-terrestrial network;detecting (960) an acknowledgement-to-nonacknowledgement (A2N) problem (140) based, at least in part, on a count of hybrid automatic repeat request (HARQ) acknowledgement (ACK) transmissions that are followed by receptions of a retransmitted downlink (DL) transport block (TB); andindicating (180, 680), to an upper layer (118), an A2N problem (140) based, at least in part, on the count of HARQ transmissions exceeding a count threshold (367).

8. The method of claim 7, wherein the detecting the A2N problem includes detecting the count of HARQ ACK transmissions exceeding a count threshold, and wherein the detecting the A2N problem is performed by a lower layer protocol in the UE.

9. The method of claim 8,wherein the count of HARQ ACK transmissions is a count (NTN ACK COUNT) of HARQ ACKs transmitted for retransmitted DL TBs that do not have the NDI toggled; and wherein the count threshold is a first threshold (NTN_NUM_A2N).

10. The method of claim 9, wherein the count (NTN_ACK_COUNT) of HARQ ACKs also tracks a first HARQ ACK sent for an initially transmitted DL TB.Docket No. 14730880600PCT11. The method of claim 8,wherein the count of HARQ ACK transmissions is a reception count (NTN_RECEPTION_COUNT) of consecutive DL TBs received that do not have the NDI toggled; andwherein the count threshold is a second threshold (NTN_RECEPTION_MAX).

12. The method of claim 11, wherein the reception count (NTN RECEPTION COUNT) tracks a first DL TB that has the NDI toggled.

13. The method of any one of claims 8 to 12, further comprising:starting a timer (ntn SilentTimer) when the count of HARQ ACK transmissions exceeds the count threshold; andwherein the indicating the A2N problem occurs when the timer expires.

14. The method of any one of claims 8 to 13, wherein the count threshold is based on at least one of:a network-provided setting;a user-configured value;a manufacturer-configured value;channel conditions;NTN radio access technology; orUE movement.

15. The method of any one of claims 7 to 14, wherein the NAS procedure is at least one of:an attach procedure;an authentication procedure;a service request procedure, ora tracking area update procedure.

16. The method of any one of claims 7 to 15, further comprising:taking at least one action based on the detecting the A2N problem, the at least one action including any combination of:restarting the NAS procedure;stopping a timer associated with the NAS procedure;increasing uplink transmission power;performing a cell (re)selection procedure; orgenerating a user interface (UI) indication.Docket No. 14730880600PCT17. An apparatus for wireless communication by a user equipment (UE), comprising:a communication interface; anda processing system configured to control the communication interface to implement any one of the methods of any one of claims 1 to 16.

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