Managing NAS timer and NAS signaling release in a user equipment in store-and-forward satellite networks

Abstract

The disclosure relates to a 5G or 6G communication system for supporting a higher data transmission rate. The disclosure provides a method comprising: receiving an ATTACH REJECT message associated with a first PLMN, wherein the ATTACH reject message is related to store and forward (S&F) satellite evolved universal mobile telecommunications system terrestrial radio access network (E-UTRAN); starting a timer based on a value of S&F wait time duration; performing an attach procedure related to a cell associated with a second PLMN; stopping the timer in case that the attach procedure is successfully performed.

Description

MANAGING NAS TIMER AND NAS SIGNALING RELEASE IN A USER EQUIPMENT IN STORE-AND-FORWARD SATELLITE NETWORKS

[0001] The present disclosure relates generally to the field of wireless communication systems. More specifically, the present disclosure pertains to methods and systems for managing the Non-Access Stratum (NAS) timer T3451 and NAS signaling release in a user equipment (UE) operating within store-and-forward (S&F) satellite networks.

[0002] 5G mobile communication technologies define broad frequency bands such that high transmission rates and new services are possible, and can be implemented not only in "Sub 6GHz" bands such as 3.5GHz, but also in "Above 6GHz" bands referred to as mmWave including 28GHz and 39GHz. In addition, it has been considered to implement 6G mobile communication technologies (referred to as Beyond 5G systems) in terahertz bands (for example, 95GHz to 3THz bands) in order to accomplish transmission rates fifty times faster than 5G mobile communication technologies and ultra-low latencies one-tenth of 5G mobile communication technologies.

[0003] At the beginning of the development of 5G mobile communication technologies, in order to support services and to satisfy performance requirements in connection with enhanced Mobile BroadBand (eMBB), Ultra Reliable Low Latency Communications (URLLC), and massive Machine-Type Communications (mMTC), there has been ongoing standardization regarding beamforming and massive MIMO for mitigating radio-wave path loss and increasing radio-wave transmission distances in mmWave, supporting numerologies (for example, operating multiple subcarrier spacings) for efficiently utilizing mmWave resources and dynamic operation of slot formats, initial access technologies for supporting multi-beam transmission and broadbands, definition and operation of BWP (BandWidth Part), new channel coding methods such as a LDPC (Low Density Parity Check) code for large amount of data transmission and a polar code for highly reliable transmission of control information, L2 pre-processing, and network slicing for providing a dedicated network specialized to a specific service.

[0004] Currently, there are ongoing discussions regarding improvement and performance enhancement of initial 5G mobile communication technologies in view of services to be supported by 5G mobile communication technologies, and there has been physical layer standardization regarding technologies such as V2X (Vehicle-to-everything) for aiding driving determination by autonomous vehicles based on information regarding positions and states of vehicles transmitted by the vehicles and for enhancing user convenience, NR-U (New Radio Unlicensed) aimed at system operations conforming to various regulation-related requirements in unlicensed bands, NR UE Power Saving, Non-Terrestrial Network (NTN) which is UE-satellite direct communication for providing coverage in an area in which communication with terrestrial networks is unavailable, and positioning.

[0005] Moreover, there has been ongoing standardization in air interface architecture / protocol regarding technologies such as Industrial Internet of Things (IIoT) for supporting new services through interworking and convergence with other industries, IAB (Integrated Access and Backhaul) for providing a node for network service area expansion by supporting a wireless backhaul link and an access link in an integrated manner, mobility enhancement including conditional handover and DAPS (Dual Active Protocol Stack) handover, and two-step random access for simplifying random access procedures (2-step RACH for NR). There also has been ongoing standardization in system architecture / service regarding a 5G baseline architecture (for example, service based architecture or service based interface) for combining Network Functions Virtualization (NFV) and Software-Defined Networking (SDN) technologies, and Mobile Edge Computing (MEC) for receiving services based on UE positions.

[0006] As 5G mobile communication systems are commercialized, connected devices that have been exponentially increasing will be connected to communication networks, and it is accordingly expected that enhanced functions and performances of 5G mobile communication systems and integrated operations of connected devices will be necessary. To this end, new research is scheduled in connection with eXtended Reality (XR) for efficiently supporting AR (Augmented Reality), VR (Virtual Reality), MR (Mixed Reality) and the like, 5G performance improvement and complexity reduction by utilizing Artificial Intelligence (AI) and Machine Learning (ML), AI service support, metaverse service support, and drone communication.

[0007] Furthermore, such development of 5G mobile communication systems will serve as a basis for developing not only new waveforms for providing coverage in terahertz bands of 6G mobile communication technologies, multi-antenna transmission technologies such as Full Dimensional MIMO (FD-MIMO), array antennas and large-scale antennas, metamaterial-based lenses and antennas for improving coverage of terahertz band signals, high-dimensional space multiplexing technology using OAM (Orbital Angular Momentum), and RIS (Reconfigurable Intelligent Surface), but also full-duplex technology for increasing frequency efficiency of 6G mobile communication technologies and improving system networks, AI-based communication technology for implementing system optimization by utilizing satellites and AI (Artificial Intelligence) from the design stage and internalizing end-to-end AI support functions, and next-generation distributed computing technology for implementing services at levels of complexity exceeding the limit of UE operation capability by utilizing ultra-high-performance communication and computing resources.

[0008] The integration of satellite communication systems into 5G networks aims to extend coverage to remote and underserved regions lacking terrestrial infrastructure. In this context, the S&F Satellite operation mode enables communication services to UE even under intermittent or temporary satellite connectivity. This mode is particularly applicable when a satellite is not connected to the ground network through a feeder link or an Inter-Satellite Link (ISL), thereby supporting delay-tolerant communication services.

[0009] In existing satellite systems, continuous end-to-end connectivity requires simultaneous activation of a service link between the UE and the satellite and a feeder link between the satellite and the ground network. Such simultaneous connectivity is difficult to guarantee, particularly for Non-Geostationary Satellite Orbit (NGSO) satellites due to their movement and dynamic topology.

[0010] The S&F Satellite operation separates end-to-end signaling and data exchange into two non-concurrent phases. In the first phase, signaling and data are exchanged between the UE and the satellite while the satellite is not connected to the ground network, and the satellite stores the information. In the second phase, once feeder link connectivity becomes available, the stored signaling and data are forwarded to the ground network. This alternating connectivity enables delay-tolerant and non-real-time services, including Internet of Things (IoT) services beyond terrestrial coverage.

[0011] The store-and-forward concept is well known in delay-tolerant networking. Within the 3rd Generation Partnership Project (3GPP) framework, a comparable example is Short Message Service (SMS), in which endpoints connect to a Short Message Service Centre (SMSC) that stores and relays messages without requiring continuous end-to-end connectivity.

[0012] Despite these advantages, technical challenges remain. When a UE receives cause code #83 indicating that a requested procedure cannot be completed due to an unavailable feeder link while a Mobility Management Entity (MME) operates in S&F mode, the UE is barred from performing signaling with satellites of the same Public Land Mobile Network (PLMN) for a duration specified in a NAS message. If the UE continues maintaining the NAS signaling connection and reserved radio resources during this period, unnecessary resource occupation occurs at the UE and at the access node, such as an eNodeB or gNodeB, increasing signaling overhead and power consumption. Current specifications do not define an optimized mechanism for handling the NAS signaling connection state after reception of cause code #83.

[0013] Further, in control plane congestion scenarios, the network may provide a back-off timer T3448 to the UE. While T3448 is active, the UE refrains from sending user data over the control plane. Even if the network subsequently resolves congestion and sends downlink control plane data, the UE continues blocking uplink control plane transmission until expiry of T3448, resulting in unnecessary delay and inefficient resource usage.

[0014] Additional issues arise during cell change or PLMN change across satellite and terrestrial access. Timer handling, including timer T3451 associated with NAS procedures, lacks coordinated behavior during such transitions. Improper continuation or restarting of T3451 may lead to redundant retransmissions, inconsistent NAS states, prolonged service interruption, and excessive signaling.

[0015] Thus, it is desired to address the above-mentioned disadvantages, issues, or other shortcomings, or at least provide a useful alternative.

[0016] Embodiments of the present disclosure is to provide an apparatus and method for effectively providing a service in a wireless communication system.

[0017] The principal object of the invention herein is to manage NAS timer T3451 and NAS Signaling Release in a UE in S&F satellite networks.

[0018] Yet another object of the invention is to provide optimized management of NAS timer T3451 during cell transitions in a store-and-forward satellite network by maintaining timer T3451 across cell transitions and defining explicit UE behavior upon expiry of timer T3451 when the UE is camped in a cell other than an S&F satellite E-UTRAN cell.

[0019] Yet another object of the invention is to provide optimized handling of the NAS signaling connection upon reception of EMM cause value #83 during S&F satellite operation by starting timer T3440 and releasing the NAS signaling connection locally upon expiry of timer T3440, thereby avoiding unnecessary retention of idle resources and reducing power consumption.

[0020] Yet another object of the invention is to provide optimized handling of timer T3448 upon reception of downlink user data via the control plane by interpreting reception of an ESM DATA TRANSPORT message as an indication of network de-congestion and stopping timer T3448, thereby allowing the UE to resume uplink user data transport without waiting for expiry of timer T3448.

[0021] In an aspect, the invention provides a method for managing NAS timer T3451 and Non-Access Stratum (NAS) Signaling Release in the UE in store-and-forward satellite networks. Further, the method includes receiving by the UE a NAS accept message or a NAS reject message including a Store-and-Forward (S&F) wait timer value or information element. The NAS message is received when the UE is camped in an S&F satellite Evolved Universal Terrestrial Radio Access Network (E-UTRAN) cell of a first Public Land Mobile Network (PLMN). Further, the method includes starting by the UE a timer T3451 in response to receiving the NAS message including the S&F wait timer value. Further, the method includes performing by the UE a cell selection or a cell reselection procedure and camping on a target cell different from an S&F satellite E-UTRAN cell. Further, the method includes initiating by the UE a NAS procedure when the timer T3451 is running and when the UE is camped on the target cell. Further, the method includes receiving by the UE a NAS accept message in response to the NAS procedure, the NAS accept message indicating successful completion of the NAS procedure. Further, the method includes stopping by the UE the timer T3451 in response to receiving the NAS accept message.

[0022] In another aspect, the invention provides a method for managing a NAS timer in a store-and-forward satellite network. Further, the method includes receiving by a UE a NAS reject message including an Evolved Mobility Management (EMM) cause value #83. The NAS reject message is received when the UE is camped on a S&F satellite E-UTRAN cell of PLMN. Further, the method includes starting by the UE a NAS timer T3440 in response to receiving the NAS reject message including EMM cause value #83. Further, the method includes releasing by the UE a NAS signaling connection locally after expiry of the timer T3440. Further, the method includes releasing by the UE all NAS and radio resources allocated for the NAS signaling connection after expiry of the timer T3440.

[0023] In yet another aspect, the invention provides the UE for managing timer T3451 and NAS Signaling Release in store-and-forward satellite networks. Further, the UE includes a memory, a processor, and a NAS Timer Controller. The NAS Timer Controller is coupled to the memory and the processor. The NAS Timer Controller receives the NAS accept message or a NAS reject message including a S&F wait timer value or information element. The NAS message is received when the UE is camped in an S&F satellite E-UTRAN cell of a first PLMN. Further, the NAS Timer Controller starts a timer T3451 in response to receiving the NAS message including the S&F wait timer value. Further, the NAS Timer Controller performs a cell selection or a cell reselection procedure and camps on a target cell different from an S&F satellite E-UTRAN cell. Further, the NAS Timer Controller initiates a NAS procedure when the timer T3451 is running and when the UE is camped on the target cell. Further, the NAS Timer Controller receives a NAS accept message in response to the NAS procedure, the NAS accept message indicating successful completion of the NAS procedure. Further, the NAS Timer Controller stops the timer T3451 in response to receiving the NAS accept message.

[0024] In yet another aspect, the invention provides the UE for managing a Non-Access Stratum (NAS) timer in a store-and-forward satellite network. The UE includes a memory, a processor, and a NAS Timer Controller. Further, the NAS Timer Controller is coupled to the memory and the processor. The NAS Timer Controller receives the NAS reject message including EMM cause value #83. The NAS reject message is received when the UE is camped on the S&F E-UTRAN cell of a PLMN. Further, the NAS Timer Controller starts a NAS timer T3440 in response to receiving the NAS reject message including EMM cause value #83. Further, the NAS Timer Controller releases a NAS signaling connection locally after expiry of the timer T3440. Further, the NAS Timer Controller releases all NAS and radio resources allocated for the NAS signaling connection after expiry of the timer T3440.

[0025] The aspects of the embodiments will be better understood with the following description and accompanying drawings. The descriptions indicate preferred embodiments and specific details for illustration, not limitation. Many changes and modifications are possible within the scope of the embodiments, which include all such modifications.

[0026] Embodiments of the present disclosure is to provide an apparatus and method for effectively providing a service in a wireless communication system.

[0027] The features, aspects, and advantages of the present invention are illustrated in the accompanying drawings, where like reference letters indicate corresponding parts across various figures. The following description, with reference to the drawings, will provide a better understanding of the embodiments.

[0028] FIG. 1 is a block diagram illustrating a S&F satellite split MME architecture according to the prior art.

[0029] FIG. 2 is a sequence diagram that illustrates a signaling scenario for the S&F satellite operation according to the prior art.

[0030] FIG. 3 is a sequence diagram that illustrates another signaling scenario for the S&F satellite operation associated with handling of timer T3451 according to the prior art.

[0031] FIG. 4 is a sequence diagram that illustrates another scenario of the UE receiving an Evolved Mobility Management (EMM) cause code #83 during S&F satellite operation according to the prior art.

[0032] FIG. 5 illustrates a sequence diagram representing another scenario arising from activation of timer T3448 according to the prior art.

[0033] FIG. 6 is a block diagram that illustrates the UE for optimized management of NAS timer operations and NAS signaling connection in the store-and-forward satellite network according to embodiments as disclosed herein.

[0034] FIG. 7A is a flowchart that illustrates a method for managing NAS timer T3451 and NAS Signaling Release in the UE in the store-and-forward satellite networks according to embodiments as disclosed herein.

[0035] FIG. 7B is a flowchart that illustrates a method for managing the NAS timer in the store-and-forward satellite network according to embodiments as disclosed herein.

[0036] FIG. 8 is a sequence diagram that illustrates the optimized management of timer T3451 during cell transitions in a store-and-forward satellite network according to embodiments as disclosed herein.

[0037] FIG. 9 is a sequence diagram that illustrates a scenario for optimized handling of timer T3451 expiry when the UE is camped in a non-S&F satellite E-UTRAN cell according to embodiments disclosed herein.

[0038] FIG. 10 is a sequence diagram illustrating optimized management of timer T3451 upon reception of a NAS accept message when the UE is camped in the non-S&F satellite E-UTRAN cell according to embodiments disclosed herein.

[0039] FIG. 11 is a sequence diagram that illustrates optimized handling of a NAS signaling connection upon reception of EMM cause code #83 during S&F satellite operation according to embodiments disclosed herein.

[0040] FIG. 12 is a sequence diagram that illustrates optimized handling of timer T3448 upon reception of downlink user data via the control plane according to embodiments disclosed herein.

[0041]

[0042] The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. Also, the various embodiments described herein are not necessarily mutually exclusive, as some embodiments can be combined with one or more other embodiments to form new embodiments. The term "or" as used herein, refers to a non-exclusive or, unless otherwise indicated. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein can be practiced and to further enable those skilled in the art to practice the embodiments herein. Accordingly, the examples are not be construed as limiting the scope of the embodiments herein.

[0043] As is traditional in the field, embodiments are described and illustrated in terms of blocks that carry out a described function or functions.　These blocks, which referred to herein as managers, units, modules, hardware components or the like, are physically implemented by analog and / or digital circuits such as logic gates, integrated circuits, microprocessors, microcontrollers, memory circuits, passive electronic components, active electronic components, optical components, hardwired circuits and the like, and optionally be driven by firmware and software. The circuits, for example, be embodied in one or more semiconductor chips, or on substrate supports such as printed circuit boards and the like.　The circuits constituting a block be implemented by dedicated hardware, or by a processor (e.g., one or more programmed microprocessors and associated circuitry), or by a combination of dedicated hardware to perform some functions of the block and a processor to perform other functions of the block. Each block of the embodiments be physically separated into two or more interacting and discrete blocks without departing from the scope of the proposed method.　Likewise, the blocks of the embodiments be physically combined into more complex blocks without departing from the scope of the proposed method.

[0044] The accompanying drawings facilitate understanding of various technical features. The embodiments are not limited by these drawings and extend to any alterations, equivalents, and substitutes. Terms like first, second, etc., are used for distinction and do not limit the elements.

[0045] The term "Store-and-Forward (S&F) satellite operation" refers to an operational mode in which a serving satellite provides communication services to a UE while the satellite does not maintain a continuous connection to the ground network. In this mode, data exchanged between the UE and the satellite is stored onboard the satellite and forwarded to the ground network when a feeder link, gateway connection, or inter-satellite link (ISL) becomes available.

[0046] The term "S&F mode" refers to a mode of operation in which the UE, the Radio Access Network (RAN), and core network entities support Store-and-Forward satellite operation. The term "S&F" is used interchangeably with "Store-and-Forward."

[0047] The term "serving satellite" refers to a satellite providing satellite access to a UE. In a Non-Geostationary Satellite Orbit (NGSO) system, the serving satellite changes dynamically due to movement of satellites within the constellation.

[0048] The term "S&F data retention period" refers to a validity duration during which stored data is retained onboard the satellite in a 5G system supporting S&F operation, after which undelivered data is discarded.

[0049] The term "UE-Satellite-UE communication" refers, in a 5G system with satellite access, to communication between UEs under coverage of one or more serving satellites using satellite access without routing through the ground network segment.

[0050] The term "S&F satellite E-UTRAN cell" refers to a satellite-based E-UTRAN cell that broadcasts an indication that the eNodeB operates in S&F mode.

[0051] The terms "MME" and "MME onboard satellite" are used synonymously. The terms "S&F mode", "S&F mode of operation", and "S&F satellite operation" are used synonymously. The terms "eNodeB"and "eNodeB onboard satellite" are used synonymously.

[0052] Accessing a Public Land Mobile Network (PLMN) via satellite access refers to accessing the PLMN through satellite Evolved Universal Terrestrial Radio Access (E-UTRA / E-UTAN) access or satellite Next Generation Radio Access Network (NG-RAN) access.

[0053] All descriptions applicable to 4G Radio Access Technology (RAT) are equally applicable to 5G RAT and corresponding network functions unless explicitly stated otherwise. Functionality described with respect to a Mobility Management Entity (MME) is equally applicable to an Access and Mobility Management Function (AMF), and functionality described with respect to an eNodeB is equally applicable to a gNodeB.

[0054] The term "NAS procedure" refers to procedures involving NAS signaling between the UE and the core network. The expression "satellite operating in S&F mode" refers to an onboard eNodeB and onboard MME configured to support S&F operation.

[0055] Examples of NAS messages include: REGISTRATION REQUEST / ATTACH REQUEST; DEREGISTRATION REQUEST / DETACH REQUEST; SERVICE REQUEST; CONTROL PLANE SERVICE REQUEST; IDENTITY REQUEST; AUTHENTICATION REQUEST; AUTHENTICATION RESULT; AUTHENTICATION REJECT; REGISTRATION REJECT / ATTACH REJECT; REGISTRATION ACCEPT / ATTACH ACCEPT; DEREGISTRATION ACCEPT / DETACH ACCEPT; SERVICE REJECT; SERVICE ACCEPT; UE CONFIGURATION UPDATE command; UE PARAMETERS UPDATE command; TRACKING AREA UPDATE REQUEST; and TRACKING AREA UPDATE ACCEPT.

[0056] S&F satellite operation in a 5G system with satellite access provides communication services to UEs under satellite coverage during intermittent or temporary absence of satellite connectivity to the ground network. This condition occurs when the satellite does not maintain an active feeder link or ISL connection, thereby enabling delay-tolerant communication services.

[0057] In a default satellite operation mode, exchange of signaling and user data between the UE and the ground network requires simultaneous availability of a service link (between UE and satellite) and a feeder link (between satellite and ground network), thereby providing continuous end-to-end connectivity among the UE, the satellite, and the ground network.

[0058] In the S&F satellite operation mode, exchange of signaling and user data occurs in two non-concurrent phases. In a first phase, signaling and data are exchanged between the UE and the satellite while the feeder link is inactive, and the data is stored onboard the satellite. In a second phase, connectivity between the satellite and the ground network becomes available, enabling forwarding of the stored data to the ground network. The satellite transitions between interaction with the UE during the first phase and interaction with the ground network during the second phase.

[0059] In existing systems, the reception of cause code #83 by the UE indicates an inability to complete a procedure due to an unavailable feeder link during the operation of a MME in the S&F mode. Following the reception of cause code #83, signaling with satellites belonging to the same PLMN remains restricted for a duration indicated in a NAS message received from the network. The maintenance of the NAS signaling connection and associated reserved resources during such a restriction period results in an additional burden on the UE and on an eNodeB, along with increased power consumption. Therefore, optimal management of the NAS signaling connection established for a NAS procedure becomes necessary. Current specifications lack a mechanism for handling such NAS signaling connection conditions following the reception of cause code #83 from the network.

[0060] Furthermore, the UE indicating support for a control plane data back-off timer may receive a congestion indication from the network for the transmission of user data over the control plane. The network provides timer T3448 together with a corresponding timer value to the UE. Activation of timer T3448 causes the suspension of user data transmission over the control plane while the timer remains active. In certain situations, de-congestion of the network occurs, and user data transmission over the control plane in the downlink direction toward the UE takes place. The ongoing operation of timer T3448 prevents the interpretation of such downlink transmission as an indication of de-congestion, resulting in the continued restriction of uplink control plane data transmission by the UE. Such a condition under current specifications requires resolution.

[0061] FIG. 1 is a block diagram illustrating a S&F satellite split MME architecture according to the prior art. The architecture includes functions deployed on board a satellite (103) and functions deployed on a ground network (104). A UE (102) accesses the satellite network through a satellite E-UTRAN access node (107a, 107b). In the illustrated configuration, a plurality of satellites identified as Satellite ID=1 to Satellite ID=N provide satellite access represented by E-UTRAN nodes (107a) and (107b). Communication between the UE (102) and the satellite E-UTRAN nodes (107a, 107b) occurs through a service link (3).

[0062] The MME functionality is split into two components: an MME-onboard (106a, 106b) located on the satellite (103) and an MME-ground (105) located in the ground network (104). The satellite E-UTRAN nodes (107a, 107b) connect to the MME-onboard entities (106a, 106b) through an S1-MME interface. The MME-onboard entities (106a, 106b) interact with the MME-ground (105), thereby enabling coordination between satellite-based functions and ground-based core network entities.

[0063] The MME-ground (105) connects with ground network components through multiple interfaces. A connection through an S6a interface provides communication with a Home Subscriber Server (HSS) (108). A connection through an SGd interface provides interaction with an SMS-GMSC / IWMSC / SMS Router (109). A connection through T6a / T6ai interfaces provides interaction with an Interworking Function-Service Capability Exposure Function (IWF-SCEF / SCEF) (110). Policy control interaction occurs with a Policy and Charging Rules Function (PCRF) (111) through a T8 interface and through a Gx interface with a PCRF (112). A Serving Gateway (SGW) (114) connects to the MME-ground (105) through an S11 interface and further communicates with the PCRF (112) through an S5 / S8 interface. The PCRF (112) connects to a Data Network / CIoT Services entity (113) through an SGi interface.

[0064] During operation, when the UE (102) initiates an Attach procedure or a Tracking Area Update (TAU) procedure, an indication of support for S&F satellite operation is provided to the MME according to existing NAS capability signaling. In situations where completion of the Attach procedure or the TAU procedure becomes infeasible due to S&F operation, the MME transmits an Attach Reject message or a TAU Reject message to the UE (102).

[0065] The Attach Reject message or TAU Reject message includes information indicating that completion of the Attach or TAU procedure cannot occur due to S&F operation and indicating that the UE (102) may re-attempt the Attach or TAU procedure in the same Public Land Mobile Network (PLMN) during a subsequent satellite pass. Such indication informs the UE (102) that information contained in the Attach Request message or TAU Request message remains stored at the MME and that network availability may occur after subsequent interaction between the satellite network and the ground network.

[0066] The Attach Reject message or TAU Reject message further includes an S&F wait timer parameter indicating a duration for which the UE (102) waits before re-attempting the Attach or TAU procedure through a current satellite or through another satellite belonging to the same PLMN. Optionally, the message may include a list of Satellite Identifiers indicating satellites through which the UE (102) may re-attempt the Attach or TAU procedure after expiry of the wait timer. The Satellite Identifiers are derived from System Information Block (SIB) information broadcast by the eNodeB. The Satellite Identifier list is provided to the UE (102) as an S&F monitoring list.

[0067] Further processing of the received information remains implementation dependent at the UE (102). During operation of the wait timer, the UE (102) may search for another terrestrial PLMN or another satellite PLMN to obtain normal service.

[0068] When the UE (102) indicates support for S&F satellite operation in an ATTACH REQUEST message and when the MME operates in S&F mode, the MME may include the S&F satellite operation parameters Information Element (IE) in an ATTACH ACCEPT message. The S&F satellite operation parameters IE may include an S&F wait time duration, an estimated uplink delivery time duration, an S&F monitoring list, or any combination of these parameters.

[0069] For the S&F satellite operation, if the UE receives the S&F satellite operation parameters IE in NAS messages and the S&F wait timer duration field is present in the S&F satellite operation parameters IE, the UE starts timer T3451 using the S&F wait timer duration value provided in the S&F satellite operation parameters IE. Operation of timer T3451 prevents continuous attempts by the UE to re-establish the connection, thereby conserving UE battery power and reducing unnecessary signaling traffic in the network.

[0070] In accordance with an embodiment of the present disclosure, a mechanism is provided for optimized handling of the NAS signaling connection when the UE (102) receives cause code #83 during S&F satellite operation. The UE (102) performs a connection release procedure upon detection of the cause code, thereby avoiding unnecessary retention of signaling resources and reducing power consumption. Further, in accordance with another embodiment, when the UE (102) receives downlink control plane data while timer T3448 is active, the UE (102) interprets the downlink transmission as an indication of network de-congestion and performs an action including stopping or adjusting the operation of timer T3448 to allow transmission of user data over the control plane.

[0071] FIG. 2 presents a sequence diagram illustrating a signaling scenario for S&F satellite operation according to prior art. A pre-requisite condition for the illustrated scenario establishes the User Equipment (UE) (102) as camped in an S&F satellite E-UTRAN cell of PLMN-1. Entities participating in the illustrated scenario include the UE (102), the MME on-board satellite of PLMN-1 (106a), the ground network including the MME-ground (105), and the MME (101) of a non-S&F satellite E-UTRAN cell of PLMN-1 or PLMN-2.

[0072] At step S1, the UE (102) initiates the NAS procedure by transmitting a NAS message to the MME on-board satellite (106a) of PLMN-1. The NAS message corresponds, for example, to an ATTACH REQUEST message. In step S2, the MME on-board satellite (106a) transmits a NAS reject message to the UE (102), such as an ATTACH REJECT message. This transmission occurs due to the unavailability of the feeder link between the satellite (103) and the ground network (104) for PLMN-1, thereby preventing completion of the NAS procedure. The NAS reject message includes an S&F wait timer and optionally an S&F monitoring list.

[0073] Upon reception of the NAS reject message, the UE (102) starts timer T3451 using the S&F wait timer value received from the MME on-board satellite (106a) at step S3. During the operation of timer T3451, the UE (102) performs a PLMN or cell selection procedure and moves to a cell that is not an S&F satellite E-UTRAN cell belonging to either PLMN-1 or PLMN-2 at step S4. Upon camping on the non-S&F satellite E-UTRAN cell, the UE (102) stops timer T3451 in accordance with existing specifications defined in 3GPP TS 24301 at step S5.

[0074] In step S6, the UE (102) transmits the NAS message to either PLMN-1 or PLMN-2 through the non-S&F satellite E-UTRAN cell. The MME (101) associated with the non-S&F satellite E-UTRAN cell rejects the NAS procedure and transmits a NAS reject message to the UE (102), leaving the NAS procedure unsuccessful at step S7. Following reception of the NAS reject message, the UE (102) performs the PLMN or cell selection procedure for service recovery and moves to a cell that is an S&F satellite E-UTRAN cell of PLMN-1 at step S8.

[0075] Upon camping on the S&F satellite E-UTRAN cell of PLMN-1, the UE (102) immediately transmits a NAS message to PLMN-1 at step S9. In step S10, the MME on-board satellite (106a) transmits a NAS reject message to the UE (102), such as an ATTACH REJECT message, including an S&F wait timer and optionally an S&F monitoring list due to the continued unavailability of the feeder link between the satellite (103) and the ground network (104).

[0076] The scenario illustrated in FIG. 2 discloses a deficiency in existing timer T3451 handling during S&F satellite operation. Upon camping on a non-S&F satellite E-UTRAN cell in step S4, the UE (102) stops timer T3451 as required by existing specifications despite the original NAS procedure remaining incomplete and unsuccessful. Stoppage of timer T3451 occurs without any successful completion or acknowledgment of the NAS procedure.

[0077] Further, upon failure of the NAS procedure in the non-S&F satellite E-UTRAN cell, the UE (102) returns to the S&F satellite E-UTRAN cell of PLMN-1 with timer T3451 in a stopped state. The absence of an active timer T3451 upon return causes the UE (102) to immediately retransmit a NAS message without observing any back-off period. The feeder link between the satellite (103) and the ground network (104) remains unavailable, resulting in a repeated NAS rejection followed by re-activation of timer T3451. This behavior produces a cycle of unnecessary NAS signaling, repeated rejection, and repeated back-off, generating additional signaling burden on the UE (102) and the MME on-board satellite (106a), increasing power consumption at the UE (102), and degrading overall network efficiency. Existing systems or specifications lack a mechanism for maintaining timer T3451 across cell transitions when the original NAS procedure remains unsuccessful, and such a gap requires resolution through optimized timer handling for S&F satellite operation.

[0078] In an embodiment the UE stops timer T3451 if the UE successfully performs an attach procedure or a tracking area updating procedure via a cell which is not a S&F satellite E-UTRAN cell or a cell being in a TA which is not in the list of TAs or in a new PLMN.

[0079] FIG. 3 presents a sequence diagram illustrating another signaling scenario for the S&F satellite operation related to the handling of timer T3451 according to the prior art. The pre-requisite condition for the illustrated scenario establishes the User Equipment (UE) (102) as camped in the S&F satellite E-UTRAN cell of PLMN-1. Entities participating in the illustrated scenario include the UE (102), the MME on-board satellite of PLMN-1 (106a), the ground network including the MME-ground (105), and the MME (101) of a non-S&F satellite E-UTRAN cell of PLMN-1 or PLMN-2.

[0080] At step S1, the UE (102) initiates the NAS procedure by transmitting a NAS message to the MME on-board satellite (106a) of PLMN-1. The NAS message corresponds, for example, to an ATTACH REQUEST message. At step S2, the MME on-board satellite (106a) transmits a NAS reject message to the UE (102), such as an ATTACH REJECT message. This transmission occurs due to the unavailability of the feeder link between the satellite (103) and the ground network (104) for PLMN-1, thereby preventing the completion of the NAS procedure. The NAS reject message includes an S&F wait timer and optionally an S&F monitoring list.

[0081] Upon reception of the NAS reject message at step S3, the UE (102) starts timer T3451 using the S&F wait timer value received from the MME on-board satellite (106a). During the operation of timer T3451 at step S4, the UE (102) performs a PLMN or cell selection procedure and moves to a cell that is not an S&F satellite E-UTRAN cell belonging to PLMN-1, PLMN-2, or any other PLMN. Following the cell move at step S5, the UE (102) initiates no NAS signaling. This absence of NAS signaling occurs, for example, due to the selected cell or tracking area being forbidden. As no NAS signaling is initiated, the UE (102) does not stop timer T3451 in accordance with existing specifications defined in 3GPP TS 24301.

[0082] The UE (102) remains camped in the current non-S&F satellite E-UTRAN cell with timer T3451 continuing to operate at step S6. Timer T3451 expires while the UE (102) remains camped in the non-S&F satellite E-UTRAN cell at step S7. Step S8 identifies the undefined condition arising upon the expiry of timer T3451 while the UE (102) is camped in a cell that is not an S&F satellite E-UTRAN cell.

[0083] The scenario illustrated in FIG. 3 exposes a second deficiency in existing timer T3451 handling during S&F satellite operation. Upon moving to a non-S&F satellite E-UTRAN cell in Step S4, the UE (102) does not initiate NAS signaling due to the cell or tracking area being forbidden. As a result, the condition for stopping timer T3451 as defined in 3GPP TS 24301 is not met, and timer T3451 continues to operate despite the UE (102) no longer being camped in an S&F satellite E-UTRAN cell.

[0084] The UE (102) remains camped in the non-S&F satellite E-UTRAN cell as further PLMN or cell selection procedures do not result in the UE (102) finding an alternative PLMN or cell. Consequently, timer T3451 expires while the UE (102) is camped in a cell that is not an S&F satellite E-UTRAN cell. Existing specifications do not define UE (102) behavior upon the expiry of timer T3451 under such a condition, leaving the UE (102) without a specified course of action. This undefined behavior upon the expiry of an S&F feature timer in a non-S&F satellite E-UTRAN cell represents a gap in current specifications that requires resolution through the explicit definition of the UE (102) behavior for such a scenario.

[0085] FIG. 4 is a sequence diagram illustrating another scenario of the UE receiving the Evolved Mobility Management (EMM) cause code #83 during the S&F satellite operation according to the prior art. The pre-requisite condition for the illustrated scenario establishes the UE (102) as camped in an S&F satellite E-UTRAN cell of PLMN-1. Entities participating in the illustrated scenario include the UE (102), the E-NodeB and the Mobility Management Entity (MME) on-board satellite of PLMN-1 (106a), the ground network including the MME-ground (105), and the E-NodeB and MME on-board satellite of PLMN-2 (106b).

[0086] At step S1, the UE (102) initiates a NAS procedure by transmitting a NAS message to the E-NodeB and MME on-board satellite of PLMN-1 (106a). The NAS message, such as an ATTACH REQUEST message, includes an indication of support for S&F satellite operation by the UE (102).

[0087] In step S2, the E-NodeB and the MME on-board satellite of PLMN-1 (106a) transmit a NAS reject message to the UE (102), such as an ATTACH REJECT message. This NAS reject message includes the EMM cause code #83, indicating that the NAS procedure cannot be completed due to the unavailability of the feeder link while the MME on-board satellite of PLMN-1 (106a) operates in S&F mode. Additionally, the NAS reject message includes an S&F wait timer and optionally an S&F monitoring list. Upon reception of the NAS reject message carrying EMM cause code #83, the UE (102) starts timer T3451 using the S&F wait timer value received from the E-NodeB and the MME on-board satellite of PLMN-1 (106a) at step S3.

[0088] Following the transmission of the NAS reject message to the UE (102), the NAS signaling connection is not released by the E-NodeB and the MME on-board satellite of PLMN-1 (106a) at step S4. Thus, the NAS signaling connection established for the NAS procedure remains active. During the period in which timer T3451 remains active, the UE (102) does not initiate any NAS procedure in accordance with existing specifications defined in 3GPP TS 24301 at step S5. Timer T3451 expires at step S6. Upon expiry of timer T3451, the UE (102) re-attempts the NAS procedure by transmitting a NAS message to the E-NodeB and the MME on-board satellite of PLMN-1 (106a) at step S7. The network accepts the NAS procedure upon re-attempt.

[0089] The scenario illustrated in FIG. 4 exposes a deficiency in the handling of the NAS signaling connection following the reception of EMM cause code #83 during S&F satellite operation. After the UE (102) is rejected with EMM cause code #83, the NAS signaling connection is not released by the network. EMM cause code #83 indicates that the NAS procedure cannot be processed due to the unavailability of the feeder link, establishing that the NAS procedure cannot be completed via the S&F satellite E-UTRAN cell. Furthermore, the UE (102) cannot initiate any NAS procedure for as long as timer T3451 remains active.

[0090] The retention of the NAS signaling connection following the reception of EMM cause code #83 results in resources remaining allocated for the UE (102) and the network. These allocated resources remain unnecessarily reserved despite not being used, as the UE (102) cannot perform any NAS procedures during the active period of timer T3451. If the NAS signaling connection is not released by the network prior to the expiry of timer T3451, the resources continue to remain allocated and reserved both at the UE (102) and in the network until that point. Additionally, the continued reservation of such idle resources drains the power reserve of the devices. The handling of the NAS signaling connection requires optimization for such scenarios, and this issue is addressed in the present embodiment.

[0091] FIG. 5 illustrates a sequence diagram representing another scenario arising from the activation of timer T3448 according to the prior art. In FIG. 5, the UE (102) remains restricted from transmitting user data over the control plane while timer T3448 is active. This scenario is applicable to the UE (102) accessing an Evolved Packet Core (EPC) via a terrestrial cell, a satellite E-UTRAN cell, and an S&F satellite E-UTRAN cell. Entities participating in the illustrated scenario include the UE (102) and the MME (101).

[0092] At step S1, the UE (102) initiates a NAS procedure by transmitting a NAS message to the MME (101), for example, an ATTACH REQUEST message. The NAS message transmitted includes an indication of support for the control plane data back-off timer by the UE (102).

[0093] At step S2, the MME (101) transmits a NAS message to the UE (102) carrying cause code #22 and a non-zero value of timer T3448. Transmission of the NAS message in Step S2 occurs due to congestion in the transport of user data via the control plane. Upon reception of the NAS message from the MME (101) at step S3, the UE (102) starts timer T3448 based on the timer value received from the MME (101).

[0094] Following the resolution of congestion in the network at step S4, the MME (101) transmits a NAS message to the UE (102), for example, an ESM DATA TRANSPORT message. Transmission of the ESM DATA TRANSPORT message corresponds to the transmission of user data in the downlink direction to the UE (102) via the control plane. Upon reception of the NAS message in Step S4 at step S5, the UE (102) continues to run timer T3448 without modification.

[0095] At step S6, the UE (102) may not initiate the transport of user data via the control plane procedure as timer T3448 remains active in accordance with existing specifications defined in 3GPP TS 24301. Timer T3448 expires at step S7. Upon expiry of timer T3448 at step S8, the UE (102) initiates the transport of user data via the control plane procedure.

[0096] The scenario illustrated in FIG. 5 discloses a deficiency in the handling of timer T3448 during control plane data transport. Upon reception of a congestion indication from the MME (101), the UE (102) starts the back-off timer T3448 and refrains from initiating any user data transport via the control plane for the duration of timer T3448. Congestion on the network side may be resolved substantially earlier than the expiry of timer T3448.

[0097] Following the resolution of congestion, the MME (101) transmits an ESM DATA TRANSPORT message to the UE (102) corresponding to the transmission of user data in the downlink direction via the control plane. The UE (102) does not consider the reception of the ESM DATA TRANSPORT message as an indication that congestion has ended. The UE (102) continues to run timer T3448 and refrains from initiating any user data transport via the control plane until the expiry of timer T3448. Continued operation of timer T3448 despite downlink user data transmission via the control plane by the MME (101) causes unnecessary delay in uplink user data transmission by the UE (102), resulting in a degraded user experience. The behavior of the UE (102) in this aspect is not optimal, and the handling of timer T3448 upon reception of downlink control plane data requires resolution. This issue is addressed in the present embodiment.

[0098] The prior art scenarios collectively identify three distinct deficiencies in existing specifications governing UE behavior during the S&F satellite operation and control plane data transport. First, upon camping on the non-S&F satellite E-UTRAN cell during the operation of timer T3451, the UE (102) stops timer T3451 regardless of whether the original NAS procedure has been successfully completed, causing the UE (102) to immediately retransmit the NAS messages upon returning to the S&F satellite E-UTRAN cell despite the feeder link remaining unavailable, thereby generating unnecessary signaling, repeated rejection, and repeated back-off. Second, upon camping on a non-S&F satellite E-UTRAN cell where no NAS signaling is initiated, timer T3451 continues to operate and subsequently expires while the UE (102) remains camped in a cell that is not an S&F satellite E-UTRAN cell, a condition for which existing specifications define no UE behavior upon timer expiry. Third, following the reception of EMM cause code #83, the NAS signaling connection established for the NAS procedure is not released by the network, resulting in idle resources remaining allocated at both the UE (102) and the network for the entire active duration of timer T3451, causing unnecessary power consumption and signaling burden. Additionally, upon reception of a downlink ESM DATA TRANSPORT message from the MME (101) during the active operation of timer T3448, the UE (102) does not interpret the downlink user data transmission via the control plane as an indication of network de-congestion and continues to refrain from initiating uplink user data transport via the control plane until the expiry of timer T3448, causing unnecessary delay and degraded user experience.

[0099] To overcome the drawbacks in the existing systems, the present invention discloses optimized handling of timer T3451 across cell transitions, explicit definition of UE behavior upon expiry of timer T3451 outside an S&F satellite E-UTRAN cell, optimized release of the NAS signaling connection upon reception of EMM cause code #83, and optimized handling of timer T3448 upon reception of downlink control plane data as an indication of network de-congestion.

[0100] FIG. 6 is block diagram that illustrates the UE (102) for optimized management of NAS timer operations and NAS signaling connection in the store-and-forward satellite network, according to embodiments as disclosed herein. Examples of the UE (101) can include, but are not limited to, Consumer Electronics (such as Mobile Phones and Smartphones), Tablets, Wearable Devices, Television, Computing Devices (such as Laptops, Notebooks, Desktops, Workstations, etc.), IoT Devices, Automotive Systems (such as connected cars, Autonomous Vehicles, Vehicle-to-Everything (V2X) communication devices, etc.), Enterprise Devices such as robotics, Specialized Equipment (such as Medical Devices, Public Safety Devices, etc.), Media Devices (such as Gaming Consoles, Streaming Devices, etc.).

[0101] Examples of the wireless communication network system include, but are not limited to, Cellular Networks (such as 2G, 3G, 4G, 5G, Beyond 5G (B5G) / 6G, or advanced cellular networks), Local Area Networks (LANs) (such as Wi-Fi, Li-Fi, etc.), Personal Area Networks (PANs) (such as Bluetooth, Zigbee, Z-Wave, etc.), Wide Area Networks (WANs) (such as Satellite Communication Networks, Long Range Wide Area Network, Narrowband IoT, Low-bandwidth communication for IoT, etc.), Metropolitan Area Networks (MANs), Machine-to-Machine (M2M), Ad Hoc and Mesh Networks, Emerging and Advanced Networks. Examples of the UE can include, but are not limited to, Consumer Electronics (such as Mobile Phones and Smartphones), Tablets, Wearable Devices, Computing Devices (such as Laptops, Notebooks, Desktops, Workstations, etc.), IoT Devices, Automotive Systems (such as connected cars, Autonomous Vehicles, Vehicle-to-Everything (V2X) communication devices, etc.), Enterprise Devices such as robotics, Specialized Equipment (such as Medical Devices, Public Safety Devices, etc.), Media Devices (such as Gaming Consoles, Streaming Devices, etc.).

[0102] The UE (102) includes the processor (601), the memory (603), an I / O interface (602) and a NAS Timer Controller (605). The processor (601) of the UE (201) communicates with the memory (603), the I / O interface (602), a NAS layer (604) and the NAS Timer Controller (605). The processor (601) is configured to execute instructions stored in the memory (603) and to perform various processes. The processor (601) can include one or a plurality of processors, can be a general-purpose processor, such as a central processing unit (CPU), an application processor (AP), or the like, a graphics-only processing unit such as a graphics processing unit (GPU), a visual processing unit (VPU), and / or an Artificial intelligence (AI) dedicated processor such as a neural processing unit (NPU). Further, the processor (601) executes NAS procedures and controls overall operation of the UE (102). The NAS Timer Controller (605) is coupled to the memory (603) and the processor (601) and governs all NAS timer operations and NAS signaling connection management for the UE (102).

[0103] Further, the memory (603) of the UE (102) includes storage locations to be addressable through the processor (601). The memory (603) is not limited to a volatile memory and / or a non-volatile memory. Further, the memory (603) can include one or more computer-readable storage media. The memory (603) can include non-volatile storage elements. For example, non-volatile storage elements can include magnetic hard discs, optical discs, floppy discs, flash memories, or forms of electrically programmable memories (EPROM) or electrically erasable and programmable (EEPROM) memories.

[0104] The I / O interface (602) transmits the information between the memory (603) and external peripheral devices. The peripheral devices are the input-output devices associated with the UE (201). The I / O interface (602) receives several information from the UE (102).

[0105] The NAS layer (604) handles NAS protocol processing and execution of NAS procedures including an Attach procedure, a Tracking Area Update procedure, and a Service Request procedure. The NAS layer (604) processes NAS messages received from the network including NAS accept messages and NAS reject messages, and interacts with the NAS timer controller (605) to trigger appropriate timer actions based on the content of the received NAS messages.

[0106] The NAS Timer Controller (605) is operatively coupled to the processor (601), the memory (603), and a radio communication interface of the UE (102). The NAS Timer Controller (605) is implemented as dedicated hardware circuitry integrated within a baseband processing subsystem of the UE (102), and is configured to directly control execution and suspension of NAS timers associated with mobility management and session management procedures in a store-and-forward satellite network environment. The NAS Timer Controller (605) comprises a multi-core hardware architecture, wherein each core performs a distinct timer control function, including monitoring timer states across cell transitions, controlling NAS signaling connection release upon reception of EMM cause code #83, and dynamically modifying timer behavior based on NAS procedure outcomes and satellite connectivity state. The controller generates hardware control signals that influence signaling resource retention, RRC state transitions, and power management behavior of the UE (102). The NAS Timer Controller (605) is implemented as an application-specific integrated circuit (ASIC) or as a dedicated logic block within a system-on-chip (SoC) baseband modem architecture. The controller includes hardware timer registers, state machines, interrupt handling logic, and power management circuitry configured to manage timer T3451, timer T3440, and timer T3448 in coordination with store-and-forward satellite operation conditions. By directly controlling NAS timer execution at the hardware level in response to satellite link availability and cell transition events, the NAS Timer Controller (605) reduces unnecessary signaling retries, prevents premature NAS connection release, minimizes power consumption, and improves communication continuity in intermittent satellite connectivity scenarios.

[0107] Further, the NAS timer controller (605) receives the NAS accept message or the NAS reject message including the S&F wait timer value or information element. The NAS message is received while the UE (102) is camped in the S&F satellite Evolved Universal Terrestrial Radio Access Network (E-UTRAN) cell of a first PLMN (also referred to as PLMN-1). The NAS timer controller (605) decodes the received NAS message to extract the S&F wait timer value, which is used to manage the timing of subsequent NAS procedures. Further, the NAS timer controller (605) starts the timer T3451 in response to receiving the NAS message including the S&F wait timer value. The timer T3451 is configured to track the duration for which the UE (102) must wait before initiating specific NAS procedures. Further, the NAS timer controller (605) performs a cell selection or a cell reselection procedure resulting in the UE (102) camping on a target cell that is not an S&F satellite E-UTRAN cell. The cell selection or reselection procedure involves evaluating signal strength and quality metrics to determine the most suitable target cell. Further, the NAS timer controller (605) initiates the NAS procedure while the timer T3451 is running and while the UE (102) is camped on the target cell. The NAS procedure may involve exchanging signaling messages with the network to establish or update the UE's registration status. Further, the NAS timer controller (605) receives the NAS accept message in response to the NAS procedure, the NAS accept message indicating successful completion of the NAS procedure. The NAS accept message may include additional parameters such as assigned network resources and security context. Further, the NAS timer controller (605) stops the timer T3451 in response to receiving the NAS accept message. The stopping of the timer T3451 signifies the end of the waiting period and the successful completion of the NAS procedure.

[0108] Further, the NAS timer controller (605) continues to run the timer T3451 in response to receiving the NAS message. The timer T3451 continues to track the waiting period even if the UE (102) transitions between different cells or PLMNs. Further, the NAS timer controller (605) performs the NAS procedure. The NAS procedure includes at least one of an Attach procedure, a Tracking Area Update (TAU) procedure, or a Service Request procedure. Each of these procedures involves specific signaling exchanges with the network to manage the UE's connectivity and mobility. The Attach procedure establishes the initial connection between the UE and the network, the TAU procedure updates the UE's location information, and the Service Request procedure is used to request specific services from the network.

[0109] Further, the NAS timer controller (605) includes a wait timer that is one of timer T3451, timer T3452, or any NAS timer with an S&F satellite wait timer value started from a NAS accept or reject message. The wait timer is configured to manage the timing of NAS procedures based on the received S&F satellite wait timer value. The NAS message received in response to the NAS procedure is one of an Attach Accept message, Attach Reject message, a Tracking Area Update Accept message, Tracking Area Update Reject message, a Service Request Accept message, or a Service Request Reject message. Each of these messages contains specific information elements that indicate the outcome of the NAS procedure and any associated timer values.

[0110] Further, the NAS timer controller (605) determines the target cell belongs to a second PLMN different from the first PLMN. The determination involves evaluating the PLMN identifiers broadcasted by the target cell and comparing them with the identifier of the first PLMN. Further, the NAS timer controller (605) includes stopping the timer T3451. The stopping of the timer T3451 is triggered by specific events such as the successful completion of a NAS procedure or the receipt of a NAS accept message. Further, the NAS timer controller (605) stops the timer T3451 associated with the first PLMN in response to receiving the NAS accept message while camped on the target cell of the second PLMN (also referred to as PLMN-2). The transition to the second PLMN may involve updating the UE's registration and security context to align with the new network.

[0111] Further, the NAS timer controller (605) receives the NAS reject message. The NAS reject message includes a reject cause that results in a subscriber identity module (SIM) of the UE (102) being marked as invalid for at least one of Evolved Packet System (EPS) services or non-EPS services. The reject cause may indicate issues such as subscription problems or network restrictions. Further, the NAS timer controller (605) stops the timer T3451 in response to receiving the NAS reject message including the SIM-invalidating reject cause. The stopping of the timer T3451 terminates the waiting period due to the rejection of the NAS procedure.

[0112] Further, the NAS timer controller (605) receives the NAS reject message and a monitoring list including one or more satellite identifiers (IDs) associated with the first PLMN. The monitoring list is used to track the availability and status of specific satellites within the first PLMN. Further, the NAS timer controller (605) stores the monitoring list. The stored monitoring list is used for future reference to optimize the UE's connectivity and mobility management.

[0113] Further, the NAS timer controller (605) determines that an available and allowable PLMN selected by the UE (102) is different from the first PLMN. The determination involves evaluating the list of available PLMNs and selecting the most suitable one based on predefined criteria such as signal strength, network policies, and user preferences.

[0114] Further, the NAS timer controller (605) receives the NAS reject message including Evolved Mobility Management (EMM) cause value #83. The NAS reject message is received while the UE (102) is camped on the S&F satellite E-UTRAN cell of the PLMN. The EMM cause value #83 indicates a specific reason for the rejection, such as network congestion or service restrictions. Further, the NAS timer controller (605) starts the NAS timer T3440 in response to receiving the NAS reject message including EMM cause value #83. The timer T3440 is configured to manage the timing of subsequent NAS procedures following the rejection. Further, the NAS timer controller (605) releases the NAS signaling connection locally after the expiry of the timer T3440. The release of the NAS signaling connection involves deallocating network resources and terminating any ongoing signaling exchanges. Further, the NAS timer controller (605) releases all NAS and radio resources allocated for the NAS signaling connection after the expiry of the timer T3440. The release of resources ensures that the network can reallocate them to other UEs or services.

[0115] Further, the NAS timer controller (605) receives the NAS reject message including EMM cause value #83. The EMM cause value #83 indicates a specific reason for the rejection, such as network congestion or service restrictions. Further, the NAS timer controller (605) transmits the NAS message to the PLMN, the NAS message indicating support of S&F satellite operation by the UE (102). The transmitted NAS message may include additional parameters such as the UE's capabilities and preferences for satellite operation.

[0116] Further, the NAS timer controller (605) receives the NAS reject message. The NAS reject message is one of the Attach Reject message, the Tracking Area Update Reject message, or the Service Reject message. Each of these messages contains specific information elements that indicate the outcome of the NAS procedure and any associated reject causes.

[0117] Further, the NAS timer controller (605) receives a NAS reject message including an EMM cause value #83 and an S&F wait timer value. The EMM cause value #83 indicates a specific reason for the rejection, such as network congestion or service restrictions. Further, the NAS timer controller (605) starts the timer T3451 in response to receiving the NAS reject message including the S&F wait timer value. The timer T3451 is configured to manage the timing of subsequent NAS procedures based on the received S&F wait timer value.

[0118] Further, the NAS timer controller (605) maintains the NAS signaling connection while the timer T3440 is running prior to the expiry of the timer T3440. The maintenance of the NAS signaling connection ensures that the UE (102) remains connected to the network and can receive any subsequent messages or updates.

[0119] Further, the NAS timer controller (605) refrains from initiating any NAS signaling procedure while the timer T3451 is running. The refraining from initiating NAS procedures ensures that the UE (102) adheres to the waiting period specified by the S&F wait timer value.

[0120] Further, the NAS timer controller (605) starts the timer T3451 concurrently with the timer T3440 in response to receiving the NAS reject message including EMM cause value #83 and the S&F wait timer value. The concurrent running of both timers ensures that the UE (102) manages the timing of subsequent NAS procedures and the release of NAS signaling connections effectively.

[0121] FIG7A is the flowchart that illustrates a method for managing NAS timer T3451 and NAS Signaling Release in the UE (102) in store-and-forward satellite networks according to embodiments as disclosed herein. At step 701, the method includes receiving a NAS accept message or a NAS reject message including the S&F wait timer value or information element by the UE (102). The NAS message is received when the UE (102) is camped in an S&F satellite E-UTRAN cell of a first Public Land Mobile Network (PLMN). The S&F wait timer value is crucial for managing the timing of subsequent NAS procedures, ensuring that the UE (102) does not prematurely reattempt NAS signaling, which could lead to network congestion and inefficiencies.

[0122] At step 702, the method includes starting timer T3451 by the UE (102) in response to receiving the NAS message including the S&F wait timer value. The timer T3451 is configured to run for a predefined duration as specified by the S&F wait timer value. This timer ensures that the UE (102) waits for an appropriate period before reattempting the NAS procedure, allowing the network to stabilize and potentially resolve any issues that caused the initial NAS reject message. At step 703, the method includes performing a cell selection or a cell reselection procedure by the UE (102) resulting in the UE (102) camping on the target cell that is not an S&F satellite E-UTRAN cell. The cell selection or reselection procedure involves evaluating various parameters such as signal strength, cell priority, and network availability to determine the most suitable cell for the UE (102) to camp on. This step ensures that the UE (102) can maintain connectivity and service continuity even when transitioning between different types of cells.

[0123] At step 704, the method includes initiating a NAS procedure by the UE (102) when the timer T3451 is running and the UE (102) is camped on the target cell. The initiation of the NAS procedure involves sending a NAS message, such as an ATTACH REQUEST, to the network to establish or re-establish a connection. This step ensures that the UE (102) can continue its communication with the network while adhering to the timing constraints imposed by the S&F wait timer. At step 705, the method includes receiving a NAS accept message by the UE (102) in response to the NAS procedure, the NAS accept message indicating successful completion of the NAS procedure. The NAS accept message confirms that the network has successfully processed the UE's (102) request and that the connection has been established. This step is critical for ensuring that the UE (102) can resume normal operations and access network services.

[0124] At step 706, the method includes stopping timer T3451 by the UE (102) in response to receiving the NAS accept message. Stopping the timer T3451 indicates that the NAS procedure has been successfully completed, and there is no need for the UE (102) to wait any longer before reattempting NAS signaling. This step ensures use of network resources and prevents unnecessary delays in the UE's (102) communication with the network.

[0125] FIG7B is the flowchart that illustrates a method for managing the NAS timer in the store-and-forward satellite network according to embodiments as disclosed herein. This method focuses on handling scenarios where the NAS procedure is rejected, and the UE (102) needs to manage its timers and resources accordingly. At step 707, the method includes receiving the NAS reject message including the EMM cause value #83 by the UE (102). The NAS reject message is received when the UE (102) is camped on the S&F satellite E-UTRAN cell of the PLMN. The EMM cause value #83 indicates a specific reason for the rejection, such as network congestion or temporary unavailability of resources, which helps the UE (102) understand the context of the rejection. At step 708, the method includes starting the NAS timer T3440 by the UE (102) in response to receiving the NAS reject message including the EMM cause value #83 in the S&F satellite E-UTRAN cell. The timer T3440 is configured to run for a predefined duration, allowing the UE (102) to wait before reattempting the NAS procedure. This step ensures that the UE (102) does not immediately retry the NAS procedure, which could exacerbate network congestion and lead to further rejections.

[0126] At step 709, the method includes releasing the NAS signaling connection locally by the UE (102) after expiry of the timer T3440. Releasing the NAS signaling connection involves deallocating any resources that were reserved for the NAS procedure, freeing them up for other potential uses. This step ensures that the UE (102) can manage its resources and avoid holding onto connections that are no longer needed. At step 710, the method includes releasing all NAS and radio resources allocated for the NAS signaling connection by the UE (102) after expiry of the timer T3440. This comprehensive release of resources ensures that the UE (102) is not consuming unnecessary network resources. This step is critical for maintaining optimal network operation and preventing resource wastage.

[0127] FIG 8 is a sequence diagram that illustrates the optimized management of timer T3451 during cell transitions in a store-and-forward satellite network according to embodiments as disclosed herein. The sequence diagram provides a detailed view of the interactions between the UE (102) and various network entities during the management of timer T3451.

[0128] Further, the pre-requisite condition establishes the UE (102) as camped in the S&F satellite E-UTRAN cell of the first PLMN. Entities participating include the UE (102), the MME on-board satellite of PLMN-1 (106a), the ground network including the MME-ground (105), and the MME (101) of a non-S&F satellite E-UTRAN cell of PLMN-1 or PLMN-2. These entities work together to manage the NAS procedures and timers.

[0129] At step S1, the UE (102) initiates a NAS procedure by transmitting a NAS message to the MME on-board satellite (106a) of PLMN-1. The NAS message corresponds, for example, to an ATTACH REQUEST message. This step marks the beginning of the NAS procedure, where the UE (102) requests to establish a connection with the network. At step S2, the MME on-board satellite (106a) transmits the NAS reject message to the UE (102), for example, an ATTACH REJECT message. Further transmission of the NAS reject message occurs due to the unavailability of the feeder link between the satellite (103) and the ground network (104) for PLMN-1, thereby preventing the completion of the NAS procedure. The NAS reject message includes an S&F wait timer and optionally an S&F monitoring list. This step ensures that the UE (102) is informed of the rejection and the reason behind it, allowing it to manage its timers accordingly.

[0130] At step S3, upon reception of the NAS reject message, the UE (102) starts timer T3451 using the S&F wait timer value received from the MME on-board satellite (106a). The timer T3451 ensures that the UE (102) waits for the specified duration before reattempting the NAS procedure, preventing premature retries that could lead to further rejections. At step S4, during the operation of timer T3451, the UE (102) performs a PLMN or cell selection procedure and moves to a cell that is not the S&F satellite E-UTRAN cell belonging to either PLMN-1 or PLMN-2. This step involves evaluating various parameters to determine the most suitable cell for the UE (102) to camp on, ensuring continuous connectivity and service availability.

[0131] At step S5, in accordance with the present embodiment, the UE (102) does not stop timer T3451 upon camping in a cell that is not an S&F satellite E-UTRAN cell, even upon initiating a NAS message to PLMN-1 or PLMN-2 in the subsequent step. Timer T3451 continues to operate irrespective of cell transitions as long as the original NAS procedure for PLMN-1 remains unsuccessful. This step ensures that the UE (102) adheres to the timing constraints imposed by the S&F wait timer, preventing premature retries of the NAS procedure. At step S6, the UE (102) transmits the NAS message to the first PLMN or PLMN-1 or second PLMN or PLMN-2 through the non-S&F satellite E-UTRAN cell. This step involves sending a new NAS message to the network, attempting to establish a connection with either the original PLMN or an alternative PLMN.

[0132] At step S7, the MME (101) associated with the non-S&F satellite E-UTRAN cell of PLMN-1 or PLMN-2 transmits the NAS message to the UE (102), either accepting or rejecting the NAS procedure. This step ensures that the UE (102) receives a response to its NAS message, allowing it to proceed with the next steps based on the outcome. At step S8, the UE (102) performs the PLMN or cell selection procedure for service recovery and moves to the cell that is the S&F satellite E-UTRAN cell of PLMN-1. Upon camping on the S&F satellite E-UTRAN cell of PLMN-1, the UE (102) may not initiate any NAS message to PLMN-1 as timer T3451 remains active for PLMN-1. Continued operation of timer T3451 prevents the UE (102) from immediately retransmitting NAS messages to PLMN-1 prior to synchronization of the UE context with the ground network (104). This step ensures that the UE (102) adheres to the timing constraints and avoids premature retries of the NAS procedure.

[0133] At step S9, timer T3451 for PLMN-1 expires. The expiration of the timer indicates that the UE (102) has waited for the specified duration and can now reattempt the NAS procedure. At step S10, upon expiry of timer T3451, the UE (102) transmits a NAS message to PLMN-1 via the S&F satellite E-UTRAN cell. Transmission of the NAS message in step S10 occurs only after the expiry of timer T3451, ensuring that the NAS procedure is re-attempted only after the duration indicated by the S&F wait timer has elapsed, by which time the feeder link between the satellite (103) and the ground network (104) is expected to be available and the NAS procedure is completed successfully. This step ensures that the UE (102) reattempts the NAS procedure at an appropriate time, improving the chances of successful completion.

[0134] FIG 8 ensures that timer T3451 is not stopped upon cell transition to the non-S&F satellite E-UTRAN cell when the original NAS procedure remains unsuccessful. Further maintaining timer T3451 across cell transitions prevents premature re-attempts of the NAS procedure upon return to the S&F satellite E-UTRAN cell of PLMN-1, thereby eliminating the cycle of unnecessary NAS signaling, repeated rejection, and repeated back-off.

[0135] FIG 9 is a sequence diagram that illustrates a scenario for optimized handling of timer T3451 expiry when the UE (102) is camped in a non-S&F satellite E-UTRAN cell according to embodiments disclosed herein. This scenario focuses on managing the timer T3451 when the UE (102) is in a non-S&F satellite E-UTRAN cell. Further, the pre-requisite condition establishes the UE (102) as camped in the non-S&F satellite E-UTRAN cell of PLMN-1. Entities participating in the scenario include the UE (102), the MME on-board satellite of PLMN-1 (106a), the ground network including the MME-ground (105), and the MME of a non-S&F satellite E-UTRAN cell of PLMN-1 or PLMN-2 (201). These entities work together to manage the NAS procedures and timers.

[0136] At Step S1, the UE (102) initiates the NAS procedure by transmitting the NAS message to the MME on-board satellite (106a) of PLMN-1. The NAS message corresponds, for example, to an ATTACH REQUEST message. This step marks the beginning of the NAS procedure, where the UE (102) requests to establish a connection with the network. At Step S2, the MME on-board satellite (106a) transmits a NAS reject message to the UE (102), for example, an ATTACH REJECT message. Transmission of the NAS reject message occurs due to the unavailability of the feeder link between the satellite (103) and the ground network (104) for PLMN-1, thereby preventing the completion of the NAS procedure. The NAS reject message includes an S&F wait timer and optionally an S&F monitoring list. This step ensures that the UE (102) is informed of the rejection and the reason behind it, allowing it to manage its timers accordingly.

[0137] At Step S3, upon reception of the NAS reject message, the UE (102) starts timer T3451 using the S&F wait timer value received from the MME on-board satellite (106a). The timer T3451 ensures that the UE (102) waits for the specified duration before reattempting the NAS procedure, preventing premature retries that could lead to further rejections. At Step S4, during the operation of timer T3451, the UE (102) performs a PLMN or cell selection procedure and moves to a non-S&F satellite E-UTRAN cell belonging to PLMN-1, PLMN-2, or any other PLMN. This step involves evaluating various parameters to determine the most suitable cell for the UE (102) to camp on, ensuring continuous connectivity and service availability.

[0138] At Step S5, following the cell move, the UE (102) initiates no NAS signaling, for example, because the selected cell or tracking area is forbidden and hence may not stop timer T3451 as per 3GPP TS 24301. This step ensures that the UE (102) adheres to the timing constraints imposed by the S&F wait timer, preventing premature retries of the NAS procedure. At Step S6, the UE (102) remains camped in the current non-S&F satellite E-UTRAN cell with timer T3451 continuing to operate. Further PLMN or cell selection procedures do not result in the UE (102) finding an alternative PLMN or cell, and the UE (102) continues to remain camped in the non-S&F satellite E-UTRAN cell. This step ensures that the UE (102) maintains connectivity and service availability while adhering to the timing constraints.

[0139] At Step S7, timer T3451 expires while the UE (102) remains camped in the non-S&F satellite E-UTRAN cell. The expiration of the timer indicates that the UE (102) has waited for the specified duration and can now reattempt the NAS procedure. At Step S8, upon expiry of timer T3451 while camped in a non-S&F satellite E-UTRAN cell, the UE (102) does not act on the timer expiry and performs usual PLMN selection, cell selection, or cell re-selection. This step ensures that the UE (102) continues to manage its connectivity and service availability, adhering to the timing constraints and avoiding premature retries of the NAS procedure.

[0140] FIG. 9 illustrates the behavior of the UE (102) upon expiry of timer T3451 when the UE (102) is camped in the non-S&F satellite E-UTRAN cell. Expiry of timer T3451 under such a condition does not trigger any S&F-specific action at the UE (102), and the UE (102) performs usual PLMN selection, cell selection, or cell re-selection to find a suitable cell or PLMN for service.

[0141] FIG. 10 is a sequence diagram illustrating optimized management of timer T3451 upon reception of a NAS accept message when the UE (102) is camped in the non-S&F satellite E-UTRAN cell according to embodiments disclosed herein. Further, a pre-requisite condition establishes the UE (102) as camped in the S&F satellite E-UTRAN cell of PLMN-1. Entities participating include the UE (102), the MME on-board satellite of PLMN-1 (106a), the ground network including the MME-ground (105), and the MME (101) of a non-S&F satellite E-UTRAN cell of PLMN-1 or PLMN-2.

[0142] At step S1, the UE (102) initiates the NAS procedure by transmitting the NAS message to the MME on-board satellite (106a) of the first PLMN or PLMN-1. The NAS message corresponds, for example, to an ATTACH REQUEST message. At step S2, the MME on-board satellite (106a) transmits the NAS reject message to the UE (102), for example, an ATTACH REJECT message. Transmission of the NAS reject message occurs due to the unavailability of the feeder link between the satellite (103) and the ground network (104) for PLMN-1, thereby preventing completion of the NAS procedure. The NAS reject message includes an S&F wait timer and optionally an S&F monitoring list.

[0143] At step S3, upon reception of the NAS reject message, the UE (102) starts timer T3451 using the S&F wait timer value received from the MME on-board satellite (106a). At step S4, during operation of timer T3451, the UE (102) performs the PLMN or cell selection procedure and moves to a cell that is not the S&F satellite E-UTRAN cell belonging to either PLMN-1 or PLMN-2. At step S5, the UE (102) does not stop timer T3451 upon camping in a cell that is not an S&F satellite E-UTRAN cell, even upon initiating a NAS message to PLMN-1 or PLMN-2 in the subsequent step. Timer T3451 continues to operate irrespective of cell transitions as long as the original NAS procedure for PLMN-1 remains unsuccessful.

[0144] At step S6, the UE (102) transmits a NAS message to PLMN-1 or PLMN-2 through the non-S&F satellite E-UTRAN cell. At step S7, the MME (101) associated with the non-S&F satellite E-UTRAN cell of PLMN-1 or PLMN-2 accepts the NAS procedure and transmits a NAS accept message to the UE (102). At step S8, upon reception of the NAS accept message, the UE (102) stops timer T3451 for PLMN-1. Stoppage of timer T3451 occurs upon successful completion of the NAS procedure in the non-S&F satellite E-UTRAN cell, confirming that the NAS procedure has been successfully completed and that continued operation of timer T3451 for the PLMN-1 is no longer required.

[0145] Further, FIG. 10 ensures that timer T3451 is stopped only upon confirmed successful completion of the NAS procedure through reception of a NAS accept message. Irrespective of the cell in which the NAS procedure is completed, stoppage of timer T3451 upon reception of the NAS accept message in the non-S&F satellite E-UTRAN cell ensures that upon a subsequent return of the UE (102) to the S&F satellite E-UTRAN cell of PLMN-1, the UE (102) initiates NAS signaling immediately without observing any further wait for the remaining duration of timer T3451 for PLMN-1 as the NAS procedure has already been successfully completed.

[0146] In an embodiment, optimized management of timer T3451 during cell transitions in the store-and-forward satellite network is achieved through the following combination of steps implemented at the UE (102). In an embodiment, when timer T3451 is running at the UE (102) for a serving PLMN, for example, PLMN-1, and the UE (102) camps in a different cell of the serving PLMN or in the cell belonging to a PLMN other than the serving PLMN, and the cell on which the UE (102) camps is not an S&F satellite E-UTRAN cell, the following behavior applies at the UE (102). When a NAS procedure, for example, an Attach procedure, the Tracking Area Update procedure, or a Service Request procedure, fails after the UE (102) moves to the new cell and the UE (102) receives the NAS reject message, for example, an ATTACH REJECT message, the TRACKING AREA UPDATE REJECT message, or the SERVICE REJECT message, the UE (102) continues to run timer T3451. When a NAS procedure succeeds and the UE (102) receives the NAS accept message, for example, an ATTACH ACCEPT message, the TRACKING AREA UPDATE ACCEPT message, or a SERVICE ACCEPT message, the UE (102) stops timer T3451.

[0147] In an embodiment, when the NAS procedure fails after the UE (102) moves to the new cell and the UE (102) receives a NAS reject message carrying a specific cause value, for example, cause value #3 or cause value #6, resulting in the USIM of the UE (102) being marked as invalid for Evolved Packet System (EPS) services or non-EPS services, the UE (102) stops timer T3451. In an embodiment, when a NAS procedure fails and the UE (102) receives a NAS reject message carrying cause value #11 or cause value #15 together with an Extended EMM cause information element carrying the value "Satellite E-UTRAN not allowed in PLMN," resulting in the PLMN being marked as a forbidden PLMN or satellite E-UTRAN access being disabled, the UE (102) stops timer T3451 or continues to run timer T3451.

[0148] In an embodiment, when timer T3451 expires and the UE (102) is camped in a cell that is not an S&F satellite E-UTRAN cell, the UE (102) ignores the timer expiry and performs no action upon the timer expiry. In an embodiment, the UE (102) stores information identifying the specific cell, tracking area, or PLMN for which timer T3451 was started. Upon the UE (102) returning to the same cell, the same tracking area, or the same S&F satellite E-UTRAN cell of the PLMN for which timer T3451 is started, the UE (102) initiates NAS signaling immediately upon camping in the cell as timer T3451 has already expired for such PLMN.

[0149] In an embodiment, when timer T3451 is running at the UE (102) for a serving PLMN, for example, PLMN-1, and the UE (102) camps in a different cell of the serving PLMN or in a cell belonging to a PLMN other than the serving PLMN, and the cell on which the UE (102) camps is not an S&F satellite E-UTRAN cell, the UE (102) continues to run timer T3451 for the serving PLMN. Upon the UE (102) camping back in an S&F satellite E-UTRAN cell of the PLMN for which timer T3451 was running, the UE (102) does not initiate any NAS signaling until expiry of timer T3451. Upon expiry of timer T3451, the UE (102) initiates the NAS signaling in the PLMN via the S&F satellite E-UTRAN cell.

[0150] In an embodiment of the present invention, the UE (102) starts timer T3440 upon reception of the NAS reject message carrying EMM cause code #83 and releases the NAS signaling connection together with all associated NAS and radio resources upon expiry of timer T3440.

[0151] FIG. 11 is a sequence diagram that illustrates optimized handling of a NAS signaling connection upon reception of EMM cause code #83 during S&F satellite operation according to embodiments disclosed herein. Further, the pre-requisite condition for the illustrated embodiment establishes the UE (102) as camped in the S&F satellite E-UTRAN cell of PLMN-1. Further entities participating in the illustrated embodiment include the UE (102), the E-NodeB and MME on-board satellite of PLMN-1 (106a), the ground network including the MME-ground (105), and the E-NodeB and MME on-board satellite of PLMN-2 (106b).

[0152] At step S1, the UE (102) initiates the NAS procedure by transmitting the NAS message to the E-NodeB and MME on-board satellite of PLMN-1 (106a), for example, the ATTACH REQUEST message. The NAS message includes an indication of support for S&F satellite operation by the UE (102). At step S2, the E-NodeB and MME on-board satellite (106a) transmits the NAS reject message to the UE (102), for example, an ATTACH REJECT message. The NAS reject message includes EMM cause code #83 indicating that the NAS procedure may not be completed due to unavailability of the feeder link while the MME on-board satellite (106a) operates in the S&F mode. The NAS reject message further includes an S&F wait timer and optionally an S&F monitoring list.

[0153] At step S3, upon reception of the NAS reject message carrying the EMM cause code #83, the UE (102) starts timer T3451 using the S&F wait timer value received from the E-NodeB and MME on-board satellite (106a). Further, the UE (102) additionally starts timer T3440 upon reception of the NAS reject message carrying EMM cause code #83 to allow the network to release the NAS signaling connection. Timer T3440 operates for a duration as defined in 3GPP TS 24301.

[0154] At step S4, following transmission of the NAS reject message, the NAS signaling connection is not released by the E-NodeB and MME on-board satellite (106a), and the NAS signaling connection established for the NAS procedure remains active. At step S5, during the period in which timer T3451 remains active, the UE (102) may not initiate any NAS procedure in accordance with existing specifications defined in 3GPP TS 24301. At step S6, upon expiry of timer T3440, the UE (102) releases the NAS signaling connection locally and releases all NAS and radio resources reserved for the NAS signaling connection. Local release of the NAS signaling connection upon expiry of timer T3440 ensures that resources allocated at the UE (102) are no longer retained unnecessarily for the remaining active duration of timer T3451.

[0155] At step S7, timer T3451 expires. At step S8, upon expiry of timer T3451, the UE (102) re-attempts the NAS procedure by transmitting a NAS message to the E-NodeB and MME on-board satellite (106a) of PLMN-1. In an embodiment, the UE (102) starts timer T3440 upon reception of a NAS message carrying EMM cause code #83, the NAS message being a NAS accept message or a NAS reject message for a duration as defined in 3GPP TS 24301. Upon expiry of timer T3440, the UE (102) releases the NAS signaling connection locally together with all NAS and radio resources reserved for the NAS signaling connection, thereby avoiding unnecessary retention of idle resources at the UE (102) and in the network during the active period of timer T3451.

[0156] In an embodiment of the present disclosure, upon reception of a NAS message carrying EMM cause code #83, the NAS message is a NAS accept message or a NAS reject message, the UE (102) starts timer T3440 for a duration as defined in 3GPP TS 24301. Upon expiry of timer T3440, the UE (102) releases the NAS signaling connection locally. Local release of the NAS signaling connection upon expiry of timer T3440 ensures that resources are not unnecessarily reserved at the UE (102) and in the network, thereby conserving battery life of the UE (102).

[0157] FIG. 12 is a sequence diagram that illustrates optimized handling of timer T3448 upon reception of downlink user data via the control plane according to embodiments disclosed herein. Further, the pre-requisite condition for the illustrated embodiment establishes the UE (102) as camped in the S&F satellite E-UTRAN cell of the PLMN-1 (first PLMN). Entities participating in the illustrated embodiment include the UE (102) and the MME (101).

[0158] At step S1, the UE (102) initiates the NAS procedure by transmitting the NAS message to the MME (101), for example, an ATTACH REQUEST message. The NAS message includes an indication of support for the control plane data back-off timer by the UE (102). At step S2, the MME (101) transmits the NAS message to the UE (102) carrying cause code #22 and a non-zero value of timer T3448 due to congestion in the transport of user data via the control plane.

[0159] At step S3, upon reception of the NAS message from the MME (101), the UE (102) starts timer T3448 based on the timer value received from the MME (101). At step S4, following resolution of congestion in the network, the MME (101) transmits the NAS message to the UE (102), for example, an ESM DATA TRANSPORT message corresponding to transmission of user data in the downlink direction to the UE (102) via the control plane. At step S5, upon reception of the ESM DATA TRANSPORT message from the MME (101), the UE (102) stops timer T3448. Reception of the ESM DATA TRANSPORT message is interpreted by the UE (102) as an indication that congestion for user data transport over the control plane has ended in the network.

[0160] At step S6, upon stopping timer T3448, the UE (102) transmits user data over the control plane without waiting for any additional duration of time. In an embodiment, upon reception of a downlink NAS message, for example, an ESM DATA TRANSPORT message from the MME (101) while timer T3448 is active, the UE (102) interprets the downlink user data transmission via the control plane as an indication that congestion for user data transport over the control plane has ended. Further, the UE (102) stops timer T3448 upon such reception and initiates user data transport via the control plane without waiting for expiry of timer T3448. This is applicable to the UE (102) accessing an Evolved Packet Core via a terrestrial cell, via a satellite E-UTRAN cell, and via an S&F satellite E-UTRAN cell.

[0161] In an embodiment of the present disclosure, the UE (102) behavior is optimized as follows: When the UE (102) indicates support for the control plane data back-off timer, the UE (102) stops timer T3448 upon reception of an ESM DATA TRANSPORT message, that is, upon reception of user data via the control plane. This ensures that the UE (102) resumes data transport as soon as congestion is resolved, improving the user experience.

[0162] In an embodiment of the present disclosure, the UE (102), which has indicated support for S&F satellite operation, starts timer T3440 upon receiving an EMM cause value #83. Upon expiry of timer T3440, the UE (102) releases the NAS signaling connection locally. In an embodiment, the UE (102), which has indicated support for the control plane data back-off timer, stops timer T3448 if running upon reception of an ESM DATA TRANSPORT message carrying user data via the control plane.

[0163] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and / or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the scope of the embodiments as described herein.

Claims

1.A method of a user equipment (UE), the method comprising:receiving an ATTACH REJECT message associated with a first PLMN, wherein the ATTACH reject message is related to store and forward (S&F) satellite evolved universal mobile telecommunications system terrestrial radio access network (E-UTRAN);starting a timer based on a value of S&F wait time duration;performing an attach procedure related to a cell associated with a second PLMN;stopping the timer in case that the attach procedure is successfully performed.2.The method of claim 1, wherein the cell is not a S&F satellite E-UTRAN cell.3.The method of claim 1, wherein the second PLMN is different with the first PLMN.4.The method of claim 1, wherein the ATTACH REJECT message includes the value of S&F wait time duration.5.A method of a mobility management entity (MME), the method comprising:transmitting an ATTACH REJECT message associated with a first PLMN, wherein the ATTACH reject message is related to store and forward (S&F) satellite evolved universal mobile telecommunications system terrestrial radio access network (E-UTRAN);performing an attach procedure related to a cell associated with a second PLMN;wherein a timer is started based on a value of S&F wait time duration;wherein the timer is stopped in case that the attach procedure is successfully performed.6.The method of claim 1, wherein the cell is not a S&F satellite E-UTRAN cell.7.The method of claim 1, wherein the second PLMN is different with the first PLMN.8.The method of claim 1, wherein the ATTACH REJECT message includes the value of S&F wait time duration.9.A user equipment (UE), comprising:a memory;a processor; anda controller coupled to the memory and the processor, wherein the controller is configured to:receive an ATTACH REJECT message associated with a first PLMN, wherein the ATTACH reject message is related to store and forward (S&F) satellite evolved universal mobile telecommunications system terrestrial radio access network (E-UTRAN),start a timer based on a value of S&F wait time duration,perform an attach procedure related to a cell associated with a second PLMN, andstop the timer in case that the attach procedure is successfully performed.10.The method of claim 1, wherein the cell is not a S&F satellite E-UTRAN cell.11.The method of claim 1, wherein the second PLMN is different with the first PLMN.12.The method of claim 1, wherein the ATTACH REJECT message includes the value of S&F wait time duration.13.A mobility management entity (MME), comprising:a memory;a processor; anda controller coupled to the memory and the processor, wherein the controller is configured to:transmit an ATTACH REJECT message associated with a first PLMN, wherein the ATTACH reject message is related to store and forward (S&F) satellite evolved universal mobile telecommunications system terrestrial radio access network (E-UTRAN), andperform an attach procedure related to a cell associated with a second PLMN,wherein a timer is started based on a value of S&F wait time duration,wherein the timer is stopped in case that the attach procedure is successfully performed.14.The method of claim 1, wherein the cell is not a S&F satellite E-UTRAN cell.15.The method of claim 1, wherein the second PLMN is different with the first PLMN.

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