Handling forbidden PLMN list on expiry of t3245 or t3247 for disaster roaming

Abstract

The disclosure relates to a 5G or 6G communication system for supporting a higher data transmission rate. Embodiments disclosed herein describe a method and a user equipment (UE) (200) for handling of forbidden public land mobile network (FPLMN) list on expiry of T3245 or T3247 for disaster roaming. The method involves the UE (200) registering for the disaster roaming services on a first PLMN (250) and the UE (200) detects whether the T3245 timer or T3247 timer is expired. Further, the UE (200) retains the first PLMN (250) in a FPLMN list or retaining the FPLMN list when a T3245 timer or a T3247 timer is expired, such that the UE (200) does not remove the first PLMN (250) from the FPLMN list or the UE (200) does not erase the FPLMN list. This invention enhances the UE's (200) ability to maintain connectivity and access to disaster roaming services, thereby improving communication reliability during emergency situations.

Description

HANDLING FORBIDDEN PLMN LIST ON EXPIRY OF T3245 OR T3247 FOR DISASTER ROAMING

[0001] The present disclosure relates to a wireless communication and more specifically relates to handling of Forbidden Public Land Mobile Network (FPLMN) list on expiry of T3245 or T3247 for disaster roaming.

[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 principal object of the present disclosure herein is to provide a method and a UE for handling the FPLMN list on expiry of T3245 or T3247 for disaster roaming.

[0009] Another object of the present disclosure herein is to provide a method when the UE is registered for disaster roaming services, the UE should not remove the PLMN (i.e., UE retains the PLMN in the FPLMN list or retain FPLMN list) where it is registered for the disaster roaming service on the expiry of the T3245 timer.

[0010] Yet another object of the present disclosure herein is to provide a method when the UE is registered for disaster roaming services, the UE should not remove the PLMN (i.e., UE retains the PLMN in the FPLMN list) where it is registered for the disaster roaming service on the expiry of the T3247 timer.

[0011] Yet another object of the present disclosure herein is to provide a method that UE deletes the forbidden PLMN-1 from the forbidden PLMN list upon determining that the disaster condition has ended.

[0012] In an aspect, the objects are achieved by providing a method for handling PLMNs in a UE during disaster roaming services. The method includes registering by the UE for the disaster roaming services on a first PLMN and detecting whether the T3245 timer or T3247 timer has expired. Further, the method includes retaining the first PLMN in an FPLMN list or retaining the FPLMN list when a T3245 timer or a T3247 timer has expired such that the UE does not remove the first PLMN from the FPLMN list or the UE does not erase the FPLMN list.

[0013] In another aspect, the objects are achieved by providing a UE for handling PLMNs during disaster roaming services. The UE includes a memory, a processor, and a PLMN controller connected to the memory and the processor. The PLMN controller registers the UE for the disaster roaming services on a first PLMN and detects whether the T3245 timer or T3247 timer has expired. Further, the PLMN controller retains the first PLMN in an FPLMN list retains the FPLMN list when a T3245 timer or a T3247 timer has expired such that the UE does not remove the first PLMN from the FPLMN list or UE does not erase the FPLMN list.

[0014] These and other aspects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating preferred embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein, and the embodiments herein include all such modifications.

[0015] According to the present disclosure, ensured service continuity is provided by enabling the UE to retain the PLMN in the FPLMN list, or retain the FPLMN list itself, when the UE is registered for disaster roaming service.

[0016] Furthermore, according to the present disclosure, a comprehensive and reliable management capability for disaster roaming is provided by deleting the PLMN from the list or erasing the FPLMN list only upon determining that the disaster condition has ended.

[0017] The invention is illustrated in the accompanying drawings, where like reference letters indicate corresponding parts. The embodiments will be better understood from the following description with reference to the drawings.

[0018] FIG. 1 is a sequence diagram that illustrates an existing method of handling the FPLMN list on the expiry of T3245 or T3247 for disaster roaming services according to the prior art.

[0019] FIG. 2 is a block diagram that illustrates the hardware components associated with the UE according to the embodiments as disclosed herein.

[0020] FIG. 3 is a flow diagram that illustrates a proposed method for handling PLMNs in a UE during disaster roaming services according to the embodiments as disclosed herein.

[0021] FIG. 4 is a sequence diagram that illustrates a proposed method of handling the FPLMN list on the expiry of T3245 or T3247 for disaster roaming where the PLMN-1 is removed from the FPLMN list and the UE enters the DEREGISTERED PLMN_SEARCH state according to the embodiments as disclosed herein.

[0022] FIG. 5 is a sequence diagram that illustrates a proposed method of handling the FPLMN list on the expiry of T3245 or T3247 for disaster roaming services where the PLMN-1 is retained in the FPLMN list or FPLMN list is retained and the UE remains registered for disaster roaming services according to the embodiments as disclosed herein.

[0023] FIG. 6 is a sequence diagram that illustrates a method of handling the FPLMN list on the expiry of T3245 or T3247 for disaster roaming where the PLMN-1 is removed from the FPLMN list and the UE remains registered for disaster roaming services according to the embodiments as disclosed herein.

[0024] The embodiments and their features are detailed with reference to the non-limiting examples shown in the drawings and described below. Well-known components and techniques are omitted to avoid unnecessary detail. The described embodiments are not mutually exclusive and can be combined to form new embodiments. The term "or" is used in a non-exclusive sense unless stated otherwise. The examples provided are for illustrative purposes to aid understanding and should not be seen as limiting the scope of the embodiments.

[0025] As is known in the field, embodiments can be described and illustrated in terms of blocks which carry out a described function or functions.　These blocks, which can be 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 can optionally be driven by firmware and software. The circuits may, 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 can 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 can be physically separated into two or more interacting and discrete blocks without departing from the scope of the disclosure.　Likewise, the blocks of the embodiments can be physically combined into more complex blocks without departing from the scope of the disclosure.

[0026] The accompanying drawings aid in understanding the technical features, but the embodiments are not limited to these drawings. The disclosure extends to any alterations, equivalents, and substitutes beyond those shown. Terms like first, second, etc., are used for distinction and do not limit the elements.

[0027] In modern telecommunications, ensuring continuous service availability is critical, especially during disaster conditions. To address this need, the concept of Minimization of Service Interruption (MINT) has been developed. MINT aims to enable User Equipment (UE) to obtain service from a Public Land Mobile Network (PLMN) offering disaster roaming services when a disaster condition affects the UE's home PLMN (HPLMN) or visited PLMNs. This functionality is crucial to maintain communication capabilities for users in disaster-stricken areas.

[0028] The MINT service is designed to allow UEs to receive service from alternative PLMNs, particularly those prepared to offer disaster roaming services. However, this service is constrained by specific time and location parameters. One of the key challenges is to minimize the impact on the 5G System and Evolved Packet System (EPS) due to potential congestion caused by the influx or outflux of Disaster Inbound Roamers.

[0029] When a UE loses coverage from its HPLMN or visited PLMN and receives information that a disaster condition applies to its HPLMN or visited PLMN, it can register with a PLMN offering disaster roaming services. The 3rd Generation Partnership Project (3GPP) system supports mechanisms that allow a PLMN operator to be aware of the areas affected by disaster conditions. It also facilitates the provision of services to Disaster Inbound Roamers within these specific regions.

[0030] The 3GPP system includes efficient means for networks to inform disaster inbound roamers when a disaster condition is no longer applicable. Additionally, it provides mechanisms to enable UEs to access PLMNs listed in their forbidden PLMN list when a disaster condition applies, and no other PLMN is available. The system supports disaster condition functionality that allows UEs to obtain information about a disaster condition affecting a specific PLMN, informs PLMN operators of affected areas, and enables Disaster Inbound Roamers to receive services within those regions. It also includes mechanisms for informing UEs when a disaster condition ends and aims to minimize congestion from disaster roaming. Furthermore, the system enables UEs to access PLMNs on their forbidden list during a disaster condition if no other PLMNs are available, and it includes charging information specific to Disaster Inbound Roamers.

[0031] Despite these advancements, existing mechanisms have limitations. The UE can avail MINT service only when a disaster condition has occurred, and no other PLMN is available except for those in the forbidden PLMN list. The forbidden list on the UE is managed by two timers, T3245 and T3247, which are initiated when a PLMN is added to the forbidden list. Upon the expiration of these timers, the forbidden list is cleared. However, the current 3GPP specification does not explicitly define the behaviour of a UE registered for disaster roaming when these timers expire.

[0032] Thus, it is desired to address the above-mentioned disadvantages or other shortcomings or at least provide a useful alternative.

[0033] Throughout the specification, the definitions of the various terms used in the embodiments are as follows:

[0034] Disaster Roaming: This is the special roaming policy that applies during a Disaster Condition.

[0035] Disaster Condition: This is the condition that a government decides when to initiate and terminate, e.g., a natural disaster. When this condition applies, users may have the opportunity to mitigate service interruptions and failures.

[0036] Disaster Inbound Roamer: A user that (a) cannot get service from the PLMN it would normally be served by due to failure of service during a Disaster Condition and (b) is able to register with other PLMNs (i.e. is able to register on the forbidden PLMN(s)). The UE selects PLMN to get the disaster roaming services as specified in TS 23.122 when the UE is unable to find the suitable PLMN and found the forbidden PLMN where disaster roaming services can be obtained.

[0037] Minimization of Service Interruption (MINT): It is a feature that aims to enable a UE to obtain service from a PLMN offering disaster roaming services when a disaster condition applies to the UE's determined PLMN with disaster condition.

[0038] Registered for Disaster Roaming Services: A UE is considered as "registered for disaster roaming services" when it has successfully completed initial registration or mobility registration for disaster roaming services.

[0039] Initial Registration for Disaster Roaming Services: A registration performed with 5GS registration type "disaster roaming initial registration" in the REGISTRATION REQUEST message.

[0040] Mobility Registration for Disaster Roaming Services: A registration performed with 5GS registration type "disaster roaming mobility registration updating" in the REGISTRATION REQUEST message.

[0041] The UE registered for the disaster roaming services determines that disaster condition has ended if (some of the conditions, other condition is also possible):

[0042] - the UE has successfully registered over non-3GPP access on a PLMN;

[0043] - the UE has successfully registered with an allowable PLMN;

[0044] - the UE is not registered for disaster roaming services and an NG-RAN cell selected for camping of the selected PLMN broadcasts neither the disaster related indication nor a "list of one or more PLMN(s) with disaster condition for which disaster roaming services is offered by the available PLMN" including the MS determined PLMN with disaster condition; or

[0045] - the UE is registered for disaster roaming services receives cause value #11 "PLMN not allowed" or #13 "Roaming not allowed in this tracking area" during a registration procedure for mobility registration update or a service request procedure or receives cause value #11 "PLMN not allowed" during a network-initiated de-registration procedure.

[0046] The current art includes timers T3245 and T3247, which are utilized in specific scenarios involving User Equipment (UE). Timer T3247 is particularly relevant when the UE receives non-integrity protected reject messages.

[0047] When the UE receives a REGISTRATION REJECT or SERVICE REJECT message without integrity protection, and the 5GMM cause value is #3, #6, #7, #11, #12, #13, #15, #27, #31, #62, #72, or #73, before the network has established a secure exchange of NAS messages for the N1 NAS signaling connection, specific actions are required. The UE must stop timer T3510 or T3517 if either is running. Subsequently, the UE must start timer T3247.

[0048] Timer T3247 is initiated with a random value uniformly drawn from the range between 30 minutes and 60 minutes, as specified in 3GPP TS 24008

[0012] . Upon expiry of timer T3247, the UE shall: for each PLMN-specific attempt counter that has a value greater than zero and less than a UE implementation-specific maximum value, remove the respective PLMN from the extension of the "forbidden PLMNs" list.

[0049] T3245: 5.3.19a.1 UE not operating in SNPN access operation mode.

[0050] When the UE adds a PLMN identity to the "forbidden PLMN list" or sets the USIM as invalid for 5GS services for 3GPP access or non-3GPP access, and timer T3245 (see 3GPP TS 24.008

[0012] ) is not running, the UE shall start timer T3245 as specified in 3GPP TS 24.008

[0012] , subclause

[0051] 4.1.1.6. Upon expiry of the timer T3245, the UE shall erase the "forbidden PLMN list" and "forbidden PLMNs for GPRS service" list and set the USIM to valid for 5GS services for 3GPP access and non-3GPP access. When the lists are erased, the UE performs cell selection according to 3GPP TS 38.304

[0028] or 3GPP TS 36.304 [25C].

[0052] FIG. 1 is a sequence diagram that illustrates an existing method of handling the FPLMN list on expiry of T3245 or T3247 for disaster roaming services according to the prior art. The PLMN-1 (150) is part of the FPLMN list; UE (100) determines that disaster condition occurred, and the PLMN-1 is available which can provide the disaster roaming services (UE (100) can only receive disaster roaming service on FPLMNs). The UE (100) selects a PLMN (e.g., PLMN-1) for disaster roaming services. The UE (100) registers with PLMN-1 (150) to receive disaster roaming services. At the timer T3245 expiry or T3247 expiry the PLMN-1 (150) may no longer as forbidden PLMN. The UE (100) behavior is not defined in the existing methods after the expiry of the T3245 timer or T3247 timer. As per the current state of art as the PLMN-1 (150) is no longer a forbidden PLMN so disaster roaming service(s) has to be stopped / ended (as the UE (100) is allowed to receive disaster roaming service on the forbidden PLMNs only).

[0053] Embodiments disclosed herein provide a method and a UE for handling the FPLMN list on expiry of T3245 or T3247 for disaster roaming. The method includes when the T3245 or T3247 expires when the UE is registered for disaster roaming services, the UE removes a PLMN ID from the FPLMN list, and the UE initiates the detach / deregistration procedure over 3GPP access in which the UE is currently registered for disaster roaming (e.g., to deregister from disaster roaming services) and enters 5GMM-DEREGISTERED_PLMN_SEARCH state and performs PLMN selection, cell selection, or cell reselection procedures. In an embodiment, the FPLMN should be retained in the list even after T3245 or T3247 expiry when the UE is registered for disaster roaming service. In an embodiment, when PLMN is removed from the FPLMN list due to T3245 or T3247 expiry, the UE can continue to remain registered for disaster roaming service. The UE continues to consider the PLMN as FPLMN though the PLMN is not part of the FPLMN list.

[0054] Referring now to the drawings, and more particularly to FIGS. 2 through 6, there are shown preferred embodiments.

[0055] FIG. 2 is a block diagram that illustrates the hardware components associated with the UE (200) according to the embodiments as disclosed herein. As illustrated, the UE (200) includes a processor (201), a memory (202), a communicator (203), and a PLMN controller (204).

[0056] Examples of the UE (200) 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.).

[0057] The processor (201) is responsible for handling PLMNs in a UE during disaster roaming services. The processor (201) communicates with the memory (202), the communicator (203), and the PLMN controller (204). The processor (201) is configured to execute instructions stored in the memory (202) and to handle the FPLMN list on the expiry of T3245 or T3247 for disaster roaming. The processor (201) may include one or a plurality of processors, maybe 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).

[0058] The memory (202) stores the operating system, application software, and temporary data used by the processor (201). The memory (202) is not limited to a volatile memory and / or a non-volatile memory. Further, the memory (202) may include a plurality of computer-readable storage media. The memory (202) may include non-volatile storage elements. For example, non-volatile storage elements may include magnetic hard disks, optical disks, floppy disks, flash memories, or forms of electrically programmable memories (EPROM) or electrically erasable and programmable (EEPROM) memories.

[0059] The memory (202) stores the operating system, application software, and temporary data used by the processor (201). The memory (202) stores instructions to be executed by the processor (201). The memory (202) may include non-volatile storage elements. Examples of such non-volatile storage elements may include magnetic hard disks, optical disks, floppy disks, flash memories, or forms of EPROM or EEPROM memories. In addition, the memory (202) may in some examples be considered a non-transitory storage medium. The term non-transitory may indicate that the storage medium is not embodied in a carrier wave or a propagated signal. However, the term non-transitory should not be interpreted that the memory (202) is non-movable. The memory (202) stores the FPLMN list, which includes one or more of list of forbidden PLMNs and / or the list of forbidden PLMNs for General Packet Radio Service (GPRS) and / or extension of the forbidden PLMNs list or a combination of them.

[0060] The communicator (203) facilitates communication between the UE (200) and the PLMN-1 (250), supporting various communication protocols such as Transmission Control Protocol / Internet Protocol (TCP / IP), User Datagram Protocol (UDP), and second generation Digital Video Broadcasting by Satellite (DVB-S2). Further, the communicator (203) is configured for communicating internally between internal hardware components via one or more networks. The communicator (203) includes an electronic circuit specific to a standard that enables wired or wireless communication. The communicator (203) facilitates retaining the first PLMN (250) in a FPLMN list when a T3245 timer or a T3247 timer is expired such that the UE (200) does not remove the first PLMN (250) from the FPLMN.

[0061] In an embodiment, the PLMN controller (204) is a hardware component engineered to manage the FPLMN list on expiry of T3245 or T3247 for disaster roaming. This hardware implementation ensures efficient and reliable execution of processes integral to maintaining the PLMNs in a UE (200) during disaster roaming services.

[0062] The PLMN controller (204) features an innovative integrated circuit structure with a multi-core architecture tailored to optimize the handling of PLMNs in the UE (200) during disaster roaming services. Each core within the architecture is specifically designed to execute distinct functions. For instance, one core is responsible for registering the UE (200) for the disaster roaming services on a first PLMN (250). Another core handles the retention of the first PLMN (250) in a FPLMN list when a T3245 timer or a T3247 timer is expired. Additional cores manage tasks such as determining whether a disaster condition has ended and finding another PLMN which provides a normal service. This hardware-centric approach not only ensures the technical robustness of the system but also highlights the structural and functional innovation embedded within the PLMN controller (204). The multi-core design and task-specific optimizations demonstrate a technical contribution to the field of wireless communication during disaster roaming services, meeting the requirements of Section 3(k) of the Patents Act by showcasing a tangible and inventive technical advancement.

[0063] In an embodiment, the PLMN controller (204) registers the UE (200) for the disaster roaming services on a first PLMN (250) and detects whether the T3245 timer or T3247 timer is expired. The PLMN controller (204) then retains the first PLMN (250) in a FPLMN list or retains the FPLMN list when a T3245 timer or a T3247 timer is expired such that the UE (200) does not remove the first PLMN (250) from the FPLMN list or the UE (200) does not erase the FPLMN list. The FPLMN list includes one or more of forbidden PLMNs and / or the list of forbidden PLMNs for GPRS and / or extension of the forbidden PLMNs list or a combination of them.

[0064] In an embodiment, the PLMN controller (204) determines whether a disaster condition has ended or finds another allowable PLMN which provides a normal service and deletes a first PLMN (250) from the FPLMN list or erasing FPLMN list when the disaster condition has ended or finds another PLMN (allowable PLMN) which provides the normal service and the first PLMN (250) is not removed from FPLMN list or FPLMN list is not erased at the T3247 or T3245 timer expiry.

[0065] In an embodiment, the PLMN controller (204) erases the "forbidden PLMN list" and "forbidden PLMNs for GPRS service" list based on the determination that the UE (200) is not registered for the disaster roaming services and timer T3245 has expired. The PLMN controller (204) then performs cell selection in response to deleting the "forbidden PLMN list" and "forbidden PLMNs for GPRS service" list.

[0066] In an embodiment, the PLMN controller (204) removes the respective PLMN from the extension of the "forbidden PLMNs" list based on the determination that the UE (200) is not registered for the disaster roaming services and timer T3247 has expired.

[0067] In an embodiment, optionally, when the UE (200) removes the PLMN from FPLMN list where UE (200) is registered for the disaster roaming service, the UE (200) determines that disaster condition has ended and applies the procedure for the disaster end condition.

[0068] In an embodiment, upon the UE (200) determining that a disaster condition has ended and selecting the PLMN previously with disaster condition, if there is a disaster return wait range stored in the ME is provided by:

[0069] 1) the PLMN providing disaster roaming services; or

[0070] 2) the selected PLMN,

[0071] , the Mobile Station (MS) shall generate a random number within the disaster return wait range and start a timer set to the generated random number. While the timer is running, the MS shall not initiate registration with the exception of performing an initial registration for emergency services, in the selected PLMN.

[0072] In an embodiment, FPLMN is a PLMN in the list of "forbidden PLMNs" and / or the list of "forbidden PLMNs for GPRS service" and / or extension of the "forbidden PLMNs" list. In an embodiment, FPLMN list can be "forbidden PLMNs" and / or the list of "forbidden PLMNs for GPRS service" and / or extension of the "forbidden PLMNs" list or a combination of them. In an embodiment, the UE (200) registers for normal service through registration procedure when camped to the 5GC / N1 mode or through attach or TAU procedure when camped to Evolved packet core / Evolved packet system (EPC / EPS) or S1 mode. In an embodiment, persistent PDU session is either a non-emergency PDU session that contains a GBR QoS flow with QoS equivalent to QoS of teleservice 11 and where there is a radio bearer associated with that PDU session over 3GPP access or an emergency PDU session where there is a radio bearer associated with that PDU session over 3GPP access. In an embodiment, persistent EPS bearer context is either a non-emergency EPS bearer context representing a GBR bearer with QoS equivalent to QoS of teleservice 11 and where there is a radio bearer associated with that context or an emergency EPS bearer context where there is a radio bearer associated with that context. In an embodiment, when the UE (200) deletes the PLMN where it is registered for the disaster roaming service from the FPLMN list, it is treated as an allowable PLMN. The comprehensive management capabilities of the PLMN controller (204) ensure seamless handling of PLMNs during disaster roaming services. This proactive approach minimizes the chances of deleting the FPLMN list and stopping the disaster roaming services by not removing the PLMN where it is registered for the disaster roaming service on the expiry of the T3245 timer or T3247 timer. By doing so, the PLMN controller (204) significantly contributes to the overall robustness and efficiency of the wireless communication during disaster roaming services.

[0073] FIG. 3 is a flow diagram that illustrates a proposed method for handling PLMNs in a UE during disaster roaming services according to the embodiments as disclosed herein. At step 301, the method includes the UE (200) registering or registered, the UE (200) for the disaster roaming services on a first PLMN (250). This registration process may involve the UE (200) sending a registration request to the first PLMN (250) and receiving a confirmation response (registration accept message). The UE (200) may also store the network parameters and authentication credentials associated with the first PLMN (250) to facilitate seamless connectivity during the disaster roaming services. Additionally, the UE (200) may prioritize the first PLMN (250) over other available networks to ensure reliable communication during the disaster scenario.

[0074] At step 302, the method includes the UE (200) detecting whether the T3245 timer or T3247 timer has expired. These timers are used to manage the duration for which the UE (200) consider the first PLMN (250) as FPLMN (i.e. PLMN-1 (250) is forbidden PLMN) thus suitable PLMN for the disaster roaming services. The UE (200) continuously monitors these timers and triggers specific actions based on their expiration status. For instance, upon expiration of the T3245 timer, the UE (200) may initiate a re-registration process on the PLMN-1 (250) for the normal service or search for alternative PLMNs that offer disaster roaming services.

[0075] At step 303, the method includes the UE (200) retaining the first PLMN (250) in an FPLMN list or retaining the FPLMN list when a T3245 timer or a T3247 timer has expired such that the UE (200) does not remove the first PLMN (250) from the FPLMN list or the UE (200) does not erase the FPLMN list. The FPLMN list is a critical component that helps the UE (200) manage network preferences during disaster scenarios. The UE (200) may update the FPLMN list dynamically based on real-time network conditions and disaster status. Further, the method includes the UE (200) determining whether a disaster condition has ended or the UE (200) finds another PLMN which provides a normal service and the UE (200) deleting a first PLMN from the FPLMN list or erasing / deleting FPLMN list when the disaster condition has ended or the UE (200) finds another PLMN (allowable PLMN) which provides the normal service and the first PLMN (250) is not removed from FPLMN list or FPLMN list is not erased / deleted at the T3247 or T3245 timer expiry. The FPLMN list includes one or more of forbidden PLMNs and / or the list of forbidden PLMNs for GPRS and / or extension of the forbidden PLMNs list or a combination of them. Furthermore, the UE (200) erases the "forbidden PLMN list" and "forbidden PLMNs for GPRS service" list based on the determination that the UE (200) is not registered for the disaster roaming services and timer T3245 has expired. The UE (200) then performs cell selection in response to deleting the "forbidden PLMN list" and "forbidden PLMNs for GPRS service" list. The UE (200) removes the respective PLMN from the extension of the "forbidden PLMNs" list based on the determination that the UE (200) is not registered for the disaster roaming services and timer T3247 has expired.

[0076] FIG. 4 is a sequence diagram that illustrates a proposed method of handling of FPLMN list on the expiry of T3245 / T3247 for disaster roaming where the PLMN-1 is removed from FPLMN list and the UE (200) enters DEREGISTERED PLMN_SEARCH state according to the embodiments as disclosed herein. Initially, the UE (200) is registered with PLMN-1 (250) for disaster roaming services. In an embodiment, at step 1, after the expiry of T3245 or T3247 and PLMN-1 (250) is part of the FPLMN list, the UE (200) deregisters with PLMN-1 for disaster roaming services. Further, the PLMN-1 (250) is removed from FPLMN list and the UE (200) enters DEREGISTERED PLMN_SEARCH state, performs PLMN selection, cell selection, or cell reselection procedure. In step-1, UE (200) deregisters with PLMN-1 (250) for disaster roaming services through de-registration procedure when the UE (200) is registered on 5GCN or through detach procedure when registered on EPC / EPS / S1 mode or locally deregisters for the disaster roaming service. In an embodiment, if the UE (200) is registered for disaster roaming services on PLMN (PLMN-1 (250) in this example) and is removed from FPLMN lists due to timer 3245 expiring, then UE (200) initiates the de-registration procedure when on 5GCN / N1 mode or detach procedure when on EPC / S1 and performs PLMN selection as specified in 3GPP TS 23122 [5]. In an embodiment, if the UE (200) is registered for disaster roaming services on PLMN (PLMN-1 (250) in this example) and is removed from FPLMN lists due to timer 3245 expiring, then UE (200) de-registers locally, aborts RRC connection if in connected mode (5GMM-CONNECTED / EMM-CONNECTED), and performs PLMN selection as specified in 3GPP TS 23122 [5].

[0077] FIG. 5 is a sequence diagram that illustrates a proposed method of handling of FPLMN list on the expiry of T3245 or T3247 for disaster roaming services where the PLMN-1 (250) is retained in the FPLMN list or FPLMN list is retained and the UE (200) remains registered for disaster roaming services according to the embodiments as disclosed herein. Initially, the UE (200) is registered on the PLMN-1 (250) for disaster roaming services. At step 1, after the expiry of T3245 or T3247 and PLMN-1 (250) is part of the FPLMN list, the PLMN-1 (250) is retained in the FPLMN list or retains the FPLMN list (i.e., UE (200) does not remove the PLMN-1 (250) from FPLMN list or FPLMN list is not erased when the UE (200) is registered for the disaster roaming services upon timer 3247 or T3245 timer expiry. The UE (200) removes PLMN-1 (250) from the FPLMN list or erases FPLMN list upon timer T3247 or T3245 when the UE (200) is not registered for the disaster roaming services) and the UE (200) remains registered for disaster roaming services. Additionally, when the UE (200) determines that a disaster condition has ended or the UE (200) found that PLMN (e.g., PLMN-2) which can provide normal service and UE (200) optionally registers for normal service, then the UE (200) deletes the PLMN-1 (250) from the respective FPLMN list if the PLMN-1 (250) was not removed or erase the FPLMN list if it was not erased due to UE (200) registration for the disaster roaming services.

[0078] FIG. 6 is a sequence diagram that illustrates a method of handling of FPLMN list on the expiry of T3245 / T3247 for disaster roaming where the PLMN-1 (250) is removed from the FPLMN list and the UE (200) remains registered for disaster roaming services according to the embodiments as disclosed herein. Initially, the UE (200) is registered with PLMN-1 (250) for disaster roaming services. In an embodiment, at step 1, after the expiry of T3245 or T3247 and PLMN-1 (250) is part of the FPLMN list, the PLMN-1 (250) is removed from the FPLMN list and the UE (200) remains registered for disaster roaming services. The MS / UE (200) periodically attempts to obtain service on an allowable PLMN of the same country as the current serving PLMN and if the UE (200) selects the PLMN-1 (250) as allowable PLMN then a) if the UE (200) is still registered with disaster roaming service on PLMN-1 (250), it shall deregister for disaster roaming services through deregistration procedure or locally deregister when on 5GC or N1 mode or detach procedure or locally detach when on EPC / S1 mode. The UE (200) then initiates registration procedure when on the 5GC / N1 mode or attach / TAU when on the EPC / S1 mode for the normal service on PLMN-1 (250). In an embodiment, if the UE (200) found another PLMN (e.g., PLMN-2), then it can select PLMN-2 and initiate registration or TAU / attach (based on UE (200) camped to N1 supported cell or S1 supported cell). If the UE (200) selects the PLMN (e.g., PLMN-3) previously with disaster condition, then UE (200) applies the procedure for UE (200) determined disaster end procedure for selecting the PLMN previously with disaster condition. In an embodiment, in all the proposed solutions, additionally, the UE (200) which is registered for the disaster roaming services and has a persistent PDU session does not initiate deregistration / locally deregister for disaster roaming service upon registered PLMN being removed from FPLMN list. The initiate deregistration procedure or locally deregister for disaster roaming service when the radio bearer associated with the persistent PDU session has been released. In an embodiment, in all the proposed solutions, additionally, the UE (200) which is registered for the disaster roaming services on EPC and has a persistent EPS bearer context does not initiate detach request / locally deregister for disaster roaming service upon registered PLMN being removed from FPLMN list. The UE (200) initiates detach procedure or locally detaches for disaster roaming service when the radio bearer associated with the persistent EPS bearer context has been released.

[0079] 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. While the preferred embodiments have been described, those skilled in the art will recognize that modifications can be made within the scope of the described embodiments.

Claims

1.A method performed by a user equipment (UE) in a wireless communication system, the method comprising:transmitting, to an entity associated with a first public land mobile network (PLMN) included in a forbidden PLMN list, a REGISTRATION REQUEST message for registration for disaster roaming service;receiving, from the entity associated with the first PLMN, a REGISTRATION ACCEPT message in response to the REGISTRATION REQUEST message;determining whether to delete the first PLMN from the forbidden PLMN list based on disaster condition, in case that a timer associated with the forbidden PLMN list expires; anddeleting the first PLMN from the forbidden PLMN list based on the determination.2.The method of claim 1, wherein determining whether to delete the first PLMN from the forbidden PLMN list based on the disaster condition comprises:determining whether the disaster condition has ended; anddetermining to delete the first PLMN from the forbidden PLMN list, in case that the disaster condition has ended.3.The method of claim 2, wherein the UE determines that the disaster condition has ended, in case that:the UE has successfully registered over non-3GPP access on a second PLMN; orthe UE has successfully registered with a third PLMN not included in the forbidden PLMN list.4.The method of claim 2, wherein the UE determines that the disaster condition has ended, in case that:the UE is not registered for the disaster roaming service and identifies that a cell broadcasts neither a disaster related indication nor a list of at least one PLMN with the disaster condition for which the disaster roaming service is offered by an available PLMN; orthe UE is registered for the disaster roaming service and receives a cause value #11 "PLMN not allowed" or a cause value #13 "Roaming not allowed in this tracking area".5.The method of claim 1, wherein deleting the first PLMN from the forbidden PLMN list is performed by:erasing the forbidden PLMN list; orremoving the first PLMN from the forbidden PLMN list.6.The method of claim 1, wherein the timer is started, in case that:the UE receives a REGISTRATION REJECT or SERVICE REJECT message without integrity protection; orthe UE adds an identity of the first PLMN to the forbidden PLMN list.7.The method of claim 1, further comprising:selecting the first PLMN included in the forbidden PLMN list in case that the disaster condition has occurred and no other PLMN is available except for at least one PLMN in the forbidden PLMN list.8.A user equipment (UE) in a wireless communication system, the UE comprising:memory storing instructions; andat least one processor coupled to the memory and configured, based at least partially on execution of the instructions, to cause the UE to:transmit, to an entity associated with a first public land mobile network (PLMN) included in a forbidden PLMN list, a REGISTRATION REQUEST message for registration for disaster roaming service;receive, from the entity associated with the first PLMN, a REGISTRATION ACCEPT message in response to the REGISTRATION REQUEST message;determine whether to delete the first PLMN from the forbidden PLMN list based on disaster condition, in case that a timer associated with the forbidden PLMN list expires; anddelete the first PLMN from the forbidden PLMN list based on the determination.9.The UE of claim 8, wherein the at least one processor is further configured, based at least partially on the execution of the instructions, to cause the UE to:determine whether the disaster condition has ended; anddetermine to delete the first PLMN from the forbidden PLMN list, in case that the disaster condition has ended.10.The UE of claim 9, wherein the at least one processor is further configured, based at least partially on the execution of the instructions, to determine that the disaster condition has ended, in case that:the UE has successfully registered over non-3GPP access on a second PLMN; orthe UE has successfully registered with a third PLMN not included in the forbidden PLMN list.11.The UE of claim 9, wherein the at least one processor is further configured, based at least partially on the execution of the instructions, to determine that the disaster condition has ended, in case that:the UE is not registered for the disaster roaming service and identifies that a cell broadcasts neither a disaster related indication nor a list of at least one PLMN with the disaster condition for which the disaster roaming service is offered by an available PLMN; orthe UE is registered for the disaster roaming service and receives a cause value #11 "PLMN not allowed" or a cause value #13 "Roaming not allowed in this tracking area".12.The UE of claim 8, wherein the deleting of the first PLMN from the forbidden PLMN list is performed by:erasing the forbidden PLMN list; orremoving the first PLMN from the forbidden PLMN list.13.The UE of claim 8, wherein the timer is started, in case that:the UE receives a REGISTRATION REJECT or SERVICE REJECT message without integrity protection; orthe UE adds an identity of the first PLMN to the forbidden PLMN list.14.The UE of claim 8, wherein the at least one processor is further configured, based at least partially on the execution of the instructions, to cause the UE to:select the first PLMN included in the forbidden PLMN list in case that the disaster condition has occurred and no other PLMN is available except for at least one PLMN in the forbidden PLMN list.

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