Patent Description:
During a disaster cellular networks often get overloaded or become unavailable and users may therefore be denied services. Disasters can be man-made such as e.g. a fire in a building or natural such as e.g. an earth quake. When a disaster happens, a lot of people may try to call emergency services or each other. Due to multiple users requesting services at the same time, the network resources can get congested and users may not be able to get the requested services. Network failure can also happen during a disaster thereby the network becoming unavailable.

<CIT> discloses a method for network reselection during a disaster. <CIT> discloses a method for a terminal and a base station to register in a network in a wireless communication system.

Another objective of embodiments of the invention is to provide a disaster condition indication mechanism for communication systems.

The above and further objectives are solved by the subject matter of the independent claims. Further advantageous embodiments of the invention can be found in the dependent claims.

If a Public Land Mobile Network (PLMN) is not able to provide services such as e.g. voice calls or mobile data services to a User Equipment (UE) due to a disaster condition, there are often other PLMNs available in the area which may be able to provide service to the UE. However, those PLMNs could be configured to be forbidden PLMNs in the UE and the UE will hence never select one of those PLMNs.

To minimization service interruptions, it would be beneficial to enable a UE of a given PLMN to obtain service from another PLMN for an area where a disaster condition applies, even if the other PLMN is a forbidden PLMN for the UE under normal conditions. PLMN selection is a procedure which enables the UE to select the most appropriate PLMN at a particular point of time. Most of the time when the UE is in the home country, the home PLMN will be the most appropriate PLMN and the home PLMN will thus be the serving PLMN. To prevent the UE from switching from the home PLMN, roaming is often disabled inside the home country. Other PLMNs in the home country may e.g. be added to a list of forbidden PLMNs so that the UE does not roam unnecessarily into these PLMNs.

Embodiments of the invention provides a disaster condition indication mechanism for communication systems thereby informing client devices, such as UEs, that a serving PLMN is in disaster condition. Thereby, the client devices may take appropriate measures e.g. initiate a PLMN selection procedure.

<FIG> shows a network node <NUM> according to an embodiment of the invention. In the embodiment shown in <FIG>, the network node <NUM> comprises a processor <NUM>, a transceiver <NUM> and a memory <NUM>. The processor <NUM> may be coupled to the transceiver <NUM> and the memory <NUM> by communication means <NUM> known in the art. The network node <NUM> may further comprise an antenna or antenna array <NUM> coupled to the transceiver <NUM>, which means that the network node <NUM> may be configured for wireless communications in a wireless communication system. That the network node <NUM> may be configured to perform certain actions can in this disclosure be understood to mean that the network node <NUM> comprises suitable means, such as e.g. the processor <NUM> and the transceiver <NUM>, configured to perform said actions.

The processor <NUM> of the network node <NUM> may be referred to as one or more general-purpose central processing units (CPUs), one or more digital signal processors (DSPs), one or more application-specific integrated circuits (ASICs), one or more field programmable gate arrays (FPGAs), one or more programmable logic devices, one or more discrete gates, one or more transistor logic devices, one or more discrete hardware components, and one or more chipsets. The memory <NUM> of the network node <NUM> may be a read-only memory, a random access memory, or a non-volatile random access memory (NVRAM).

The transceiver <NUM> of the network node <NUM> may be a transceiver circuit, a power controller, an antenna, or an interface which communicates with other modules or devices. In embodiments, the transceiver <NUM> of the network node <NUM> may be a separate chipset or being integrated with the processor <NUM> in one chipset. While in some embodiments, the processor <NUM>, the transceiver <NUM>, and the memory <NUM> of the network node <NUM> are integrated in one chipset.

With reference to <FIG>, according to embodiments of the invention, the network node <NUM> is associated with a serving PLMN <NUM> for a first client device <NUM>. The network node <NUM> is configured to: transmit a first control message <NUM> to the first client device <NUM> upon determining that the serving PLMN <NUM> for the first client device <NUM> is in a disaster condition. The first control message <NUM> indicates that the serving PLMN <NUM> for the first client device <NUM> is in the disaster condition.

<FIG> shows a flow chart of a corresponding method <NUM> which may be executed in a network node <NUM>, such as the one shown in <FIG>. The method <NUM> for a network node <NUM> being associated with a serving PLMN <NUM> for a first client device <NUM> comprises: transmitting <NUM> a first control message <NUM> to the first client device <NUM> upon determining that the serving PLMN <NUM> for the first client device <NUM> is in a disaster condition. The first control message <NUM> indicates that the serving PLMN <NUM> for the first client device <NUM> is in the disaster condition.

In the previous embodiments of the invention, the network node <NUM> is associated with the serving PLMN for a client device. That may be understood to mean that the network node <NUM> is part of the serving PLMN, e.g. a base station of a RAN or a function of a core network. However, the present solution may also involve the case when the network node <NUM> is not associated with the serving PLMN for a client device. Therefore, in embodiments of the invention the network node <NUM> is further configured to transmit a second control message <NUM> to a client device upon determining that a serving PLMN for the second client device is in a disaster condition. The second control message <NUM> indicates that the serving PLMN for the client device is in the disaster condition. This is also illustrated in <FIG> in which the network node denoted <NUM>' transmits the second control message <NUM> to a client device. Thereby, the client device may be informed about the disaster condition of its serving PLMN even when its serving PLMN is down. In such cases the network node <NUM> may be a network access node of a RAN, and the second control message <NUM> may be a SIB. In embodiments of the invention, the second control message <NUM> may also indicate the Identity (ID) of the serving PLMN so that the client device easily can identity the serving PLMN.

<FIG> shows a client device <NUM> according to an embodiment of the invention. In the embodiment shown in <FIG>, the client device <NUM> comprises a processor <NUM>, a transceiver <NUM> and a memory <NUM>. The processor <NUM> is coupled to the transceiver <NUM> and the memory <NUM> by communication means <NUM> known in the art. The client device <NUM> may be configured for both wireless and wired communications in wireless and wired communication systems, respectively. The wireless communication capability is provided with an antenna or antenna array <NUM> coupled to the transceiver <NUM>, while the wired communication capability is provided with a wired communication interface <NUM> coupled to the transceiver <NUM>. That the client device <NUM> is configured to perform certain actions can in this disclosure be understood to mean that the client device <NUM> comprises suitable means, such as e.g. the processor <NUM> and the transceiver <NUM>, configured to perform said actions.

The processor <NUM> of the client device <NUM> may be referred to as one or more general-purpose CPUs, one or more DSPs, one or more ASICs, one or more FPGAs, one or more programmable logic devices, one or more discrete gates, one or more transistor logic devices, one or more discrete hardware components, and one or more chipsets. The memory <NUM> of the client device <NUM> may be a read-only memory, a random access memory, or a NVRAM.

The transceiver <NUM> of the client device <NUM> may be a transceiver circuit, a power controller, an antenna, or an interface which communicates with other modules or devices. In embodiments, the transceiver <NUM> of the client device <NUM> may be a separate chipset or being integrated with the processor <NUM> in one chipset. While in some embodiments, the processor <NUM>, the transceiver <NUM>, and the memory <NUM> of the client device <NUM> are integrated in one chipset.

With reference to <FIG> and <FIG>, according to embodiments of the invention, the client device <NUM> which is configured to be served by a serving PLMN <NUM> is further configured to receive a first control message <NUM> from a first network node <NUM> associated with the serving PLMN <NUM> for the client device <NUM>, wherein the first control message <NUM> indicates that the serving PLMN <NUM> is in the disaster condition; and/or receive a second control message <NUM> from a second network node <NUM>' associated with a visiting PLMN <NUM> for the client device <NUM>, wherein the second control message <NUM> indicates that the serving PLMN <NUM> is in the disaster condition.

In embodiments of the invention, the second network node <NUM>' may be a network access node of a RAN, and the second control message <NUM> is a SIB broadcasted by the second network node <NUM>'.

It is noted that the client device <NUM> may receive the first control message <NUM> only; receive the second control message <NUM> only; or receive both the first control message <NUM> and the second control message <NUM>.

<FIG> shows a flow chart of a corresponding method <NUM> which may be executed in a client device <NUM>, such as the one shown in <FIG>. The client device <NUM> is configured to be served by a serving PLMN <NUM>. The method <NUM> comprises: receiving <NUM> a first control message <NUM> from a first network node <NUM> associated with the serving PLMN <NUM> for the client device <NUM>, wherein the first control message <NUM> indicates that the serving PLMN <NUM> is in the disaster condition; and/or receiving <NUM> a second control message <NUM> from a second network node <NUM>' associated with a visiting PLMN <NUM> for the client device <NUM>, wherein the second control message <NUM> indicates that the serving PLMN <NUM> is in the disaster condition.

When the client device <NUM> is informed or aware that the serving PLMN <NUM> is in the disaster condition the client device <NUM> may try to register to another PLMN that is not in disaster condition. Thereby, service interruption for the client device <NUM> is avoided or shortened. Therefore, in embodiments of the invention, the client device <NUM> is configured to obtain a PLMN list comprising one or more visiting PLMNs. The client device <NUM> is further configured to register at a visiting PLMN in the PLMN list upon receiving the first control message <NUM> from the first network node <NUM> or the second control message <NUM> from the second network node <NUM>'.

There are a number of different ways for the client device <NUM> to obtain the PLMN list. Non-limiting examples may be any of:.

In embodiments of the invention, the PLMN list comprises an identity of each PLMN in the PLMN list so that the PLMNs can be identified by the client device/UE.

For registration synchronization and resource control in the communication system <NUM> the first control message <NUM> and/or the second control message <NUM> may further indicate at least one timer T defining a start register time instance at the visiting PLMN <NUM> for the first client device <NUM> and/or a re-registration time instance at the serving PLMN <NUM> for the first client device <NUM>. The timer defining a start register time instance may also be understood as a timer defining a minimum wait time to start registration at the visiting PLMN. The timer defining a re-registration time instance may also be understood as a timer defining a minimum wait time to start re-registration at the previously served PLMN which was under disaster condition.

In the following disclosure further exemplary implementation cases of the present solution will be described. The present mechanism for disaster condition indication may be realized using different types of control signalling and involving one or more communication procedures. These implementation cases are fully or partially set in a 3GPP context hence the terminology and system architecture herein used but embodiments of the invention are not limited thereto. Furthermore, a network node may determine that the serving PLMN is in disaster condition in a number of different ways which is out of the scope of the present disclosure. However, it may be mentioned that the network node <NUM> or the network may be informed by a government agency, an operator, etc..

<FIG> illustrates when an indication about a disaster condition is carried or comprised in system information of the serving PLMN. When a UE (corresponding to a client device) is served by a PLMN in disaster condition and the serving PLMN goes into a disaster condition, the serving PLMN in disaster condition broadcasts an indication in system information that the serving PLMN is in disaster condition. Hence, a new indication in SIB may be broadcasted as the first control message <NUM> by a network access node <NUM> of a RAN to one or more UEs (however only one UE is illustrated in <FIG>). The network access node <NUM> may e.g. be a gNB of the serving PLMN.

Furthermore, <FIG> and <FIG> illustrate cases when an indication about a disaster condition is provided in Non-Access Stratum (NAS) signalling. In such embodiments the network node <NUM> may be an Access and Mobility management Function (AMF) of a core network.

For a service request procedure, in step I in <FIG>, a UE is served by a PLMN in disaster condition and the UE performs a service request by transmitting a service request message to an AMF associated with the serving PLMN for the UE. In step II in <FIG>, the service request is rejected by the AMF as the serving PLMN is already in disaster condition, and in step III in <FIG>, the AMF rejects the service request by sending a service reject message as the first control message <NUM> indicating that the serving PLMN is in the disaster condition to the UE. The service reject message may in this respect comprise a new cause value indicating that the serving PLMN is in the disaster condition. In step IV in <FIG>, the UE receives the service reject message from the AMF and may e.g. perform a PLMN selection procedure in search of a PLMN not in disaster condition. In this respect a PLMN list comprising one or more visiting PLMNs may be used.

Correspondingly, for a registration request procedure, in step I in <FIG>, the UE is served by a PLMN in disaster condition and performs a registration request by sending a registration request message to the AMF. In step II in <FIG>, the registration request is rejected by the AMF since the serving PLMNB is in disaster condition, and in step III the AMF sends a registration reject message as the first control message <NUM> to the UE rejecting the registration request. The registration reject message may comprises a new cause value indicating that the serving PLMN is in the disaster condition. In step IV in <FIG>, the UE as previously described may perform a PLMN selection procedure upon reception of the registration reject message.

In <FIG>, an AMF initiates a de-registration procedure by sending a de-registration request message with a new cause value to re-direct a UE to another PLMN not in disaster condition. Therefore, in Step I in <FIG>, the serving PLMN in disaster condition via AMF performs a de-registration request by sending a de-registration request message as the first control message <NUM> to the UE. The de-registration request message may comprise a new cause value indicating that the serving PLMN is in disaster condition.

The network may also initiate a configuration update command procedure by sending a configuration update command message with a new indication to the UE that the serving PLMN is in disaster condition and the UE needs to move to another PLMN not in disaster condition. Therefore, in Step I in <FIG>, the serving PLMN in disaster condition via the AMF performs a configuration update command procedure by sending a configuration update command message as the first control message <NUM> to the UE.

For both cases in step II in <FIG>, the UE may upon reception of the de-registration request message or the configuration update command message initiate a PLMN selection procedure as previously described.

In a general case the UE may perform a NAS signalling procedure and gets no response from the serving PLMN, e.g. since there is no radio resources available. In such case the UE may perform a scan on neighbouring PLMNs to see if their SIBs indicate that the serving PLMN is in the disaster condition. This is more or less in line with the embodiment shown in <FIG> in which a second control message <NUM> is employed by visiting PLMNs to inform UEs that their serving PLMN is in disaster condition.

Moreover, <FIG> and <FIG> illustrate cases when an indication about a disaster condition is provided in RRC messages, e.g. by a RAN Node (denoted "RN" in <FIG>) such as a gNB.

<FIG> illustrates two different cases using RRC messages for indicating disaster condition. Establishment of RRC connection is a first step for a UE to go to connected mode. NAS messages can only be transmitted after that the UE is in connected mode. Usually during a disaster, RAN resources get congested and the network can reject a RRC connection establishment message. So, by adding the present indication in RRC messages makes it possible for the network to inform about the disaster condition of the serving PLMN even if the RRC connection fails. Hence, a more robust control signalling is usually provided by the use of RRC signalling.

In a first case in <FIG>, a RRC reject message with disaster indication and redirection information is employed. When a UE tries to establish or resume a RRC connection, the serving RAN node can reject the RRC connection and send a RRC connection reject message as the first control message <NUM> to the UE in step I in <FIG>. The RRC connection reject message comprises an indication that the serving PLMN is in disaster condition and may further comprise redirecting information so as to redirect the UE to cells of other PLMNs not in disaster condition.

Therefore, in embodiments of the invention, the network node <NUM> may be configured to redirect the client device <NUM> from a serving PLMN <NUM> to a visiting PLMN <NUM> for a client device <NUM> upon determining that the serving PLMN <NUM> for the client device <NUM> is in a disaster condition. In this respect the previously mentioned PLMN list may be used for disaster condition PLMN selection. Also the previously mentioned timer(s) T may be used so that the client device is aware of when to register or re-register.

The visiting PLMN <NUM> may belong to a 3GPP or a non-3GPP system. Generally, there may be two different access systems, which means there are two ways for the UE to access the core network. One may be 3GPP which e.g. is GSM, WCDMA, LTE, NR and the other may be non-3GPP such as through a WiFi connection. So, the UE may move from a 3GPP system to a non-3GPP system, or vice versa.

In a second case in <FIG>, a RRC release message may instead be employed. When the UE tries to resume a RRC connection, the serving RAN node can release the RRC connection and send a RRC connection release message as the first control message <NUM> to the UE in step I in <FIG>. The RRC connection release message indicates that the serving PLMN is in disaster condition and may additionally indicate redirection information.

For both cases in <FIG>, the UE may in step II upon reception of the RRC connection reject message or the RRC connection release message initiate a PLMN selection procedure as previously described.

<FIG> illustrates an embodiment when a new RRC message type is instead employed which e.g. may be labelled a RRC serving PLMN disaster condition message or any other suitable labelling. Hence, the serving RAN node may use the new RRC message type as a response message when the UE tries to establish or resume a RRC connection as shown in <FIG>. In step I the UE transmits a RRC connection message to the serving RAN node. The RRC connection message is rejected by the serving RAN node in step II which transmits the new RRC message type to the UE as a reponse message in step III. Upon reception of the new RRC message type the UE may in step IV initiate a PLMN selection procedure. However, the new RRC message type may also be a stand alone message type and not a response message type as illustrated in <FIG>. This implies that the UE does not have to transmit a request message. Thereby, by using the new RRC message type the UE is informed that the serving PLMN is in disaster condition and the UE may be redirected to cells belonging to one or more other PLMNs not in disaster condition.

Finally, <FIG> illustrate when information about a disaster condition is provided in a paging procedure. Generally, a UE performs a PLMN scan to find available PLMNs which means that the UE has to read the SIB which is broadcasted. The serving PLMN or the serving RAN node can page the UE to inform that the serving PLMN is in disaster condition. Therefore, the serving RAN node may transmit a paging message as the first control message <NUM> indicating that the serving PLMN is in disaster condition. The paging channel is monitored by all UEs and the paging message is received by all UEs so by using paging messages a plurality of UEs can be reached.

Moreover, embodiments of the invention also relates to a further mechanism in which a client device <NUM> is informed that a disaster condition is over for its serving PLMN.

From a network node point of view, the network node <NUM> may further be configured to transmit a third control message <NUM> to a client device <NUM> upon determining that a disaster condition for a serving PLMN for the client device <NUM> is over. Hence, the third control message <NUM> indicates that the disaster condition for the serving PLMN for the client device <NUM> is over. This is illustrated in <FIG> where a network node herein denoted second network node <NUM>' transmits the third control message <NUM> to the client device <NUM>.

From a client device 300point of view and with further reference to <FIG>, the client device 300may further be configured to receive the third control message <NUM> from the second network node <NUM>' associated with a visiting PLMN <NUM> for the client device <NUM>. The third control message <NUM> indicates that the disaster condition is over for the serving PLMN <NUM>. Thereby, the client device 300may try to re-register at the serving PLMN <NUM> after the disaster condition has ended.

The signalling of the third control message <NUM> may be performed with the same or corresponding methods as the ones used for the first control message <NUM> signalling. Therefore, the third control message <NUM> may be:.

Embodiments of the invention may be implemented in different communication standards. For example, the present solution may impact 3GPP TS <NUM> and TS <NUM> - NAS. The proposed changes may impact NR RRC specs, such as and <NUM> respectively. For example, the sections for "System information acquisition", "RRC Connection Reject" and "RRC Connection Release". Further, a new Information Element (IE) can be added for "RRCReject" and "RRCRelease" messages. New <NUM> Mobility Management (5GMM) cause value to indicate disaster condition may e.g. be added to 3GPP TS <NUM> in Table <NUM>. <NUM> is herein exemplified in underlined bold face type denoted "Disaster Condition".

The network node <NUM> in this disclosure includes but is not limited to: a NodeB in wideband code division multiple access (WCDMA) system, an evolutional Node B (eNB) or an evolved NodeB (eNodeB) in LTE systems, or a relay node or an access point, or an in-vehicle device, a wearable device, or a gNB in the fifth generation (<NUM>) networks.

Further, the network node <NUM> herein may be denoted as a radio network access node, an access network access node, an access point, or a base station, e.g. a radio base station (RBS), which in some networks may be referred to as transmitter, "gNB", "gNodeB", "eNB", "eNodeB", "NodeB" or "B node", depending on the technology and terminology used. The radio network access nodes may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. The radio network access node can be a station (STA), which is any device that contains an IEEE <NUM>-conformant MAC and PHY interface to the wireless medium. The radio network access node may also be a base station corresponding to the <NUM> wireless systems.

However, the network node <NUM> may also be a node of a core network. The network node <NUM> may e.g. be AMF as previously mentioned but may also be a Session Management Function (SMF) or a Policy Control Function (PCF).

The client device <NUM> in this disclosure includes but is not limited to: a UE such as a smart phone, a cellular phone, a cordless phone, a session initiation protocol (SIP) phone, a wireless local loop (WLL) station, a personal digital assistant (PDA), a handheld device having a wireless communication function, a computing device or another processing device connected to a wireless modem, an in-vehicle device, a wearable device, an integrated access and backhaul node (IAB) such as mobile car or equipment installed in a car, a drone, a device-to-device (D2D) device, a wireless camera, a mobile station, an access terminal, an user unit, a wireless communication device, a station of wireless local access network (WLAN), a wireless enabled tablet computer, a laptop-embedded equipment, an universal serial bus (USB) dongle, a wireless customer-premises equipment (CPE), and/or a chipset. In an Internet of things (IOT) scenario, the client device <NUM> may represent a machine or another device or chipset which performs communication with another wireless device and/or a network equipment.

The UE may further be referred to as a mobile telephone, a cellular telephone, a computer tablet or laptop with wireless capability. The UE in this context may e.g. be portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile device, enabled to communicate voice and/or data, via the radio access network, with another entity, such as another receiver or a server. The UE can be a station (STA), which is any device that contains an IEEE <NUM>-conformant media access control (MAC) and physical layer (PHY) interface to the wireless medium (WM). The UE may also be configured for communication in 3GPP related LTE and LTE-Advanced, in WiMAX and its evolution, and in fifth generation wireless technologies, such as NR.

Moreover, it is realized by the skilled person that embodiments of the network node <NUM> and the client device <NUM> comprises the necessary communication capabilities in the form of e.g., functions, means, units, elements, etc., for performing the solution. Examples of other such means, units, elements and functions are: processors, memory, buffers, control logic, encoders, decoders, rate matchers, de-rate matchers, mapping units, multipliers, decision units, selecting units, switches, interleavers, de-interleavers, modulators, demodulators, inputs, outputs, antennas, amplifiers, receiver units, transmitter units, DSPs, MSDs, TCM encoder, TCM decoder, power supply units, power feeders, communication interfaces, communication protocols, etc. which are suitably arranged together for performing the solution.

Especially, the processor(s) of the network node <NUM> and the client device <NUM> may comprise, e.g., one or more instances of a Central Processing Unit (CPU), a processing unit, a processing circuit, a processor, an Application Specific Integrated Circuit (ASIC), a microprocessor, or other processing logic that may interpret and execute instructions. The expression "processor" may thus represent a processing circuitry comprising a plurality of processing circuits, such as, e.g., any, some or all of the ones mentioned above. The processing circuitry may further perform data processing functions for inputting, outputting, and processing of data comprising data buffering and device control functions, such as call processing control, user interface control, or the like.

Claim 1:
A network node (<NUM>) for a communication system (<NUM>), the network node (<NUM>) being associated with a serving Public Land Mobile Network, PLMN, (<NUM>) for a first client device (<NUM>), and wherein the network node (<NUM>) is configured to:
transmit a first control message (<NUM>) to the first client device (<NUM>) upon determining that the serving PLMN (<NUM>) for the first client device (<NUM>) is in a disaster condition, wherein the first control message (<NUM>) indicates that the serving PLMN (<NUM>) for the first client device (<NUM>) is in the disaster condition,
wherein the network node (<NUM>) is an Access and Mobility management Function, AMF, of a core network, and wherein the first control message (<NUM>) is a registration reject message, a de-registration request message, a configuration update command message, or a service reject message.