System, method and apparatus for cell-off signal in a mobile network

Abstract

A first base station 510 (BTS, gNB, eNB) transmits a signal 710 to an associated wireless communication unit 550 (UE, user equipment), the signal indicating subsequent switch off 705 a first communica

Description

[0001] The technical field relates generally to a system, methods and apparatus for cell-off signal functionality in a wireless network. In particular, example implementations include a system, methods and devices for a user equipment UE and a network base station, such as a gNodeB (gNB) to provide network energy savings. Background

[0002] In recent years, there has been a rapid development in communications technologies that are compliant with third generation partnership project (3GPP™) standards. A 4th generation (4G) wireless communication standard (sometimes referred to as long term evolution (LTE™) was designed to support mobile internet and higher speeds for activities, such as video streaming and gaming. The 3GPP™ standards then developed a fifth generation (5G) of mobile wireless communications, which provides a step change in the delivery of better and faster communications, for example powering businesses, improving communications within homes and spearheading advances such as driverless cars. However, as the industry looks toward the future, it is clear that 5G networks are just the beginning.

[0003] A sixth generation (6G) wireless communication standard is currently under development, as the planned successor to 5G, and will likely be significantly faster. Like its predecessors, 6G networks will likely be broadband cellular networks, in which the service area is divided into small geographical areas called cells. 6G networks are expected to be even more diverse than their predecessors and are likely to support applications beyond current mobile use scenarios, such as virtual and augmented reality (VR / AR), ubiquitous instant communications, pervasive intelligence and the Internet of Things (loT). It is expected that mobile network operators will adopt flexible decentralized business models for 6G, with local spectrum licensing, spectrum sharing, infrastructure sharing, and intelligent automated management underpinned by mobile edge computing, artificial intelligence (AI), short-packet communication and blockchain technologies.

[0004] Currently, there are more than 110 countries committed to a net zero emissions target by 2050. What the Paris Agreement attempts to uphold is making sure global temperatures stay within 2C by 2100, but preferably closer to 1.5C. The motivation of reducing the energy emissions and increase the energy efficiency of the telecoms sector is more urgent than before. Also considering the price of energy are going up and the increasing traffic load of the telecoms system, mobile network operators are keen to optimize the costs of ongoing operations (opex). Energy-saving measures in network operations are necessary for NR radio equipment and other components of telecommunications systems.

[0005] 5G NR is the latest cellular generation. 5G NR features several new innovations that allow for higher throughput, lower latency and extreme flexibility. Compared to the previous generations, the 5G New Radio (NR) offers a significant energy-efficiency improvement in its first release (3GPP Rel-15), i.e., cell activation / deactivation over Xn / X2 / Fl interface via coordination between peer eNB / gNBs, sparser RS and SS signals, URLLC, CU / DU architecture and MR-DC, etc. However, based on the GSMA report ‘5G energy efficiencies: Green is the new black’ (https: / / data.gsmaintelligence.com / api-web / v2 / research-file-download?id=54165956&file=241120-5G-energy.pdf) published in 2020, Network opex tends to account for around 25% of Verizon’s cost base, or 10% of revenue. In addition, over 90% of network costs are spent on energy, consisting mostly of fuel and electricity consumption.

[0006] Some important aspects of 5G NR, which relate to energy-efficiency include the following: (i) Beam-based procedures. The device will take in to account the beams in a cell in several procedures to better accommodate the advancements in MIMO and beamforming seen over the last decade, (ii) Ultra-lean carriers: Reduction in the number of “always-on” signals where the network may broadcast reference signals a lot more infrequently compared to previous generations, and allow a network to reduce the amount of system information broadcasted, (iii) More efficient state transitions: A new RRC state is introduced, RRCINACTIVE. In RRCINACTIVE, the UE performs similar actions as in RRC IDLE, i.e., measuring and performing the cell reselection procedure to ensure that the UE is camping on the best cell. The network will save the UE context in the gNB and the UE will save the RRC configuration. This ensures that the state transition from RRCINACTIVE and RRCCONNECTED can be completed in a much smaller number of steps compared to moving from RRCIDLE to RRC CONNECTED. In a network where there are a lot of state transitions, this can reduce latency and improve capacity as there is a lot less need for control signals to occupy capacity and resources.

[0007] The inventor has recognized and appreciated that relevant 5G NR RRC procedures that impact energy-efficiency includes paging. Paging is done in order to allow for a network to be able to reach a UE when the UE is in a more power efficient state (RRC IDLE or RRCIN ACTIVE). To read possible pages from the network, the UE monitors for PDCCH in occasions called Paging Occasions. There are two main of types of paging - Core Network-initiated paging and RAN-initiated paging. Core Network-initiated paging is due to presence of downlink data or Core Network signaling for the UE while as RAN-initiated paging is for a UE in RRC INACTIVE (which may also be due to downlink data or signaling from a core network). A UE in RRC IDLE only monitors for Core Network-initiated paging, where a UE may use a default or UE-specific cycle. A UE in RRC INACTIVE monitors for both Core Network-initiated and RAN-initiated paging. For monitoring for paging in RAN-initiated paging the UE applies a UE-specific cycle. The Paging Frame (the Radio Frame that a Paging Occasion occurs) and Paging Occasion (the specific subframe within a Radio Frame where the paging is signalled) of a UE is derived partly on network configurations but also based the ID of the UE, which is derived based on temporary UE identifier 5G-S-TMSI. The UEID that is used to determine paging occasion is calculated as UE ID = 5G-S-TMSI mod 1024 (except for eDRX where it is calculated as UE ID = 5G-S-TMSI mod 4096). If the UE has not been allocated a 5G-S-TMSI, UE ID = 0 is used. When a UE has detected a page being sent in one of its Paging Occasions the UE checks whether the paging record matches its own identity. In general, a UE in RRC IDLE checks whether the paging record matches its ng-5G-S-TMSI while a UE in RRC INACTIVE checks whether the paging record matches its i-RNTI. A UE in RRC IDLE indicates to the upper layers regarding the received page, where the upper layers (NAS) will determine the course of action. A UE in RRC INACTIVE will perform the RRC Resume procedure if the identity matches. The ng-5G-S-TMSI is given by an AMF while a i-RNTI is given by a gNB in SuspendConfig.

[0008] One way to enter RRC idle or RRC inactive mode is by the network releasing the UE through the RRC release procedures. The RRC release procedures are initiated when the UE receives a RRCRelease message from the gNB. The RRCRelease message sent from the gNB may in turn have been triggered by the either the gNB or the AMF. This can for instance be due to any of the following reasons: load balancing, re-direction (both in RRC idle and RRC inactive) to other frequencies or RATs, UE context release triggered by the AMF core node (CN), Suspend indication to send the UE to RRC inactive, and Failure to retrieve UE context when UE resumes RRC connection from RRC inactive.

[0009] System information is information that is broadcasted by a cell for a wide range of purposes. System information is divided into a set of System Information Blocks (SIB). Some system information is required for a UE to access a cell. Without having acquired these system information blocks the UE may not be allowed to access a cell. In example of such a SIB is SIB1 which contains access information, for instance the PLMN of the cell, the cell identity, the tracking area code as well as cell selection information. SIB1 also contains the serving cell radio configuration.

[00010] Another set of SIBs contain information on other frequencies and RATs for the purpose of idle and inactive mode cell reselection as well as related parameters. These are for instance in SIB2-SIB5.

[00011] To further reduce energy consumption and improve the efficiency of the 3GPP system, in the releases later than Rei-15, some of the working groups (WGs) in RAN, SA and CT have completed or are developing mechanisms to increase energy saving or energy efficiency. To reduce the energy consumption of RAN part, in Rel-18, RAN WG started to study and specify the techniques on network energy savings (RAN WID in RP-223540 / RP-230566 Sept. 2023), and RAN will further work on network energy saving improvement in Rel-19 (RP-234065) on supporting on-demand SSB SCell operation for UEs in connected mode, on-demand SIB1 for UEs in idle / inactive mode, and adaptation of common signal / channel transmissions.

[00012] SA5 started their work on Energy efficiency of the 5G system in Rel-16. In Rel-17 (TR 28.813 - Study on new aspects of Energy Efficiency (EE) for 5G) and Rel-18 (TR 28.913), SA5 extended its scope from RAN only to the whole 5G system. The specified techniques are documented in TS 28.310 ‘Management and orchestration; Energy efficiency of 5G’ and the corresponding KPIs and measurements related to Energy efficiency (EE) are documented TS 28.552 ‘Management and orchestration; 5G performance measurements’ and TS 28.554 ‘Management and orchestration; 5G end to end Key Performance Indicators (KPI)’. In Rel-19, SA5 will keep working on energy efficiency and energy saving aspects of 5G networks and services according to the SID approved in SP-231723 in Dec 2023.

[00013] SAI is currently working on the potential requirements and solutions on Rel-19 Energy Efficiency as a service criteria (acronym: EnergyServ). This topic will be 100% completed by TSG 102 (Dec, 2023). The outcome of the study phase is documented in TR 22.882 - Study on Energy Efficiency as service criteria). And some of the specified SAI stage 1 requirements, e.g. the max. energy credit, might be down streamed to SA2 for further stage 2 work.

[00014] Within the 3GPP™ standard, it is known that Network energy savings (NES) is a Release 18 Work Item, focused on introducing methods to allow for energy savings for a network [1], rather than UEs. This is because a significant amount of OPEX for operators is spent on energy costs. The work item followed a Study Item where a base station energy consumption model was developed and different methods for energy savings were evaluated. The Study Item resulted in a Technical Report 38.864 [2],

[00015] The indicated objectives of the work item are: (i) specify SSB-less SCell operation. This allows a network to de-activate the SSBs on cells other than the PCell in a cell that operates Carrier Aggregation, (ii) specify enhancement on cell DTX / DRX mechanism. Here, DRX is a legacy feature that allows a UE to power down monitoring to save UE power consumption. Here also, Cell DTX / DRX allows a network to power down either transmission or reception operation. This is done by configuring a UE to not monitor or to not transmit in certain opportunities, (iii) specify techniques in spatial and power domain. Here, this is focused on enhancements on CSI and beam management-related procedures; and enhancements on CSI-related procedures to enable efficient adaptation of power offset values between PDSCH and CSI-RS. (iv) specify mechanisms to prevent legacy UEs from camping on cells using Rei-18 NES. (v) specify CHO procedure enhancements for cells in NES mode, (vi) Inter-node beam activation.

[00016] The Cell DTX / DRX is introduced to allow for a network to reduce power consumption by partly turning off transmit and receive functionality, as illustrated in FIG. 1 and FIG. 2.

[00017] Referring now to FIG. 1, a schematic diagram 100 of the known cell DTX 100 is illustrated, along with its configured fields. Here, a gNodeB (gNB) 110 is communicating with a user equipment (UE) 120. The operation of the gNB 110 includes some instances where the gNB is placed in a ‘Transmit OFF’ state 130. During so-called ‘DTX non-active duration’ 142, the UE 120 will not monitor PDCCH 160 and also skips SPS occasions 152. During this time, the UE may still transmit in the uplink, such as transmissions via Configured Grants (PUSCH) and Scheduling Requests (PUCCH). When the UE 120 does not monitor PDCCH 160, the cell supported by the gNB 110 operates a cell DTX non-active time 142, during a cell DTX-on duration timer 144. A cell DTX-start offset 146 defines a time between an operational SPS occasion 150 and the cell DTX-on duration timer 144 commencing, and a cell DTX cycle is defined between individual operational SPS occasions 150. When Cell DTX is configured and during the.

[00018] Similarly, referring now to FIG. 2, a schematic diagram of the known cell DRX 200 is illustrated, along with its configured fields. Here, a gNodeB (gNB) 210 is communicating with a user equipment (UE) 220. The operation of the gNB 210 includes some instances where the gNB is placed in a ‘Receive OFF’ state 230. Here, when Cell DRX is configured, the UE 220 shall not perform transmissions during the so-called DRX non-active duration 242. This includes transmissions on Configured Grant (CG) occasions 250 and Scheduling Request (SR) resources, during a cell DRX-on duration timer 244. This to ensure that nothing is being transmitted by the UE 220 so that a gNB 210 does not have to monitor for any transmissions. A cell DRX-start offset 246 defines a time between an operational CG occasion 250 and the cell DRX-on duration timer 244 commencing, and a cell DRX cycle is defined between individual operational CG occasions 250.

[00019] The Cell DTX 100 and cell DRX 200 are dedicatedly configured per UE in RRC CONNECTED, which means that there may be flexibility in how the cell or gNB is turned OFF. For instance a specific sector can be turned OFF, or the whole cell or gNB may be turned OFF. While Cell DTX and / or Cell DRX is on-going, the cell shall still not affect random access procedure, SSB transmissions, paging and system information broadcasting.

[00020] Both Cell DTX 100 and cell DRX 200 have an on-duration, which is the active duration and a cycle that specifies the periodic repetition of the active duration and the nonactive duration. The Cell DTX 100 and Cell DRX 200 are both configured via RRC, but the activation to start the Cell DTX cycle 148 and Cell DRX cycle 248 are performed via DCI via a new DCI format. For the new DCI format a new RNTI, nes-RNTI, is introduced. The DCI to activate or deactivate Cell DTX 100 or Cell DRX 200 are intended to indicate things such as: Field for activation / deactivation of Cell DTX; Field for activation / deactivation of Cell DRX; and Field for which serving cell that the activation / deactivation concerns.

[00021] The intended Cell DTX 100 and Cell DRX 200 are to be configured mMAC-CellGroupConfig, which is a part of CellGroupConfig, which in turn may be a part of RRCReconfiguration.

[00022] RRC Resume is performed to bring a UE 120, 220 out of an RRC inactive state. RRC Resume is started by the UE 120, 220 first synchronizing via random access and then transmitting RRCResumeRequest which contains the identifier of the UE 120, 220, the i-RNTI, which is specifically used for RRC inactive. If the gNB 110, 210 is able to locate the UE context, i.e., the configuration of the UE 120, 220, the gNB 110, 210 will reply with RRCResume, which may for instance contain a full configuration (else UE 120, 220 will store UE Inactive AS context for the connected mode configuration). The UE 120, 220 will restore security and the previous RRC configuration and then send the RRCResumeComplete, upon the procedure is completed the UE 120, 220 will have completed the RRC Resume procedures

[00023] Referring now to FIG. 3, a message sequence chart 300 illustrates a known RRC Resume procedure. The messages in RRC Resume procedures are ‘RRCResumeRequest or RRCResumeRequest 1’, ‘RRCResume’ and ‘RRCResumeComplete’. RRC Resume 350 is performed to bring a UE 310 out of the RRC inactive state. A RRCRelease with suspend / config message 355 is sent from a gNB 320 to a UE 310. The UE enters an RRC inactive mode 365 and subsequently receives a trigger for RRC resume (to enter RRC connected mode) 370. The trigger can occur in a number of ways. A UE 310 initiated trigger can happen if there is uplink traffic in the buffer. In this case the resume cause value used is mt-Access. A UE 310 initiated trigger can happen if there is a RAN Notification Area Update. This is triggered when the UE 310 in RRC inactive 365 camps on a cell which has a RAN-AreaCode which is not part of the UEs RAN Notification Area. The UEs RAN Notification Area is configured to a UE 310 as part of the RRCRelease message when released to RRC inactive. A UE initiated trigger can happen if there is an expiry of timer T380, the periodic RAN Notification Area Update (RNAU) timer. In this case the cause value is rna-Update. Alternatively, a Network-triggered event can occur when the UE 310 receives a Paging message with a paging record matching its i-RNTI, i.e., a RAN-page.

[00024] RRC Resume is started by the UE 310 first synchronizing via random access and then transmitting a RRCResumeRequest message 375, which contains the identifier of the UE, the i-RNTI, which is specifically used for RRC inactive, i.e., resume identity and the resume cause. If the gNB 320 is able to locate the UE context, i.e., the configuration of the UE 310, the gNB 320 will reply with a RRCResume message 380, which may for instance contain a full configuration (else the UE 310 will use stored UE Inactive AS context for the connected mode configuration). This can optionally contain a number of configurations to reconfigure the UE if necessary. It can further include specific commands or configurations such as whether UE shall restore SCells, whether to restore SCG, SCG configurations and more. It may also contain a request for UE to report idle mode measurements in RRCResumeComplete. The UE 310 will restore security and the previous RRC configuration and then send the RRCResumeComplete message 385, which may contain a number of indications from the UE; and upon the procedure being completed the UE 310 will have completed the RRC Resume procedures.

[00025] There are some cases where RRC resume procedure may be diverted, aborted or cases where a gNB may respond by not continuing with the RRC Resume procedures. These cases include: (i) T319 expiry: The T319 is the UE timer that puts a limit on how long a UE may perform RRC Resume. Upon expiry the UE autonomously goes to RRC idle and lets upper layers deal with the re-connection (ii) Receiving RRCSetup in response to RRCResumeRequest: This can for instance occur if a gNB us unable to retrieve the UE context or any other errors preventing RRC Resume from being established. (iii) Receiving RRCReject in response to RRCResumeRequest: This may occur when the cell is overloaded or similar. In this case the UE may remain in RRC inactive and may be configured with a waitTime (T302), whereupon expiry the UE may re-attempt RRC Resume procedures. (iv) Receiving RRCRelease in response to RRCResumeRequest: This is for instance used when the RNAU is being performed and the network swiftly sends the UE back to RRC inactive (v) Inability to comply with RRCResume: In this case the UE will autonomously move to RRC idle.

[00026] Referring now to FIG. 4, a message sequence chart 400 is illustrated of a known reestablishment procedure after a radio link failure (RLF) 440, although re-establishment procedures can also be performed when a UE 210 fails a handover, as well as in cases of configuration failure. The message sequence chart 400 includes communications between a UE 410, an old gNB 420 and a new gNB 430. The known re-establishment procedure after a radio link failure (RLF) is declared at 440, are as follows. It is noted that such a re-establishment procedure may also occur after a Handover failure. At 445, idle mode cell selection is performed at UE 410. The UE 410 first performs random access and then, at 450, sends an RRC Reestablishment request to the new gNB 430. At 450, the new gNB 430 retrieves the UE 410 context from old gNB 420 (if the gNB 430 is not the same as the old gNB 420). At 460, the old gNB 420 returns the UE context to the new gNB 430. At 465, the new gNB 430 replies to the UE 410 with RRC Re-establishment and potentially reconfigures UE 410 if needed, or continues using the same RRC configuration as previously configured. If reconfiguring the UE 410, the new gNB 430 replies to the UE 410 with RRCSetup. At 470, the UE 410 responds with a RRC re-establishment is complete message.

[00027] Thus, it is known that the Cell DTX / DRX is introduced to allow a gNB (or a cell) to power down part of its receiver or transmit circuits momentarily to save energy. The time scale of the periods in which a gNB receiver or transmit circuit is shut off can be as low as 1 millisecond up to 1.6 seconds and the periodicity can be from 10 milliseconds up to 10 seconds.

[00028] However, the inventor has recognized and appreciated that one issue with this is that a base station scheduler is normally implemented considering that the receiver or transmitter is always turned ‘ON’. This makes the implementation of cell DTX / DRX much more complex, as it touches core parts of a base station / gNB operation, and thus is much more expensive to implement and ultimately to deploy.

[00029] Similarly, at the other end of design considerations, it is desirable to implement power saving features in order to completely shut down a cell for as long a period of time as possible. This can, for instance, be performed when the network detects that the traffic in the cell is low, such as during night time. This feature is likely to be a lot easier to implement in a base station / gNB, as a base station / gNB would often have already implemented procedure for shutting down a cell in a graceful manner. For instance, for maintenance or software or firmware updates of a base station / gNB, the base station / gNB may need to shut down a cell.

[00030] However, the inventor has recognized and appreciated that it is important to provide devices, circuits and methods for power saving, for example that falls between the complexity and short-term granularity of cell DTX / DRX and the long term and relatively easy to implement Cell-OFF procedures. [00031 ] Thus, the inventor has recognised and appreciated that a further need exists for devices, circuits and methods to shut off a cell and its procedures. Such procedures are currently not specified, but rather rely on a set of existing procedures that are normally used, for instance, for mobility or for access control. These known procedures are used, for instance, to handover UEs via connected mode handover or releasing a UE via RRC release. Furthermore, access control may be used where the cell is barred and / or the idle and inactive mode parameters are reconfigured to encourage the idle and inactive mode UEs to change cell. The inventor has recognised and appreciated that all of these procedures typically take a long time to complete and involve a lot of network implementation complexity. Summary

[00032] In a first aspect, a wireless communication system is described that comprises a plurality of base stations supporting communications in respective communication cells and a plurality of wireless communication units. A first wireless communication unit is associated with a first base station supporting communications on a first communication cell, wherein: the first base station comprises a transmitter arranged to transmit a first signal to at least the first wireless communication unit wherein the first signal indicates that the first cell is to be subsequently switched off; the first wireless communication unit comprises a receiver arranged to receive the first signal; and a processor and a transmitter operably coupled to the receiver and arranged to process the first signal and in response thereto perform mobility to a second base station supporting communications on a second communication cell; and the first base station switches off the first communication cell. In this manner, a mechanism to shut off a cell and associated procedures are provided that avoid taking a long time to complete and avoid involving a lot of network implementation complexity.

[00033] In a second aspect, a wireless communication unit supported by a base station in a wireless communication system is described. The wireless communication unit comprises: a receiver arranged to receive a first signal from the base station; a processor operably coupled to the receiver and arranged to process the first signal and identify therefrom that the first cell is to be subsequently switched off; and a transmitter operably coupled to the processor and in response to the processed first signal perform mobility to a second base station supporting communications on a second communication cell.

[00034] In a third aspect, a method for a wireless communication unit that is supported by a base station in a first communication cell in a wireless communication system is described. The method at the wireless communication unit comprises: receiving a first signal from the base station; processing the first signal and identifying therefrom that the first cell is to be subsequently switched off; and in response thereto performing mobility to a second base station supporting communications on a second communication cell. Brief Description of the Drawings

[00035] Further details, aspects and embodiments will be described, by way of example only, with reference to the drawings. In the drawings, similar reference numbers are used to identify like or functionally similar elements. Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. FIG. 1 illustrates a schematic diagram of Cell DTX along with its configured fields. FIG. 2 illustrates a schematic diagram of Cell DRX along with its configured fields. FIG. 3 illustrates a message sequence chart of a known RRC Resume procedure. FIG. 4 illustrates a message sequence chart of a known re-establishment procedure after a radio link failure (RLF). FIG. 5 illustrates a block diagram of a base station communicating with a UE, adapted in accordance with some example embodiments. FIG. 6 illustrates a simplified example of a Cell-off signal in a wireless network, adapted in accordance with some example embodiments FIG. 7 illustrates a simplified example message sequence chart of a base station, such as a gNB, communicating with a UE, where the UE operating in a high-level procedure of the Cell-off signal, in accordance with some examples. FIG. 8 illustrates a simplified example message sequence chart of a base station, such as a gNB, communicating with a UE, where the UE is considering migrating to cells that are part of the pre-configured cells, which the network has indicated in advance, in accordance with some examples. FIG. 9 illustrates two optional message sequence charts showing how the UE may re-establish to another cell, in accordance with some examples described herein. FIG. 10 illustrates UE monitors for paging in Paging Occasions, which is also used to deliver the Group Release message, in accordance with some examples described herein.

[00036] Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and / or relative positioning of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various examples. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various examples. It will be further appreciated that certain actions and / or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required. It will also be understood that the terms and expressions used herein have the ordinary technical meaning as is accorded to such terms and expressions by persons skilled in the technical field as set forth above except where different specific meanings have otherwise been set forth herein. Detailed Description

[00037] Examples herein described are focused on devices, circuits and methods for dynamic, efficient Cell-Off procedures for power saving, for example that fall between the complexity and short-term granularity of cell DTX / DRX and the long term and relatively easy to implement Cell-OFF procedures.

[00038] While examples herein described are generally described in terms of 5G NR, all proposals, embodiments, and examples are envisaged as being able to also apply for eNBs, NG-eNBs (eNBs connected via 5GC), as well as all related, newly defined and / or existing: RRC signaling and / or messages, X2, Xn, SI, NG, and / or Fl signaling and messages, and / or related network entities (e.g. MME, AMF, other). It is envisaged that examples herein described may also apply to any type of 6G technology. It is envisaged that 6G technology equivalent to the following 4G and 5G concepts may be employed in implementing the concepts described herein. In particular, it is envisaged that 4G and 5G devices that are in RRC connected state, where the UE has established a connection with a radio access network (RAN), i.e., a cell, gNB or similar identity, may benefit from the examples described herein.

[00039] As different terms are used for similar operations across 4G, 5G and 6G technologies, at least some of the following meanings, interpretations and definitions may be applied across the various intended technologies when applying the concepts herein described. ‘Cell’: This may be a different concept in a 6G system. For instance, in a cell-less case a UE may attach, connect and be associated with a beam or other similar identity, in contrast to a ‘cell’, per se in a 4G or 5G sense. ‘RRC idle’: Generally, this is understood to be when a UE is not in a RRC connected state, i.e., not having established a connection. ‘RRC idle’ also means that UE will be camping on a cell or similar identity and then performing measurements and evaluating to find a better cell or similar identity. ‘ 5G RRC inactive’: Here in a 5G system, a UE may be in a state similar to RRC idle where the UE stores the RRC configuration and resumes the RRC connection using the configuration. The network also stores the UE context and uses it to restore the UE connection. ‘5GRRC procedures (RRC Setup, RRC Resume, RRC Re-establishment, RRC Reconfiguration)’: In this 5G context, these include any procedures that aims to establish a connection with a cell, a (base station) gNB or similar identity. For instance, a procedure that aims to establish a 5G-6GDual Connectivity setting with a 5G and 6G cell. ‘Random access’: understood to be the process of synchronizing the medium access control (MAC) layer via sending a preamble and receiving a message that synchronizes the uplink, as well as following messages to resolve any contention. Radio Link Failure (RLF): is understood to be a failure of the radio link, which may be a failure based on measured radio signals, or based on operation in the cell, such as a number of retransmissions, random access failures, the radio beams failing etc. After the RLF, the UE may try to reselect to another cell and re-establish the RRC connection. ‘Handover: is understood to be performing active mobility to another cell, gNB or similar identity. ‘Releasing RRC connection’: is understood to be the UE being released via messages, such as RRC Release that releases the RRC connection the UE has to one or more cells. This may also include the UE

[00040] Referring now to FIG. 5, a block diagram of a base station 510, such as a 5G or 6G gNodeB (gNB), communicating with a wireless communication unit (such as a UE 550) is illustrated, where the respective communications units have been adapted in accordance with some example embodiments.

[00041] The gNB wireless base station 510 contains an antenna 502, for receiving transmissions, coupled to an antenna switch or duplexer 504 that provides isolation between receive and transmit chains within the gNB wireless base station 510. One or more receiver chains, as known in the art, include receiver front-end circuitry 506 (effectively providing reception, filtering and intermediate or base-band frequency conversion). The receiver front-end circuitry 506 is coupled to a signal processor 508 (generally realized by a digital signal processor (DSP)). A skilled artisan will appreciate that the level of integration of receiver circuits or components may be, in some instances, implementation-dependent.

[00042] The controller 514 maintains overall operational control of the gNB wireless base station 510. The controller 514 is also coupled to the receiver front-end circuitry 506 and the signal processor 508. In some examples, the controller 514 is also coupled to a frequency generation circuit 517 and a memory device 516 that selectively stores operating regimes, such as decoding / encoding functions, synchronization patterns, code sequences, and the like. A timer 518 is operably coupled to the controller 514 to control the timing of operations (e.g., transmission or reception of time-dependent signals) within the gNB wireless base station 510.

[00043] As regards the transmit chain, this essentially includes an input 520, coupled in series through transmitter / modulation circuitry 522 and a power amplifier 524 to the antenna 502, antenna array, or plurality of antennas. The transmitter / modulation circuitry 522 and the power amplifier 524 are operationally responsive to the controller 514. The signal processor 508 in the transmit chain may be implemented as distinct from the signal processor in the receive chain. Alternatively, a single processor may be used to implement a processing of both transmit and receive signals, as shown in FIG. 5. Clearly, the various components within the gNB wireless base station 510 can be realized in discrete or integrated component form, with an ultimate structure therefore being an application-specific or design selection.

[00044] The processor 508 and a transmitter part of the transceiver (e.g., transmitter / modulation circuitry 522) of the gNB wireless base station 510 are configured to transmit a cell-off signal is a message sent by a gNB wireless base station 510 that indicates to UE 550 that are attached, connected or camping on a cell, supported by the gNB wireless base station 510, in anticipation of the gNB wireless base station 510 turning ‘OFF’ communications on the cell. The gNB wireless base station 510 may send a pre-warning ‘cell-OFF’ signal in say a transmission / broadcast of a future / imminent turning its supported ‘cell-OFF’. This ‘cell-OFF’ signal is received by at least one UE 550, which in response thereto implements a mobility procedure. In examples herein described, the processor 508 and transmitter / modulation circuitry 522 (and in some instances receiver front-end circuitry 556 (at least) of the gNB wireless base station 510, may implement any of the processes described herein, for example following the example approaches of FIG. 6 to FIG. 10, to transmit the cell-off signal message, for example depending upon a state or mode of operation that the gNB wireless base station 510 is presently in, or available useful communication or logical channels.

[00045] FIG. 5 also shows a high-level block diagram of the wireless communication unit (a user equipment (UE) 550 in 3GPP™ parlance) that contains an antenna 552, for receiving transmissions, coupled to an antenna switch or duplexer 554 that provides isolation between receive and transmit chains within the wireless communication unit UE 550. One or more receiver chains, as known in the art, include receiver front-end circuitry 556 (effectively providing reception, filtering and intermediate or base-band frequency conversion). The receiver front-end circuitry 556 is coupled to a signal processor 558 (generally realized by a digital signal processor (DSP)). A skilled artisan will appreciate that the level of integration of receiver circuits or components may be, in some instances, implementation-dependent.

[00046] The controller 564 maintains overall operational control of the UE 550. The controller 564 is also coupled to the receiver front-end circuitry 556 and the signal processor 558. In some examples, the controller 564 is also coupled to a frequency generation circuit 567 and a memory device 566 that selectively stores operating regimes, such as decoding / encoding functions, synchronization patterns, code sequences, and the like. A timer 568 is operably coupled to the controller 564 to control the timing of operations (e.g., transmission or reception of time-dependent signals) within the UE 550.

[00047] As regards the transmit chain, this essentially includes an input 570, coupled in series through transmitter / modulation circuitry 572 and a power amplifier 574 to the antenna 552, antenna array, or plurality of antennas. The transmitter / modulation circuitry 572 and the power amplifier 574 are operationally responsive to the controller 564.

[00048] The signal processor 558 in the transmit chain may be implemented as distinct from the signal processor in the receive chain. Alternatively, a single processor may be used to implement a processing of both transmit and receive signals, as shown in FIG. 5. Clearly, the various components within the UE 550 can be realized in discrete or integrated component form, with an ultimate structure therefore being an application-specific or design selection.

[00049] The processor 558 and receiver front-end circuitry 556 collaborate to receive and decode a cell-off signal message from a supporting base station, e.g., gNB 510, which effectively informs supported UEs, such as UE 550, to perform a mobility procedure to another cell or network, e.g., a second gNB wireless base station. In this context, it is envisaged that the mobility procedure to another cell or network may include another frequency, another (or the same) radio access technology (RAT).

[00050] In examples herein described, the processor 558 and receiver front-end circuitry 556 (at least) of the UE 550 may implement any of the processes described herein, for example following the example approaches of FIG. 6 to FIG. 10, to receive and respond to the cell-off signal message, for example depending upon a state or mode of operation that the UE 550 is presently applying.

[00051] Referring now to FIG. 6, a simplified overview example of a Cell-off signal in a wireless network is illustrated, adapted in accordance with some examples. As illustrated, a cell-off signal is a message sent by a gNB wireless base station 510 that indicates to UEs 550, 551 that are attached, connected or camping on a cell 601, supported by the gNB wireless base station 510, in anticipation of the gNB wireless base station 510 turning ‘OFF’ communications on the cell. The cell-off signal message effectively informs supported UEs 550, 551 to perform a mobility procedure 690 to another cell or network, e.g., second gNB wireless base station 611 or third gNB wireless base station 609. In this context, it is envisaged that the mobility procedure 690 to another cell or network may include another frequency, another (or the same) radio access technology (RAT), such as 2G GERAN, 3G, 4GE-UTRAN and 5GNR, or another public land mobile network (PLMN).

[00052] Referring now to FIG. 7, a simplified (high-level) example message sequence chart 700 of a base station, such as a gNB wireless base station 510, communicating with a UE 550, where the UE operating in a high-level procedure of the Cell-off signal is illustrated, in accordance with some examples. The simplified example message sequence chart 700 starts at 705 with the network, e.g., the gNB wireless base station 510, deciding to turn ‘OFF’ the cell. At 710, the network, e.g., the gNB wireless base station 510, sends / broadcasts a ‘cell-OFF’ signal, which is received by at least one UE 550.

[00053] The inventor has realized and appreciated that the operation of a UE in a RRC state where it is connected may be different from the case where the UE is in an RRC state where it is not connected. However, in some examples, it is envisaged that the following approaches may not necessarily be taken, such that the UEs 510 need to operate differently depending on the RRC state.

[00054] In one example, it is envisaged that the ‘cell-off signal 710 may compromise the network, perhaps indicating that multiple cells will be switched off, not only the current cell that UE is associated with. In some examples, it may be understood that multiple cells are being switched off may be explicit in the ‘cell-off signal 710, i.e., the ‘cell-off signal 710 indicates those cells that are being switched off, including or not including the cell that sends the signal. In some examples, it may also be explicitly based on some pre-configured set of cells, which shall be assumed to be about to be turned ‘OFF’ when receiving the indication.

[00055] These multiple cells can be cells associated with the same gNB or the same cell site or base station. It can also be associated with a different gNB or another cell site or base station. In another aspect of the invention, the network may further indicate that operation on the frequency of the cell has ceased. This means that the cellular network may cease operation of multiple cells on the frequency instead of only the specific cell. This can indicate to UEs to migrate to other cells which are not on that specific frequency.

[00056] Upon receipt of this broadcast ‘cell-OFF’ signal, the UE performs a mobility operation to another cell or network at 715. At 720, the network, e.g., the gNB wireless base station 510, turns off the cell. Action of a connected mode UE when receiving cell-off signal.

[00057] In one example, when a UE 550, which may be in 'connected mode, receives the cell-off signal at 710, the UE 550 will be indicated to migrate to other cells.

[00058] When the UE 550 has received an cell-off indication, the UE 550 needs to migrate to the other cells. The inventor has recognized and appreciated that one potential issue here is that if there is a single signal that indicates that the UE 550 shall migrate, then it is not possible to indicate to specific UEs which cell they should migrate to. Thus, this scenario is different from a typical handover, where a UE 550 is provided with a cell identity to perform a handover to. In order to resolve this issue, in some examples, the UE 550 may be pre-configured with certain cells that the UE 550 shall attempt to migrate to if the cell-off signal is received. These cells may be dedicatedly configured by RRC or may be configured in a broadcasted manner via system information.

[00059] Thus, as an example, when the UE 550 connects to a cell, the UE 550 may be configured with cell-off fallback cells, say via RRC. When migrating, the UE 550 should either migrate by either only attempting migration to these cells, or the UE 550 shall prioritize these cells during the migration process. The difference between these two examples, is that in the case of prioritizing these cells the UE 550 may still consider migrating to cells that are not part of the pre-configured cells. The inventor has recognized and appreciated that this can be useful in cases where there may be cells that may be more suitable than the pre-configured fallback cells, which the network has indicated in advance. The example scenario of indicating pre-configured cell-off signals may be seen in FIG. 8. In this manner, the UE 550 performs fallback, where the UE 550 may consider migrating to cells that are part of the pre-configured cells.

[00060] Referring now to FIG. 8, a simplified example message sequence chart 800 of a base station, such as a gNB wireless base station 510, communicating with a UE 550, where the UE 550 is considering migrating to a new cell that may or may not be part of the pre-configured cells is illustrated, in accordance with some examples. The simplified example message sequence chart 800 starts at 802, with the network, e.g., the gNB wireless base station 510, sending / broadcasting a signal that configures UEs, such as UE 550, with at least one fall-back cell detail, for the UE 550 to use if / when a ‘cell-OFF’ signal is received. This configuration signal is received by at least one UE 550. Subsequently, at 805 the network, e.g., the gNB wireless base station 510, decides to turn ‘OFF’ the cell. At 810, the network, e.g., the gNB wireless base station 510, sends / broadcasts a ‘cell-OFF’ signal, which is received by at least one UE 550. Upon receipt of this broadcast ‘cell-OFF’ signal, the UE performs a mobility operation to another cell or network at 815, notably using the configuration of the at least one fall-back cell details received at 802. At 820, the network, e.g., the gNB wireless base station 510, turns off the cell.

[00061] In some alternative examples, if the UE 550 is not configured with pre-configured fallback cells when receiving the cell-off signal, the UE may either be configured to use any other procedure, such as cell selection, or it may ignore the cell-off signal at 810.

[00062] In some examples, the UE 550 may be arranged to search and measure these cells in order to assess whether they are suitable to migrate to. In some examples, the UE 550 may also search other cells or frequencies or RATs for other suitable cells, for instance if the indicated cells are not suitable, i.e., cannot be detected or with which the UE 550 may have too poor signal quality with.

[00063] Referring now to FIG. 9, two optional message sequence charts showing how the UE may re-establish to another cell are illustrated, in accordance with some examples described herein. In a first message sequence chart 900, the UE performs migration by re-establishing, for instance via RRC re-establishment, to another cell. The first message sequence chart 900 includes a base station, such as a gNB wireless base station 510, communicating with a UE 550, and also another gNB wireless base station 609, 611 that the UE 550 may migrate to.

[00064] The simplified example message sequence chart 900 starts at 905 with the network, e.g., the gNB wireless base station 510, deciding to turn ‘OFF’ the cell. At 910, the network, e.g., the gNB wireless base station 510, sends / broadcasts a ‘cell-OFF’ signal, which is received by at least one UE 550. In this example the UE performs re-establishment at 915, i.e., cell selection and selects another cell, e.g., gNB wireless base station 609, 611, to attach to.

[00065] For instance, in this example, the UE 550 receiving the cell-off signal at 910 triggers the UE to initiate a RRC re-establishment procedure at 915. The cell, e.g., gNB wireless base station 609, 611, that the UE 550 triggers re-establishment to may be one of the pre-configured cells, or any cell in the cell selection procedure of the re-establishment procedures. This is because one of the first actions of the RRC re-establishment procedure is that the UE 550 will perform cell selection. In some examples, the RRC re-establishment procedure may include actions such as: stopping certain timers, resetting states and releasing relevant configuration. The above procedures may, for instance, only be performed if AS security is established in advance.

[00066] In some examples, at 920, the RRC re-establishment procedure, performed by the UE 550 with the gNB wireless base station 609, 611, may also allow for the new cell, e.g., gNB wireless base station 609, 611, to retrieve the UE 550 context from the cell that indicated the cell-off signal, say via Xn. The UE 550 may, thus, indicate in the re-establishment procedure that the UE 550 received a cell-off signal at 910, for instance via an RRC re-establishment cause, for instance via RRC Re-establishment Request message. In some examples, the RRC reestablishment procedure at 920, performed by the UE 550 with the gNB wireless base station 609, 611, may include the UE 550 sending the RRC re-establishment request message to the selected gNB wireless base station 609, 611 at 922. In response thereto, at 924, the UE 550 receives an RRC Re-establishment message from the gNB wireless base station 609, 611 to confirm the request. At 926, the UE 550 sends the RRC Re-establishment Complete message to the gNB wireless base station 609, 611 in order to finish the procedure.

[00067] A second message sequence chart 950 of FIG. 9, again includes a base station, such as a gNB wireless base station 510, communicating with a UE 550, and also another gNB wireless base station 609, 611 that the UE 550 may migrate to. In this example, the UE 550 performs migration, for instance upon receiving the cell-off signal, by using the cell-off signal to trigger a Radio Link Failure (RLF) state. The second simplified example message sequence chart 950 starts at 955 with the network, e.g., the gNB wireless base station 510, deciding to turn ‘OFF’ the cell. At 960, the network, e.g., the gNB wireless base station 510, sends / broadcasts a ‘cell-OFF’ signal, which is received by at least one UE 550. In this example the UE performs reestablishment at 965, i.e., cell selection and selects another cell, e.g., gNB wireless base station 609, 611, to attach to. In this example, upon receiving the cell-off signal, the UE 550 uses the cell-off signal to trigger a Radio Link Failure (RLF) state at 965. The RLF would trigger the UE 550 to perform RRC Re-establishment at 970, where the UE 550 first performs cell selection. In some examples, it is envisaged that the UE 550 may log the RLF failure reason or cause, i.e., receiving cell-off indication, in an RLF report. This RLF report may be sent to a network at a later time if the network requests an RLF report. During the cell selection procedure the UE 550 will measure and search for cells and then select a cell with which to perform the RRC Reestablishment procedure at 975, to another cell such as the selected gNB wireless base station 609, 611. In some examples, the RRC re-establishment procedure at 975, performed by the UE 550 with the gNB wireless base station 609, 611, may include the UE 550 sending the RRC reestablishment request message to the selected gNB wireless base station 609, 611 at 982. In response thereto, at 984, the UE 550 receives an RRC Re-establishment message from the gNB wireless base station 609, 611 to confirm the request. At 986, the UE 550 sends the RRC Reestablishment Complete message to the gNB wireless base station 609, 611 in order to finish the procedure

[00068] In some examples, if AS security is activated, the UE 550 performs the operations 965, 970, 975, 982, 984, 986 as part of the RRC re-establishment procedures above, else the UE 550 moves directly to RRC idle mode. If the UE 550 moves directly to idle mode, the UE 550 may subsequently need to perform RRC idle mode procedures to migrate to another cell.

[00069] In one envisioned example, the cell-off signal may trigger an RRC resume procedure at the UE 550. Thus, when the UE 550 receives the cell-off signal from the network, e.g., the gNB wireless base station 510, the UE 550 may be triggered to perform an RRC resume procedure towards other cells, such as the gNB wireless base station 609, 611. This can for instance be performed by the UE 550 being released to RRC inactive state when receiving the cell-off signal. The UE 550 may also be triggered to perform a cell selection or cell reselection procedure when being released to RRC inactive via the cell-off signal. In order to ensure that the UE 550 connects, or reports to a new cell, the cell-off signal may also indicate to the UE 550 to trigger a RAN Area Update procedure. This is a procedure that is used when a UE 550 performs RRC inactive mode mobility, whereby if the UE 550 camps on a cell outside of the RAN Notification area defined by cells potentially tracking areas, the UE 550 performs RRC Resume to notify the cell that it is camping on a new RAN notification area.

[00070] In an alternative envisioned example, receiving the cell-off signal may also trigger any other type of RRC, MAC or lower layer procedure that triggers the UE 550 to perform any type of mobility to another cell. For instance, it is envisioned in other examples that the cell-off signal may trigger a conditional reconfiguration, LI-mobility or similar.

[00071] In an alternative envisioned example, receiving the cell-off signal may trigger the UE 550 to indicate to the new cell, such as the gNB wireless base station 609, 611, that the previous cell sent out a ‘cell-off’ signal. In some examples, this could for instance aid the new cell, such as the gNB wireless base station 609, 611, to reserve resources if there are a lot of new UEs expected to enter the cell. In some examples, it is envisioned that this may be indicated in a Msg5, i.e., an RRC Complete message.

[00072] In some examples, if the UE 550 is in a dual connectivity or a multi-connectivity setup, the actions of a UE 550 may be different. This may depend upon whether the supporting cell, e.g., gNB wireless base station 510, that sends out the cell-off signal is the main or secondary node of a UE 550. The main node (MN) of the dual connectivity connection, can be the PCell and the secondary node (SN) of the dual connectivity connection, can become the PSCell.

[00073] If the UE 550 receives a cell-off signal from a PCell, the UE 550 can either be configured to follow a set of fallback cells as configured by the network, or the network, e.g., gNB wireless base station 510, may configure the UE 550 to change the PCell to the PSCell, in other words the secondary node becomes the main node. When this switch occurs, the UE 550 may indicate to the secondary node that the secondary node has been switched to the main node.

[00074] If the UE receives a cell-off signal from a PSCell, the inventor has identified that there are also some options of the actions of the UE 550. For example, the UE 550 may be configured to follow a set of fallback cells for the PSCell connection, which the UE 550 then uses to find a new PSCell. The UE 550 may also be required to indicate to the PCell which cell was selected. In some examples, the cells for the UE 550 to migrate the Secondary Node may be configured in a different manner compared to the fallback cells. This is because the Main node and the Secondary Node likely need to have tight integration via Xn in order for a dual connectivity connection to be established. In some examples, the UE 550 may also be configured to completely switch off the PSCell and the UE 550 may then indicate this to the PCell. In this case the UE 550 will switch off or release the PSCell and then not attempt to perform any mobility of the secondary node.

[00075] In some examples, it is envisioned that the UE 550 action when receiving the cell-off signal may also include releasing the RRC connection with the cell or any other cells. This includes releasing the RRC configuration of the cells, as well as resetting all of the layers, etc. Action of an idle or inactive mode UE when receiving cell-off signal.

[00076] In some examples, it is envisioned that the UE 550 may also be pre-configured with fallback cells or frequencies for the UEs in idle or inactive mode, to be used following receipt of a cell-off signal. In some examples, it is envisioned that this may be configured via broadcasted methods in system information. In some examples, it is envisioned that it may also be preconfigured via RRC release when a UE 550 is released from a cell. Such configuration may, for instance, only be specific to RRC inactive. This may further enhance the RRC inactive mode compared to RRC idle, as mobility is made more enhanced for RRC inactive compared to RRC idle

[00077] In some examples, it is envisioned that when a UE 550 receives a cell-off signal in idle or inactive mode, the UE 550 may be configured to connect to the cell that it has been indicated to migrated to. This can for instance be to notify the new cell that a previous cell has been turned off, for instance via an indication that it migrated to the cell based on a cell-off signal. It is noteworthy here that, normally, idle and inactive mode cell reselection would not trigger the UE to notify or connect to the new cell. In some examples, the UE 550 may also include the cell identifier (ID) or any other identifier to indicate which cell that was turned off. In some examples, it is envisioned that this may also be a part of an RRC cause, part of an RRC establishment cause, RRC resume cause, or similar. Connecting to the cell it has migrated to may also be a way of ensuring that the UE 550 can be reachable. The inventor has recognized and appreciated that this may be especially important if a cell is turned ‘OFF’ and the network does not have full control of how the UEs migrate. Such a procedure may be termed a Cell Migration Update, or Cell-off Migration Update or similar.

[00078] In an alternative example, when a UE 550 receives a cell-off signal, in idle or inactive mode, the UE 550 may be configured to camp on the cell that it has been indicated to migrate to. Thus, the UE may, for instance, be triggered to perform cell reselection to one of the indicated cells, or frequency or any other network. The UE may, for instance, be triggered to connect to the cell based on any other triggers to connect to the cell. For instance, the UE may be configured to connect to a cell on different tracking area, which may trigger a tracking area update by the UE. It is also envisioned that the UE does not necessarily need to connect to the new cell if the network knows roughly which cell that the UEs have migrated to. This is because if the network knows what cells that the UE have migrated to, then the network knows how to reach the UE.

[00079] In a special case for a UE 550 being in RRC inactive mode, it is envisioned in some examples that receiving a cell-off signal while the UE 550 is in RRC inactive may, for instance, trigger the UE 550 to perform a RAN Notification Area Update after the UE 550 has selected or re-selected another.

[00080] In some examples, where receiving the cell-off signal trigger a cell selection, it is envisioned that this can be useful if for instance multiple cells are turned off and it is expected that the network topology may change as a result of the cell being turned off. This is because the cell selection procedures triggers the UE 550 to search frequencies according to saved information etc., as opposed to cell reselection that largely uses parameters, such as frequencies and RATs, configured by the cell. The inventor has recognized and appreciated that these parameters may potentially be outdated, once the cell-off signal is received.

[00081] In some examples, it is envisaged that the cell-off signal may alternatively trigger the UE 550 in RRC idle or RRC inactive to consider the cell to be barred. This action may thus trigger the UEs to not consider the cell to be camped on, if it is currently being camped on. It may also trigger all UEs to not consider the cell for cell reselection or cell selection. In combination with triggering cell selection or cell reselection upon receiving the cell-off signal, it will cause all UEs to perform mobility away from the cell. Cell-Off Signal.

[00082] In some examples, it is envisaged that the cell-off signal may be implemented and sent in one or more of several different ways. In this manner, this can affect which UEs may be able to read and acquire the cell-off signal message. In some examples, in order for the signal to only be a single type of message, there is a need for the signal to be acquired for UEs that are in any RRC state

[00083] Referring now to FIG. 10, a diagram 1000 shows a UE 550 that is arranged to monitor for paging in paging occasions, which is also used to deliver the Group Release message, in accordance with some examples described herein. Again, a base station, such as a gNB wireless base station 510, is communicating with a UE 550. The simplified example message sequence chart 700 starts at 705 with the network, e.g., the gNB wireless base station 510.

[00084] In some examples, it is envisaged that a Paging message may be used to indicate that the cell will turn ‘OFF’. This envisioned approach has the benefit that the signal is already designed to be received when the UE 550 is in an idle mode state. This can either be in the payload of the Paging message, which can be a bit indicating that the cell will turn off and that UE 550 shall perform actions to move to other cells. The payload of the Paging message may be in a PDSCH 1010, i.e., the downlink data channel, which in turn contains an RRC message. In some examples, a so-called Paging Short message may be used. The Paging Short message is a short message that is contained within the PDCCH channel 1005, that is received by a UE 550 when monitoring for paging assignments in so-called Paging Occasion (PO) 1015. The POs 1015 are UE-defined occasions where a specific UE 550 monitors for paging assignments. The UE 550 in RRC connected may be required to monitor for paging for this purpose, which can be configured by the network.

[00085] In some examples, it is envisaged that the cell-off signal may be a so-called group-release message. In this example, it is envisaged that this may be configured as a release message that is sent to multiple UEs. For example, this message may be sent over a Multicast Control Channel (MCCH), which is reachable by all UEs, instead of being a dedicated release message. Furthermore, in some examples, this can be an RRC message, for instance an RRC Release message. This can be receivable only in RRC connected or in any other RRC state such as RRC idle and RRC inactive.

[00086] In this example, it is envisaged that the paging framework may be used to send the group RRC release, by using the PDCCH 1005 used for indicating PDSCH 1010 used for delivering Paging messages. This PDSCH 1010 will then deliver the Group Release message, as a result the PCCH (Paging Control Channel) may be used to send the Group Release message. It is envisaged that there may be an indication in the PDCCH 1005 or in the PDSCH 1010 that the specific message is a Group Release message. This can potentially allow the message to be received in RRC idle and RRC inactive.

[00087] In some examples, it is envisaged that a new Control Channel may be introduced to handle the group releases, such as the RCCH (Release Control Channel). Here, this can also be a control channel that is combined with the channel for paging, RPCCH - Release Paging Control Channel.

[00088] A yet further envisioned example is where the UE 550 is configured to monitor specifically for a new message, e.g., a Cell-off indication (COI) message. With such a COI message, it is envisaged that this can be configured to coincide with the paging monitoring, or in other examples it can be separate therefrom. In this example, the UE 550 may thus be configured with COI message opportunities in which the UE 550 monitors for COI when the UE 550 is in any RRC state. When the UE 550 is RRC connected, such monitoring may either be precisely the same as for RRC idle or RRC inactive, or it may be different, for instance a UE 550 being configured to monitor more frequently. This monitoring may be made more infrequent in order for UEs to save power. For instance, the COI occasions can be configured for all UEs every, say, 1, 5, 10, 20 seconds.

[00089] A still yet further envisioned example is where a new type of dynamic system information is introduced. This can be a dynamic release SIB, which can, for instance, be achieved by replacing certain system information blocks with the cell-off signal. There may thus be signal that indicates where the expected SIB1 is sent, the network then sends to the UE 550 a release SIB, indicating that the cell is turning ‘OFF’ and that the UE 550 should migrate. It is envisaged that other information may also be sent. In some examples, it is envisaged that the MIB may also be replaced by the cell-off signal, or certain content may be replaced.

[00090] In some examples, it is envisioned that the cell-off signal may be sent in a MAC CE by the network, e.g., gNB wireless base station 510, to a UE 550. This can for instance be a broadcasted and secured MAC CE. Such MAC CE may be encrypted or integrity-protected or both. One benefit of this approach is that a MAC CE can be sent out faster compared to an RRC signal. Content of cell off signal. [00091 ] In accordance with some examples, it is envisaged that the content of the cell-off signal may include one (or more) of the following: Fallback, migration or “cell-off’ cells. These are the cells that the UE 550 may migrate to when the UE 550 receives the cell-off indication. In some examples, this may consist of the Physical Cell ID (PCI), logical Cell ID. In some examples, this may also be considered to be the migration cells. Fallback, migration or “cell-off’ frequencies. In some examples, these may be one or more frequencies that the UE 550 should migrate to if the UE 550 receives a cell-off indication. In some examples, this can be represented by one or more carriers, which may be signalled by an ARFCN value. Whether the UE 550 shall move to other cells, and which cells or network (frequency, RAT or similar) that the UE 550 shall move to. When the cell will turn ‘OFF’. How long a time the UE 550 has, in order to migrate to one or more cell(s). In some examples, this can for instance be a timer duration, where during the timer the UE shall attempt to migrate to one or more cell(s). If the UE fails to migrate to one or more indicated cells, then the UE may be configured to search for other cells. This can for instance be done via a cell selection algorithm, in other words an example is that after the timer has expired and the UE has not migrated to one or more indicated cells, the UE performs cell selection to potentially select a cell that was not indicated.

[00092] The cell off signal may also indicate whether other cells or network (one or more frequencies, one or more RATs or similar) are being turned ‘OFF’. In some examples, this may be used by the UE 550 to not perform or attempt to perform migration to one of these cells. This can be important as the cells, frequencies or RATs may not be turned ‘OFF’ at the same time. This also allows for more flexibility and less stringent synchronization when turning of a larger amount of cells or network.

[00093] Priorities of the signalled fallback cells. In some examples, this is envisaged as being, say, a number from, say, ‘1’ to ‘8’, which gives the priority of a fallback or migration cell. In some examples, this can be used if there are multiple fallback cells detected and one of them needs to be selected. The subcarrier spacing of one or more cells or one or more frequencies. Security Aspects.

[00094] In some envisaged examples, the network, e.g., gNB 510, may be configured to send messages that indicate that the cell is turning ‘OFF’. This may have some adverse impact on the network and the services that it provides. A malicious hacker may seek to utilize these impacts, for instance to cause service interruption by indicating that a cell that should not be turned off, is about to turn ‘OFF’. Thus, examples below propose a few scenario implementations that may be employed to reduce, minimize or prevent such a malicious attack.

[00095] For example, a serious attack that could be imagined with the cell-off signal is that an attacker may indicate that the UE 550 shall fallback to another RAT, which is less secure than that of a 5G NR or 6G network. For instance, an attacker may attempt to send a cell-off signal in order to get a UE 550 to fallback to a less-secure 2G or 3G, which have worse security compared to other RATs. To prevent this, it is envisaged that the cell-off signaling may be encrypted and / or integrity-protected. This may require that one or more key(s), which is common among one or more groups of UE(s), is used to receive the signal. Thus, it is envisaged that a specific key can be introduced for the cell-off signal. This can be setup when the UE 550 sets up security with a cell, or with a specific network.

[00096] In some envisaged examples, in order for the UE 550 to not ignore a cell-off signal, the network, e.g., gNB 510, may need to indicate or configure in advance that the cell may utilize this type of signal. In other words, if the network, e.g., gNB 510, has not configured or indicated in advance that a cell ‘OFF’ signal may be sent, the UE 550 will ignore the cell off signal.

[00097] In some envisaged examples, the cell-off signal may only be allowed on certain types of cells. This can for instance be on so-called capacity cells, only be allowed on certain frequencies, for instance cells above a certain frequency, or only be allowed on cells with a certain bandwidth. This can advantageously prevent cells that are more crucial for things like coverage to not be turned off by a malicious attacker.

[00098] In some envisaged examples, the UE may only be allowed to migrate to certain RATs when a cell-off signal is received, in other words restrictions may be placed on the RATs that the UE 550 may be allowed / instructed to migrate to. The allowed RATs may for instance be 4G E-UTRA and 5G and conversely the UE 550 may not be allowed to migrate to 2G or 3G. In some examples, it is envisaged that the allowed RATs may be configurable, so that the cell may be updated according to the latest security updates or developments. For instance, if 4G E-UTRA is in the future not considered safe, the network may be able to configure the network to not be allowed to fallback to a 4G E-UTRA RAT when receiving the cell-off signal, but only be allowed to fallback to 5G NR or a 6G RAT. Similarly to the above, in some examples, it is envisaged that the UE 550 may only be allowed to fallback to certain types of Core Networks. The UE 550 may not be allowed to fallback to a 4G Core, i.e., EPC, but may only be allowed to fallback to a 5G Core or a 6G Core.

[00099] In some envisaged examples, there may be security-related conditions when a UE 550 should accept a cell-off signal. In other words, the UE 550 will only start the migration procedure if certain security-related conditions are fulfilled when receiving the cell-off signal. This example scenario may be used to prevent an attacker from sending a cell-off signal in the hope to shut down a network or a part of a network. [000100] In some envisaged examples, the UE 550 may be configured with a token that needs to be included in a cell-off signal before a UE 550 will accept a certain cell-off signal, and subsequently start the migration procedure. It is envisaged that this token may be a bit string, say 24 bits long, that the UE 550 is configured with in advance, and that the UE 550 needs to receive before accepting a cell-off signal. Multiple UEs may be configured with the same token, or each UE 550 may be configured with a unique token. If the UE 550 receives a cell-off signal without such a token, the UE 550 will not consider any subsequently received cell-off signal. [000101] In some envisaged examples, if the UE 550 receives too many cell-off signals, the UE 550 will not accept another cell-off signals. This may be that UE 550 has received too many cell-off signal attempts close in time. Network Aspects [000102] In some envisaged examples, the network may indicate, or is required to indicate, to other cells or gNBs e.g., gNBs 609, 611 from FIG. 6, if a cell-‘OFF’ signal has been sent out. It is envisaged that this can help other cells and core network functionality (e.g. user plane or data plane management or session management functionality / function) to re-balance its resources. In some envisaged examples, a network node (gNB 510, cell or similar) may indicate to another network node that it is required or that the network node wants to be made aware if the other network node turns off a cell, or sends out a cell-off signal. [000103] In some envisaged examples, the gNB 510 may, after having sent out the cell-off signal in the cell, send the UE 550 contexts of the UEs that are currently attached to the cell to neighbouring gNBs, e.g., gNBs 609, 611 from FIG. 6. This may be perfomed in anticipation of the UE context being required for some of the methods mentioned above, e.g., in anticipation of the UE 550 performing RRC re-establishment, RRC resume or any other method to the cells that the UE 550 is performing migration to. [000104] In some envisaged examples, the core network may send assistance information for deciding ‘on’ / ’off, e.g., by indicating the following information to the gNB / base station: [000105] Traffic characteristics: e.g. the uplink (UL) and / or downlink (DL) traffic / data Periodicity, UL / DL / overall data volume, data rate (max., guaranteed, etc.). Based on the Traffic characteristics information, the gNB 510 may determine when to the turn off / on the cell and the duration of cell on / off status. Traffic characteristics can be cell level, UE level, or for groups of UEs (e.g. RRC connected UEs, RRC inactive UEs, UEs requires higher service quality or higher service priority, etc.). [000106] Conditions of neighbor cells: e.g., Congestion / service load level / traffic level / number of UEs / PDU sessions / of neighbor cells. The information of neighbor cells will help gNB 510 to determine whether to turn off the cell to transfer the load to other cells, or whether to turn on the cell to steer some UEs to the new cell to avoid congestion and service degradation. [000107] Indication of End of Data Burst: similar to the core network assisted DRX configuration for RRC connected UEs in 5G, the core network may indicate the End of Data Burst and then the gNB may determine to switch off the cell once receives this information. The indication of end of data burst / transmission can be associated to any UE 550 in the cell, or specific UEs / specific PDU sessions in gNB interests (e.g., RRC connected UEs, RRC inactive UEs, UEs requires higher service quality or higher service priority, etc.). [000108] Indication of data arrival: the core network may indicate to the gNB 510 there is data arrived for the cell / UE 550 serviced by the cell that has been turned ‘OFF’. If there is no other cell serving the UE 550, for a suitable service quality issue, the gNB 510 may determine to turn on the beam / cell / TRP to serve this UE 550 upon receving the data arrival indication. [000109] In some envisaged examples, it is envisaged that the concepts described herein may be used in a non-terrestrial cell to indicate that the NTN cell will be turned off. [000110] In some envisaged examples, it is envisaged that the cell-off signal may be a single type of signal that is sent one time, in order to signal to all UEs supported by a base station, such as gNB 510, that a cell is being turned ‘OFF’. In some instance, however, it is envisaged that there may be a need to repeat the cell-‘OFF’ signal if UEs are not continuously monitoring the cell, or they are transitioning to the cell, but not yet fully listening in the cell that is about to turn ‘OFF’. [000111] In some envisaged examples, it is envisaged that the concepts described herein may also be used at the end of a cell switch ‘OFF’ procedure, where the cell or gNB 510 may first try to gracefully handover UEs to maintain service continuity. If these procedures fail or take too long a time, for instance due to slow handover procedures, handovers failing or too many UEs in the cell, the cell or gNB 510 may start employing the cell-off signal in order to vacate the UEs rapidly. [000112] In some of the examples herein described, the term “network” may encompass the core network or a base station (such as a 5G gNB), as both may be employed in the techniques herein described. Therefore, in and across some examples, the terms “network” and “base station” and “gNB” have been used interchangeably. [000113] In accordance with some examples, proposed changes to the 3GPP™ standard are as highlighted {emphasis added} and as illustrated below: [000114] Example #1: ----------------------Example based on 38.331 VI8.2.0---------------------- Table 6.5-1: Short Messages Bit Short Message 1 systemlnfoModification If set to 1: indication of a BCCH modification other than SIB6, SIB7, SIB8 and posSIBs. 2 etwsAndCmasIndication If set to 1: indication of an ETWS primary notification and / or an ETWS secondary notification and / or a CMAS notification. 3 stopPagingMonitoring This bit can be used for only operation with shared spectrum channel access and if nrofPDCCH-MonitoringOccasionPerSSB-InPO is present. If set to 1: indication that the UE may stop monitoring PDCCH occasion(s) for paging in this Paging Occasion as specified in TS 38.304

[20] , clause 7.1. 4 systemlnfoModification-eDRX If set to 1: indication of a BCCH modification other than SIB6, SIB7, SIB8 and posSIBs. This indication applies only to UEs using IDLE eDRX cycle longer than the BCCH modification period. 5 cellOfflndication If set to 1: Indicates that network will turn off the cell and that the UE shall migrate to other cells. 6-8 Not used in this release of the specification, and shall be ignored by UE if received. ----------------------Example based on 38.331 VI8.2.0---------------------- [000115] In particular, it is envisaged that the aforementioned inventive concept can be applied by a semiconductor manufacturer to any integrated circuit comprising a signal processor configured to perform any of the aforementioned operations. Furthermore, the inventive concept can be applied to any circuit that is able to configure, process, encode and / or decode signals for wireless distribution. It is further envisaged that, for example, a semiconductor manufacturer may employ the inventive concept in a design of a stand-alone device, such as a digital signal processor, or application-specific integrated circuit (ASIC) and / or any other sub-system element. [000116] It will be appreciated that, for clarity purposes, the above description has described example embodiments with reference to different functional units and processors. However, it will be apparent that any suitable distribution of functionality between different functional units or processors, for example with respect to the signal processor may be used without detracting from the concepts described herein. For example, functionality illustrated to be performed by separate processors or controllers may be performed by the same processor or controller. Hence, references to specific functional units are only to be seen as references to suitable means for providing the described functionality, rather than indicative of a strict logical or physical structure or organization. [000117] Aspects may be implemented in any suitable form including hardware, software, firmware or any combination of these. Examples may optionally be implemented, at least partly, as computer software running on one or more data processors and / or digital signal processors or configurable circuit components such as field programmable gate array (FPGA) devices. Thus, the elements and components of an example may be physically, functionally and logically implemented in any suitable way. Indeed, the functionality may be implemented in a single unit, in a plurality of units or as part of other functional units. [000118] Although the concepts have been described in connection with some examples, it is not intended to be limited to the specific form set forth herein. Rather, the scope is limited only by the accompanying claims. Additionally, although a feature may appear to be described in connection with particular embodiments, one skilled in the art would recognize that various features of the described examples may be combined in other examples. In the claims, the term ‘comprising’ does not exclude the presence of other elements or steps. [000119] Furthermore, although individually listed, a plurality of means, elements or method steps may be implemented by, for example, a single unit or processor. Additionally, although individual features may be included in different claims, these may possibly be advantageously combined, and the inclusion in different claims does not imply that a combination of features is not feasible and / or advantageous. Also, the inclusion of a feature in one category of claims does not imply a limitation to this category, but rather indicates that the feature is equally applicable to other claim categories, as appropriate. [000120] In accordance with examples herein described, a wireless communication unit, e.g., in a form of a user equipment, a base station, e.g., in a form of a gNB, a wireless communication system and a number of methods are provided to enable the UE to move to another cell supported by a different base station in response to receiving a cell ‘OFF’ signal from a supporting base station, wherein the aforementioned disadvantages with prior art arrangements have been substantially alleviated. Abbreviations / D efinitions In the present disclosure, the following acronyms / definitions are used. 3 GPP 3rd Generation Partnership Project 5G 5th Generation 5GC 5G Core 5QI 5G QoS Identifier 5GS 5G System 5GSM 5G System Session Management 5GMM 5G System Mobility Management AF Application Function AI Artificial Intelligence AM Acknowledged Mode AMF Access and Mobility Management Function AS Application Server ASP Application Service Provider AUSF Authentication Server Function CDN Content Delivery Network CN Core Network DCAF Data Collection Application Function DNAI Data Network Access Identifier DNN Data Network Name DNS Domain Name Server DRB Data Radio Bearer gNB Evolved Node B EPC Evolved Packet Core FEC Forward Error Correction FQDN Fully Qualified Domain Name GBR Guaranteed Bit Rate gNB Next generation Node B GPSI Generic Public Subscription Identifier HSS Home Subscriber Service IAB Integrated Access and Backhaul ID Identity / Identifier IIoT Industrial Internet of Things IMEI International Mobile Equipment Identities IP Internet Protocol I-SMF Intermediate SMF LADN Local Area Data Network LLSSM Lower Layer SSM MBMS Multimedia Broadcast / Multicast Service MBS Multicast / Broadcast Service MBSF Multicast / Broadcast Service Function MBSTF Multicast / Broadcast Service Transport Function MB-SMF Multicast / Broadcast Session Management Function MB-UPF Multicast / Broadcast User Plane Function ML Machine Learning MME Mobility Management Entity MN Master Node MNF Monitoring Network Function MNO Mobile Network Operator MT Mobile Termination NAS Non-Access Stratum NEF Network Exposure Function NRF Network Repository Function NG-RAN Next Generation Radio Access Network NG-gNB Next Generation gNB NSA Non-Standalone NSSF Network Slice Selection Function NTN Non-Terrestrial Networks NW Network NWDAF Network Data Analytics Function OS Operating System OSAPP OS Application PCF Policy Control Function PCO Protocol Configuration Options PDR Packet Detection Rule PDU Protocol Data Unit PTM Point To Multipoint PTP Point to Point QFI QoS Flow Identifier (ID) QoS Quality of Service RACH Random Access Channel RAN Radio Access Network RRC Radio Resource Control RSD Route Selection Descriptor RSRP Reference Signal Received Power RSRQ Reference Signal Received Quality RSS Reference Signal Strength RSSI Received Signal Strength Indicator. SA Standalone SDAP Service Data Adaptation Protocol SDU Service Data Unit SGW Serving Gateway SIM Subscriber Identity Module SLA Service Level Agreement SM Session Management SMF Session Management Function SN Secondary Node S-NSSAI Single Network Slice Selection Assistance Information SSB Synchronization Signal Block SSM Source Specific IP Multicast address ssc Session and Service Continuity SRB Signalling Radio Bearer SUPI Subscription Permanent Identifier TA Tracking Area TAI Tracking Area Identity TE Terminal Equipment TM Transparent Mode TMGI Temporary Mobile Group Identity TS Technical Specification UDM Unified Data Manager UDR Unified Data Repository UE User Equipment UL Uplink UM Unacknowledged Mode UP User Plane UPF User Plane Function URLLC Ultra-Reliable and Low-Latency Communication URSP UE Route Selection Policy

Claims

1. A wireless communication system (600) comprises a plurality of base stations supporting communications in respective communication cells and a plurality of wireless communication units, wherein a first wireless communication unit (550) is associated with a first base station (510) supporting communications on a first communication cell (610), wherein:the first base station (510) comprises a transmitter (524) arranged to transmit a first signal (710) to at least the first wireless communication unit (550) wherein the first signal (710) indicates that the first cell is to be subsequently switched off;the first wireless communication unit (550) comprises a receiver (556) arranged to receive the first signal; and a processor (558) and a transmitter (572, 574) operably coupled to the receiver (556) and arranged to process the first signal (710) and in response thereto perform mobility (690) to a second base station (611) supporting communications on a second communication cell; andthe first base station (510) switches off the first communication cell (610).

2. The wireless communication system of Claim 1, wherein the first wireless communication unit being associated with the first base station comprises the first wireless communication unit being in one of the following operational states: camped on the first cell, connected to the first cell, attached to the first cell.

3. The wireless communication system of Claim 1 or Claim 2, wherein the first base station (510) broadcasts the first signal (710) to a plurality of wireless communication units (550) supported in the first communication cell the first signal indicates that the first cell is to be subsequently switched off.

4. The wireless communication system of any preceding Claim wherein the first signal indicates that a plurality of cells that includes the first cell are to be subsequently switched off.

5. The wireless communication system of Claim 4 wherein the first signal indicates that a frequency used by the plurality of cells is to be subsequently switched off.

6. The wireless communication system of any preceding Claim wherein the first wireless communication unit (550) is in a radio resource connected, RRC, mode.

7. The wireless communication system of Claim 6, wherein the first signal identifies a plurality of cells that are to be subsequently switched off, either explicitly or based on a preconfigured set of communication cells.

8. The wireless communication system of any preceding Claim wherein the pre-configured set of communication cells identify a number of communication cells that the first wireless communication unit (550) is instructed to migrate to.

8. The wireless communication system of any preceding Claim wherein the pre-configured set of communication cells are configured via broadcasted system information.

9. The wireless communication system of Claim 7 or Claim 8, wherein the first wireless communication unit (550) is arranged to prioritize the pre-configured set of communication cells that the first wireless communication unit (550) is instructed to migrate to during the migration process.

10. The wireless communication system of Claim 6, wherein the first wireless communication unit (550) migrates to another cell using RRC re-establishment.

11. The wireless communication system of Claim 10, wherein the second base station (611) is arranged to retrieve a context of the first wireless communication unit (550) from the first base station that transmit the first signal.

12. The wireless communication system of Claim 6, wherein the first wireless communication unit (550) is arranged to indicate in RRC re-establishment that the first wireless communication unit (550) received the first signal in a RRC Re-establishment Request message.

13. The wireless communication system of Claim 6, wherein the first wireless communication unit (550) is arranged to send the RRC re-establishment request message to the first base station, and in response thereto, receives an RRC Re-establishment message from the first base station 609, 611 to confirm the RRC re-establishment request.

14. The wireless communication system of Claim 6, wherein the first wireless communication unit (550) is arranged to migrate to a second base station, following receipt of the first signal, where the first signal is arranged to trigger a radio link failure, RLF, state, wherein the RLF triggers (970) the first wireless communication unit (550) to perform RRC Re-establishment.

15. The wireless communication system of Claim 6, wherein the first signal is arranged to trigger the first wireless communication unit (550) to perform one of: an RRC resume procedure towards the second base station, released to a RRC inactive state, a cell selection or cell reselection procedure when being released to RRC inactive, RRC inactive mode mobility, radio access network, RAN, Area Update procedure, RAN Notification Area Update, release an RRC connection with the first base station.

16. The wireless communication system of any preceding Claim, wherein the first signal is arranged to trigger the first wireless communication unit (550) to identify to the second base station that the first base station had sent out a first signal.

17. The wireless communication system of any preceding Claim, wherein the first signal is one of: paging message, a short paging message, a group-release message.

18. The wireless communication system of any preceding Claim, wherein the first signal is arranged to replace one of: a dynamic release system information block, SIB, a main information block, MIB.

19. The wireless communication system of any preceding Claim, wherein the first signal is broadcasted in one of: a medium access control, MAC, control element, CE, a secured MAC CE, an encrypted first signal, an integrity-protected first signal.

20. The wireless communication system of any preceding Claim wherein the mobility 690 to the second base station (611) performed by the first wireless communication unit (550) comprises the processor (558) of the first wireless communication unit (550) being arranged to perform at least one of the following: switch to an alternative frequency, switch to an alternative radio access technology, RAT, switch to an alternative public land mobile network, PLMN.

21. A wireless communication unit (550) supported by a base station (510) in a wireless communication system (600), wherein the wireless communication unit (550) comprises:a receiver (556) arranged to receive a first signal from the base station (510);a processor (558) operably coupled to the receiver (556) and arranged to process the first signal (710) and identify therefrom that the first cell is to be subsequently switched off; anda transmitter (572, 574) operably coupled to the processor (558) and in response to the processed first signal (710) perform mobility (690) to a second base station (611) supporting communications on a second communication cell.

22. A method for a wireless communication unit (550) that is supported by a base station (510) in a first communication cell in a wireless communication system (600), the method at the wireless communication unit (550) comprising:receiving a first signal from the base station (510);processing the first signal (710) and identifying therefrom that the first cell is to be subsequently switched off; and in response theretoperforming mobility (690) to a second base station (611) supporting communications on a second communication cell.IntellectualPropertyOfficeApplication GB2510503.2Search report under Section 17 of the Patents Act 1977Date search completed: 21 October 2025Claims searched: 1-22International classificationSubclass and subgroup Valid from H04W36 / 00 01 / 01 / 2009 H04W52 / 02 01 / 01 / 2009Field of searchWorldwide search of patent documents classified in the following areas of the IPC:H04WDatabases used in the preparation of this search report:SEARCH-NPL; SEARCH-PATENTDocuments considered to be relevantPatent literatureCategory Relevant claims Document of relevance X 1-22 US 2024 / 0098585 A1 HWANG et al., See paragraphs [0049], and [0050]Intellectual Property Office is an operating name of the Patent Office www.gov.uk / ipo43X 1-22 WO 2023 / 170613 A1 NOKIA TECHNOLOGIES OY, See paragraphs [0070], [0082] and [0083] X 1-22 WO 2023 / 201747 A1 ZTE CORP, See page 12 X 1-22 GB 2618316 A NEC CORP, See page 2, lines 25-28 X 1-22 WO 2024 / 063541 A1 SAMSUNG ELECTRONICS CO LTD, See paragraphs [9] and [10] X 1-22 KR 1020240040624 A SAMSUNG ELECTRONICS CO LTD, See paragraphs [0161] and [0167]Non-patent literatureCategory Relevant claims Document of relevanceCategoriesLetter or symbol Description X Document indicating lack of novelty or inventive step. Y Document indicating lack of inventive step, if combined with another document of the same category. & Member of the same patent family. A Document indicating technological background. P Document published on or after the priority date but before the fling date of the present application.Letter or symbol Description E Earlier application published on or after the filing date of the present application.

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