GB2568513A - Paging systems - Google Patents

Abstract

A paging message is transmitted in a cellular wireless communication network wherein the paging message comprises a group indication which indicates at least one group of UEs to which the paging message applies, and at least one UE indication. Also provided is the transmitting of a paging indication from a base station which indicates that a paging message is available and the at least one UE indication providing an identifier of the UE being paged. A paging message is processed at a UE, wherein the UE determines if it is part of the indicated group of UEs and determines if the UE is further identified as an unpaged UE in the group of UEs. The base station may utilise beam-sweeping transmission means and the paging message may be transmitted on all beams of the beam-sweeping transmission means. The identifier of the at least one paged and/or at least one unpaged UE may be the S-TMSI or IMSI of the UE. A paging format indicator may be transmitted in a paging DCI.

Description

PAGING SYSTEMS

Technical Field [0001] The current disclosure relates to systems and methods for paging user equipment (UE) in a cellular wireless network, and in particular to such methods for use with beam-sweeping.

Background [0002] Wireless communication systems, such as the third-generation (3G) of mobile telephone standards and technology are well known. Such 3G standards and technology have been developed by the Third Generation Partnership Project (3GPP). The 3^rd generation of wireless communications has generally been developed to support macro-cell mobile phone communications. Communication systems and networks have developed towards a broadband and mobile system.

[0003] The 3rd Generation Partnership Project has developed the so-called Long Term Evolution (LTE) system, namely, an Evolved Universal Mobile Telecommunication System Territorial Radio Access Network, (E-UTRAN), fora mobile access network where one or more macro-cells are supported by a base station known as an eNodeB or eNB (evolved NodeB). More recently, LTE is evolving further towards the so-called 5G or NR (new radio) systems where one or more cells are supported by a base station known as a gNB.

[0004] In cellular wireless systems, wireless coverage is provided by a set of base stations, each covering a “cell”. UEs are free to roam between those cells. In order to reduce power usage by UEs, and improve usage of radio resources, UEs may not be in constant communication with a base station, albeit a connection to the PLMN is maintained. For example, a UE may be in RRC idle mode. The PLMN, and each base station, may not therefore be aware of the precise location of the UE when a signal needs to be transmitted to the UE.

[0005] The standards therefore implement a paging procedure in which base stations transmit a paging signal. UEs are configured to listen for such paging signals at defined intervals. If a signal is received which is decoded as being for a particular UE that UE “wakes up” and establishes a communication link with the appropriate base station, for example using a random access procedure.

[0006] Base stations may be configured with a beam-sweeping antenna or antenna panel which allows signals to be directed in only certain directions, which can improve radio resource efficiency and coverage. However, due to the unknown location of each UE it is necessary to transmit the paging signal on all beams in a given cell, even though the UE is positioned, at most, in one of them. Paging in a beam-sweeping system thus increases the paging overhead.

[0007] A system is thus required to reduce the overhead incurred when implementing a paging system in a beam-sweeping scenario.

Summary [0008] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

[0009] There is provided a method of paging UEs in a cellular wireless communication network, comprising the steps of transmitting a paging indication from a base station, indicating a paging message is available; and transmitting a paging message, wherein the paging message comprises a group indication which indicates at least one group of UEs to which the paging message applies, and at least one UE indication, each UE indication indicating a paged UE to which the paging message applies, wherein the at least one UE indication comprises an identifier of the UE being paged.

[0010] The group indication of at least one group may be formed as a bitmap.

[0011] The base station may utilise a beam-sweeping transmission means and the paging message is transmitted on all beams of the beam-sweeping transmission means.

[0012] The paging message may further comprise at least one unpaged UE indication, each unpaged UE indication indicating an unpaged UE in the at least one paged group of UEs, to which the paging message does not apply, wherein the unpaged UE indication comprises an identifier of th the unpaged UE.

[0013] The identifier of the at least one paged and/or at least one unpaged UE may be the STMSI orlMSI of the UE.

[0014] The method may further comprise the step of transmitting from the base station a paging format indicator.

[0015] The paging format indicator may comprise an indication that a paging message comprises the group indication.

[0016] The paging format indicator may be transmitted in a paging DCI or in a paging message.

[0017] The paging message may be the paging message to which the paging format indicator relates.

[0018] The method may further comprise the step of transmitting, in a paging DCI, an indication of UE groups to which a subsequent paging indication may apply.

[0019] The paging message may have a fixed format in which the group indication is at a fixed position in the paging message and the at least one UE indication follows the group indication.

[0020] The method may further comprise indicating at least one group of UEs, in a paging DCI transmitted by the base station, to which the paging message does not apply.

[0021] The method may further comprise the steps of allocating at least one universal P-RNTI and at least one group-common P-RNTI to at least one UE, and utilising the group-common P-RNTI to scramble a paging indication message such that only UEs allocated to the groupcommon P-RNTI can decode the paging indication.

[0022] UEs may be grouped in a number of groups which remains static or semi-static.

[0023] There is also provided a method of processing a paging message, the method performed at a UE on a message received from a base station of a cellular wireless communication network; the method comprising the steps of receiving the paging message; determining if the UE is in a group of UEs indicated by the message as being paged; and determining if the UE is further identified as an unpaged UE in the group of UEs.

[0024] The UE may be further identified by an identifier of the UE.

[0025] The identifier may be the S-TMSI or IMSI of the UE.

[0026] The UE may return to a sleep mode if the UE is not in a group of UEs indicated as being paged and not paged individually by its UE ID, or if the UE is in a paged group and the UE is further indicated as being unpaged.

[0027] The non-transitory computer readable medium may comprise at least one from a group consisting of: a hard disk, a CD-ROM, an optical storage device, a magnetic storage device, a Read Only Memory, a Programmable Read Only Memory, an Erasable Programmable Read Only Memory, EPROM, an Electrically Erasable Programmable Read Only Memory and a Flash memory.

Brief description of the drawings [0028] Further details, aspects and embodiments of the invention will be described, by way of example only, with reference to the drawings. Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. Like reference numerals have been included in the respective drawings to ease understanding.

[0029] Figure 1 shows a decision tree for receiving a paging signal.

Detailed description [0030] In the LTE paging system, a UE in idle mode wakes up at defined Paging Occasions (PO) in a Paging Frame (PF) and monitors the PDCCH to check for a Paging Indication (PI).

If an indication for the UE is received a related Paging Message (PM) carried on PDSCH is decoded to ascertain if it is for the particular UE. Pls are directed to all UEs configured in a certain PO and therefore the indicated PM is not applicable for all UEs which decode the PM based on receipt of the PI. The PF is a radio frame that may contain one or more POs. The PO and PF for each UE are derived from the UE-ID and the current network configuration (DRX cycle and parameter nB), thus enabling UEs to be distributed across POs. PDCCH scrambled with P-RNTI in Common Search Space (C-SS) is used for scheduling the PM, and the same PM is sent by all eNBs in a given tracking area, or in multiple tracking areas for later releases of LTE, where the UE is expected.

[0031] When beam-sweeping is implemented the PI & PM should be repeated on each beam as the precise location of the UE is not known. This leads to an increase in UE power consumption (UE needs to wake up for the PO in each beam, which will be at different times), and an increase in paging overhead due to the repetition.

[0032] Set out below are various mechanisms for reducing the paging overhead in both static and beam-sweeping systems, and which also provide power saving and reduced UE false alarms.

[0033] The most applicable paging mechanism is likely to vary depending on network configuration and deployment. To enable flexibility a Paging Format Indicator (PFI) is added to the paging DCI (DCI Scrambled with P-RNTI). The PFI indicates the paging techniques that will be utilised, and in particular the format of the PM which a UE can expect. The following options may be available for PM content:-

1. Paging group indication.

2. UE-ID (S-TMSI or IMSI) indication.

3. Combined group indication and UE-ID.

4. Compressed UE-ID.

[0034] Any suitable format may be utilised for the PFI. Furthermore, the PFI could be located in the PM, rather than in DCI, in a fixed location.

[0035] As opposed to identifying individual UEs in the PM, UEs can be grouped and an indication of which group is being paged included in the UE. The use of a group indication can provide a very large reduction in PM length as the group indication can be much shorter than the UE-ID used to identify a particular UE.

[0036] While this reduces (potentially very significantly) the amount of data transmitted in PMs, it may also increase the number of UEs that start an access procedure when it is not needed. It is unlikely every UE in a group is being paged, but all UEs in the indicated group receiving the PM will start an access procedure as it appears the PM is for them. The false access procedures will create network overhead, but techniques are known for rapidly concluding false access requests thus minimising the impact. Furthermore, the reduction in PM length can be so significant that the overall effect is beneficial for the network.

[0037] The paging group indication may be in the form of a bitmap, with each bit of the indicator corresponding to a group.

[0038] One method to associate UEs to paging groups is through some deterministic computation utilizing some or all of the following parameters: UE ID, cell ID and system information. A way to associate UEs to groups is using the UE ID (IMSI or S-TMSI) modulo number of groups.

[0039] As indicated in option 3 above, the group indication may be used in combination with an indication of individual UEs. For example, if a group only contains a single UE (or small number) to be paged it may be more efficient to identify that UE explicitly, rather than the group. The network can thus balance paging overhead against the impact of false paging and select the most appropriate balance. Such balancing may take into account group sizes, cell sizes, number of beams, user density, and over network dynamics. Although the number of groups in a cell can be changed dynamically, this is relatively complex as group/UE associates must be updated on a dynamic basis for all UEs affected. For this reason, it may be preferable to keep the number of groups in a cell semi-static.

[0040] The PFI (in the DCI or PM itself) may indicate that the PM contains a mix of a group indication and individual UEs. Alternatively, a fixed format may be utilised for the PM with the group indication in a set location and the remainder of the PM comprising UE-IDs, with the total length being known from the DCI. This avoids the gNB having to indicate the PM format. This kind of fixed location assignment to the paging group indication within the paging message lets all the user understand the content of the paging message without any additional signalling. Thus, no PFI style flag is required in this case.

[0041] As an example of the improvement that may be achieved, consider a system with 1000 UEs assigned to a particular PO in a cell with 64 beams. There is a requirement to page 50 of the UEs.

[0042] With a conventional approach the paging message will be 2000 bits long (50 UEs x 40bits/UE), giving a total paging message load of 64 beams x 2000 = 128 kbits.

[0043] In the above technique, the UEs may be divided into 50 groups, giving 20 UEs per group. As an example, 10 groups each carry 4 of the UEs to be paged, and 10 groups each carry a single UE to be paged, giving 20 active groups for this PO.

[0044] The network decides to page the ten groups with multiple UEs on a group basis (50 bits total for the group indication), and the 10 other UEs individually. The total PM load is thus (50 + (10 * 40)) * 64 = 28.8kbits (compared to 128 kbits above). From the group indications 10 x 6 UEs = 60 will falsely initiate access procedures.

[0045] In a further example the number of groups may be increased to 200, each having 5 users. Among the 50 to be paged 12 groups carry 3 UEs, and 14 have a single UE each, giving 26 active groups. Here the total PM load is 200 (group bitmap) + 14 x 40 = 760 bits x 64 beams = 48.64 kbits, with 12 x 2 = 24 falsely paged UEs. The careful selection of the number of groups and group sizes can thus have a very significant effect on the total paging load and the false paging alerts.

[0046] Presuming at least one UE of a paged group is not being paged there will be at least one false access attempt. To avoid the false attempts the PM may also comprise UE-IDs in indicated groups that are not paged. Thus the gNB can indicate a group being paged if the majority of the users in this group are to be paged. To reduce the false paging alerts for the non-paged UEs in this group (marked as paged by the group in the PM), the gNB can explicitly add these UE IDs in the PM as well. When a UE sees its group paged in the PM and further its UE ID appears as well in the PM, it concludes that it is not paged effectively and does not take further action. Using the logic shown in Figure 1 this technique can reduce the number of false access requests.

[0047] At 10 a UE receives a paging message and decides at 11 whether the UE is in a paged group. If the UE is not in a paged group at 12 the UE checks if it is identified explicitly and concludes whether the UE is paged 13 or not paged 14. If the UE identifies that it is present in a paged group, at 15 the UE checks if it is identified explicitly in the PM. If the UE is identified explicitly this is an indication that the UE is not paged as shown at 16. If the UE is not identified explicitly, the UE is paged 17.

[0048] The effect of this logic is that non-paged UEs in a paged group do not attempt an access request, thus preventing false access requests. Presuming group indication is used where more than half of the group is paged then the overhead of including this negative indication is less than the overheard of explicitly identifying all of the paged UEs (rather than using groups). The PM load is thus reduced, and false access attempts are avoided. This method allows the base station (or gNB) to reduce false paging alerts at the expense of some additional paging load (IDs of unpaged UEs).It is not mandatory for a gNB to reduce the false paging alerts to zero but the proposed scheme allows the gNB to choose at each paging occasion an appropriate amount of paging load and an acceptable rate of false paging alert as a function of system parameters, number of users in the cell, number of users configured in a PO and the number of paged UEs.

[0049] It is also possible to indicate the UE groups in the paging DCI instead of the common paging indication which triggers all the users configured for a specific PO to decode the paging message to confirm if they are paged or not. The DCI may include an indication of active groups such that only those groups stay awake to receive and decode the PM, all other groups can immediately return to DRX after the Paging DCI. The group indication could be a bitmap, or any appropriate coding that can convey the required information in the small size available in the paging DCI. Size constraints in the DCI may make large numbers of bits for a group indication in paging DCI disadvantageous. Hence, a reduced number of groups may be indicated in the paging DCI, and only the UEs associated to active groups decode the PM associated to this paging DCI. Then PM can have large number of groups or finer granularity group indication for active super groups combined with the UE ID based paging. This technique provides multi-layer grouping, with the first level in the Paging DCI giving power savings to inactive group members, and the second level reducing overhead and false alarms as indicated above.

[0050] For a flexible load paging message carrying both paging group indication and UE IDs, the paging message overhead can be further reduced by compressing the UE-IDs to reduce the transmitted data. The compression reduces the data required, albeit with a small risk of compressing two UE-IDs to the same value and hence introducing ambiguity. Even in such a situation both UEs will initiate an access attempt, one of which will be false and can be refused.

[0051] In conventional approaches a single paging RNTI (P-RNTI) is used for scrambling the PI on PDCCH, thus all UEs scheduled for the particular PO and receiving the PI try to read the paging message. To improve upon this, more than one P-RNTI may be available in each cell. A group common P-RNTI is assigned to all UEs allocated to a corresponding group. Thus, only the UEs allocated to a particular P-RNTI can receive the PI and hence continue to listen to the PM. Non-indicated groups of UEs thus reduce power consumption as they do not stay awake to receive and process the PM. A drawback of this approach is the increased DL overhead for PI transmission if a large number of groups are being paged.

[0052] A network may have a pre-defined pool of RNTIs which are used as group common PRNTIs, which pool of group common P-RNTIs can be known a-priori by all UEs. UEs can be associated to groups in any appropriate manner, for example based on UE-ID, or a combination of UE-ID and other system information such as cell ID, SFN, or PO number.

[0053] This approach of group common P-RNTIs may be equally attractive for non-beam sweeping applications. In the conventional approach all UEs allocated to a PO listen and decode the PM, even if the PM was only for a single UE. The allocation of one universal and one group-common RNTI for each UE provides potentially significant savings. A further advantage of multiple group common P-RNTIs is a potential increase in paging capacity for dense cells. However, the universal P-RNTI is more attractive where a PM is intended for all, or most, UEs in a cell; for example when the PM relates to a change in system information.

[0054] Although the foregoing description has been given with particular reference to beamsweeping systems, the disclosure is also relevant to non-beam sweeping systems.

[0055] Although not shown in detail any of the devices or apparatus that form part of the network may include at least a processor, a storage unit and a communications interface, wherein the processor unit, storage unit, and communications interface are configured to perform the method of any aspect of the present invention. Further options and choices are described below.

[0056] The signal processing functionality of the embodiments of the invention especially the gNB and the UE may be achieved using computing systems or architectures known to those who are skilled in the relevant art. Computing systems such as, a desktop, laptop or notebook computer, hand-held computing device (PDA, cell phone, palmtop, etc.), mainframe, server, client, or any other type of special or general purpose computing device as may be desirable or appropriate for a given application or environment can be used. The computing system can include one or more processors which can be implemented using a general or special-purpose processing engine such as, for example, a microprocessor, microcontroller or other control module.

[0057] The computing system can also include a main memory, such as random access memory (RAM) or other dynamic memory, for storing information and instructions to be executed by a processor. Such a main memory also may be used for storing temporary variables or other intermediate information during execution of instructions to be executed by the processor. The computing system may likewise include a read only memory (ROM) or other static storage device for storing static information and instructions for a processor.

[0058] The computing system may also include an information storage system which may include, for example, a media drive and a removable storage interface. The media drive may include a drive or other mechanism to support fixed or removable storage media, such as a hard disk drive, a floppy disk drive, a magnetic tape drive, an optical disk drive, a compact disc (CD) or digital video drive (DVD) read or write drive (R or RW), or other removable or fixed media drive. Storage media may include, for example, a hard disk, floppy disk, magnetic tape, optical disk, CD or DVD, or other fixed or removable medium that is read by and written to by media drive. The storage media may include a computer-readable storage medium having particular computer software or data stored therein.

[0059] In alternative embodiments, an information storage system may include other similar components for allowing computer programs or other instructions or data to be loaded into the computing system. Such components may include, for example, a removable storage unit and an interface , such as a program cartridge and cartridge interface, a removable memory (for example, a flash memory or other removable memory module) and memory slot, and other removable storage units and interfaces that allow software and data to be transferred from the removable storage unit to computing system.

[0060] The computing system can also include a communications interface. Such a communications interface can be used to allow software and data to be transferred between a computing system and external devices. Examples of communications interfaces can include a modem, a network interface (such as an Ethernet or other NIC card), a communications port (such as for example, a universal serial bus (USB) port), a PCMCIA slot and card, etc. Software and data transferred via a communications interface are in the form of signals which can be electronic, electromagnetic, and optical or other signals capable of being received by a communications interface medium.

[0061] In this document, the terms ‘computer program product’, ‘computer-readable medium’ and the like may be used generally to refer to tangible media such as, for example, a memory, storage device, or storage unit. These and other forms of computer-readable media may store one or more instructions for use by the processor comprising the computer system to cause the processor to perform specified operations. Such instructions, generally referred to as ‘computer program code’ (which may be grouped in the form of computer programs or other groupings), when executed, enable the computing system to perform functions of embodiments of the present invention. Note that the code may directly cause a processor to perform specified operations, be compiled to do so, and/or be combined with other software, hardware, and/or firmware elements (e.g., libraries for performing standard functions) to do so.

[0062] The non-transitory computer readable medium may comprise at least one from a group consisting of: a hard disk, a CD-ROM, an optical storage device, a magnetic storage device, a Read Only Memory, a Programmable Read Only Memory, an Erasable Programmable Read Only Memory, EPROM, an Electrically Erasable Programmable Read Only Memory and a Flash memory [0063] In an embodiment where the elements are implemented using software, the software may be stored in a computer-readable medium and loaded into computing system using, for example, removable storage drive. A control module (in this example, software instructions or executable computer program code), when executed by the processor in the computer system, causes a processor to perform the functions of the invention as described herein.

[0064] Furthermore, the inventive concept can be applied to any circuit for performing signal processing functionality within a network element. 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 microcontroller of a digital signal processor (DSP), or application-specific integrated circuit (ASIC) and/or any other sub-system element.

[0065] It will be appreciated that, for clarity purposes, the above description has described embodiments of the invention with reference to a single processing logic. However, the inventive concept may equally be implemented byway of a plurality of different functional units and processors to provide the signal processing functionality. Thus, 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 organisation.

[0066] Aspects of the invention may be implemented in any suitable form including hardware, software, firmware or any combination of these. The invention may optionally be implemented, at least partly, as computer software running on one or more data processors and/or digital signal processors or configurable module components such as FPGA devices. Thus, the elements and components of an embodiment of the invention 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.

[0067] Although the present invention has been described in connection with some embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention 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 embodiments may be combined in accordance with the invention. In the claims, the term ‘comprising’ does not exclude the presence of other elements or steps.

[0068] 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.

[0069] Furthermore, the order of features in the claims does not imply any specific order in which the features must be performed and in particular the order of individual steps in a method claim does not imply that the steps must be performed in this order. Rather, the steps may be performed in any suitable order. In addition, singular references do not exclude a plurality. Thus, references to ‘a’, ‘an’, ‘first’, ‘second’, etc. do not preclude a plurality.

[0070] Although the present invention has been described in connection with some embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention 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 recognise that various features of the described embodiments may be combined in accordance with the invention. In the claims, the term ‘comprising’ or “including” does not exclude the presence of other elements.

Claims (16)

Claims

1. A method of paging UEs in a cellular wireless communication network, comprising the steps of transmitting a paging indication from a base station, indicating a paging message is available; and transmitting a paging message, wherein the paging message comprises a group indication which indicates at least one group of UEs to which the paging message applies, and at least one UE indication, each UE indication indicating a paged UE to which the paging message applies, wherein the at least one UE indication comprises an identifier of the UE being paged.

2. A method of paging UEs according to claim 1, wherein the group indication of at least one group is formed as a bitmap.

3. A method of paging UEs according to claim 1 or claim 2, wherein the base station utilises a beam-sweeping transmission means and the paging message is transmitted on all beams of the beam-sweeping transmission means.

4. A method of paging UEs according to any preceding claim, wherein the paging message further comprises at least one unpaged UE indication, each unpaged UE indication indicating an unpaged UE in the at least one paged group of UEs, to which the paging message does not apply, wherein the unpaged UE indication comprises an identifier of th the unpaged UE.

5. A method of paging UEs according to any preceding claim, wherein the identifier of the at least one paged and/or at least one unpaged UE is the S-TMSI or IMSI of the UE.

6. A method of paging UEs according to any preceding claim, further comprising the step of transmitting from the base station a paging format indicator.

7. A method of paging UEs according to claim 6, wherein the paging format indicator comprises an indication that a paging message comprises the group indication.

8. A method of paging UEs according to claim 6 or claim 7, wherein the paging format indicator is transmitted in a paging DCI or in a paging message.

9. A method of paging UEs according to claim 8, wherein the paging message is the paging message to which the paging format indicator relates.

10. A method according to any preceding claim, further comprising the step of transmitting, in a paging DCI, an indication of UE groups to which a subsequent paging indication may apply.

11. A method of paging UEs according to claim 1, wherein the paging message has a fixed format in which the group indication is at a fixed position in the paging message and the at least one UE indication follows the group indication.

10. A method of paging UEs according to any preceding claim, further comprising the step of indicating at least one group of UEs, in a paging DCI transmitted by the base station, to which the paging message does not apply.

11. A method of paging UEs according to any preceding claim, further comprising the steps of allocating at least one universal P-RNTI and at least one group-common P-RNTI to at least one UE, and utilising the group-common P-RNTI to scramble a paging indication message such that only UEs allocated to the group-common P-RNTI can decode the paging indication.

12. A method of paging UEs according to any preceding claim, wherein UEs are grouped in a number of groups which remains static or semi-static.

13. A method of processing a paging message, the method performed at a UE on a message received from a base station of a cellular wireless communication network; the method comprising the steps of receiving the paging message;

determining if the UE is in a group of UEs indicated by the message as being paged; and determining if the UE is further identified as an unpaged UE in the group of UEs.

14. A method according to claim 13, wherein the UE is further identified by an identifier of the UE.

15. A method according to claim 14, wherein the identifier is the S-TMSI or IMSI of the UE.

16. A method according to any of claims 13 to 15, wherein the UE returns to a sleep mode if the UE is not in a group of UEs indicated as being paged and not paged individually by its UE ID, or if the UE is in a paged group and the UE is further indicated as being unpaged.