WO2015020588A2

WO2015020588A2 - A network node and mobile device for use in a communication network, and methods of operating the same and computer program products

Info

Publication number: WO2015020588A2
Application number: PCT/SE2014/050825
Authority: WO
Inventors: Andreas HÖGLUND; Magnus Stattin
Original assignee: Telefonaktiebolaget L M Ericsson (Publ)
Priority date: 2013-08-09
Filing date: 2014-07-01
Publication date: 2015-02-12
Also published as: WO2015020588A3

Abstract

There is provided a method of operating a network node (10) in a communication network (2) to provide timing information for a mobile device (12), the network defining an extended period that is longer than a predefined period in the network, the predefined period in the network corresponding to the time taken to transmit a predefined plurality of frames, the method comprising broadcasting a plurality of information blocks, IBs, to the mobile device (103, 105), each IB indicating a current frame number in the predefined plurality of frames; wherein, when the current frame number is equal to a selected frame number or a frame number in a selected subset of the frame numbers in the predefined plurality of frames, the method further comprises the step of broadcasting one or more additional bits that identify the current predefined period in the extended period (105).

Description

A network node and mobile device for use in a communication network, and methods of operating the same and computer program products

Technical Field

The technology described relates to communication networks, and in particular to techniques for allowing mobile devices to operate with an extended system frame number (SFN) period, for example for the purpose of extending a discontinuous reception (DRX) period. Background

In a typical cellular radio system, radio or wireless terminals (also known as mobile stations and/or user equipment units (UEs)) communicate via a radio access network (RAN) to one or more core networks. The radio access network (RAN) covers a geographical area which is divided into cell areas, with each cell area being served by a base station, e.g., a radio base station (RBS), which in some networks may also be called, for example, a "NodeB" (in a Universal Mobile Telecommunications System (UMTS) network) or "eNodeB" (in a Long Term Evolution (LTE) network). A cell is a geographical area where radio coverage is provided by the radio base station equipment at a base station site. Each cell is identified by an identity within the local radio area, which is broadcast in the cell. The base stations communicate over the air interface operating on radio frequencies with the user equipment units (UEs) within range of the base stations.

In some radio access networks, several base stations may be connected (e.g., by landlines or microwave) to a radio network controller (RNC) or a base station controller (BSC). The radio network controller supervises and coordinates various activities of the plural base stations connected thereto. The radio network controllers are typically connected to one or more core networks. The Universal Mobile Telecommunications System (UMTS) is a third generation mobile communication system, which evolved from the Global System for Mobile Communications (GSM). Universal Terrestrial Radio Access Network (UTRAN) is essentially a radio access network using wideband code division multiple access (WCDMA) for user equipment units (UEs). In a forum known as the Third Generation Partnership Project (3GPP), telecommunications suppliers propose and agree upon standards for third generation networks and UTRAN specifically, and investigate enhanced data rate and radio capacity. The Third Generation Partnership Project (3GPP) has undertaken to evolve further the UTRAN and GSM based radio access network technologies. A number of releases for the Evolved Universal Terrestrial Radio Access Network (E-UTRAN) specification have issued, and as with most specifications, the standard is likely to evolve. The Evolved Universal Terrestrial Radio Access Network (E-UTRAN) comprises the Long Term Evolution (LTE) and System Architecture Evolution (SAE).

Long Term Evolution (LTE) is a variant of a 3GPP radio access technology where the radio base station nodes are connected to a core network (via Access Gateways (AGWs)) rather than to radio network controller (RNC) nodes. In general, in LTE the functions of a radio network controller (RNC) node are distributed between the radio base stations nodes (eNodeB's in LTE) and AGWs. As such, the radio access network (RAN) of an LTE system has what is sometimes termed a "flat" architecture including radio base station nodes without reporting to radio network controller (RNC) nodes.

A currently popular vision of the future of cellular networks includes machines or other autonomous devices communicating between each other (or with an application server) without human interaction. A typical scenario is to have sensors sending measurements infrequently, where each of the transmissions would consist of only small amounts of data. This type of communication is called machine to machine (M2M) communication in the literature, or machine-type communication (MTC), in 3GPP.

UEs in cellular systems (such as 3GPP WCDMA, LTE) are most commonly battery driven and the power consumption of these devices is therefore an important factor.

In the context of MTC, many of the devices are expected to be battery operated as well. Sensors and other devices may reside in remote locations and the number of deployed devices could be so large that it would be practically infeasible to replace or frequently recharge the batteries in these kinds of devices. Thus, it is an important goal to aim for reduction in the power consumption when considering improvements for current cellular systems. An existing means to reduce the battery power consumption is to use discontinuous reception (DRX), a feature in which the UE's receiver is switched off except at configured intervals. Currently the longest specified DRX cycle lengths are 2.56 seconds and 5.12 seconds for EUTRA and UTRA, respectively. However, it would be beneficial to extend the DRX cycle lengths beyond currently specified values to further reduce the battery power consumption, especially for the benefit of MTC devices where there is no possibility for interactive charging of the battery on a regular basis. Although longer DRX cycle lengths naturally cause larger delays in the downlink, this is typically not a problem for delay insensitive traffic such as that generated by MTC devices.

However, the DRX cycle length is currently limited by a System Frame Number (SFN) period. The SFN is used by UEs to keep synchronisation with the network and is used as a timing reference. In LTE the SFN period is 1024 radio frames equal to 10.24 seconds and in High-Speed Packet Access (HSPA) the SFN period is 4096 radio frames equal to 40.96 seconds.

In E-UTRA a UE needs 10 bits to determine the SFN since it takes 1024 different values. Eight of these bits are broadcast by the network in a system frame number field in the master information block (MIB). The MIB is broadcast for 40ms during which the same information (including the value in the system frame number field) is repeated four times, i.e. every 10ms. As the MIB only carries eight of the bits for the SFN, the last two bits, which give four values for the SFN within the 40ms period, are retrieved implicitly by the UE from the different scrambling codes used for the four copies of the MIB broadcast in each 10ms period.

Summary

With a DRX cycle length longer than the SFN period (1024 radio frames equal to 10.24 seconds for LTE and 4096 radio frames equal to 40.96 seconds for High-Speed Packet Access (HSPA)) there would have to be a way to index the SFN periods in order to tell them apart within the extended DRX cycle length. For example, if the DRX cycle length for LTE was extended to 40.96 seconds, it would be necessary to index the four SFN periods occurring within that extended DRX cycle length in order for the UE to tell them apart. This index can correspond to using additional bits to extend the SFN range. If, for example, two index/expansion bits are used, this could either be viewed as labelling each SFN period (1024 frames) with an index from 1 to 4 or expanding the maximal SFN from 1024 radio frames to 4096 radio frames. Note however that these additional bits would only be read by UEs configured to operate with extended DRX since legacy UEs (i.e. UEs configured according to earlier versions of the standards) would not be able to interpret SFN values larger than 1024.

Thus, it is necessary to find useful ways of communicating these additional SFN bits from the network to the UE.

One possible solution is to include the additional SFN bits in the system information (SI) that is broadcast by the network to the UEs. The SI includes the MIB and other information required by the UEs to communicate reliably with the network. The other information is distributed between different system information blocks (SIBs) which are scheduled in different ways. As indicated above, the eight bits of the SFN are placed in the MIB which is scheduled with a fixed period, with the other two bits of the SFN being derived from the scrambling code used with each copy of the MIB broadcast over a 40ms period. Other SI such as Cell ID and cell barring information is placed in System Information Block type 1 (SIB1), which is also scheduled periodically but with a different fixed periodicity to the MIB. There are various other SIBs which contain other SI and are scheduled dynamically. In order to find the dynamically scheduled SIBs, the UE needs to acquire a scheduling list field which is included in SIB1 and which indicates the scheduling of the dynamically scheduled SIBs. In other words, the acquisition of other SIBs requires the acquisition of SIB type 1 first. System Information (SI), Master Information Block (MIB) and System Information Block type 1 (SIB1) are defined in section 5.2 (and subsections) of 3GPP TS 36.331 v11.3.0 (2013-03).

Thus, if the additional SFN bits are included in either an existing SIB or in a new SIB, which could be introduced for this purpose, a UE would first need to read SIB1 in order to obtain the scheduling information of the SIB containing the additional bits. That means, if a UE is waking up from a very long DRX cycle, the UE will typically need to read at least three information blocks in order to obtain the full extended SFN, which will have an adverse impact on the MTC UE's battery lifetime. Even if the additional bits were put directly into SIB1 , the requirement to read this SIB could have a bad enough impact on battery life to make it unfeasible. This negative impact is illustrated in Figure 1 (for a worst case scenario). The worst case scenario would be that SIB1 would have to be read once every DRX cycle with a reading time of 80 ms, and assuming bad radio conditions plus a 10 ms sync time. Using a simple power consumption model, the battery life is plotted against the DRX cycle length for this worst case scenario. In the model it is assumed that SIB1 only has to be read for DRX cycle lengths longer than 10.24 seconds which causes a discrete step in the curve. The other curves show the battery life for two fixed start-up times before the transmission, 10ms and 100ms. Not surprisingly, the battery life when SIB1 has to be read is equal to that of a fixed sync time of 10 ms before the discrete step and afterwards it is very close to that of a 100 ms fixed sync time.

In view of the problems with including the additional SFN bits in SIB1 or other SIBs, it would be preferable to include the additional bits in the MIB with the other SFN bits since the MIB is currently used by the UEs to obtain the SFN. However, since the MIB is broadcast very frequently, it is required to have a very small payload.

Currently, there are ten 'spare' bits in the MIB that do not have a defined function or purpose which could be used to indicate the additional SFN bits. However, the spare bits are intended to allow EUTRAN to be enhanced with new features throughout its lifetime and careful consideration must be given before allocating these bits to new purposes.

Using more than, say, two of these bits may therefore be difficult, especially since only a relatively small fraction of all new UEs may make use of (or be able to make use of) extended DRX cycles. Unfortunately, the gain in terms of battery life is rather modest if only one or a couple of bits are used. The document R2-131691 entitled "Analysis of standardization impacts of MTCe UEPCOP solutions" submitted by Ericsson and ST- Ericsson to RAN2#82 in Fukuoka, Japan on 20-24 May 2013 models power consumption with extended DRX and suggests that the maximum DRX cycle length (which corresponds to the extended SFN period) should be increased by at least a factor of 10, requiring at least four additional SFN bits, in order to obtain significant gains, especially for long inter-arrival-times. Thus, in summary, it is impractical or highly unlikely that enough of the spare bits in the MIB could be dedicated to purpose of extending DRX cycles. Using only one or two bits to extend the SFN and thus the maximum possible DRX cycle would not provide sufficient battery consumption gains for, for example, MTC devices.

In view of these difficulties, it is proposed to broadcast the additional bit or bits required to extend the SFN range (and thus extend the maximum DRX cycle) only occasionally. In particular, the additional bit or bits can be broadcast only during a radio frame having a selected SFN or radio frames having a selected subset of the SFNs in an SFN period. In this way, one or more of the 10 spare bits currently available in the MIB during the selected SFN or subset of SFNs can be used for expanding the SFN range, while ensuring that those bits are still available in the MIB during remaining SFNs for use for any future E-UTRAN features. Alternatively, the one or more additional bits can be broadcast in a separate or new information block, IB, during a radio frame having a selected SFN in an SFN period or during radio frames having a selected subset of the SFNs in an SFN period. In this way it would be possible to use enough bits (e.g. up to the maximum 10 spare bits if the additional bits are included in the MIB, or more if the additional bits are transmitted in a separate IB) to obtain sufficiently long DRX cycles to provide substantial battery life gains for MTC devices.

In the case of a 10-bit SFN that is communicated to UEs 12 using an 8-bit value in an SFN field in an MIB and different scrambling codes for four repeats of the MIB in a 40ms block, the content of the MIB should be the same for each of those repetitions, and in particular the value in the 8-bit SFN field is the same for each of those repetitions, which means, for example, that the 8-bit SFN field can have a Ό' value for the 10-bit SFN values 0, 1 , 2 and 3. Therefore, it will be appreciated that when the one or more additional bits are incorporated into the MIB, they can be broadcast for one or more selected values of the 8-bit SFN field in the MIB. Thus, where a single value for the 8-bit SFN field is selected, this means that there will be a subset of four consecutive (10-bit) SFN values where the one or more additional bits are broadcast. Where multiple values for the 8-bit SFN field are selected (e.g. Ό' and '128'), the subset of 10-bit SFNs in which the additional bits are broadcast will then include multiple sets of four consecutive 10-bit SFN values (e.g. 0, 1 , 2, 3, 512, 513, 514, 515). Where the one or more additional bits are to be broadcast in a separate or new information block, IB, the one or more additional bits may be broadcast in an IB during a radio frame having a single (10-bit) SFN value, or a subset of (10-bit) SFN values (e.g. 0, 1 , 2, 3 as above).

For example, extended SFN period (and thus the maximum DRX cycle length) can be configured to correspond to four standard SFN periods, so two additional bits will need to be broadcast by the network for the mobile device to determine the SFN within the extended SFN period. These additional bits may, for example, only be broadcast using two spare bits in the MIB when the SFN is SFN = 0, which means that the spare bits will still be available for other purposes 1023/1024^th of the time.

According to a specific aspect, there is provided a method of operating a network node in a communication network to provide timing information for a mobile device the network defining an extended period that is longer than a predefined period in the network, the predefined period in the network corresponding to the time taken to transmit a predefined plurality of frames. The method comprises broadcasting a plurality of information blocks, IBs, to the mobile device, each IB indicating a current frame number in the predefined plurality of frames; wherein, when the current frame number is equal to a selected frame number or a frame number in a selected subset of the frame numbers in the predefined plurality of subframes, the method further comprises the step of broadcasting one or more additional bits that identify the current predefined period in the extended period.

In some embodiments, the network node is to provide timing information for a mobile device operating in a discontinuous reception (DRX) mode, with a maximum DRX cycle period for the mobile device corresponding to the length of the extended period.

In some embodiments, the step of broadcasting one or more additional bits comprises broadcasting the one or more additional bits in the IB indicating the selected frame number or the IBs indicating the selected subset of the frame numbers in the predefined plurality of subframes.

In some embodiments, the step of broadcasting one or more additional bits comprises broadcasting the one or more additional bits in a separate IB to the IB indicating the current frame number. In some embodiments, the predefined periods in the network are system frame number, SFN, periods and the frame number is an SFN. In some embodiments the predefined plurality of frames comprises 1024 or 4096 frames. In some embodiments, the IBs are master information blocks, MIBs.

In some embodiments the step of broadcasting comprises incrementing the indicated current frame number with each broadcast of the IB. In some embodiments, the method further comprises the step of transmitting the one or more additional bits with other signalling transmitted to the mobile device. In some embodiments, the one or more additional bits are only included with the other signalling when the current frame number is not equal to a selected frame number or a frame number in a selected subset of the frame numbers in the predefined plurality of subframes. In some embodiments, the other signalling is radio resource control, RRC, connection setup signalling and/or hand-over signalling.

According to another specific aspect, there is provided a network node for use in a communication network to provide timing information for a mobile device the network defining an extended period that is longer than a predefined period in the network, the predefined period in the network corresponding to the time taken to transmit a predefined plurality of frames. The network node comprises a transceiver module and a processing module; the processing module being configured to control the transceiver module to broadcast a plurality of information blocks, IBs, to the mobile device, each IB indicating a current frame number in the predefined plurality of frames; wherein the processing module is further configured to control the transceiver module to broadcast one or more additional bits that identify the current predefined period in the extended period when the current frame number is equal to a selected frame number or a frame number in a selected subset of the frame numbers in the predefined plurality of subframes.

According to another specific aspect, there is provided a method of operating a mobile device in a communication network, the network defining an extended period that is longer than a predefined period in the network, the predefined period in the network corresponding to the time taken to transmit a predefined plurality of frames. The method comprises operating a receiver in the mobile device to receive an information block, IB, broadcast by a network node in the communication network, the IB indicating a respective current frame number in the predefined plurality of frames; determining whether the current frame number is equal to a selected frame number or a frame number in a selected subset of the frame numbers in the predefined plurality of subframes; if so, reading one or more additional bits broadcast by the network node, the one or more additional bits identifying the current predefined period in the extended period; and processing the current frame number in the IB and the one or more additional bits to determine the current frame number in the extended period. In some embodiments, the mobile device is operating a mobile device in a discontinuous reception, DRX, mode in a communication network, with a maximum DRX cycle period for the mobile device corresponding to the length of the extended period.

In some embodiments, the mobile device has a selected DRX cycle length that is longer than a predefined period up to the maximum DRX cycle period, and the step of processing comprises using the determined current frame number in the extended period to determine the current frame number in the selected DRX cycle length.

In some embodiments, the step of reading one or more additional bits comprises reading the one or more additional bits from the IB received in the step of operating.

In some embodiments, the step of reading one or more additional bits comprises reading the one or more additional bits from a separate IB to the IB indicating the current frame number.

In some embodiments, the predefined periods in the network are system frame number, SFN, periods and the frame number is an SFN. In some embodiments the predefined plurality of frames comprises 1024 or 4096 frames. In some embodiments, the IBs are master information blocks, MIBs.

In some embodiments, the method further comprises the steps of determining if the mobile device has previously received one or more additional bits if the current frame number is not equal to a selected frame number or a frame number in a selected subset of the frame numbers in the predefined plurality of subframes; and if the mobile device has previously received one or more additional bits, processing the current frame number in the IB and the one or more additional bits to determine the current frame number in the extended period.

In some embodiments, the method further comprises the steps of calculating the time until the next selected frame number or a frame number in the selected subset of frame numbers using the current frame number in the IB if the mobile device has not previously received one or more additional bits; and operating the receiver to receive another IB after the calculated time has elapsed. In some embodiments, the method further comprises the step of receiving the one or more additional bits with other signalling transmitted by the network node. In some embodiments, the one or more additional bits are only included with the other signalling when the current frame number is not equal to a selected frame number or a frame number in a selected subset of the frame numbers in the predefined plurality of subframes. In some embodiments, the other signalling is radio resource control, RRC, connection setup signalling and/or hand-over signalling.

According to another specific aspect, there is provided a mobile device for use in a communication network, the network defining an extended period that is longer than a predefined period in the network, the predefined period in the network corresponding to the time taken to transmit a predefined plurality of frames. The mobile device comprises a receiver or transceiver module and a processing module; wherein the processing module is configured to operate the receiver or transceiver to receive an information block, IB, broadcast by a network node in the communication network, the IB indicating a respective current frame number in the predefined plurality of frames, determine whether the current frame number is equal to a selected frame number or a frame number in a selected subset of the frame numbers in the predefined plurality of subframes; and to read one or more additional bits broadcast by the network node if the current frame number is equal to a selected frame number or a frame number in a selected subset of the frame numbers, the one or more additional bits identifying the current predefined period in the extended period, and process the current frame number in the IB and the one or more additional bits to determine the current frame number in the extended period.

According to another aspect, there is provided a network node for use in a communication network to provide timing information for a mobile device, the network defining an extended period that is longer than a predefined period in the network, the predefined period in the network corresponding to the time taken to transmit a predefined plurality of frames. The network node comprises a processor and a memory, said memory containing instructions executable by said processor whereby said network node is operative to broadcast a plurality of information blocks, IBs, to the mobile device, each IB indicating a current frame number in the predefined plurality of frames; and broadcast one or more additional bits that identify the current predefined period in the extended period when the current frame number is equal to a selected frame number or a frame number in a selected subset of the frame numbers in the predefined plurality of frames.

According to a further aspect, there is provided a mobile device for use in a communication network, the network defining an extended period that is longer than a predefined period in the network, the predefined period in the network corresponding to the time taken to transmit a predefined plurality of frames. The mobile device comprises a processor and a memory, said memory containing instructions executable by said processor whereby said mobile device is operative to receive an information block, IB, broadcast by a network node in the communication network, the IB indicating a respective current frame number in the predefined plurality of frames; determine whether the current frame number is equal to a selected frame number or a frame number in a selected subset of the frame numbers in the predefined plurality of frames; read one or more additional bits broadcast by the network node if the current frame number is equal to a selected frame number or a frame number in a selected subset of the frame numbers, the one or more additional bits identifying the current predefined period in the extended period, and process the current frame number in the IB and the one or more additional bits to determine the current frame number in the extended period.

According to a further aspect, there is provided a network node for use in a communication network to provide timing information for a mobile device, the network defining an extended period that is longer than a predefined period in the network, the predefined period in the network corresponding to the time taken to transmit a predefined plurality of frames. The network node is adapted to broadcast a plurality of information blocks, IBs, to the mobile device, each IB indicating a current frame number in the predefined plurality of frames; and broadcast one or more additional bits that identify the current predefined period in the extended period when the current frame number is equal to a selected frame number or a frame number in a selected subset of the frame numbers in the predefined plurality of frames.

According to another aspect, there is provided a mobile device for use in a communication network, the network defining an extended period that is longer than a predefined period in the network, the predefined period in the network corresponding to the time taken to transmit a predefined plurality of frames. The mobile device comprises a receiver and the mobile device is adapted to operate the receiver to receive an information block, IB, broadcast by a network node in the communication network, the IB indicating a respective current frame number in the predefined plurality of frames; determine whether the current frame number is equal to a selected frame number or a frame number in a selected subset of the frame numbers in the predefined plurality of frames; read one or more additional bits broadcast by the network node if the current frame number is equal to a selected frame number or a frame number in a selected subset of the frame numbers, the one or more additional bits identifying the current predefined period in the extended period, and process the current frame number in the IB and the one or more additional bits to determine the current frame number in the extended period Yet another aspect provides a computer program product having computer readable code embodied therein, the computer readable code being configured such that, on execution by a suitable computer or processor, the computer or processor is caused to perform any of the methods described above. Brief Description of the Drawings

Figure 1 is a graph illustrating the battery life for different DRX cycle lengths when SIB1 has to be read each time that a UE wakes up from DRX compared to fixed sync times of 10ms and 100ms; Figure 2 is a non-limiting example block diagram of an LTE cellular communications network;

Figure 3 is a block diagram of a mobile device according to an embodiment; Figure 4 is a block diagram of a base station according to an embodiment; Figure 5 is a block diagram of a core network node according to an embodiment;

Figure 6 is a schematic illustration of the transmission of two additional bits used to extend an SFN period according to an embodiment;

Figure 7 is a flow chart illustrating a method of operating a network node according to an embodiment; and Figure 8 is a flow chart illustrating a method of operating a mobile device according to an embodiment.

Detailed Description

The following sets forth specific details, such as particular embodiments for purposes of explanation and not limitation. But it will be appreciated by one skilled in the art that other embodiments may be employed apart from these specific details. In some instances, detailed descriptions of well known methods, nodes, interfaces, circuits, and devices are omitted so as not obscure the description with unnecessary detail. Those skilled in the art will appreciate that the functions described may be implemented in one or more nodes using hardware circuitry (e.g., analog and/or discrete logic gates interconnected to perform a specialized function, ASICs, PLAs, etc.) and/or using software programs and data in conjunction with one or more digital microprocessors or general purpose computers. Nodes that communicate using the air interface also have suitable radio communications circuitry. Moreover, the technology can additionally be considered to be embodied entirely within any form of computer-readable memory, such as solid-state memory, magnetic disk, or optical disk containing an appropriate set of computer instructions that would cause a processor to carry out the techniques described herein.

Hardware implementation may include or encompass, without limitation, digital signal processor (DSP) hardware, a reduced instruction set processor, hardware (e.g., digital or analog) circuitry including but not limited to application specific integrated circuit(s) (ASIC) and/or field programmable gate array(s) (FPGA(s)), and (where appropriate) state machines capable of performing such functions. In terms of computer implementation, a computer is generally understood to comprise one or more processors, one or more processing modules or one or more controllers, and the terms computer, processor, processing module and controller may be employed interchangeably. When provided by a computer, processor, or controller, the functions may be provided by a single dedicated computer or processor or controller, by a single shared computer or processor or controller, or by a plurality of individual computers or processors or controllers, some of which may be shared or distributed. Moreover, the term "processor" or "controller" also refers to other hardware capable of performing such functions and/or executing software, such as the example hardware recited above.

Although the description is given for user equipment (UE), it should be understood by the skilled in the art that "UE" is a non-limiting term comprising any mobile or wireless device or node equipped with a radio interface allowing for at least one of: transmitting signals in uplink (UL) and receiving and/or measuring signals in downlink (DL). A UE herein may comprise a UE (in its general sense) capable of operating or at least performing measurements in one or more frequencies, carrier frequencies, component carriers or frequency bands. It may be a "UE" operating in single- or multi-radio access technology (RAT) or multi-standard mode. As well as "UE", the term "mobile device" is used interchangeably in the following description, and it will be appreciated that such a device, particularly a MTC device, does not necessarily have to be 'mobile' in the sense that it is carried by a user. Instead, the term "mobile device" encompasses any device that is capable of communicating with communication networks that operate according to one or more mobile communication standards, such as GSM, UMTS, LTE, etc.

A cell is associated with a base station, where a base station comprises in a general sense any node transmitting radio signals in the downlink (DL) and/or receiving radio signals in the uplink (UL). Some example base stations, or terms used for describing base stations, are eNodeB, eNB, Node B, macro/micro/pico/femto radio base station, home eNodeB (also known as femto base station), relay, repeater, sensor, transmitting- only radio nodes or receiving-only radio nodes. A base station may operate or at least perform measurements in one or more frequencies, carrier frequencies or frequency bands and may be capable of carrier aggregation. It may also be a single-radio access technology (RAT), multi-RAT, or multi-standard node, e.g., using the same or different base band modules for different RATs. It should be noted that use of the term "network node" as used herein can refer to a base station, such as an eNodeB, a network node in the RAN responsible for resource management, such as a radio network controller (RNC), or a core network node, such as a mobility management entity (MME).

The signalling described is either via direct links or logical links (e.g. via higher layer protocols and/or via one or more network nodes). For example, signalling from a coordinating node may pass another network node, e.g., a radio node.

It will be appreciated that although the following description of the embodiments relates to EUTRAN, the principle of occasionally broadcasting one or more additional bits in an information block as described herein is equally applicable to UTRAN and similar wireless communication systems.

Figure 2 shows an example diagram of an EUTRAN architecture as part of an LTE-based communications system 2. Nodes in the core network 4 include one or more Mobility Management Entities (MMEs) 6, a key control node for the LTE access network, and one or more Serving Gateways (SGWs) 8 which route and forward user data packets while acting as a mobility anchor. They communicate with base stations 10 referred to in LTE as eNBs, over an interface, for example an S1 interface. The eNBs 10 can include the same or different categories of eNBs, e.g. macro eNBs, and/or micro/pico/femto eNBs. The eNBs 10 communicate with each other over an interface, for example an X2 interface. The S1 interface and X2 interface are defined in the LTE standard. A UE 12 can receive downlink data from and send uplink data to one of the base stations 10 with that base station 10 being referred to as the serving base station of the UE 12.

Figure 3 shows a user equipment (UE) 12 that can be used in one or more of the non- limiting example embodiments described. The UE 12 may in some embodiments be a mobile device that is configured for machine-to-machine (M2M) or machine-type communication (MTC). The UE 12 comprises a processing module 30 that controls the operation of the UE 12. The processing module 30 is connected to a receiver or transceiver module 32 with associated antenna(s) 34 which are used to receive signals from or both transmit signals to and receive signals from a base station 10 in the network 2. To make use of discontinuous reception (DRX), the processing module 30 can be configured to deactivate the receiver or transceiver module 32 for specified lengths of time. The user equipment 12 also comprises a memory module 36 that is connected to the processing module 30 and that stores program and other information and data required for the operation of the UE 12.

Figure 4 shows a base station 10 (for example a NodeB or an eNodeB) that can be used in example embodiments described. It will be appreciated that although a macro eNB will not in practice be identical in size and structure to a micro eNB, for the purposes of illustration, the base stations 10 are assumed to include similar components. Thus, the base station 10 comprises a processing module 40 that controls the operation of the base station 10. The processing module 40 is connected to a transceiver module 42 with associated antenna(s) 44 which are used to transmit signals to, and receive signals from, user equipments 12 in the network 2. The base station 10 also comprises a memory module 46 that is connected to the processing module 40 and that stores program and other information and data required for the operation of the base station 10. The base station 10 also includes components and/or circuitry 48 for allowing the base station 10 to exchange information with other base stations 10 (for example via an X2 interface) and components and/or circuitry 49 for allowing the base station 10 to exchange information with nodes in the core network 4 (for example via the S1 interface). It will be appreciated that base stations for use in other types of network (e.g. UTRAN or WCDMA RAN) will include similar components to those shown in Figure 3 and appropriate interface circuitry 48, 49 for enabling communications with the other network nodes in those types of networks (e.g. other base stations, mobility management nodes and/or nodes in the core network).

Figure 5 shows a core network node 6, 8 that can be used in the example embodiments described. The node 6, 8 comprises a processing module 50 that controls the operation of the node 6, 8. The processing module 50 is connected to components and/or circuitry 52 for allowing the node 6, 8 to exchange information with the base stations 10 with which it is associated (which is typically via the S1 interface). The node 6, 8 also comprises a memory module 56 that is connected to the processing module 50 and that stores program and other information and data required for the operation of the node 6, 8. It will be appreciated that only the components of the UE 12, base station 10 and core network node 6, 8 required to explain the embodiments presented herein are illustrated in Figures 3, 4 and 5. As described above, an extended SFN period is provided that is longer than a normal SFN period. The length of the extended SFN period is typically an integer multiple of the length of an SFN period. When used for DRX, the extended SFN period sets the maximum DRX cycle length for a DRX UE 12, although it will be appreciated that a particular UE 12 may use a DRX cycle length that is longer than a normal SFN period up to the extended SFN period. One or more additional bits used to communicate the extended SFN range could be broadcast by the network node 10 relatively infrequently at predetermined times. For example, the one or more additional bits can be broadcast in a particular SFN of an SFN period (e.g. SFN=0), or a subset of the SFN values in an SFN period (e.g. SFN = 0, SFN = 512, etc.). It will be appreciated that where a subset of SFN values in the SFN period are selected, the subset of SFN values do not have to be uniformly distributed throughout the SFN period. In other words, the one or more additional bits are only broadcast by the network node 10 in some (i.e. not all) of the SFNs in an SFN period. This infrequent broadcast of the additional bits means that the one or more additional bit(s) can be communicated using the spare bits included in the MIB. That is, the spare bit or bits in the MIB can be reserved for the purpose of extending the SFN range only for, for example, SFN=0, which means that it may be possible to use all 10 spare bits to extend the SFN range. For all other SFN values (or other SFN values not specified in the subset of SFN values), the spare bits would still be free to use for any future feature.

Figure 6 is a schematic illustration of how additional bits can be communicated in an MIB or other information block IB that is frequently transmitted by the network node 10 according to an embodiment. Each block 60 represents an SFN period signalled in a master information block (MIB) (or other information block (IB) that is used to signal frame numbering). The 1024 values for SFN are indicated to the UEs in the conventional manner, i.e. with an 8-bit System Frame Number field, and the remaining two bits being derived by a UE 12 from the different scrambling codes used for the four copies of the MIB broadcast in each 10ms period. In this embodiment, the extended SFN period/maximum DRX cycle length 62 corresponds to the length of four SFN periods 60, which means that two additional bits need to be communicated to the UE 12. The extended SFN period 62 in this embodiment is therefore 4096 frames. It will be appreciated that extended SFN periods 62 of alternative lengths can be formed corresponding to more or less than four SFN periods 60. It will also be appreciated that the aspects described herein are not limited to maximum DRX cycle lengths that are an integer multiple of the SFN period 60.

Within the extended SFN period 62 shown in Figure 6, each of the SFN periods is labeled 1-4 respectively (indicated by reference number 64). Each SFN period 60 has a corresponding value for the two additional bits 66 that can be read by the UE 12. In this illustrated embodiment, the additional bits 66 are transmitted in the MIB for SFN = 2 in each SFN period 60. The transmission of these additional bits is noted by line 68 in each SFN period 60. Thus, the additional bits 66 broadcast in the MIB when SFN = 2 only takes up 1/1024^th of the broadcasting resources, in terms of air interface load and what is left for future features, in comparison to broadcasting the additional bits in every 10ms radio frame.

It will be appreciated that in the case of E-UTRAN, a MIB contains an 8-bit value in an SFN field, and each instance of a MIB is broadcast four times using different scrambling codes. A UE determines the SFN from the 8-bit value in the SFN field in a MIB and the scrambling code used to transmit that instance of the MIB. Thus, a MIB having a particular value of the 8-bit value in the SFN field will be broadcast four times before the 8-bit value is incremented. Where the one or more additional bits 66 are included in the MIB, they can be included for a particular value or subset of values of the 8-bit value in the SFN field. For example, the additional bits 66 could be broadcast in the MIB when the 8-bit value represents 0, which means, when combined with the different scrambling codes used to broadcast that MIB, the additional bits 66 will be broadcast in the subset of SFNs 0, 1 , 2 and 3.

In an alternative embodiment, rather than use the spare bits in the MIB, a secondary or supplementary MIB or other information block IB (such as an existing or new SIB) can be provided to carry the additional bit or bits, which is only broadcast or transmitted during a particular SFN of an SFN period, or during a subset of the SFN values in an SFN period. Figure 7 illustrates a method of operating a network node, such as a base station 10, according to an embodiment. The operation of the base station 10 enables UEs 12 to operate with an extended DRX cycle longer than an SFN period up to the maximum DRX cycle length (given by the extended SFN period 62). In step 101 , the network node 10 (and in particular the processing module 40) determines whether the current SFN is equal to a selected SFN value (e.g. SFN = 0) or an SFN in a selected subset of SFNs (e.g. comprising SFN=0, SFN= 256, SFN=512, SFN=768, etc.). Where the additional bits are to be transmitted in an MIB, it will be appreciated that, rather than defining a selected subset of SFN values (e.g. 0, 1 , 2, 3) for which the additional bits are to be transmitted, the SFN values may be defined in terms of a selected value or subset of values of the 8- bit SFN field in the MIB (e.g. the selected 8-bit SFN field can be 0 which corresponds to 10-bit SFNs 0, 1 , 2, 3).

If not, the processing module 40 forms an information block, IB (preferably an MIB) that indicates the current SFN and broadcasts the IB to UEs 12 in the cell of the node 10 using the transceiver module 42 (step 103).

If the current SFN is equal to a selected SFN value or an SFN in a selected subset of SFNs, then the processing module 40 forms an information block, IB (preferably an MIB) that indicates the current SFN and an IB indicating the one or more additional bits required to identify the current SFN period in the extended SFN period. In some embodiments, the current SFN and the one or more additional bits are included in the same IB, but in other embodiments the one or more additional bits are included in a separate IB to the current SFN. The base station 10 then broadcasts the IB(s) to UEs 12 in the cell of the node 10 using the transceiver module 42 (step 105).

The current SFN can then be incremented for broadcast in the next IB (it being appreciated that the value provided in the system frame number (SFN) field in the MIB will be incremented by one following four repeats of the current value with the different scrambling codes) - step 107. The method then returns to step 101 for the next SFN in the SFN period 60.

As noted above, it will be appreciated that the base station 10/network 2 can define the extended SFN period 62 for the purpose of enabling longer DRX cycles than the current maximum of an SFN period, as well as for other purposes. Figure 8 illustrates a method of operating a mobile device, such as a UE 12, according to an embodiment. In this illustrated embodiment, the UE 12 is operating in a discontinuous reception (DRX) mode with a selected DRX cycle period that is longer than an SFN period 60 up to the length of the extended SFN period 62 defined in the network 2 (which sets the maximum DRX cycle length). The length of the DRX cycle for the UE 12 is typically selected by the network 2, but in some cases it can be selected by the UE 12 itself. Operating in the DRX mode means that the receiver or transceiver module 32 in the UE 12 is typically deactivated or powered down and is only activated at specific intervals to receive paging messages from the network 2. However, in order to ensure that the UE 12 activates the receiver or transceiver module 32 at the right time, the UE 12 needs to determine the current SFN within the extended SFN period 62 in order to synchronise with the network 2. Thus, in step 1 11 the processing module 30 activates the receiver or transceiver module 32 to receive an information block, IB, broadcast by a network node 10. The IB indicates the current SFN in an SFN period 60.

In step 1 13, the processing module 30 reads the IB to determine the current SFN (which as noted above can be determined by reading an 8-bit value in an SFN field in the IB and determining a further two-bit value from the repetition of the MIB that the UE 12 is reading when the received IB is an MIB).

In step 1 15, the processing module 30 determines whether the current SFN read in step 1 13 is a selected SFN or one of a selected subset of SFNs. As noted above, this step may comprise examining the current SFN in the SFN period 60 or the just the value in the 8-bit SFN field, depending on the way in which the selected SFN or subset of SFNs is defined. The identity of the selected SFN or selected subset of SFNs may be predefined in a specification (possibly as a function of some other parameter(s)) or it may be provided by the network 2 on occurrence of a specific event or events, for example when a UE 12 registers/attaches to the network 2 (e.g., at power-on). It may also be possible to provide the SFN identity/identities at hand-in (RRC_CONNECTED state) or when a connection is otherwise established or setup. In RRCJDLE state the UE 12 is not under tight network control and may change cells without signalling to/from the network 2. For the specific case where a UE 12 makes a cell change between cells belonging to different Tracking Areas or should perform periodic Tracking Area updates, signalling towards the network 2 can be enforced and hence provisioning of SFN identities could be possible. In other or further embodiments, the provision of the SFN identity/identities to a UE 12 may be triggered by other events to those described.

If the current SFN is equal to the or a selected SFN (or the current 8-bit SFN value is equal to the or a selected 8-bit SFN value), then the processing module 30 reads one or more additional bits that identify the current SFN period in the extended SFN period (step 1 17). As noted above, the one or more additional bits may be included in the same IB as the current SFN, or they may be included in another IB broadcast by the base station 10 during the selected SFN. The processing module 30 then processes the current SFN indicated in the IB and the one or more additional bits to determine the current SFN in the extended SFN period 62. Now that the UE 12 has determined the current SFN, it is considered to be synchronised with the network 2. In addition, once the current SFN in the extended SFN period 62 is determined, the processing module 30 can determine the current frame number in the selected DRX cycle length.

If at step 1 15 it is determined that the current SFN is not equal to a selected SFN or selected one of a subset of SFNs, the processing module 30 determines if one or more additional bits have previously been received from the base station 10 (step 121). If so, the method moves to step 119 and the processing module 30 processes the current SFN and the previously received additional bit(s) to determine the SFN in the extended SFN period.

It will be appreciated that one potential downside to the infrequent transmission of the one or more additional bits proposed above is that a UE 12 which has lost track of or not yet received the SFN period index (i.e. the information contained by the one or more additional SFN bits) will have to wait until the one or more additional bits are next broadcast by the base station 10 to obtain them (e.g. when SFN = 0 if that is the selected SFN). That can mean waiting for at most 10 seconds, which may not be a problem for a delay tolerant MTC device 12 which already has chosen to have a DRX cycle longer than 10 seconds. This is also not particularly problematic from a power consumption point of view. In some embodiments the UE 12 can continue monitoring the MIBs broadcast by the base station 10 until the additional bits are signalled, but in other embodiments, following a determination in step 121 that one or more additional bits have not previously been received, the processing module 30 uses the current SFN indicated in the IB received in step 11 1 to calculate how long the UE 12 should wait (e.g. with the receiver deactivated) until the one or more additional bits will again be broadcast by the base station 10 (step 123). It will be appreciated that as the UE 12 knows which SFN or SFNs the one or more additional bits will be transmitted in each SFN period 60, and as each frame has a fixed length (e.g. 10ms), the processing module 30 can readily calculate the time from the current SFN in an SFN period 60 indicated in the IB until the next selected SFN where the additional bits are broadcast. The processing module 30 then deactivates the receiver or transceiver module 32 for the calculated wait period (step 125). The method then returns to step 1 11 in which the receiver or transceiver module 32 is activated to receive an IB from the base station 10 (which should contain the one or more additional bits).

In a further embodiment, to avoid a UE 12 from getting out of sync with the network 2 and/or to reduce the time required for a UE 12 to obtain synchronisation with the network 2 when, e.g., the UE 12 is first powered on or hands-in to the cell managed by the base station 10 (or on occurrence of another event, such as when the UE 12 wishes to establish a connection), the one or more additional bits could be 'piggy-backed' onto other signalling transmitted to the UE 12 by the base station 10, such as RRC connection setup signalling or a hand-over response from the target cell, thus avoiding the need for the UE 12 to wait until the next occasion when the one or more additional bits are broadcast in an MIB or other IB. As another alternative, on occurrence of one of the above events (e.g. when the UE 12 is powered on, hands-in to the cell, or wishes to establish a connection) the base station 10 could indicate the remaining number of SFNs until the next broadcast of the one or more additional bits.

It will be appreciated that the network uses DRX to know when a particular UE 12 is reachable (for paging, etc.). So, even though in some embodiments a UE 12 can be configured to wake up out of DRX (i.e. activate the receiver or transceiver module 32) just to read the one or more additional bits, in more preferable and practical embodiments, the network (e.g. the base station 10) can synchronise the broadcast of the one or more additional bits with the normal DRX 'wake-up' time for a UE 12 operating in a DRX mode so that the UE 12 does not need to perform extra wake-ups to read the additional bits. This means that the network will broadcast the one or more additional bits in an SFN or subset of SFNs in which a UE 12 is scheduled to wake-up out of DRX according to their current DRX cycle.

It will be further appreciated that the teachings of the present disclosure can be used more generally to communicate timing information (e.g. a frame number) to a UE in an efficient manner. In particular, if a network operates with a predefined period having a plurality of frames, a subset of the information required for a UE to determine the current frame number can be broadcast in each frame, and the remaining information that is required by the UE to identify the current frame number in the predefined period can be broadcast only in certain frames in the predefined period. Following the teachings of the present disclosure, the one or more additional bits are broadcast only when the subset of information required for the UE to determine the current frame number has a certain value or a set of values.

For example, if in a given network (which does not have to be LTE) the predefined period has 4096 frames, which can be represented by a 12-bit value, 8 bits (e.g. the 8 least significant bits) of the frame number can be broadcast in each frame, and the remaining 4 bits (the 4 most significant bits) can be broadcast only occasionally, for example when the 8 least significant bits have a certain value (e.g. 0), or when the 8 least significant bits have one of a subset of values (e.g. 0, 63, 127, 191). Modifications and other variants of the described embodiment(s) will come to mind to one skilled in the art having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the embodiment(s) is/are not to be limited to the specific examples disclosed and that modifications and other variants are intended to be included within the scope of this disclosure. Although specific terms may be employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. Various non-limiting embodiments are set out in the following statements:

1. A method of operating a network node in a communication network to provide timing information for a mobile device, the network defining an extended period that is longer than a predefined period in the network, the predefined period in the network corresponding to the time taken to transmit a predefined plurality of frames. The method comprising broadcasting a plurality of information blocks, IBs, to the mobile device, each IB indicating a current frame number in the predefined plurality of frames; wherein, when the current frame number is equal to a selected frame number or a frame number in a selected subset of the frame numbers in the predefined plurality of frames, the method further comprises the step of broadcasting one or more additional bits that identify the current predefined period in the extended period.

2. A method as in statement 1 , wherein the network node is to provide timing information for a mobile device operating in a discontinuous reception, DRX, mode, with a maximum

DRX cycle period for the mobile device corresponding to the length of the extended period.

3. A method as in statement 1 or 2, wherein the step of broadcasting one or more additional bits comprises broadcasting the one or more additional bits in the IB indicating the selected frame number or in the IBs indicating the selected subset of the frame numbers.

4. A method as in statement 3, wherein the IBs indicating the current frame number are Master Information Blocks, MIBs.

5. A method as in statement 4, wherein a MIB comprises a value in a frame number field and each MIB having a particular value in the frame number field is broadcast four times using four different scrambling codes, the combination of the value in the frame number field and the scrambling code used for the broadcast indicating the current frame number in the predefined plurality of frames.

6. A method as in statement 5, wherein the selected subset of frame numbers in the predefined plurality of frames comprises the frame numbers having a selected value in the frame number field. 7. A method as in statement 1 or 2, wherein the step of broadcasting one or more additional bits comprises broadcasting the one or more additional bits in a separate I B to the IB that indicates the current frame number.

8. A method as in statement 7, wherein the IBs indicating the current frame number are Master Information Blocks, MIBs.

9. A method as in statement 8, wherein the separate IB is a secondary or supplementary MIB or other information block.

10. A method as in any preceding statement, wherein the predefined periods in the network are system frame number, SFN, periods and the frame number is an SFN. 1 1. A method as in any preceding statement, wherein the predefined plurality of frames comprises 1024 or 4096 frames.

12. A method as in any preceding statement, wherein the step of broadcasting comprises incrementing the indicated current frame number with each broadcast of the IB.

13. A method as in any preceding statement, wherein the subset of selected frame numbers comprises less than the total number of frame numbers in the predefined plurality of frames. 14. A method as in any preceding statement, wherein the method further comprises the step of transmitting the one or more additional bits with other signalling transmitted to the mobile device.

15. A method as in statement 14, wherein the one or more additional bits are only included with the other signalling when the current frame number is not equal to a selected frame number or a frame number in a selected subset of the frame numbers in the predefined plurality of frames.

16. A method as in statement 14 or 15, wherein the other signalling is radio resource control, RRC, connection setup signalling and/or hand-over signalling. 17. A method as in any preceding statement, the method further comprising the step of transmitting to a mobile device the identity of the selected frame number or selected subset of the frame numbers in which the one or more additional bits are broadcast when the mobile device registers or attaches to the network, and/or when the mobile device hands-in to a cell in the network and/or during connection setup.

18. A computer program product having computer readable code embodied therein, the computer readable code being configured such that, on execution by a suitable computer or processor, the computer or processor is caused to perform the method of any of statements 1-17.

19. A network node for use in a communication network to provide timing information for a mobile device, the network defining an extended period that is longer than a predefined period in the network, the predefined period in the network corresponding to the time taken to transmit a predefined plurality of frames. The network node is adapted to broadcast a plurality of information blocks, IBs, to the mobile device, each IB indicating a current frame number in the predefined plurality of frames; and broadcast one or more additional bits that identify the current predefined period in the extended period when the current frame number is equal to a selected frame number or a frame number in a selected subset of the frame numbers in the predefined plurality of frames.

20. A network node as in statement 19, wherein the network node is for providing timing information to a mobile device operating in a discontinuous reception, DRX, mode, with a maximum DRX cycle period for the mobile device corresponding to the length of the extended period.

21. A network node as in statement 19 or 20, wherein the network node is adapted to broadcast the one or more additional bits in the IB indicating the selected frame number or in the IBs indicating the selected subset of the frame numbers.

22. A network node as in statement 21 , wherein the IBs indicating the current frame number are Master Information Blocks, MIBs. 23. A network node as in statement 22, wherein a MIB comprises a value in a frame number field and the network node is adapted to broadcast each MIB having a particular value in the frame number field four times using four different scrambling codes, the combination of the value in the frame number field and the scrambling code used for the broadcast indicating the current frame number in the predefined plurality of frames.

24. A network node as in statement 23, wherein the selected subset of frame numbers in the predefined plurality of frames comprises the frame numbers having a selected value in the frame number field.

25. A network node as in statement 19 or 20, wherein the network node is adapted to broadcast the one or more additional bits in a separate IB to the IB that indicates the current frame number. 26. A network node as in statement 25, wherein the IBs indicating the current frame number are Master Information Blocks, MIBs.

27. A network node as in statement 26, wherein the separate IB is a secondary or supplementary MIB or other information block.

28. A network node as in any of statements 19-27, wherein the predefined periods in the network are system frame number, SFN, periods and the frame number is an SFN.

29. A network node as in any of statements 19-28, wherein the predefined plurality of frames comprises 1024 or 4096 frames.

30. A network node as in any of statements 19-29, wherein the network node is adapted to increment the indicated current frame number with each broadcast of the IB. 31. A network node as in any of statements 19-30, wherein the subset of selected frame numbers comprises less than the total number of frame numbers in the predefined plurality of frames. 32. A network node as in any of statements 19-31 , wherein the network node is further adapted to transmit the one or more additional bits with other signalling transmitted to the mobile device. 33. A network node as in statement 32, wherein the network node is adapted to only include the one or more additional bits with the other signalling when the current frame number is not equal to a selected frame number or a frame number in a selected subset of the frame numbers in the predefined plurality of frames. 34. A network node as in statement 32 or 33, wherein the other signalling is radio resource control, RRC, connection setup signalling and/or hand-over signalling.

35. A network node as in any of statements 19-34, wherein the network node is further adapted to transmit to a mobile device the identity of the selected frame number or selected subset of the frame numbers in which the one or more additional bits are broadcast when the mobile device registers or attaches to the network, and/or when the mobile device hands-in to a cell in the network and/or during connection setup.

36. A method of operating a mobile device in a communication network, the network defining an extended period that is longer than a predefined period in the network, the predefined period in the network corresponding to the time taken to transmit a predefined plurality of frames. The method comprises operating a receiver in the mobile device to receive an information block, IB, broadcast by a network node in the communication network, the IB indicating a respective current frame number in the predefined plurality of frames; determining whether the current frame number is equal to a selected frame number or a frame number in a selected subset of the frame numbers in the predefined plurality of frames; if so, reading one or more additional bits broadcast by the network node, the one or more additional bits identifying the current predefined period in the extended period; and processing the current frame number in the IB and the one or more additional bits to determine the current frame number in the extended period.

37. A method as in statement 36, wherein the mobile device is operating in a discontinuous reception, DRX, mode in a communication network, with a maximum DRX cycle period for the mobile device corresponding to the length of the extended period. 38. A method as in statement 37, wherein the mobile device has a selected DRX cycle length that is longer than a predefined period up to the maximum DRX cycle period, and wherein the method further comprises the step of using the determined current frame number in the extended period to determine the current frame number in the selected DRX cycle length.

39. A method as in statement 36, 37 or 38, wherein the step of reading one or more additional bits comprises reading the one or more additional bits from the IB received in the step of operating.

40. A method as in statement 39, wherein the IBs indicating the current frame number are Master Information Blocks, MIBs.

41. A method as in statement 40, wherein a MIB comprises a value in a frame number field and each MIB having a particular value in the frame number field is broadcast four times using four different scrambling codes, wherein the value in the frame number field and the scrambling code used for the broadcast is processed to determine the current frame number in the predefined plurality of frames. 42. A method as in statement 41 , wherein the selected subset of frame numbers in the predefined plurality of frames comprises the frame numbers having a selected value in the frame number field.

43. A method as in statement 36, 37 or 38, wherein the step of reading one or more additional bits comprises reading the one or more additional bits from a separate IB to the

IB indicating the current frame number.

44. A method as in statement 43, wherein the IBs indicating the current frame number are Master Information Blocks, MIBs.

45. A method as in statement 44, wherein the separate IB is a secondary or supplementary MIB or other information block.

46. A method as in any of statements 36-45, the predefined periods in the network are system frame number, SFN, periods and the frame number is an SFN. 47. A method as in any of statements 36-46, wherein the predefined plurality of frames comprises 1024 or 4096 frames. 48. A method as in any of statements 36-47, wherein the subset of selected frame numbers comprises less than the total number of frame numbers in the predefined plurality of frames.

49. A method as in any of statements 36-48, the method further comprises the steps of determining if the mobile device has previously received one or more additional bits if the current frame number is not equal to a selected frame number or a frame number in a selected subset of the frame numbers in the predefined plurality of frames; and if the mobile device has previously received one or more additional bits, processing the current frame number in the IB and the previously received one or more additional bits to determine the current frame number in the extended period.

50. A method as in any of statements 36-49, wherein the method further comprises the steps of calculating the time until the next selected frame number or a frame number in the selected subset of frame numbers using the current frame number in the IB if the mobile device has not previously received one or more additional bits; and operating the receiver to receive another IB after the calculated time has elapsed.

51. A method as in any of statements 36-50, the method further comprising the step of receiving the one or more additional bits with other signalling transmitted by the network node.

52. A method as in statement 51 , wherein the other signalling is radio resource control, RRC, connection setup signalling and/or hand-over signalling. 53. A method as in any of statements 36-52, the method further comprising the step of receiving the identity of the selected frame number or selected subset of the frame numbers in which the one or more additional bits are broadcast when the mobile device registers or attaches to the network, and/or when the mobile device hands-in to a cell in the network and/or during connection setup. 54. A computer program product having computer readable code embodied therein, the computer readable code being configured such that, on execution by a suitable computer or processor, the computer or processor is caused to perform the method of any of statements 36-53.

55. A mobile device for use in a communication network, the network defining an extended period that is longer than a predefined period in the network, the predefined period in the network corresponding to the time taken to transmit a predefined plurality of frames. The mobile device comprises a receiver and the mobile device is adapted to operate the receiver to receive an information block, IB, broadcast by a network node in the communication network, the IB indicating a respective current frame number in the predefined plurality of frames; determine whether the current frame number is equal to a selected frame number or a frame number in a selected subset of the frame numbers in the predefined plurality of frames; read one or more additional bits broadcast by the network node if the current frame number is equal to a selected frame number or a frame number in a selected subset of the frame numbers, the one or more additional bits identifying the current predefined period in the extended period, and process the current frame number in the IB and the one or more additional bits to determine the current frame number in the extended period.

56. A mobile device as in statement 55, wherein the mobile device is adapted to operate in a discontinuous reception, DRX, mode in a communication network, with a maximum DRX cycle period for the mobile device corresponding to the length of the extended period.

57. A mobile device as in statement 56, wherein the mobile device is adapted to select a DRX cycle length that is longer than a predefined period up to the maximum DRX cycle period, and wherein the mobile device is further adapted to use the determined current frame number in the extended period to determine the current frame number in the selected DRX cycle length.

58. A mobile device as in statement 55, 56 or 57, wherein the mobile device is adapted to read the one or more additional bits from the received IB that indicates the current frame number. 59. A mobile device as in statement 58, wherein the IBs indicating the current frame number are Master Information Blocks, MIBs.

60. A mobile device as in statement 59, wherein a MIB comprises a value in a frame number field and the mobile device is adapted to receive each MIB having a particular value in the frame number field four times using four different scrambling codes, and wherein the mobile device is adapted to process the value in the frame number field and the scrambling code used for the MIB to determine the current frame number in the predefined plurality of frames.

61. A mobile device as in statement 60, wherein the selected subset of frame numbers in the predefined plurality of frames comprises the frame numbers having a selected value in the frame number field. 62. A mobile device as in statement 55, 56 or 57, wherein the mobile device is adapted to read one or more additional bits from a separate I B to the IB indicating the current frame number.

63. A mobile device as in statement 62, wherein the IBs indicating the current frame number are Master Information Blocks, MIBs.

64. A mobile device as in statement 63, wherein the separate IB is a secondary or supplementary MIB or other information block. 65. A mobile device as in any of statements 55-64, the predefined periods in the network are system frame number, SFN, periods and the frame number is an SFN.

66. A mobile device as in any of statements 55-65, wherein the predefined plurality of frames comprises 1024 or 4096 frames.

67. A mobile device as in any of statements 55-66, wherein the subset of selected frame numbers comprises less than the total number of frame numbers in the predefined plurality of frames. 68. A mobile device as in any of statements 55-67, wherein the mobile device is adapted to determine if the mobile device has previously received one or more additional bits if the current frame number is not equal to a selected frame number or a frame number in a selected subset of the frame numbers in the predefined plurality of frames; process the current frame number in the IB and the previously received one or more additional bits to determine the current frame number in the extended period if the mobile device has previously received one or more additional bits.

69. A mobile device as in any of statements 55-68, wherein the mobile device is adapted to calculate the time until the next selected frame number or a frame number in the selected subset of frame numbers using the current frame number in the IB if the mobile device has not previously received one or more additional bits; and receive another IB after the calculated time has elapsed. 70. A mobile device as in any of statements 55-69, wherein the mobile device is adapted to receive the one or more additional bits with other signalling transmitted by the network node.

71. A mobile device as in statement 70, wherein the other signalling is radio resource control, RRC, connection setup signalling and/or hand-over signalling.

72. A mobile device as in any of statements 55-71 , wherein the mobile device is adapted to receive the identity of the selected frame number or selected subset of the frame numbers in which the one or more additional bits are broadcast when the mobile device registers or attaches to the network, and/or when the mobile device hands-in to a cell in the network and/or during connection setup.

73. A network node for use in a communication network to provide timing information for a mobile device, the network defining an extended period that is longer than a predefined period in the network, the predefined period in the network corresponding to the time taken to transmit a predefined plurality of frames. The network node comprises a processor and a memory, said memory containing instructions executable by said processor whereby said network node is operative to broadcast a plurality of information blocks, IBs, to the mobile device, each IB indicating a current frame number in the predefined plurality of frames; and broadcast one or more additional bits that identify the current predefined period in the extended period when the current frame number is equal to a selected frame number or a frame number in a selected subset of the frame numbers in the predefined plurality of frames. 74. A network node as in statement 73, wherein the network node is for providing timing information to a mobile device operating in a discontinuous reception, DRX, mode, with a maximum DRX cycle period for the mobile device corresponding to the length of the extended period. 75. A network node as in statement 73 or 74, wherein said network node is further operative to broadcast the one or more additional bits in the IB indicating the selected frame number or in the IBs indicating the selected subset of the frame numbers.

76. A network node as in statement 75, wherein the IBs indicating the current frame number are Master Information Blocks, MIBs.

77. A network node as in statement 76, wherein a MIB comprises a value in a frame number field and said network node is further operative to broadcast each MIB having a particular value in the frame number field four times using four different scrambling codes, the combination of the value in the frame number field and the scrambling code used for the broadcast indicating the current frame number in the predefined plurality of frames.

78. A network node as in statement 77, wherein the selected subset of frame numbers in the predefined plurality of frames comprises the frame numbers having a selected value in the frame number field.

79. A network node as in statement 73 or 74, wherein said network node is further operative to broadcast the one or more additional bits in a separate IB to the IB that indicates the current frame number.

80. A network node as in statement 79, wherein the IBs indicating the current frame number are Master Information Blocks, MIBs.

81. A network node as in statement 80, wherein the separate IB is a secondary or supplementary MIB or other information block. 82. A network node as in any of statements 73-81 , wherein said network node is further operative to increment the indicated current frame number with each broadcast of the IB. 83. A network node as in any of statements 73-82, wherein the subset of selected frame numbers comprises less than the total number of frame numbers in the predefined plurality of frames.

84. A network node as in any of statements 73-83, wherein said network node is further operative to transmit the one or more additional bits with other signalling transmitted to the mobile device.

85. A network node as in statement 84, wherein said network node is further operative to only include the one or more additional bits with the other signalling when the current frame number is not equal to a selected frame number or a frame number in a selected subset of the frame numbers in the predefined plurality of frames.

86. A network node as in statement 84 or 85, wherein the other signalling is radio resource control, RRC, connection setup signalling and/or hand-over signalling.

87. A network node as in any of statements 73-86, wherein said network node is further operative to transmit to a mobile device the identity of the selected frame number or selected subset of the frame numbers in which the one or more additional bits are broadcast when the mobile device registers or attaches to the network, and/or when the mobile device hands-in to a cell in the network and/or during connection setup.

88. A mobile device for use in a communication network, the network defining an extended period that is longer than a predefined period in the network, the predefined period in the network corresponding to the time taken to transmit a predefined plurality of frames. The mobile device comprises a processor and a memory, said memory containing instructions executable by said processor whereby said mobile device is operative to receive an information block, IB, broadcast by a network node in the communication network, the IB indicating a respective current frame number in the predefined plurality of frames; determine whether the current frame number is equal to a selected frame number or a frame number in a selected subset of the frame numbers in the predefined plurality of frames; read one or more additional bits broadcast by the network node if the current frame number is equal to a selected frame number or a frame number in a selected subset of the frame numbers, the one or more additional bits identifying the current predefined period in the extended period, and process the current frame number in the IB and the one or more additional bits to determine the current frame number in the extended period.

89. A mobile device as in statement 88, wherein said mobile device is further operative to operate in a discontinuous reception, DRX, mode in a communication network, with a maximum DRX cycle period for the mobile device corresponding to the length of the extended period.

90. A mobile device as in statement 89, wherein said mobile device is further operative to select a DRX cycle length that is longer than a predefined period up to the maximum DRX cycle period, and wherein said mobile device is further operative to use the determined current frame number in the extended period to determine the current frame number in the selected DRX cycle length.

91. A mobile device as in statement 88, 89 or 90, wherein said mobile device is further operative to read the one or more additional bits from the received IB that indicates the current frame number.

92. A mobile device as in statement 91 , wherein the IBs indicating the current frame number are Master Information Blocks, MIBs.

93. A mobile device as in statement 92, wherein a MIB comprises a value in a frame number field and said mobile device is further operative to receive each MIB having a particular value in the frame number field four times using four different scrambling codes, and wherein said mobile device is further operative to process the value in the frame number field and the scrambling code used for the MIB to determine the current frame number in the predefined plurality of frames.

94. A mobile device as in statement 93, wherein the selected subset of frame numbers in the predefined plurality of frames comprises the frame numbers having a selected value in the frame number field. 95. A mobile device as in statement 88, 89 or 90, wherein said mobile device is further operative to read one or more additional bits from a separate IB to the IB indicating the current frame number.

96. A mobile device as in statement 95, wherein the IBs indicating the current frame number are Master Information Blocks, MIBs.

97. A mobile device as in statement 96, wherein the separate IB is a secondary or supplementary MIB or other information block.

98. A mobile device as in any of statements 88-97, wherein the subset of selected frame numbers comprises less than the total number of frame numbers in the predefined plurality of frames.

99. A mobile device as in any of statements 88-98, wherein said mobile device is further operative to determine if the mobile device has previously received one or more additional bits if the current frame number is not equal to a selected frame number or a frame number in a selected subset of the frame numbers in the predefined plurality of frames; process the current frame number in the IB and the previously received one or more additional bits to determine the current frame number in the extended period if the mobile device has previously received one or more additional bits.

100. A mobile device as in any of statements 88-99, wherein said mobile device is further operative to calculate the time until the next selected frame number or a frame number in the selected subset of frame numbers using the current frame number in the IB if the mobile device has not previously received one or more additional bits; and receive another IB after the calculated time has elapsed. 101. A mobile device as in any of statements 88-100, wherein said mobile device is further operative to receive the one or more additional bits with other signalling transmitted by the network node.

102. A mobile device as in statement 101 , wherein the other signalling is radio resource control, RRC, connection setup signalling and/or hand-over signalling. 103. A mobile device as in any of statements 88-102, wherein said mobile device is further operative to receive the identity of the selected frame number or selected subset of the frame numbers in which the one or more additional bits are broadcast when the mobile device registers or attaches to the network, and/or when the mobile device hands- in to a cell in the network and/or during connection setup.

104. A method of operating a network node in a communication network to provide timing information for a mobile device, the network defining a predefined period corresponding to the time taken to transmit a predefined plurality of frames. The method comprises: broadcasting a plurality of information blocks, IBs, to the mobile device, each IB providing a subset of the information required for a mobile device to determine a current frame number in the predefined plurality of frames; wherein, when the value of the subset of the information required for a mobile device to determine the current frame number is equal to a selected value or a subset of values, the method further comprises the step of broadcasting one or more additional bits that enable a mobile device to identify the current frame number in the predefined plurality of frames.

105. A network node for use in a communication network to provide timing information for a mobile device, the network defining a predefined period corresponding to the time taken to transmit a predefined plurality of frames. The network node is adapted to broadcast a plurality of information blocks, IBs, to the mobile device, each IB providing a subset of the information required for a mobile device to determine a current frame number in the predefined plurality of frames; broadcast one or more additional bits that enable a mobile device to identify the current frame number in the predefined plurality of frames when the value of the subset of the information required for a mobile device to determine the current frame number is equal to a selected value or a subset of values.

106. A method of operating a mobile device in a communication network, the network defining a predefined period corresponding to the time taken to transmit a predefined plurality of frames. The method comprises: operating a receiver in the mobile device to receive an information block, IB, broadcast by a network node in the communication network, the IB providing a subset of the information required for a mobile device to determine a current frame number in the predefined plurality of frames; determining whether the value of the subset of the information is a selected value or one of a subset of values; if so, reading one or more additional bits broadcast by the network node, the one or more additional bits enabling the mobile device to identify the current frame number in the predefined plurality of frames; and processing the information in the IB and the one or more additional bits to determine the current frame number in the predefined plurality of frames.

107. A mobile device for use in a communication network, the network defining a predefined period corresponding to the time taken to transmit a predefined plurality of frames. The mobile device is adapted to operate a receiver in the mobile device to receive an information block, IB, broadcast by a network node in the communication network, the IB providing a subset of the information required for a mobile device to determine a current frame number in the predefined plurality of frames; determine whether the value of the subset of information is a selected value or one of a subset of values; read one or more additional bits broadcast by the network node if the value of the subset of information is a selected value or one of a subset of values, the one or more additional bits enabling the mobile device to identify the current frame number in the predefined plurality of frames; and process the information in the IB and the one or more additional bits to determine the current frame number in the predefined plurality of frames.

Claims

1. A method of operating a network node (10) in a communication network (2) to provide timing information for a mobile device (12), the network defining an extended period that is longer than a predefined period in the network, the predefined period in the network corresponding to the time taken to transmit a predefined plurality of frames, the method comprising:

broadcasting (103) a plurality of information blocks, IBs, to the mobile device, each IB indicating a current frame number in the predefined plurality of frames;

wherein, when the current frame number is equal to a selected frame number or a frame number in a selected subset of the frame numbers in the predefined plurality of frames, the method further comprises the step of broadcasting (105) one or more additional bits that identify the current predefined period in the extended period.

2. A method as claimed in claim 1 , wherein the network node is to provide timing information for a mobile device operating in a discontinuous reception, DRX, mode, with a maximum DRX cycle period for the mobile device corresponding to the length of the extended period.

3. A method as claimed in claim 1 or 2, wherein the step of broadcasting (105) one or more additional bits comprises broadcasting the one or more additional bits in the IB indicating the selected frame number or in the IBs indicating the selected subset of the frame numbers.

4. A method as claimed in claim 3, wherein the IBs indicating the current frame number are Master Information Blocks, MIBs, and wherein a MIB comprises a value in a frame number field and each MIB having a particular value in the frame number field is broadcast four times using four different scrambling codes, the combination of the value in the frame number field and the scrambling code used for the broadcast indicating the current frame number in the predefined plurality of frames.

5. A method as claimed in claim 1 or 2, wherein the step of broadcasting (105) one or more additional bits comprises broadcasting the one or more additional bits in a separate IB to the IB that indicates the current frame number.

6. A method as claimed in claim 5, wherein the IBs indicating the current frame number are Master Information Blocks, MIBs.

7. A method as claimed in claim 6, wherein the separate IB is a secondary or supplementary MIB or other information block.

8. A method as claimed in any preceding claim, wherein the predefined periods in the network are system frame number, SFN, periods and the frame number is an SFN.

9. A method as claimed in any preceding claim, wherein the subset of selected frame numbers comprises less than the total number of frame numbers in the predefined plurality of frames.

10. A method as claimed in any preceding claim, wherein the method further comprises the step of:

transmitting the one or more additional bits with other signalling transmitted to the mobile device.

1 1. A method as claimed in claim 10, wherein the one or more additional bits are only included with the other signalling when the current frame number is not equal to a selected frame number or a frame number in a selected subset of the frame numbers in the predefined plurality of frames.

12. A method as claimed in claim 10 or 1 1 , wherein the other signalling is radio resource control, RRC, connection setup signalling and/or hand-over signalling.

13. A method as claimed in any preceding claim, the method further comprising the step of:

transmitting to a mobile device the identity of the selected frame number or selected subset of the frame numbers in which the one or more additional bits are broadcast when the mobile device registers or attaches to the network, and/or when the mobile device hands-in to a cell in the network and/or during connection setup.

14. A computer program product having computer readable code embodied therein, the computer readable code being configured such that, on execution by a suitable computer or processor, the computer or processor is caused to perform the method of any of claims 1-13.

15. A network node (10) for use in a communication network (2) to provide timing information for a mobile device (12), the network defining an extended period that is longer than a predefined period in the network, the predefined period in the network corresponding to the time taken to transmit a predefined plurality of frames, the network node (10) being adapted to:

broadcast a plurality of information blocks, IBs, to the mobile device, each IB indicating a current frame number in the predefined plurality of frames; and

broadcast one or more additional bits that identify the current predefined period in the extended period when the current frame number is equal to a selected frame number or a frame number in a selected subset of the frame numbers in the predefined plurality of frames.

16. A network node (10) as claimed in claim 15, wherein the network node is for providing timing information to a mobile device (12) operating in a discontinuous reception, DRX, mode, with a maximum DRX cycle period for the mobile device corresponding to the length of the extended period.

17. A network node (10) as claimed in claim 15 or 16, wherein the network node is adapted to broadcast the one or more additional bits in the IB indicating the selected frame number or in the IBs indicating the selected subset of the frame numbers.

18. A network node (10) as claimed in claim 15 or 16, wherein the network node is adapted to broadcast the one or more additional bits in a separate IB to the IB that indicates the current frame number.

19. A network node (10) as claimed in any of claims 15-18, wherein the subset of selected frame numbers comprises less than the total number of frame numbers in the predefined plurality of frames.

20. A network node (10) as claimed in any of claims 15-19, wherein the network node is further adapted to transmit the one or more additional bits with other signalling transmitted to the mobile device (12).

21. A network node (10) as claimed in any of claims 15-20, wherein the network node is further adapted to transmit to a mobile device (12) the identity of the selected frame number or selected subset of the frame numbers in which the one or more additional bits are broadcast when the mobile device registers or attaches to the network (2), and/or when the mobile device hands-in to a cell in the network and/or during connection setup.

22. A method of operating a mobile device (12) in a communication network (2), the network defining an extended period that is longer than a predefined period in the network, the predefined period in the network corresponding to the time taken to transmit a predefined plurality of frames, the method comprising:

operating (11 1) a receiver in the mobile device to receive an information block, IB, broadcast by a network node (10) in the communication network, the IB indicating a respective current frame number in the predefined plurality of frames;

determining (1 15) whether the current frame number is equal to a selected frame number or a frame number in a selected subset of the frame numbers in the predefined plurality of frames;

if so, reading (117) one or more additional bits broadcast by the network node, the one or more additional bits identifying the current predefined period in the extended period; and

processing (1 19) the current frame number in the IB and the one or more additional bits to determine the current frame number in the extended period.

23. A method as claimed in claim 22, wherein the mobile device (12) is operating in a discontinuous reception, DRX, mode in a communication network (2), with a maximum

24. A method as claimed in claim 23, wherein the mobile device (12) has a selected DRX cycle length that is longer than a predefined period up to the maximum DRX cycle period, and wherein the method further comprises the step of using the determined current frame number in the extended period to determine the current frame number in the selected DRX cycle length.

25. A method as claimed in claim 22, 23 or 24, wherein the step of reading (1 17) one or more additional bits comprises reading the one or more additional bits from the IB received in the step of operating (1 11).

26. A method as claimed in claim 22, 23 or 24, wherein the step of reading (1 17) one or more additional bits comprises reading the one or more additional bits from a separate IB to the IB indicating the current frame number.

27. A method as claimed in any of claims 22-26, wherein the subset of selected frame numbers comprises less than the total number of frame numbers in the predefined plurality of frames.

28. A method as claimed in any of claims 22-27, the method further comprises the steps of determining (121) if the mobile device (12) has previously received one or more additional bits if the current frame number is not equal to a selected frame number or a frame number in a selected subset of the frame numbers in the predefined plurality of frames; and if the mobile device has previously received one or more additional bits, processing (119) the current frame number in the IB and the previously received one or more additional bits to determine the current frame number in the extended period.

29. A method as claimed in any of claims 22-28, wherein the method further comprises the steps of calculating (123) the time until the next selected frame number or a frame number in the selected subset of frame numbers using the current frame number in the IB if the mobile device (12) has not previously received one or more additional bits; and operating (1 11) the receiver to receive another IB after the calculated time has elapsed.

30. A method as claimed in any of claims 22-29, the method further comprising the step of receiving the one or more additional bits with other signalling transmitted by the network node (10).

31. A method as claimed in any of claims 22-30, the method further comprising the step of:

receiving the identity of the selected frame number or selected subset of the frame numbers in which the one or more additional bits are broadcast when the mobile device (12) registers or attaches to the network (2), and/or when the mobile device hands-in to a cell in the network and/or during connection setup.

32. A computer program product having computer readable code embodied therein, the computer readable code being configured such that, on execution by a suitable computer or processor, the computer or processor is caused to perform the method of any of claims 22-31.

33. A mobile device (12) for use in a communication network (2), the network defining an extended period that is longer than a predefined period in the network, the predefined period in the network corresponding to the time taken to transmit a predefined plurality of frames, wherein the mobile device comprises a receiver and the mobile device is adapted to:

operate the receiver to receive an information block, IB, broadcast by a network node (10) in the communication network, the IB indicating a respective current frame number in the predefined plurality of frames;

determine whether the current frame number is equal to a selected frame number or a frame number in a selected subset of the frame numbers in the predefined plurality of frames;

read one or more additional bits broadcast by the network node if the current frame number is equal to a selected frame number or a frame number in a selected subset of the frame numbers, the one or more additional bits identifying the current predefined period in the extended period, and

process the current frame number in the IB and the one or more additional bits to determine the current frame number in the extended period.

34. A mobile device (12) as claimed in claim 33, wherein the mobile device is adapted to read the one or more additional bits from the received IB that indicates the current frame number.

35. A mobile device (12) as claimed in claim 33 or 34, wherein the mobile device is adapted to read one or more additional bits from a separate IB to the IB indicating the current frame number.

36. A mobile device (12) as claimed in any of claims 33-35, wherein the subset of selected frame numbers comprises less than the total number of frame numbers in the predefined plurality of frames.

37. A mobile device (12) as claimed in any of claims 33-36, wherein the mobile device is adapted to determine if the mobile device has previously received one or more additional bits if the current frame number is not equal to a selected frame number or a frame number in a selected subset of the frame numbers in the predefined plurality of frames; process the current frame number in the IB and the previously received one or more additional bits to determine the current frame number in the extended period if the mobile device has previously received one or more additional bits.

38. A mobile device (12) as claimed in any of claims 33-37, wherein the mobile device is adapted to calculate the time until the next selected frame number or a frame number in the selected subset of frame numbers using the current frame number in the IB if the mobile device has not previously received one or more additional bits; and receive another IB after the calculated time has elapsed.

39. A mobile device (12) as claimed in any of claims 33-38, wherein the mobile device is adapted to receive the one or more additional bits with other signalling transmitted by the network node (10).

40. A mobile device (12) as claimed in any of claims 33-39, wherein the mobile device is adapted to receive the identity of the selected frame number or selected subset of the frame numbers in which the one or more additional bits are broadcast when the mobile device registers or attaches to the network (2), and/or when the mobile device hands-in to a cell in the network and/or during connection setup.

41. A network node for use in a communication network to provide timing information for a mobile device, the network defining an extended period that is longer than a predefined period in the network, the predefined period in the network corresponding to the time taken to transmit a predefined plurality of frames, the network node comprising a processor and a memory, said memory containing instructions executable by said processor whereby said network node is operative to: broadcast a plurality of information blocks, IBs, to the mobile device, each IB indicating a current frame number in the predefined plurality of frames; and

42. A network node as claimed in claim 41 , wherein the network node is for providing timing information to a mobile device operating in a discontinuous reception, DRX, mode, with a maximum DRX cycle period for the mobile device corresponding to the length of the extended period.

43. A network node as claimed in claim 41 or 42, wherein said network node is further operative to broadcast the one or more additional bits in the IB indicating the selected frame number or in the IBs indicating the selected subset of the frame numbers.

44. A network node as claimed in claim 41 or 42, wherein said network node is further operative to broadcast the one or more additional bits in a separate IB to the IB that indicates the current frame number.

45. A network node as claimed in any of claims 41-44, wherein the subset of selected frame numbers comprises less than the total number of frame numbers in the predefined plurality of frames.

46. A network node as claimed in any of claims 41-45, wherein said network node is further operative to transmit the one or more additional bits with other signalling transmitted to the mobile device.

47. A network node as claimed in claim 46, wherein said network node is further operative to only include the one or more additional bits with the other signalling when the current frame number is not equal to a selected frame number or a frame number in a selected subset of the frame numbers in the predefined plurality of frames.

48. A network node as claimed in any of claims 41-47, wherein said network node is further operative to transmit to a mobile device the identity of the selected frame number or selected subset of the frame numbers in which the one or more additional bits are broadcast when the mobile device registers or attaches to the network, and/or when the mobile device hands-in to a cell in the network and/or during connection setup.

49. A mobile device for use in a communication network, the network defining an extended period that is longer than a predefined period in the network, the predefined period in the network corresponding to the time taken to transmit a predefined plurality of frames, the mobile device comprising a processor and a memory, said memory containing instructions executable by said processor whereby said mobile device is operative to: receive an information block, IB, broadcast by a network node in the communication network, the IB indicating a respective current frame number in the predefined plurality of frames;

50. A mobile device as claimed in claim 49, wherein said mobile device is further operative to operate in a discontinuous reception, DRX, mode in a communication network, with a maximum DRX cycle period for the mobile device corresponding to the length of the extended period.

51. A mobile device as claimed in claim 50, wherein said mobile device is further operative to select a DRX cycle length that is longer than a predefined period up to the maximum DRX cycle period, and wherein said mobile device is further operative to use the determined current frame number in the extended period to determine the current frame number in the selected DRX cycle length.

52. A mobile device as claimed in claim 49, 50 or 51 , wherein said mobile device is further operative to read the one or more additional bits from the received IB that indicates the current frame number.

53. A mobile device as claimed in claim 49, 50 or 51 , wherein said mobile device is further operative to read one or more additional bits from a separate IB to the IB indicating the current frame number.

54. A mobile device as claimed in any of claims 49-53, wherein the subset of selected frame numbers comprises less than the total number of frame numbers in the predefined plurality of frames.

55. A mobile device as claimed in any of claims 49-54, wherein said mobile device is further operative to determine if the mobile device has previously received one or more additional bits if the current frame number is not equal to a selected frame number or a frame number in a selected subset of the frame numbers in the predefined plurality of frames; process the current frame number in the IB and the previously received one or more additional bits to determine the current frame number in the extended period if the mobile device has previously received one or more additional bits.

56. A mobile device as claimed in any of claims 49-55, wherein said mobile device is further operative to calculate the time until the next selected frame number or a frame number in the selected subset of frame numbers using the current frame number in the IB if the mobile device has not previously received one or more additional bits; and receive another IB after the calculated time has elapsed.

57. A mobile device as claimed in any of claims 49-56, wherein said mobile device is further operative to receive the one or more additional bits with other signalling transmitted by the network node.

58. A mobile device as claimed in any of claims 49-57, wherein said mobile device is further operative to receive the identity of the selected frame number or selected subset of the frame numbers in which the one or more additional bits are broadcast when the mobile device registers or attaches to the network, and/or when the mobile device hands- in to a cell in the network and/or during connection setup.