Field

The present disclosure relates to telecommunications apparatus and methods.

Description of Related Art

The "background" description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.

The present disclosure relates to wireless telecommunications systems and methods. Mobile communication systems have evolved over the past ten years or so from the GSM System (Global System for Mobile communications) to the 3G system and now include packet data communications as well as circuit switched communications. The third generation partnership project (3GPP) is developing a fourth generation mobile communication system referred to as Long Term Evolution (LTE) in which a core network part has been evolved to form a more simplified architecture based on a merging of components of earlier mobile radio network architectures and a radio access interface which is based on Orthogonal Frequency Division Multiplexing (OFDM) on the downlink and Single Carrier Frequency Division Multiple Access (SC-FDMA) on the uplink.

Third and fourth generation mobile telecommunication systems, such as those based on the 3GPP defined UMTS and Long Term Evolution (LTE) architectures, are able to support a more sophisticated range of services than simple voice and messaging services offered by previous generations of mobile telecommunication systems.

For example, with the improved radio interface and enhanced data rates provided by LTE systems, a user is able to enjoy high data rate applications such as mobile video streaming and mobile video conferencing that would previously only have been available via a fixed line data connection. The demand to deploy third and fourth generation networks is therefore strong and the coverage area of these networks, i.e. geographic locations where access to the networks is possible, is expected to increase rapidly.

The anticipated widespread deployment of third and fourth generation networks has led to the parallel development of a class of devices and applications which, rather than taking advantage of the high data rates available, instead take advantage of the robust radio interface and increasing ubiquity of the coverage area. Examples include so-called machine type communication (MTC) applications, some of which are in some respects typified by semi-autonomous or autonomous wireless communication devices (MTC devices) communicating

small amounts of data on a relatively infrequent basis. Examples include so-called smart meters which, for example, are located in a customer's home and periodically transmit data back to a central MTC server relating to the customer's consumption of a utility such as gas, water, electricity and so on. Smart metering is merely one example of potential MTC device

applications. Other examples include vehicle communications systems (for example, vehicle-to-vehicle ("V2V"), vehicle-to-pedestrian ("V2P") or vehicle-to-infrastructure/network ("V2I/N") systems, referred to generically as "V2X" arrangements. Further information on characteristics of MTC-type devices can be found, for example, in the corresponding standards, such as ETSI TS 122 368 V1 1 .6.0 (2012-09) / 3GPP TS 22.368 version 1 1 .6.0 Release 1 1 ).

In MTC arrangements, including V2X systems, technical issues can arise in the provision (by a base station) or acquisition (by a terminal device) of so-called system

information. In broad summary, system information, or at least some aspects of system information, in existing wireless telecommunications systems, such as LTE-based

telecommunications systems, is transmitted as System Information Blocks (SIBs). Receipt of the SIBs is required in order for a terminal device to be able to communicate with a cell, for reduced capability devices such as MTC devices, these SIBs can be large in comparison to the data handling capabilities of the device. This can also be an issue in the context of vehicle-based devices, where the movement of the vehicle (and the potential small size of cells defined, for example, by road-side units (RSUs) means that the time spent by a terminal device in a particular cell may be short. Similarly, in the context of coverage enhancement, it is sometimes difficult for a terminal device (whether reduced capability or not) to receive large SIBs. There is therefore a need for schemes which allow system information to be communicated to terminal devices operating on restricted frequency resources in wireless telecommunications systems. There is also a need for schemes which allow system information to be communicated to terminal devices operating in a coverage enhancement situation.

It is a constant aim to improve the operation and efficiency of wireless network systems. Summary

The present disclosure can address or mitigates the problems discussed above.

Respective aspects and features of the present disclosure are defined in the appended claims.

It is to be understood that both the foregoing general description and the following detailed description are exemplary, but are not restrictive, of the present technology.

Brief description of the drawings

A more complete appreciation of the disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings

wherein like reference numerals designate identical or corresponding parts throughout the several views, and wherein:

Figure 1 schematically represents an example of a LTE-type wireless telecommunication network;

Figure 2 schematically represents some aspects of a LTE downlink radio frame structure;

Figure 3 schematically represents some aspects of a LTE downlink radio subframe structure;

Figure 4 schematically illustrates a base station;

Figure 5 schematically illustrates a terminal device;

Figure 6 is a schematic diagram showing a controller of a terminal device;

Figure 7 schematically illustrates system information storage;

Figure 8 is a schematic flowchart showing operations of a terminal device;

Figure 9 is a schematic flowchart showing operations relating to base stations;

Figure 10 is a schematic flowchart illustrating operations of a terminal device;

Figure 1 1 is a schematic flowchart illustrating operations of a base station;

Figure 12 schematically illustrates a system information data structure;

Figure 13 is a schematic flowchart illustrating operations of a terminal device;

Figure 14 is a schematic flowchart illustrating operations of a terminal device;

Figure 15 is a summary flowchart of operations of a terminal device;

Figures 16 and 17 are summary flowcharts of operations of a base station;

Figures 18 to 21 are summary flowcharts illustrating operations of a terminal device; and

Figures 22 to 24 are summary flowcharts illustrating operations of a base station.

Detailed description of the embodiments

Figure 1 provides a schematic diagram illustrating some basic functionality of a wireless telecommunications network / system 100 operating in accordance with LTE principles. Various elements of Figure 1 and their respective modes of operation are well-known and defined in the relevant standards administered by the 3GPP (RTM) body.

The network 100 includes a plurality of base stations 101 connected to a core network 102. Each base station provides a coverage area 103 (for example, a cell) within which data can be communicated to and from terminal devices 104. Data are transmitted from base stations 101 to terminal devices 104 within their respective coverage areas 103 via a radio downlink. Data are transmitted from terminal devices 104 to the base stations 101 via a radio uplink. The core network 102 routes data to and from the terminal devices 104 via the respective base stations 101 and provides functions such as authentication, mobility

management, charging and so on. Terminal devices may also be referred to as mobile stations, user equipment (UE), user terminal, mobile radio, and so forth. Base stations may also be referred to as transceiver stations / nodeBs / e-NodeBs, and so forth.

Mobile telecommunications systems such as those arranged in accordance with the 3GPP defined Long Term Evolution (LTE) architecture use an orthogonal frequency division multiplex (OFDM) based interface for the radio downlink (so-called OFDMA) and a single carrier frequency division multiplex based interface for the radio uplink (so-called SC-FDMA).

Figure 2 shows a schematic diagram illustrating an OFDM based LTE downlink radio frame 201 . The LTE downlink radio frame is transmitted from an LTE base station (known as an enhanced Node B) and lasts 10 ms. The downlink radio frame comprises ten subframes, each subframe lasting 1 ms. A primary synchronisation signal (PSS) and a secondary

synchronisation signal (SSS) are transmitted in the first and sixth subframes of the LTE frame. A physical broadcast channel (PBCH) is transmitted in the first subframe of the LTE frame.

Figure 3 is a schematic diagram of a grid which illustrates the structure of an example conventional downlink LTE subframe (corresponding in this example to the first, i.e. left-most, subframe in the frame of Figure 2). The subframe comprises a predetermined number of symbols which are transmitted over a 1 ms period. Each symbol comprises a predetermined number of orthogonal sub-carriers distributed across the bandwidth of the downlink radio carrier.

The example subframe shown in Figure 3 comprises 14 symbols and 1200 sub-carriers spread across a 20MHz bandwidth. The smallest allocation of user data for transmission in LTE is a resource block comprising twelve sub-carriers transmitted over one slot (0.5 subframe). For clarity, in Figure 3, each individual resource element (a resource element comprises a single symbol on a single subcarrier) is not shown, instead each individual box in the subframe grid corresponds to twelve sub-carriers transmitted on one symbol.

Figure 3 shows resource allocations for four LTE terminals 340, 341 , 342, 343. For example, the resource allocation 342 for a first LTE terminal (UE 1 ) extends over five blocks of twelve sub-carriers (60 sub-carriers), the resource allocation 343 for a second LTE terminal (UE2) extends over six blocks of twelve sub-carriers and so on.

Control channel data are transmitted in a control region 300 (indicated by dotted-shading in Figure 3) of the subframe comprising the first n symbols of the subframe where n can vary between one and three symbols for channel bandwidths of 3MHz or greater and where n can vary between two and four symbols for channel bandwidths of 1.4MHz. For the sake of providing a concrete example, the following description relates to carriers with a channel bandwidth of 3MHz or greater so the maximum value of n will be 3. The data transmitted in the control region 300 includes data transmitted on the physical downlink control channel (PDCCH), the physical control format indicator channel (PCFICH) and the physical HARQ indicator channel (PHICH).

PDCCH contains control data indicating which sub-carriers on which symbols of the subframe have been allocated to specific LTE terminals. Thus, the PDCCH data transmitted in the control region 300 of the subframe shown in Figure 3 would indicate that UE1 has been allocated the block of resources identified by reference numeral 342, that UE2 has been allocated the block of resources identified by reference numeral 343, and so on.

PCFICH contains control data indicating the size of the control region (i.e. between one and three symbols).

PHICH contains HARQ (Hybrid Automatic Request) data indicating whether or not previously transmitted uplink data has been successfully received by the network.

Symbols in a central band 310 of the time-frequency resource grid are used for the transmission of information including the primary synchronisation signal (PSS), the secondary synchronisation signal (SSS) and the physical broadcast channel (PBCH). This central band 310 is typically 72 sub-carriers wide (corresponding to a transmission bandwidth of 1.08 MHz). The PSS and SSS are synchronisation signals that once detected allow an LTE terminal device to achieve frame synchronisation and determine the cell identity of the enhanced Node B transmitting the downlink signal. The PBCH carries information about the cell, comprising a master information block (MIB) that includes parameters that LTE terminals use to properly access the cell. Data transmitted to individual LTE terminals on the physical downlink shared channel (PDSCH) can be transmitted in other resource elements of the subframe.

Figure 3 also shows a region of PDSCH containing system information and extending over a bandwidth of R344.

An LTE frame also includes reference signals which are not shown in Figure 3 in the interests of clarity.

Figure 4 schematically illustrates a base station 101 in more detail. The base station 101 includes a transmitter (Tx) 400 for transmitting signals via a wireless access interface (and via an antenna 430) to the one or more communications devices or UEs, and a receiver (Rx) 410 to receive signals from the one or more terminal devices within the coverage area of the base station. A controller 420 controls the transmitter 400 and the receiver 410 to transmit and receive the signals via the wireless access interface. The transmitter 400 and receiver 410 together form a transceiver. The controller 420 may perform a function of controlling the allocation of communications resource elements of the wireless access interface and may in some examples include a scheduler for scheduling transmissions via the wireless access interface for both an uplink and the downlink. Operations of a base station discussed in connection with the description below may be undertaken or overseen, at least in part, by the controller 420. Figure 4 therefore provides an example of a base station for use in a wireless telecommunications system, the base station comprising a transceiver 400, 410 configured to perform wireless communication with a terminal device; and a controller 420 configured to control the transceiver.

In examples, the arrangement of Figure 4 provides a base station for use in a wireless telecommunications system, the base station comprising: a transceiver (such as 400, 410) to perform wireless communication with a terminal device; and a controller (such as 420) to control the transceiver to transmit system information defining communication parameters and (as discussed below, for example as the area ID) identification data indicating a group of two or more base stations having at least part of the system information in common.

In other examples, it is not necessary for each base station to transmit the system information (or all of the system information). Instead, a base station can transmit a reference to system information which the terminal device may already hold, such as system information corresponding to a neighbouring base station (so that there is at least a good chance, especially in a system of small cells such as an array of road side units, that the terminal device will have already downloaded the system information or - if not - that the terminal device will soon move into a cell corresponding to a base station which is transmitting the full system information). The reference could be, for example, an area I D (see below) which is the same as the area I D of the neighbouring cell. Or the reference could be an indicator code, for example formed of a preamble to show that it is an indicator code, followed by a data item indicating a selection, amongst a set of possible sets or instances of system information, which one should be used in connection with that base station. Or the reference could be a simple code saying "re-use (some or all of) whatever system information you currently hold" on the basis that the terminal device's most recent interaction will have been with a geographically adjacent cell. Operating under arrangements such as these, the base station of Figure 4 provides an example of a base station for use in a wireless telecommunications system, the base station comprising: a transceiver to perform wireless communication with a terminal device; and a controller to control the transceiver to transmit reference data referencing a set of system information defining communication parameters of that base station; the controller being configured to control the transceiver to conduct wireless communication in accordance with the referenced system information.

Figure 4, when operating in accordance with the principles and details set out below, provides an example of a base station for use in a wireless telecommunications system, the base station comprising: a transceiver to perform wireless communication with a terminal device; and a controller to control the transceiver to transmit system information defining communication parameters and identification data indicating a group of two or more base stations having at least part of the system information in common; in which: the system information comprises a plurality of system information blocks; the controller is configured to control the transceiver to transmit (i) a complete instance of a system information block; and (ii) a partial instance of the system information block containing difference information with respect to an instance of system information applicable to another base station.

Figure 4, when operating in accordance with the principles and details set out below, provides an example of a base station for use in a wireless telecommunications system, the base station comprising: a transceiver to perform wireless communication with a terminal device; and a controller to control the transceiver to transmit system information defining communication parameters; in which: the system information comprises a plurality of system information blocks; the controller is configured to control the transceiver to transmit a timer reset message to instruct a terminal device to increase a remaining portion of a validity period maintained by that base station for system information held by that base station.

Figure 4, when operating in accordance with the principles and details set out below, provides an example of a base station for use in a wireless telecommunications system, the base station comprising: a transceiver to perform wireless communication with a terminal device; and a controller to control the transceiver to transmit reference data referencing a set of system information defining communication parameters of that base station; the controller being configured to control the transceiver to conduct wireless communication in accordance with the referenced system information.

Figure 5 schematically illustrates a terminal device 104 in more detail. The terminal device 104 includes a transmitter 500 associated with an antenna 530 for transmitting signals on the uplink of the wireless access interface to the base station 101 and a receiver 510 for receiving signals transmitted by the base station 101 on the downlink via the wireless access interface. The transmitter 500 and the receiver 510 are controlled by a controller 520. The transmitter 500 and receiver 510 together form a transceiver. Operations of a terminal device discussed in connection with the description below may be undertaken or overseen, at least in part, by the controller 520. In some example embodiments of the present disclosure, the terminal device 104 is a so-called Low Complexity Machine Type Communication (LC-MTC) terminal device or narrowband internet-of-things (NB-IOT) device. NB-IOT devices are used to connect various electronic and other items to a network such as the internet. They are often characterised by low cost manufacture and deployment, low complexity, low power consumption and the like. An example of such device is smart electricity meter. Typical NB-IOT provision is expected to occupy a low bandwidth, such as only 180 kHz of bandwidth. Figure 5 therefore provides an example of a terminal device for use in a wireless telecommunications system, the terminal device comprising: a transceiver 500, 510 configured to perform wireless communication with a base station; and a controller 520 configured to control the transceiver.

The base station and the terminal device, as just described, can be implemented, at least in part, by computer software which, when executed by a computer (such as a processor device acting as the controller in each case), causes the computer to perform the described

methods of operation. Such computer software may be provided by a non-transitory machine readable storage medium storing the computer software.

The base station of Figure 4 and the terminal device of Figure 5, in the context of an arrangement such as that shown in Figure 1 , provide an example of a telecommunications system comprising one or more such terminal devices and one or more such base stations.

Figure 5, when operating in accordance with the principles and details set out below, provides an example of a terminal device for use in a wireless telecommunications system, the terminal device comprising: a transceiver to perform wireless communication with a base station and to obtain system information defining communication parameters from system information data received from that base station; system information storage; and a controller to detect whether the system information storage already holds at least some of the system information applicable to a newly communicating base station and to control the transceiver to obtain any portions of the system information not already held by the terminal device, in which: the system information comprises a plurality of system information blocks; and the controller is configured to detect parts of a system information block stored by the system information storage which are applicable to the newly communicating base station and to obtain other parts of that system information block as a partial system information block from the newly communicating base station.

Figure 5, when operating in accordance with the principles and details set out below, provides an example of a terminal device for use in a wireless telecommunications system, the terminal device comprising: a transceiver to perform wireless communication with a base station and to obtain system information defining communication parameters from system information data comprising a plurality of information blocks; system information storage; and a controller to detect whether the system information storage already holds at least some of the system information applicable to the newly communicating base station and to control the transceiver to obtain any portions of the system information from the newly communicating base station which are not already held by the terminal device; in which the controller is configured to detect whether identification data associated with information blocks transmitted by the newly communicating base station corresponds to identification data associated with information blocks stored by the system information storage; in which the identification data comprises area information identifying a group of base stations and a value tag identifying a version of one or more of the information blocks.

Figure 5, when operating in accordance with the principles and details set out below, provides an example of a terminal device for use in a wireless telecommunications system, the terminal device comprising: a transceiver to perform wireless communication with a base station and to obtain system information defining communication parameters from system information data transmitted by that base station; system information storage configured to store the system information and one or more associated value tags identifying a version of respective portions of the system information; and a controller to detect whether the system information storage already holds at least some of the system information applicable to the newly communicating base station and to control the transceiver to obtain any portions of the system information not already held by the terminal device from the base station; the controller being configured to detect an instruction to obtain updated system information and, in response to detection of the instruction, to obtain from the base station an updated version of only those portions of the system information having a value tag indicating a version of those portions different to the corresponding value tag held by the system information storage.

Figure 5, when operating in accordance with the principles and details set out below, provides an example of a terminal device for use in a wireless telecommunications system, the terminal device comprising: a transceiver to perform wireless communication with a base station and to obtain system information defining communication parameters from system information data transmitted by that base station; system information storage; and a controller to detect whether the system information storage already holds at least some of the system information applicable to the newly communicating base station and to control the transceiver to obtain any portions of the system information not already held by the terminal device from the base station; the controller being configured to maintain a validity timer indicating a validity period of the system information and, in response to the end of the validity period, to obtain updated system information from the base station; the controller being responsive to a timer reset message received from the base station before the end of the validity period to alter the validity timer so as to increase a remaining portion of the validity period.

Figure 6 is a schematic diagram showing a controller of a terminal device such as the controller 520 of Figure 5.

As discussed above, the controller is connected so as to control operations of a transceiver (not shown in Figure 6). The controller comprises a detector 600, a comparator 610, a system information store 620 and an operations controller 630. The detector 600 is arranged, in respect of a newly acquired (newly communicating) base station, to detect so-called system information transmitted (for example, broadcast, though in other examples at least part of the communication could be directed to a terminal device) by the base station. This is part of the arrangement by which the terminal device establishes communication with the base station. The system information provides various communications parameters which are needed by the terminal device for such communication.

The detector detects at a first stage a so-called Master Information Block (MIB). The MIB is the first piece of information which the terminal device acquires after it achieves downlink synchronisation with a base station. The MIB provides fundamental information which is needed for the terminal device to obtain other information relating to that base station.

The MIB is transmitted according to a fixed schedule having a periodicity of 40ms, with multiple repetitions being made within the 40ms period. In some examples, the MIB can change at the 40ms period but is transmitted by the base station every 10ms within that period. The MIB is detected first as it includes information relating to how the terminal device can receive the first of a set of system information blocks (SIBs), and in particular the MIB provides information as to how to receive a first system information block (SIB1 ). For example, it may refer to scheduling information for the broadcast of SIB1.

In turn, the system information block SIB1 contains cell access information as well as scheduling for other SIBs. The contents of the various system information blocks in example embodiments are given in the following discussion.

Master Information Block (MIB)

As mentioned above, this is the first piece of information which the terminal device seeks to download after establishing download synchronisation with a newly acquired (newly communicating) cell. It contains basic parameters defining the download channel and includes information required to receive SIB1 .

SystemlnformationBlockTypel

This includes information relating to terminal device cell access and defines the schedule of other SIBs. It is therefore needed before the other SIBs can be obtained.

SystemlnformationBlockType2

The SystemlnformationBlockType2 contains radio resource configuration information that is common for all terminal devices.

SystemlnformationBlockType3

The SystemlnformationBlockType3 contains cell re-selection information common for intra-frequency, inter-frequency and/ or inter-RAT cell re-selection.

SystemlnformationBlockType4

The SystemlnformationBlockType4 contains neighbouring cell related information relevant only for intra-frequency cell re-selection. The IE includes cells with specific re-selection parameters as well as blacklisted cells.

SystemlnformationBlockType5

The SystemlnformationBlockType5 contains information relevant only for inter-frequency cell re-selection i.e. information about other E-UTRA frequencies and inter-frequency

neighbouring cells relevant for cell re-selection. The IE includes cell re-selection parameters common for a frequency as well as cell specific re-selection parameters.

Other SIBs

A similar concept can be applied to further SIBs. Those listed above are the essential ones for NB-IOT, but for v2x case there may be further SIBs (e.g. SIB6 for inter-RAT mobility)

In other words, in examples, the system information comprises a master information block, obtained by a terminal device before the terminal device obtains the system information blocks; the system information blocks comprise a succession of a first system information block and one or more further system information blocks; the master information block provides one or more parameters for reception of the first system information block; and the first system information block provides one or more parameters for reception of the one or more further system information blocks.

The system information received from a base station can define one or both of: (i) communication parameters for communication with that base station; and (ii) communication parameters for communicating with other terminal devices operating under the control of communication parameters received from that base station, in a device-to-device communication operation.

In examples, the system information data received from the base station can be system information data broadcast by the base station, for example using a mechanism described above in connection with Figure 3.

CLAIMS

1 . A terminal device for use in a wireless telecommunications system, the terminal device comprising:

a transceiver to perform wireless communication with a base station and to obtain system information defining communication parameters from system information data received from that base station;

system information storage; and

a controller to detect whether the system information storage already holds at least some of the system information applicable to a newly communicating base station and to control the transceiver to obtain any portions of the system information not already held by the terminal device, in which:

the system information comprises a plurality of system information blocks; and the controller is configured to detect parts of a system information block stored by the system information storage which are applicable to the newly communicating base station and to obtain other parts of that system information block as a partial system information block from the newly communicating base station.

2. A terminal device according to claim 1 , in which the controller is configured to detect whether identification data associated with system information received from the newly communicating base station corresponds to identification data associated with system information stored by the system information storage.

3. A terminal device according to claim 1 , in which the system information storage is configured to store two or more instances of system information, each instance corresponding to one or more respective base stations.

4. A terminal device according to claim 3, in which the system information storage is configured to store two or more distinct instances of system information most recently obtained by the terminal device.

5. A terminal device according to claim 1 , in which:

the system information comprises a master information block, obtained by a terminal device before the terminal device obtains the system information blocks;

the system information blocks comprise a succession of a first system information block and one or more further system information blocks;

the master information block provides one or more parameters for reception of the first system information block; and

the first system information block provides one or more parameters for reception of the one or more further system information blocks.

6. A terminal device according to claim 5, in which the identification data is carried by one or both of the master information block and the first system information block.

7. A terminal device according to claim 6, in which, in response to reception of a first system information block carrying identification data which corresponds to system information stored by the system information store, the controller is configured to control the transceiver not to receive the further system information blocks.

8. A terminal device according to claim 2, in which the system information storage is configured to store, as the identification data, a set of one of more base station identifiers applicable to at least respective portions of an instance of stored system information.

9. A terminal device according to claim 8, in which the base station identifiers comprise one or more selected from the list consisting of:

cell identifier;

area identifier;

information block tag;

tracking area identifier; and

public land mobile network identifier.

10. A terminal device according to claim 1 , in which the system information received from a base station defines one or both of:

communication parameters for communication with that base station; and

communication parameters for communicating with other terminal devices operating under the control of communication parameters received from that base station, in a device-to-device communication operation.

1 1 . A terminal device according to claim 1 , in which the system information data received from the base station is system information data broadcast by the base station.

12. A terminal device for use in a wireless telecommunications system, the terminal device comprising:

a transceiver to perform wireless communication with a base station and to obtain system information defining communication parameters from system information data comprising a plurality of information blocks;

system information storage; and

a controller to detect whether the system information storage already holds at least some of the system information applicable to the newly communicating base station and to control the transceiver to obtain any portions of the system information from the newly communicating base station which are not already held by the terminal device;

in which the controller is configured to detect whether identification data associated with information blocks transmitted by the newly communicating base station corresponds to identification data associated with information blocks stored by the system information storage; in which the identification data comprises area information identifying a group of base stations and a value tag identifying a version of one or more of the information blocks.

13. A terminal device according to claim 12, in which the group of base stations identified by the area information identifies those base stations to which the value tag is applicable.

14. A terminal device according to claim 12, in which:

the system information comprises a master information block, obtained by a terminal device before the terminal device obtains the system information blocks;

the system information blocks comprise a succession of a first system information block and one or more further system information blocks;

the master information block provides one or more parameters for reception of the first system information block; and

the first system information block provides one or more parameters for reception of the one or more further system information blocks.

15. A terminal device according to claim 14, in which a respective value tag is associated with each of the master information block, the first system information block and the further system information blocks.

16. A terminal device for use in a wireless telecommunications system, the terminal device comprising:

a transceiver to perform wireless communication with a base station and to obtain system information defining communication parameters from system information data transmitted by that base station;

system information storage configured to store the system information and one or more associated value tags identifying a version of respective portions of the system information; and a controller to detect whether the system information storage already holds at least some of the system information applicable to the newly communicating base station and to control the transceiver to obtain any portions of the system information not already held by the terminal device from the base station;

the controller being configured to detect an instruction to obtain updated system information and, in response to detection of the instruction, to obtain from the base station an updated version of only those portions of the system information having a value tag indicating a version of those portions different to the corresponding value tag held by the system information storage.

17. A terminal device according to claim 16, in which the instruction is a paging instruction received from the base station.

18. A terminal device according to claim 16, in which:

the system information comprises a master information block, obtained by a terminal device before the terminal device obtains the system information blocks;

the system information blocks comprise a succession of a first system information block and one or more further system information blocks;

the master information block provides one or more parameters for reception of the first system information block; and

the first system information block provides one or more parameters for reception of the one or more further system information blocks.

19. A terminal device according to claim 18, in which the instruction is included in the master information block or the first system information block.

20. A terminal device according to claim 16, in which the controller is configured to maintain a validity timer indicating a validity period of the system information, the instruction being detected in response to the end of the validity period.

21 . A terminal device according to claim 20, in which the controller is responsive to a timer reset message received from the base station before the end of the validity period to alter the validity timer so as to increase a remaining portion of the validity period.

22. A terminal device according to claim 21 , in which the controller is responsive to the timer reset message to reset the validity timer to indicate that full validity period is remaining.

23. A terminal device according to claim 22, in which the timer reset message is a paging message received from the base station.

24. A terminal device for use in a wireless telecommunications system, the terminal device comprising:

a transceiver to perform wireless communication with a base station and to obtain system information defining communication parameters from system information data transmitted by that base station;

system information storage; and

a controller to detect whether the system information storage already holds at least some of the system information applicable to the newly communicating base station and to control the transceiver to obtain any portions of the system information not already held by the terminal device from the base station;

the controller being configured to maintain a validity timer indicating a validity period of the system information and, in response to the end of the validity period, to obtain updated system information from the base station;

the controller being responsive to a timer reset message received from the base station before the end of the validity period to alter the validity timer so as to increase a remaining portion of the validity period.

25. A terminal device according to claim 24, in which the controller is responsive to the timer reset message to reset the validity timer to indicate that full validity period is remaining.

26. A terminal device according to claim 25, in which the timer reset message is a paging message received from the base station.

27. A terminal device according to claim 24, in which the timer reset message is included in a first system information message received from the base station and the alteration to the validity timer applies to one or more further system information messages.

28. A terminal device according to claim 24, in which the controller is configured to infer the timer reset message from a first system information message received from the base station for which the controller detects whether the system information storage already holds system

information corresponding to that message, and the alteration to the validity timer applies to one or more further system information messages.

29. A base station for use in a wireless telecommunications system, the base station comprising:

a transceiver to perform wireless communication with a terminal device; and

a controller to control the transceiver to transmit system information defining communication parameters and identification data indicating a group of two or more base stations having at least part of the system information in common; in which:

the system information comprises a plurality of system information blocks;

the controller is configured to control the transceiver to transmit (i) a complete instance of a system information block; and (ii) a partial instance of the system information block containing difference information with respect to an instance of system information applicable to another base station.

30. A base station according to claim 29, in which:

the system information comprises a master information block and two or more system information blocks;

the system information blocks comprise a succession of a first system information block and one or more further system information blocks;

the master information block provides one or more parameters for reception, by a terminal device, of the first system information block; and

the first system information block provides one or more parameters for reception, by a terminal device, of the one or more further system information blocks.

31 . A base station according to claim 30, in which the controller is configured to control the transceiver to transmit the identification data in one or both of the master information block and the first system information block.

32. A base station according to claim 29, in which the controller is configured to control the transceiver to broadcast the system information.

33. A set of two or more base stations each according to claim 29, in which the identification data and at least part of the system information are common between the set of two or more base stations.

34. A base station for use in a wireless telecommunications system, the base station comprising:

a transceiver to perform wireless communication with a terminal device; and

a controller to control the transceiver to transmit system information defining communication parameters; in which:

the system information comprises a plurality of system information blocks;

the controller is configured to control the transceiver to transmit a timer reset message to instruct a terminal device to increase a remaining portion of a validity period maintained by that base station for system information held by that base station.

35. A base station for use in a wireless telecommunications system, the base station comprising:

a transceiver to perform wireless communication with a terminal device; and

a controller to control the transceiver to transmit reference data referencing a set of system information defining communication parameters of that base station;

the controller being configured to control the transceiver to conduct wireless communication in accordance with the referenced system information.

36. A wireless data signal transmitted by a base station, the wireless data signal comprising system information blocks defining communication parameters and identification data indicating a group of two or more base stations having at least part of the system information in common, the system information blocks including (i) a complete instance of a system information block; and (ii) a partial instance of the system information block containing difference information with respect to an instance of system information applicable to another base station.

37. A wireless data signal transmitted by a base station, the wireless data signal comprising system information blocks defining communication parameters and, from time to time, a timer reset message to instruct a terminal device to increase a remaining portion of a validity period maintained by that base station for system information held by that base station.

38. A method of operation of a terminal device for use in a wireless telecommunications system, the method comprising:

obtaining system information defining communication parameters from system information data received from a base station, the system information comprising a plurality of system information blocks;

storing the system information;

detecting whether the system information storage already holds at least some of the system information applicable to a newly communicating base station; and

obtaining any portions of the system information not already stored by detecting parts of a stored system information block which are applicable to the newly communicating base station and obtaining other parts of that system information block as a partial system information block from the newly communicating base station.

39. Computer software which, when executed by a computer, causes the computer to perform the method of claim 38.

40. A machine-readable non-transitory storage medium which stores computer software according to claim 39.

41 . A method of operation of a terminal device for use in a wireless telecommunications system, the method comprising:

obtaining system information defining communication parameters from system information data comprising a plurality of information blocks;

storing the system information;

detecting whether the system information storage already holds at least some of the system information applicable to a newly communicating base station;

obtaining any portions of the system information from the newly communicating base station which are not already stored; and

detecting whether identification data associated with information blocks transmitted by the newly communicating base station corresponds to identification data associated with stored information blocks;

in which the identification data comprises area information identifying a group of base stations and a value tag identifying a version of one or more of the information blocks.

42. Computer software which, when executed by a computer, causes the computer to perform the method of claim 41 .

43. A machine-readable non-transitory storage medium which stores computer software according to claim 42.

44. A method of operation of a terminal device for use in a wireless telecommunications system, the method comprising:

obtaining system information defining communication parameters from system information data transmitted by a base station;

storing the system information and one or more associated value tags identifying a version of respective portions of the system information; and

detecting whether the system information storage already holds at least some of the system information applicable to the newly communicating base station;

obtaining any portions of the system information not already held by the terminal device from the base station;

detecting an instruction to obtain updated system information; and

in response to detection of the instruction, obtaining from the base station an updated version of only those portions of the system information having a value tag indicating a version of those portions different to the corresponding stored value tag.

45. Computer software which, when executed by a computer, causes the computer to perform the method of claim 44.

46. A machine-readable non-transitory storage medium which stores computer software according to claim 45.

47. A method of operation of a terminal device for use in a wireless telecommunications system, the method comprising:

obtaining system information defining communication parameters from system information data transmitted by a base station;

storing the system information;

detecting whether the system information storage already holds at least some of the system information applicable to the newly communicating base station;

obtaining any portions of the system information not already stored by the terminal device from the base station;

maintaining a validity timer indicating a validity period of the system information;

in response to the end of the validity period, obtaining updated system information from the base station; and

in response to a timer reset message received from the base station before the end of the validity period, altering the validity timer so as to increase a remaining portion of the validity period.

48. Computer software which, when executed by a computer, causes the computer to perform the method of claim 47.

49. A machine-readable non-transitory storage medium which stores computer software according to claim 48.

50. A method of operation of a base station for use in a wireless telecommunications system, the method comprising:

performing wireless communication with a terminal device; and

transmitting system information defining communication parameters and identification data indicating a group of two or more base stations having at least part of the system information in common, in which the system information comprises a plurality of system information blocks, by transmitting (i) a complete instance of a system information block; and (ii) a partial instance of the system information block containing difference information with respect to an instance of system information applicable to another base station.

51 . Computer software which, when executed by a computer, causes the computer to perform the method of claim 50.

52. A machine-readable non-transitory storage medium which stores computer software according to claim 51 .

53. A method of operation of a base station for use in a wireless telecommunications system, the method comprising:

performing wireless communication with a terminal device; and

transmitting system information defining communication parameters, in which the system information comprises a plurality of system information blocks; and

transmitting a timer reset message to instruct a terminal device to increase a remaining portion of a validity period maintained by that base station for system information held by that base station.

54. Computer software which, when executed by a computer, causes the computer to perform the method of claim 53.

55. A machine-readable non-transitory storage medium which stores computer software according to claim 54.

56. A method of operation of a base station for use in a wireless telecommunications system, the method comprising:

transmitting reference data referencing a set of system information defining communication parameters of that base station; and

performing wireless communication with a terminal device in accordance with the referenced system information.

57. Computer software which, when executed by a computer, causes the computer to perform the method of claim 56.

58. A machine-readable non-transitory storage medium which stores computer software according to claim 57.