TELECOMMUNICATIONS APPARATUS AND METHODS
BACKGROUND
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 invention relates to wireless telecommunications systems and methods, and in
particular to systems and methods for restricted bandwidth / virtual carrier operation in wireless
telecommunication systems.
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 semiautonomous
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. Further information on characteristics of MTC-type devices can be found, for
example, in the corresponding standards, such as ETSI TS 122 368 V 10.530 (201 1-07) / 3GPP
TS 22.368 version 10.5.0 Release 10) [1].
Whilst it can be convenient for a terminal such as an MTC-type terminal to take advantage of
the wide coverage area provided by a third or fourth generation mobile telecommunication
network there are at present disadvantages. Unlike a conventional third or fourth generation
mobile terminal such as a smartphone, a primary driver for MTC-type terminals will be a desire
for such terminals to be relatively simple and inexpensive. The type of functions typically
performed by an MTC-type terminal (e.g. simple collection and reporting / reception of relatively
small amounts of data) do not require particularly complex processing to perform, for example,
compared to a smartphone supporting video streaming. However, third and fourth generation
mobile telecommunication networks typically employ advanced data modulation techniques and
support wide bandwidth usage on the radio interface which can require more complex and
expensive radio transceivers and decoders to implement. It is usually justified to include such
complex elements in a smartphone as a smartphone will typically require a powerful processor
to perform typical smartphone type functions. However, as indicated above, there is now a
desire to use relatively inexpensive and less complex devices which are nonetheless able to
communicate using LTE-type networks.
With this in mind there has been proposed a concept of so-called "virtual carriers" operating
within the bandwidth of a "host carrier", for example, as described in GB 2 487 906 [2], GB 2
487 908 [3], GB 2 487 780 [4], GB 2 488 513 [5], GB 2 487 757 [6], GB 2 487 909 [7], GB 2 487
907 [8] and GB 2 487 782 [9]. One principle underlying the concept of a virtual carrier is that a
frequency subregion within a wider bandwidth host carrier is configured for use as a selfcontained
carrier for at least some types of communications with certain types of terminal
device.
In some implementations, such as described in references [2] to [9], all downlink control
signalling and user-plane data for terminal devices using the virtual carrier are conveyed within
the frequency subregion. A terminal device operating on the virtual carrier is made aware of the
restricted frequency band and need only receive and decode a corresponding subset of
transmission resources to receive data from the base station. An advantage of this approach is
to provide a carrier for use by low-capability terminal devices capable of operating over only
relatively narrow bandwidths. This allows devices to communicate on LTE-type networks,
without requiring the devices to support full bandwidth operation. By reducing the bandwidth of
the signal that needs to be decoded, the front end processing requirements (e.g., FFT, channel
estimation, subframe buffering etc.) of a device configured to operate on a virtual carrier are
reduced since the complexity of these functions is generally related to the bandwidth of the
signal received.
Other virtual carrier approaches for reducing the required complexity of devices configured to
communicate over LTE-type networks are proposed in GB 2 497 743 [10] and GB 2 497 742
[ 1 1]. These documents propose schemes for communicating data between a base station and a
reduced-capability terminal device whereby physical-layer control information for the reducedcapability
terminal device is transmitted from the base station using subcarriers selected from
across a full host carrier frequency band (as for conventional LTE terminal devices). However,
higher-layer data for reduced-capability terminal devices (e.g. user-plane data) is transmitted
using only subcarriers selected from within a restricted frequency band which is smaller than
and within the system frequency band. Thus, this is an approach in which user-plane data for a
particular terminal device may be restricted to a subset of frequency resources (i.e. a virtual
carrier supported within the transmission resources of a host carrier), whereas control signalling
is communicated using the full bandwidth of the host carrier. The terminal device is made aware
of the restricted frequency band, and as such need only buffer and process data within this
restricted frequency band during periods when higher-layer data is being transmitted. The
terminal device buffers and processes the full system frequency band during periods when
physical-layer control information is being transmitted. Thus, the reduced-capability terminal
device may be incorporated in a network in which physical-layer control information is
transmitted over a wide frequency range, but only needs to have sufficient memory and
processing capacity to process a smaller range of frequencies for the higher-layer data. This
approach may sometimes be referred to as a "T-shaped" allocation because area of the
downlink time-frequency resource grid to be used by the reduced-capability terminal device
typically comprises a generally T-shape.
Virtual carrier concepts thus allow terminal devices having reduced capabilities, for example in
terms of their transceiver bandwidth and/or processing power, to be supported within LTE-type
networks. As noted above, this can be useful for to allow relatively inexpensive and low
complexity devices to communicate using LTE-type networks.
In some situations more than one virtual carrier may be supported in a host carrier. In this case
the different virtual carriers are located at different frequencies within the host carrier bandwidth
and individual terminal devices are allocated to one of the virtual carriers. This approach can be
used to increase the number of terminal devices that can be supported using virtual carrier
communications. However, in order to do this, it is necessary for individual terminal devices and
the base station establish which frequency particular resources (i.e. which of the plurality of
virtual carriers) is to be used by a given terminal device. Typically this requires some level of
control signalling to be exchanged between the base station and the respective terminal
devices, for example for the base station to inform the terminal device of which virtual carrier it
is to be allocated to. This need for terminal device specific control signalling to be exchanged
between the base station and the terminal devices gives rise to some drawbacks. For example,
there can be an increase in signalling complexity with information being exchanged in dedicated
signalling during connection establishment, and more generally, it gives rise to an increase in
control signalling overhead in the telecommunications system, particularly in the case where
there are a high number of devices in a cell.
Accordingly, there is a desire for approaches for allocating specific terminal devices to specific
virtual carriers in wireless telecommunications systems.
SUMMARY
According to a first aspect of the present disclosure, there is provided a method of operating a
terminal device in a wireless telecommunications system in which downlink communications are
made by a base station using a radio interface that spans a system frequency bandwidth (host
carrier) and supports at least some communications with at least some terminal devices within a
plurality of restricted frequency bands (virtual carriers) which are narrower than and within the
system frequency bandwidth, the method comprising: selecting a restricted frequency band
from among the plurality of restricted frequency bands based on an identifier for the terminal
device; and configuring the terminal device to receive downlink communications from the base
station within the selected restricted frequency band.
According to a second aspect of the present disclosure, there is provided a terminal device for
use in a wireless telecommunications system in which downlink communications are made by a
base station using a radio interface that spans a system frequency bandwidth and supports at
least some communications with at least some terminal devices within a plurality of restricted
frequency bands which are narrower than and within the system frequency bandwidth, the
terminal device comprising a processor unit and a transceiver unit, and wherein the processor
unit is configured to select a restricted frequency band from among the plurality of restricted
frequency bands based on an identifier for the terminal device and to configure the transceiver
unit to receive downlink communications from the base station within the selected restricted
frequency band.
According to a third aspect of the present disclosure, there is provided a method of operating a
base station in a wireless telecommunications system in which downlink communications are
made by the base station using a radio interface that spans a system frequency bandwidth and
supports at least some communications with at least some terminal devices within a plurality of
restricted frequency bands which are narrower than and within the system frequency bandwidth,
the method comprising: selecting a restricted frequency band to be used for downlink
communications for a terminal device from among the plurality of restricted frequency bands
based on an identifier for the terminal device; and transmitting downlink communications to the
terminal device within the selected restricted frequency band.
According to a fourth aspect of the present disclosure, there is provided a base station for use in
a wireless telecommunications system in which downlink communications are made by the
base station using a radio interface that spans a system frequency bandwidth and supports at
least some communications with at least some terminal devices within a plurality of restricted
frequency bands which are narrower than and within the system frequency bandwidth, the base
station comprising a processor unit and a transceiver unit, and wherein the processor unit is
configured to select a restricted frequency band to be used for downlink communications with a
terminal device from among the plurality of restricted frequency bands based on an identifier for
the terminal device; and to configure the transceiver unit to transmit downlink communications
to the terminal device within the selected restricted frequency band.
Further respective aspects and features are defined by the appended claims.
The foregoing paragraphs have been provided by way of general introduction, and are not
intended to limit the scope of the following claims. The described embodiments, together with
further advantages, will be best understood by reference to the following detailed description
taken in conjunction with the accompanying drawings.
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 represents some aspects of a LTE downlink radio subframe structure
associated with a host carrier supporting three virtual carriers;
Figure 5 schematically represents an adapted LTE-type wireless telecommunications system
arranged in accordance with an example of the present disclosure; and
Figure 6 is a signalling ladder-diagram schematically representing methods of operation in
accordance with certain examples of the present disclosure.
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 and also described in many books
on the subject, for example, Holma, H. and Toskala, A. [ 1 2].
The network 100 includes a plurality of base stations 101 connected to a core network 102.
Each base station provides a coverage area 103 (i.e. 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 1ms 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 (i.e. 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. A conventional LTE frame will also include reference signals which are not
shown in Figure 3 in the interests of clarity.
Figure 4 is a diagram which is similar to and will in many respect be understood from Figure 3.
However, Figure 4 differs from Figure 3 in schematically representing a downlink radio
subframe corresponding to a host carrier in which a plurality (in this case three) virtual carriers
401 , 402, 403 (VCs) are supported. The virtual carriers are labelled as VC1 , VC2 and VC3 for
ease of reference, as schematically indicated in Figure 4. The general operation of the virtual
carriers represented in Figure 4 may be in accordance with previously-proposed schemes, for
example as described in any of the above-identified documents [2] to [ 1 1]. Each virtual carrier
thus represents a restricted subset of downlink transmission resources within the overall
transmission resource grid associated with the host carrier which may be used for
communicating at least some information with certain types of terminal devices, for example,
reduced capability machine type communication terminal devices.
Thus, a conventional (i.e. non-reduced capability) terminal device may be supported using the
full bandwidth of the resource grid represented in Figure 4 in accordance with conventional LTE
techniques. Downlink communications for a reduced capability terminal device, on the other
hand, may be restricted to transmission resources within one of the virtual carriers to which the
terminal device has been allocated.
In some cases the entirety of the downlink communications for the reduced-capability terminal
device (i.e. including control signalling and higher layer / user-plane data) may be conveyed
within the transmission resources of one of the virtual carriers, for example in accordance with
the principles proposed in the above identified documents [2] to [9]. This may be appropriate, for
example, for a terminal device which cannot receive the full bandwidth of the host carrier (and
hence cannot receive the entirety of the control region 300).
In other cases the reduced capability terminal device may be able to receive the full-bandwidth
of the host carrier (and hence receive and decode the control region 300), but may be restricted
as to its ability to buffer and decodes the entirety of the PDSCH region, and so may buffer and
decode only a subset of the downlink transmission resources spanning the virtual carrier to
which the terminal device has been allocated, for example in accordance with the "T-shaped
allocation" principles proposed in the above identified documents [ 10] and [ 1 1].
However, regardless of the specific manner of virtual carrier operation to be employed in a
given implementation, a terminal device to be supported using a virtual carrier needs to
establish which particular restricted frequency range is being used for the virtual carrier to which
it has been allocated. For example, a reduced-capability terminal device which is to be
supported using virtual carrier operation in the context of the downlink subframe transmission
resource grid represented in Figure 4 must establish whether it is to be supported on virtual
carrier VC1 , VC2 or VC3. As discussed above, one approach would be for the base station to
inform the reduced-capability terminal device of the virtual carrier to which it has been allocated
through dedicated signalling exchange during a connection procedure. However, again as noted
above, this can give rise to increased signalling complexity and increased control signalling
overhead.
Figure 5 schematically shows a telecommunications system 500 according to an embodiment of
the present disclosure. The telecommunications system 500 in this example is based broadly
around an LTE-type architecture which supports a plurality of virtual carriers such as
schematically represented in Figure 4. Many aspects of the operation of the telecommunications
system 500 are known and understood and are not described here in detail in the interest of
brevity. Operational aspects of the telecommunications system 500 which are not specifically
described herein may be implemented in accordance with any known techniques, for example
according to the current LTE-standards with modifications as appropriate to incorporate virtual
carrier operation, such as disclosed in GB 2 487 906 [2], GB 2 487 908 [3], GB 2 487 780 [4],
GB 2 488 5 13 [5], GB 2 487 757 [6], GB 2 487 909 [7], GB 2 487 907 [8], GB 2 487 782 [9], GB
2 497 743 [10] and GB 2 497 742 [12], the entire contents of which are incorporated herein by
reference.
The telecommunications system 500 comprises a core network part (evolved packet core) 502
coupled to a radio network part. The radio network part comprises a base station (evolvednodeB)
504 coupled to a plurality of terminal devices. In this example, two terminal devices are
shown, namely a first terminal device 506 and a second terminal device 508. It will of course be
appreciated that in practice the radio network part may comprise a plurality of base stations
serving a larger number of terminal devices across various communication cells. However, only
a single base station and two terminal devices are shown in Figure 5 in the interests of
simplicity.
As with a conventional mobile radio network, the terminal devices 506, 508 are arranged to
communicate data to and from the base station (transceiver station) 504. The base station is in
turn communicatively connected to a serving gateway, S-GW, (not shown) in the core network
part which is arranged to perform routing and management of mobile communications services
to the terminal devices in the telecommunications system 500 via the base station 504. In order
to maintain mobility management and connectivity, the core network part 502 also includes a
mobility management entity (not shown) which manages the enhanced packet service, EPS,
connections with the terminal devices 506, 508 operating in the communications system based
on subscriber information stored in a home subscriber server, HSS. Other network components
in the core network (also not shown for simplicity) include a policy charging and resource
function, PCRF, and a packet data network gateway, PDN-GW, which provides a connection
from the core network part 502 to an external packet data network, for example the Internet. As
noted above, the operation of the various elements of the communications system 500 shown in
Figure 5 may be broadly conventional, for example in accordance with established telecoms
standards and the principles set out in the referenced documents mentioned herein, apart from
where modified to provide functionality in accordance with embodiments of the present
disclosure as discussed herein.
In this example, it is assumed the first terminal device 506 is a conventional smartphone type
terminal device communicating with the base station 504 in a conventional manner. This
conventional terminal device 506 comprises a transceiver unit 506a for transmission and
reception of wireless signals and a processor unit 506b configured to control the device 506.
The processor unit 506b may comprise a processor unit which is suitably configured /
programmed to provide the desired functionality using conventional programming / configuration
techniques for equipment in wireless telecommunications systems. The transceiver unit 506a
and the processor unit 506b are schematically shown in Figure 5 as separate elements.
However, it will be appreciated that the functionality of these units can be provided in various
different ways, for example using a single suitably programmed general purpose computer, or
suitably configured application-specific integrated circuit(s) / circuitry. As will be appreciated the
conventional terminal device 506 will in general comprise various other elements associated
with its operating functionality.
In this example, it is assumed the second terminal device 508 is a machine-type communication
(MTC) terminal device 504 adapted to operate in a virtual carrier (VC) mode in accordance with
embodiments of the present disclosure when communicating with the base station 504. As
discussed above, machine-type communication terminal devices can in some cases be typically
characterised as semi-autonomous or autonomous wireless communication devices
communicating small amounts of data. Examples include so-called smart meters which, for
example, may be located in a customer's house and periodically transmit information back to a
central MTC server data relating to the customer's consumption of a utility such as gas, water,
electricity and so on. MTC devices may in some respects be seen as devices which can be
supported by relatively low bandwidth communication channels having relatively low quality of
service (QoS), for example in terms of latency. It is assumed here the MTC terminal device 508
in Figure 5 is such a device.
The MTC device 508 comprises a transceiver unit 508a for transmission and reception of
wireless signals and a processor unit 508b configured to control the MTC device 508. The
processor unit 508b may comprise various sub-units, for example a VC selection unit, for
providing functionality in accordance with some embodiments of the present disclosure as
explained further herein. These sub-units may be implemented as discrete hardware elements
or as appropriately configured functions of the processor unit. Thus the processor unit 508b
may comprise a processor which is suitably configured / programmed to provide the desired
functionality described herein using conventional programming / configuration techniques for
equipment in wireless telecommunications systems. The transceiver unit 508a and the
processor unit 508b are schematically shown in Figure 5 as separate elements for ease of
representation. However, it will be appreciated that the functionality of these units can be
provided in various different ways, for example using a single suitably programmed general
purpose computer, or suitably configured application-specific integrated circuit(s) / circuitry, or
using a plurality of discrete circuitry / processing elements for providing different elements of the
desired functionality. It will be appreciated the MTC device 508 will in general comprise various
other elements associated with its operating functionality in accordance with established
wireless telecommunications techniques.
The base station 504 comprises a transceiver unit 504a for transmission and reception of
wireless signals and a processor unit 504b configured to control the base station 504 to operate
in accordance with embodiments of the present disclosure as described herein. The processor
unit 506b may again comprise various sub-units, such as a VC selecting unit and scheduling
unit, for providing functionality in accordance with embodiments of the present disclosure as
explained further below. These sub-units may be implemented as discrete hardware elements
or as appropriately configured functions of the processor unit. Thus, the processor unit 504b
may comprise a processor which is suitably configured / programmed to provide the desired
functionality described herein using conventional programming / configuration techniques for
equipment in wireless telecommunications systems. The transceiver unit 504a and the
processor unit 504b are schematically shown in Figure 5 as separate elements for ease of
representation. However, it will be appreciated that the functionality of these units can be
provided in various different ways, for example using a single suitably programmed general
purpose computer, or suitably configured application-specific integrated circuit(s) / circuitry or
using a plurality of discrete circuitry / processing elements for providing different elements of the
desired functionality. It will be appreciated the base station 504 will in general comprise various
other elements associated with its operating functionality in accordance with established
wireless telecommunications techniques.
Thus, the base station 504 is configured to communicate data with both the conventional
terminal device 506 and the terminal device 508 according to an embodiment of the disclosure
over respective communication links 510, 512. The communication link 5 10 for communications
between the base station 504 and the conventional terminal device 506 is supported by a host
carrier (e.g. potentially making use of the full range of transmission resources schematically
represented in Figure 4). The communication link 5 12 for communications between the base
station 504 and the reduced-capability MTC terminal device 508 is supported by a virtual carrier
(e.g. making use of resources within a selected one of the virtual carriers schematically
represented in Figure 4). Once the MTC terminal device 508 and the base station 504 have
established / agreed what virtual carrier frequencies are to be used for supporting
communications with the MTC terminal device 508 (i.e. selecting a virtual carrier on which the
machine type communication terminal device 508 is to be supported) in accordance with
embodiments of the present disclosure, subsequent data communication between the base
station 504 and the MTC terminal device 508 may operate on the selected virtual carrier
generally in accordance with any of the previously-proposed schemes for virtual carrier
operation. For example, the MTC terminal device 508 may operate such that all control-plane
and user-plane signalling from the base station 504 which is addressed to the terminal device
508 is made within the virtual carrier bandwidth. Alternatively, control-plane signalling from the
base station 504 which is addressed to the terminal device 508 may be made within the fullbandwidth
of the control region 300 represented in Figure 4, with higher-layer data (user-plane
data) being communicated within the restricted bandwidth of the selected virtual carrier.
Figure 6 is a signalling ladder diagram schematically representing modes of operation for the
terminal device 508 and the base station 504 schematically presented in Figure 5 in accordance
with some embodiments of the present disclosure. The modes of operation represented in
Figure 6 are configured to allow the terminal device 508 and the base station 504 to in effect
independently select which of a plurality of available virtual carriers currently supported by the
base station is to be used for downlink communications from the base station to the terminal
device 508 in a virtual carrier mode.
Thus, in a first Step S 1 represented in Figure 6 the base station 504 establishes configuration
parameters for a plurality of virtual carriers it is to support. The configuration parameters for the
virtual carriers may comprise, for example, an indication of the number of virtual carriers and / or
their frequencies. It will be appreciated there are many different ways in which configuration
information relating to the frequencies of the virtual carriers can be characterised in different
implementations. For example, the frequency locations associated with a particular virtual
carrier (restricted frequency band) may be represented by an indication of a centre frequency
and a bandwidth, or by upper and lower bounding frequencies. In an implementation where the
bandwidths of the virtual carriers are fixed / predefined, for example at 1.4 MHz, the
configuration information relating to the frequencies of the virtual carriers may comprise a single
frequency value indicating the location of the virtual carrier in the frequency space of the host
carrier (for example a centre frequency, or a lower or upper frequency indicating whether the
virtual carrier is located).
In this example implementation it is assumed the base station has a wide degree of flexibility in
scheduling resources to be used for supporting the virtual carrier operations. Thus, the base
station may be configured to choose the number of virtual carriers to be implemented and the
frequencies at which the virtual carriers will be located (and potentially in some examples their
respective bandwidths) based on current traffic conditions. For example, if current traffic
conditions indicate the base station is required to support a large number of reduced capability
terminal devices, a higher number of virtual carriers may be configured for use than if the
current traffic conditions indicate the base station is required to support a smaller number of
reduced capability terminal devices. It is further assumed the base station 504 in this particular
example implementation has flexibility in determining the frequency locations for the virtual
carriers that are to be used. The base station may make this determination in accordance with
conventional techniques. For example taking account of channel conditions at different
frequencies. In other example implementations the base station may, for example, be able to
choose the number of virtual carriers to implement, but the frequencies at which the virtual
carriers are to be located may be predefined within the telecommunications system. For
example, predefined frequency locations may be standardised for different numbers of virtual
carriers.
For the sake of a concrete example, it is assumed here that in Step S 1 the base station 504
determines that it is to support three virtual carrier at frequency locations as schematically
represented by VC1 , VC2 and VC3 in Figure 4. Step S 1 may be repeated on an on-going basis
to allow the base station to continually optimise the selected number and frequencies of virtual
carriers in accordance with changing traffic conditions. Alternatively, the frequency parameters
established for the virtual carriers which are to be supported by the base station may be
relatively static. In some examples the virtual carrier configuration parameters for a base station
may be fixed. For example, the parameters may be established and fixed during initial
deployment of the base station (for example, the relevant configuration parameters may be
predefined for the wireless telecommunications system).
In Step S2 the MTC terminal device 508 seeks initial access to the radio network associated
with the base station 504, for example in response to the terminal device 508 being powered
on. Once powered on the terminal device 508 in this example initiates a conventional LTE-type
network camp-on procedure to acquire the parameters needed to access the radio network.
Thus, in accordance with broadly conventional techniques, the terminal device 508
synchronises with the base station's radio frame structure and decodes PBCH, PCFICH, and so
forth, so the terminal device 508 is in a position to be able to acquire system information (SI)
using known techniques (i.e. in accordance with previously-proposed reduced-capability
terminal device camp-on procedures in networks supporting virtual carrier operation).
Thus as schematically represented in Step S3 of Figure 6, the base station 504 transmits
system information (SI) on a BCCH (broadcast control channel) and this is received by the
terminal device 508 as part of its usual camp-on procedures is in accordance with known
techniques.
However, in accordance with certain embodiments of the present disclosure, the system
information broadcast by the base station 504 differs from conventional system information
broadcast in an LTE-type network in that the system information includes additional information
on the frequency parameters for the virtual carriers supported by the base station (as
established in Step S1).
In this particular LTE-based example it is assumed this information is conveyed using newlydefined
parameters conveyed in otherwise conventional system information block 2 (SIB2)
signalling. For example, one or more new information elements may be used to convey the
relevant configuration parameters. As noted above, there are various different ways in which the
parameters may be characterised for the respective virtual carriers, for example in terms of a
centre frequency and bandwidth, upper and lower bounding frequencies, a single frequency
location with an assumed (i.e. fixed) bandwidth, and so forth. Furthermore, the information to be
conveyed can be characterised in various ways. For example in terms of specific frequencies or
in terms of index values identifying frequencies in accordance with a predefined association.
Thus, the exact manner in which the information is conveyed to the terminal device may differ
for different implementations. Where an indication of frequency is provided for each virtual
carrier supported by the base station, the total number of virtual carriers can be determined
from the amount of frequency information provided and so might not be separately conveyed in
the system information.
Thus, on receiving the system information, in particular SIB2 (system information block 2) in this
particular LTE-based example, in Step S3 of Figure 6, the terminal device 508 is made aware of
relevant configuration parameters for the virtual carriers supported by the base station. In
particular, the terminal device in this example is informed of the number of virtual carriers being
supported, NVc, and their respective frequency locations, F 1 F2, ... FNVc, through the system
information signalling received from the base station. For example, with reference to this
example implementation as schematically represented in Figure 4, the system information
transmitted by the base station is adapted in accordance with an embodiment of the present
disclosure to indicate the base station is currently supporting three virtual carriers (i.e. Nvc=3) at
centre frequencies F 1 (for VC1 ) , F2 (for VC2) and F3 (for VC3). In this example implementation
it is assumed the virtual carriers supported in the wireless telecommunications systems are all
of a predefined fixed width in frequency space, such as 1.4 MHz, and so the system information
provided from the base station does not need to provide any indication of the widths of the
respective virtual carriers.
In Step S4 the terminal device 508 (more specifically the processor unit 508b of the terminal
device) selects one of the available plurality of virtual carriers (restricted bandwidth carriers)
supported by the base station as the virtual carrier on which it will assume it will be supported
by the base station. The terminal device does this autonomously (i.e. without specific instruction
from the base station) based on an identifier for the terminal device. In this example the
identifier used by the terminal device for this purpose is the international mobile subscriber
identity (IMSI) number associated with the device. The IMSI is a number permanently
associated with the subscriber identity module (SIM) used by the terminal device. In Step S4 the
terminal device thus makes a selection of one of the NVc virtual carriers supported by the base
station in a way that depends on the identity of the terminal device.
In this specific example the terminal device 508 determines a remainder value obtained when
dividing the identifier (IMSI) by the number of virtual carriers supported by the base station (NVc)
and uses this as an index value (IND) to select one of the available virtual carriers (VC1 , VC2,
VC3). That is to say the terminal device determines the value for IND according to the following
equation:
IND = IMSI mod(Nvc) ....Equation 1.
Thus for this example in which the base station supports three virtual carriers (i.e. Nv c = 3),
Equation 1 provides a value for IND of 0, 1 or 2. This value is then used as an index to identify
one of the available plurality of virtual carriers. For example, the virtual carriers may be
considered as being arranged in order of decreasing frequency (or any other predefined order)
and the terminal device may select one of them based on the value of IND. In particular, for an
index value of IND the terminal device may select the virtual carrier associated with position
(IND+1 ) in the list of available virtual carriers. I.e., if IND = 0, the terminal device selects the first
virtual carrier in the list (e.g. VC1 ) ; if IND = 1, the terminal device selects the second virtual
carrier in the list (e.g. VC2), and so on.
Thus, in Step S4 the processor unit 508b of the terminal device 508 autonomously selects one
of the available virtual carriers (VC1 , VC2, VC3) based on an identifier associated with the
terminal device. Having chosen one of the virtual carriers, the terminal device can establish the
corresponding frequency parameters for the virtual carrier, for example its centre frequency
(e.g. based on configuration information received from the base station or from predefined
associations for the wireless telecommunications system) . In accordance with embodiments of
the present disclosure the terminal device is adapted to assume subsequent communications
from the base station will be received using the selected virtual carrier. Accordingly, in Step S5
the transceiver unit 508a of the terminal device 508 is appropriately configured to receive
subsequent downlink communications from the base station on the selected virtual carrier. This
aspect of the processing of Figure 6 may be performed in accordance with conventional
techniques for virtual carrier operations in wireless telecommunications systems once it has
been established which virtual carrier frequencies are to be used by the terminal device.
Thus, following Step S5 in Figure 6 the terminal device 508 has received information on what
virtual carriers are being supported by the base station to which it wishes to attach, has selected
one of the virtual carriers in which it expects to receive downlink UK is from the base station,
and has configured its transceiver in readiness for receiving such communications. Significantly,
this has been achieved without any dedicating signalling between the base station and the
terminal device. Indeed, in accordance with the example method represented in Figure 6 , the
terminal device has reached this stage without the base station even being aware that the
terminal device is in the process of connecting to the base station.
In Step S6 represented in Figure 6, the terminal device 508 continues its attachment procedure
by transmitting a request to access the base station, which in this example based on an LTEtype
architecture, is a conventional RRC (Radio Resource Control) Connection Request. In
accordance with established techniques, the request for connection establishment includes an
identifier for the terminal device, and in particular in this example includes an indication of the
terminal device's IMSI. On receiving the connection request signalling in Step S6, the base
station is configured to determine that the request is from a reduced capability terminal device
implementing procedures in accordance with the principles described herein. This may be
based, for example, on a device type classifier included in the connection request or based on a
network-side lookup table linking the terminal device's IMSI with its status as a reduced
capability terminal device implementing methods in accordance with embodiments of the
present disclosure.
Having received the connection request from the terminal device in Step S6, the base station is
made aware of the identifier used by the terminal device when determining the selected virtual
carrier in Step S4 and can therefore independently determine which virtual carrier was selected
by the terminal device. Thus, in Step S7 the base station 504 (in particular its processor unit
504b) identifies the virtual carrier selected by the terminal device using the terminal device
identifier received in association with the connection request in Step S6 by applying Equation 1
in the same way as by the terminal device.
Thus, in Step S7 the processor unit 504b of the base station 504 independently determines the
virtual carrier selected by the terminal device based on the identifier received from the terminal
device in association with connection setup signalling. Having selected one of the virtual
carriers, the base station can establish the corresponding frequency parameters for the virtual
carrier, for example its centre frequency. In accordance with embodiments of the present
disclosure the base station is adapted to assume subsequent downlink communications for the
terminal device should be made using the selected virtual carrier (i.e. the selected virtual carrier
is the one on which the terminal device is to be allocated downlink resources).
Accordingly, in Step S8 the transceiver unit 504a of the base station 504 is appropriately
configured to transmit downlink communications to the terminal device on the selected virtual
carrier (in practice this configuration may simply involve a scheduling unit of the base station
storing an indication of what virtual carrier should be used for scheduling subsequent
communications with the terminal device). This aspect of the processing of Figure 6 may be
performed in accordance with conventional techniques for virtual carrier operations in wireless
telecommunications systems once in which it has been established which virtual carrier is to be
used for a given terminal device (i.e. once a terminal device has been allocated to a virtual
carrier).
Thus, following Step S8 in Figure 6, both the terminal device 508 and the base station 504 have
independently determined a selected one of the available plurality of virtual carriers which is to
be used for subsequent downlink communications between the base station 504 and the
terminal device 508. Significantly, this has been achieved without any additional dedicated
signalling being exchanged between the base station and the terminal device.
Once the terminal device 508 and the base station 504 have independently established /
selected the virtual carrier which is to be used in accordance with embodiments of the present
disclosure, subsequent operations in the wireless telecommunications system may be made in
accordance with conventional virtual carrier techniques. Thus, as schematically represented in
Step S9 in Figure 6, subsequent communications between the base station 504 and the
terminal device 508 may proceed in accordance with conventional techniques for virtual carrier /
restricted bandwidth operation.
The subsequent virtual carrier operation may follow any of the previously proposed techniques.
For example, the VC operation represented in Step S9 may follow an approach such as
described in reference documents [2] to [9] in which downlink communications received by the
terminal device within the selected virtual carrier (restricted frequency band) comprise both
user-plane data and control-plane data, wherein the control-plane data comprise indications of
resource allocations for user-plane data for the terminal device on the virtual carrier. In other
examples the VC operation represented in Step S9 may follow a "T-shape allocation" approach,
such as described in reference documents [10] and [ 1 1] in which downlink communications
received by the terminal device within the selected virtual carrier comprise user-plane data while
control-plane data comprising indications of resource allocations for user-plane data on the
virtual carrier are received with communications spanning frequencies outside the selected
virtual carrier (e.g. in a control region spanning the system frequency bandwidth). Other modes
of virtual carrier operation could equally be employed.
Thus, in accordance with certain embodiments of the present disclosure as schematically
represented in Figure 6, a reduced-capability terminal device 508 and a base station 504 may in
effect come to an agreement as to the frequency characteristics of a virtual carrier is to be used
for downlink communications without requiring any dedicated signalling to be exchanged
between them beyond that normally exchanged in a wireless telecommunications system.
It will be appreciated these methods of operation for the terminal device 508 and the base
station 504 are merely some example implementations in accordance with certain embodiments
of the present disclosure. Variations and modifications to the approaches discussed above and
represented in Figure 6 can be adopted in accordance with other example implementations of
certain embodiments of the present disclosure.
For example, it will be appreciated that in some example implementations, steps corresponding
to those represented in Figure 6 may be performed in a different order. For example, the steps
of a terminal device selecting a virtual carrier from a plurality of available virtual carriers (Step
S4 in Figure 6) and configuring its transceiver appropriately (Step S5 in Figure 6) could equally
be performed after the step of the terminal device initiating the RRC connection request (Step
S6 in Figure 6).
It will also be appreciated that in some example implementations the configuration parameters
for the virtual carriers may be predefined for the wireless telecommunications system. For
example, it may be predetermined that the base station will support four virtual carriers at
particular frequency locations. In this case the terminal device may be adapted to take account
of this predefined information when selecting the virtual carrier to use based on its identity
without needing to receive configuration parameters from the base station regarding the virtual
carriers being supported. That is to say, in some implementations the system information
communicated from the base station to the terminal device during the initial access procedure
(such as schematically represented in Step S3 of Figure 6) may be conventional without
containing any information regarding configuration parameters for the virtual carriers. Instead
the terminal device is simply preconfigured with the relevant information regarding the
predefined configuration parameters to allow the selection of a virtual carrier in a step
corresponding to Step S4 of Figure 6 to be made.
In other examples the determination of the selected virtual carrier may be based on a different
identifier for the terminal device. For example, rather than using the IMSI for the terminal device,
a network-derived temporary identifier for the terminal device, such as a cell-radio network
temporary identifier (C-RNTI) may be used. However, it will be appreciated this would require a
degree of dedicated communication between the base station and the terminal device to be
performed before a selected virtual carrier is agreed, for example in order for the base station to
allocate the C-RNTI to the terminal device.
Furthermore, it will be appreciated in some examples the process of selecting a virtual carrier
may be performed more than once. For example, a terminal device may initially select a virtual
carrier in accordance with the principles described above when the terminal device is initially
powered on. However, the base station may subsequently determine that a change in the need
to support reduced capability devices (e.g. an increase or decrease in the number of reduced
capability devices requiring virtual carrier support) should be met by changing the number of
virtual carriers being supported. The base station may thus update the system information being
broadcast to reflect a change in its virtual carrier configuration parameters. A terminal device
recognising the update in system information may thus in effect repeat Steps S4 and S5
represented in Figure 6, while the base station likewise in effect repeat steps corresponding to
Step S7 and S8 represented in Figure 6, thereby allowing continued VC operation on the newlyselected
virtual carrier.
Thus there has been described a wireless telecommunications system in which downlink
communications are made using a radio interface that spans a system frequency bandwidth
(host carrier) and supports at least some communications from a base station to least some
terminal devices within a plurality of restricted frequency bands (virtual carriers) which are
narrower than and within the system frequency bandwidth. A terminal device conveys an
indication of its identity, e.g. an IMSI, to the base station during an initial connection procedure
as the terminal device seeks to access the radio interface. The terminal device and the base
station both determine a selected restricted frequency band from among the plurality of
restricted frequency bands based on the identity of the terminal device in the same way. Thus
the terminal device and the base station select the same restricted frequency band and can
accordingly configure their respective transceivers to allow for downlink communications
between them within the selected restricted frequency band.
Further particular and preferred aspects of the present invention are set out in the
accompanying independent and dependent claims. It will be appreciated that features of the
dependent claims may be combined with features of the independent claims in combinations
other than those explicitly set out in the claims.
Thus, the foregoing discussion discloses and describes merely exemplary embodiments of the
present invention. As will be understood by those skilled in the art, the present invention may be
embodied in other specific forms without departing from the spirit or essential characteristics
thereof. Accordingly, the disclosure of the present invention is intended to be illustrative, but not
limiting of the scope of the invention, as well as other claims. The disclosure, including any
readily discernible variants of the teachings herein, define, in part, the scope of the foregoing
claim terminology such that no inventive subject matter is dedicated to the public.
Some respective features of the present disclosure are defined by the following two groups of
numbered paragraphs:
First group of numbered paragraphs:
1. A method of operating a terminal device in a wireless telecommunications system in
which downlink communications are made by a base station using a radio interface that spans a
system frequency bandwidth and supports at least some communications with at least some
terminal devices within a plurality of restricted frequency bands which are narrower than and
within the system frequency bandwidth, the method comprising:
selecting a restricted frequency band from among the plurality of restricted frequency
bands based on an identifier for the terminal device; and
configuring the terminal device to receive downlink communications from the base
station within the selected restricted frequency band.
2. The method of clause 1, wherein the identifier for the terminal device comprises an
International Mobile Subscriber Identity, IMSI, associated with the terminal device.
3. The method of clause 1 or 2, wherein the selected restricted frequency band is
determined from a remainder value obtained when dividing a number associated with the
identifier for the terminal device by the number of the plurality of restricted frequency bands
supported by the base station.
4. The method of any of clauses 1 to 3, further comprising the terminal device establishing
configuration information relating to the plurality of restricted frequency bands supported by the
base station from system information received from the base station.
5. The method of clause 4, wherein the configuration information comprises an indication of
the number of the plurality of restricted frequency bands supported by the base station and / or
an indication of frequencies for the restricted frequency bands.
6. The method of any of clauses 1 to 5, further comprising the terminal device establishing
configuration information relating to the plurality of restricted frequency bands supported by the
base station from information received from the base station before or during an initial
connection procedure for the terminal device on the radio interface.
7. The method of clause 6, wherein the configuration information comprises an indication of
the number of the plurality of restricted frequency bands supported by the base station and / or
an indication of frequencies for the restricted frequency bands.
8. The method of any of clauses 1 to 7, wherein configuration information relating to the
plurality of restricted frequency bands supported by the base station is predefined for the
wireless telecommunications system.
9. The method of clause 8, wherein the configuration information comprises an indication of
the number of the plurality of restricted frequency bands supported by the base station and / or
an indication of frequencies for the restricted frequency bands.
10. The method of any of clauses 1 to 9, wherein downlink communications received by the
terminal device within the selected restricted frequency band comprise user-plane data and
control-plane data, and wherein the control-plane data comprise an indication of resources
within the selected restricted frequency band to be used for communicating the user-plane data
11. The method of any of clauses 1 to 10, wherein the downlink communications received by
the terminal device within the selected restricted frequency band comprise user-plane data, and
wherein the method further comprises the terminal device receiving control-plane data on
frequency resources from across the system frequency bandwidth, wherein the control-plane
data comprise an indication of resources within the selected restricted frequency band to be
used for communicating the user-plane data.
12. The method of any of clauses 1 to 12, wherein the method further comprises conveying
an indication of the identifier for the terminal device from the terminal device to the base station.
13. The method of clause 12, wherein the indication of the identifier for the terminal device is
conveyed from the terminal device to the base station before or during an initial connection
procedure for the terminal device on the radio interface.
14. The method of clause 12, wherein the indication of the identifier for the terminal device is
conveyed in association with radio resource control, RRC, connection request signalling.
15. A terminal device for use in a wireless telecommunications system in which downlink
communications are made by a base station using a radio interface that spans a system
frequency bandwidth and supports at least some communications with at least some terminal
devices within a plurality of restricted frequency bands which are narrower than and within the
system frequency bandwidth, the terminal device comprising a processor unit and a transceiver
unit, and wherein the processor unit is configured to select a restricted frequency band from
among the plurality of restricted frequency bands based on an identifier for the terminal device
and to configure the transceiver unit to receive downlink communications from the base station
within the selected restricted frequency band.
Second group of numbered paragraphs:
1. A method of operating a base station in a wireless telecommunications system in which
downlink communications are made by the base station using a radio interface that spans a
system frequency bandwidth and supports at least some communications with at least some
terminal devices within a plurality of restricted frequency bands which are narrower than and
within the system frequency bandwidth, the method comprising:
selecting a restricted frequency band to be used for downlink communications for a
terminal device from among the plurality of restricted frequency bands based on an identifier for
the terminal device; and
transmitting downlink communications to the terminal device within the selected
restricted frequency band.
2. The method of clause 1, wherein the identifier for the terminal device comprises an
International Mobile Subscriber Identity, IMSI, associated with the terminal device.
3. The method of clause 1 or 2, wherein the selected restricted frequency band is
determined from a remainder value obtained when dividing a number associated with the
identifier for the terminal device by the number of the plurality of restricted frequency bands
supported by the base station.
4. The method of any of clauses 1 to 3, further comprising conveying configuration
information relating to the plurality of restricted frequency bands supported by the base station
to the terminal device in system information transmitted by the base station.
5. The method of clause 4, wherein the configuration information comprises an indication of
the number of the plurality of restricted frequency bands supported by the base station and / or
an indication of frequencies for the restricted frequency bands.
6. The method of any of clauses 1 to 5, further comprising conveying configuration
information relating to the plurality of restricted frequency bands supported by the base station
to the terminal device before or during an initial connection procedure for the terminal device on
the radio interface.
7. The method of clause 6, wherein the configuration information comprises an indication of
the number of the plurality of restricted frequency bands supported by the base station and / or
an indication of frequencies for the restricted frequency bands.
8. The method of any of clauses 1 to 7, wherein configuration information relating to the
plurality of restricted frequency bands supported by the base station is predefined for the
wireless telecommunications system.
9. The method of clause 8, wherein the configuration information comprises an indication of
the number of the plurality of restricted frequency bands supported by the base station and / or
an indication of frequencies for the restricted frequency bands.
10. The method of any of clauses 1 to 9, wherein downlink communications transmitted to
the terminal device within the selected restricted frequency band comprise user-plane data and
control-plane data, and wherein the control-plane data comprise an indication of resources
within the selected restricted frequency band to be used for communicating the user-plane data
11. The method of any of clauses 1 to 10, wherein the downlink communications transmitted
to the terminal device within the selected restricted frequency band comprise user-plane data,
and wherein the method further comprises transmitting control-plane data to the terminal device
on frequency resources from across the system frequency bandwidth, wherein the control-plane
data comprise an indication of resources within the selected restricted frequency band to be
used for communicating the user-plane data.
1 . The method of any of clauses 1 to 11, wherein the method further comprises receiving
an indication of the identifier for the terminal device from the terminal device.
13. The method of clause 12, wherein the indication of the identifier for the terminal device is
received from the terminal device before or during an initial connection procedure for the
terminal device on the radio interface.
14. The method of clause 12, wherein the indication of the identifier for the terminal device is
received from the terminal device in association with radio resource control, RRC, connection
request signalling.
15. A base station for use in a wireless telecommunications system in which downlink
communications are made by the base station using a radio interface that spans a system
frequency bandwidth and supports at least some communications with at least some terminal
devices within a plurality of restricted frequency bands which are narrower than and within the
system frequency bandwidth, the base station comprising a processor unit and a transceiver
unit, and wherein the processor unit is configured to select a restricted frequency band to be
used for downlink communications with a terminal device from among the plurality of restricted
frequency bands based on an identifier for the terminal device; and to configure the transceiver
unit to transmit downlink communications to the terminal device within the selected restricted
frequency band.
REFERENCES
[ 1 ] ETSI TS 122 368 V 10.530 (201 1-07) / 3GPP TS 22.368 version 10.5.0 Release 10)
[2] GB 2 487 906 (UK patent application GB 1101 970 0)
[3] GB 2 487 908 (UK patent application GB 1101 981 7)
[4] GB 2 487 780 (UK patent application GB 1101 966 8)
[5] GB 2 488 5 13 (UK patent application GB 1101 983 3)
[6] GB 2 487 757 (UK patent application GB 1101 853 8)
[7] GB 2 487 909 (UK patent application GB 1101 982 5)
[8] GB 2 487 907 (UK patent application GB 1101 980 9)
[9] GB 2 487 782 (UK patent application GB 1101 972 6)
[ 1 0] GB 2 497 743 (UK patent application GB 1121 767 6)
[ 1 1] GB 2 497 742 (UK patent application GB 1121 766 8)
Holma H. and Toskala A, "LTE for UMTS OFDMA and SC-FDMA based radio access",
John Wiley and Sons, 2009

CLAIMS
What is claimed is:
1. A method of operating a terminal device in a wireless telecommunications system in
which downlink communications are made by a base station using a radio interface that spans a
system frequency bandwidth and supports at least some communications with at least some
terminal devices within a plurality of restricted frequency bands which are narrower than and
within the system frequency bandwidth, the method comprising:
selecting a restricted frequency band from among the plurality of restricted frequency
bands based on an identifier for the terminal device; and
configuring the terminal device to receive downlink communications from the base
station within the selected restricted frequency band.
2. The method of claim 1, wherein the identifier for the terminal device comprises an
International Mobile Subscriber Identity, IMSI, associated with the terminal device.
3. The method of claim 1, wherein the selected restricted frequency band is determined
from a remainder value obtained when dividing a number associated with the identifier for the
terminal device by the number of the plurality of restricted frequency bands supported by the
base station.
4. The method of claim 1, further comprising the terminal device establishing configuration
information relating to the plurality of restricted frequency bands supported by the base station
from system information received from the base station.
5. The method of claim 4, wherein the configuration information comprises an indication of
the number of the plurality of restricted frequency bands supported by the base station and / or
an indication of frequencies for the restricted frequency bands.
6. The method of claim 1, further comprising the terminal device establishing configuration
information relating to the plurality of restricted frequency bands supported by the base station
from information received from the base station before or during an initial connection procedure
for the terminal device on the radio interface.
7. The method of claim 6, wherein the configuration information comprises an indication of
the number of the plurality of restricted frequency bands supported by the base station and / or
an indication of frequencies for the restricted frequency bands.
8. The method of claim 1, wherein configuration information relating to the plurality of
restricted frequency bands supported by the base station is predefined for the wireless
telecommunications system.
9. The method of claim 8, wherein the configuration information comprises an indication of
the number of the plurality of restricted frequency bands supported by the base station and / or
an indication of frequencies for the restricted frequency bands.
10. The method of claim 1, wherein downlink communications received by the terminal
device within the selected restricted frequency band comprise user-plane data and controlplane
data, and wherein the control-plane data comprise an indication of resources within the
selected restricted frequency band to be used for communicating the user-plane data
11. The method of claim 1, wherein the downlink communications received by the terminal
device within the selected restricted frequency band comprise user-plane data, and wherein the
method further comprises the terminal device receiving control-plane data on frequency
resources from across the system frequency bandwidth, wherein the control-plane data
comprise an indication of resources within the selected restricted frequency band to be used for
communicating the user-plane data.
12. The method of claim 1, wherein the method further comprises conveying an indication of
the identifier for the terminal device from the terminal device to the base station.
13. The method of claim 12, wherein the indication of the identifier for the terminal device is
conveyed from the terminal device to the base station before or during an initial connection
procedure for the terminal device on the radio interface.
14. The method of claim 12, wherein the indication of the identifier for the terminal device is
conveyed in association with radio resource control, RRC, connection request signalling.
15. A terminal device for use in a wireless telecommunications system in which downlink
communications are made by a base station using a radio interface that spans a system
frequency bandwidth and supports at least some communications with at least some terminal
devices within a plurality of restricted frequency bands which are narrower than and within the
system frequency bandwidth, the terminal device comprising a processor unit and a transceiver
unit, and wherein the processor unit is configured to select a restricted frequency band from
among the plurality of restricted frequency bands based on an identifier for the terminal device
and to configure the transceiver unit to receive downlink communications from the base station
within the selected restricted frequency band.