COMMUNICATIONS SYSTEM. INFRASTRUCTURE EQUIPMENT AND METHOD
Field of the Invention
The present invention relates to communications systems and infrastructure equipment for
transmitting and receiving data, and methods of transmitting and receiving data.
Background of the Invention
Fourth generation mobile telecommunication systems, such as those based on the 3GPP
defined UMTS and Long Term Evolution (LTE) architecture are able t o support more sophisticated
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 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 t o increase rapidly.
The anticipated widespread deployment of 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, which are typified by semi-autonomous or autonomous wireless communication
devices (i.e. MTC devices) transmitting and receiving small amounts of data on a relatively
infrequent basis. Examples include so-called smart meters which, for example, are located in a
customer's house and periodically transmit information back t o a central MTC server data relating to
the customers consumption of a utility such as gas, water, electricity and so on.
The nature of MTC devices may lead to their disposal in locations where communication
with mobile telecommunications systems such as those mentioned above may prove unreliable,
even when taking into account increasing coverage. For instance, MTC devices such as smart meters
may be located in the basement of a house or other hard t o reach locations where signals from
mobile telecommunications system may not be received at a sufficient strength because they have
propagated over highly attenuating channels. Consequently, devices such as smart meters may be
unable t o perform reliable detection and estimation of data conveyed by the signals. Scenarios such
as this may also occur when devices are near the border of a geographic area served a by mobile
telecommunications system. Overcoming these problems by further extending the coverage of
mobile communications networks would allow an increased number of devices t o be supported by
mobile communications networks.
The use of decreased coding rates and reduced order modulations schemes present a
potential solution t o improving the reliability of detection and estimation of data at a device.
However, often a restricted set of possible modulation and coding rates are supported by devices,
especially low cost ones such as MTC devices, and therefore improvement via coding changes may
be limited. Recently it has been suggested that transmission repetition may present an alternative
solution t o extending coverage t o mobile devices which are currently unable to be reliably served by
a mobile communications network.
Summary of the Invention
According to an example embodiment, there is provided a communications system
comprising an infrastructure equipment for forming part of a mobile communications network
where the infrastructure equipment is arranged to transmit and receive data t o and from a user
device via a wireless access interface. The wireless access interface is provided by the infrastructure
equipment using a plurality of Orthogonal Frequency Division Multiplexing (OFDM) subcarriers and
the plurality of OFDM subcarriers extend across a first bandwidth. The infrastructure equipment is
configured to transmit repeatedly signals representing a same instance of user device payload data
in a second bandwidth, where the second bandwidth is less than and within the first bandwidth and
includes a subset of the OFDM subcarriers. The user device is configured to receive one or more of
the signals repeatedly transmitted across the second bandwidth, to store in a memory signals
representing the repeatedly transmitted signals received across the second bandwidth and t o
combine the stored signals. The user device is also configured to detect the user device payload data
from the combined signals, where the user device has been provided with an indication of the
second bandwidth.
According to another example embodiment, the infrastructure equipment is configured t o
transmit repeatedly signals representing a same instance of user device control data in the first
bandwidth, the user device control data providing an indication of a location of the signals
representing the user device payload data in the second bandwidth. The user device is configured t o
receive one or more of the signals representing the user device control data repeatedly transmitted
across the first bandwidth, to store in the memory signals representing the repeatedly transmitted
signals received across the first bandwidth, and to combine the stored signals representing the
repeatedly transmitted signals received across the first bandwidth. The user device is also configured
t o detect the user device control data from the combined signals representing the repeatedly
transmitted signals received across the first bandwidth, where the detection of the user device
payload data from the combined signals received across the second bandwidth is based on the
indication of the location of the signals representing the user device payload data in the second
bandwidth.
Repeating transmissions of signals representing user device payload data enables a user
device which is unable t o detect and estimate user payload data from a single instance of the signal,
t o combine multiple signal instances I. The combined signals may then be utilised t o increase the
strength of the received signal or provide additional coding bits and therefore improve an accuracy
of the subsequent data estimation. The repetition of signals representing a same instance of data
provides an alternative to decreasing a coding rate and or modulation order of data when
attempting to increase the accuracy of data detection and estimation at a receiver of a user device
when attempting, for example, to increase the coverage of a mobile network. The use of repetition
may be useful for example, when it is not possible to alter coding rates or modulation orders or they
can not be further reduced because of compatibility requirements within a system Repetition may
also present an alternative t o coding rates changes, when the capabilities of intended receiving
devices are limited. For instance, a machine type communications (MTC) device may be unable t o
perform complex decoding procedures but can receive multiple instance of signal and combine the
received signals. Transmitting repetitions of signals representing user device payload data within a
second bandwidth which is less than and within the first system bandwidth reduces the signals that
a user device is required t o store and combine when the location of signals representing the user
device payload data within the second bandwidth is not yet known. For instance, before user device
control data has been detected and estimated, the user device is required t o store signals from the
second bandwidth as opposed to across the first bandwidth. This approach therefore reduces
memory requirements at the user device for storing repeated signals representing user payload data
whilst still allowing the storage and accumulation of the signals representing the user device control
data and the user device payload data to be substantially concurrent, therefore reducing the
acquisition time of the user device payload data.
The expression "signals representing a same instance of user device payload data or user
device control data" is used t o include various techniques for transmitting data which represent the
same user data, which can be combined t o increase the likelihood of correctly recovering the user
data. In one example the repeated transmission of the signals representing the user data is a
repetition of the same signals. In other examples the user data may be encoded so that incremental
redundancy can be used in which an amount of parity of codeword digits are increased by the
repeated transmission of the signals, such that the repeated signals may be different.
According t o another example embodiment, the wireless access interface provided by the
plurality of OFDM subcarriers is divided into a plurality of time periods and the repeated signals
representing the user device payload data are transmitted in a same set of resources of the wireless
access interface in a first time period and in a second time period.
Repeating of signals representing the user device payload data in the same set of resources
within different time period means that the channel over the signals propagate may be substantially
similar and therefore may simplify the combining of the signals. It may also be beneficial because the
user device is only required to detect and estimate data from a particular portion of the second
bandwidth.
According to another example embodiment, the infrastructure equipment is configured t o
transmit the indication of the second bandwidth to the user device prior to the repeated
transmissions of the signals representing the user device control data.
Transmitting an indication of the second bandwidth to the user device prior to the
transmission of control data allows the user device to reduce the bandwidth across which is receives
signals that may include user device payload data t o the second bandwidth without having first t o
have received signals representing the user device control data. Consequently, the signals
representing the user device control data and the signals representing the user device payload data
may be received and stored simultaneously.
According to another example embodiment, the user device is configured to receive user
device payload data within a virtual carrier of a predetermined bandwidth, the second bandwidth
being approximately equal to the predetermined bandwidth, and the predetermined bandwidth
includes a set of the OFDM subcarriers that is substantially similar to the OFDM subcarriers that
form the subset of the OFDM subcarriers included in the second bandwidth.
Configuring the second bandwidth to be approximately equal to a virtual carrier bandwidth
allows the repetition of signals t o be integrated with the virtual carrier concept for user devices such
as machine type communication (MTC) devices. This allows the operation of such devices to be
simplified because it reduces the bandwidth that MTC devices operate to receive payload data
compared to having a second bandwidth which is separate from the virtual carrier.
Various further aspects and features of the present invention are defined in the appended
claims, including but not limited to, an infrastructure equipment and methods of communicating
between a user device and an infrastructure equipment
Brief Description of the Drawings
Embodiments of the present disclosure will now be described by way of example only with
reference to the accompanying drawing in which like parts are provided with corresponding
reference numerals and in which:
Figure 1 provides a schematic diagram of a wireless communications system;
Figure 2 provides a schematic diagram of a receiver of a user device of the communications
system of Figure 1;
Figure 3 provides a schematic diagram of LTE subframes;
Figure 4 provides a schematic diagram of LTE subframes where signal repetition is
implemented;
Figure 5 provides a schematic diagram of a receiver of a user device configured to receive
repeated signals;
Figure 6 provides a schematic diagram of LTE subframes where signal repetition is
implemented;
Figure 7 provides a schematic diagram of LTE subframes where signal repetition is
implemented in accordance with an embodiment of the present technique;
Figure 8 provides a schematic diagram of LTE subframes where signal repetition is
implemented in accordance with an embodiment of the present technique;
Figure 9 provides a schematic diagram of LTE subframes where signal repetition is
implemented in accordance with an embodiment of the present technique; and
Figure 10 provides a schematic diagram of LTE subframes where signals repetition and
windowed signal reception is implemented in accordance with an embodiment of the present
technique.
Detailed Description of Example Embodiments
Mobile Communications System
Figure 1 provides a schematic diagram of a mobile communications system 100 for
transmitting and receiving data to and from one or more user devices, where the communications
system may for example operate in accordance with 3GPP Long Term Evolution (LTE). The
communications system comprises infrastructure equipment 101 such as a base station or enhanced
nodeB (eNodeB) which forms part of a mobile communications network and is configured to provide
a wireless access interface to one or more user devices 102 103. The user devices 102 103 may for
example be mobile phones, machine type communication (MTC) devices such as smart meters or
information aggregation devices in cars or medical devices, or tablet computers. Within the wireless
access interface the infrastructure equipment transmits signals representing the data t o the one or
more user devices. In Figure 1 user devices 103 provides an example of a smart meter located in the
basement of a house. The infrastructure equipment 101 is communicatively linked via
communication link 104 to a core network 105 which may in turn be linked to further infrastructure
equipment 106 and other communications networks and systems, where the further infrastructure
equipment may itself be linked t o one or more user devices 102.
In examples where the system 100 is an LTE system, the wireless access interface will be
provided in accordance with orthogonal frequency division multiplexing (OFDM) where downlink
resources are temporally divided in a plurality of time periods and divided in frequency into a
plurality of subcarriers where the subcarriers form in the time domain OFDM symbols that convey
signals which represent data t o be transmitted to the user devices. The data transmitted t o the users
devices may consist of control plane data and user plane data where the control plane data coveys
control data required by the user devices in order to communicate in the downlink (from
infrastructure equipment to user device) and uplink (from user device to infrastructure equipment)
with the infrastructure equipment, and user plane data conveys user device payload data. Further
discussion of the wireless access interface is presented below.
User Device Receiver
Figure 2 provides a schematic diagram of a simplified receiver that may be found in a user
device configured t o receive and transmit data in the communications system of Figure 1. In an
example where the system 100 is an LTE system, the receiver may for example be an OFDM receiver.
An antenna 201 receives signals transmitted from the infrastructure equipment over a channel and
passes them to a baseband converter 202 which down converts the received signal t o baseband
frequencies. The baseband signal is then sampled by a sampler 203 at a sampling rate suitable for
the baseband frequencies. A synchroniser 204 is then configured to detect the timing of the control
plane data and user plane data before processing of the synchronised signal by a control data
estimator 205 and a payload data estimator 206. The control data estimator estimates user device
control data from signals representing the control data and provides information to payload data
estimator which is required t o estimate the user device payload data from the signals representing
the user device payload data. As mentioned above, Figure 2 provides a simplified OFDM receiver and
therefore a number of elements of an OFDM have not been included. For example, frequency offset
correction, transformation of the received signal into the frequency domain for equalisation and
data estimation, guard interval removal etc. However, the processes performed by these elements
and further elements may be performed using any suitable processing means known in the art.
Downlink Resource Allocation
Figure 3 provides a simplified example of downlink resource allocation, which may for
example being applicable in an LTE system. The downlink resources are temporally divided into
periods referred t o as subframes 301 where a time period referred to as a radio frame may be
formed from 10 subframes and the subframes may be 1ms in duration. The downlink resources are
divided in frequency into a plurality of subcarriers, where the number of subcarriers may vary
between approximately 128 and 2048 dependent upon the bandwidth of the downlink resources,
where possible downlink bandwidths may include for example 1.25MHz, 2.5MHz, 5MHz, 10MHz,
15MHz and 20MHz. Each subframe may be further divided in time into two 0.5ms slots where a slot
comprising 12 subcarriers may be referred to as a resource block.
Each subframe includes control or signalling data which may for example be transmitted
over a physical channel such as a physical downlink control channel (PDCCH) in LTE, where the
control data indicates which downlink resources, in terms of subcarriers, slots and timing within the
subframes, have been allocated to each of the user devices currently being served by the
infrastructure equipment via the wireless access interface. Payload data is transmitted in the
downlink over a data channel such as a physical downlink shared channel (PDSCH) in LTE, where the
control data indicates to a user device a location in the data channel in which its payload data will be
transmitted and the parameters required to estimate the payload data. Payload data may for
example include uplink resource allocations, a request for information from the infrastructure
equipment or information for an application running on the user device In Figure 3, three downlink
subframes of an LTE system are illustrated where control data is transmitted over the physical
downlink control channel (PDCCH) and user device payload data is transmitted across the physical
downlink shared channel (PDSCH). In an example reception routine, a user device, such as an MTC
device, detects signals representing control data transmitted across the PDCCH 302 303 at the
beginning of each subframe 301. The user device will then estimate the control data received across
the PDCCH of each subframe in order establish whether it has been allocated resources in the PDSCH
of the corresponding subframe. If within the control data of the PDCCH there is no indication of user
payload data intended for the user device i.e. PDCCH 302, the user device will not attempt t o receive
signals which from the following PDSCH i.e. PDSCH 304. However, if the estimated control data
indicates t o the user device that there is data intended for it in the PDSCH i.e. PDCCH 305, the user
device will receive signals that form the relevant portion 306 of the following PDSCH 307 that the
control data has specified, and subsequently estimate the user payload data from the received
signals. As can be seen from Figure 3, the resources 306 in the PDSCH allocated t o a user device may
not extend over all the subcarriers in the subframe and/or over the full temporal length of the
PDSCH in the subframe. This, along with the control data conveyed by signals transmitted across the
PDCCH allows for the allocation of resources in the PDSCH t o a plurality of user devices.
A user device is configured t o detect and estimate payload data conveyed in the PDSCH.
Accurate detection and estimation of data is dependent on a number of factors, for instance,
knowledge of the location of the signals representing the payload data in a subframe and reception
of the signals representing the user payload data at a sufficient signal strength and quality. In turn,
knowledge of the location of the signals representing the payload data is dependent upon receiving
the signals across the PDCCH at a sufficient signal strength and quality so that the user device
control data can be detected and accurately estimated. Consequently, receiving signals representing
user device control data and payload data at a sufficient signal strength are both required in order t o
detect and recover payload data in the downlink of an LTE communication system or any other
equivalent communications system.
During conventional operation of a user device in an LTE network, if the user device control
data cannot be accurately estimated and recovered from the signals transmitted and received across
the PDCCH and/or the user device payload data cannot be accurately estimated and recovered from
the PDSCH, the user device data is unable t o be received by the user device. This may occur for
example when the channel between the infrastructure equipment and the user device is highly
attenuating thus resulting in highly attenuated signals being received at the receiver. In such a case,
the user device may indicate t o the infrastructure equipment that the user payload data has or has
not been received correctly via an ACK or NACK message and the infrastructure equipment will
prepare t o resend the payload data. The data may be retransmitted in a subsequent subframe,
where each of the instances of the user device control data and associated payload data are
independent from one another and may be transmitted in different portions of the PDCCH and
PDSCH, respectively. This procedure may be sufficiently robust for user devices which experience
variable channels due t o mobility for instance, because poor channel conditions may improve in the
near future. Consequently, subsequent transmission(s) of signals representing the user device
control data and payload data may be able t o be received at a sufficient strength and quality that
the user device control data and payload data can be accurately detected and estimated. However,
in the case of user devices which are not mobile and/or are unlikely t o experience channel
conditions sufficient for reliable detection and estimation of control and or payload data, the above
described procedure is unlikely t o be sufficiently robust. The use of reduced coding rates and
reduced order modulation schemes may be able to mitigate the effects of some poor channels, but
it is likely that there will still be channels of poor enough quality that user devices are unable to
reliable detect and estimate control and or payload data from received signals. Furthermore, there
may be limits within a system that restrict the coding rates and modulation orders that may be used.
For example, user device capabilities, compatibility issues and system parameters may lead to
minimum coding rates which are supported by the system, thus limiting the gains in estimation
accuracy that obtained by limiting the coding rate. Furthermore, devices such as MTC devices, which
are low complexity and low power, may not have the capability to perform decoding of data which
has been encoded with complex encoding techniques.
User device 103 of Figure 1 is an example of a non-mobile user device which may not
experience channel conditions sufficient for accurate detection and estimation of control and or
payload data from received signals. As can be seen from Figure 1, user device 103 is stationary and
located in the basement of a house and therefore signals representing user device control data and
payload data may be received at a signal strength and or quality which is not sufficient for accurate
data detection and estimation, even with the use of low codes rates and modulation orders.
Consequently, smart meter 103 provides an example of a user device where the above described
reception routine may be insufficient to achieve the accurate recovery of user device control and
payload data. As well as user devices in hard to reach locations i.e. basements, user device which are
near the border of a cell served by infrastructure equipment may also experience similar problems
due to reception of highly attenuated signals.
Signal Repetition
In order to address the above highlighted deficiencies and problems, it has been previously
proposed that a form of signal repetition may be utilised in order to improve the strength and or
quality of the signal received at user devices. In particular, when the received signal strength of a
single instance of signals representing data is insufficient t o enable reliable data detection and
estimation. Repeating transmission of signals representing data provides a more simple
arrangement for improving the detection and estimation of communicated data without significantly
increasing processing power requirements and can be used for low data rate and delay tolerant
applications. Furthermore, repetition can use coding, modulation and other communications
parameters which are determined by a standard, such as LTE, and therefore may be compatible with
that standard.
Figure 4 provides a schematic illustration of a series of subframes where an example signal
repetition procedure is implemented. The principle of signal repetition is signals that represent a
same instance of control and/or payload data for a user device are repeatedly transmitted by the
infrastructure equipment over one or more subframes or frames. The signals may be in a
substantially similar position or in substantially similar set of resources of the wireless access
interface in each of the subframes or frames so that they propagate over a substantially similar
channel. However in some examples the repeated signals may be transmitted in different resources
in each subframe or frame where differences in channel across which the signals are transmitted are
mitigated for example by equalisation. In other examples the signals may be repeated within a same
subframe or frame. The receiver of the user device is then configured t o receive each of the
repeated signals and to store signals representing the repeated signals in a memory, where the
stored signals may take the form of sampled un-demodulated baseband signals, soft estimates of
the data, or hard estimates of the data. The receiver then aggregates, accumulates or combines the
stored signals, by summation or averaging for example, so that the relative received strength of the
combined signals representing the user device control data and payload data is increased or
additional coding bits are available for data estimation and correction. The user device then
proceeds to estimate the control data from the combined signal, where the control data indicates
the location of the payload data in the combined signal representing the payload data intended for
the user device. By the following this procedure it is then possible for the accuracy of detection and
estimation of the user control and payload data to be increased. Returning to Figure 4, signals
representing control data are repeated in the PDCCH 401 of three consecutive subframes. The
repeated signals of the PDCCH 401 which represent control data are stored and then accumulated
402 and the control data intended for the user device estimated from the accumulated PDCCH at
403. The estimated control data provides the user device with an indication of the location in the
PDSCH of signals representing the user device's payload data 404. The user device then stores and
accumulates the signals received from the indicated location 404 of the PDSCH in the next three
subframes. The user device then recovers an estimate of its payload data from the accumulated
PDSCH signal at 405. In this manner an increased likelihood of a correct estimation of the payload
data can be achieved without substantially altering parameters of the signals and data such as
transmit power, coding rates and or modulation schemes. Accordingly, a transmitter and a receiver
performing the above describe repetition can be compatible with other LTE devices because signal
transmission characteristics such as coding rates have not been modified.
Figure 5 provides a simplified schematic diagram of an example user device receiver which is
configured to receive repeated data transmissions. The structure of the receiver is substantially
similar t o that illustrated in Figure 2 but further includes a memory 501 such as a buffer memory
which is configured t o store received repeated signals. The memory 501 stores the received signals
representing the user device control data and the payload data, and under the control of a controller
502, passes the signals to the signal data estimator 205 and the payload data estimator 206. The
signals may be passed to the relevant estimator when a predetermined number of repeated signals
have been received or when the accumulated signals achieve an amplitude, via summation for
example, sufficient t o enable reliable detection and estimation of the data t o be achieved. However,
the exact process by which the received signals are combined may vary and is discussed in more
detail below. The controller may also be communicatively linked t o the other elements of the
receiver in order to configure the elements to store and accumulate signals from the relevant
portions of the PDSCH as indicated by recovered control data. For example, the controller may
require information from the control data estimator in order t o configure the receiver to receive and
store signals representing data from appropriate parts of the PDSCH. The memory 501 may include
separate memories for the storage and accumulation of signals representing the control data the
payload data or other forms of data. Furthermore the configuration of the functional elements of
the receiver may vary depending on the form of repetition being utilised. For example, for repetition
techniques where signals are combined after initial detection and estimation has taken place, an
additional estimator stage(s) may be required or the organisation of the receiver adapted
accordingly.
In order for the repetition structure of Figure 4 t o be implemented, the user device may
require an indication of commencement of the repetition so that it can begin to store the relevant
received signals. However, this may cause problems if the indication signal itself cannot be received
without repetition. An alternative implementation is to configure the memory 501 t o be a buffer
type memory that stores a maximum number of instances of signals and once the limit is reached,
discards the oldest signal instance and stores the most recently received signal instance. This process
can continue for example until the accumulated signal reaches a signal strength which is sufficient
for accurate data detection and estimation, thus indicating the buffer is predominantly made up of
the desired repeated signals. This may occur for example due t o the correlation between the
repeated signals representing the user data and the lack of correlation between the portions of the
frames orsubframes which are not repeated i.e. portions of the PDCCH which do not apply t o the
user device and therefore change between frames or subframes in which the signals for the user
device are repeated. Another alternative is for the infrastructure t o continue t o repeat signals until
an acknowledgment is received from the user device indicating that the data represented by the
repeated signals has been accurately detected and estimated.
Although, the repetition scheme depicted in Figure 4 provides a number of advantages,
there are also associated costs. For example, increased resources are utilised in order t o send data
t o the user device, where in Figure 4 approximately three times the normal resources are utilised t o
transmit the payload data t o the user device. Although this is an obvious disadvantage, it may be
mitigated by the fact that communication involving repetition may be predominantly used in off
peak periods where usage of the communications system is low, for example, during the night. This
also fits in with the properties of low cost MTC devices such as smart meters which are likely t o have
delay tolerant data and therefor transmit data during off peak periods.
In LTE systems, in order t o maintain compatibility with legacy LTE user devices that do not
support repetition, there may have t o be a one-to-one correspondence between control data
indicating where user device payload data is located in the corresponding PDSCH and the actual
location of the payload data. For example, even though the payload data transmitted in 406 is not
detected by the user device, the payload still has to be transmitted or the corresponding resources
not used by another user device because the control data corresponding t o 406 will still specify that
there is data for the user device in portion 406 of the PDSCH. If this were not the case, it may be
possible for the scenario where two different portions of the control data specify that payload data
for two different user devices are at the same location in the PDSCH. The requirement of one-to-one
mapping of PDSCH resources t o one user device therefore results in an inefficient use of downlink
resources. However, in some examples the one-to-one mapping may be broken by signalling the
change prior t o the commencement of any repetition.
In some examples of signal repetition, in addition t o transmitting signals representing
identical control data and payload data for a particular user device in a substantially identical
location in each frame or subframe, the entirety of the frames or subframes may have t o be
repeated in a substantially identical manner. This therefore decreases flexibility and further reduces
efficiency. Furthermore, in some examples where channel conditions or coding rates etc. for
transmitting data t o a user device are poor and or high, a large number of repetitions may be
required for a signal of sufficient strength/ or sufficient information t o be accumulated at the user
device. Consequently, because the accumulation of the signals representing the control data and the
payload data are not performed concurrently, the delay in receiving the payload data may be
significant. For example, if a required number of repetitions in terms of subframes is large i.e. 100, it
may be up t o 200 subframes before the payload data can be recovered. In such an example, if the
subframes are 1ms in duration, a 200 subframe delay may result in a delay of 0.2s, which may be
unacceptable in some scenarios or t o some user devices. Further still, with large repetition numbers
user devices may have t o be in a receiving mode for a significant period of time as opposed t o a
reduced power mode, therefore consuming an increased amount of power. This may be particularly
problematic for low power, battery power devices such as MTC devices, whose time spent receiving
and transmitting signals should be kept to a minimum if possible.
Repetition has been described in general terms up to this point, however, there are a
number of alternative implementations of repetition and therefore a number of different methods
for accumulating and combining received repeated signals. Two example repetition techniques are
chase combining and incremental redundancy, which may be implemented as part of hybrid ACK
procedures. Chase combining includes repeatedly transmitting a same instance of signals or portions
of a same instance of signals that represent a same instance of data and then combing these signals
at the receiver either pre or post demodulation. Consequently, chase combining may be viewed as
increasing the signal-to-interference-plus -noise ratio (SINR) of the received signal. Incremental
redundancy includes repeating signals which are different but represent a same instance of data, for
example different coded versions or different code bits of all or part of a same instance of data may
be transmitted during each repetition. Consequently, incremental redundancy may be viewed as
increasing the strength of the error correction coding at the receiver with the reception of each
repeated signal. At a user device receiving repeated signals, there are a variety of methods that may
be used t o accumulate or combine the received repeated signals. For example, in chase combining
stored sampled baseband signals that represent the repeated signals may be combined via equalgain
combining or maximum-ratio combining. The combining may also be performed either preequalisation
or post-equalisation. In another example, combining of the signals may occur once soft
or hard decisions have been performed on each of the received equalised repeated signals. For
instance, an average may be taken over the soft decision from each instance of the repeated signals
and then a hard decision taken to estimate the data. Alternatively, a majority vote system may be
employed with hard decisions from each of the repeated signals. For incremental redundancy,
combining of baseband signals may not be possible due t o the differing repeated signals and
therefore combining of signals representing soft or hard decisions may be more appropriate.
The aforementioned repetition and combining methods are merely examples and any
suitable methods known in the art may be used. Different methods of repetition and of combining
the received repeated signals each have their own advantages and disadvantages. For instance, if
sampled baseband signals are combined, it is the received signals representing the user device
control data and the payload data that are required to be stored as opposed to the data estimates
themselves. Therefore, it is sampled versions of portions of the baseband signal that are stored.
Storing signals in this manner may require significantly more memory than storage of signals
representing estimates of the underlying data as sampling has t o be performed at a frequency and
with a number of quantisation levels that are sufficient t o achieve a combined signal from which
control data and or payload data can be accurately detected and estimated. The actual sampling
frequency will be dependent on, among other things, the baseband frequencies via the sampling
theorem, and the number of quantisation levels is likely to be dependent on, among other things, at
least the modulation scheme, coding rates, and the required signal-to-noise ratio (SNR). However, if
signals are combined post-equalisation and or -post-demodulation, then memory requirements may
be reduced. In another example, if incremental redundancy is utilised, different coding bits are
transmitted with each repetition and so cannot merely be combined via summation. This approach
may therefore require increased memory compared to chase combining of soft or hard decisions
because one symbol in memory corresponds to one received symbol, whereas in chase combing one
symbol in memory may be a summation of multiple repeated symbols. In examples where
combining of signals representing the user payload data is performed post-equalisation and after
preliminary soft or hard estimates, it may be required that user device control data has already been
detected and estimated. The user device control data may be required because it includes
information on the location and coding etc. of the user payload data that is necessary t o detect and
estimate the user device payload data. Consequently, such a method may be suited t o examples of
signal repetition where control data is received and estimated prior t o reception of the repeated
signals representing the user payload data. With regards t o repeated signals representing user
device control data, estimation of the data contained therein may be performed at any point after
reception, independent of the combining method. This approach is possible by virtue of information
on the location of control information in frame or subframe and any coding of the control data being
predefined and therefore known by the user device prior t o reception.
Figure 6 provides an alternative implementation of signal repetition which may decrease the
acquisition time of the payload data. In contrast t o Figure 4 where accumulation of signals
representing control data and payload data is done during different subframes, in Figure 6 whilst the
signals transmitted across the PDCCH 601 are being accumulated all the signals transmitted across
the PDSCH 602 are buffered. Once the location of the signals representing the user device payload
data in the PDSCH is known and the parameters of the payload data are known, the payload data
may be detected and estimation from the buffered accumulated signal at 604. If further
accumulation is required after estimation of the control data, the receiver can store and accumulate
only the relevant part of the PDSCH signals 605 indicated by the recovered control data. Although
this implementation may reduce acquisition delays, it requires a significant amount of memory in
order t o store and accumulate all or a substantial proportion of the signals which represent the
PDSCH data prior to detection and estimation of the user device control data. In the case of low cost
and reduced power devices such as MTC devices, this may not be a practical solution.
Narrow Bandwidth Signal Repetition
Figure 7 illustrates an example embodiment of a repetition procedure in accordance with
the present technique. Repetition of signals representing user device control data 701, using for
example chase combining or incremental redundancy as previously described, is performed within
the system bandwidth or first bandwidth of the system in a manner similar t o that described with
reference to Figures 4 or 6. However, signals representing the user device payload data are
transmitted using chase combining or incremental redundancy for example, within a predetermined
second bandwidth 702 within the PDSCH, where the second bandwidth is narrower than the first
bandwidth of the system or current subframe and is also within the first bandwidth. The signals
representing the user device payload data may or may not extend across the entirety of the second
bandwidth and signals representing payload data for other user device(s) may also be transmitted
across the second bandwidth. Consequently, a subset of the subcarriers of the data channel PDSCH
are utilised for transmitting the repeated signals representing the user device payload data. A
receiver as illustrated in Figure 5 may therefore store and accumulate signals representing the
received signals or the control data contained therein whilst simultaneously storing and
accumulating signals representing received signals or the payload data contained therein without
storing and/or accumulating signals transmitted across the entirety or a significant portion of the
PDSCH bandwidth or first bandwidth. This is in contrast t o existing techniques as previously
described with reference t o Figure 6.
In some example embodiments the second bandwidth could be formed by a Virtual carrier
arrangement. To support MTC terminals, it has been proposed t o introduce a "virtual carrier"
operating within a bandwidth of one or more "host carriers": the proposed virtual carrier concept
preferably integrates within the communications resources of conventional OFDM based radio
access technologies and subdivides frequency spectrum in a similar manner to OFDM. Unlike data
transmitted o n a conventional OFDM type downlink carrier, data transmitted on the virtual carrier
can be received and decoded without needing t o process the full bandwidth of the downlink OFDM
host carrier. Accordingly, data transmitted on the virtual carrier can be received and decoded using
a reduced complexity receiver unit: with concomitant benefits such as increased simplicity,
increased reliability, reduced form-factor and lower manufacturing cost. The virtual carrier concept
is described in a number of co-pending patent applications (including GB 1101970.0 [2], GB
1101981.7 [3], GB 1101966.8 [4], GB 1101983.3 [5], GB 1101853.8 [6], GB 1101982.5 [7], GB
1101980.9 [8] and GB 1101972.6 [9]), the contents of which are incorporated herein by reference.
Once a sufficient number of instances of the repeated signals representing the control data,
and in particular the user device control data, have been accumulated and combined, the user
device control data is detected and estimated 703. In this case, a sufficient number of instances may
for example refer to accumulating signals until the data can be detected, until a predetermined
number of signals have been accumulated, or until the infrastructure equipment ceases repeating
the relevant signals. Subsequently, if a sufficient number of repetitions of signals representing the
user device payload have been accumulated and combined, the user device payload data is detected
and estimated 704 from the appropriate location in the accumulated signals from the second
bandwidth. This procedure enables accumulation of the signals representing the user device payload
data to be performed concurrently with the accumulation of the signals representing the user device
control data without buffering or storing signals transmitted and received across all of or a
substantial portion of the PDSCH. Therefore improvements in the speed of data acquisition may be
achieved compared to the procedure described with reference t o Figure 4, whilst also reducing the
memory requirements compared to the procedure described with reference to Figure 6. For
example, if the PDSCH is 128 subcarriers in bandwidth and the predetermined bandwidth is 12
subcarriers, the user device may require approximately 90% less memory to store signals that
include signals representing the user device payload data compared to storing all signals received
from across the first bandwidth or the PDSCH. Consequently, by the use of large numbers of
repetitions and use of the reception techniques described above, coverage of a mobile
communications network may be extended to areas where user devices receive a weak signal which
would normally not be sufficient for communicating with the network, without significantly
increasing the memory requirements, costs or battery consumption of the user devices. This may be
particularly relevant for battery powered devices such as MTC devices for example which require
both their costs and energy consumption t o be reduced and therefore may not be suited t o existing
repetition techniques.
In order for a user device to have knowledge of the second bandwidth, additional signalling
indicating the second bandwidth may be required t o be transmitted to the user device prior to
commencement of repetition, for example, when a user device enters the coverage of an
infrastructure equipment such as a base station or eNB. Alternatively, the second bandwidth may be
hardcoded into repetition compatible user devices. In the former case, the infrastructure equipment
may be configured to select an appropriate second bandwidth based on for example resource
allocation demands, channel conditions, the number of device requiring repetition etc. As
mentioned above, in some embodiments of the present technique, the second bandwidth may be
equivalent t o o r substantially similar to a predetermined bandwidth of a virtual carrier (VC), which
has been proposed in order t o simplify the operation of MTC devices. In such an embodiment a
separate second bandwidth in addition t o the VC may not be required and therefore signalling of the
second bandwidth may not be necessary, thus leading t o improvements in system efficiency. In
other embodiments of the present technique, the same predefined bandwidth may be allocated t o
multiple user devices requiring repeated signals. In this case, multiple different signals may be
repeated within the second bandwidth of each subframe. In further embodiments the second
bandwidth may be defined relative to the first bandwidth or the bandwidth of the PDSCH of each
subframe. In such an embodiment the number of subcarriers in a radio frame or subframe or even
OFDM symbol t o OFDM symbol may change without the infrastructure having t o re signal the
second bandwidth. For example, the second bandwidth may be defined as subcarriers 36 t o 60 o r
the subcarriers 5/8xSt t o 6/8xSt where St is the total number of subcarriers. However, regardless of
the means by which the second bandwidth is indicated t o the user device, improvements in power
consumption and memory requirements can be achieved at the user device when large repetition
numbers are utilised t o extend the coverage of a mobile communications network.
In other embodiments, control information required t o be received by the user device may
be represented by signals which are transmitted over a bandwidth smaller than the first bandwidth
or the available bandwidth of the subframe. The signals representing user device payload data may
also be repeated separately from signals representing user device control data, such as, in systems
where a one-to-one mapping from control data t o the location of user device payload data is not
required. This embodiment would therefore further simplify the reception routine of the user device
and the cost and complexity of the user device because it will be required t o operate over a reduced
bandwidth.
In some embodiments, due t o low coding rates, increased transmission power, increased
frequency diversity etc., a larger number of instances of signals representing payload data may be
required to be received compared t o signals representing control data if the payload data is t o be
detected and estimated accurately. For instance, in some networks control data may be transmitted
with lower coding rates and lower order modulations schemes compared t o payload data. Figure 8
provides an illustration of a repetition procedure in accordance with the present technique where a
larger number instances of signals representing payload data are required to be accumulated
compared t o signals representing control data. In Figure 8, three repetitions of signals forming the
PDCCH 801 and representing user device control data are required t o be stored and accumulated
whereas five instances of the signals representing the payload 802 data are required. Whilst the
signals received across the PDCCH are being accumulated, knowledge of the location of the signals
representing the payload data with the second bandwidth is unknown and therefore the receiver of
the user device stores and accumulates signals from the entirety o r a significant proportion of the
second bandwidth 702 of subframes 803. Once the control data has been detected and estimated
from the accumulated signals representing the control data, and the location of the signals
representing the payload data known, the receiver commences storing and accumulating only the
signals from the specified location within the second bandwidth of frames 804. In some examples,
because of the time taken to estimate the control data from the accumulated and combined control
signals, the receiver may continue t o buffer signals from the entirety of the second bandwidth until
subframe three of Figure 8 because knowledge of the location of the payload data signals within the
predetermined bandwidth is not known until after the commencement of the PDSCH of frame three.
Figure 9 provides an illustration of a repetition procedure in accordance with an example of
the present technique where additional control information is transmitted outside of the PDCCH, for
example, in an enhanced PDCCH (ePDCCH) in an LTE system. In this case the ePDCCH 901 may be
located within the second bandwidth 702 so that the user device is able to receive the control data
represented by signals transmitted over the ePDCCH without having to receive signals transmitted
across the entirety or a substantial portion of the first bandwidth. The ePDCCH may convey
additional control data required in order t o detect and estimate the user device payload data and
therefore may be required to be detected and estimated prior to detection and estimation of the
payload data in the second bandwidth. Alternatively, the ePDCCH may convey information relating
t o uplink criteria and therefore should be received in a similar manner t o signals transmitted over
the PDSCH.
As previously described, the user device may require an indication of when signal repetition
is set to commence so that the appropriate signals from the PDCCH and PDSCH can be stored and
accumulated. Such an indication may be transmitted at a low code rate and modulation order so
that the probability that it can be received without the need for repetition is maximised. However, in
embodiments where an indication is not provided or cannot be reliably detected and estimated, a
buffering procedure as previously described and shown in Figure lOmay be used. In Figure 10,
buffering of the signals transmitted across the PDCCH and the predetermined bandwidth 702 begins
at 1001. Three instances of the signals representing the user device control data and payload data
are required t o be accumulated and therefore the next three subframes are then buffered in the
window 1002. The window then moves o r slides by one subframe as each subframe is received as
represented by windows 1003 and 1004, where a movement of one subframes represents the oldest
received signals from a subframe being replaced in the buffer memory by relevant signals received
from the most recent subframe. During the window represented by 1004, three instances of the
PDCCH and PDSCH signals that include signals representing the user device control data 1005 and
payload data 1006 have been stored and accumulated. Therefore the control data and the payload
data may be detected and estimated, and the current accumulation procedure halted. The point at
which a required number of repetitions have been stored may be indicated by the accumulated
signals passing an amplitude threshold for example o r substantially error-free decoding of the
transmitted data.
Although embodiments of the present technique have been described with reference to the
physical channels PDCCH and PDSCH of an LTE wireless communications interface, embodiments
may also be applied to other physical channels of an LTE system, either individually or in
combination with other channels. Likewise, although embodiments have been described with
reference t o a LTE systems and wireless access interfaces, embodiments of the present technique
are not limited t o LTE systems and may be implemented in any systems which have wireless access
resources divided into temporal periods and or resources which may be divided up for the provision
of a multiple access interface. Similarly, different repetition techniques and or combining techniques
t o those described above may also be used in conjunction with embodiments of the present
technique.
Various further aspects and features of the present technique are defined in the appended
claims and various combinations of the features of the dependent claims may be made with those of
the independent claims other than the specific combinations recited for the claim dependency.
Modifications may also be made t o the embodiments hereinbefore described without departing
from the scope of the present invention. For instance, although a feature may appear to be
described in connection with particular embodiments, one skilled in the art would recognise that
various features of the described embodiments may be combined in accordance with the disclosure.
The following numbered clauses provide further aspects and examples of the present
disclosure:

CLAIMS
1. A communications system comprising an infrastructure equipment for forming part
of a mobile communications network arranged to transmit and receive data t o and from a user
device via a wireless access interface, the wireless access interface being provided by the
infrastructure equipment using a plurality of Orthogonal Frequency Division Multiplexing (OFDM)
subcarriers, the plurality of OFDM subcarriers extending across a first bandwidth, and the
infrastructure equipment is configured
to transmit repeatedly signals representing a same instance of user device payload data in a
second bandwidth, the second bandwidth being less than and within the first bandwidth and
including a subset of the OFDM subcarriers,
and user device is configured
to receive one or more of the signals repeatedly transmitted across the second bandwidth,
to store in a memory signals representing the repeatedly transmitted signals received across
the second bandwidth,
to combine the stored signals, and
to detect the user device payload data from the combined signals, the user device having
been provided with an indication of the second bandwidth.
2. A communications system according to clause 1, wherein the infrastructure
equipment is configured
to transmit repeatedly signals representing a same instance of user device control data in
the first bandwidth, the user device control data providing an indication of a location of the signals
representing the user device payload data in the second bandwidth, and the user device is
configured
to receive one or more of the signals representing the user device control data repeatedly
transmitted across the first bandwidth,
to store in the memory signals representing the repeatedly transmitted signals received
across the first bandwidth,
to combine the stored signals representing the repeatedly transmitted signals received
across the first bandwidth, and
to detect the user device control data from the combined signals representing the
repeatedly transmitted signals received across the first bandwidth, the detection of the user device
payload data from the combined signals received across the second bandwidth being based on the
indication of the location of the signals representing the user device payload data in the second
bandwidth.
3. A communications system according to clauses 1 or 2, wherein the wireless access
interface provided by the plurality of OFDM subcarriers is divided into a plurality of time periods and
the repeated signals representing the user device payload data are transmitted in a same set of
resources of the wireless access interface in a first time period and in a second time period.
4. A communications system according to clause 2, wherein the infrastructure
equipment is configured to transmit the indication of the second bandwidth to the user device prior
t o the repeated transmissions of the signals representing the user device control data.
5. A communications system according to any of clauses 1 t o 4, wherein the user
device is configured to receive user device payload data within a virtual carrier of a predetermined
bandwidth, the second bandwidth being approximately equal to the predetermined bandwidth, and
the predetermined bandwidth includes a set of the OFDM subcarriers that is substantially similar to
the OFDM subcarriers that form the subset of the OFDM subcarriers included in the second
bandwidth.
6. A communications system according t o any of claims 1 to 5, wherein the
communication system operates in accordance with 3GPP LTE.
7. A communications system according to any of clauses 1 t o 6, wherein a number of
repeated transmissions of signals representing the user device payload data is greater than a
number of repeated transmissions of the signals representing the user device control data.
8. An infrastructure equipment for forming part of a mobile communications network
arranged t o transmit and to receive data to and from a user device via a wireless access interface,
the wireless access interface being provided by the infrastructure equipment using a plurality of
Orthogonal Frequency Division Multiplexing (OFDM) subcarriers, the plurality of OFDM subcarriers
extending across a first bandwidth, and the infrastructure equipment is configured
to transmit repeatedly signals representing a same instance of user device payload data in a
second bandwidth, the second bandwidth being less than and within the first bandwidth and
including a subset of the OFDM subcarriers
9. An infrastructure equipment according to clause 8, wherein the infrastructure
equipment is configured
t o transmit repeatedly signals representing a same instance of user device control data in
the first bandwidth, the user device control data providing an indication of a location of the signals
representing the user device payload data in the second bandwidth
10. A method of transmitting and receiving data in a communications system comprising
an infrastructure equipment for forming part of a mobile communications network arranged to
transmit and t o receive data t o and from a user device via a wireless access interface, the wireless
access interface being provided by the infrastructure equipment using a plurality of Orthogonal
Frequency Division Multiplexing (OFDM) subcarriers, the plurality of OFDM subcarriers extending
across a first bandwidth, and the method comprising
transmitting repeatedly signals representing a same instance of user payload data in a
second bandwidth from the infrastructure equipment, the second bandwidth being less than and
within the first bandwidth and including a subset of the OFDM subcarriers;
receiving one or more of the repeatedly transmitted signals across the second bandwidth at
the user device,
storing in a memory signals representing the repeatedly transmitted signals received across
the second bandwidth at the user device,
combining the stored signals at the user device, and
detecting the user device payload data from the combined signals at the user device, the
user device having been provided with an indication of the second bandwidth.
11. A method according t o clause 10, the method comprising
transmitting repeatedly signals representing a same instance of user device control data in
the first bandwidth from the infrastructure equipment, the user device control data providing an
indication of a location of the signals representing the user device payload data in the second
bandwidth,
receiving one or more of the signals representing the user device control data repeatedly
transmitted across the first bandwidth at the user device,
storing in the memory signals representing the repeatedly transmitted signals received
across the first bandwidth,
combining the stored signals representing the repeatedly transmitted signals received across
the first bandwidth, and
detecting the user device control data from the combined signals representing the
repeatedly transmitted signals received across the first bandwidth, the detection of the user device
payload data from the combined signals received across the second bandwidth being based on the
indication of the location of the signals representing the user device payload data in the second
bandwidth.
12. A method of transmitting data from an infrastructure equipment for forming part of
a mobile communications network arranged to transmit and receive data to and from a user device
via a wireless access interface, the wireless access interface being provided by the infrastructure
equipment using a plurality of Orthogonal Frequency Division Multiplexing (OFDM) subcarriers, the
plurality of OFDM subcarriers extending across a first bandwidth, the method comprising
transmitting repeatedly signals representing a same instance of user device payload data in
a second bandwidth, the second bandwidth being less than and within the first bandwidth and
including a subset of the OFDM subcarriers.
13. A method according t o clause 12, the method comprising
transmitting repeatedly signals representing a same instance of user device control data in
the first bandwidth from the infrastructure equipment, the user device control data providing an
indication of a location of the signals representing the user device payload data in the second
bandwidth.
Claims
1. A communications system comprising an infrastructure equipment for forming part
of a mobile communications network arranged t o transmit and receive data to and from a user
device via a wireless access interface, the wireless access interface being provided by the
infrastructure equipment using a plurality of Orthogonal Frequency Division Multiplexing (OFDM)
subcarriers, the plurality of OFDM subcarriers extending across a first bandwidth, and the
infrastructure equipment is configured
to transmit repeatedly signals representing a same instance of user device payload data in a
second bandwidth, the second bandwidth being less than and within the first bandwidth and
including a subset of the OFDM subcarriers,
and user device is configured
t o receive one or more of the signals repeatedly transmitted across the second bandwidth,
t o store in a memory signals representing the repeatedly transmitted signals received across
the second bandwidth,
t o combine the stored signals, and
t o detect the user device payload data from the combined signals, the user device having
been provided with an indication of the second bandwidth.
2. A communications system as claimed in Claim 1, wherein the infrastructure
equipment is configured
t o transmit repeatedly signals representing a same instance of user device control data in
the first bandwidth, the user device control data providing an indication of a location of the signals
representing the user device payload data in the second bandwidth, and the user device is
configured
t o receive one or more of the signals representing the user device control data repeatedly
transmitted across the first bandwidth,
to store in the memory signals representing the repeatedly transmitted signals received
across the first bandwidth,
t o combine the stored signals representing the repeatedly transmitted signals received
across the first bandwidth, and
t o detect the user device control data from the combined signals representing the
repeatedly transmitted signals received across the first bandwidth, the detection of the user device
payload data from the combined signals received across the second bandwidth being based on the
indication of the location of the signals representing the user device payload data in the second
bandwidth.
3. A communications system as claimed in Claim 1, wherein the wireless access
interface provided by the plurality of OFDM subcarriers is divided into a plurality of time periods and
the repeated signals representing the user device payload data are transmitted in a same set of
resources of the wireless access interface in a first time period and in a second time period.
4. A communications system as claimed in claim 2, wherein the infrastructure
equipment is configured t o transmit the indication of the second bandwidth to the user device prior
t o the repeated transmissions of the signals representing the user device control data.
5. A communications system as claimed in Claim 1, wherein the user device is
configured t o receive user device payload data within a virtual carrier of a predetermined
bandwidth, the second bandwidth being approximately equal t o the predetermined bandwidth, and
the predetermined bandwidth includes a set of the OFDM subcarriers that is substantially similar t o
the OFDM subcarriers that form the subset of the OFDM subcarriers included in the second
bandwidth.
6. A communications system as claimed in Claim 1, wherein the communication system
operates in accordance with 3GPP LTE.
7. A communications system as claimed in Claim 1 , wherein a number of repeated
transmissions of signals representing the user device payload data is greater than a number of
repeated transmissions of the signals representing the user device control data.
8. An infrastructure equipment for forming part of a mobile communications network
arranged t o transmit and t o receive data t o and from a user device via a wireless access interface,
the wireless access interface being provided by the infrastructure equipment using a plurality of
Orthogonal Frequency Division Multiplexing (OFDM) subcarriers, the plurality of OFDM subcarriers
extending across a first bandwidth, and the infrastructure equipment is configured
to transmit repeatedly signals representing a same instance of user device payload data in a
second bandwidth, the second bandwidth being less than and within the first bandwidth and
including a subset of the OFDM subcarriers.
9. An infrastructure equipment as claimed in Claim 8, wherein the infrastructure
equipment is configured
to transmit repeatedly signals representing a same instance of user device control data in
the first bandwidth, the user device control data providing an indication of a location of the signals
representing the user device payload data in the second bandwidth.
10. A method of transmitting and receiving data in a communications system comprising
an infrastructure equipment for forming part of a mobile communications network arranged to
transmit and t o receive data t o and from a user device via a wireless access interface, the wireless
access interface being provided by the infrastructure equipment using a plurality of Orthogonal
Frequency Division Multiplexing (OFDM) subcarriers, the plurality of OFDM subcarriers extending
across a first bandwidth, and the method comprising
transmitting repeatedly signals representing a same instance of user payload data in a
second bandwidth from the infrastructure equipment, the second bandwidth being less than and
within the first bandwidth and including a subset of the OFDM subcarriers;
receiving one or more of the repeatedly transmitted signals across the second bandwidth at
the user device,
storing in a memory signals representing the repeatedly transmitted signals received across
the second bandwidth at the user device,
combining the stored signals at the user device, and
detecting the user device payload data from the combined signals at the user device, the
user device having been provided with an indication of the second bandwidth.
11. A method as claimed in Claim 10, the method comprising
transmitting repeatedly signals representing a same instance of user device control data in
the first bandwidth from the infrastructure equipment, the user device control data providing an
indication of a location of the signals representing the user device payload data in the second
bandwidth,
receiving one or more of the signals representing the user device control data repeatedly
transmitted across the first bandwidth at the user device,
storing in the memory signals representing the repeatedly transmitted signals received
across the first bandwidth,
combining the stored signals representing the repeatedly transmitted signals received across
the first bandwidth, and
detecting the user device control data from the combined signals representing the
repeatedly transmitted signals received across the first bandwidth, the detection of the user device
payload data from the combined signals received across the second bandwidth being based on the
indication of the location of the signals representing the user device payload data in the second
bandwidth.
12. A method of transmitting data from an infrastructure equipment for forming part of
a mobile communications network arranged to transmit and receive data to and from a user device
via a wireless access interface, the wireless access interface being provided by the infrastructure
equipment using a plurality of Orthogonal Frequency Division Multiplexing (OFDM) subcarriers, the
plurality of OFDM subcarriers extending across a first bandwidth, the method comprising
transmitting repeatedly signals representing a same instance of user device payload data in
a second bandwidth, the second bandwidth being less than and within the first bandwidth and
including a subset of the OFDM subcarriers.
13. A method as claimed in Claim 12, the method comprising
transmitting repeatedly signals representing a same instance of user device control data in
the first bandwidth from the infrastructure equipment, the user device control data providing an
indication of a location of the signals representing the user device payload data in the second
bandwidth.
14. A communications system as substantially hereinbefore described with reference to
the accompanying drawings.
15. An infrastructure equipment as substantially hereinbefore described with reference
to the accompanying drawings.