POWER DENSITY BOOSTING IN UPLINK SHARED CHANNELS
TECHNICAL FIELD OF THE DISCLOSURE
The present disclosure relates communications devices, infrastructure equipment for mobile
communications networks, mobile communications networks and systems and methods of transmitting
and receiving data via mobile communications networks.
BACKGROUND OF THE DISCLOSURE
Mobile communications systems continue to be developed to provide wireless
communications services to a greater variety of electronic devices. In more recent years, third and
fourth generation mobile telecommunication systems, such as those based on the 3GPP defined UMTS
and Long Term Evolution (LTE) architectures have been developed to support more sophisticated
communications services to personal computing and communications devices 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
may 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.
More recently it has been recognised that rather than providing high data rate communications
services to certain types of electronics devices, it is also desirable to provide communications services
to electronics devices that are simpler and less sophisticated. For example, so-called machine type
communication (MTC) applications may be semi-autonomous or autonomous wireless communication
devices which may communicate small amounts of data on a relatively infrequent basis. Some
examples include so-called smart meters which, for example, are 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. Other examples include applications
to automotive technology and medical devices
As will be appreciated it is desirable to provide arrangements for reducing power consumption
and therefore increasing battery life of communications devices operating to communicate data via
mobile communications networks.
SUMMARY OF THE DISCLOSURE
Embodiments of the present disclosure can provide in one example a communications device,
which transmits data to or receives data from a mobile communications network. The mobile
communications network includes one or more network elements which are arranged to form a
wireless access interface for transmitting and receiving the data. The communications device
comprises a transmitter unit configured to transmit signals representing the data on an up-link of the
wireless access interface to the mobile communications network and a receiver unit configured to
receive signals representing the data transmitted on a down-link from the mobile communications
network via the wireless access interface. The wireless access interface provides a plurality of
communications resource elements across a frequency range for the down-link and the up-link, the
communications resource elements being formed by dividing sub-carriers at different frequencies into
a plurality of time periods, one or more of the sub-carriers being provided to form, in the time
domain, frequency division multiplexed symbols, each of the time periods comprising a predetermined
number of the frequency division multiplexed symbols. The up-link includes a shared channel
providing the communications resources for allocation to the communications device by the mobile
communications network for transmitting the data on the up-link to the mobile communications
network. The shared channel provides communications resources which are shared with other
communications terminals and comprising in the time domain, the predetermined number of frequency
division multiplexed symbols in each time period for allocation to the communications device. A
controller is configured to control the transmitter unit to transmit the signals and the receiver unit to
receive the signals to transmit or receive the data. The controller is configured to control the
transmitter unit and the receiver unit to transmit to the mobile communications network a request to
transmit data in a smaller number of frequency division multiplexed symbols than are available on the
shared channel, to receive from the mobile communications network an indication of a sub-set of the
predetermined number of frequency division multiplexed symbols in which the communications
device should transmit the data on the shared channel, and to transmit signals representing the data in
the shared channel to occupy a smaller number of frequency division multiplexed symbols than the
number of the predetermined number of frequency division multiplexed symbols of the time period of
the shared channel.
By reducing a number of frequency division multiplexed symbols on which the signalling
information is transmitted in the control channel to be less than the predetermined number of symbols
available on the shared channel, embodiments of the present disclosure can provide a corresponding
reduction in power consumed by the communications device. Accordingly there is an improvement in
the battery life of the communications device. The term frequency division multiplexed symbols is
used to describe a time and frequency division multiplexing technique such as OFDM or SC-FDMA
which modulates sub-carriers on the frequency domain and forms symbols from the modulated subcarriers
in the time domain.
In one example, the controller is configured to transmit the signals representing the signalling
information in the smaller number of frequency division multiplexed symbols within the time period
of the shared channel starting at a different one of the predetermined number of frequency division
multiplexed symbols. Each of the different starting frequency division multiplexed symbols represents
further information, which may in one example form part of the signalling information. Therefore by
providing a variation in the starting position of the signals representing the signalling information in a
smaller number of the predetermined number of frequency division multiplexed symbols the reduction
in communications capacity provided by the reduction in the number of symbols can be compensated
by increasing the data signalling capacity. This is achieved by varying the starting position of the
transmission of the signalling information.
Embodiments of the present technique can also be applied to the transmission of data in a
control channel of a mobile communications network. In one example there is provided a
communications device for transmitting data to or receiving data from a mobile communications
network. The mobile communications network includes one or more network elements which are
arranged to form a wireless access interface for transmitting and receiving the data. The
communications device comprises a transmitter unit configured to transmit signals representing the
data on an up-link of the wireless access interface to the mobile communications network and a
receiver unit configured to receive signals representing the data transmitted on a down-link from the
mobile communications network via the wireless access interface. The wireless access interface
provides a plurality of communications resource elements across a frequency range for the down-link
and the up-link, the communications resource elements being formed by dividing sub-carriers at
different frequencies into a plurality of time periods, one or more of the sub-carriers being provided to
form, in the time domain, frequency division multiplexed symbols, each of the time periods
comprising a predetermined number of the frequency division multiplexed symbols. The up-link
includes a control channel for transmitting signalling information from the communications device to
the mobile communications network in accordance with a predetermined format in which signals
which representing the signalling information occupy, in the time domain, the predetermined number
of frequency division multiplexed symbols of the control channel. A controller is configured to
control the transmitter unit to transmit the signals and the receiver unit to receive the signals to
transmit or receive the data. The controller is configured to adapt the transmission of the signals
representing the signalling information transmitted, by the transmitter unit, in the control channel to
occupy a smaller number of the predetermined number of frequency division multiplexed symbols of
the time period of the control channel.
In some examples the communications devices are reduced capability devices such as MTC
devices, such as smart meters or medical devices.
Various further aspects and embodiments of the disclosure are provided in the appended
claims, including but not limited to, an infrastructure equipment (or network element of a mobile
communications network), a communications device and method of communicating to a
communications device using a mobile communications network element.
BRIEF DESCRIPTION OF DRAWINGS
Embodiments of the present disclosure will now be described by way of example only with
reference to the accompanying drawings in which like parts are provided with corresponding reference
numerals and in which:
Figure 1 provides a schematic diagram illustrating an example of a conventional mobile
communications system;
Figure 2 provides a schematic diagram illustrating an arrangement of channels of a wireless
access interface for ten down-link sub-frames of a conventional LTE wireless access interface;
Figure 3 provides a schematic diagram illustrating a conventional LTE downlink radio subframe;
Figure 4 provides a schematic illustration of an example arrangement for an uplink shared
channel (PUSCH) with DM-RS symbols and normal or extended cyclic-prefix operation;
Figure 5 is a schematic illustration of a sub-frame illustrating a position of uplink control
channels, PUCCH, and an up-link shared channel, PUSCH within one sub-frame of an up-link;
Figure 6 is a schematic block diagram illustrating the formation of a PUCCH format 1/la/lb;
Figure 7 is a schematic block diagram illustrating an arrangement for forming a PUCCH
format 2/2a/2b;
Figure 8a is a schematic illustration of a transmission of signals within a control channel in
accordance with one example of the present technique; and Figure 8b is a schematic illustration of the
transmission of signals within a control channel in accordance with another example of the present
technique;
Figure 9 is a part schematic block diagram part flow diagram illustrating operations performed
by a controller to generate signal transmissions in accordance with the present technique;
Figure 10a is a schematic illustration showing an arrangement for transmissions of signals
within a time slot of a sub-frame in a reduced number of frequency division multiplexed symbols (SCFDMA)
symbols and in which a DM-RS symbol is transmitted in a first position A; Figure 10b
provides a corresponding schematic illustration showing an arrangement for transmission of signals in
which the DM-RS symbol is in a second position B;
Figure 11 is a schematic representation showing an example of an up-link control channel
(PUCCH) transmission distributed across two physical resource blocks;
Figure 12 is a schematic representation of a sub-frame in which transmissions of signals
representing data in an uplink shared channel (PUSCH) is varied within a smaller number of frequency
division multiplexed (SC-FDMA) symbols in accordance with the present technique;
Figure 13a is a part schematic block diagram part flow diagram illustrating the transmission of
permitted reduced timeslot formats within the PUSCH using a broadcast channel; Figure 13b is a part
schematic part flow diagram illustrating an arrangement in which a reduced capability device indicates
to the eNodeB its desire to transmit signals representing data in a shared channel using a smaller
number of frequency division multiplexed (SC-FDMA) symbols than are available; Figure 13c is a
part schematic block diagram part flow diagram illustrating a further example arrangement in which a
PRACH is used to signal a smaller number of frequency division multiplexed symbols which can be
used by a communications device to transmit data on the shared channel; and Figure 13d is a
corresponding part schematic part flow diagram illustrating a conventional transmission on a PRACH
followed by the grant of a communications resource with an indication of the format which can be
used to transmit signals in a smaller number of frequency division multiplexed (SC-FDMA) symbols
than are available;
Figure 14 is a schematic block diagram of an example mobile communications system
according to an example embodiment of the present technique;
Figure 15 is a flow diagram illustrating the operation of a communications device transmitting
in a control channel in accordance with the present technique; and
Figure 16 is a flow diagram illustrating the operation of a communications device transmitting
data in a shared channel in accordance with the present technique.
DESCRIPTION OF EXAMPLE EMBODIMENTS
Example Network
Figure 1 provides a schematic diagram illustrating the basic functionality of a conventional
mobile communications system. In Figure 1, a mobile communications network 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 communications devices 104. Data is
transmitted from a base station 101 to a communications device 104 within a coverage area 103 via a
radio downlink. Data is transmitted from a communications device 104 to a base station 101 via a
radio uplink. The core network 102 routes the data to and from the base stations 104 and provides
functions such as authentication, mobility management, charging and so on. The base stations 101
provide a wireless access interface comprising the radio uplink and the radio downlink for the
communications devices and form examples of infrastructure equipment or network elements for the
mobile communications network, and may be, for the example of LTE, an enhanced Node B (eNodeB
or eNB).
The term communications devices will be used to refer to a communications terminal or
apparatus which can transmit or receive data via the mobile communications network. Other terms
may also be used for communications devices such as personal computing apparatus, remote terminal,
transceiver device or user equipment (UE) which may or may not be mobile.
Example Down-link Configuration
Mobile telecommunications systems such as those arranged in accordance with the 3GPP
defined Long Term Evolution (LTE) architecture use an orthogonal frequency division multiplexing
(OFDM) based radio access interface for the radio downlink (so-called OFDMA) and the radio uplink
(so-called SC-FDMA). Data is transmitted on the radio uplink and on the radio downlink on a plurality
of orthogonal sub-carriers. 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 and
lasts 10 ms. The downlink radio frame comprises ten sub-frames, each sub-frame lasting 1 ms, and
each sub-frame comprises two slots, each slot lasting 0.5ms. A primary synchronisation signal (PSS)
and a secondary synchronisation signal (SSS) are transmitted in the first and sixth sub-frames
(conventionally numbered as sub-frame 0 and 5) of the LTE frame, in the case of frequency division
duplex (FDD) system. A physical broadcast channel (PBCH) is transmitted in the first sub-frame of
the LTE frame. The PSS, SSS and PBCH are discussed in more detail below.
Figure 3 provides a schematic diagram providing a grid which illustrates the structure of an
example of a conventional downlink LTE sub-frame. The sub-frame 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 sub-frame shown in Figure 3 comprises 14 symbols and 1200 sub-carriers
spaced across a 20MHz bandwidth. The smallest unit on which data can be transmitted in LTE is
twelve sub-carriers transmitted over one slot. For clarity, in Figure 3, each individual resource element
is not shown, but instead each individual box in the sub-frame grid corresponds to twelve sub-carriers
transmitted on one symbol.
Figure 3 shows resource allocations for four communications devices 340, 341, 342, 343. For
example, the resource allocation 342 for a first communications device (UE 1) extends over five
blocks of twelve sub-carriers, the resource allocation 343 for a second communications device (UE2)
extends over six blocks of twelve sub-carriers and so on.
Control channel data is transmitted in a control region 300 of the sub-frame comprising the
first n symbols of the sub-frame 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. 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).
The PDCCH contains control data indicating which sub-carriers on which symbols of the subframe
have been allocated to specific communications devices (UEs). Thus, the PDCCH data
transmitted in the control region 300 of the sub-frame shown in Figure 3 would indicate that UE1 has
been allocated the first block of resources 342, that UE2 has been allocated the second block of
resources 343, and so on. In sub-frames where it is transmitted, the PCFICH contains control data
indicating the duration of the control region in that sub-frame (i.e. between one and four symbols) and
the PHICH contains HARQ (Hybrid Automatic Request) data indicating whether or not previously
transmitted uplink data has been successfully received by the network.
In certain sub-frames, symbols in a central band 310 of the sub-frame are used for the
transmission of information including the primary synchronisation signal (PSS), the secondary
synchronisation signal (SSS) and the physical broadcast channel (PBCH) mentioned above. 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 sequences that once detected allow a communications
device 104 to achieve frame synchronisation and determine the cell identity of the base station
(eNodeB) transmitting the downlink signal. The PBCH carries information about the cell, comprising
a master information block (MIB) that includes parameters that the communications devices require to
access the cell. The data transmitted to individual communications devices on the physical downlink
shared channel (PDSCH) can be transmitted in the remaining blocks of communications resource
elements of the sub-frame.
Figure 3 also shows a region of PDSCH containing system information and extending over a
bandwidth of R344. Thus in Figure 3 the central frequency carries control channels such as the PSS,
SSS and PBCH and therefore implies a minimum bandwidth of a receiver of a communications
device.
The number of sub-carriers in an LTE channel can vary depending on the configuration of the
transmission network. Typically this variation is from 72 sub carriers contained within a 1.4MHz
channel bandwidth to 1200 sub-carriers contained within a 20MHz channel bandwidth as shown in
Figure 3. As is known in the art, subcarriers carrying data transmitted on the PDCCH, PCFICH and
PHICH are typically distributed across the entire bandwidth of the sub-frame. Therefore a
conventional communications device must be able to receive the entire bandwidth of the sub-frame in
order to receive and decode the control region.
Example Up-Link Configuration
PUSCH Structure
According to an example embodiment the up-link of a wireless access interface which
operates in accordance with LTE is under the control of the eNodeB, which receives buffer status
reports (BSR) from UEs to aid scheduling decisions. As with the down-link, the up-link includes a
communications channel which provides shared resource known as a physical up-link shared channel
(PUSCH) providing resources, which are granted in downlink control information (DCI) messages
sent on PDCCH. Communications resources are granted to UEs on a resource block group (RBG)
basis, where an RBG can contain two, three or five RBs. The grant of PUSCH resources are in
contiguous frequency resources to allow transmission with a low cubic metric since this improves
power amplifier efficiency. The exception to this is that, from LTE Rel-10, PUSCH may be granted in
two separate 'clusters', with each cluster being individually in contiguous frequency resources. More
details can be found relevant 3GPP specifications, for example TS 36.211, TS 36.212, TS 36.213 and
TS 36.331.
The eNodeB can sound the uplink channel by configuring the UE to send a sounding reference
signal (SRS), described below. If the bandwidth and quality of the SRS are sufficient, the eNodeB can
use frequency- selective scheduling for PUSCH where the same resource blocks are typically used in
both slots of a sub-frame. This is rational since the eNodeB has good knowledge of which resources
are best for the UE across a wide bandwidth. Alternatively, if the SRS quality is not good enough (or
no SRS are configured), then LTE supports frequency-diverse scheduling (also known as frequency
non-selective scheduling). In this case, two frequency-hopping options are available to automatically
exploit the frequency diversity of the channel:
· Inter-sub-frame hopping where the resource allocation frequency hops between the r e
transmissions of a HARQ process. This gives frequency diversity among the re-transmissions.
• Intra- and inter-sub-frame hopping where the resource allocation frequency hops at the slot
boundary and also between the re-transmissions of a HARQ process. This gives frequency
diversity within a single transmission of a transport block as well as between the retransmissions.
The hopping mode which is used is broadcast within the cell. In both cases, the hopping can
be in a pre-determined pseudo-random pattern configured by the radio resource control (RRC) or via
an explicit hopping offset signalled along with the Up-link resource grant on PDCCH.
Figure 4 provides an example representation of an uplink frame structure. As shown in Figure
4, each frame of the uplink is comprised of 10 sub-frames in correspondence with the downlink. Each
of these sub-frames is comprised of two time slots 401, 402. Each slot is comprised of seven symbols
in the time domain, and in the frequency domain each of the symbols provides a plurality of
subcarriers which are assigned to the same UE. The resource blocks are assigned in the frequency
domain on the basis of 12 subcarriers so that a UE may be assigned Nxl2 subcarriers in the frequency
domain. Typically, in accordance with a conventional operation, a UE is assigned all of the seven
symbols in the time slot 401, 402. As shown in Figure 4, two examples 404, 406 represent the symbols
in each slot which include the PUSCH 408 which, as explained above provides shared physical
channel for uplink resources and a modulation reference symbol (DM-RS) 410. Each of the symbols
in the time slot includes a cyclic-prefix CP 412 which in correspondence with the principles of OFDM
operation provides a repetition of the samples from the wanted channel in a guard period in order to
allow for inter-symbol interference.
DM-RS for PUSCH
The demodulation of reference symbols (DM-RS) 410 for the PUSCH are transmitted only in
RBs for which the PUSCH has been granted. They occur in every time slot 401, 402 and for normal
cyclic prefix operation, DM-RS occupy the fourth SC-FDMA symbol as shown in the first example
representation 404 while for extended cyclic prefix operation, as shown in the second example 406
they occupy the third SC-FDMA symbol, as illustrated in Figure 4.
The sequence length for DM-RS is equal to the number of subcarriers allocated to PUSCH for
this UE, and 12 cyclic time shifts are supported on a DM-RS SC-FDMA symbol to allow orthogonal
multiplexing for e.g. multi-user MIMO. If a multi-clustered PUSCH is in use, a sequence of the length
of the total number of allocated subcarriers is generated, and is split between the two clusters for
transmission.
Figure 5 provides a representation of the structure of a sub-frame for the uplink in the
frequency domain. As indicated above each sub-frame is comprised of two time slots 401, 402 within
which there is transmitted seven symbols in the time domain and in the frequency domain each symbol
is comprised of sub-carriers allocated to the same UE on the basis of Nxl2 subcarriers. However
Figure 5 is a simplified presentation of the up-link which does not shown the transmission of
individual symbols, but shows an example implementation of an uplink control channel which for the
example of LTE would be the physical uplink control channel (PUCCH).
PUCCH Structure
As shown in Figure 5 resource blocks which are allocated to a UE from the shared physical
channel PUSCH occupy a central portion of the frequency band 420 whereas the PUCCH is formed at
the edges of the frequency band 422, 424. A PUCCH region is therefore two RBs, one in each slot of
a sub-frame, which are positioned close to opposite ends of the system bandwidth. Precisely which
RBs a PUCCH is allocated depends on the uplink control information (UCI) it is carrying (the socalled
'format' of the PUCCH) and on how many RBs the eNodeB allocates in total for PUCCH in a
sub-frame. Unlike the PUSCH and the PDSCH, for the example implementation of LTE, the resources
for PUCCH are not signalled explicitly on PDCCH, but are instead signalled by RRC configuration
combined, in some cases, with implicit information relating to the location of PDCCH. The RRC
configuration itself is partly cell-specific and partly UE-specific, which parts depending on the format.
For the example of LTE networks, in Rel-8 and Rel-9, a UE never has PUSCH and PUCCH in
the same sub-frame to preserve the low cubic-metric of the transmission. Therefore, when UCI is to be
transmitted in a sub-frame where the UE is to have PUSCH, the UCI is multiplexed onto PUSCH and
PUCCH is not sent. From Rel-10, simultaneous PUSCH and PUCCH can be configured.
As shown in Figure 5, the PUCCH is comprised of different formats. The PUCCH formats
convey UCI as follows:
· Format 1: Scheduling Request (SR)
• Format 1a : 1-bit HARQ ACK/NACK with or without SR
• Format lb: 2-bit HARQ ACK/NACK with or without SR
• Format 2 : CSI in 20 coded bits (with 1- or 2-bit HARQ ACK/NACK in extended CP)
• Format 2a: CSI and 1-bit HARQ ACK/NACK
· Format 2b: CSI and 2-bit HARQ ACK/NACK
• Format 3: Multiple ACK/NACKs for carrier aggregation with optional SR
The order in which the various PUCCH formats are mapped to RBs in a sub-frame with
multiple PUCCH formats is shown in Figure 5, with 2/2a/2b at the band edge, followed by a mixedformat
PUCCH (if present) and then 1/la/lb. The number of PUCCH regions available for 2/2a/2b is
broadcast in the cell.
The Format 3 is configured from among the PUCCH regions which may be allocated to
format 2. The eNodeB scheduler ensures that the regions occupied by PUCCH formats 2/2a/2b and 3
do not overlap.
DM-RS for PUCCH
The DM-RS are transmitted separately for the PUCCH and PUSCH. As for the PUSCH, they
are transmitted only in RBs for which a UE has PUCCH configured, and they occur in every such slot.
DM-RS occupy different SC-FDMA symbols depending on the PUCCH format. An example of such
an arrangement is shown in Figure 6, in which the transmission of format 1/la/lb and its DM-RS for
normal cyclic prefix operation is presented. As shown in Figure 6 for example the PUCCH is
arranged to transmit an ACK/NACK symbol to the eNodeB which is a typical example of control
information transmitted by the UE on the PUCCH. The ACK/NACK symbol 450 is multiplied by a
receiver spreading code rO of length- 12 by a multiplier 452 before the signal is fed to each of seven
cyclic-prefix formers 454. The cyclic-shifters 454 serve to shift the samples of the ACK/NACK
symbol using a Zadoff-Chu sequence. Each of the signals from the cyclic-shifters 454 are received by
a multiplier 456 and multiplied by a coefficient of a Walsh-Hadamard sequence in order to spread the
spectrum of the ACK/NACK symbol 450 within the time-slot 401, 402. The outputs from the
multipliers 456 are fed to an inverse Fourier transformer (IFFT) 458 which convert the sub-carriers
which are formed in the frequency domain for the symbol into the time domain and transmitted as a
symbol of the PUCCH within the timeslot 401, 402. As shown in Figure 6 the timeslot 401, 402
comprises four PUCCH symbols, two each at either end of the time-slot 460, 462 and a central portion
464 provides three DM-RS symbols. Therefore for this example, there are three symbols carrying
DM-RS, and the time slot carrying the single ACK/NACK symbol 450 is repeated with cyclic timeshifts
and a Walsh-Hadamard code on the remaining SC-FDMA symbols. The UE is therefore able to
code division multiplex the transmission of the ACK/NACK symbol 450 using the cyclic shifts and
Walsh-Hadamard codes. Therefore each UE sending PUCCH format 1/la/lb in the same PUCCH
region uses a different combination of Walsh-Hadamard code and cyclic shifts of a base Zadoff-Chu
sequence.
A further example of the PUCCH in format 2 is shown in Figure 7. Figure 7 provides an
example in which channel state information (CSI) is a further example of control information which is
transmitted in the PUCCH. The CSI comprises ten coded bits 480, which are fed to a QPSK
modulator 482, which serves to form the ten coded CSI bits into five QPSK symbols. Thus format 2
uses QPSK modulation which carry two bits per modulation symbol. The QPSK modulator 482 forms
five QPSK symbols dO, dl, d2, d3 and d4 for transmission on five PUCCH symbols 490, 492, 494,
496, 498. Each of the five QPSK symbols are fed to a multiplier 484 which multiplies each of the five
QPSK symbols by a length 12 spreading code, such as the Walsh-Hadamard sequence as for the above
example. The output from multipliers 484 are fed to a cyclic-shifter and an inverse Fourier transformer
(IFFT) 486, which serve to cyclically shift the spread spectrum QPSK symbols by a cyclic shift code
and form the SC-FDMA symbols in the time domain by performing an inverse Fourier transform.
Thus each of the five PUCCH symbols 490, 492, 494, 496, 498 are formed into the time domain and
transmitted with two DM-RS symbols 499, 500. As shown in Figure 7, three of the PUCCH symbols
form a central part of the timeslot 401 and two are transmitted at each end of the timeslot with the
DM-RS symbols 499, 500 interposed between the three semper central PUCCH symbols and the two
edge PUCCH symbols.
For the example transmission of format 2/2a/2b illustrated in Figure 7, it is necessary to carry
more control information (UCI data), so there are fewer RS and the coded CSI is QPSK modulated
before being spread symbol-wise onto the remaining SC-FDMA symbols. Therefore a UE multiplexes
the control information with other UEs in format 2 using the cyclic shifts, in which each UE sending
PUCCH format 2/2a/2b in the same PUCCH region uses a different set of cyclic shifts of a base
Zadoff-Chu sequence.
For the further example of Format 3, which is used to transmit control information, this format
provides for transmitting the same time-domain pattern as format 2/2a/2b. The baseband processing is
a hybrid of formats 1 and 2 with the addition of phase shifts on the repetitions, and it is not based on
Zadoff-Chu sequences. It is not set out in detail here since it is not used in the example embodiments
of the invention.
SRS structure
The sounding reference signal (SRS) can be configured by the eNodeB to allow sounding of
the Up-link channel in order to facilitate, e.g., frequency-selective scheduling. SRS can be configured
across any bandwidth, but since a UE is typically power limited, it may be that only a limited
bandwidth can be sounded with sufficient quality in one transmission. The full details of SRS
configuration are not described in detail here. However the salient points are:
· SRS are always transmitted in the final SC-FDMA symbol of a sub-frame in which a UE is
configured to send them.
• SRS can be configured on a periodic basis, or they can be triggered by eNodeB.
• There is a cell-specific RRC configuration amounting to telling all UEs the sub-frames in
which periodic SRS may occur from any UE in the cell. No UE sends PUSCH or PUCCH in
the relevant SC-FDMA symbols.
• There is a UE-specific RRC configuration of the periodic sub-frame pattern the UE shall send
SRS according to, as well as other relevant items such as their bandwidth, frequency-domain
position and a hopping configuration.
According to the example embodiment of LTE, the PUSCH/PUCCH and SRS are never
transmitted simultaneously. The PUCCH format 2/2a/2b takes priority over a simultaneouslyconfigured
SRS transmission. The PUCCH format la/lb can be configured to take priority over
simultaneously-configured SRS, or its transmission can be shortened by one SC-FDMA symbol with
consequential alterations to the PUCCH construction. The PUSCH is rate-matched around the RBs
containing SRS.
Energy storage in terminal devices
Today, wireless terminals without a fixed power supply store their energy in a battery/ies.
Batteries are good for energy storage, because they are slow to discharge, typically being designed to
supply a reasonably constant current for a long period. They cannot usually provide sudden bursts of
current. But to drive a power amplifier (PA) to high power outputs, such a burst of current is needed
nevertheless. Simple battery storage is therefore not ideal when better performance of a terminal could
be obtained by transmitting with a much shorter duration than usual at correspondingly higher power
density. To allow the wireless terminal transmitter to provide a burst of power, a capacitor, or
capacitor-like technique, can be inserted between the battery and the power amplifier. Such a capacitor,
or capacitor-like technique, can have a charge/discharge characteristic which is controllable and
amenable to rapidly releasing a large proportion of its energy (at high current), before recharging from
the battery.
Many wireless terminals are battery powered. This can be true whether they are mobile, such
as smartphones, or reduced capability terminals such as for example mobile or fixed reduced
capability devices such as smart meters. The intensive signal processing and potentially high transmit
powers required to operate these devices in accordance with modern wireless standards such as LTE
can result in a short battery life. For smartphones and similar devices, this can mean that frequent re
charge cycles are needed which can limit the appeal to the end user or limit the extent to which the
capabilities of the device can be fully exploited. For some smart meters and similar devices, such as
those conducting machine-type communications (MTC), battery life may approximately equate to
device life, because it has been proposed that MTC devices are to be installed in inaccessible locations
and it can be expensive for a utility company, for example, which owns the meter to replace the device
or its battery.
These problems can be alleviated by technical improvements that reduce terminal transmission
power consumption at the physical layer and, among such improvements, those with a small impact on
data rate are of particular interest. One of the simplest methods to reduce power consumption is merely
to turn off the terminal's transmit hardware for a greater proportion of the time. But this is not
desirable in general, since it will reduce the ability of the terminal to communicate. A further problem,
of particular pertinence to the smart-meter MTC terminal scenario is coverage. MTC devices may be
installed in places such as deep residential basements from where it is hard for conventional LTE radio
transmissions to reliably reach the eNodeB. This can result in high transmit power and/or r e
transmissions to reach required performance levels, both of which are disadvantageous to battery life.
Therefore, in such cases, it is desirable instead of reducing total transmit power, to keep the
transmission power constant and concentrated into a shorter transmission duration, resulting in a
higher received power-density at the eNodeB which can translate into higher reliability on the uplink.
Flashbulb Principle
According to the present technique a UE is restricted to only a few tens of microseconds of
transmission per sub-frame, which is referred to in the following description as a 'flashbulb'
transmission, but the precise temporal location and duration of transmission can be controlled by a
controller controlling the UE transmitter. A particularly relevant way of enabling this kind of
transmission is to store energy, which is accumulated by a UE's transmitter from a power source or a
battery over a period of time and to release the energy in a burst, rather as if the power source charges
a capacitor which is discharged quickly as has been explained above. According to the present
technique an amount of time for which a terminal is required to transmit to send a certain number of
bits is reduced, resulting in a more efficient use of radio resource and power efficient operation of the
uplink. According to some embodiments for the example application to LTE, the transmission of the
control information on an uplink control channel such as the PUCCH is used to convey further
information or form part of the control information. This can be achieved for example by the steps
that (i) the SC-FDMA symbol at which the transmission begins; and/or (ii) the location of reference
signal(s) transmissions within the overall transmission and (iii) which of a predefined set of possible
reference symbol sequences is used by the UE are used at the eNodeB as additional states to interpret
the modulated symbols contained in REs covered by the transmission. It is assumed that, since the
decoding of the Up-link occurs at the eNodeB, processing power and time is not a significant
constraint.
Example embodiments of the present technique will now be described with reference to the
example of an LTE network with application to the PUCCH and PUSCH and their respective
associated DM-RS. According to some example embodiments one or more of the following aspects
may characterise the operation of a communications device (UE):
· Transmission from a flashbulb-capable UE is always in contiguous SC-FDMA symbols.
• A UE transmitter can be controlled to position a burst of transmission accurately to begin in
any SC-FDMA symbol of a given sub-frame and further to control the duration of the burst of
transmission to as little as one SC-FDMA symbol.
• Transmission should preserve the single-carrier nature of the LTE Up-link as per Rel-1 1.
· Existing Up-link physical channels and signals should all be supported to some degree, but
can be re-designed where needed.
Transmission of Flashbulb UE in PUCCH
As explained above, embodiments of the present technique can provide an arrangement in
which a UE can reduce its power consumption by reducing its transmission time for transmitting a
predetermined message in a first time period which is shorter than a second time period, which has
been allocated for the transmission of that information by a conventional UE. A system which has
been configured to transmit specific information in the second time period, whereas according to the
present technique the UE is adapted to transmit the information in a shorter first time period, which is
less than the second allocated time period. A communications device (UE) operating in this way is
referred to as a 'flashbulb UE'. One example application will now be described with reference to the
transmission of control information by a Flashbulb UE in the PUCCH of an LTE based wireless access
interface. As explained above with reference to Figure 5, the PUCCH is one physical resource block
(PRB) wide in each slot of a sub frame, and positioned at opposite edges of the bandwidth 422, 424 in
the two slots 401, 402. The precise arrangement of data and DM-RS onto the SC-FDMA symbols of a
PRB varies between the PUCCH formats as explained above.
In one example embodiment, the UE is given a configuration by the eNodeB that it can send
control information on the PUCCH of a given duration within a time-domain resource that is longer
than the configured duration, thus giving the UE the choice of where to position its transmission. That
is to say that the transmission time of the signals representing the control information is shorter than
the temporal length of the PUCCH provided by the wireless access interface, and therefore the
Flashbulb UE has a choice of where to position the transmission. The position in the time domain
serves to convey further information to the eNodeB or conveys part of the control information and in
one form can be to index a higher-order modulation scheme based on the lower-order data carried on
the SC-FDMA symbols themselves.
One example illustration is shown in Figures 8a and 8b. Figures 8a and 8b provide an
illustration of the resource elements which form the resource blocks of the PUCCH within a sub-frame.
As explained above, the sub-frame comprises two time-slots 401, 402. As shown in Figures 8a and 8b
the example of the PUCCH shown provides seven OFDM symbols per time slot 401, 402, which are
number 0 to 6. Each symbol comprises a block of 12 OFDM sub-carriers in the frequency domain.
This corresponds to a conventional arrangement explained above with reference to Figure 5, 6 and 7.
A conventional UE would transmit control information in all of the seven symbols and the 12 subcarriers
of the timeslot and in both timeslots 401, 402, as explained above. According to present
technique however a flashbulb UE is configured to transmit on only three of the seven OFDM symbols
across the OFDM subcarriers and furthermore the three symbols whilst being contiguous in time can
vary in position thus conveying further information to the eNodeB. In some examples transmission
only occurs in one of the timeslots and not the other. Thus as shown in Figure 8a the control
information is transmitted only on symbols numbered 4, 5 and 6 in Figure 8a and symbols numbered 5,
6 and 7 in Figure 8b. Accordingly, the position of the transmission by the flashbulb UE conveys
further information, which may form part of the control information as explained below. Therefore the
example illustration shown in Figures 8a and 8b which illustrates a PUCCH comprising of a single
resource block the Flashbulb UE has the following configuration:
• Width of transmission = 3 symbols
• Transmission to be confined within symbols numbered 3 to 6 inclusive
• DM-RS for PUCCH to occupy one symbol
Thus as shown in Figures 8a and 8b, the UE can transmit a pair of data symbols in SC-FDMA
symbols (3, 4, 5) or (4, 5, 6), which in one example can be interpreted as different information sets,
which are called 'Set and 'Set 2' respectively. Then the position-based modulation options are as
depicted in Table 1 below, where a BPSK-based example has been used for simplicity of presentation
but without loss of generality. This particular flashbulb arrangement is most relevant to PUCCH
format 2/2a/2b which would use QPSK pairs instead of the BPSK pairs we have used here for clarity.
So by way of example, in Figure 8a, an eNodeB detecting nothing in SC-FDMA symbol 3, '0' in SCFDMA
symbol 4 and T in SC-FDMA symbol 6 concludes that the actual information data being
conveyed is Ί 0 . Upon detecting the transmission in Figure 8b, the eNodeB concludes that the actual
information data being conveyed is '001 ' .
Table 1
An example of a UE operating in accordance with the present technique is shown in Figure 9.
In Figure 9 a flashbulb UE 501 includes a transceiver unit 502 and a controller 504. A transceiver unit
52 contains a transmitter and receiver adapted to transmit and receive signals via the wireless access
interface provided by the mobile communications network. The controller controls the transceiver to
transmit and receive the data which is then fed to or received from a higher layer application which is
not shown. However what is relevant to the illustration of the present technique is the operation of a
controller which is presented in the form of a flow diagram as operation steps within the controller 504
within a bubble 506. As shown in Figure 5 binary data which is representing the control information is
generated as a first step 508 which is then fed to a bit to symbol grouping 510 in order to transmit the
binary data on the modulation symbols which have been adapted to represent the control information
in accordance with the present technique. The modulation symbols are then received at a flashbulb
mapping step 510 which is configured to map the modulation symbols onto the frequency division
multiplexed symbols and subcarriers of the PUCCH channel in accordance with the information to be
conveyed. The mapping of the modulation symbols onto the selected frequency division multiplexed
sub carriers is determined in accordance with a table providing the allowable mapping of the
frequency division multiplexed symbols and providing an indication of the information which that
conveys. For example a data store 514 provides a representation of the mapping information
identified in table 1. Accordingly the flashbulb mapping step 512 generates an indication of a binary
pair on an output 516 and the frequency division multiplexed symbol set 518 which are fed to the
transceiver unit 502 on corresponding outputs 516, 518 as shown within the flashbulb UE 501.
Therefore as illustrated in Figure 9 a binary data stream is grouped into sets of 'grouped' symbols of
the relevant size by step 510. For example 3 bits (similar to 8-PSK) in Table 1, are used to determine
whether 'Set or 'Set 2' of the SC-FDMA symbols should be used, and which binary pair should be
transmitted as output at step 516 and the two data-carrying symbols of step 518.
As a result of the arrangement shown in Figure 9, three bits can be transmitted by signalling
only two, equivalent to transmitting an 8-PSK signal using BPSK. However, three SC-FDMA
symbols have been used for the purpose and four symbols are reserved although the fourth symbol
uses no transmit power. Accordingly in comparison to a conventional UE, fewer SC-FDMA symbols
and therefore less transmit power is used, than would conventionally have been needed since, to
transmit a hypothetical three 'grouped' symbols in current PUCCH 2/2a/2b structures would require at
least four symbols including DM-RS.
More symbol sets could be created to increase the number of states that can be transmitted.
For example the next power of two would require a set of five symbols to be reserved for this example
transmission, so that there are four possible sets of contiguous symbols to choose from.
The mapping in Table 1 would have a bit error rate (BER) resulting from potentially incorrect
detection at the eNodeB of the received control information. Gray coding is a known technique for
minimising a bit error rate by positioning modulated symbols with bit changes close together.
According to one example a Gray code mapping of the information from Table 1 could be as shown
below in table 2, where only one bit in a group of bits which forms a modulated symbol changes
between adjacent binary pairs within a set and only one bit in a modulated symbol changes between
each symbol set within a binary pair.
Table 2 : A Gray mapping relevant to Table 1.
Vary Position of DM-RS
In another example embodiment the controller 504 of the Flashbulb UE is arranged to vary the
position of the DM-RS symbol as part of the transmission provided that three symbols are still timecontiguous.
In the example, in which one DM-RS is transmitted as any of the three symbols contained
wholly within either of 'Set or 'Set 2', according to which set has been chosen for data transmission,
a total of twenty four states can be transmitted using two binary bits. Since twenty four is not an
integer power of two, it may be sufficient to define only two permissible positions for the DM-RS
symbol within each set of SC-FDMA symbols, resulting in sixteen states equivalent to four bits. This
is illustrated in Figure 10a and 10b where the BPSK pair of modulation symbols are being transmitted,
which are represented as 0, 1 and corresponds to the example configuration of Figure 8a and 8b. Thus
Figures 10a and 10b provide a representation of the transmission of BPSK symbols within a first
timeslot 140 of a sub-frame. In contrast to the example shown in Figures 8a and 8b, the uplink
transmission of DM-RS symbol varies from a first position 552 in Figure 10a to a second position of
552 in Figure 10b. For the example shown in Figures 10a and 10b, the modulation symbols both
indicate the same value of 0 and 1. However by changing the position of the DM-RS symbol
additional information can be signalled.
Thus as illustrated in Figure 10a and 10b the first and second modulation symbols transmitted
are 0 and 1. A mapping of the combination of SC-FDMA symbol set and DM-RS positions from
binary pair to quaternary symbols is shown in Table 3. This table could also be Gray mapped in
various ways following the example of Table 2. Table 3 below provides an indication of the possible
signalling information being transmitted on a control channel. The eNodeB then detects whether the
DM-RS symbol is in position 'A' , that is shown in Figure 10a or in a position 'B' that is shown in
Figure 10b. If the transmitted DM-RS symbol is in position 'A' , then the second column indicates that
the control information could be either Ό OO or Ό 10 depending on whether the frequency division
multiplexed symbols were transmitted as set one or set two. For the examples shown in Figure 10a
and 10b the signals were transmitted in frequency division multiplexed symbols 4, 5 and 6 and
therefore correspond to set two. Accordingly, Figure 10a represents a transmission of signalling
information Ό 10 whereas the transmitted signals represented in Figure 10b represents signalling
information 10 . As can be appreciated therefore by changing the position of the DM-RS reference
symbols, further information can be signalled without requiring any increase in the modulation level or
transmission of more frequency division multiplexed symbols thereby shortening the transmission by
the Flashbulb UE.
It could be preferable in cases where not all possible DM-RS locations are permitted, such as
in this example, to separate the permitted positions as widely as possible in time in order to reduce
mis-detection probability among DM-RS symbol positions, which is illustrated in Figures 10a and 10b.
Table 3
A further increase to the efficiency of transmission of control information can be achieved by
using more than one sequence for generating the DM-RS. If either of two possible sequences can be
used, then following the sixteen-state example presented above on Figure 3 can be used to create thirty
two signalling states, which is equivalent to 5 bits.
An example of a reduction in power consumption resulting which can be achieved using the
above described embodiments can be considered using a PUCCH format 2/2a/2b, where, within one
slot, five QPSK symbols and two DM-RS symbols are sent, requiring seven SC-FDMA symbols in
total. In the example given above, by replacing the BPSK pairs with QPSK pairs, only three SCFDMA
symbols are required thus reducing the power consumed by approximately 57%. An
alternative embodiment provides an arrangement in which the Flashbulb UE does not reduce its total
transmission power consumption but instead concentrates its power into the much-reduced time
duration of the transmission, so increasing the power density with which it will be received by the
eNodeB, thereby improving the Up-link coverage in the cell. Any mixture of the two is clearly also
beneficial compared to known methods.
Use of Physical Resource Blocks (PRB)
In the example embodiments presented above, the transmission of the signals carrying the
control information is within the first time slot 401 of the sub-frame. However the transmission could
equally be arranged in the second time slot 402. Furthermore a conventional operation provides a UE
with PUCCH resource at opposite band edges in the two slots 401, 402 of a sub-frame. In accordance
with some example embodiments the Flashbulb UE is required to transmit signals representing the
control information across different frequency bands in the first and second time slots 401, 402.
However the break in transmission would imply that the UE used symbols not contiguous with the end
of the first slot, for example as shown in Figure 8a. This would violate the time-domain
contiguousness requirement. Therefore, in some embodiments the physical resource block (PRB) at
the opposite band edge in the second slot 402 is granted to a second 'Flashbulb' UE which would be
configured similarly to, but independently of, the first UE in the first time slot 401. Similarly, the
second PRB in the first time slot 401 could be granted to a third Flashbulb UE, and the second PRB in
the second time slot 402 to a fourth Flashbulb UE. This would be a different scheduling arrangement
than that depicted for current PUCCH in Figure 5. Therefore in some embodiments the resources
provided by the PUCCH can be used by more than one Flashbulb UE, so that the resources are more
completely utilised.
In an alternative example embodiment, in order to maintain some of the frequency diversity of
the existing PUCCH design for at least one UE, the UE can be granted resources in contiguous SCFDMA
symbols but split across the two time slots and across the two band edges at the slot boundary.
This is illustrated in Figure 11. In Figure 11, the transmission of flashbulb UE extends across the first
timeslot 401 and the second is timeslot 402. As illustrated in Figure 11 the transmission occurs in
frequency division multiplexed symbols numbered 4 to 9. In accordance with this example the
transmission is split across the first frequency band 560 and a second frequency band 562 which in
accordance with the example illustrated in Figure 5 is split at either edge of the allocated up-link
frequency band. As shown in Figure 11 three of the frequency division multiplexed symbols 570, 572,
574 are allocated for transmitting frequency division modulation symbols whereas symbols numbered
5 and 8 are allocated for transmitting DM-RS symbols 576, 578. For the example illustrated in Figure
11 the flashbulb UE would be configured as follows:
• Width of transmission = 5 symbols
• Transmission to be confined within symbols numbered 4 to 9 inclusive
• DM-RS for PUCCH to occupy one symbol in each slot were PUCCH is sent
To show the extent of this case, the transmission is shown as containing three data symbols
and two DM-RS symbols. The UE is allowed to vary the distribution of the PUCCH transmission
between the two slots: in this particular example it has a reservation of three symbols in each slot.
DM-RS will be needed in each slot since the transmissions in the two slots are widely separated in the
frequency domain. In general, a UE might not use any of its granted resources in one of the slots.
As will be appreciated a combination of the example embodiment illustrated in Figure 11 can
be combined with the other example embodiments disclosed in Figures 8 to 10.
PUCCH format l a and l b
In PUCCH format l a and lb, one or two information bits carrying ACK/NACK are sent
respectively in BPSK or QPSK modulated symbols. In existing LTE, the ACK/NACK bit is sent on
(up to) four SC-FDMA symbols per slot using what amounts to repetition coding, with DM-RS on the
remaining three SC-FDMA symbols. This generally results in a lower signal to noise ratio operating
point than for format 2/2a/2b.
According to example embodiments some of the possible states of the signal transmission can
be created to be assigned to ACK and some states to NACK. This means that even in the presence of
incorrectly determining the transmitted state, the information bit is still decoded correctly. The
principle of Gray coding could again be useful here so that logically adjacent states map to the same
information bit. In the example of Table 2, one possible Gray code mapping is shown, realised on the
assumption that the most common error is within a binary pair being mis-detected in the wrong
frequency division multiplexed (SC-FDMA) symbol set, which for ACK/NACK is presented in table 4.
Table 4
A Gray code mapping realised on the basis that the most common error is within a frequency
division multiplexed (SC-FDMA) symbol set where the binary pair is mis-detected could be as shown
in table 5:
Table 5
Similar mappings can be developed for the method also using DM-RS timing illustrated by
Figure 10a and 10b and Table 3. This example is for PUCCH format la; QPSK pairs would be used
for format lb. An advantage is provided for this embodiment whereby transmission is robust to
decoding errors at the eNodeB but still uses less transmission power than the conventional LTE
scheme, as it uses only three SC-FDMA symbols rather than the seven in a timeslot (or fourteen in a
sub-frame).
UE Time Multiplexing
As explained above, according to some example embodiments, the resources of the PUCCH
which are not used by a flashbulb UE are allocated to another flashbulb UE so that the available
resources can be time multiplexed between a plurality of UEs. Clearly as shown in the above examples,
not all resource elements in the PRB illustrated above are being used. The unused resource elements
could be assigned to one or more other UEs, who would have a correspondingly different
configuration to the Flashbulb UE used in the example. Continuing the above example, within the one
PRB, a second UE would be able to have three-symbols reserved in SC-FDMA symbols (0, 1, 2),
within which one possible configuration is to transmit one data symbol and one DM-RS symbol (i.e.
two SC-FDMA symbols in total) time-contiguously and the other example embodiments as explained
above. This UE would have a lower Up-link data rate than the first UE if both operated otherwise
identically.
Therefore as will be appreciated from the above discussion, embodiments of the present
technique can provide an arrangement in which a plurality of flashbulb UEs are multiplexed within a
one PRB. In contrast in other embodiments flashbulb transmissions could be multiplexed from a
plurality of UEs in a number of different PRBs.
Since PUCCH allows code multiplexing of UEs in the same resource elements, in some
embodiments UEs can be given overlapping flashbulb reservations and these reservations can overlap
in all, or only some, of their SC-FDMA symbols.
Transmission of Flashbulb UE in PUSCH
On conventional PUSCH, one modulated symbol is sent independently on each resource
element of a granted PRB. This arrangement contrasts with the PUCCH where one modulated symbol
is sent with frequency spreading across all 12 resource elements in a SC-FDMA symbol. Even with
this constraint, in some embodiments a mobile communications network can be arranged to provide a
facility for transmitting data on the shared channel of the wireless access interface, which for LTE is
the PUSCH, whilst conforming to the flashbulb transmission principles. In this example, data is
transmitted by a UE in a smaller number of frequency division multiplexed symbols than are provided
in each time slot of a PUSCH. However in contrast to the transmissions on PUSCH in known systems,
the transmission on the PUSCH according to the invention are such that the REs are no longer
independent over the time domain.
An example illustration is shown in Figure 12. In Figure 12 which reflects the up-link frame
structure shown in Figure 5, two timeslots are shown 401, 402 of the up-link sub-frame which have
been allocated for transmission to a UE. However in accordance with the present technique if the UE
is a reduced capability UE or operating as a Flashbulb UE then as will be explained below the eNodeB
has been adapted to allow the UE to transmit data in a smaller number of the frequency division
multiplexed (SC-FDMA) symbols in each of the time slots in order to reduce a transmission time and
therefore power consumed in accordance with the flashbulb UE principles outlined above. Thus as
shown in Figure 12 the hashed symbols 600, which are numbered 3, 4 and 5 of the seven symbols of
the first time slot 401 represents a transmission of the flashbulb UE 600 whereas in the second time
slot the symbols number 4, 5 and 6 of the seven available SC-FDMA symbols are used to transmit the
data 601 by the Flashbulb UE.
As will be appreciated all of the embodiments of the present technique which have been
described with reference to the PUCCH explained above can be applied to the PUSCH. Accordingly
as indicated by an arrow 602, 604 the position of the transmissions in the reduced number of SCFDMA
symbols can vary in position in order to provide additional information or to convey part of the
data which is transmitted to the eNodeB by the Flashbulb UE.
As indicated above in order for the mobile communications network to allow a UE to perform
the Flashbulb technique in which only some of the seven symbols of a time slot of the sub-frame are
used then the eNodeB needs to be configured to receive the data transmitted on a smaller number of
SC-FDMA symbols. Figures 13a, 13b, 13c, and 13c provide example embodiments in which a
signalling exchange between a reduced capability UE and an eNodeB is performed in order to provide
an arrangement for transmitting data in a smaller number of the SC-FDMA symbols which are
available in a time slot 401, 402. In Figure 13a the eNodeB 620 transmits a broadcast message 622 to
the UE 624 within the cell indicating the PUCCH transmission format which can be used by a
flashbulb type UE to transmit data in a smaller number of SC-FDMA symbols that are available within
each slot. In other embodiments eNodeB 620 provides transmission formats for flashbulb techniques
for the PUSCH. Thus in the present example of Figure 13a once the PUCCH/PUSCHtransmission
formats for flashbulb UEs have been transmitted in the cell then any UE which is requested and
granted resources on the PUSCH and/or PUCCH will transmit data in a smaller number of SC-FDMA
symbols than are available in each slot.
In contrast in Figure 13b a UE 630 transmits as part of a set up procedure, which establishes a
context, an indication that it is a reduced capability UE using a message 632. The eNodeB responds by
providing the transmission format indicating the symbols of the timeslot which can be used for
transmitting data on the shared channel 634. An alternative in Figure 13c represents an arrangement in
which the UE 638 transmits a PRACH 640 by which it is indicated that the UE 638 is a reduced
capability UE. In other words, the UE 638 is indicating that it wishes to use the flashbulb principles in
which data is transmitted in a smaller number of SC-FDMA symbols. In response the eNodeB 620
grants resources on the PUSCH and/or PUCCH and indicates in the resource grant 642 that the UE
should use a certain number of the SC-FDMA symbols which is less than the predetermined number
of symbols of the timeslot for transmitting data. Finally in Figure 13d a UE 640 transmits a
conventional PRACH transmission 646 to the eNodeB 620. In the example shown in Figure 13d the
eNodeB 620 and the UE 644 have already established that the UE 644 is a flashbulb type UE or
reduced capability device and accordingly when the grant of resources on the PUSCH and/or PUCCH
is transmitted on a message 650 there is indicated the SC-FDMA symbols which the UE should use to
transmit data on the PUSCH.
According to examples shown in Figures 13a, 13b, 13c, 13d an arrangement is provided for
identifying the symbols of each of the timeslots in which a UE can transmit data on the shared channel
thus implementing the principles explained above for the PUCCH on the shared channel PUSCH,
although the principles can also be applied to the PUCCH. Using this arrangement, the UE is given a
configuration including a reservation of a subset of the SC-FDMA symbols within a PRB. Then,
separately on each frequency-domain subcarrier, the time-contiguous resource elements within the
PUSCH reservation can be used jointly to transmit a modulated symbol in the manner shown in, e.g.
Table 2. For this example, there is no particular restriction to BPSK pairs, and any permitted
modulation scheme could be used, e.g. 64-QAM. Thus, the UE can transmit any pattern of information
bits (of a suitable length) on each frequency subcarrier. There could be a reduction in the peak PUSCH
data-rate that could be achieved, but according to the example embodiment in which power
conservation is a significant requirement, it may well also be the case that the UE's typical data rate is
low and the peak rate is not of primary concern.
In essence, applying the present technique to the PUSCH demonstrates that there is no
particular insistence that the transmission be across all subcarriers of an SC-FDMA symbol, in contrast
to the frequency-domain spreading that is used on PUCCH.
PRACH
Of the existing LTE PRACH formats according to Release 11 of 3GPP specifications, format
4 already fits flashbulb operations, since its duration is only two SC-FDMA symbols, but it is
restricted to use only in TDD modes. This format can therefore be used with the example shown in
Figures 13b and 13c. Existing specifications could be relaxed to allow PRACH format 4 to be used by
FDD UEs as well as TDD UEs as long as an FDD UE is operating in flashbulb mode. This would be
aided by allowing FDD systems to configure more than one PRACH resource in a PRACH
opportunity so that flashbulb and legacy UEs need not interfere in this respect. Signalling of this
would need to be added in the cell broadcast information (currently in SIB2). A UE capable of
operation in either conventional or flashbulb mode could be left with a choice of the manner and
resources in which it access PRACH, or the cell could further broadcast instructions, or specifications
could contain instructions, regarding what such UEs must do. If the UE has the choice, then the
eNodeB can use the manner of PRACH access to determine the flashbulb capability (or, at least, a
preference) of a UE, reducing the need for later RRC message exchanges for the purpose. Other
possibilities, where the basic principles may be already known to the art, include predefining certain
among the random access preambles as to be selected among by UEs wishing to indicate flashbulb
operation and the rest for UEs operating conventionally.
Alternatively, a UE could operate in conventional LTE mode during initial cell acquisition
procedures, including PRACH transmissions, and then move to, or be configured by eNodeB into,
flashbulb operation once an RRC connection has been established.
Transmission of Sounding Reference Signal (SRS)
In a conventional LTE network, SRS can occupy the final SC-FDMA symbol of a sub-frame,
so that the eNodeB can use the channel estimate reliably in the next sub-frame. The sub-frames and
frequency resources in which a UE sends SRS are controlled by the eNodeB, but can extend across
essentially any bandwidth if the UE has sufficient transmit power. In sub-frames where a UE is
sending PUCCH and/or PUSCH, those transmissions are shortened by one SC-FDMA symbol if SRS
are also present. There are two cases with respect to Flashbulb operation:
· The UE has only SRS in this sub-frame. The UE effectively operates in flashbulb mode in
conventional systems; or
• The UE has flashbulb PUCCH and/or PUSCH as well as SRS in this sub-frame. The timecontiguity
requirement of flashbulb operation is not met in general.
In some example embodiments a flashbulb UEs may have only intermittent data to transmit
and so it may be preferable to rely on a triggered SRS, available from Rel-10 LTE, so that the UE
sends SRS at the very end of one sub-frame and flashbulb PUCCH/PUSCH can then be scheduled
efficiently. In a similar way, an eNodeB scheduler behaviour could be to configure UEs from which it
is expecting SRS in a given sub-frame to have flashbulb reservations that are contiguous with the final
SC-FDMA symbol of the sub-frame. This would amount to the UE having no choice of the SC-FDMA
symbols in which they must transmit, but it would still be able to position DM-RS for
PUCCH/PUSCH as shown in Figures 10a and 10b and Table 3.
In summary existing SRS and flashbulb PUCCH/PUSCH operation can co-exist given suitable
eNodeB scheduling behaviour.
According to the embodiments identified above, a communications device, which may be an
MTC type device operating as Flashbulb UE can significantly reduce its power consumption because
the controller of the transceiver unit transmits signals representing the data in a subset of SC-FDMA
symbols of a PRB which are available to it. In one example given above, power consumption is
reduced by 57% without reducing the number of bits transferred per PRB. Alternatively, the power
consumption could be maintained but concentrated into the reduced resources occupied by flashbulb
operation, thus increasing the Up-link coverage in the cell. This in turn would tend to reduce the need
for re-transmissions from UEs as well as the downlink signalling from the eNodeB to trigger and
control them. These two advantages can be mutually traded-off against one another to achieve any mix
of power-consumption reduction and coverage extension that a device manufacturer desires.
If more than one UE is multiplexed into a PRB, then the capacity of the transmission channel
can allow one or more other UEs to have Up-link resources per sub-frame.
General
eNodeB Decoding
In order to decode a flashbulb transmission, the eNodeB according to one implementation
would have to search blindly over the possible transmissions that a UE could have made. This will
tend to increase the decoding time and processing effort at the eNodeB, but significantly greater
amounts of both are available there than at the UE. A mis-decoding at the eNodeB of a flashbulb
transmission could trigger the same procedures as in conventional LTE.
Flashbulb Resource Grants
The resource grants and reservations for flashbulb Up-link transmission would need to include
the conventional information regarding which PRBs a UE is granted as well as which SC-FDMA
symbols it can assume are reserved for it. These reservations could be;
• Included in the grant on PDCCH by expanding the contents of, or creating new, DCI
messages;
• Configured semi-statically by RRC per UE;
• Broadcast in the cell as a function of, e.g. UE identity for those cases where UEs can be
multiplexed into the same REs.
Accordingly embodiments of the present technique can be used to request and receive
resource grants in a way which is backwardly compatible with conventional UEs and LTE networks
since a non-flashbulb UE can be granted PRBs that are distinct from PRBs assigned to flashbulb UEs.
UE modes
A given UE might be able to operate in conventional LTE mode as well as flashbulb mode
depending on its power consumption requirements at a given time. Such a UE could signal to the
eNodeB that it wishes to move to/from conventional to flashbulb operation by, e.g., asserting/releasing
a flag at RRC. A simpler UE might only be able to indicate that it can operate in flashbulb mode, but
not be able to indicate a wish to change mode. In either case, if the eNodeB decides to put a UE into
flashbulb operation, it can indicate as much either in a PDCCH message on a per-sub-frame basis or
semi-statically at RRC. In general, then, a suitably-capable UE might be instructed to move to and
from flashbulb operation on a per-sub-frame basis or at any time.
MTC Up-link transmissions
Depending on the physical implementation of the flashbulb operation of a UE, it may be that
there is a delay between individual flashbulb transmissions. As such, embodiments of the present
technique can provide an advantage for MTC UEs where Up-link transmissions can tend to be small
and occasional. Although the capacitor-like UE energy storage mentioned above provides an example
of performing the Flashbulb like transmission, embodiments of the present technique are not limited to
this method of implementing the Flashbulb transmission and other techniques are possible.
Example embodiments of the present technique can therefore provide the following
advantages:
• A UE receives an Up-link resource reservation, and is not directed by eNodeB as to which part
of it is used for transmission, whereas at present an Up-link grant is used in its entirety with
rate-matching as necessary.
· The timing of the start of a transmission conveys part of the information being sent in the
transmission, whereas the UE presently has no time-domain freedom from the eNodeB
grant/configuration for PUSCH/PUCCH.
• The timing of the transmission of RS associated with PUSCH/PUCCH conveys part of the
information being sent in the transmission, whereas this is not the case at present.
· For PUCCH format 1/la/lb in particular, the transmission of HARQ ACK/NACK in any of
multiple states provides a robust transmission without using the existing LTE technique
(which is essentially time-domain repetition).
• For PUSCH in particular, the joint transmission of data over several SC-FDMA symbols
within one frequency sub-carrier is different to current operation, where each RE is entirely
independent.
• For PRACH in particular, a UE capable of both conventional and flashbulb operation is able
to communicate this at an early stage of operation by its choice of resources for and manner of
PRACH transmission.
• The eNodeB has a new capability to alter the mode of operation of a UE between conventional
and flashbulb operation according to any of (i) the UE's capability; (ii) the UE's preference
among its capabilities; (iii) the eNodeB's preference. As a result, the mode of operation of a
UE can be a hybrid of conventional LTE and flashbulb LTE, in any particular time-domain
pattern per sub-frame.
Example Mobile Communications System
Figure 14 provides a schematic diagram showing part of an adapted LTE mobile
communications system. The system includes an adapted eNode 1401 connected to a core network
1408 which communicates data to a plurality of conventional LTE devices 1402 and reduced
capability devices 1403 within a coverage area (i.e. cell) 1404. Each of the reduced capability devices
1403 has a transceiver unit 1405 which includes a receiver unit capable of receiving data across a
reduced bandwidth and a transmitter unit capable of transmitting data across a reduced bandwidth
when compared with the capabilities of the transceiver units 1406 included in the conventional LTE
devices 1402.
The adapted eNodeB 1401 is configured to allow the reduced capability devices to transmit
signals on the Up-link PUCCH or PUSCH using the Flashbulb techniques described above for
example with reference to Figures 1 to 13. A transmitter and receiver unit 1409 forms a wireless
access interface under the control of a controller 1411, which also performs the function of an adapted
scheduler. The reduced capability devices 1403 are thus able to receive and transmit data using the
up-link in accordance with an operation which can conserve power according to the present technique
as summarised by the flow diagram for the PUCCH as shown in Figure 15 and by the flow diagram for
the PUSCH as shown in Figure 16. Figure 15 is summarised as follows:
SI: As with a conventional operation a communications device (UE) transmits and
receives data via a wireless access interface provided by a mobile communications network. The
wireless access interface includes an uplink control channel for transmitting signalling information in
accordance with a predetermined format in which signals representing the signalling information
occupy a predetermined number of frequency division multiplexed (SC-FDMA) symbols of a time
period of the control channel. The time period may be a sub-frame or a time slot of the sub-frame into
which the frame is divided.
S2: The UE adapts the transmission of signals representing the signalling information in
the control channel to occupy a smaller number of the predetermined number of frequency division
multiplexed symbols of the time period of the control channel. By reducing the transmission time by
transmitting signalling information in a smaller number of frequency division multiplexed symbols
than are available on the control channel then there is a corresponding reduction in power
consumption.
S4: An eNodeB of the mobile communications network is adapted to search the control
channel to detect the signals representing the signalling information which has been transmitted in the
smaller number of frequency division multiplexed symbols.
S6: Optionally in one example, the UE varies the starting symbol in which the reduced
number of frequency division multiplexed symbols are transmitted between one of a plurality of
predetermined start symbols. Thus each different starting frequency division multiplexed symbol
provides an indication of further information. In one example, the further information forms part of the
signalling information which is being transmitted.
Figure 16 provides an example illustration of the operation of another example embodiment
where the UE transmits data on a shared channel (PUSCH) of the wireless access interface provided
by the mobile communications network and a corresponding reduction in power consumption is
achieved. The operation of a UE is for this example embodiment represented in Figure 16 which are
summarised as follows:
S8: A UE transmits and receives data via a wireless access interface in accordance with a
conventional operation. However the wireless access interface includes an uplink with a shared
channel providing communications resources which are shared with other communications devices
and comprises in the time domain a predetermined number of frequency division multiplexed symbols
in each time period for allocation to communications devices. Again, the time period may be a subframe
or a time slot of the sub-frame into which the frame is divided.
S10: The UE transmits to the mobile communications network an indication that the
communications device is a reduced capability device. Alternatively, the UE transmits an indication
that it wishes to operate as a flashbulb UE or provide some indication that the UE is to reduce a
number of frequency division multiplexed symbols which are available for transmission on the shared
channel.
S12: The UE receives from the eNodeB of the mobile communications network an
indication of a subset of the predetermined number of frequency division multiplexed symbols in
which the communications device should transmit the data on the shared channel. The indication of
the subset of frequency division multiplexed symbols, in one example, can be transmitted on a
broadcast signal or provided at call setup or may be provided in response to each request for grant of
uplink shared channel resources.
S14: The UE then transmits signals representing the data in the shared channel to occupy a
smaller number of the frequency division multiplexed symbols than the number which are available
within the time period of the shared channel.
Various further aspects and features of the present disclosure are defined in the appended
claims. 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. Although
embodiments of the present disclosure have been described with reference to LTE, it will be
appreciated that other embodiments find application with other wireless communication systems such
as UMTS.
The following numbered clauses provide further example aspects:
1. A communications device for transmitting data to or receiving data from a mobile
communications network, the mobile communications network including one or more network
elements which are arranged to form a wireless access interface for transmitting and receiving the
data, the communications device comprising
a transmitter unit configured to transmit signals representing the data on an up-link of the
wireless access interface to the mobile communications network,
a receiver unit configured to receive signals representing the data transmitted on a down-link
from the mobile communications network via the wireless access interface, the wireless access
interface providing a plurality of communications resource elements across a frequency range for the
down-link and the up-link, the communications resource elements being formed by dividing subcarriers
at different frequencies into a plurality of time periods, one or more of the sub-carriers being
provided to form, in the time domain, frequency division multiplexed symbols, each of the time
periods comprising a predetermined number of the frequency division multiplexed symbols, wherein
the up-link includes a shared channel providing the communications resources for allocation to the
communications device by the mobile communications network for transmitting the data on the up
link to the mobile communications network, the shared channel providing communications resources
which are shared with other communications terminals and comprising in the time domain, the
predetermined number of frequency division multiplexed symbols in each time period for allocation to
the communications device, and
a controller configured to control the transmitter unit to transmit the signals and the receiver
unit to receive the signals to transmit or receive the data, wherein the controller is configured to
control the transmitter unit and the receiver unit
to transmit to the mobile communications network a request to transmit data in a smaller
number of frequency division multiplexed symbols than are available on the shared channel,
to receive from the mobile communications network an indication of a sub-set of the
predetermined number of frequency division multiplexed symbols in which the communications
device should transmit the data on the shared channel, and
to transmit signals representing the data in the shared channel to occupy a smaller number of
frequency division multiplexed symbols than the number of the predetermined number of frequency
division multiplexed symbols of the time period of the shared channel.
2. A communications device according to clause 1, wherein the controller is configured
to transmit the signals representing the data in the smaller number of frequency division multiplexed
symbols within the time period of the shared channel starting at a different one of the predetermined
number of frequency division multiplexed symbols, each of the different starting frequency division
multiplexed symbols representing further information.
3. A communications device according to clause 1 or 2, wherein the controller is
configured to transmit the signals representing the data with one or more reference symbols included
in the number of frequency division multiplexed symbols to assist in demodulating the received signal
to recover the data, and a position of the one or more reference symbols within the transmitted
frequency division multiplexed symbols is varied between a plurality of locations within the
transmitted symbols, each of the locations representing further information.
4. A communications device according to clause 2 or 3, wherein the further information
forms part of the data being transmitted by the controller.
5. A communications device according to any of clauses 1 to 4, wherein the shared
channel comprises a plurality of frequency division multiplexed symbols in the time domain and a
plurality of sub-carriers in the frequency domain and transmission of the signalling information
includes a contiguous sub-set of the frequency division multiplexed symbols starting at one of the
predetermined frequency division multiplexed symbols.
6. A communications device according to any of clauses 1 to 5, wherein the controller is
configured to transmit the data by mapping data symbols representing the frequency division
multiplexed symbols by modulating the sub-carriers of the shared channel with modulation symbols
representing the data symbols, the modulation order of the modulation symbols being so that the data
can be transmitted in a temporal length which is less than the temporal length of the time period of the
shared channel.
7. A communications device according to any of clauses 1 to 6, wherein the time period
of the shared channel is formed from a sub-frame of a frame into which the up-link is divided.
8. A communications device according to clause 7, wherein the shared channel is formed
from two time slots into which the sub-frame is divided and the predetermined number of frequency
division multiplexed symbols is the number of symbols in one of the time slots.
9. A communications device according to any of clauses 1 to 9, wherein the controller is
configured in combination with the receiver unit
to receive control information from the mobile communications network for configuring the
transmission of the signals representing the data in the shared channel, whereby other communications
devices can be configured to adapt transmissions of signals in the same shared channel with the
transmission of the signals representing the data by the communications device, and the controller is
configured in combination with the transmitter unit
to configure the transmitter unit in accordance with the control information received from the
mobile communications network to transmit the signals representing the data in the shared channel.
10. A method of transmitting data to or receiving data from a mobile communications
network, the mobile communications network including one or more network elements which are
arranged to form a wireless access interface for transmitting and receiving the data, the method
comprising
transmitting signals representing the data on an up-link of the wireless access interface to the
mobile communications network,
receiving signals representing the data transmitted on a down-link from the mobile
communications network via the wireless access interface, the wireless access interface providing a
plurality of communications resource elements across a frequency range for the down-link and the up
link, the communications resource elements being formed by dividing sub-carriers at different
frequencies into a plurality of time periods, one or more of the sub-carriers being provided to form, in
the time domain, frequency division multiplexed symbols, each of the time periods comprising a
predetermined number of the frequency division multiplexed symbols, wherein the up-link includes a
shared channel providing the communications resources for allocation to the communications device
by the mobile communications network for transmitting the data on the up-link to the mobile
communications network, the shared channel providing communications resources which are shared
with other communications terminals and comprising in the time domain, the predetermined number
of frequency division multiplexed symbols in each time period for allocation to the communications
device, and
controlling the transmitting the signals and the receiving the signals to transmit or receive the
data, wherein the controlling the transmitting includes
transmitting to the mobile communications network a request to transmit data in a smaller
number of frequency division multiplexed symbols than are available on the shared channel,
receiving from the mobile communications network an indication of a sub-set of the
predetermined number of frequency division multiplexed symbols in which the communications
device should transmit the data on the shared channel, and
transmitting signals representing the data in the shared channel to occupy a smaller number of
frequency division multiplexed symbols than the number of the predetermined number of frequency
division multiplexed symbols of the time period of the shared channel.
11. A method according to clause 10, wherein the controlling the transmitting includes
transmitting the signals representing the data in the smaller number of frequency division multiplexed
symbols within the time period of the shared channel starting at a different one of the predetermined
number of frequency division multiplexed symbols, each of the different starting frequency division
multiplexed symbols representing further information.
12. A method according to clause 10 or 11, wherein the controlling the transmitting
includes transmitting the signals representing the data includes transmitting one or more reference
symbols included in the number of frequency division multiplexed symbols to assist in demodulating
the received signal to recover the data, and
varying a position of the one or more reference symbol within the transmitted frequency
division multiplexed symbols between a plurality of locations within the transmitted symbols, each of
the locations representing further information.
13. A method according to clause 11 or 12, wherein the further information forms part of
the data being transmitted by the controller.
14. An infrastructure equipment for forming part of a mobile communications network
and providing a wireless access interface for transmitting data to and receiving data from a
communications device, the infrastructure equipment comprising
a transmitter unit configured to transmit signals representing the data on a down-link of the
wireless access interface to the mobile communications network,
a receiver unit configured to receive signals representing the data transmitted on an up-link
from the mobile communications network via the wireless access interface, the wireless access
interface providing a plurality of communications resource elements across a frequency range for the
down-link and the up-link, the communications resource elements being formed by dividing subcarriers
at different frequencies into a plurality of time periods, one or more of the sub-carriers being
provided to form, in the time domain, frequency division multiplexed symbols, each of the time
periods comprising a predetermined number of the frequency division multiplexed symbols, wherein
the up-link includes a shared channel providing the communications resources for allocation to the
communications device by the infrastructure equipment for transmitting the data on the up-link to the
infrastructure equipment, the shared channel providing communications resources which are shared
with other communications terminals and comprising in the time domain, the predetermined number
of frequency division multiplexed symbols in each time period for allocation to the communications
device, and
a controller configured to control the receiver unit to receive the signals and the transmitter
unit to transmit the signals to transmit or receive the data, wherein the controller is configured to
control the transmitter unit and the receiver unit
to receive from a communications device a request to transmit data in a smaller number of
frequency division multiplexed symbols than are available on the shared channel,
to transmit to the communications device an indication of a sub-set of the predetermined
number of frequency division multiplexed symbols in which the communications device should
transmit the data on the shared channel, and
to receive signals representing the data in the shared channel within a smaller number of
frequency division multiplexed symbols than the number of the predetermined number of frequency
division multiplexed symbols of the time period of the shared channel.
15. An infrastructure equipment according to clause 14, wherein the controller is
configured to receive the signals representing the data in the smaller number of frequency division
multiplexed symbols within the time period of the shared channel starting at a different one of the
predetermined number of frequency division multiplexed symbols, each of the different starting
frequency division multiplexed symbols representing further information.
16. An infrastructure equipment according to clause 14 or 15, wherein the controller is
configured to receive the signals representing the data in the smaller number of frequency division
multiplexed symbols within the time period of the shared channel, the received signals representing
the data with one or more reference symbols included in the number of frequency division multiplexed
symbols to assist in demodulating the received signal to recover the data, the one or more reference
symbols transmitted with the data bearing symbols varying in location with respect to a position of the
data bearing symbols, each of the locations representing further information, and
the controller is configured to detect the further information based on the location of the one
or more reference symbols.

CLAIMS
1. A communications device for transmitting data to or receiving data from a mobile
communications network, the mobile communications network including one or more network
elements which are arranged to form a wireless access interface for transmitting and receiving the
data, the communications device comprising
a transmitter unit configured to transmit signals representing the data on an up-link of the
wireless access interface to the mobile communications network,
a receiver unit configured to receive signals representing the data transmitted on a down-link
from the mobile communications network via the wireless access interface, the wireless access
interface providing a plurality of communications resource elements across a frequency range for the
down-link and the up-link, the communications resource elements being formed by dividing subcarriers
at different frequencies into a plurality of time periods, one or more of the sub-carriers being
provided to form, in the time domain, frequency division multiplexed symbols, each of the time
periods comprising a predetermined number of the frequency division multiplexed symbols, wherein
the up-link includes a shared channel providing the communications resources for allocation to the
communications device by the mobile communications network for transmitting the data on the up
link to the mobile communications network, the shared channel providing communications resources
which are shared with other communications terminals and comprising in the time domain, the
predetermined number of frequency division multiplexed symbols in each time period for allocation to
the communications device, and
a controller configured to control the transmitter unit to transmit the signals and the receiver
unit to receive the signals to transmit or receive the data, wherein the controller is configured to
control the transmitter unit and the receiver unit
to transmit to the mobile communications network a request to transmit data in a smaller
number of frequency division multiplexed symbols than are available on the shared channel,
to receive from the mobile communications network an indication of a sub-set of the
predetermined number of frequency division multiplexed symbols in which the communications
device should transmit the data on the shared channel, and
to transmit signals representing the data in the shared channel to occupy a smaller number of
frequency division multiplexed symbols than the number of the predetermined number of frequency
division multiplexed symbols of the time period of the shared channel.
2. A communications device as claimed in Claim 1, wherein the controller is configured
to transmit the signals representing the data in the smaller number of frequency division multiplexed
symbols within the time period of the shared channel starting at a different one of the predetermined
number of frequency division multiplexed symbols, each of the different starting frequency division
multiplexed symbols representing further information.
3. A communications device as claimed in Claim 1, wherein the controller is configured
to transmit the signals representing the data with one or more reference symbols included in the
number of frequency division multiplexed symbols to assist in demodulating the received signal to
recover the data, and a position of the one or more reference symbols within the transmitted frequency
division multiplexed symbols is varied between a plurality of locations within the transmitted symbols,
each of the locations representing further information.
4. A communications device as claimed in Claim 2, wherein the further information
forms part of the data being transmitted by the controller.
5. A communications device as claimed in Claim 1, wherein the shared channel
comprises a plurality of frequency division multiplexed symbols in the time domain and a plurality of
sub-carriers in the frequency domain and transmission of the signalling information includes a
contiguous sub-set of the frequency division multiplexed symbols starting at one of the predetermined
frequency division multiplexed symbols.
6. A communications device as claimed in Claim 1, wherein the controller is configured
to transmit the data by mapping data symbols representing the frequency division multiplexed symbols
by modulating the sub-carriers of the shared channel with modulation symbols representing the data
symbols, the modulation order of the modulation symbols being so that the data can be transmitted in a
temporal length which is less than the temporal length of the time period of the shared channel.
7 . A communications device as claimed in Claim 1, wherein the time period of the
shared channel is formed from a sub-frame of a frame into which the up-link is divided.
8. A communications device as claimed in Claim 7 , wherein the shared channel is
formed from two time slots into which the sub-frame is divided and the predetermined number of
frequency division multiplexed symbols is the number of symbols in one of the time slots.
9. A communications device as claimed in Claim 1, wherein the controller is configured
in combination with the receiver unit
to receive control information from the mobile communications network for configuring the
transmission of the signals representing the data in the shared channel, whereby other communications
devices can be configured to adapt transmissions of signals in the same shared channel with the
transmission of the signals representing the data by the communications device, and the controller is
configured in combination with the transmitter unit
to configure the transmitter unit in accordance with the control information received from the
mobile communications network to transmit the signals representing the data in the shared channel.
10. A method of transmitting data to or receiving data from a mobile communications
network, the mobile communications network including one or more network elements which are
arranged to form a wireless access interface for transmitting and receiving the data, the method
comprising
transmitting signals representing the data on an up-link of the wireless access interface to the
mobile communications network,
receiving signals representing the data transmitted on a down-link from the mobile
communications network via the wireless access interface, the wireless access interface providing a
plurality of communications resource elements across a frequency range for the down-link and the uplink,
the communications resource elements being formed by dividing sub-carriers at different
frequencies into a plurality of time periods, one or more of the sub-carriers being provided to form, in
the time domain, frequency division multiplexed symbols, each of the time periods comprising a
predetermined number of the frequency division multiplexed symbols, wherein the up-link includes a
shared channel providing the communications resources for allocation to the communications device
by the mobile communications network for transmitting the data on the up-link to the mobile
communications network, the shared channel providing communications resources which are shared
with other communications terminals and comprising in the time domain, the predetermined number
of frequency division multiplexed symbols in each time period for allocation to the communications
device, and
controlling the transmitting the signals and the receiving the signals to transmit or receive the
data, wherein the controlling the transmitting includes
transmitting to the mobile communications network a request to transmit data in a smaller
number of frequency division multiplexed symbols than are available on the shared channel,
receiving from the mobile communications network an indication of a sub-set of the
predetermined number of frequency division multiplexed symbols in which the communications
device should transmit the data on the shared channel, and
transmitting signals representing the data in the shared channel to occupy a smaller number of
frequency division multiplexed symbols than the number of the predetermined number of frequency
division multiplexed symbols of the time period of the shared channel.
11. A method as claimed in Claim 10, wherein the controlling the transmitting includes
transmitting the signals representing the data in the smaller number of frequency division multiplexed
symbols within the time period of the shared channel starting at a different one of the predetermined
number of frequency division multiplexed symbols, each of the different starting frequency division
multiplexed symbols representing further information.
12. A method as claimed in Claim 10, wherein the controlling the transmitting includes
transmitting the signals representing the data includes transmitting one or more reference symbols
included in the number of frequency division multiplexed symbols to assist in demodulating the
received signal to recover the data, and
varying a position of the one or more reference symbol within the transmitted frequency
division multiplexed symbols between a plurality of locations within the transmitted symbols, each of
the locations representing further information.
13. An infrastructure equipment for forming part of a mobile communications network
and providing a wireless access interface for transmitting data to and receiving data from a
communications device, the infrastructure equipment comprising
a transmitter unit configured to transmit signals representing the data on a down-link of the
wireless access interface to the mobile communications network,
a receiver unit configured to receive signals representing the data transmitted on an up-link
from the mobile communications network via the wireless access interface, the wireless access
interface providing a plurality of communications resource elements across a frequency range for the
down-link and the up-link, the communications resource elements being formed by dividing subcarriers
at different frequencies into a plurality of time periods, one or more of the sub-carriers being
provided to form, in the time domain, frequency division multiplexed symbols, each of the time
periods comprising a predetermined number of the frequency division multiplexed symbols, wherein
the up-link includes a shared channel providing the communications resources for allocation to the
communications device by the infrastructure equipment for transmitting the data on the up-link to the
infrastructure equipment, the shared channel providing communications resources which are shared
with other communications terminals and comprising in the time domain, the predetermined number
of frequency division multiplexed symbols in each time period for allocation to the communications
device, and
a controller configured to control the receiver unit to receive the signals and the transmitter
unit to transmit the signals to transmit or receive the data, wherein the controller is configured to
control the transmitter unit and the receiver unit
to receive from a communications device a request to transmit data in a smaller number of
frequency division multiplexed symbols than are available on the shared channel,
to transmit to the communications device an indication of a sub-set of the predetermined
number of frequency division multiplexed symbols in which the communications device should
transmit the data on the shared channel, and
to receive signals representing the data in the shared channel within a smaller number of
frequency division multiplexed symbols than the number of the predetermined number of frequency
division multiplexed symbols of the time period of the shared channel.
14. An infrastructure equipment as claimed in Claim 13, wherein the controller is
configured to receive the signals representing the data in the smaller number of frequency division
multiplexed symbols within the time period of the shared channel starting at a different one of the
predetermined number of frequency division multiplexed symbols, each of the different starting
frequency division multiplexed symbols representing further information.
15. An infrastructure equipment as claimed in Claim 13, wherein the controller is
configured to receive the signals representing the data in the smaller number of frequency division
multiplexed symbols within the time period of the shared channel, the received signals representing
the data with one or more reference symbols included in the number of frequency division multiplexed
symbols to assist in demodulating the received signal to recover the data, the one or more reference
symbols transmitted with the data bearing symbols varying in location with respect to a position of the
data bearing symbols, each of the locations representing further information, and
the controller is configured to detect the further information based on the location of the one
or more reference symbols.
16. An infrastructure equipment or a mobile communications device substantially as
hereinbefore described with reference to the drawings.
17. A method of communicating data to and/or from a communications device
substantially as hereinbefore described with reference to the drawings.