METHOD AND TERMINAL DEVICE FOR ALLOCATING RESOURCES
IN A PLURALITY OF SUBFRAMES
BACKGROUND OF THE INVENTION
The present invention relates to wireless telecommunications systems and methods,
and in particular to systems and methods for allocating transmission resources in wireless
telecommunication systems.
Mobile communication systems have evolved over the past ten years or so from the
GSM System (Global System for Mobile communications) to the 3G system and now include
packet data communications as well as circuit switched communications. The third generation
partnership project (3GPP) is developing a fourth generation mobile communication system
referred to as Long Term Evolution (LTE) in which a core network part has been evolved to
form a more simplified architecture based on a merging of components of earlier mobile radio
network architectures and a radio access interface which is based on Orthogonal Frequency
Division Multiplexing (OFDM) on the downlink and Single Carrier Frequency Division
Multiple Access (SC-FDMA) on the uplink.
Third and fourth generation mobile telecommunication systems, such as those based
on the 3GPP defined UMTS and Long Term Evolution (LTE) architectures, are able to
support a more sophisticated range of services than simple voice and messaging services
offered by previous generations of mobile telecommunication systems.
For example, with the improved radio interface and enhanced data rates provided by
LTE systems, a user is able to enjoy high data rate applications such as mobile video
streaming and mobile video conferencing that would previously only have been available via
a fixed line data connection. The demand to deploy third and fourth generation networks is
therefore strong and the coverage area of these networks, i.e. geographic locations where
access to the networks is possible, is expected to increase rapidly.
The anticipated widespread deployment of third and fourth generation networks has
led to the parallel development of a class of devices and applications which, rather than taking
advantage of the high data rates available, instead take advantage of the robust radio interface
and increasing ubiquity of the coverage area. Examples include so-called machine type
communication (MTC) applications, some of which are in some respects typified by semiautonomous
or autonomous wireless communication devices (MTC devices) communicating
small amounts of data on a relatively infrequent basis. Examples include so-called smart
meters which, for example, are located i a customer's home and periodically transmit data
back to a central MTC server relating to the customer's consumption of a utility such as gas,
water, electricity and so on. Smart metering is merely one example of potential MTC device
applications. Further information on characteristics of MTC-type devices can be found, for
example, in the corresponding standards, such as ETSI TS 122 368 V 0.530 (2011-07) /
3GPP TS 22.368 version 10.5.0 Release 10) [1].
Whilst it can be convenient for a terminal such as an MTC-type terminal to take
advantage of the wide coverage area provided by a third or fourth generation mobile
telecommunication network there are at present disadvantages. Unlike a conventional third or
fourth generation mobile terminal such as a smartphone, a primary driver for MTC-type
terminals will be a desire for such terminals to be relatively simple and inexpensive. The type
of functions typically performed by an MTC-type terminal (e.g. simple collection and
reporting / reception of relatively small amounts of data) do not require particularly complex
processing to perform, for example, compared to a smartphone supporting video streaming.
However, third and fourth generation mobile telecommunication networks typically employ
advanced data modulation techniques and support wide bandwidth usage on the radio
interface which can require more complex and expensive radio transceivers and decoders to
implement. It is usually justified to include such complex elements in a smartphone as a
smartphone will typically require a powerful processor to perform typical smartphone type
functions. However, as indicated above, there is now a desire to use relatively inexpensive
and less complex devices which are nonetheless able to communicate using LTE-type
networks.
With this in mind there has been proposed a concept of so-called "virtual carriers"
operating within the bandwidth of a "host carrier", for example, as described in co-pending
UK patent applications numbered GB 1101970.0 [2], GB 1101981.7 [3], GB 1101966.8 [4],
GB 1101983.3 [5], GB 1101853.8 [6], GB 1101982.5 [7], GB 1101980.9 [8] and GB
1101972.6 [9]. A main principle underlying the concept of a virtual carrier is that a frequency
subregion within a wider bandwidth host earner is configured for use as a self-contained
carrier, for example including all control signalling within the frequency subregion. An
advantage of this approach is to provide a carrier for use by low-capability terminal devices
capable of operating over only relatively narrow bandwidths. This allows devices to
communicate on LTE-type networks, without requiring the devices to support full bandwidth
operation. By reducing the bandwidth of the signal that needs to be decoded, the front end
processing requirements (e.g., FFT, channel estimation, subframe buffering etc.) of a device
configured to operate on a virtual carrier are reduced since the complexity of these functions
is generally related to the bandwidth of the signal received.
There are, however, some potential drawbacks with some implementations of the
"virtual carrier" approach. For example, in accordance with some proposed approaches the
available spectrum is hard partitioned between the virtual carrier and the host carrier. This
hard partitioning can be inefficient for a number of reasons. For example, the peak data rate
that can be supported by high-rate legacy devices is reduced because high-rate devices can
only be scheduled a portion of the bandwidth (and not the whole bandwidth). Also, when the
bandwidth is partitioned in this way there can be a loss of trunking efficiency (there is a
statistical multiplexing loss).
What is more, in some respects the virtual carrier approach represents a relatively
significant departure from the current operating principles for LTE-type networks. This means
relatively substantial changes to the current standards might be required to incorporate the
virtual carrier concept into the LTE standards framework, thereby increasing the practical
difficulty of rolling out these proposed implementations.
Another proposal for reducing the required complexity of devices configured to
communicate over LTE-type networks is proposed in co-pending UK patent applications
numbered GB 1121767.6 [ 1 1] and GB 121766.8 [12]. These applications propose schemes
for communicating data between a base station and a reduced-capability terminal device in an
LTE-type wireless telecommunications system operating over a system frequency band.
Physical-layer control information for the reduced-capability terminal device is transmitted
from the base station using subcarriers selected from across the system frequency band as for
conventional LTE terminal devices. However, higher-layer data for reduced-capability
terminal devices (e.g. ATC user-plane data) is transmitted using only subcarriers selected
from within a restricted frequency band which is smaller than and within the system
frequency band. The terminal device is aware of the restricted frequency band, and as such
need only buffer and process data within this restricted frequency band during periods where
higher-layer data is being transmitted. The terminal device buffers and processes the full
system frequency band during periods when physical-layer control information is being
transmitted. Thus, the reduced-capability terminal device may be incorporated in a network in
which physical-layer control information is transmitted over a wide frequency range, but only
needs to have sufficient memory and processing capacity to process a smaller range of
frequencies for the higher-layer data.
There are, however, some potential drawbacks with some implementations of the
schemes proposed in GB 1121767.6 [ 1 1] and GB 1121766.8 [12]. For example, the
scheduling flexibility available to the base station may be reduced because of the requirement
to allocate resources to reduced-capability devices within a narrowed frequency band.
Furthermore, where there is at least flexibility in selecting the reduced frequency band to be
used, there can be a need for additional signalling between the base station and the reducedcapability
terminal devices to negotiate (i.e. agree) the frequency range to be used. This is
because the reduced-capability terminal device and the base station both need to know the
narrowed bandwidth to be used such that the terminal device knows which part of the frame
structure to buffer, and the base station knows to allocate resources for the reduced capability
terminal device within this bandwidth.
Another proposal for reducing the required complexity of devices configured to
communicate over LTE-type networks is proposed in the discussion document Rl-1 131 13
from Pantech submitted for the 3GPP TSG-RAN WG1 #66bis meeting in Zhuhai, China, 10
October 2011 to 14 October 2011 [12]. The proposal is for low-complexity terminal devices
to be allocated a limited number of physical resource blocks as compared to a device with is
fully LTE-compliant. This scheduling restriction means terminal devices can implement their
turbo decoding function more simply, thereby reducing the processing complexity required.
However, while this can be helpful in reducing the processing capability required for
turbo decoding, significant amounts of a device's processing requirements are associated with
front-end digital signal processing functions prior to turbo decoding. Such front-end digital
signal processing functions include, for example, FFT / IFFT (fast Fourier transform / inverse
fast Fourier transform), channel estimation, equalization, digital filtering, etc.
Accordingly, there remains a desire for approaches which allow relatively inexpensive
and low complexity devices to communicate using LTE-type networks.
SUMMARY OF THE INVENTION
According to an aspect of the invention there is provided a method of operating a base
station in a telecommunications system comprising the base station and a plurality of terminal
devices arranged to communicate with the base station over a radio interface supporting a
downlink shared channel for conveying user-plane data from the base station to the terminal
devices and a downlink control channel for conveying control-plane data from the base station
to the terminal devices, wherein the control-plane data conveys information on physical
resource allocations for the downlink shared channel for respective ones of the terminal
devices, and wherein the radio interface is based on a radio frame structure comprising a
plurality of subframes, wherein each subframe comprises a control region for supporting the
downlink control channel and a user-plane region for supporting the downlink shared channel,
and wherein the method comprises transmitting in the control region of a first radio subframe
an indication of a physical resource allocation for a first terminal device on the shared
downlink channel in the user-plane region of a second radio subframe, and subsequently
transmitting user-plane data on the physical resource allocation for the first terminal device on
the shared downlink channel in the user-plane region of the second radio subframe.
In accordance with some embodiments the second radio subframe is transmitted a
predefined interval after the first radio subframe.
In accordance with some embodiments the predefined interval is of a duration which
corresponds with a predefined number of subframes.
In accordance with some embodiments the second radio subframe is transmitted a
selectable interval after the first radio subframe and the physical resource allocation for the
first terminal device is transmitted in association with an indication of a selected interval.
In accordance with some embodiments the indication of the selected interval
comprises an indication of a number of subframes.
In accordance with some embodiments the control region of the first radio subframe is
further used to transmit a physical resource allocation for a second terminal device on the
shared downlink channel in the user-plane region of the first radio subframe.
In accordance with some embodiments the first terminal device is a terminal device of
a first type and the second terminal device is a terminal device of a second type, the second
type being different from the first type.
In accordance with some embodiments the physical resource allocation for the first
terminal device is transmitted using a first format for conveying control-plane data and the
physical resource allocation for the second terminal device is transmitted using a second
format for conveying control-plane data, the second format being different from the first
format.
In accordance with some embodiments the physical resource allocation for the first
terminal device is transmitted using a first format for conveying control-plane data and the
physical resource allocation for the second terminal device is transmitted using a second
format for conveying control-plane data, the second format being the same as the first format.
In accordance with some embodiments the first terminal and second terminal devices
are of the same type.
In accordance with some embodiments the method further comprises determining an
estimate of extent to which available resources in the control region of the first and / or
second radio subframe will be used to convey physical resource allocations for terminal
devices before transmitting the control region of the first radio subframe, and, based on the
estimate, deciding to use the first radio subframe to convey an indication of a physical
resource allocation in the second radio subframe.
In accordance with some embodiments the first terminal device is a machine-type
communication, MTC, terminal device.
In accordance with some embodiments the telecommunications system is based
around a 3rd Generation Partnership Project, 3GPP, architecture.
According to another aspect of the invention there is provided a base station for use in
a telecommunications system comprising the base station and a plurality of terminal devices
arranged to communicate with the base station over a radio interface supporting a downlink
shared channel for conveying user-plane data from the base station to the terminal devices and
a downlink control channel for conveying control-plane data from the base station to the
terminal devices, wherein the control-plane data conveys information on physical resource
allocations for the downlink shared channel for respective ones of the terminal devices, and
wherein the radio interface is based on a radio frame structure comprising a plurality of
subframes, wherein each subframe comprises a control region for supporting the downlink
control channel and a user-plane region for supporting the downlink shared channel, and
wherein the base station is configured to transmit in the control region of a first radio
subframe an indication of a physical resource allocation for a first terminal device on the
shared downlink channel in the user-plane region of a second radio subframe and to
subsequently transmit user-plane data on the physical resource allocation for the first terminal
device on the shared downlink channel in the user-plane region of the second radio subframe.
According to another aspect of the invention there is provided a method of operating a
telecommunications system comprising a base station and a plurality of terminal devices
arranged to communicate over a radio interface supporting a downlink shared channel for
conveying user-plane data from the base station to the terminal devices and a downlinlc
control channel for conveying control-plane data from the base station to the terminal devices,
wherein the control-plane data is arranged to convey information on physical resource
allocations for the downlink shared channel for respective ones of the terminal devices, and
wherein the radio interface is based on a radio frame structure comprising a plurality of
subframes, wherein each subframe comprises a control region for supporting the downlink
control channel and a user-plane region for supporting the downlink shared channel, and
wherein the method comprises using the control region of a first radio subframe to convey an
indication of a physical resource allocation for a first terminal device on the shared downlink
channel in the user-plane region of a second radio subframe, the second radio frame being
subsequent to the first radio subframe.
According to another aspect of the invention there is provided a telecommunications
system comprising a base station and a plurality of terminal devices arranged to communicate
over a radio interface supporting a downlink shared channel for conveying user-plane data
from the base station to the terminal devices and a downlinli control channel for conveying
control-plane data from the base station to the terminal devices, wherein the control-plane
data is arranged to convey information on physical resource allocations for the downlink
shared channel for respective ones of the terminal devices, and wherein the radio interface is
based on a radio frame structure comprising a plurality of subframes, wherein each subframe
comprises a control region for supporting the downlink control channel and a user-plane
region for supporting the downlink shared channel, and wherein the telecommunications
system is configured such that the control region of a first radio subframe is used to convey an
indication of a physical resource allocation for a first terminal device on the shared downlink
channel in the user-plane region of a second radio subframe, the second radio frame being
subsequent to the first radio subframe.
According to another aspect of the invention there is provided a method of operating a
terminal device for communicating with a base station in a telecommunications system over a
radio interface supporting a downlink shared channel for conveying user-plane data from the
base station to the terminal device and a downlink control channel for conveying controlplane
data from the base station to the terminal device, wherein the control-plane data
conveys information on physical resource allocations for the downlink shared channel for the
terminal device, and wherein the radio interface is based on a radio frame structure
comprising a plurality of subframes, wherein each subframe comprises a control region for
supporting the downlink control channel and a user-plane region for supporting the downlink
shared channel, and wherein the method comprises receiving in the control region of a first
radio subframe an indication of a physical resource allocation for the terminal device on the
shared downlink channel in the user-plane region of a second radio subframe, and
subsequently receiving user-plane data on the physical resource allocation for the terminal
device on the shared downlink channel in the user-plane region of the second radio subframe.
In accordance with some embodiments the second radio subframe is received a
predefined interval after the first radio subframe.
In accordance with some embodiments the predefined interval is of a duration which
corresponds with a predefined number of subframes.
In accordance with some embodiments second radio subframe is received a selectable
interval after the first radio subframe and the physical resource allocation for the terminal
device is received in association with an indication of a selected interval.
In accordance with some embodiments the indication of the selected interval
comprises an indication of a number of subframes.
In accordance with some embodiments the control region of the first radio subframe is
further used to convey a physical resource allocation for a further terminal device on the
shared downlink channel in the user-plane region of the first radio subframe.
In accordance with some embodiments the terminal device is a terminal device of a
first type and the further terminal device is a terminal device of a second type, the second type
being different from the first type.
In accordance with some embodiments the physical resource allocation for the
terminal device is received using a first format for conveying control-plane data and the
physical resource allocation for the further terminal device is in a second format for
conveying control-plane data, the second format being different from the first format.
In accordance with some embodiments the physical resource allocation for the
terminal device is received using a first format for conveying control-plane data and the
physical resource allocation for the further terminal device is in a second format for
conveying control-plane data, the second format being the same as the first format.
According to another aspect of the invention there is provided a terminal device for
communicating with a base station in a telecommunications system over a radio interface
supporting a downlink shared channel for conveying user-plane data from the base station to
the terminal device and a downlink control channel for conveying control-plane data from the
base station to the terminal device, wherein the control-plane data conveys information on
physical resource allocations for the downlink shared channel for the terminal device, and
wherein the radio interface is based on a radio frame structure comprising a plurality of
subframes, wherein each subframe comprises a control region for supporting the downlink
control channel and a user-plane region for supporting the downlink shared channel, and
wherein the terminal device is configured to receive in the control region of a first radio
subframe an indication of a physical resource allocation for the terminal device on the shared
downlink channel in the user-plane region of a second radio subframe and to subsequently
receive user-plane data on the physical resource allocation for the terminal device on the
shared downlink channel in the user-plane region of the second radio subframe.
It will be appreciated that features and aspects of the invention described above in
relation to the first and other aspects of the invention are equally applicable and may be
combined with embodiments of the invention according to the different aspects of the
invention as appropriate, and not just in the specific combinations described above.
BRIEF DESCRIPTION OF DRAWINGS
Embodiments of the present invention will now be described by way of example only
with reference to the accompanying drawings where like parts are provided with
corresponding reference numerals and in which:
Figure 1 provides a schematic diagram illustrating an example of a conventional
mobile telecommunication system;
Figure 2 provides a schematic diagram illustrating a conventional LTE radio frame;
Figure 3 provides a schematic diagram illustrating an example of a conventional LTE
downlink radio subframe;
Figure 4 provides a schematic diagram illustrating a conventional LTE "camp-on"
procedure;
Figure 5 schematically represents a wireless telecommunications system according to
an embodiment of the invention;
Figure 6 schematically represents two arbitrary downlink subframes for
communicating with a conventional terminal device operating in the wireless
telecommunications system of Figure 5;
Figure 7 schematically represents two arbitrary downlink subframes for
communicating with a terminal device operating according to an embodiment of the invention
in the wireless telecommunications system of Figure 5;
Figure 8 schematically represents three arbitrary downlink subframes for
communicating with terminal devices in accordance with another embodiment of the
invention; and
Figure 9 schematically represents two arbitrary downlink subframes for
communicating with terminal devices in accordance with another embodiment of the
invention.
DESCRIPTION OF EXAMPLE EMBODIMENTS
Figure 1 provides a schematic diagram illustrating some basic functionality of a
mobile telecommunications network / system 100 operating in accordance with LTE
principles and which may be adapted to implement embodiments of the invention as described
further below. Various elements of Figure 1 and their respective modes of operation are wellknown
and defined in the relevant standards administered by the 3GPP (RTM) body and also
described in many books on the subject, for example, Holma H. and Toskala A [13]. It will be
appreciated that operational aspects of the telecommunications network which are not
specifically described below may be implemented in accordance with any known techniques,
for example according to the relevant standards.
The network 100 includes a plurality of base stations 101 connected to a core network
102. Each base station provides a coverage area 103 (i.e. a cell) within which data can be
communicated to and from terminal devices 104. Data is transmitted from base stations 101 to
terminal devices 104 within their respective coverage areas 103 via a radio downlink. Data is
transmitted from terminal devices 104 to the base stations 101 via a radio uplink. The core
network 102 routes data to and from the terminal devices 104 via the respective base stations
101 and provides functions such as authentication, mobility management, charging and so on.
Terminal devices may also be referred to as mobile stations, user equipment (UE), user
terminal, mobile radio, and so forth. Base stations may also be referred to as transceiver
stations / nodeBs / e-nodeBs, and so forth.
Mobile telecommunications systems such as those arranged in accordance with the
3GPP defined Long Term Evolution (LTE) architecture use an orthogonal frequency division
modulation (OFDM) based interface for the radio downlink (so-called OFDMA) and a single
carrier frequency division multiple access scheme (SC-FDMA) on the radio uplink. Figure 2
shows a schematic diagram illustrating an OFDM based LTE downlink radio frame 201. The
LTE downlink radio frame is transmitted from an LTE base station (known as an enhanced
Node B) and lasts 10 ms. The downlink radio frame comprises ten subframes, each subframe
lasting 1 ms. A primary synchronisation signal (PSS) and a secondary synchronisation signal
(SSS) are transmitted in the first and sixth subframes of the LTE frame. A physical broadcast
channel (PBCH) is transmitted in the first subframe of the LTE frame.
Figure 3 is a schematic diagram of a grid which illustrates the structure of an example
conventional downlink LTE subframe. The subframe comprises a predetermined number of
symbols which are transmitted over a 1ms period. Each symbol comprises a predetermined
number of orthogonal subcarriers distributed across the bandwidth of the downlink radio
carrier.
The example subframe shown in Figure 3 comprises 14 symbols and 1200 subcarriers
spread across a 20MHz bandwidth and in this example is the first subframe in a frame (hence
it contains PBCH). The smallest allocation of physical resource for transmission in LTE is a
resource block comprising twelve subcarriers transmitted over one subframe. For clarity, in
Figure 3, each individual resource element is not shown, instead each individual box in the
subframe grid corresponds to twelve subcarriers transmitted on one symbol.
Figure 3 shows in hatching resource allocations for four LTE terminals 340, 341, 342,
343. For example, the resource allocation 342 for a first LTE terminal (UE 1) extends over
five blocks of twelve subcarriers (i.e. 60 subcarriers), the resource allocation 343 for a second
LTE terminal (UE2) extends over six blocks of twelve subcarriers (i.e. 72 subcarriers), and so
on.
Control channel data is transmitted in a control region 300 (indicated by dottedshading
in Figure 3) of the subframe comprising the first "n" symbols of the subframe where
"n" can vary between one and three symbols for channel bandwidths of 3MHz or greater and
where "n" can vary between two and four symbols for a channel bandwidth of 1.4MHz. For
the sake of providing a concrete example, the following description relates to host carriers
with a channel bandwidth of 3MHz or greater so the maximum value of "n" will be 3 (as in
the example of Figure 3). The data transmitted in the control region 300 includes data
transmitted on the physical downlink control channel (PDCCH), the physical control format
indicator channel (PCFICH) and the physical HARQ indicator channel (PHICH). These
channels transmit physical layer control information.
PDCCH contains control data indicating which subcarriers of the subframe have been
allocated to specific LTE terminals. This may be referred to as physical -layer control
signalling / data. Thus, the PDCCH data transmitted in the control region 300 of the subframe
shown in Figure 3 would indicate that UE1 has been allocated the block of resources
identified by reference numeral 342, that UE2 has been allocated the block of resources
identified by reference numeral 343, and so on.
PCFICH contains control data indicating the size of the control region (i.e. between
one and three symbols for channel bandwiths of 3 MHz or greater and between two and four
symbols for channel bandwidths of 1.4 MHz).
PHICH contains HARQ (Hybrid Automatic Request) data indicating whether or not
previously transmitted uplink data has been successfully received by the network.
Symbols in a central band 10 of the time-frequency resource grid are used for the
transmission of information including the primary synchronisation signal (PSS), the
secondary synchronisation signal (SSS) and the physical broadcast channel (PBCH). This
central band 310 is typically 72 subcarriers wide (corresponding to a transmission bandwidth
of 1.08 MHz). The PSS and SSS are synchronisation signals that once detected allow an LTE
terminal device to achieve frame synchronisation and determine the physical layer cell
identity of the enhanced Node B transmitting the downlink signal. The PBCH carries
information about the cell, comprising a master information block (MIB) that includes
parameters that LTE terminals use to properly access the cell. Data transmitted to individual
LTE terminals on the physical downlink shared channel (PDSCH) can be transmitted in other
resource elements of the subframe. In general PDSCH conveys a combination of user-plane
data and non-physical layer control-plane data (such as Radio Resource Control (RRC) and
Non Access Stratum (NAS) signalling ) . The user-plane data and non-physical layer controlplane
data conveyed on PDSCH may be referred to as higher layer data (i.e. data associated
with a layer higher than the physical layer).
Figure 3 also shows a region of PDSCH containing system information and extending
over a bandwidth of R344. A conventional LTE subframe will also include reference signals
which are discussed further below but not shown in Figure 3 in the interests of clarity.
The number of subcarriers 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 subcarriers contained within a 20MHz channel
bandwidth (as schematically shown in Figure 3). As is known in the art, data transmitted on
the PDCCH, PCFICH and PHICH is typically distributed on the subcarriers across the entire
bandwidth of the subframe to provide for frequency diversity. Therefore a conventional LTE
terminal must be able to receive the entire channel bandwidth in order to receive and decode
the control region.
Figure 4 illustrates an LTE "camp-on" process, that is, the process followed by a
terminal so that it can decode downlink transmissions which are sent by a base station via a
downlink channel. Using this process, the terminal can identify the parts of the transmissions
that include system information for the cell and thus decode configuration information for the
cell.
As can be seen in Figure 4, in a conventional LTE camp-on procedure, the terminal
first synchronizes with the base station (step 400) using the PSS and SSS in the centre band
and then decodes the PBCH (step 401). Once the terminal has performed steps 400 and 401, it
is synchronized with the base station.
For each subframe, the terminal then decodes the PCFICH which is distributed across
the entire bandwidth of carrier 320 (step 402). As discussed above, an LTE downlink carrier
can be up to 20 MHz wide (1200 subcarriers) and a standard LTE-compliant terminal
therefore has to have the capability to receive and decode transmissions on a 20 MHz
bandwidth in order to decode the PCFICH. Accordingly, at the PCFICH decoding stage, with
a 20MHz carrier band, the terminal operates at a larger bandwidth (bandwidth of R320) than
during steps 400 and 401 (bandwidth of R310) relating to synchronization and PBCH
decoding.
The terminal then ascertains the PHICH locations (step 403) and decodes the PDCCH
(step 404), in particular for identifying system information transmissions and for identifying
its personal allocation grants. The allocation grants are used by the terminal to locate system
information and to locate its data in the PDSCH. Both system information and personal
allocations are transmitted on PDSCH and scheduled within the carrier band 320. Steps 403
and 404 also require a standard LTE-compliant terminal to operate on the entire bandwidth
R32o of the carrier band.
At steps 402 to 404, the terminal decodes information contained in the control region
300 of a subframe. As explained above, in LTE, the three control channels mentioned above
(PCFICH, PHICH and PDCCH) can be found across the control region 300 of the carrier
where the control region extends over the range R32o and occupies the first one, two or three
OFDM symbols of each subframe as discussed above. In a subframe, typically the control
channels do not use all the resource elements within the control region 300, but they are
scattered across the entire region, such that an LTE terminal has to be able to simultaneously
receive the entire control region 300 for decoding each of the three control channels.
The terminal can then decode the PDSCH (step 405) which contains system
information or data transmitted for this terminal.
As explained above, in an LTE subframe the PDSCH generally occupies groups of
resource elements which are neither in the control region nor in the resource elements
occupied by PSS, SSS or PBCH. The data in the blocks of resource elements 340, 341, 342,
343 allocated to the different mobile communication terminals (UEs) shown in Figure 3 have
a smaller bandwidth than the bandwidth of the entire carrier, although to decode these blocks
a terminal first receives the PDCCH spread across the frequency range R320 to determine if the
PDCCH indicates that a PDSCH resource is allocated to the UE and should be decoded. Once
a UE has received the entire subframe, it can then decode the PDSCH in the relevant
frequency range (if any) indicated by the PDCCH. So for example, UE 1 discussed above
decodes the whole control region 300 to determine its resource allocation and then extracts
the relevant data from the corresponding resource block 342.
Figure 5 schematically shows a telecommunications system 500 according to an
embodiment of the invention. The telecommunications system 500 in this example is based
broadly on an LTE-type architecture. As such many aspects of the operation of the
telecommunications system 500 are standard and well understood and not described here in
detail in the interest of brevity. Operational aspects of the telecommunications system 500
which are not specifically described herein may be implemented in accordance with any
known techniques, for example according to the LTE-standards.
The telecommunications system 500 comprises a core network part (evolved packet
core) 502 coupled to a radio network part. The radio network part comprises a base station
(evolved-nodeB) 504, a first terminal device 508 and a second terminal device 506. It will of
course be appreciated that in practice the radio network part may comprise a plurality of base
stations serving a larger number of terminal devices across various communication cells.
However, only a single base station and two terminal devices are shown in Figure 5 in the
interests of simplicity.
The terminal devices 506, 508 are arranged to communicate data to and from the base
station (transceiver station) 504. The base station is in turn communicatively connected to a
serving gateway, S-GW, (not shown) in the core network part which is arranged to perform
routing and management of mobile communications services to the terminal devices in the
telecommunications system 500 via the base station 504. In order to maintain mobility
management and connectivity, the core network part 502 also includes a mobility
management entity (not shown) which manages the enhanced packet service, EPS,
connections with the terminal devices 506, 508 operating in the communications system based
on subscriber information stored in a home subscriber server, HSS. Other network
components in the core network (also not shown for simplicity) include a policy charging and
resource function, PCRF, and a packet data network gateway, PDN-GW, which provides a
connection from the core network part 502 to an external packet data network, for example
the Internet. As noted above, the operation of the various elements of the communications
system 500 shown in Figure 5 may be broadly conventional apart from where modified to
provide functionality in accordance with embodiments of the invention as discussed herein.
In this example, it is assumed the second terminal device 506 is a conventional smartphone
type terminal device communicating with the base station 504. Thus, and as is
conventional, this second terminal device 506 comprises a transceiver unit 506a for
transmission and reception of wireless signals and a controller unit 506b configured to control
the smart phone 506. The controller unit 506b may comprise a processor unit which is
suitably configured / programmed to provide the desired functionality using conventional
programming / configuration techniques for equipment in wireless telecommunications
systems. The transceiver unit 506a and the controller unit 506b are schematically shown in
Figure 5 as separate elements. However, it will be appreciated that the functionality of these
units can be provided in various different ways, for example using a single suitably
programmed integrated circuit. As will be appreciated the smart phone 506 will in general
comprise various other elements associated with its operating functionality.
In this example, it is assumed the first terminal device 508 is a machine-type
communication (MTC) terminal device according to an embodiment of the invention. As
discussed above, these types of device may be typically characterised as semi-autonomous or
autonomous wireless communication devices communicating small amounts of data.
Examples include so-called smart meters which, for example, may be located in a customer's
house and periodically transmit information back to a central MTC server data relating to the
customer's consumption of a utility such as gas, water, electricity and so on. MTC devices
may in some respects be seen as devices which can be supported by relatively low bandwidth
communication channels having relatively low quality of service (QoS), for example in terms
of latency. It is assumed here the MTC terminal device 508 in Figure 5 is such a device. It
will, however, the appreciated that embodiments of the invention may also be incremented for
other types of terminal device.
As with the smart phone 506, the MTC device 508 comprises a transceiver unit 508a
for transmission and reception of wireless signals and a controller unit 508b configured to
control the MTC device 508. The controller unit 508b may comprise a processor unit which is
suitably configured / programmed to provide the desired functionality described herein using
conventional programming / configuration techniques for equipment in wireless
telecommunications systems. The transceiver unit 508a and the controller unit 508b are
schematically shown in Figure 5 as separate elements for ease of representation. However, it
will be appreciated that the functionality of these units can be provided in various different
ways following established practices in the art, for example using a single suitably
programmed integrated circuit. It will be appreciated the MTC device 508 will in general
comprise various other elements associated with its operating functionality (e.g. a power
source, possibly a user interface, and so forth).
The base station 504 comprises a transceiver unit 504a for transmission and reception
of wireless signals and a controller unit 504b configured to control the base station 504. The
controller unit 504b may comprise a processor unit which is suitably configured /
programmed to provide the desired functionality described herein using conventional
programming / configuration techniques for equipment in wireless telecommunications
systems. The transceiver unit 504a and the controller unit 504b are schematically shown in
Figure 5 as separate elements for ease of representation. However, it will be appreciated that
the functionality of these units can be provided in various different ways following
established practices in the art, for example using a single suitably programmed integrated
circuit. It will be appreciated the base station 504 will in general comprise various other
elements associated with its operating functionality. For example, the base station 504 will in
general comprise a scheduling entity responsible for scheduling communications. The
functionality of the scheduling entity may, for example, be subsumed by the controller unit
504b.
Thus, the base station 504 is configured to communicate data with the smart phone
506 over a first radio communication link 510 and communicate data with the MTC device
508 over a second radio communication link 12. Both radio links may be supported within a
single radio frame structure associated with the base station 504.
It is assumed here the base station 504 is configured to communicate with the smart
phone 506 over the first radio communication link 510 in accordance with the established
principles of LTE-based communications. It will be appreciated the base station may readily
obtain information indicating the different classes of terminal device which are attached to the
base station in accordance with conventional techniques. That is to say, the base station will
be aware that the smart phone is of a device class that includes conventional smartphones and
the MTC device is of a device class that includes MTC devices.
Figure 6 schematically represents two arbitrary downlink subframes (identified as
subframe "n" and subframe "n+1 " ) as seen by the smart phone 506 according to the
established LTE standards as discussed above. Each subframe is in essence a simplified
version of what is represented in Figure 3. Thus, each subframe comprises a control region
600 supporting the PCFICH, PHICH and PDCCH channels as discussed above and a PDSCH
region 602 for communicating higher-layer data (for example user-plane data and nonphysical
layer control-plane signalling) to respective terminal devices, such as the smart
phone 506, as well as system information, again as discussed above. For the sake of giving a
concrete example, the frequency bandwidth (BW) of the carrier with which the subframes are
associated is taken to be 20 MHz. Also schematically shown in Figure 6 by black shading are
example PDSCH downlink allocations 604 for the smart phone 506. In accordance with the
defined standards, and as discussed above, individual terminal devices derive their specific
downlink allocations for a subframe from PDCCH transmitted in the control region 600 of the
subframe. For the arbitrary example shown in Figure 6, the smart phone 506 is allocated
downlink resources spanning a relatively small fraction of the 20 MHz bandwidth near to the
upper end of the carrier frequency in subframe n, and is allocated a larger fraction of the
available 20 MHz bandwidth at a lower frequency in subframe "n+1" . The specific
allocations of PDSCH resources for the smart phone are determined by a scheduler in the
network based on the data needs for the device in accordance with standard techniques.
Although the smart phone 506 is typically only allocated a subset of the available
PDSCH resources in any given subframe, the smart phone 506 could be allocated these
resources anywhere across the full PDSCH bandwidth (BW). Accordingly, the smart phone
will in the first instance receive and buffer each entire subframe. The smart phone 506 will
then process each subframe to decode PDCCH to determine what resources are allocated on
PDSCH, and then process the data received during PDSCH symbols of the subframe and
extracts the relevant higher-layer data therefrom.
Thus, referring to Figure 6, the smart phone 506 represented in Figure 5 buffers for
each subframe the entire control region 600 (shaded dark grey in Figure 6) and the entire
PDSCH region 602 (transmitted in the resources contained in the areas shaded light grey and
black in Figure 6), and extracts the higher-layer data allocated to the smart phone (transmitted
in the resources contained in the area shaded black in Figure 6) from the PDSCH region 602
based on allocation information conveyed in the control region 600.
The inventor has recognised that the requirement for terminal devices to buffer and
process each complete subframe to identify and extract what will typically be only a small
fraction of the total PDSCH resources contained in the subframe for the terminal device
introduces a significant processing overhead. Accordingly, the inventor has conceived of
approaches in accordance with which example embodiments of the invention may allow for a
terminal device, for example an MTC device, to operate generally in accordance with the
principles of existing networks, but without needing to buffer and process an entire subframe
to identify and extract its own higher-layer data from that subframe.
This can be achieved in accordance with some embodiments of the invention by
delaying the timing of certain resource allocations relative to the timing of the transmission of
control data pertaining for the resource allocations as compared with conventional techniques.
This approach may conveniently be referred to as a "delayed grant" or "delayed allocation"
approach. As described above, in accordance with conventional techniques the control region
of a given subframe is used for allocating resources within that subframe. For example, in an
LTE system, PDCCH in subframe "n" is used for allocating resources on PDSCH in subframe
"n". However, in accordance with embodiments of the invention an alternative approach is
conceived of in which the control region of a given subframe is used for allocating resources
within a different and subsequent subframe. For example, in the general context of an LTEtype
system, PDCCH is subframe "n" may be used for certain types of terminal device for
allocating resources on PDSCH in subframe "n + X", where X is a non-zero positive integer.
This delayed-allocation approach can allow a terminal device to receive and process control
data to identify its resource allocations before the allocated resources are transmitted. The
terminal device may thus be configured to receive and decode only the relevant parts of the
subsequent downlink subframe carrying the allocated resources. That is to say, the terminal
device does not need to buffer each subframe to ensure it has access to its allocated resources
specified in the allocation information of the control data for the subframe once it has decoded
the control data. Instead, the terminal device is able to decode the control data during the
delay period to identify which (if any) downlink resource allocations are upcoming, and the
subsequently receive and process the corresponding portions of the relevant downlink
subframe accordingly.
Figure 7 schematically represents an approach for communicating data with a terminal
device according to an embodiment of the invention. More specifically, Figure 7
schematically represents two arbitrary downlink subframes (identified as subframe "n" and
subframe "n+1" ) as interpreted by the MTC device 508 according to an embodiment of the
invention. Figure 7 is in some respects similar to Figure 6, and aspects of Figure 7 which
directly correspond to aspects of Figure 6 are not described again in detail. In this example it
is assumed the elements and general principles of the frame structure employed for
communicating with the MTC device 508 are the same as the elements frame structure used
for communicating with the conventional smartphone device 506, except where modified as
discussed below. That is to say, the frame structure used for communicating with the MTC
device 508 comprises a PDCCH, PDSCH, following general LTE principles. Furthermore,
and as discussed above in relation to Figure 5, in this particular example communications with
the MTC device 508 and the smart phone device 506 are supported within the same frame
transmissions from the base station 504. That is to say, the base station communicates with
the conventional smart phone 506 and the MTC device 508 according to an embodiment of
the invention using the same frames.
Various elements of each subframe in Figure 7 are in essence represented as simplified
versions of corresponding elements of what is represented in Figure 3. Thus, each subframe
comprises a control region 700 supporting channels corresponding to the PCFICH, PHICH
and PDCCH channels as discussed above and a PDSCH region 702 for communicating
higher-layer data (for example user-plane data and non-physical layer control-plane
signalling) to respective terminal devices, such as the smart phone 506 and MTC device 508,
as well as system information, again as discussed above. For the sake of giving a concrete
example, the frequency bandwidth (B ) of the carrier with which the subframes are
associated is taken to be 20 MHz. Although not shown in Figure 7 for simplicity, the PDSCH
regions 702 may include PDSCH downlink allocations for the smart phone 508 similar to
those shown with black shading in Figure 6. In accordance with the general principles
underlying the relevant standards, and as discussed above, individual conventional terminal
devices, such as the smart phone 508, operating within wireless telecommunications systems
according to embodiments of the invention may derive their specific downlink allocations for
a subframe from information transmitted on PDCCH in the control region 700 of the relevant
subframe, again as represented in Figure 6. The control regions 700 represented in Figure 7
may thus be used in accordance with these established principles to identify resource
allocations for conventional terminal devices, such as the smart phone 506, within the same
subframe. This aspect of communications with conventional devices supported by the
subframes schematically represented in Figure 7 may be the same as described above, for
example with reference to Figure 6.
However, in accordance with an embodiment of the invention, the control regions 700
of the subframes represented in Figure 7 also carry delayed resource allocation information
for terminal devices operating in accordance with embodiments of the invention. Thus, in the
example shown in Figure 7, the control region 700 in subframe "n" carries resource allocation
information for downlink resources 704 allocated to the MTC device 508 in subframe "n+1".
The MTC device 508 is configured to receive and decode the control region 700 in subframe
"n" in accordance with broadly conventional techniques. The MTC device 508 may then
process the control region from subframe "n" to identify its resource allocations (if any)
during the remaining period of subframe "n". This may be performed according to the same
general principles as for conventional devices, the only difference being a difference in the
subframe in which the resource allocations are to be transmitted by the base station. That is to
say, for a conventional terminal device any resource allocations conveyed in the control
region 700 of subframe "n" are associated with resource allocations on PDSCH in subframe
"n", whereas for a terminal device operating in accordance with an embodiment of the
invention, resource allocations conveyed in the control region 700 of subframe "n" are
associated with resource allocations on PDSCH in subframe "n+1". Thus, having decoded the
control region 700 of subframe "n" and identified a resource allocation 704 in subframe "n+1"
therefrom, the MTC device 508 is already aware before transmission of subframe "n+1"
which subcarriers of PDSCH in subframe "n+1" have been allocated to the MTC device 508.
The MTC device may thus buffer and process these subcarriers accordingly. Because a
terminal device 508 operating in accordance with an embodiment of the invention is aware
which PDSCH resources need to be received and decoded before they are transmitted, there is
no need for the device to buffer and process the entire subframe to extract its resource
allocations after they have been transmitted. This simplifies the processing and storage
requirements of a device operating in accordance with an embodiment of the invention,
thereby simplifying the device and helping reduce its cost.
In the example shown in Figure 7, the terminal devices operating according to an
embodiment of the invention is allocated resources on PDSCH in a subframe that is delayed
relative to the subframe conveying the indication of the resource allocations one subframe.
That is to say, indications of resource allocations on PDSCH in a subframe "n+1" are
conveyed using PDCCH in subframe "n". For the sake of convenience in terminology, this
may be summarised as the delaying of resource allocations by one subframe. It will be
appreciated that in other examples the allocated resources may be delayed by other intervals
(other numbers of subframes) relative to the transmission of the information indicating the
allocation of the resources. An example of this is schematically represented in Figure 8.
Figure 8 is similar to, and will be understood from Figure 7. However, Figure 8 is
different from Figure 7 in that in addition to showing subframes "n" and "n+1" as in Figure 7,
Figure 8 also schematically represents subframe "n+2".
In the example shown in Figure 8, the control region 700 of subframe "n" may be used
for allocating resources to conventional terminal devices in subframe "n" (not shown for
simplicity) and to terminal devices according to embodiments of the invention in subframe
"n+1", as discussed above with reference to Figure 7. However in addition, the control region
700 of subframe "n" in this example also carries an indication of a resource allocation 706 on
PDSCH in subframe "n+2" for a terminal device operating according to an embodiment of the
invention. Thus, in the example shown in Figure 8, the control region 700 in subframe "n"
carries resource allocation information for downlink resources 704, 706 allocated to terminal
devices in subframes "n+1" and "n+2". Whilst this shows an example in which terminal
devices according to embodiments of the invention may be allocated physical downlink
resources on PDSCH in subframes having different delays relative to the subframe in which
the resource allocation information is transmitted on PDCCH, in other examples it may be the
case that the same delay is used for all delayable terminal devices. The extent of the delay
may be set according to how much time the respective terminal devices need to process the
PDCCH to determine their allocations on PDSCH. In general it may be preferable for the
delay to be as short as possible while still allowing the terminal devices enough time to
properly decode PDCCH to allow them to configure themselves to receive PDSCH on the
allocated subcarriers.
In many cases it will be beneficial if the terminal device is aware of the delay that is to
be employed by the base station and there are a number of different ways in which
information on the delay can be established by / shared between the base station 504 and
terminal device 508.
In some cases the delay may be standardised within the wireless communications
system. For example, it may be decided that any terminal device and base station which are to
operate within the wireless communication system in accordance with an implementation of
an embodiment of the invention should assume a delay of one subframe (or other fixed
number of subframes). This provides a simple approach, but with limited flexibility. It will be
appreciated that the delay to be used may be established by the base station and terminal
device in various ways based on predefined standards. For example, rather than explicitly
define the delay, a mechanism for deriving the delay may be defined. For example, the
standards may specify that all terminal devices which are to operate in accordance with
embodiments of the invention (e.g. based on device class) are to derive a delay from an
identifier that is known to both the base station and the terminal device. For example, in a
simple implementation any terminal devices associated with an odd-numbered IMSI may
assume a first delay while any terminal devices associated with an even IMSI may assume a
second delay. This provides a simple mechanism for employing multiple delays which can
help in sharing the available resources, for example when there is a desire to communicate
with a large number of terminal devices using delayed resource allocations in accordance with
an embodiment of the invention at around the same time.
However, to improve overall scheduling flexibility it may be preferable in some
implementations for the delay to be selected by the base station and conveyed to the terminal
device. For a semi-permanent delay (e.g. One that remains fixed for the duration of a given
connection), this could be done during a cell-attach procedure. The operating capabilities of
the terminal device will typically set some limits on the delay that may be used. For example
a given terminal device may be unable to operate using a delay having a duration below some
threshold. This may be accounted for by standardisation, for example by limiting the
minimum delay that may be used by the base station for that particular terminal device (for
example based on the type/class of terminal device), or based on the exchange of capability
messages between the base station and terminal device.
However, in cases where the delay may be selected from a range of possible delays,
for example by the base station scheduler function based on current traffic conditions, in
general it is expected that the most convenient and flexible manner to indicate a selected delay
to be used by the base station for transmitting user plane data (or other higher layer data) on
PDSCH after having transmitted an indication of the subcarriers (i.e. resource allocations) on
PDCCH in a previous subframe will be to transmit an indication of the delay in association
with the transmission of the indication of the resources to be allocated. For example, this
might be done by adopting a new format for the resource allocation messages on PDCCH
which allow for the indication of a delay. For example, the indication of the delay may be an
indication of a number of subframes following the current subframe in which the allocated
PDSCH resource is to be transmitted.
For example, with reference to Figure 8, the PDCCH signalling in control region 700
of subframe "n" indicating the allocation of the PDSCH resources 704 in subframe "n+1" may
be associated with an indication of one subframe delay. Similarly, the PDCCH signalling in
control region 700 of subframe "n" indicating the allocation of the PDSCH resources 706 in
subframe "n+2" may be associated with an indication of two subframes delay. In the context
of LTE, an indication of the delay may be provided by adopting a modified downlink control
information (DCI) format. Thus, delayed-grant resource allocations such as described above
may be associated with a modified DCI format as compared to conventional resource
allocations in which the resources are allocated in the same subframe as the PDCCH
indication of the resources.
This provides a base station scheduler with enhanced flexibility in communicating
data with terminal devices following a delayed grant approach in accordance with
embodiments of the invention. This is because the base station is free to schedule downlink
transmissions on PDCCH in multiple subsequent subframes, thereby allowing the base station
to better accommodate changes in traffic. Furthermore, a base station may be configured to
recognise that different types of terminal device have different capabilities (e.g. based on a
defined class type shared during a camp on procedure or defined in a register of the network
for the terminal device) and to allocate different delays accordingly. For example particularly
low capability devices may be provided with greater delays to give them more time to decode
PDCCH before transmission of any corresponding user plane data that has been allocated on
PDSCH.
In some examples the terminal device may not be aware in advance of a delay that is
to be used by the base station between transmitting resource allocation information on
PDCCH and transmitting the associated user-plane data on PDSCH. For example, in some
implementations the base station may be configured to allocate delayed resources for a
terminal device according to an embodiment of the invention by providing an indication of
the relevant subcarriers on PDCCH in subframe "n" as discussed above. The base station may
then transmit user plane data on the allocated subcarriers in a subsequent subframe "n+X"
having an arbitrary delay (i.e. a delay "X" that is selected by the base station and not known to
the terminal device). In such a system, a terminal device operating in accordance with an
embodiment of the invention may decode PDCCH in subframe "n" and identify the allocated
subcarriers as discussed above go to sleep. Because the terminal device in this example will
not know the subframe in which the actual resources will be transmitted (i.e. the terminal
device does not know "X"), the terminal device may simply proceed to attempt to decode the
relevant subcarriers identified in the resource allocation on PDCCH in subframe "n" on the
next and every subsequent subframe until the terminal devices able to successfully decode the
relevant resources on PDSCH.
It will be appreciated that whilst the above embodiments have focused primarily on
delaying PDSCH transmissions for certain types of terminal device relative to other types of
terminal device, the concept of delayed grant allocations may be applied more generally. For
example, even when communicating with a terminal device having the ability to buffer and
decode an entire subframe in a conventional manner such that it is possible to allocate
PDSCH resources in the same subframe as the PDCCH resources indicating the allocation (as
is currently done), it may nonetheless be advantageous in some circumstances to allocate
delayed grants. For example, this can help provide a base station scheduler with a greater
degree of flexibility for sharing the available PDCCH resources for allocating PDSCH
resources in different subframes.
For example, it is in principle possible that there will not be sufficient PDCCH
resources to allocate all of the available PDSCH resources in any given subframe. This might
be the case, for example, where there are lots of terminal devices allocated small amounts of
resources on PDSCH. In such circumstances it is possible there are not be enough resources
available on PDCCH to individually allocate all the available PDSCH resources to the large
number of terminal devices in a single subframe. This can be the case even if there are there
are sufficient PDSCH resources to carry the data to be communicated. n a conventional LTE
system this issue can therefore potentially lead to a waste of resources in that available
PDSCH resources cannot be allocated because of a lack of PDCCH resources. However, in
accordance with embodiments of the invention, a base station scheduling function which is
aware of an upcoming subframe in which there are insufficient PDCCH resources to allocate
all of the available PDSCH resources for the subframe may allocate those PDSCH resources
on PDCCH in an earlier subframe. The implementation principles for doing this follow those
described above for the case of delaying grant for a reduced-capability terminal device, a
difference being the reason behind the decision to allocate downlink resources for a terminal
device in a subframe which is later than the subframe carrying the indication of the allocation
of downlink resources. In the examples described above for reduced-capability terminal
devices the delayed grant is to provide the terminal devices with sufficient time to decode the
resource allocation information before needing to receive and decode the allocated (granted)
resources. However, in accordance with other embodiments of the invention, the delayed
grant may be to allow the base station scheduling function to use available PDCCH resources
to allocate PDSCH resources in other subframes for which there would otherwise be
insufficient PDCCH resources.
This principle is schematically represented in Figure 9. Figure 9 is in general similar
to, and will be understood, from Figures 6, 7 and 8. Thus, each subframe comprises a control
region 900 and a PDSCH region 902. For Figure 9 it is assumed that PDSCH in subframe
"n+1" is to be used for conveying user plane data to a large number of separate terminal
devices (which might readily happen when communicating with the MTC-type devices
requiring only small amounts of information at any time, for example). The conventional
aspects of the base station scheduling function may be responsible for managing the resource
allocations which results in this situation. Because of the large number of individual terminal
devices to be allocated resources in subframe "n+1", the corresponding control region 900 in
subframe "n+1 " is heavily utilised, and may indeed become full before it has been possible to
allocate all the available PDSCH resources in subframe "n+1". n accordance with an
embodiment of the invention, the base station scheduler is configured to identify this situation
has arisen (the base station can readily identify this because the base station is ultimately
responsible for the scheduling) and to determine whether it is possible to advance-allocate
PDSCH resources in subframe "n+1" using control signalling on PDCCH in subframe "n",
thereby avoiding wastage of PDSCH resources in subframe "n+1" which might otherwise not
be allocatable. If the base station determines it is possible to advance-allocate PDSCH
resources in subframe "n+1" using control signalling on PDCCH in subframe "n" (e.g.
because there is a terminal device to be scheduled on PDSCH in subframe "n+1" which
supports delayed grant as described above and there are available resources on PDSCH in
subframe "n" to convey the resource allocation information), the base station may be
configured to allocate resources to one or more terminal devices on PDSCH in subframe
"n+1" using control signalling on PDCCH in subframe "n" following the principles of the
above-described techniques. This is represented in Figure 9 by heavy arrows schematically
representing PDSCH resource allocations in subframe "n+1 " being conveyed in the respective
control regions 900 of subframes "n" and "n+1". The control region 900 subframe "n" is
schematically shown with lighter shading than the control region 900 of subframe "n+1" to
indicate the reduced utilisation of the available PDCCH resources in this subframe.
Thus, in accordance with various embodiments of the invention a telecommunications
system may be configured to support a system of resource allocations in which information
conveying an indication of a resource allocation in one subframe is transmitted in another
subframe. In some situations this might be performed to give certain types of terminal device
more time to decode the resource allocation information before needing to decode the
resource allocation itself. In other situations this might be performed to allow the base station
to employ underutilised allocation resources in one subframe to allocate resources in another
subframe. These two types of situation might be conveniently referred to as "delayed grant" or
"advanced allocation".
It will be appreciated that the above-described functionality may be implemented with
appropriate configuration of the relevant elements of the telecommunication system elements
(e.g. the base station and terminal devices) in accordance with conventional techniques for
providing such types of functionality. Typically this will be through appropriate programming
of the relevant elements. For example, the scheduling of downlink resource allocations on
PDSCH for the various terminal devices operating within the telecommunication system and
the timing of the associated signalling on PDCCH for providing operation in accordance with
an embodiment of the invention may be governed by appropriate modification of a base
station scheduler otherwise operating in accordance with conventional techniques.
Although embodiments of the invention have been described primarily with reference
to an LTE mobile radio network, it will be appreciated that the present invention can be
applied to other forms of network such as GSM, 3G / UMTS, CDMA2000, etc.
Thus, there has been described a method of operating a telecommunications system
comprising a base station and a plurality of terminal devices arranged to communicate over a
radio interface supporting a downlink shared channel for conveying user-plane data from the
base station to the terminal devices and a downlink control channel for conveying controlplane
data from the base station to the terminal devices, wherein the control-plane data is
arranged to convey information on physical resource allocations for the downlink shared
channel for respective ones of the terminal devices, and wherein the radio interface is based
on a radio frame structure comprising a plurality of subframes, wherein each subframe
comprises a control region for supporting the downlink control channel and a user-plane
region for supporting the downlink shared channel, and wherein the method comprises using
the control region of a first radio subframe to convey an indication of a physical resource
allocation for a first terminal device on the shared downlink channel in the user-plane region
of a second radio subframe, the second radio frame being subsequent to the first radio
subframe.
Further particular and preferred aspects of the present invention are set out in the
accompanying independent and dependent claims. It will be appreciated that features of the
dependent claims may be combined with features of the independent claims in combinations
other than those explicitly set out in the claims.
REFERENCES
[I] ETSI TS 122 368 V10.530 (201 1-07) / 3GPP TS 22.368 version 10.5.0 Release 10)
[2] UK patent application GB 1101970.0
[3] UK patent application GB 1101981.7
[4] UK patent application GB 1101966.8
[5] UK patent application GB 1101983 .3
[6] UK patent application GB 1101853 .8
[7] UK patent application GB 101982.5
[8] UK patent application GB 1 0 1980.9
[9] UK patent application GB 1101972.6
[10] UK patent application GB 1121767.6
[I I] UK patent application GB 11 1766.
[12] Rl-1131 13, Pantech USA, 3GPP TSG-RAN WGl #66bis meeting, Zhuhai, China, 10
October 20 to 14 October 201 1
[13] Holma H. and Toskala A, "LTE for UMTS OFDMA and SC-FDMA based radio
access", John Wiley and Sons, 2009
CLAIMS
1. A method of operating a terminal device for communicating with a base station in a
telecommunications system over a radio interface supporting a downlink shared channel for
conveying user-plane data from the base station to the terminal device and a downlink control
channel for conveying control-plane data from the base station to the terminal device, wherein
the control-plane data conveys information on physical resource allocations for the downlink
shared channel for the terminal device, and wherein the radio interface is based on a radio
frame structure comprising a plurality of subframes, wherein each subframe comprises a
control region for supporting the downlink control channel and a user-plane region for
supporting the downlink shared channel, and wherein the method comprises receiving in the
control region of a first radio subframe an indication of a physical resource allocation for the
terminal device on the shared downlink channel in the user-plane region of a second radio
subframe, and subsequently receiving user-plane data on the physical resource allocation for
the terminal device on the shared downlink channel in the user-plane region of the second
radio subframe.
2. The method of claim 1, wherein the second radio subframe is received a predefined
interval after the first radio subframe.
3. The method of claim 2, wherein the predefined interval is of a duration which
corresponds with a predefined number of subframes.
4. The method of claim 1, wherein second radio subframe is received a selectable
interval after the first radio subframe and the physical resource allocation for the terminal
device is received in association with an indication of a selected interval.
5. The method of claim 2, wherein the indication of the selected interval comprises an
indication of a number of subframes.
6. The method of any preceding claim, wherein the control region of the first radio
subframe is further used to convey a physical resource allocation for a further terminal device
on the shared downlink channel in the user-plane region of the first radio subframe.
7. The method of claim 6, wherein the terminal device is a terminal device of a first type
and the further terminal device is a terminal device of a second type, the second type being
different from the first type.
8. The method of claim 6 or 7, wherein the physical resource allocation for the terminal
device is received using a first format for conveying control-plane data and the physical
resource allocation for the further terminal device is in a second format for conveying controlplane
data, the second format being different from the first format.
9. The method of claim 6 or 7, wherein the physical resource allocation for the terminal
device is received using a first format for conveying control-plane data and the physical
resource allocation for the further terminal device is in a second format for conveying controlplane
data, the second format being the same as the first format.
10. The method of any preceding claim, wherein the terminal device is a machine-type
communication, MTC, terminal device.
11. The method of any preceding claim, wherein the telecommunications system is based
around a 3rd Generation Partnership Project, 3GPP, architecture.
12. A terminal device for communicating with a base station in a telecommunications
system over a radio interface supporting a downlink shared channel for conveying user-plane
data from the base station to the terminal device and a downlink control channel for
conveying control-plane data from the base station to the terminal device, wherein the
control-plane data conveys information on physical resource allocations for the downlink
shared channel for the terminal device, and wherein the radio interface is based on a radio
frame structure comprising a plurality of subframes, wherein each subframe comprises a
control region for supporting the downlink control channel and a user-plane region for
supporting the downlink shared channel, and wherein the terminal device is configured to
receive in the control region of a first radio subframe an indication of a physical resource
allocation for the terminal device on the shared downlink channel in the user-plane region of a
second radio subframe and to subsequently receive user-plane data on the physical resource
allocation for the terminal device on the shared downlinlc channel in the user-plane region of
the second radio subframe.
13. The terminal device of claim 12, wherein the terminal device is configured to receive
the second radio subframe a predefined interval after the first radio subframe.
14. The terminal device of claim 13, wherein the predefined interval is of a duration which
corresponds with a predefined number of subframes.
5. The terminal device of claim 12, wherein the terminal device is configured to receive
the second radio subframe a selectable interval after the first radio subframe and to receive an
indication of a selected interval in association with the physical resource allocation for the
terminal device.
16. The terminal device of claim 13, wherein the indication of the selected interval
comprises an indication of a number of subframes.
17. The terminal device of any of claims 12 to 16, wherein the control region of the first
radio subframe also comprises a physical resource allocation for a further terminal device on
the shared downlink channel in the user-plane region of the first radio subframe.
18. The terminal device of claim 17, wherein the terminal device is a terminal device of a
first type and the further terminal device is a terminal device of a second type, the second type
being different from the first type.
19. The terminal device of claim 17 or 18, wherein the physical resource allocation for the
terminal device is received using a first format for conveying control-plane data and the
physical resource allocation for the further terminal device is in a second format for
conveying control-plane data, the second format being different from the first format.
20. The terminal device of claim 17 or 18, wherein the physical resource allocation for the
terminal device is received using a first format for conveying control-plane data and the
physical resource allocation for the further terminal device is in a second format for
conveying control-plane data, the second format being the same as the first format.
2 1. The terminal device of any one of claims 17 to 20, wherein the terminal device and
further terminal device are of the same type.
22. The terminal device of any of claims 12 to 21, wherein the terminal device is a
machine-type communication, MTC, terminal device.
23. The terminal device of any of claims 1 to 22, wherein the telecommunications system
is based around a 3rd Generation Partnership Project, 3GPP, architecture.