DESCRIPTION
Title of Invention
PHYSICAL DOWNLINK CONTROL CHANNEL COVERAGE ENHANCEMENT
FOR MACHINE-TYRE COMMUNICATION
Technical Field
The present invention relates to mobile communications devices and networks,
particularly but not exclusively those operating according to the 3rd Generation Partnership
Project (3GPP) standards or equivalents or derivatives thereof. The invention has particular
although not exclusive relevance to the Long Term Evolution (LTE) of UTRAN (called Evolved
Universal Terrestrial Radio Access Network (E-UTRAN)), including LTE-Advanced.
Background Art
In a mobile (cellular) communications network, user devices (also known as User
Equipment (UE), for example mobile telephones) communicate with remote servers or with
other user devices via base stations. In their communication with each other, user devices and
base stations use licensed radio frequencies, which are typically divided into frequency bands
and/or time blocks.
In order to be able to communicate via the base stations, user devices need to monitor
control channels operated by the base stations. One of these control channels, the so-called
Physical Downlink Control Channel (PDCCH) carries the scheduling assignments and other
control information. The PDCCH serves a variety of purposes. Primarily, it is used to convey
the scheduling decisions to individual user devices, i.e. scheduling assignments for uplink and
downlink communication.
The information carried on the PDCCH is referred to as downlink control information
(DCI). Physical control channels, such as the PDCCH, are transmitted on an aggregation of one
or several consecutive Control Channel Elements (CCEs), where a control channel element
corresponds to nine Resource Element Groups (REGs). Each REG has four Resource Elements
(REs).
Recent developments in telecommunications have seen a large increase in the use of
machine-type communications (MTC) user devices which are networked devices arranged to
communicate and perform actions without human assistance. Examples of such devices include
smart meters, which can be configured to perform measurements and relay these measurements
to other devices via a telecommunication network. Machine-type communications are also
known as machine 2 machine (M2M) communications. It is envisaged that MTC user devices
will play an important role in the implementation of the concept of the "internet of things". It is
common for MTC devices, such as smart meters or domestic appliances, to remain in a fixed
location or exhibit low mobility. Such devices may also be deployed deep inside buildings
where network coverage is low. For example, some MTC user devices may be installed in the
basement of a residential building or in a location shielded by foil-backed insulation or
metallised windows. These MTC devices will experience greater penetration losses on the air
interface than normal user devices.
The lack of network coverage, in combination with the often limited functionality of
MTC user devices, can result in such MTC user devices having a low data rate and therefore
there is a risk of some messages or channels, such as the PDCCH, not being received by an MTC
user device. In order to mitigate this risk, it is desirable to increase the coverage of the PDCCH
(and/or, where applicable, the evolved physical downlink control channel, EPDCCH).
One approach proposed for the enhancement of coverage is the repetition of (E)PDCCH
across multiple subframes. However, enhancing coverage presents challenges relating to how
carrier frequencies should be aggregated, how and where to signal a control channel in radio
frames, and how to ensure that user equipment, including MTC and legacy devices, can
efficiently locate and interpret the control signalling.
Summary of Invention
The present invention seeks to provide systems, devices and methods which at least
partially address the above issues.
The present invention provides a communications node (such as a base station) that
schedules resources for use by a plurality of user devices, including legacy user devices and nonlegacy
user devices, for communicating with the communications node, the communications
node comprising: means for generating control data for transmission to the user devices, the
control data including common control data for reception and decoding by a plurality of user
devices and user specific control data for reception and decoding by a specific user device; and
means for transmitting the generated control data in a sequence of subframes for reception by the
user devices; wherein the means for generating is configured to generate common control data
for reception and decoding by the non-legacy user devices which cannot be decoded by the
legacy user devices; and wherein the means for transmitting is configured to transmit repeats of
the common control data generated for reception and decoding by non-legacy user devices
within a plurality of subframes.
In one exemplary embodiment, the control data is transmitted using a plurality of control
channel elements, CCEs, and the common control data for reception and decoding by the nonlegacy
user devices is transmitted using an aggregation of at least sixteen CCEs that cannot be
decoded by the legacy user devices.
In another exemplary embodiment, the common control data for reception and decoding
by the non-legacy user devices is encrypted using an encryption key that is unavailable to the
legacy user devices.
In another exemplary embodiment, the control data is transmitted in a physical downlink
common control channel, PDCCH, wherein common control data for legacy user devices is
located in a First part of the PDCCH and user specific control data for legacy user devices is
located in a second part of the PDCCH; and wherein the common control data for the non-legacy
user devices is located in the second part of the PDCCH.
In another exemplary embodiment, each subframe includes a physical downlink common
control channel, PDCCH, part and a physical downlink shared channel, PDSCH, part and
wherein the common control data for reception and decoding by the non-legacy user devices is
transmitted within the PDSCH part of the subframe.
The communications node may be configured to transmit signalling information to the
non-legacy user devices identifying the subframes in which the common control data for
reception and decoding by the non-legacy user devices is transmitted. In this case, the data
identifying the subframes may identify only multimedia broadcast single frequency network,
MBSFN, subframes as carrying the common control data for reception and decoding by the nonlegacy
user devices. Alternatively, the data identifying the subframes may identify multimedia
broadcast single frequency network, MBSFN, subframes and non-MBSFN subframes as carrying
the common control data for reception and decoding by the non-legacy user devices. In this case,
the communications node may avoid placing the common control data for reception and
decoding by the non-legacy user devices and channel state information reference signals, CSI-RS,
in the same subframe.
Typically, the communications node is configured to transmit said signalling information
using a physical broadcast channel, PBCH. Where the communications node communicates
with the user devices using radio frames having N subframes, the signalling information may
comprise N bits, one bit for identifying if a corresponding one of the N subframes carries the
common control data for reception and decoding by the non-legacy user devices. Alternatively,
the signalling information may comprise M bits, where M is less than N, that identify one of a
number of predetermined configuration of the N subframes that will carry the common control
data for reception and decoding by the non-legacy user devices. Where the data identifying the
subframes identifies multimedia broadcast single frequency network, MBSFN, subframes and
non-MBSFN subframes as carrying the common control data for reception and decoding by the
non-legacy user devices, the M bits may jointly or separately encode which MBSFN subframes
and which non-MBSFN subframes of a radio frame will carry the common control data for
reception and decoding by the non-legacy user devices.
In some exemplary embodiments, the communications node is configured to transmit the
common control data for reception and decoding by the non-legacy user devices in subframes
that do not include channel state information reference signals, CSI-RS, or channel reference
signals, CRS - or that do not include both CSI-RS and CRS reference signals. Alternatively, the
communications node may transmit the common control data for reception and decoding by the
non-legacy user devices in subframes that include channel state information reference signals,
CSI-RS, or channel reference signals, CRS; and avoids using resources to carry the common
control data for reception and decoding by the non-legacy user devices that are used (or might be
used) to carry the CSI-RS or the CRS.
In some exemplary embodiments, the communications node transmits signalling
information to the non-legacy user devices identifying the location within a subframe of the
common control data for reception and decoding by the non-legacy user devices. There may be
a fixed number of possible locations within a subframe where the common control data may be
located, and in this case the communications node signals data identifying one of the possible
locations. Alternatively, there may be a fixed number of possible locations within a subframe for
the common control data for reception and decoding by the non-legacy user devices, and the
communications node may transmit the common control data in a location that depends upon a
static or semi static system variable, such as a cell ID associated with the communications node.
In some exemplary embodiments, the communications node signals data identifying a
size of the common control data for reception and decoding by the non-legacy user devices. In
this case, the size of the common control data may be one of a plurality of possible sizes and the
communications node may signal data indicating one of the plurality of sizes to the non-legacy
user devices.
Typically the common control data is carried on a plurality of resource blocks, RBs, that
may be either arranged contiguously within a subframe or dispersed within the subframe.
The present invention also provides a communications node that schedules resources for
use by a plurality of user devices for communicating with the communications node, the
communications node comprising: means for generating control data for transmission to the user
devices, the control data including common control data for reception and decoding by a
plurality of user devices and user specific control data for reception and decoding by a specific
user device; means for generating reference signals for use in controlling communications
between the communications node and the user devices; and means for transmitting the
generated reference signals and the generated control data in a sequence of subframes for
reception by the user devices, each subframe including a physical downlink common control
channel, PDCCH, part and a physical downlink shared channel, PDSCH, part; wherein generated
reference signals and common control data for reception and decoding by a plurality of user
devices are transmitted within the PDSCH part of the subframe; and wherein the means for
transmitting is configured to transmit said common control data and said reference signals within
the PDSCH part of subframes using different resource blocks contained therein.
The communications node may be configured to carry the common control data in
subframes that do not include channel state information reference signals, CSI-RS, or channel
reference signals, CRS.
The communications node may be configured to transmit the common control data in
subframes that include channel state information reference signals, CSI-RS, or channel reference
signals, CRS; and may be configured to avoid using resources to carry the common control data
that are used to carry the CSI-RS or the CRS.
In some exemplary embodiments, the communications node transmits signalling
information to the user devices identifying the location and/or size, within a subframe, of the
common control data.
Typically, the communications node starts said common control data on a starting symbol
of the subframe that is known in advance by the non-legacy user devices. The starting symbol
may be different depending on the type of subframe; and the non-legacy user device maintains
knowledge of the starting symbol to help identify the location of the control data within the
received subframe.
The present invention also provides a communications system comprising the above
described communications node and at least one user device for receiving and decoding the
common control data to control communications between the user device and the
communications node.
In one exemplary embodiment, the user device comprises: means for receiving control
data transmitted by the communications node, the control data including common control data
for reception and decoding by the user device and user specific control data for reception and
decoding by a specific user device; wherein the received common control data is for reception
and decoding by non-legacy user devices and cannot be decoded by legacy user devices; wherein
the means for receiving is configured to receive a plurality of subframes comprising said
common control data; means for combining the control data received from the plurality of
subframes; and means for decoding the combined common control data.
In another exemplary embodiment, the user device comprises: means for receiving
subframes transmitted by the communications node, the subframes comprising control data
including common control data for reception and decoding by a plurality of user devices and user
specific control data for reception and decoding by a specific user device; wherein the subframes
include reference signals transmitted by the communications node for use in controlling
communications between the communications node and the user device; and wherein the means
for receiving is configured to receive a plurality of subframes comprising said common control
data; wherein each subframe includes a physical downlink common control channel, PDCCH,
part and a physical downlink shared channel, PDSCH, part; wherein received reference signals
and common control data are received within the PDSCH part of the subframe using different
resource blocks contained within the PDSCH part; means for combining the control data
received from the plurality of subframes; and means for decoding the combined common control
data.
In another exemplary embodiment, the user device comprises: means for receiving
subframes transmitted by the communications node, the subframes comprising control data
including common control data for reception and decoding by a plurality of user devices and user
specific control data for reception and decoding by a specific user device; wherein the subframes
include reference signals transmitted by the communications node for use in controlling
communications between the communications node and the user device; and wherein the means
for receiving is configured to receive a plurality of subframes comprising said common control
data; wherein each subframe includes a physical downlink common control channel, PDCCH,
part and a physical downlink shared channel, PDSCH, part; wherein received reference signals
and common control data are received within the PDSCH part of the subframe using different
resource blocks contained within the PDSCH part; means for identifying the common control
data within the PDSCH part of the subframes using information about the location, or the
expected location, of the reference control signals; means for combining the control data
received from the plurality of subframes; and means for decoding the combined common control
data.
Aspects of the invention extend to corresponding systems, methods, and computer
program products such as computer readable storage media having instructions stored thereon
which are operable to program a programmable processor to carry out a method as described in
the aspects and possibilities set out above or recited in the claims and/or to program a suitably
adapted computer to provide the apparatus recited in any of the claims.
Each feature disclosed in this specification (which term includes the claims) and/or
shown in the drawings may be incorporated in the invention independently (or in combination
with) any other disclosed and/or illustrated features. In particular but without limitation the
features of any of the claims dependent from a particular independent claim may be introduced
into that independent claim in any combination or individually.
Brief Description of Drawings
Embodiments of the invention will now be described by way of example only with
reference to the attached figures in which:
Figure 1 schematically illustrates a telecommunication system;
Figure 2 schematically illustrates a generic frame structure used in communications over
the wireless links of the system shown in Figure 1;
Figure 3 schematically illustrates the way in which the frequency subcarriers are divided
into resource blocks and the way that a time slot is divided into a number of OFDM symbols;
Figure 4 is a block diagram illustrating the main components of the user device shown in
Figure 1;
Figure 5 is a block diagram illustrating the main components of the base station shown in
Figure 1;
Figure 6 illustrates a number of subframes forming part of a radio frame for the
telecommunications system of Figure 1;
Figure 7 illustrates a modified PDCCH structure in which a block of CCE elements
forming part of a USS portion of a legacy PDCCH is used for repetitive signalling of control
information for MTC devices;
Figure 8 illustrates the way in which an EPDCCH can be repeated in a number of
subframes forming part of a radio frame for reception by an MTC device;
Figure 9 illustrates one radio frame made up of 10 subframes and illustrating the possible
locations of MBSFN subframes;
Figure 10 shows a simplified illustration of a typical resource grid corresponding to a
subframe used in the telecommunication system of Figure 1;
Figure 11 is a simplified illustration of exemplary resource grids corresponding to a non-
MBSFN subframe and an MBSFN subframe according to an option A;
Figure is a simplified illustration of exemplary resource grids corresponding to a non-
MBSFN subframe and an MBSFN subframe according to an option B;
Figure 13 is a simplified illustration of an exemplary resource grid corresponding to
MBSFN subframes according to an option C;
Figure 1 is a simplified illustration of exemplary resource grids corresponding to a non-
MBSFN subframe and an MBSFN subframe according to an option D; and
Figure 15 is a view for use in describing another solution to design an enhanced CSS
(ECCS) in EPDCCH for low cost MTC.
Description of Embodiments
Overview
Figure 1 schematically illustrates a mobile (cellular) telecommunication system 1 in
which communication between user devices 3-0, 3-1 and 3-2 is supported by a base station 5 and
a core network 7. In this exemplary embodiment, user devices 3-0 and 3-1 are mobile
telephones, and user device 3-2 is a machine-type communications (MTC) user device. As
shown, user devices 3-0, 3-1 and 3-2 are located within a cell 6 operated by the base station 5.
In the system illustrated in Figure 1, the base station 5 shown is an Evolved Universal
Terrestrial Radio Access Network (E-UTRAN) base station. Such base stations are commonly
referred to as eNBs (Evolved NodeBs).
The base station 5 is configured to transmit an (E)PDCCH for reception by the user
devices 3 in the cell, the (E)PDCCH allocating uplink and downlink resources to the user devices.
Also, base station 5 is configured to provide reference signals which the user devices 3
are operable to receive and use to determine signal quality. Based on the result of measurements,
the user devices 3 generate and send a report back to the base station 5. This feedback
mechanism is called channel quality indication (CQI) and, it is employed to fine-tune the
operation of the base station 5, including resource allocation, scheduling and power of
transmission.
As will be described in more detail below, the base station 5 repeats PDCCH
transmissions for the MTC user device 3-2 and various alternative techniques for doing so are
described below. However, before describing these alternatives, a brief overview of the LTE
frame structure will now be given that will help to understand these alternative techniques.
LTE subframe data structure
Figure 2 schematically illustrates a generic frame structure used in communications over
the wireless links of the system shown in Figure 1.
An orthogonal frequency division multiple access (OFDMA) technique is used for the
downlink to allow the base station 5 to transmit user data over the air interface to the respective
user devices 3; and a single carrier frequency division multiple access (SC-FDMA) technique is
used for the uplink to allow the user devices 3 to transmit their data over the air interface to the
base station 5. Different sub-carriers are allocated by the base station 5 (for a predetermined
amount of time) to each user device 3 depending on the amount of data to be sent in each
direction. These sub-carriers and temporal allocations are defined as physical resource blocks
(PRBs) in the LTE specifications. PRBs thus have a time and frequency dimension. The base
station 5 dynamically allocates PRBs for each device that it is serving and signals the allocations
for each subframe (TTI) to each of the scheduled user devices 3 in a control channel, e.g.
(E)PDCCH.
As shown in Figure 2, the generic frame structure agreed for LTE communications over
the air interface includes a frame 13 which is 0 msec long and which comprises ten subframes
of 1msec duration (known as a Transmission Time Interval (TTI)). Each subframe or TTI
comprises two slots 17 of 0.5 msec duration. Each slot 17 comprises either six or seven
OFDMA symbols 19, depending on whether the normal or extended cyclic prefix (CP) is
employed.
Figure 3 schematically illustrates the way in which the frequency subcarriers are divided
into resource blocks and the way that a time slot is divided into a number of OFDM symbols.
The total number of available sub-carriers depends on the overall transmission bandwidth
of the system. The LTE specifications define parameters for system bandwidths from 1.4 MHz
to 20 MHz and one PRB is currently defined to comprise either 12 or 24 consecutive subcarriers
for one slot. A PRB over two slots is also defined by the LTE specifications as being the
smallest element of resource allocation assigned by the base station scheduler. These subcarriers
are then modulated onto a component carrier to up-convert the signal to the desired
transmission bandwidth.
The transmitted signal thus comprises N W subcarriers for a duration of N sym b symbols.
Each box in the grid represents a single sub-carrier for one symbol period and is referred to as a
resource element. As shown in Figure 3, in this case each PRB 1 is formed from 1
consecutive sub-carriers and (in this example) seven symbols for each subcarrier; although in
practice the same allocations are made in the second slot of each subframe as well. The control
channel that includes the resource allocation data for the user devices 3 is generally transmitted
in consecutive CCEs within the first three OFDM symbols of each subframe 15.
User device
Figure 4 is a block diagram illustrating the main components of the user device 3 shown
in Figure 1. The user device 3 may be an MTC user device 3-2 or a mobile (or 'cellular')
telephone capable of operating in a multi-carrier environment. The user device 3 comprises a
transceiver circuit 401 which is operable to transmit signals to, and to receive signals from, the
base station 5 via at least one antenna 403. Typically, the user device 3 also includes a user
interface 405 which allows a user to interact with the user device 3, however this user interface
405 may be omitted for some MTC user devices.
The operation of the transceiver circuit 401 is controlled by a controller 407 in
accordance with software stored in memory 409. The software includes, among other things, an
operating system 4 11, a communication control module 413, a measurement module 415, an
(E)PDCCH configuration module 417 and an (E)PDCCH reception module 419.
The communication control module 413 is operable for managing communication with
the base station 5. The measurement module 415 receives measurement configuration
information from the base station 5 for the purposes of configuring the user device 3 to take
measurements of the CSI-RS (Channel State Information Reference Signal).
The measurement module 415 determines reference signal received power (RSRP) for
the cells. In this exemplary embodiment, the measurement module 415 is operable to carry out
signal quality measurements during the periods when the user device 3 is not scheduled to
communicate with the base station 5. Based on the result of measurements, the measurement
module 415 generates and sends a CSI report (including the CQI) back to the base station 5.
The (E)PDCCH configuration module 417 is operable to receive and process (E)PDCCH
configuration information received from the base station 5, such as information identifying the
location and size of the (E)PDCCH and/or an associated search space.
The (E)PDCCH reception module 419 is operable to search for, identify and decode an
(E)PDCCH, for example receiving DCI which signals a resource allocation for the user device.
Base Station
Figure 5 is a block diagram illustrating the main components of the base station 5 shown
in Figure 1. The base station 5 comprises an E-UTRAN multi-carrier capable base station
comprising a transceiver circuit 501 which is operable to transmit signals to, and to receive
signals from, the user device 3 via one or more antennas 503. The base station 5 is also operable
to transmit signals to and to receive signals from a core network 7 via a network interface 505.
The operation of the transceiver circuit 501 is controlled by a controller 507 in accordance with
software stored in memory 509.
The software includes, among other things, an operating system 5 11, a communication
control module 513, a reference signal module 515, an (E)PDCCH configuration module 517
and an (E)PDCCH transmission module 519.
The communication control module 513 is operable to control communication with the
user devices 3. The communication control module 513 is also responsible for scheduling the
resources to be used by the user devices 3 served by this base station 5.
The reference signal module 515 is operable to transmit reference signals for reception by
the user devices 3, to allow the user devices 3 to carry out signal quality measurements. The
reference signal module 515 controls which reference signals are transmitted and in which
resource elements and in which subframes.
The (E)PDCCH configuration module 517 is operable to generate and transmit
(E)PDCCH configuration information for the user devices 3, such as information identifying the
location and size of the (E)PDCCH and/or an associated search space.
The (E)PDCCH transmission module 519 is operable to transmit an (E)PDCCH, for
example comprising DCI which signals a resource allocation for a user device.
In the above description, the user device 3 and the base station 5 are described for ease of
understanding as having a number of discrete modules. Whilst these modules may be provided
in this way for certain applications, for example where an existing system has been modified to
implement the invention, in other applications, for example in systems designed with the
inventive features in mind from the outset, these modules may be built into the overall operating
system or code and so these modules may not be discernible as discrete entities.
Enhanced Coverage (E)PDCCH - (E)PDCCHRepetition
As discussed above, it is common for MTC user devices 3-2, such as smart meters or
domestic appliances, to remain in a fixed location or exhibit low mobility; and to experience
greater penetration losses on the air interface than normal user devices. One approach proposed
for the enhancement of coverage is the repetition of the (E)PDCCH for MTC user devices 3-2
across multiple subframes.
Figure 6 illustrates the way in which such repetition may be performed within five
subframes 15. As shown in Figure 6, the first part 142 of each subframe 15 is used to carry the
PDCCH. The remainder of each subframe 15 comprises the physical downlink shared channel
(PDSCH) 143. The PDSCH resources for each user device 3 are allocated using control
information carried in the PDCCH 142.
In this illustration, the PDCCH 142 of each subframe 1 includes control information for
both MTC user devices 3-2 and legacy user devices 3-0 and 3-1. The PDCCH data for an MTC
user device 3-2 is repeated in subframes 1 to 4. This PDCCH data informs the MTC user device
3-2 of an allocation of resources 147 within the PDSCH of subframe 5 for the MTC user device
3-2. Thus the MTC user device 3-2 can combine the multiple PDCCH repetitions across
subframes 1 to 4 before decoding the PDCCH to determine its allocated resources 147 within the
PDSCH.
In contrast, the PDCCH information for legacy user devices 3 is in general not repeated
across multiple subframes 15. The resources allocated to a particular legacy user device 3 within
the PDSCH 145 of a subframe 15 are typically indicated in the PDCCH 142 of that subframe.
As illustrated in Figure 6, the particular resources allocated within the PDSCH may vary in each
subframe.
Although not shown in Figure 6, the PDCCH 1 2 consists of an aggregation of one or
more consecutive control channel elements (CCEs), where a CCE occupies a fraction of the base
station's available physical resource blocks (PBRs). In LTE, each CCE corresponds to nine
resource element groups, where each resource element group corresponds to eight bits of
controlled data assuming QPSK modulation. The total number of CCEs available in a cell
depends on the system bandwidth of the cell and the number of OFDM symbols reserved for
PDCCH transmission in a given subframe. As stated above, in this embodiment the first three
OFDM symbols of each subframe are dedicated to carrying the PDCCH control data.
In order for an MTC user device 3-2 to be able to successfully receive its (E)PDCCH, it
is necessary for the MTC user device 3-2 to know the location of the CCEs in each subframe
carrying the repetition of the PDCCH, along with the start subframe and end subframe for the
repetition and the timing of the subframe in which the resources 147 are allocated relative to the
last of the subframes carrying the repeated PDCCH for the MTC user device 3-2. In the example
shown in Figure 6, subframe 1 is the start subframe, subframe 4 is the end subframe for the
PDCCH repetitions and the allocated resources 147 are located in subframe 5.
Those involved in the 3GPP standards have discussed how the (E)PDCCH and PDSCH
will be configured for MTC user devices 3-2 where the enhanced coverage of the (E)PDCCH is
implemented using repetition. It has been agreed that the relationship of PDSCH timing to
(E)PDCCH timing shall be known to user devices, for example, this timing may be fixed or the
MTC user devices 3-2 may be configured to derive it from other system information. It has also
been agreed that, from the perspective of an MTC user device 3-2, the possible starting
subframes of the (E)PDCCH repetitions are limited to a subset of subframes within a frame 13.
It has also been agreed that where the (E)PDCCH is repeated across multiple subframes, the
resources 147 that are being allocated by the (E)PDCCH shall not be transmitted before the end
of the (E)PDCCH repetitions. More specifically, if subframe n is the last (E)PDCCH repetition
then the PDSCH starts at subframe n + k, where k > 0.
It has also been agreed that the repetition of the (E)PDCCH can be configured for
different signal to noise ratio (SNR) levels depending on the channel quality indication (CQI)
determined by a user device. For example, an MTC user device 3-2 located near the edge of the
cell, the (E)PDCCH may be repeated 64 times, whereas an MTC user device located close to the
centre of the cell may receive only 16 repetitions. Varying the level of repetition of the
(E)PDCCH helps to optimise power management within the MTC user devices minimising
unnecessary repetitions.
Search Spaces
User devices 3 do not know in advance when they will be signalled a resource allocation
in the PDSCH, or which CCEs in the PDCCH will be used to signal those allocated resources.
Therefore, each user device 3 must scan the resources used for carrying the PDCCH for resource
allocation messages in every subframe 15. In order to keep the complexity of the process within
reasonable limits, each user device 3 searches only a subset of the CCEs in a subframe. This
subset, including all the possible locations of a PDCCH, is referred to as a search space. Each
possible location of an (E)PDCCH is referred to as an '(E)PDCCH Candidate'.
As illustrated in Figure 6, there are two types of search space: a common search space
(CSS) 151 and a UE-specific search space (USS) 153. A UE is required to monitor both
common and UE-specific search spaces.
The common search space 151 carries downlink control information which is common to
all user devices 3. For example, the common search space 151 may include system information
blocks (SIBs) which contain information related to cell access parameters, random access
channel (RACH) message 2 (i.e. Random-Access Response) and RACH message 4 (i.e.
Contention Resolution), and the paging channel (PCH). The maximum number of CCEs present
in the common search space is 16.
The UE-specific search space 153 carries downlink control information for particular
user devices, such as UE-specific resource allocations.
Ideally, the size of a search space should be as small as possible to minimise the
processing burden on the user devices 3. However, smaller search spaces also place greater
restrictions on the base station's scheduling algorithm.
The number of CCEs making up one (E)PDCCH candidate is called the aggregation level,
and the user device 3 search space contains (E)PDCCHs with a mixture of aggregation levels.
Table 1 shows the typical size of search spaces, which is based on the size of the legacy PDCCH
search space.
Table 1
While the agreements discussed above have been reached, there are still numerous
problems to be solved in the implementation of enhanced coverage of (E)PDCCH for MTC user
devices 3-2.
For example, it is not clear which search space candidates should be used for (E)PDCCH
and in turn which search space candidates should be monitored by a user device. One possibility
is that the location of the enhanced coverage (E)PDCCH could be based on the already defined
search space candidates used for legacy PDCCH, as shown in Table 1. As shown, at aggregation
level 8 there are only two candidates for the defined search space and therefore the MTC user
device 3-2 would only need to check two possible locations for each DCI format. For any given
transmission, there could be downlink (DL) and/or uplink (UL) DCI formats. Therefore, in this
case, the MTC user device 3-2 could assume that for each repetition, the same first candidate is
used for the DL-DCI format and the same second candidate is used for the UL-DCI format, in
order to facilitate coherent combining of data from the repetitions.
To date, the discussions surrounding the repetition of the (E)PDCCH have related to the
repetition of the USS 153. There has been little or no discussion of the repetition of the CSS 151.
However, the inventors have realised that repeating the CSS 151 presents further problems. In
particular, the USS 153 is configured so that it can only be decoded by the user device 3 to
which it relates and so repeating the USS 153 in several subframes does not cause problems for
other user devices 3. However, since the CSS 151 is intended for receipt by all user devices 3,
there is a risk that legacy user devices 3 may mistakenly decode each repetition of the repeated
(E)PDCCH as an allocation of the resources 147 in the subframe carrying the repeated
(E)PDCCH. The embodiments discussed below aim to address or at least alleviate this problem.
Provision for Legacy User Devices in Enhanced CoveragePDCCH
It is important that the development of enhanced coverage PDCCH retains backwards
compatibility with legacy user devices. The inventors propose using the legacy common search
space (CSS) for the enhanced coverage PDCCH channel intended for the MTC user devices 3-2
and therefore repetition of PDCCH control information will be implemented in the common
search space as well as the UE-specific space (USS).
According to a first exemplary embodiment, confusion by legacy user devices is avoided
by employing an increased aggregation level for the PDCCH of MTC user devices 3-2.
Specifically, an aggregation level of 16 is employed, which means that the PDCCH takes up the
entire CSS 151 (as the maximum number of CCEs present in the common search space is 16).
Legacy user devices 3 are only configured to be able to decode up to an aggregation level of 8
(see Table 1) and therefore the legacy user devices 3 will not be able to decode a PDCCH at
aggregation level 6 and thus the mistaken decoding of the repeated PDCCH by legacy user
devices 3 is avoided.
However, as the use of aggregation level 16 will result in the whole CSS 151 of a
subframe being consumed, there will not be any CCEs available for the base station 5 to
schedule other control information. This may result in the blocking of the CSS 151 in a number
of consecutive subframes. Accordingly, the use of repeated PDCCH at aggregation level 16
must be carefully considered to take into account these effects.
According to a second embodiment, the repeated PDCCH for MTC user devices uses an
aggregation level lower than that of 16, for example aggregation levels 4 or 8, and instead a
specific scrambling is applied to the PDCCH for MTC user devices 3-2. Preferably, this
scrambling is applied using a new Radio Network Temporary Identifier (RNTI).
Advantageously, scrambling prevents legacy devices 3 from mistakenly trying to decode any of
the PDCCH repetitions, and avoids all of the available CCEs of the CSS 151 being consumed as
can occur in the first embodiment (although there is still a possibility of blocking of the CSS in a
number of consecutive subframes).
New Common Search Space in PDCCH for MTC User Devices
Figure 7 illustrates a PDCCH according to a third embodiment. In this embodiment, the
PDCCH includes the legacy CSS 151 comprising 16 CCEs and the USS 153 comprising N CCEs.
However, as illustrated in Figure 7, the USS 153 comprises a new common search space for
MTC user devices 3-2, labelled MTC-CSS 161. The new MTC-CSS 161 allows MTC user
devices 3-2 to receive the common control information, while avoiding legacy user devices 3
attempting to decode this information, because the MTC-CSS 161 is not provided in the legacy
CSS search space 151.
In this example, the MTC-CSS 161 consists of 16 CCEs and starts immediately after the
legacy CSS 1 1. In this way the MTC user devices 3-2 know where to look for the MTC-CSS -
which reduces the search space for the MTC-CSS. Of course, the same advantage is achieved
regardless of where the MTC-CSS 161 is located within the USS, as long as its location is
known by the MTC user devices 3-2 in advance.
In this embodiment, the base station 5 prioritises the MTC-CSS 161 over the UE-specific
control information contained in the USS. Therefore, there is a degree of blocking of CCEs in
the USS. However, as there are more CCEs in the USS than in the CSS, the blocking probability
for a given user device is not severe.
Common Search Space in EPDCCH for MTC User Devices
As those skilled in the art will appreciate, the PDCCH is understood to be contained
within a set of symbols at the start of the subframe, for example the first three symbols. As there
is limited space within the PDCCH, it was proposed to transmit additional control data in the rest
of the subframe traditionally used for carrying the PDSCH. This additional control data was
defined to be contained within the "evolved" physical downlink control channel (EPDCCH).
The way in which repetition of the EPDCCH can be achieved will now be explained.
Figure 8 illustrates a series of five subframes 15 forming part of a radio frame according
to a fourth exemplary embodiment. In this exemplary embodiment, a common search space for
MTC user devices 3-2 is provided in the EPDCCH. In this example, each subframe 15 includes
a PDCCH 142 provided over the first three OFDM symbols. The remainder of each subframe
comprises a PDSCH region 143 which can hold further transmissions such as the physical
broadcast channel, PBCH, and the EPDCCH.
MTC user devices 3-2 often operate over a reduced bandwidth compared to typical user
devices, and therefore in this exemplary embodiment the EPDCCH is provided within a reduced
bandwidth of 1.4 MHz, which corresponds to 6 resource blocks.
In Figure 8, the PDSCH region 143 of subframe 0 comprises a PBCH transmission 173
which signals the location and size of an EPDCCH CSS 171 .
In order to signal the location of the EPDCCH CSS 171, multiple possible locations
(NEPDccHjocation) for the EPDCCH are predefined. The number of different locations is given by:
NRB
DL
-^EPDCCH location ~ ~
Where is the number of resource blocks across the whole downlink system
bandwidth.
Typically, the downlink system bandwidth may be 20MHz, which corresponds to 100
resource blocks. Therefore, in this case there are 16 different possible locations for the
EPDCCH CSS.
One of the possible locations is signaled in the PBCH 173. Signalling the location of the
EPDCCH CSS 171 transmitted by the base station 5 using the PBCH 173 beneficially allows the
base station 5 to flexibly choose the location.
Currently in PBCH 173, there are a total of 24 bits, in which 14 are used. Therefore,
there are 10 spare bits in PBCH 173 which can be used to signal the EPDCCH CSS 171.
Methods for using these 10 bits to signal this information to the MTC user device 3-2 are
discussed further below.
In order to signal the size of the EPDCCH CSS 171, the base station (E)PDCCH
transmission module 519 is configured by the (E)PDCCH configuration module 517 to use one
of a number of possible sizes for the EPDCCH CSS 171, in this exemplary embodiment either 2,
4 or 6 PRBs within the reduced bandwidth of .4 MHz. Therefore, one of the possible
configurations is signaled by the base station 5 in the PBCH 173. Preferably, the 2, 4 or 6 PRBs
are contiguous.
Common Search Space in EPDCCHfor MTC User Devices - Accommodating Rate Matching
Parameters
When allocating the EPDCCH, the base station 5 must ensure there is no conflict with
some of the reference signals that are transmitted within some subframes and the MTC user
device 3-2 must know which resource elements will form part of the EPDCCH and which
resource elements carry the reference signals. However, not all subframes of a radio frame will
carry all reference signals.
In LTE, providing broadcast data, in particular mobile television, is a key aspect.
Broadcast services such as mobile television are provided by dedicated resources in the form of a
multicast-broadcast single-frequency network (MBSFN). These MBSFN subframes do not carry
all of these reference signals. It has been decided that a number of particular subframes within a
radio frame are designated as potential MBSFN subframes.
Figure 9 illustrates one radio frame 13 made up of 10 subframes 15 numbered 0 to 9. In
common with previous Figures, the first part of each subframe comprises a PDCCH region 142
and the latter part of each subframe comprises a PDSCH region 143. In the example illustrated
in Figure 9, the radio frame 13 is a frequency division duplex (FDD) frame and accordingly
subframes 1, 2, 3, 6, 7 and 8 are designated as potential MBSFN subframes. It is noted that, for
a time division duplex (TDD) frame, subframes 2, 3, 4, 7, 8 and 9 are designated as being
potential MBSFN subframes.
In this example, the non-MBSFN subframes 0, 4, 5 and 9 include a PDCCH region 142
which comprises three OFDM symbols, while MBSFN subframes 1, 2, 3, 6, 7 and 8 include a
reduced PDCCH region 2 which comprises only two OFDM symbols.
Furthermore, the physical broadcast channel (PBCH) is provided in particular subframes
of a radio frame, in this example subframes 0 and 5 are designated as possible PBCH subframes.
Reference Signals
Figure 10 shows a simplified illustration of a typical resource grid of a subframe used in
the telecommunication system 1 of Figure 1. The subframe comprises a number of resource
elements defined in time (i.e. in columns corresponding to 'symbols' along the horizontal axis of
Figure 10) and frequency (i.e. in rows corresponding to each 'sub-carrier' along the vertical axis
of Figure 10). Each EPDCCH consists of an aggregation of control channel elements ('CCEs').
The PDCCH 142 is carried in the first part of the subframe 15, as shown generally in the left
hand side area of the subframe 15 of Figure 10.
Some resource elements of the subframe are also used to carry cell reference signals
(CRS) 154 and demodulation reference signals (DM RS) 155, both of which are transmitted by
the base station 5 periodically, at predetermined intervals and predetermined locations within a
subframe. These signals are used to provide reference signal levels and to inform the user device
3 about the current operation of the base station 5. Resource elements can be transmitted at
varying energy levels but the CRS 154 resource elements are always transmitted at a known (e.g.
a default) energy level. The user device 3 can thus carry out signal quality measurements over
the CRS 154 resource elements and, based on these measurements, can indicate to the base
station 5 the perceived signal quality of a given frequency band (of a given cell) operated by the
base station 5.
In addition to CRS and DM-RS, the base station 5 may also transmit a channel state
information reference signal (CSI-RS). The CSI-RS is used by user devices to determine the
channel state and to report channel quality information (CQI) to the base station 5. CSI-RS is
essentially an extension of the rate matching parameter CRS. In LTE Rel. 8, CRS was designed
for use in channel estimation for up to four layer spatial multiplexing, where each antenna port
(numbered ports 1 to 3) has a separate CRS. However, extension of the reference signals was
required when LTE Rel. 10 introduced further antenna nodes to support additional layer spatial
multiplexing (up to 8 layer spatial multiplexing). The CSI-RS reference signal was added in
preference to extending the CRS to 8 layers as this would have added undesirable signalling
overhead. CSI-RS is transmitted on different antenna ports (15 to 22) than CRS (0 to 3),
although the same physical antennas may be used. Furthermore, while CRS only uses
time/frequency orthogonality, CSI-RS uses code domain orthogonality in addition.
MBSFN subframes (such as subframes 1, 2, 3, 6, 7, 8 in Figure 9) do not carry cell
specific reference signals such as CRS or CSI-RS because MBSFN subframes are not cellspecific.
As explained above, it is necessary for user devices to be aware of which resource
elements of the subframe contains the EPDCCH CSS 171.
In LTE Rel-1 1 a mapping parameter re-MappingQCL-Configld-rl 1 (as described in
3GPP TS 36.213 section 9.1.4.3, the full disclosure of which is hereby incorporated by
reference) is used by user devices to determine the mapping of the EPDCCH CSS to resource
elements. The mapping parameter includes a CRS ports count parameter, denoted crs-
PortsCount-rll. This parameter is communicated to user devices on the PBCH. The mapping
parameter also includes a CRS frequency shift parameter, crs-FreqShift-rl 1. This CRS
frequency shift parameter is determined by a user device using the cell ID.
However, Rel-1 1 does not currently define how to inform a user device of other
important ratematching parameters, in particular the configuration of MBSFN subframes within
the radio frame, the location of channel state information reference signals (CSI-RS) in
neighbouring cells, and the starting OFDM symbol of the EPDDCH CSS. These three
parameters are respectively denoted as:
mbsfn-SubframeConfigList-r11;
csi-RS-ConfigZPId-rll;
pdsch-Start-rl 1.
A further ratematching parameter for the user devices 3 is the location of the CSI-RS in
the serving cell. This parameter is denoted qcl-CSI-RS-ConfigNZPId-rl 1. In this exemplary
embodiment, the location of the CSI-RS in the serving cell is configured in the same way as the
location of CSI-RS in neighbouring cells, and therefore the qcl-CSI-RS-ConfigNZPId-rl 1 can be
determined based on csi-RS-ConfigZPId-rl1.
In order for user devices to locate the EPDCCH CSS it is necessary for the MTC user
device 3-2 to obtain knowledge of the MBSFN subframe configuration, the CSI-RS
configuration and the starting symbol of the EPDCCH CSS. Below are presented four options
for providing these parameters, described with reference to Figures 11 to 14.
Option A
Figure 1 is a simplified illustration of exemplary resource grids 901 and 903, resource
grid 901 corresponding to a non-MBSFN subframe and resource grid 903 corresponding to an
MBSFN subframe.
As shown, the non-MBSFN subframe 901 carries CRS type reference signals 154a and
154b corresponding to antenna ports 0 to 3. The resource elements used to carry CRS are
distributed throughout the time and frequency domain, where CRS for ports 0 and 1 are
transmitted at symbols 1, 5, 8 and 12. The CRS for ports 2 and 3 are transmitted at symbols 2
and 9. The repetition of CRS resource elements corresponding to a particular port across the
frequency domain illustrates the fact that CRS transmissions are frequency shifted for improved
frequency diversity.
As shown in Figure 11, the MBSFN subframe 903 does not include any CRS signals
outside of the PDCCH because the CRS transmissions are cell specific. However, the
demodulation reference signals (DMRS) 155 are carried by resource elements in both the non-
MBSFN subframe 901 and the MSBSFN subframe 903. In this example, the DMRS resource
elements are located at symbols 6, 7, 13 and 14 and are also frequency shifted.
According to option A, the PBCH channel is used to signal to the MTC user device 3-2
which subframes out of the six possible MBSFN subframes of the radio frame are used for
EPDCCH CSS 171. These MBSFN subframes will not carry any CRS or CSI-RS transmissions
outside of the PDCCH, and therefore all of the unshaded resource elements in the MBSFN
subframe 903 can form part of the EPDCCH CSS 171.
Although all of these unshaded elements are available for EPDCCH CSS 171, it is noted
that in most embodiments a subset of the subcarriers will be indicated by the PBCH 173 as
carrying the EPDCCH CSS 171, and therefore the EPDCCH CSS 171 may only occupy a subset
of the carriers illustrated in Figure 11.
Furthermore, if any other non-MBSFN subframes are signalled, in the PBCH 173, to be
used for EPDCCH CSS 171, then the MTC user device 3-2 assumes that there are no CSI-RS
transmissions present in the indicated non-MBSFN subframes. Therefore, the EPDCCH CSS
transmission can occupy all of the unshaded resource elements shown in the non-MBSFN
subframe 901. However, as these non-MBSFN subframes include DMRS or CRS transmissions,
the corresponding resource elements are not available for the EPDCCH CSS 171.
Accordingly, in option A the base station (E)PDCCH transmission module 519 is
configured by the (E)PDCCH configuration module 5 7 to avoid placing the EPDCCH CSS 71
and CSI-RS in the same subframe. Alternatively, the base station (E)PDCCH transmission
module 519 is configured by the (E)PDCCH configuration module 517 to puncture the
corresponding CSI-RS resource elements (RE) when mapping EPDCCH CSS 171 to resource
elements. In this case, if an EPDCCH CSS resource element collides with a CSI-RS location,
then the CSI-RS is transmitted in that location while the EPDCCH CSS resource element is not
transmitted in that location.
In option A, as shown in Figure 11, the starting OFDM symbol for the EPDCCH CSS
171 is always fixed to the fourth OFDM symbol of the subframe for non-MBSFN subframes, as
in these subframes the size of the PDCCH is three symbols. In MBSFN subframes, the starting
OFDM symbol for the EPDCCH CSS 171 is fixed to the third OFDM symbol of the subframe,
as in these subframes the size of the PDCCH is two symbols. In other exemplary embodiments,
the starting OFDM symbol could be another symbol (known in advance) or the starting symbol
could be signalled to the MTC user device 3-2 as well.
Option B
Figure 12 is a simplified illustration of exemplary resource grids 1001 and 1003, resource
grid 1001 corresponding to a non-MBSFN subframe and resource grid 1003 corresponding to an
MBSFN subframe.
As in option A, the non-MBSFN subframe 1001 carries CRS type reference signals 154a
and 154b corresponding to antenna ports 0 to 3, and the DMRS 155 are carried by resource
elements in both the non-MBSFN subframe 1001 and the MSBSFN subframe 1003. In this
option, the PBCH channel is used to signal to the MTC user device 3-2 which subframes out of
the six possible MBSFN subframes of the radio frame are used for the EPDCCH CSS 171. The
MBSFN subframes will not carry any CRS or CSI-RS transmissions outside of the PDCCH, and
therefore all of the unshaded resource elements in MBSFN subframe 1003 can form part of the
EPDCCH CSS 171.
However, according to option B, the non-MBSFN subframe 1001 also carries CSI-RS
type reference signals 157 corresponding to antenna ports 0 to 7. All of the possible
configurations of CSI-RS 157 are indicated in subframe 1001 of Figure 12. Therefore, if non-
MBSFN subframes are signalled, in the PBCH 173, to be used for the EPDCCH CSS 171, then
the MTC user device 3-2 assumes that all possible CSI-RS transmissions are present in the
indicated non-MBSFN subframes. Therefore, the MTC user device 3-2 will exclude all of the
potential CSI-RS REs from the EPDCCH CSS 171. The EPDCCH CSS 171 can occupy all of
the unshaded resource elements shown in the non-MBNSFN subframe 1001, which is a lower
total number of resource elements than in option A.
As in option A, although all of these unshaded elements are available for EPDCCH CSS
17 , it is noted that in most exemplary embodiments a subset of the subcarriers will be indicated
by the PBCH 173 as carrying the EPDCCH CSS 171, and therefore the EPDCCH CSS 171 may
only occupy a subset of the carriers illustrated in Figure 12.
Thus, in accordance with option B, the base station 5 can place the EPDCCH CSS 171
and the CSI-RS in the same subframe.
In option B, like in option A and as shown in Figure 12, the starting OFDM symbol for
the EPDCCH CSS 171 is fixed to the fourth OFDM symbol of the non-MBSFN subframes while
in MBSFN subframes the EPDCCH CSS 171 is fixed to the third OFDM symbol. Fixing the
starting OFDM symbol reduces the amount of information that has to ne signalled to the MTC
user device 3-2.
Option C
Figure 13 is a simplified illustration of an exemplary resource grid 1103 corresponding to
an MBSFN subframe.
As in options A and B, in option C the PBCH channel is used to signal to the MTC user
device 3-2 which subframes out of the six possible MBSFN subframes of the radio frame are
used for the EPDCCH CSS 171. The MBSFN subframes 1103 will not carry any CRS or CSIRS
transmissions outside of the PDCCH, and therefore all of the unshaded resource elements in
the MBSFN subframe 1103 can form part of the EPDCCH CSS 171. The DMRS 155 is also
carried by resource elements in the MSBSFN subframe 1103.
According to option C, the EPDCCH CSS 171 is not transmitted in non-MBSFN
subframes. Therefore, there is no issue of how to transmit CRS and/or CSI-RS in the same
subframe as the EPDCCH CSS 171.
As in options A and B, although all of the unshaded elements of subframe 1103 are
available for the EPDCCH CSS 171, it is noted that in most embodiments a subset of the
subcarriers will be indicated by the PBCH 173 as carrying the EPDCCH CSS 171, and therefore
the EPDCCH CSS 171 may only occupy a subset of the carriers illustrated in Figure 13.
As in options A and B and as shown in Figure 13, the starting OFDM symbol for the
EPDCCH CSS 171 is fixed to the third OFDM symbol of the MBSFN subframe. As before,
fixing the starting OFDM symbol reduces the amount of data that has to be signalled to the MTC
user device 3-2.
Option D
Figure 14 is a simplified illustration of exemplary resource grids 1201 and 1203, resource
grid 1201 corresponding to a non-MBSFN subframe and resource grid 1203 corresponding to an
MBSFN subframe.
In option D, the PBCH channel is used to signal to the MTC user device 3-2 which
subframes are used for EPDCCH CSS 171, regardless of whether the subframes are MBSFN
subframes or non-MBSFN subframes.
As in the previous options, the non-MBSFN subframe 1201 carries CRS type reference
signals 154a and 154b corresponding to antenna ports 0 to 3, and the DMRS 5 are carried by
resource elements in both the non-MBSFN subframe 1201 and the MSBSFN subframe 1203.
As illustrated in Figure 14, the non-MBSFN subframe 1201 does not carry CSI-RS
transmissions, and therefore in option D the base station (E)PDCCH transmission module 519 is
configured by the (E)PDCCH configuration module 517 to avoid placing the EPDCCH CSS 171
and the CSI-RS in the same subframe.
In option D, the MTC user device 3-2 does not distinguish between non-MBSFN and
MBSFN subframes, and therefore the user device 3 assumes that the same ratematching
parameters are used in the non-MBSFN subframe 1201 and the MBSFN subframe 1203. As a
result, the user device will exclude "assumed CRS" resource elements 158 from the EPDCCH
CSS 171 of MBSFN subframes - even though those resource elements are not actually being
used to carry the CRS signals. Similarly, the user device will exclude "assumed PDCCH"
resource elements 159 at the third OFDM symbol from the EPDCCH CSS 171 of MBSFN
subframes, even though MBSFN subframes do not include PDCCH at the third OFDM symbol.
Therefore, all of the unshaded resource elements in non-MBSFN subframe 12 and
those in MBSFN subframe 1203 can form part of the EPDCCH CSS 171.
As in the previous options, although all of these unshaded elements are available for
EPDCCH CSS 171, it is noted that in most embodiments a subset of the subcarriers will be
indicated by the PBCH 173 as carrying the EPDCCH CSS 171, and therefore the EPDCCH CSS
171 may only occupy a subset of the carriers illustrated in Figure 14.
In option D as shown in Figure 14, the starting OFDM symbol for the EPDCCH CSS 171
is fixed to the fourth OFDM symbol of the subframe for both non-MBSFN and MBSFN
subframes, as the user device 3 is configured to exclude the third symbol from the EPDCCH
CSS 171 for MSBFN subframes.
Signalling of EPDCCH CSS Information
As discussed above, the physical broadcast channel PBCH 173 has only 10 spare bits
available for use in signaling information about the location and size of the EPDCCH CSS 171
and in which subframes it is repeated. Three options for utilizing these 10 bits of the PBCH 173
are described below.
Option 1
In this option, all 0 bits of the PBCH 173 are used by the base station 5 to signal which
subframes of a radio frame are used to carry the repeated EPDCCH CSS 171. Therefore, as
there are 10 subframes in a radio frame, each bit corresponds to a single subframe. The
subframes may be indicated as "on" or "off with respect to the EPDCCH CSS 171, e.g. a value
of 0 means no EPDCCH CSS is present and a value of 1 means the EPDCCH CSS 171 is present.
Accordingly, option 1 allows for every possible configuration of subframes to be signaled.
However, this option consumes all available bits so there is no room for other signaling
parameters such as the subband for the EPDCCH CSS (NEPDCCH location) nd the number of PRBs
configured for EPDCCH CSS 171. Therefore, if this option is used then the location and size of
the EPDCCH CSS 171 must be fixed in advance or must be determinable from some other
information - such as from the cell ID or signaled using other control information.
Option 2
In this option, the number of bits used to signal which subframes in a radio frame carry
the EPDCCH CSS 171 is reduced, therefore reducing the flexibility in defining which subframes
can be used. In this option, separate bits are coded for identifying which MBSFN subframes are
used to carry the EPDCCH CSS 171 and which non-MBSFN subframes are used to carry the
EPDCCH CSS 171. Table 2 below illustrates one example coding scheme that can be used in
this option. As shown two bits are provided for identifying which MBSFN subframes are used
to carry the EPDCCH CSS 171 and two bits are provided for identifying which non-MBSFN
subframes are used to carry the EPDCCH CSS 171. Thus there are 8 different subframe
configurations with this coding.
Table 2
The remaining six bits of the available ten bits in the PBCH 73 can then be used to
signal the location and size of the EPDCCH CSS 171 within the band.
Option 3
This option also uses a reduced number of bits to signal which subframes are used to
carry the EPDCCH CSS 171. However in option 3 joint coding of non-MBSFN and MBSFN
subframes is used. Table 3 below illustrates one example joint coding scheme that can be used
in this option. As shown three bits are provided for identifying which subframes are used to
carry the EPDCCH CSS 171. As can be seen from Table 3, there are still eight different
subframe configurations with this joint coding scheme which saves one bit compared to the
coding scheme used in option 2 discussed above.
Table 3
Thus the remaining seven bits of the available ten bits in the PBCH 173 can be used to
signal the location and size of the EPDCCH CSS 171 within the band.
Modifications and alternatives
Detailed exemplary embodiments have been described above. As those skilled in the art
will appreciate, a number of modifications and alternatives can be made to the above exemplary
embodiments whilst still benefiting from the inventions embodied therein.
In the above description relating to the EPDCCH CSS 171, the EPDCCH CSS 171 is
provided within a reduced bandwidth of 1.4 MHz, and the location of this reduced bandwidth is
signalled by the PBCH 173. In an alternative exemplary embodiment, the EPDCCH CSS 171 is
not provided within a reduced bandwidth of 1.4 MHz. Instead, the PRBs reserved for the
EPDCCH CSS 171 are distributed over the system bandwidth (e.g. of 20MHz).
For example, the base station (E)PDCCH transmission module 519 may be configured by
the (E)PDCCH configuration module 517 to use a fixed number of PRBs for the EPDCCH CSS
171, in blocks of 2, 4 or 6 PRBs, which are distributed over the system bandwidth in a preconfigured
pattern. The MTC user device 3-2 will be pre-configured with the pattern and then
may determine the size of the blocks - 2, 4, or 6 PRBs either from signaling information
received from the base station 5 over the PBCH or by calculation using some cell specific
information - such as the cell ID.
The base station 5 may define a number of possible locations where the EPDCCH CSS
171 can be located, with the locations being chosen in neighbouring cells to minimize inter cell
interference. In this case, the selected location could also be signaled to the MTC user device
over the PBCH 173 or it could be determined from some (semi) static information, such as from
the cell ID.
In the above exemplary embodiments, a radio frame comprised 10 subframes. As those
skilled in the art will appreciate a radio frame may include any number of subframes. Further,
the PDCCH region of a subframe may comprise any number of OFDM symbols.
The legacy CSS 151 and the MTC-CSS 161 illustrated in Figure 7 each comprise 16
CCEs, however as those skilled in the art will appreciate, both CSSs may comprise any number
ofCCEs.
Although the MTC-CSS 161 as illustrated in Figure 7 commences immediately after the
legacy CSS, the MTC-CSS can be allocated anywhere in the USS. Preferably, the location
within the USS is fixed.
In many of the exemplary embodiments described above, the EPDCCH is provided
within a reduced bandwidth of 1.4 MHz. This is not essential, other bandwidths are possible.
Similarly, in Figures 8 and 10 to 14, the EPDCCH CSS 171 starts immediately after the
PDCCH, specifically on the fourth OFDM symbol. However, the EPDCCH CSS 171 may be
configured to start at any symbol.
In the description above, the location of the CSI-RS in the serving cell is configured in
the same way as the location of CSI-RS in neighbouring cells, and therefore the qcl-CSI-RSConfigNZPId-
rl 1 can be determined based on csi-RS-ConfigZPId-rl 1. Alternatively, the
location of CSI-RS may be configured differently in serving and neighbouring cells, and
therefore both qcl-CSI-RS-ConfigNZPId-rl 1 and csi-RS-ConfigZPId-rl 1 are signalled to the user
device 3 by the base station 5. In either case, when both parameters are configured, user devices
are configured to assume no data (PDSCH/EPDCCH) is mapped on those locations (e.g. the
EPDCCH CSS 171 does not include the resource elements carrying CSI-RS).
In the above description, information relating to the EPDCCH CSS 171, such as its
location and size, is signaled in the PBCH 1 3. Alternatively or additionally, some or all of this
information can be obtained by the user device in a different manner - for example the location
and size may be signaled on a different channel.
Furthermore, the location of the EPDCCH CSS 171 may not be signaled in the PBCH
173 and may instead be determined based upon other information, such as the Cell ID associated
with the base station 5. Specifically, this may be determined in a cyclical manner, e.g by Cell ID
mod NEPDCCHjocation- This has the benefit of reducing the amount of data that has to be signaled
to the MTC user device, although in this case it is not practical to change the location based on
prevailing radio conditions.
It will be appreciated that although the communication system 1 is described in terms of
base stations 5 operating as E-UTRAN base stations, the same principles may be applied to base
stations operating as macro or pico base stations, femto base stations, relay nodes providing
elements of base station functionality, home base stations (HeNB), or other such communication
nodes.
In the above exemplary embodiments, an LTE telecommunications system was described.
As those skilled in the art will appreciate, the signalling techniques described in the present
application can be employed in other communications systems, including earlier 3GPP type
systems. Other communications nodes or devices may include user devices such as, for example,
personal digital assistants, laptop computers, web browsers, etc.
In the exemplary embodiments described above, the base stations 5 and user devices 3
each include transceiver circuitry. Typically, this circuitry will be formed by dedicated hardware
circuits. However, in some exemplary embodiments, part of the transceiver circuitry may be
implemented as software run by the corresponding controller.
In the above exemplary embodiments, a number of software modules were described. As
those skilled in the art will appreciate, the software modules may be provided in compiled or uncompiled
form and may be supplied to the base station or the user device as a signal over a
computer network, or on a recording medium. Further, the functionality performed by part or all
of this software may be performed using one or more dedicated hardware circuits.
Various other modifications will be apparent to those skilled in the art and will not be
described in further detail here.
The following is a detailed description of the way in which the present inventions may be
implemented in the currently proposed 3GPP standard. Whilst various features are described as
being essential or necessary, this may only be the case for the proposed 3GPP standard, for
example due to other requirements imposed by the standard. These statements should not,
therefore, be construed as limiting the present invention in any way.
Introduction
In RAN1#75, it has been agreed that repetition of (E-)PDCCH across multiple subframes
is supported for UEs in enhanced coverage mode of low cost MTC. The agreements are
as follows:
Agreements:
For UEs in enhanced coverage mode for MTC
> For UE-specific search space,
(E)PDCCH to schedule PDSCH is supported.
Repetition of (E)PDCCH with multiple levels is supported.
From the UE perspective, the possible starting sub-frames of (E)PDCCH
repetitions are limited to a subset of sub-frames.
For UEs in enhanced coverage mode for MTC, if/when PDSCH is indicated via
(E)PDCCH:
> The relation of PDSCH timing to (E)PDCCH timing shall be known to UE and
shall not be configurable by higher layer parameter dedicated only for this
purpose and shall not be indicated by (E)PDCCH. FFS on how to derive it or
fixed by spec.
> Assigned PDSCH is transmitted not before end of (E)PDCCH, i.e., if subframe n
is the last (E)PDCCH repetition then PDSCH start n + k (k > 0)
In this contribution, we discuss some details of the (E)PDCCH relating USS and CSS
search space design for enhanced coverage of low cost MTC UEs and provide some proposals at
the end.
UE Specific search space for MTC
In RAN1#75, repetition in time domain has been agreed for (E-)PDCCH for low cost
MTC UEs in coverage enhanced mode. This means that UE has to combine (E-)PDCCH
repetitions across multiple subframes in time domain. In order UE to do that, UE has to know
the location of CCEs from the search space in each subframe as well as the start and end of
subframes carrying the repetition of the (E-)PDCCH.
As discussed in the last meeting [5] and email discussion after the meeting, one possible
way to determine the location of CCEs from the UE specific search space (USS) is to use the
same legacy PDCCH candidates "m " in Table 9.1.1-1 (TS 36.213 section 9.1) with same
aggregation level in each repetition, so that UE can combine each candidate with the same
candidate from the repeated subframes. For example aggregation level 8, there are two
candidates based on existing Table 9.1.1-1, MTC UE can combine each candidate from each
repeated subframe, and when it reaches the final repetition subframe, it tries to decode blindly
these candidates similar to Release-8 (e.g. DL/UL DCI formats).
For E-PDCCH, the same principle as PDCCH can be applied. However, it is FFS
whether to support higher aggregation levels than currently supported by E-PDCCH search space
in order to reduce the number of repetitions in time-domain.
Furthermore, the timing of (E-)PDCCH to PDSCH has been agreed in the last meeting
which states that if subframe n is the last (E-)PDCCH repetition then PDSCH start n + k (k > 0).
We think that the parameter "k" should be decided in such a way that the complexity of the
scheduling decisions are minimised, for example k = 1.
Proposal 1: agree to determine the location of CCEsfrom the USS by using the same
legacy (E-)PDCCH candidates "m "with same aggregation level in each repetition, so that UE
can combine them respectively.
Common search space for MTC
Common search space in PDCCH: common information such as SIB, RACH message
2/4 and PCH for MTC UEs can be sent on legacy common search space (CSS). However, as
PDCCH for low cost MTC would be repeated in multiple subframes before trying the actual
decoding of the PDCCH, the legacy UE may be confused or decode mistakenly the individual
repeated PDCCH in those subframes where there is no corresponding PDSCH carrying common
control information. So, there are different possible solutions as follows:
■ One way to avoid the legacy UE to decode repeated PDCCH is to use aggregation
level 16 (AL16) for low cost MTC. However, this AL16 will consume the whole CSS
space, meaning that there will not be any remaining CCEs for eNB to schedule some
other important control information. Therefore, this solution causes blocking of CSS
in number of consecutive subframes. So, it is not efficient solution.
■ Another way is to apply a specific scrambling on PDCCH that is intended solely for
low cost MTC. This kind of scrambling could be a new R TI (i.e. MTC-RNTI).
However, based on this solution, there is still concern that MTC UEs may consume a
lot of resources which may cause blocking of CSS in number of consecutive
subframes.
Common search space in EPDCCH: Another solution is to design an enhanced CSS
(ECSS) in EPDCCH for low cost MTC as shown on Figure 15. While this solution solves the
above issue, it also provides additional benefits of applying higher aggregation levels which will
reduce the number of repetitions in time domain, power boosting, as well as interference
coordination among cells. Some design principles for ECSS are:
■ The resources for ECSS in EPDCCH can be signaled in PBCH.
■ The ratematching parameters for ECSS can be determined as follows:
• Number of CRS ports, CRS-shift of non-MBSFN subframes used for ECSS
can be acquired from PBCH.
• MBSFN subframes used for ECSS can be added in PBCH.
• eNB can avoid placing ECSS on subframe(s) that contains CSI-RS
• Starting symbol for ECSS can be always fixed to 4th and 3rd OFDM symbol
for non-MBSFN and MBSFN subframes respectively.
• Antenna port numbers and their initialization parameters (e.g. ci j value) can
be fixed and or derived from Cell ID.
Proposal 2: consider a solution of how to avoid the legacy UE to decode mistakenly the
individual repeated PDCCH in subframes where there is no corresponding PDSCH carrying
common control information.
Proposal 3: consider to introduce enhanced CSS (ECSS) in EPDCCH for low cost
MTC as it provides benefits of applying higher aggregation levels which will reduce the
number of repetitions in time domain, power boosting as well as interference coordination
among cells.
Conclusion
In this contribution, we have discussed some details of the design of (E)PDCCH relating
USS and CSS search spaces for enhanced coverage of low cost MTC UEs and we have the
following proposals:
Proposal 1: agree to determine the location of CCEsfrom the USS by using the same
legacy (E-)PDCCH candidates "m" with same aggregation level in each repetition, so that UE
can combine them respectively.
Proposal 2: consider a solution of how to avoid the legacy UE to decode mistakenly the
individual repeated PDCCH in subframes where there is no corresponding PDSCH carrying
common control information.
Proposal 3 : consider to introduce enhanced CSS (ECSS) in EPDCCH for low cost MTC
as it provides benefits of applying higher aggregation levels which will reduce the number of
repetitions in time domain, power boosting as well as interference coordination among cells.
The whole or part of the exemplary embodiments disclosed above can be described as,
but not limited to, the following supplementary notes.
(Supplementary note 1). A communications node operable to schedule resources for use by
a plurality of user devices, including legacy user devices and non-legacy user devices, for
communicating with the communications node, the communications node comprising:
means for generating control data for transmission to the user devices, the control data
including common control data for reception and decoding by a plurality of user devices and user
specific control data for reception and decoding by a specific user device; and
means for transmitting the generated control data in a sequence of subframes for
reception by the user devices;
wherein the means for generating is configured to generate common control data for
reception and decoding by the non-legacy user devices which cannot be decoded by the legacy
user devices; and
wherein the means for transmitting is configured to transmit repeats of the common
control data generated for reception and decoding by non-legacy user devices within a plurality
of subframes.
(Supplementary note 2). A communications node according to Supplementary note 1,
wherein the control data is transmitted using a plurality of control channel elements, CCEs, and
wherein the common control data for reception and decoding by the non-legacy user devices is
transmitted using an aggregation of at least sixteen CCEs that cannot be decoded by the legacy
user devices.
(Supplementary note 3). A communications node according to Supplementary note 1,
wherein the common control data for reception and decoding by the non-legacy user devices is
encrypted using an encryption key that is unavailable to the legacy user devices.
(Supplementary note 4). A communications node according to Supplementary note 1,
wherein the control data is transmitted in a physical downlink common control channel, PDCCH,
wherein common control data for legacy user devices is located in a first part of the PDCCH and
user specific control data for legacy user devices is located in a second part of the PDCCH; and
wherein the common control data for the non-legacy user devices is located in the second part of
the PDCCH.
(Supplementary note 5). A communications node according to Supplementary note 1,
wherein each subframe includes a physical downlink common control channel, PDCCH, part and
a physical downlink shared channel, PDSCH, part and wherein the common control data for
reception and decoding by the non-legacy user devices is transmitted within the PDSCH part of
the subframe.
(Supplementary note 6). A communications node according to Supplementary note 5,
wherein the communications node is configured to transmit signalling information to the nonlegacy
user devices identifying the subframes in which the common control data for reception
and decoding by the non-legacy user devices is transmitted.
(Supplementary note 7). A communications node according to Supplementary note 6,
wherein the data identifying the subframes identifies only multimedia broadcast single frequency
network, MBSFN, subframes as carrying the common control data for reception and decoding by
the non-legacy user devices.
(Supplementary note 8). A communications node according to Supplementary note 6,
wherein the data identifying the subframes identifies multimedia broadcast single frequency
network, MBSFN, subframes and non-MBSFN subframes as carrying the common control data
for reception and decoding by the non-legacy user devices.
(Supplementary note 9). A communications node according to Supplementary note 8,
wherein the communications node is configured to avoid placing the common control data for
reception and decoding by the non-legacy user devices and channel state information reference
signals, CSI-RS, in the same subframe.
(Supplementary note 10). A communications node according to any of Supplementary notes
6 to 9, wherein the communications node is configured to transmit said signalling information
using a physical broadcast channel, PBCH.
(Supplementary note 11). A communications node according to any of Supplementary notes
6 to 10, wherein the communications node is configured to communicate with the user devices
using radio frames having N subframes and wherein the signalling information comprises N bits,
corresponding to one bit for identifying if a corresponding one of the N subframes carries the
common control data for reception and decoding by the non-legacy user devices.
(Supplementary notes 12). A communications node according to any of Supplementary notes
6 to 11, wherein the communications node is configured to communicate with the user devices
using radio frames having N subframes and wherein the signalling information comprises M bits,
where M is less than N, that identify one of a number of predetermined configuration of the N
subframes that will carry the common control data for reception and decoding by the non-legacy
user devices.
(Supplementary note 13). A communications node according to Supplementary note 12,
wherein the data identifying the subframes identifies multimedia broadcast single frequency
network, MBSFN, subframes and non-MBSFN subframes as carrying the common control data
for reception and decoding by the non-legacy user devices and wherein the M bits jointly encode
which MBSFN subframes and which non-MBSFN subframes of a radio frame will carry the
common control data for reception and decoding by the non-legacy user devices.
(Supplementary note 14). A communications node according to any of Supplementary notes
5 to 13, wherein the communications node is configured to transmit the common control data for
reception and decoding by the non-legacy user devices in subframes that do not include channel
state information reference signals, CSI-RS, or channel reference signals, CRS.
(Supplementary note 15). A communications node according to any of Supplementary notes
5 to 13, wherein the communications node is configured to transmit the common control data for
reception and decoding by the non-legacy user devices in subframes that include channel state
information reference signals, CSI-RS, or channel reference signals, CRS; and is configured to
avoid using resources to carry the common control data for reception and decoding by the nonlegacy
user devices that are used to carry the CSI-RS or the CRS.
(Supplementary note 16). A communications node according to any of Supplementary notes
1 to 15, wherein the communications node is configured to transmit signalling information to the
non-legacy user devices identifying the location within a subframe of the common control data
for reception and decoding by the non-legacy user devices.
(Supplementary note 17). A communications node according to Supplementary note 16,
wherein there is a fixed number of possible locations within a subframe for the common control
data for reception and decoding by the non-legacy user devices, and wherein the
communications node is configured to signal data identifying one of the possible locations.
(Supplementary note 18). A communications node according to any of Supplementary notes
1 to 15, wherein there is a fixed number of possible locations within a subframe for the common
control data for reception and decoding by the non-legacy user devices, and wherein the
communications node is configured to transmit the common control data for reception and
decoding by the non-legacy user devices in a location that depends upon a static or semi static
system variable, such as a cell ID associated with the communications node.
(Supplementary note 19). A communications node according to any of Supplementary notes
1 to 18, wherein the communications node is configured to signal data identifying a size of the
common control data for reception and decoding by the non-legacy user devices.
(Supplementary note 20). A communications node according to Supplementary note 19,
wherein the size of the common control data for reception and decoding by the non-legacy user
devices is one of a plurality of possible sizes and wherein the communications node is
configured to signal data indicating one of the plurality of sizes.
(Supplementary note 21). A communications node according to any of Supplementary notes
1to 20, wherein the common control data for reception and decoding by the non-legacy user
devices is carried on a plurality of resource blocks, RBs, and wherein the RBs are either arranged
contiguously within a subframe or are dispersed within a subframe.
(Supplementary note 22). A communications node operable to schedule resources for use by
a plurality of user devices for communicating with the communications node, the
communications node comprising:
means for generating control data for transmission to the user devices, the control data
including common control data for reception and decoding by a plurality of user devices and user
specific control data for reception and decoding by a specific user device;
means for generating reference signals for use in controlling communications between
the communications node and the user devices; and
means for transmitting the generated reference signals and the generated control data
in a sequence of subframes for reception by the user devices, each subframe including a physical
downlink common control channel, PDCCH, part and a physical downlink shared channel,
PDSCH, part;
wherein generated reference signals and common control data for reception and decoding
by a plurality of user devices are transmitted within the PDSCH part of the subframe; and
wherein the means for transmitting is configured to transmit said common control data
and said reference signals within the PDSCH part of subframes using different resource blocks
contained therein.
(Supplementary note 23). A communications node according to Supplementary note 22,
wherein the communications node is configured to carry the common control data in subframes
that do not include channel state information reference signals, CSI-RS, or channel reference
signals, CRS.
(Supplementary note 24). A communications node according to Supplementary note 22 or 23,
wherein the communications node is configured to transmit the common control data in
subframes that include channel state information reference signals, CSI-RS, or channel reference
signals, CRS; and is configured to avoid using resources to carry the common control data that
are used to carry the CSI-RS or the CRS.
(Supplementary note 25). A communications node according to any of Supplementary notes
22 to 24, wherein the communications node is configured to transmit signalling information to
the user devices identifying the location within a subframe of the common control data.
(Supplementary note 26). A communications node according to Supplementary note 25,
wherein there is a fixed number of possible locations within a subframe for the common control
data and wherein the communications node is configured to signal data identifying one of the
possible locations.
(Supplementary note 27). A communications node according to Supplementary note 25,
wherein there is a fixed number of possible locations within a subframe for the common control
data and wherein the communications node is configured to transmit the common control data in
a location that depends upon a static or semi static system variable, such as a cell ID associated
with the communications node.
(Supplementary note 28). A communications node according to any of Supplementary notes
22 to 27, wherein the communications node is configured to transmit signalling information to
the non-legacy user devices identifying the subframes in which the common control data is
transmitted.
(Supplementary note 29). A communications node according to Supplementary note 28,
wherein the data identifying the subframes identifies only multimedia broadcast single frequency
network, MBSFN, subframes as carrying the common control data.
(Supplementary note 30). A communications node according to Supplementary notes 28 or
29, wherein the data identifying the subframes identifies multimedia broadcast single frequency
network, MBSFN, subframes and non-MBSFN subframes as carrying the common control data.
(Supplementary note 31). A communications node according to Supplementary note 30,
wherein the communications node is configured to avoid placing the common control data for
reception and decoding by the non-legacy user devices and channel state information reference
signals, CSI-RS, in the same subframe.
(Supplementary note 32). A communications node according to any of Supplementary notes
28 to 3 , wherein the communications node is configured to transmit said signalling information
using a physical broadcast channel, PBCH.
(Supplementary note 33). A communications node according to any of Supplementary notes
28 to 32, wherein the communications node is configured to communicate with the user devices
using radio frames having N subframes and wherein the signalling information comprises N bits,
corresponding to one bit for identifying if a corresponding one of the N subframes carries the
common control data.
(Supplementary note 34). A communications node according to any of Supplementary notes
28 to 33, wherein the communications node is configured to communicate with the user devices
using radio frames having N subframes and wherein the signalling information comprises M bits,
where M is less than N, that identify one of a number of predetermined configuration of the N
subframes that will carry the common control data.
(Supplementary note 35). A communications node according to Supplementary note 34,
wherein the data identifying the subframes identifies multimedia broadcast single frequency
network, MBSFN, subframes and non-MBSFN subframes as carrying the common control data
and wherein the M bits jointly encode which MBSFN subframes and which non-MBSFN
subframes of a radio frame will carry the common control data.
(Supplementary note 36). A communications node according to any of Supplementary notes
1 to 35, wherein the non-legacy user devices include Machine Type Communications, MTC,
user devices.
(Supplementary note 37). A communications node according to any of Supplementary notes
1 to 36, wherein the communications node starts said common control data on a starting symbol
of the subframe that is known in advance by the non-legacy user devices.
(Supplementary note 38). A communications system comprising a communications node
according to any of Supplementary notes 1 to 37 and at least one user device for receiving and
decoding the common control data to control communications between the user device and the
communications node.
(Supplementary note 39). A user device for communicating with a communications node,
characterised in that the user device is configured to operate with the communications node of
any of Supplementary notes 1 to 37 and adapted to be able to receive and decode the common
control data to control communications with the communications node.
(Supplementary note 40). A method performed by a communications node that schedules
resources for use by a plurality of user devices, including legacy user devices and non-legacy
user devices, for communicating with the communications node, the method comprising:
generating control data for transmission to the user devices, the control data including
common control data for reception and decoding by a plurality of user devices and user specific
control data for reception and decoding by a specific user device; and
transmitting the generated control data in a sequence of subframes for reception by the
user devices;
wherein the generating generates common control data for reception and decoding by
the non-legacy user devices which cannot be decoded by the legacy user devices; and
wherein the transmitting transmits repeats of the common control data generated for
reception and decoding by non-legacy user devices within a plurality of subframes.
(Supplementary note 41). A method performed by a communications node that schedules
resources for use by a plurality of user devices for communicating with the communications
node, the method comprising:
generating control data for transmission to the user devices, the control data including
common control data for reception and decoding by a plurality of user devices and user specific
control data for reception and decoding by a specific user device;
generating reference signals for use in controlling communications between the
communications node and the user devices; and
transmitting the generated reference signals and the generated control data in a
sequence of subframes for reception by the user devices, each subframe including a physical
downlink common control channel, PDCCH, part and a physical downlink shared channel,
PDSCH, part;
wherein generated reference signals and common control data for reception and decoding
by a plurality of user devices are transmitted within the PDSCH part of the subframe; and
wherein the transmitting is configured to transmit said common control data and said
reference signals within the PDSCH part of subframes using different resource blocks contained
therein.
(Supplementary note 42). A communications node operable to schedule resources for use by
a plurality of user devices, including legacy user devices and non-legacy user devices, for
communicating with the communications node, the communications node comprising:
a control configuration module for generating control data for transmission to the user
devices, the control data including common control data for reception and decoding by a
plurality of user devices and user specific control data for reception and decoding by a specific
user device; and
a transmitter for transmitting the generated control data in a sequence of subframes for
reception by the user devices;
wherein the control configuration module is configured to generate common control
data for reception and decoding by the non-legacy user devices which cannot be decoded by the
legacy user devices; and
wherein the transmitter is configured to transmit repeats of the common control data
generated for reception and decoding by non-legacy user devices within a plurality of subframes.
(Supplementary note 43). A communications node operable to schedule resources for use by
a plurality of user devices for communicating with the communications node, the
communications node comprising:
a control configuration module for generating control data for transmission to the user
devices, the control data including common control data for reception and decoding by a
plurality of user devices and user specific control data for reception and decoding by a specific
user device;
a reference signal module for generating reference signals for use in controlling
communications between the communications node and the user devices; and
a transmitter for transmitting the generated reference signals and the generated control
data in a sequence of subframes for reception by the user devices, each subframe including a
physical downlink common control channel, PDCCH, part and a physical downlink shared
channel, PDSCH, part;
wherein generated reference signals and common control data for reception and decoding
by a plurality of user devices are transmitted within the PDSCH part of the subframe; and
wherein the transmitter is configured to transmit said common control data and said
reference signals within the PDSCH part of subframes using different resource blocks contained
within the PDSCH part.
(Supplementary note 44). A user device for communicating with a communications node, the
user device comprising:
means for receiving control data transmitted by the communications node, the control
data including common control data for reception and decoding by the user device and user
specific control data for reception and decoding by a specific user device;
wherein the received common control data is for reception and decoding by non-legacy
user devices and cannot be decoded by legacy user devices;
wherein the means for receiving is configured to receive a plurality of subframes
comprising said common control data;
means for combining the control data received from the plurality of subframes; and
means for decoding the combined common control data.
(Supplementary note 45). A user device for communicating with a communications node, the
user device comprising:
means for receiving subframes transmitted by the communications node, the subframes
comprising control data including common control data for reception and decoding by a plurality
of user devices and user specific control data for reception and decoding by a specific user
device;
wherein the subframes include reference signals transmitted by the communications node
for use in controlling communications between the communications node and the user device;
and
wherein the means for receiving is configured to receive a plurality of subframes
comprising said common control data;
wherein each subframe includes a physical downlink common control channel, PDCCH,
part and a physical downlink shared channel, PDSCH, part;
wherein received reference signals and common control data are received within the
PDSCH part of the subframe using different resource blocks contained within the PDSCH part;
means for combining the control data received from the plurality of subframes; and
means for decoding the combined common control data.
(Supplementary note 46). A user device for communicating with a communications node, the
user device comprising:
a receiver for receiving control data transmitted by the communications node, the
control data including common control data for reception and decoding by the user device and
user specific control data for reception and decoding by a specific user device;
wherein the received common control data is for reception and decoding by non-legacy
type user devices and cannot be decoded by legacy type user devices;
wherein the receiver is configured to receive a plurality of subframes comprising said
common control data; and
a control channel reception module for combining the control data received from the
plurality of subframes and for decoding the combined common control data.
(Supplementary note 47). A user device for communicating with a communications node, the
user device comprising:
a receiver for receiving subframes transmitted by the communications node, the
subframes comprising control data including common control data for reception and decoding by
a plurality of user devices and user specific control data for reception and decoding by a specific
user device;
wherein the subframes include reference signals transmitted by the communications node
for use in controlling communications between the communications node and the user device;
and
wherein the receiver is configured to receive a plurality of subframes comprising said
common control data;
wherein each subframe includes a physical downlink common control channel, PDCCH,
part and a physical downlink shared channel, PDSCH, part;
wherein received reference signals and common control data are received within the
PDSCH part of the subframe using different resource blocks contained within the PDSCH part;
and
a control channel reception module for combining the control data received from the
plurality of subframes and for decoding the combined common control data.
(Supplementary note 48). A method performed by a user device that communicates with a
communications node, the method comprising:
receiving control data transmitted by the communications node, the control data
including common control data for reception and decoding by the user device and user specific
control data for reception and decoding by a specific user device;
wherein the received common control data is for reception and decoding by non-legacy
user devices and cannot be decoded by legacy user devices;
wherein the receiving receives a plurality of subframes comprising said common control
data;
combining the control data received from the plurality of subframes; and
decoding the combined common control data.
(Supplementary note 49). A method performed by a user device that communicates with a
communications node, the method comprising:
receiving subframes transmitted by the communications node, the subframes comprising
control data including common control data for reception and decoding by a plurality of user
devices and user specific control data for reception and decoding by a specific user
device;
wherein the subframes include reference signals transmitted by the communications node
for use in controlling communications between the communications node and the user device;
and
wherein the receiving receives a plurality of subframes comprising said common control
data;
wherein each subframe includes a physical downlink common control channel, PDCCH,
part and a physical downlink shared channel, PDSCH, part;
wherein received reference signals and common control data are received within the
PDSCH part of the subframe using different resource blocks contained within the PDSCH part;
combining the control data received from the plurality of subframes; and
decoding the combined common control data.
(Supplementary note 50). A communications node operable to schedule resources for use by
a plurality of user devices, including first type user devices and second type user devices, for
communicating with the communications node, the communications node comprising:
means for generating control data for transmission to the user devices, the control data
including common control data for reception and decoding by a plurality of user devices and user
specific control data for reception and decoding by a specific user device; and
means for transmitting the generated control data in a sequence of subframes for
reception by the user devices;
wherein the means for generating is configured to generate common control data for
reception and decoding by second type user devices which cannot be decoded by first type user
devices; and
wherein the means for transmitting is configured to transmit repeats of the common
control data generated for reception and decoding by second type user devices within a plurality
of subframes.
(Supplementary note 51). A communications node according to Supplementary note 50,
wherein the first type user devices are legacy user devices and wherein the second type user
devices are non-legacy user devices.
(Supplementary note 52). A communications node operable to schedule resources for use by
a plurality of user devices for communicating with the communications node, the
communications node comprising:
means for generating control data for transmission to the user devices, the control data
including common control data for reception and decoding by a plurality of user devices and user
specific control data for reception and decoding by a specific user device;
means for transmitting the generated control data in a sequence of subframes for
reception by the user devices, each subframe including a physical downlink common control
channel, PDCCH, part and a physical downlink shared channel, PDSCH, part;
wherein the means for transmitting is configured to transmit repeats of the common
control data generated for reception and decoding by non-legacy user devices within a plurality
of subframes; and
wherein the communications node is configured to transmit signalling information to the
non-legacy user devices identifying the subframes in which the common control data for
reception and decoding by the non-legacy user devices is transmitted.
(Supplementary note 53). A user device for communicating with a communications node, the
user device comprising:
means for receiving subframes transmitted by the communications node, the subframes
comprising control data including common control data for reception and decoding by a plurality
of user devices and user specific control data for reception and decoding by a specific user
device;
wherein the subframes include reference signals transmitted by the communications node
for use in controlling communications between the communications node and the user device;
and
wherein the means for receiving is configured to receive a plurality of subframes
comprising said common control data;
wherein each subframe includes a physical downlink common control channel, PDCCH,
part and a physical downlink shared channel, PDSCH, part;
wherein received reference signals and common control data are received within the
PDSCH part of the subframe using different resource blocks contained within the PDSCH part;
means for identifying the common control data within the PDSCH part of the subframes
using information about the location, or the expected location, of the reference control signals;
means for combining the control data received from the plurality of subframes; and
means for decoding the combined common control data.
(Supplementary note 54). A user device according to Supplementary note 53, wherein the
means for identifying is further configured to use data signalled from the communications node
to identify the common control data within the PDSCH part of the subframes.
This application is based upon and claims the benefit of priority from United Kingdom
patent application No. 1401459.1, filed on January 28, 2014, the disclosure of which is
incorporated herein in its entirety by reference.
WO 2015/115579 PCT/JP2015/052603
CLAIMS
. A communications node operable to schedule resources for use by a plurality of user
devices, including legacy user devices and non-legacy user devices, for communicating with the
communications node, the communications node comprising:
means for generating control data for transmission to the user devices, the control data
including common control data for reception and decoding by a plurality of user devices and user
specific control data for reception and decoding by a specific user device; and
means for transmitting the generated control data in a sequence of subframes for
reception by the user devices;
wherein the means for generating is configured to generate common control data for
reception and decoding by the non-legacy user devices which cannot be decoded by the legacy
user devices; and
wherein the means for transmitting is configured to transmit repeats of the common
control data generated for reception and decoding by non-legacy user devices within a plurality
of subframes.
2. A communications node according to claim 1, wherein the control data is transmitted
using a plurality of control channel elements, CCEs, and wherein the common control data for
reception and decoding by the non-legacy user devices is transmitted using an aggregation of at
least sixteen CCEs that cannot be decoded by the legacy user devices.
3. A communications node according to claim 1, wherein the common control data for
reception and decoding by the non-legacy user devices is encrypted using an encryption key that
is unavailable to the legacy user devices.
4. A communications node according to claim 1, wherein the control data is transmitted in a
physical downlink common control channel, PDCCH, wherein common control data for legacy
user devices is located in a first part of the PDCCH and user specific control data for legacy user
devices is located in a second part of the PDCCH; and wherein the common control data for the
non-legacy user devices is located in the second part of the PDCCH.
5. A communications node according to claim 1, wherein each subframe includes a physical
downlink common control channel, PDCCH, part and a physical downlink shared channel,
PDSCH, part and wherein the common control data for reception and decoding by the nonlegacy
user devices is transmitted within the PDSCH part of the subframe.
6. A communications node according to claim 5, wherein the communications node is
configured to transmit signalling information to the non-legacy user devices identifying the
subframes in which the common control data for reception and decoding by the non-legacy user
devices is transmitted.
7. A communications node according to claim 6, wherein the data identifying the subframes
identifies only multimedia broadcast single frequency network, MBSFN, subframes as carrying
the common control data for reception and decoding by the non-legacy user devices.
8. A communications node according to claim 6, wherein the data identifying the subframes
identifies multimedia broadcast single frequency network, MBSFN, subframes and non-MBSFN
subframes as carrying the common control data for reception and decoding by the non-legacy
user devices.
9. A communications node according to claim 8, wherein the communications node is
configured to avoid placing the common control data for reception and decoding by the nonlegacy
user devices and channel state information reference signals, CSI-RS, in the same
subframe.
10. A communications node according to any of claims 6 to 9, wherein the communications
node is configured to transmit said signalling information using a physical broadcast channel,
PBCH.
11. A communications node according to any of claims 6 to 10, wherein the communications
node is configured to communicate with the user devices using radio frames having N subframes
and wherein the signalling information comprises N bits, corresponding to one bit for identifying
if a corresponding one of the N subframes carries the common control data for reception and
decoding by the non-legacy user devices.
12. A communications node according to any of claims 6 to 11, wherein the communications
node is configured to communicate with the user devices using radio frames having N subframes
and wherein the signalling information comprises M bits, where M is less than N, that identify
one of a number of predetermined configuration of the N subframes that will carry the common
control data for reception and decoding by the non-legacy user devices.
13. A communications node according to claim 12, wherein the data identifying the
subframes identifies multimedia broadcast single frequency network, MBSFN, subframes and
non-MBSFN subframes as carrying the common control data for reception and decoding by the
non-legacy user devices and wherein the M bits jointly encode which MBSFN subframes and
which non-MBSFN subframes of a radio frame will carry the common control data for reception
and decoding by the non-legacy user devices.
14. A communications node according to any of claims 5 to 13, wherein the communications
node is configured to transmit the common control data for reception and decoding by the nonlegacy
user devices in subframes that do not include channel state information reference signals,
CSI-RS, or channel reference signals, CRS.
15. A communications node according to any of claims 5 to 13, wherein the communications
node is configured to transmit the common control data for reception and decoding by the nonlegacy
user devices in subframes that include channel state information reference signals, CSIRS,
or channel reference signals, CRS; and is configured to avoid using resources to carry the
common control data for reception and decoding by the non-legacy user devices that are used to
carry the CSI-RS or the CRS.
16. A communications node according to any of claims 1 to 15, wherein the communications
node is configured to transmit signalling information to the non-legacy user devices identifying
the location within a subframe of the common control data for reception and decoding by the
non-legacy user devices.
17. A communications node according to claim 16, wherein there is a fixed number of
possible locations within a subframe for the common control data for reception and decoding by
the non-legacy user devices, and wherein the communications node is configured to signal data
identifying one of the possible locations.
18. A user device for communicating with a communications node, characterised in that the
user device is configured to operate with the communications node of any of claims 1 to 17 and
adapted to be able to receive and decode the common control data to control communications
with the communications node.
19. A method performed by a communications node that schedules resources for use by a
plurality of user devices, including legacy user devices and non-legacy user devices, for
communicating with the communications node, the method comprising:
generating control data for transmission to the user devices, the control data including
common control data for reception and decoding by a plurality of user devices and user specific
control data for reception and decoding by a specific user device; and
transmitting the generated control data in a sequence of subframes for reception by the
user devices;
wherein the generating generates common control data for reception and decoding by
the non-legacy user devices which cannot be decoded by the legacy user devices; and
wherein the transmitting transmits repeats of the common control data generated for
reception and decoding by non-legacy user devices within a plurality of subframes.
20. A user device for communicating with a communications node, the user device
comprising:
means for receiving control data transmitted by the communications node, the control
data including common control data for reception and decoding by the user device and user
specific control data for reception and decoding by a specific user device;
wherein the received common control data is for reception and decoding by non-legacy
user devices and cannot be decoded by legacy user devices;
wherein the means for receiving is configured to receive a plurality of subframes
comprising said common control data;
means for combining the control data received from the plurality of subframes; and
means for decoding the combined common control data.