U.S. patent application number 17/564358 was filed with the patent office on 2022-05-05 for communication system.
This patent application is currently assigned to NEC Corporation. The applicant listed for this patent is NEC Corporation. Invention is credited to Robert ARNOTT, Yassin Aden AWAD.
Application Number | 20220141868 17/564358 |
Document ID | / |
Family ID | |
Filed Date | 2022-05-05 |
United States Patent
Application |
20220141868 |
Kind Code |
A1 |
AWAD; Yassin Aden ; et
al. |
May 5, 2022 |
COMMUNICATION SYSTEM
Abstract
A communication system is disclosed in which communication
devices communicate with a base station using radio frames made up
of a sequence of subframes and a frequency band made up of
frequency subbands. The base station identifies a subframe in which
a broadcast message, carrying information for at least one
communication device, is to be broadcast; transmits, in a control
channel, in a frequency subband in a current subframe that precedes
the identified subframe, control information to identify said
subframe in which said broadcast message is to be broadcast; and
transmits the broadcast message in the identified subframe.
Inventors: |
AWAD; Yassin Aden;
(Uxbridge, GB) ; ARNOTT; Robert; (London,
GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NEC Corporation |
Tokyo |
|
JP |
|
|
Assignee: |
NEC Corporation
Tokyo
JP
|
Appl. No.: |
17/564358 |
Filed: |
December 29, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15564582 |
Oct 5, 2017 |
11246156 |
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PCT/JP2016/001950 |
Apr 8, 2016 |
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17564358 |
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International
Class: |
H04W 74/00 20060101
H04W074/00; H04W 72/04 20060101 H04W072/04 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 10, 2015 |
GB |
1506151.8 |
Claims
1. A method performed by a user equipment (UE), the method
comprising; communicating with a base station; receiving, from the
base station, a physical downlink control channel (PDCCH) including
Downlink Control Information (DCI) including first information
related to at least one part of bandwidth to receive for physical
downlink shared channel (PDSCH) and second information related to
at least one subframe to receive for the PDSCH; and receiving, in
corresponding at least one subframe and on the corresponding at
least one part of the bandwidth, the PDSCH based on the first
information and the second information.
2. The method according to claim 1, wherein the PDCCH for the UE is
multiplexed with PDCCHs for other UEs.
3. The method according to claim 1, wherein the PDSCH physical
downlink shared channel for the UE includes a multiplexed data of
other UEs.
4. A method performed by a base station, the method comprising;
communicating with a user equipment (UE); transmitting, to the UE,
a physical downlink control channel (PDCCH) including Downlink
Control Information (DCI) including first information related to at
least one part of bandwidth to transmit for physical downlink
shared channel (PDSCH) and second information related to at least
one subframe to transmit for the PDSCH; and transmitting, in
corresponding at least one subframe and on the corresponding at
least one part of the bandwidth, the PDSCH based on the first
information and the second information.
5. A user equipment (UE) comprising; a controller; and a
transceiver, wherein the controller is configured to: control the
transceiver to communicate with a base station, control the
transceiver to receive, from the base station, a physical downlink
control channel (PDCCH) including Downlink Control Information
(DCI) including first information related to at least one part of
bandwidth to receive for physical downlink shared channel (PDSCH)
and second information related to at least one subframe to receive
for the PDSCH, and control the transceiver to receive, in
corresponding at least one subframe and on the corresponding at
least one part of the bandwidth, the PDSCH based on the first
information and the second information.
6. A base station comprising; a controller; and a transceiver,
wherein the controller is configured to: control the transceiver to
communicate with a user equipment (UE); control the transceiver to
transmit, to the UE, a physical downlink control channel (PDCCH)
including Downlink Control Information (DCI) including first
information related to at least one part of bandwidth to transmit
for physical downlink shared channel (PDSCH) and second information
related to at least one subframe to transmit for the PDSCH, and
control the transceiver to transmit, in corresponding at least one
subframe and on the corresponding at least one part of the
bandwidth, the PDSCH based on the first information and the second
information.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a continuation application of
U.S. patent application Ser. No. 15/564,582 filed on Oct. 5, 2017,
which is a National Stage Entry of international application
PCT/JP2016/001950, filed on Apr. 9, 2016, which claims the benefit
of priority from British Patent Application 1506151.8 filed on Apr.
10, 2015, the disclosures of all of which are incorporated in their
entirety by reference herein.
TECHNICAL FIELD
[0002] 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
[0003] In a mobile (cellular) communications network, (user)
communication devices (also known as user equipment (UE), for
example mobile telephones) communicate with remote servers or with
other communication devices via base stations. In their
communication with each other, communication devices and base
stations use licensed radio frequencies, which are typically
divided into frequency bands and/or time blocks.
[0004] In order to be able to communicate via the base stations,
communication devices need to monitor control channels operated by
the base stations. One of these control channels, the so-called
physical downlink control channel (PDCCH) and/or the so-called
evolved PDCCH (EPDCCH) in Rel-13, carries the scheduling
assignments and other control information. The (E)PDCCH serves a
variety of purposes. Primarily, it is used to convey the scheduling
decisions to individual communication devices, i.e. scheduling
assignments for uplink and downlink communication.
[0005] The information carried on the (E)PDCCH is referred to as
downlink control information (DCI). Physical control channels, such
as the (E)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).
[0006] Another control channel, the so-called physical random
access channel (PRACH) is provided for synchronising transmissions
between a communication device and the network (e.g. when setting
up an initial access for the communication device and/or whenever
re-synchronisation is necessary). In the current standard
specification (from Rel-8), the resource (preamble, time,
frequency) allocated to the PRACH is configured in advance and the
applicable PRACH parameters are broadcast by the network as part of
system information in the so-called System Information Block 2
(SIB2). One of the parameters specifies the so-called random access
preamble, which consists of a cyclic prefix part and a sequence
part. The length of the preamble (i.e. the overall length of the
two parts combined) depends on the frame structure and the random
access configuration.
[0007] When an idle mode communication device needs to communicate
with other communication nodes, it needs to change its operation
mode to the so-called radio resource control (RRC) connected mode
(from RRC idle mode). In order to do so, the communication device
performs a random access (RA) procedure with a suitable base
station (e.g. a base station having the strongest signal and/or a
base station that the communication device is authorised to use).
The random access procedure includes the communication device
selecting and transmitting to the base station (over the PRACH
advertised via the SIB2) an appropriate preamble sequence along
with a temporary identifier for identifying the communication
device for the base station. The temporary identifier is also
referred to as the random access radio network temporary identifier
(RA-RNTI), which unambiguously identifies the time-frequency
resource using which the communication device transmitted the
random access preamble. If the communication device's transmission
is received successfully, then the base station sends an
appropriate random access response (in which the base station
identifies the communication device using the received temporary
identifier) and allocates resources for the communication device
for communicating with the network.
[0008] Thus, once the base station responds to a preamble
transmission by the communication device with an appropriate random
access response (RAR), the communication device is able to request
in its next message the establishment of an RRC connection (and/or
the like) using the allocated resources. Once an RRC connection is
established between the communication device and the base station,
the communication device is able to communicate with other
communication nodes via that base station (and via the core
network) using the appropriate resources allocated to it by the
base station.
[0009] Recent developments in telecommunications have seen a large
increase in the use of machine-type communications (MTC) 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 communication devices are also known as
machine-to-machine (M2M) communication devices.
[0010] MTC devices connect to the network (after performing an
appropriate random access procedure, if necessary) whenever they
have data to send to or receive from a remote `machine` (e.g. a
server) or user. MTC devices use communication protocols and
standards that are optimised for mobile telephones or similar user
equipment. However, MTC devices, once deployed, typically operate
without requiring human supervision or interaction, and follow
software instructions stored in an internal memory. MTC devices
might also remain stationary and/or inactive for a long period of
time. The specific network requirements to support MTC devices have
been dealt with in the 3GPP technical specification (TS) 22.368
V13.1.0, the contents of which are incorporated herein by
reference.
[0011] For the Release 13 (Rel-13) version of the standards
relating to MTC devices, support for a reduced bandwidth of 1.4 MHz
in downlink and uplink is envisaged. Thus, some MTC devices will
support only a limited bandwidth (typically 1.4 MHz) compared to
the total LTE bandwidth and/or they may have fewer/simplified
components. This allows such `reduced bandwidth` MTC devices to be
made more economically compared to MTC devices supporting a larger
bandwidth and/or having more complicated components. Beneficially,
the EPDCCH is transmitted over a relatively narrow frequency
spectrum (1.4 Mhz) that makes it compatible with Rel-13 reduced
bandwidth MTC devices.
[0012] The lack of network coverage (e.g. when deployed indoors),
in combination with the often limited functionality of MTC devices,
can result in such MTC devices having a low data rate and therefore
there is a risk of some messages or channels, such as the EPDCCH,
not being received by an MTC device. In order to mitigate this
risk, it has been proposed to increase the coverage of
transmissions to support such MTC devices (e.g. corresponding to 20
dB for frequency division duplex (FDD) transmissions).
[0013] One approach proposed for the enhancement of coverage, for
so-called `coverage enhanced MTC devices`, is the repetition of the
same information (e.g. a DCI sent over the EPDCCH) across multiple
subframes (e.g. two, three, or four subframes). In other words, for
coverage enhanced (CE) MTC devices, the base station duplicates the
transmitted information in the time domain (the base station
re-transmits the same information in one or more subframes
subsequent to the subframe in which that information is first
sent). Such a coverage enhanced MTC device can be configured to
combine the multiple copies of the (same) information received in
the multiple subframes, and after combining the received
information, the coverage enhanced MTC device is more likely to be
able to decode the received information successfully than based on
a single copy of the transmitted information. Similarly to the
repetition of the same information by the base station, coverage
enhanced MTC devices are also configured to duplicate (in the time
domain) information transmitted to the base station to facilitate
successful reception of that information at the base station.
[0014] In practice, MTC devices may be deployed in different
locations and they may experience different channel conditions.
Therefore, the number of repetitions may need to be tailored for
each device's situation or coverage level, and each MTC device
informs its serving base station of the amount of coverage required
(e.g. 5 dB/10 dB/15 dB/20 dB coverage enhancement) to allow the
base station to adjust its control signalling appropriately.
SUMMARY OF INVENTION
Technical Problem
[0015] In the current 3GPP standards, so-called cross-subframe
scheduling is supported for unicast physical downlink shared
channel (PDSCH) transmissions, which makes it possible to send
control data to a single MTC device in one subframe for scheduling
transmissions for that MTC device in another (subsequent) subframe.
However, such cross-subframe scheduling is relatively inflexible
and limited.
[0016] Accordingly, the present invention seeks to provide systems,
devices and methods which alleviate or at least partially
ameliorate the above issues by providing improved cross-subframe
scheduling.
[0017] In particular, the inventors have realised that it would be
beneficial to provide cross-subframe scheduling for broadcast
transmissions (such as RA messages 2, 4, and paging messages) as
well, especially for MTC devices, and have conceived an efficient
way of achieving such cross-subframe scheduling for broadcast
transmissions. However, such cross-subframe scheduling not
currently possible for broadcast transmissions, is not trivial, and
cannot be achieved by simply re-using the existing procedures
available for unicast transmissions over the PDSCH. This is
especially true for MTC devices, which might operate over a limited
bandwidth and hence they cannot receive both the control data (in
one subframe) relating to a scheduled broadcast transmission and
monitor the associated broadcast transmissions (such as a RAR or
paging message) in the same or in another subframe. A further
problem primarily associated with MTC devices is that since all MTC
devices are allocated the same PRACH resources, the same temporary
identifier may be used by more than one MTC device (since the
RA-RNTI is derived from the PRACH resource used for sending the
first message of the random access procedure). Consequently, the
base station may be required to transmit associated RAR messages
with the same RA-RNTI across different subframes (in time) and over
different resource blocks in order to be able to respond to each
MTC device within the prescribed time window. However, MTC devices
(due to their limited bandwidth and low complexity) are unable to
concurrently monitor all possible subframe and resource block
combinations in order to check for their own preamble sequence ID
in the RAR messages having their (common) RA-RNTI.
Solution to Problem
[0018] In one aspect, the invention provides a mobile station which
communicates with a base station, the mobile station comprising;
means for receiving a first parameter and a second parameter; means
for transmitting a first message; means for receiving a control
channel based on the first parameter and the second parameter; and
means for decoding a downlink shared channel associated with the
control channel based on information in the control channel,
wherein the first parameter is related to at least one sub-frame to
receive the control channel, wherein the second parameter is
related to at least one narrow band to receive the control
channel.
[0019] In one aspect, the invention provides a base station which
communicates with a mobile station, the base station comprising;
means for transmitting a first parameter and a second parameter;
means for receiving a first message; means for transmitting a
control channel based on the first parameter and the second
parameter; and means for transmitting a downlink shared channel
associated with the control channel based on the control part of
the first message, wherein the first parameter is related to at
least one sub-frame to receive the control channel, wherein the
second parameter is related to at least one narrow band to receive
the control channel.
[0020] Aspects of the invention extend to corresponding 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.
[0021] 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.
[0022] Exemplary embodiments of the invention will now be described
by way of example only with reference to the attached figures in
which:
BRIEF DESCRIPTION OF DRAWINGS
[0023] FIG. 1 schematically illustrates a telecommunication system
to which embodiments of the invention may be applied;
[0024] FIG. 2 is a block diagram illustrating the main components
of the communication device shown in FIG. 1; FIG. 3 is a block
diagram illustrating the main components of the base station shown
in FIG. 1;
[0025] FIG. 4 illustrates exemplary ways in which random access
related transmissions (with cross-subframe scheduling) can be
realised in the system shown in FIG. 1;
[0026] FIG. 5 illustrates an exemplary way in which paging
transmissions (with cross-subframe scheduling) can be employed in
the system shown in FIG. 1;
[0027] FIG. 6 illustrates a modification of the random access
related transmissions shown in FIG. 4;
[0028] FIG. 7 illustrates another modification of the random access
related transmissions shown in FIG. 4;
[0029] FIG. 8 illustrates another modification of the random access
related transmissions shown in FIG. 4;
[0030] FIG. 9 illustrates another modification of the random access
related transmissions shown in FIG. 4;
[0031] FIG. 10 illustrates another modification of the random
access related transmissions shown in FIG. 4; and
[0032] FIG. 11 illustrates another modification of the random
access related transmissions shown in FIG. 4.
DESCRIPTION OF EMBODIMENTS
Overview
[0033] FIG. 1 schematically illustrates a mobile (cellular)
telecommunication system 1 in which communication devices 3 (such
as mobile telephone 3-1 and MTC device 3-2) can communicate with
each other and/or with other communication nodes via an E-UTRAN
base station 5 (denoted `eNB`) and a core network 7. As those
skilled in the art will appreciate, whilst one mobile telephone
3-1, one MTC device 3-2, and one base station 5 are shown in FIG. 1
for illustration purposes, the system, when implemented, will
typically include other base stations and communication
devices.
[0034] The base station 5 is connected to the core network 7 via an
S1 interface. The core network 7 includes, amongst others: a
gateway for connecting to other networks, such as the Internet
and/or to servers hosted outside the core network 7; a mobility
management entity (MME) for keeping track of the locations of the
communication devices 3 (e.g. the mobile telephone and the MTC
device) within the communication network 1; and a home subscriber
server (HSS) for storing subscription related information (e.g.
information identifying which communication device 3 is configured
as a machine-type communication device) and for storing control
parameters specific for each communication device 3.
[0035] Each communication device 3 may fall into one or more
categories of UEs. A first category of UEs include communication
devices that support only an earlier release of the LTE standard
(e.g. Rel-8, Rel-9, Rel-10, Rel-11, and/or Rel-12). Such
communication devices are commonly referred to as legacy UEs
(assuming that the base station 5 is operating in accordance with
Rel-13 of the LTE standards). It will be appreciated that some
communication devices that belong to this category may not support
the EPDCCH (only PDCCH). A second category of UEs include
communication devices that support the current release of the LTE
standard (e.g. Rel-13 and/or later). A third category of UEs
include reduced bandwidth UEs (e.g. Rel-13 MTC devices capable of
using a 1.4 Mhz bandwidth only), which are not able to communicate
over the entire bandwidth available in the cell of the base station
5. A fourth category of UEs includes coverage enhanced UEs (e.g.
some MTC devices), which require certain base station
functionalities to be simplified and/or relaxed (although such
coverage enhanced UEs may support other functionalities as
normal).
[0036] In this example, the mobile telephone 3-1 comprises a Rel-13
UE, and the MTC device 3-2 comprises a reduced bandwidth MTC device
(which may also be configured for an appropriate level of coverage
enhancement). Although not shown in FIG. 1, it is assumed that a
number of other MTC devices are also present within the cell of the
base station 5.
[0037] The base station 5 is configured to transmit a physical
downlink control channel (PDCCH) and an evolved PDCCH (EPDCCH) for
reception by the communication devices 3 located within the base
station's 5 cell. The (E)PDCCH allocates uplink and downlink
resources to the communication devices 3. One difference between
the PDCCH and the EPDCCH is that the EPDCCH uses a relatively
narrow frequency spectrum (1.4 Mhz) that makes it compatible with
Rel-13 reduced bandwidth MTC devices, whilst PDCCH uses a wider
frequency spectrum in order to provide backward compatibility with
legacy communication devices.
[0038] The so-called common search space (CSS) carries downlink
control information (DCI) in the cell which is common to all
communication devices 3. For example, the CSS may include: system
information blocks (SIBs) which contain information related to cell
access parameters; random access channel (RACH) messages (e.g. a
Random Access Response (RAR) and/or Contention Resolution); and/or
the paging channel (PCH). In LTE Rel-13, the CSS (also referred to
as `eCSS`) forms part of the EPDCCH. The (time-frequency) resources
allocated for the CSS may be indicated via the so-called physical
broadcast channel (PBCH) or via system information block #1
(SIB1).
[0039] Due to the reduced bandwidth of 1.4 MHz in downlink and
uplink, the MTC device 3-2 cannot receive the PDCCH which is
densely spread across the entire cell bandwidth (i.e. it may be
transmitted over frequencies falling outside the 1.4 MHz supported
by the MTC device 3-2). However, the MTC device 3-2 can receive the
EPDCCH CSS (eCSS) which is transmitted over 6 RBs, i.e. within the
1.4 MHz band supported by the MTC device 3-2.
[0040] Furthermore, the base station's 5 bandwidth includes a
number of subbands (e.g. non-overlapping subbands), each subband
having 6 RBs (or less). Beneficially, since bandwidth reduced MTC
devices are able to communicate over a maximum of 1.4 MHz bandwidth
(which roughly corresponds to 6 RBs), the communication device 3-2
is able to send and receive (eCSS and other) data over the
particular subband that its transceiver is currently tuned to.
Advantageously, the base station 5 has some scheduling flexibility
in the frequency location by being able to select an appropriate
subband for communicating paging/RAR messages (and/or the like) to
the communication devices 3 within its cell.
[0041] In order to achieve such scheduling flexibility, the base
station 5 transmits control data via the eCSS in a subband of a
particular subframe, and the control data includes information
(DCI) which informs communication devices 3 in the base station's 5
cell that random access/paging transmission is scheduled (and for
which communication device(s) 3) in a subsequent subframe.
[0042] Thus, effectively, the eCSS (in the EPDCCH) comprises a
common search space for dynamic scheduling of random access (RA)
messages (which are transmitted over the PDSCH). In this case, DCI
format transmitted via the eCSS includes the number of physical
resource blocks (PRBs), transport block size (TBS), frequency
locations (and/or the like) associated with the RA message
scheduled via that DCI format.
[0043] Communication devices 3 within the base station's 5 cell are
configured to monitor the control information transmitted via the
eCSS in order to determine whether any RA/paging transmission is
scheduled for them.
[0044] However, whilst the base station 5 is typically configured
to transmit the eCSS on a subband located around the central
portion of the base station's bandwidth (i.e. a subband allocated
to the EPDCCH), RA/paging messages may be (and often need to be)
transmitted over a different subband (e.g. over a channel, such as
the PDSCH, that is allocated to a different subband to the EPDCCH
subband).
[0045] Therefore, when employing cross-subframe scheduling, the
base station 5 is advantageously configured to indicate via the
eCSS (using an appropriately formatted DCI) which subsequent
subframe and which subband will carry the RA/paging message for
which communication device(s) 3. For RAR Message 2, communication
devices 3 sharing the same RA-RNTI (e.g. MTC devices that initiated
a random access procedure using the same PRACH resources) are
grouped into a number of different groups (at least for the given
scheduling round). For each group of communication devices, the
base station 5 schedules the associated RA/paging message such that
an appropriate `retuning time` is included between the transmission
of the eCSS scheduling a particular RA/paging message (in one
subframe), and the transmission of the corresponding RA/paging
message (in a subsequent subframe). The appropriate retuning time
is determined in such a way that if the eCSS and the RA/paging
message are transmitted over the same subband, then the retuning
time is effectively zero subframes, and if the eCSS and the
RA/paging message are transmitted over different subbands, then the
retuning time is one subframe (although it may also be set to more
than one subframe, if appropriate).
[0046] Thus, for example, if the RA/paging message for a given
communication device 3 in a particular group is scheduled for
transmission over a different subband to the subband carrying the
eCSS, then the base station 5 schedules the RA/paging message (via
the associated DCI) such that a retuning time of at least one
subframe is provided between transmission of the eCSS and
transmission of the RA/paging message scheduled by (the DCI
included in) the eCSS. Such retuning time of one subframe makes it
possible for the scheduled communication device 3 to timely tune
its transceiver to the subband carrying the RA/paging message (from
the subband carrying the eCSS).
[0047] Similarly, if the RA/paging message for a communication
device 3 of a given group is scheduled for transmission over the
same subband as the subband carrying the eCSS (but in a different
subframe), then the base station 5 schedules the RA/paging message
such that a retuning time of zero subframes is provided between
transmission of the eCSS and transmission of the RA/paging message
(since the scheduled communication device's 3 transceiver is
already tuned to the correct subband carrying the RA/paging
message).
[0048] In other words, the base station 5 employs a cross-subframe
scheduling (at least for MTC devices) in which an associated
retuning time is dependent on: the group of communication devices
for which the broadcast transmission is scheduled; and/or the
subband used for transmitting the control information (eCSS) and
the subband carrying the broadcast message scheduled by that
control information.
[0049] Moreover, paging messages are transmitted in this system
separately for MTC devices (e.g. low-complexity and/or coverage
enhanced MTC devices) and for other communication devices. Paging
messages for MTC devices support PDSCH subframe bundling/repetition
with multiple bundle sizes/repetition levels (in accordance with
the required level of coverage enhancement). Beneficially, the base
station 5 paging the communication device 3-2 has knowledge that
the communication device 3-2 comprises a low-complexity (bandwidth
reduced) MTC device and/or an MTC device configured for coverage
enhancement. The base station 5 also has knowledge of the amount of
coverage enhancement (repetitions) required during paging message
transmission.
[0050] Similarly, RAR messages (i.e. message 2) for MTC devices are
also transmitted separately from RAR messages for other
communication devices. Furthermore, in this system, multiple RAR
messages can be multiplexed for a plurality of communication
devices (e.g. that belong to the same group). Beneficially, when
multiplexing is used, each multiplexed message includes RAR
messages for those communication devices (of the respective group)
that are operating with the same level of coverage enhancement.
[0051] In more detail, a number of RAR messages can be multiplexed
together (e.g. similarly to multiplexing employed in Rel-8) into
one unit of TBS. The exact transport block size (i.e. the number of
bits transferred in a 1 ms transport block size) is dependent on
the modulation and coding scheme (MCS) and the number of resource
blocks assigned to the communication device. Details of how the
exact TBS can be derived are given in section 7.1.7 of 3GPP TS
36.213 V12.5.0, the contents of which are included herein by
reference.
[0052] Beneficially, the base station 5 may be configured to
control the number of messages that are being multiplexed, and
include in each multiplexed transmission only such messages that
need to be transmitted with the same level of coverage enhancement
(e.g. multiplex RAR messages for such MTC devices that are
configured with the same CE level). For example, RAR messages for
low-complexity MTC devices in normal coverage may be multiplexed
into a first RAR message (that does not require repetition) and RAR
messages for MTC devices configured for (a particular level of) CE
may be multiplexed into a different RAR message (with repetitions
as appropriate).
[0053] It will also be appreciated that the base station may
multiplex RAR messages intended only for a first set of MTC devices
(for example, MTC devices in normal coverage) and to transmit
conventional (non-multiplexed) RAR messages for a second set of MTC
devices (such as CE mode MTC devices and/or MTC devices configured
with a particular CE level, e.g. 5 dB, 10 dB, and/or 15 dB).
[0054] It will be appreciated that when multiple messages are
multiplexed, the resulting payload increases (and depending on the
applicable CE level, the number of repetitions in time domain may
also increase). Beneficially, however, the above described dynamic
cross-subframe scheduling (using eCSS to indicate TBS size and
assigned PRB resources)--preferably in combination with grouping of
communication devices--can be employed to compensate for a
potential payload increase resulting from multiplexing of multiple
messages, without requiring the MTC devices to monitor both the
eCSS and each RAR/paging transmission at the same time (which may
be transmitted over different 1.4 MHz subbands).
[0055] In summary, the base station is advantageously able to
indicate to MTC devices within its cell the resources used for
their associated broadcast transmissions (e.g. RA and/or paging
message transmissions), and schedule broadcast transmissions in
such a way (e.g. only after an appropriate retuning time and/or
only for a given group) that even limited bandwidth MTC devices can
receive their associated broadcast transmissions. In other words,
the base station ensures that it responds to each communication
device's preamble transmission using communication resources that
the respective communication device is able to use in the
particular subframe in which the associated RAR message is
transmitted. Similarly, the base station is configured to page each
communication device in a subframe in which that communication
device's transceiver is tuned (or can be tuned) to the
communication resources carrying the associated paging message.
[0056] <Communication Device>
[0057] FIG. 2 is a block diagram illustrating the main components
of the communication device 3 shown in FIG. 1. The communication
device 3 may be an MTC device or a mobile (or `cellular`) telephone
configured as a machine-type communication device. The
communication device 3 comprises a transceiver circuit 31 which is
operable to transmit signals to, and to receive signals from, the
base station 5 via at least one antenna 33. Typically, the
communication device 3 also includes a user interface 35 which
allows a user to interact with the communication device 3, however
this user interface 35 may be omitted for some MTC devices.
[0058] The operation of the transceiver circuit 31 is controlled by
a controller 37 in accordance with software stored in memory 39.
The software includes, among other things, an operating system 41,
a communication control module 43, an eCSS module 44, an MTC module
45, a random access module 47, and a paging module 48.
[0059] The communication control module 43 controls communications
between the communication device 3 and the base station 5 and/or
other communication nodes (via the base station 5). The
communication control module 43 also ensures that the transceiver
31 is tuned to the subband/frequency (e.g. it remains tuned to the
same subband or it is timely re-tuned to a different subband)
associated with the communication resources scheduled/allocated for
this communication device 3.
[0060] The eCSS module 44 monitors eCSS transmissions by the base
station 5 and determines whether the eCSS transmissions include
information indicating that cross-subframe broadcast transmissions
are being scheduled for the communication device 3, and determines
the communication resources (e.g. subframe/subband) associated with
such broadcast transmissions. If appropriate, the eCSS module 44
notifies the communication control module 43 to (re-)tune the
transceiver 31 to the frequency/subband indicated via the eCSS.
[0061] The MTC module 45 is operable to carry out machine-type
communication tasks. For example, the MTC module 45 may collect
data for sending (e.g. periodically and/or upon detecting a
trigger) to a remote server (via the transceiver circuit 31).
[0062] The random access module 47 is responsible for obtaining and
maintaining synchronisation of transmissions with the network. For
example, the random access module 47 may send (via the transceiver
circuit 31) a random access transmission (including a selected
preamble sequence) to the base station 5 when the communication
device 3 needs to establish an RRC connection with the network. The
random access module 47 receives a random access response from the
base station 5 (using the communication resources determined by the
eCSS module 44).
[0063] The paging module 48 receives (over appropriate
communication resources determined by the eCSS module 44) and
processes paging messages addressed to the communication device
3.
[0064] <Base Station>
[0065] FIG. 3 is a block diagram illustrating the main components
of the base station 5 shown in FIG. 1. The base station 5 comprises
an E-UTRAN base station (eNB) comprising a transceiver circuit 51
which is operable to transmit signals to, and to receive signals
from, the communication devices 3 via one or more antennas 53. The
base station 5 is also operable to transmit signals to and to
receive signals from a core network 7 via an appropriate core
network interface 55 (such as an S1 interface). The operation of
the transceiver circuit 51 is controlled by a controller 57 in
accordance with software stored in memory 59.
[0066] The software includes, among other things, an operating
system 61, a communication control module 63, a paging module 65, a
random access control module 67, and a UE group allocation module
69.
[0067] The communication control module 53 controls communications
with the communication devices 3. The communication control module
53 is also responsible for scheduling (via the eCSS) the resources
to be used by the communication devices 3 served by this base
station 5. Although not shown in FIG. 3, the communication control
module 53 includes a broadcast portion which is responsible for
broadcasting system information (such as configuration of the cell
of the base station 5) and/or other broadcast transmissions for
receipt by the communication devices 3 located within the cell of
the base station 5. For example, the broadcast portion transmits
the PRACH configuration(s) employed in the cell and/or the messages
generated by the other modules (e.g. paging/RA messages).
[0068] The paging module 65 generates and transmits paging messages
(via the communication control module 63) for communication devices
3 located within the cell of the base station 5.
[0069] The random access control module 67 is responsible for
communications over the PRACH. The random access control module 67
handles (generates, sends, and receives) messages relating to the
random access procedure performed with communication devices 3
located within the cell of the base station 5.
[0070] The UE group allocation module 69 allocates each
communication device 3 to a group (and/or UE category) based on a
parameter associated with the communication device 3 (for example,
based on the received preamble sequence, e.g. the time/frequency
resource the preamble sequence is sent on and/or the selected
preamble). When appropriate, the UE group allocation module 69
notifies the communication control module 63 about each
communication device's 3 allocated group/category so that the
communication control module 63 can adjust the operation of its
broadcast portion accordingly.
[0071] In the above description, the communication 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.
[0072] <Operation--Random Access Procedure>
[0073] FIG. 4 illustrates exemplary ways in which random access
messages (RA msg2/4) transmissions (with cross-subframe scheduling)
can be employed in the communication system 1 shown in FIG. 1.
[0074] It will be appreciated that the base station 5 is configured
to transmit a `SIB2` in its cell for reception by the communication
devices 3. The SIB2 includes the appropriate parameters for the
PRACH resource configuration currently in use in the cell of the
base station 5.
[0075] As explained above, the communication devices 3 need to
establish an RRC connection with the base station 5 in order to be
able to communicate with other devices via that base station 5 (and
the core network 7). Therefore, each communication device 3 is
configured to perform an appropriate random access procedure (via
the PRACH) in order to synchronise their transmissions with the
base station 5 and to indicate to the network the reason for
establishing the RRC connection. In this cell, each type of
communication device has its own set of PRACH parameters.
Therefore, the resources allocated for initiating a random access
procedure by the MTC device 3-2 are different to the resources
allocated for the mobile telephone 3-1.
[0076] It will be appreciated that each MTC device may be
configured to estimate (e.g. before initiating a random access
procedure) an appropriate CE level (0-3) for that MTC device based
on, for example, downlink signal quality measurements, such as
reference signal received power (RSRP) measurements. Based on the
estimated CE level, the MTC devices can determine the number of
repetitions required when communicating messages of the random
access procedure.
[0077] In summary, the random access procedure includes the
following messages: [0078] Message 1 (`Msg1`): the MTC device
transmits a PRACH preamble sequence to the base station with
appropriate time domain repetitions (if any); [0079] Message 2
(`Msg2`): the base station transmits (broadcasts) a Random Access
Response (with appropriate repetitions, if any) to the MTC device
within a time window determined based on the subframe in which the
MTC device's Msg1 was transmitted; [0080] Message 3 (`Msg3`): the
MTC device transmits its associated mobile terminal identity to the
network (with appropriate repetitions, if any); and [0081] Message
4 (`Msg4`): the base station transmits a contention resolution
message (with appropriate repetitions, if any) to a specific
terminal.
[0082] However, the resources allocated for the MTC device 3-2 are
shared by other MTC devices that belong to the same category.
Accordingly, when more than one MTC devices initiate random access
procedures substantially concurrently, the base station 5 needs to
schedule appropriate resources for transmitting respective RAR
messages (Msg2) to each such MTC device within a short time period
(defined by the time window starting from Msg1).
[0083] In order to be able to respond to each MTC device, and to
ensure that each MTC device knows which subband to monitor for its
RAR message (even if the RA-RNTI is shared by a plurality of MTC
devices), the base station 5 allocates (using its UE group
allocation module 69) each MTC device to a group. Next, the base
station 5 informs each group of MTC device about their respective
allocated RAR resources via the EPDCCH (using an appropriately
formatted DCI).
[0084] The eCSS comprises a common search space, using which the
base station 5 is able to dynamically schedule (using its random
access control module 67) RAR messages for communication devices 3
located within its cell. In order to do so, the base station 5
includes in the DCI format information indicating which subband
(identified by its subband index) is scheduled for the PDSCH
carrying the RAR message as well as the associated resource
allocation (number of RBs) within that subband.
[0085] In more detail, subframes denoted `x` and `y` (in FIG. 4)
include a respective eCSS 70 for those MTC devices that are
scheduled to receive an RAR message from the base station 5 in one
of the subsequent subframes (assuming cross-subframe scheduling is
in place). Each MTC device (but at least those MTC devices that
recently initiated a random access procedure) monitors the eCSS 70
by turning on their transceiver 31 (and tuning it to the subband
carrying the eCSS 70) at least for the duration of the eCSS
transmission (subframes x and y in FIG. 4).
[0086] The eCSS 70 includes one or more appropriate DCI(s), each of
which comprises information identifying the subframe and the
physical resource block (subband, timing) that carries the RAR for
the MTC devices belonging to a particular group. Each MTC device
that receives the eCSS transmission (via its associated eCSS module
44) is configured to determine (using its associated random access
module 47) whether any received DCI is for the group of
communication devices that that MTC belongs to.
[0087] In one option, the DCI indicates that the RAR message will
be transmitted over the same subband 71 as the subband carrying the
eCSS 70 but in a different subframe (subframe x+1 in the example
shown in FIG. 4). In other words, the base station's 5 RAR
transmissions use physical resource block(s) that fall within the
subband 71 that the communication device's 3 transceiver circuit 31
is already tuned to (because it is tuned to receiving the eCSS in
subframe x).
[0088] In accordance with another option, the DCI indicates that
the RAR message will be transmitted over a different subband 71'
than the subband carrying the eCSS 70. In this case, the DCI also
indicates that the RAR message will be transmitted after an
appropriate retuning time after the transmission of the eCSS 70.
For example, the DCI may indicate that the RAR message will be
transmitted in subframe x+2 (or later). Preferably, the RAR message
is transmitted after subframe x+1 but prior to subframe y (carrying
the next eCSS 70 transmission). By employing an appropriate
retuning time, it is possible for the scheduled communication
devices 3 to tune their transceiver circuit 31 (from the subband
carrying the eCSS) to the subband carrying their respective
RAR/paging message.
[0089] An advantage associated with scheduling RAR messages via the
EPDCCH CSS is that the resulting scheduling flexibility contributes
to an efficient system operation as well as reduces the blocking
probability for RAR messages.
[0090] In addition, eCSS makes it possible to multiplex a number of
RAR messages (e.g. RAR messages with the same coverage level) into
a single TBS thus further improving system efficiency (e.g. by
reducing the associated overhead). However, if such multiplexing is
not appropriate (or not required), this approach also makes it
possible to employ single (non-multiplexed) RAR message
transmissions to at least some communication devices.
[0091] The above described dynamic scheduling via eCSS may also be
used for scheduling message 4 of the random access procedure (when
cross-subframe scheduling is in place). It will be appreciated that
in this case, the DCI format also includes the subband used for
transmitting Msg4.
[0092] <Operation--Paging>
[0093] FIG. 5 illustrates an exemplary way in which paging
transmissions (with cross-subframe scheduling) can be employed in
the communication system 1 shown in FIG. 1.
[0094] Similarly to the way in which RAR messages are scheduled (as
described above with reference to FIG. 4), paging messages (that
are transmitted over the PDSCH) may also be scheduled using the
eCSS (transmitted over the EPDCCH). In this case, since the paging
message size can vary (not fixed), the DCI format (included in the
eCSS) preferably also includes information identifying at least one
of: an MCS associated with the paging message; a TBS associated
with the paging message; and a number of RBs allocated for the
paging message.
[0095] If the frequency location for the PDSCH carrying the paging
message is different to the frequency location for the eCSS, then
cross-subframe scheduling is used. In this case, the paging message
is scheduled for transmission over one of the available subbands
(not exceeding 1.4 MHz/6 RBs) and the associated subband number
(index) is also included in the DCI format. This approach
beneficially increases scheduling flexibility at the base station 5
and may also decrease the blocking probability of the paging
message.
[0096] As shown in FIG. 5, subframes denoted `x` and `y` each
include a respective eCSS 70A, 70B for those MTC devices that are
scheduled to receive a paging message from the base station 5 in
one of the subsequent subframes (assuming cross-subframe scheduling
is in place). Each MTC device monitors the eCSS 70 by turning on
their transceiver circuit 31 (and tuning it to the subband carrying
the eCSS 70) at least for the duration of the eCSS transmission
(subframes x and y in FIG. 5).
[0097] The DCI included in the eCSS 70A (in subframe x) indicates
that a paging message will be transmitted (after an appropriate
retuning time) in subband 71A (identified by its associated subband
index) for communication devices 3 identified as `UE2`, `UE3`, and
`UE5`. Similarly, the DCI included in the eCSS 70B (in subframe y)
indicates that a paging message will be transmitted (after an
appropriate retuning time) in subband 71B (identified by its
associated subband index) for communication devices 3 identified as
`UE4`, `UE7`, and `UE8`.
[0098] Thus each identified communication devices 3 are able tune
its transceiver circuit 31 to its respective allocated subband 71
(at least for the duration of the paging transmission) and listen
to the paging messages broadcast in that subband 71.
[0099] However, each communication devices 3 is configured to tune
its transceiver circuit 31 back to subband carrying the eCSS 70
after the paging message is transmitted (including any repetition
if CE is used) so that they can continue to receive control
information (DCI) from the base station 5 without delay.
[0100] Advantageously, the base station's 5 transmissions are
scheduled such that there is sufficient retuning time provided
after each paging message and before transmitting a subsequent eCSS
(e.g. there is at least one subframe before each one of subframes x
and y and the end of the preceding paging transmission).
[0101] <Modifications and Alternatives>
[0102] 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.
[0103] FIGS. 6 to 11 illustrate further exemplary ways in which
broadcast transmissions (such as RAR transmissions) can be
scheduled via the eCSS for bandwidth reduced MTC devices.
[0104] FIG. 6 illustrates a modification of the random access
procedure in which RAR transmissions are scheduled via the eCSS. In
this case, both the eCSS and Msg2 are always transmitted on the
same subband.
[0105] In this example, each one of UE1 to UE6 has the same
RA-RNTI. The base station allocates (using its UE group allocation
module 69) UE1, UE2, and UE3 to a first group, and allocates UE4,
UE5, and UE6 to a second group.
[0106] The eCSS transmitted in both subframe x and subframe y
includes the RA-RNTI that is common to UE1 to UE6. However, in a
first transmission round (in subframe x+1) scheduled via the eCSS
transmitted in subframe x, the RAR includes preamble IDs for
communication devices belonging to the first group. Accordingly,
the RAR messages multiplexed into this message are intended for the
UE1, UE2, and UE3 belonging to the first group. This also means
that although communication devices belonging to the second group
have also received and decoded the RAR message in subframe x+1,
this message does not include their associated preamble IDs.
Consequently, each communication devices belonging to the second
group determines (using their associated random access module 47)
that this RAR message does not include a valid response for that
communication device, and continues monitoring the EPDCCH for
further eCSS transmissions (i.e. in subframe y). On the other hand,
the communication devices belonging to the first group determine
that the RAR message in subframe x+1 includes a valid random access
response, and proceed to generating and transmitting Msg3 to the
base station.
[0107] In the next transmission round (in subframe y+1) scheduled
via the eCSS transmitted in subframe y, the RAR includes preamble
IDs for communication devices belonging to the second group. Thus
in subframe y+1, the communication devices belonging to the second
group also determine that the RAR message in subframe y+1 includes
a valid random access response, and proceed to generating and
transmitting Msg3 to the base station.
[0108] It will be appreciated that any group may include a single
communication device, in which case no multiplexing is used for
that group. It will also be appreciated that RAR messages for more
than one groups may be multiplexed together.
[0109] Thus in this example RAR messages are multiplexed (if
applicable) and transmitted on a per group basis in the time
domain, using the same subband as the eCSS. Advantageously, there
is no need to provide any retuning time and/or include a subband
index in the DCI format, whilst still benefitting from some of the
flexibility associated with the eCSS based RAR scheduling described
with reference to FIG. 4.
[0110] FIG. 7 illustrates another modification of the random access
procedure in which RAR transmissions are scheduled via the eCSS. In
this case, RAR messages for different groups of communication
devices are transmitted over different subbands.
[0111] In this case, a single TBS carrying one or more RAR messages
with the same RA-RNTI (but for different communication devices) and
with the same coverage level is scheduled on any subband. This
means that the subband for the eCSS and the subband for the RAR
messages may be different, hence scheduling flexibility can be
achieved to some degree.
[0112] As can be seen, the eCSS included in subframe x schedules a
(multiplexed) RAR transmission for the group of communication
devices with identifiers UE1 to UE3 (but with the RA-RNTI that is
common to other communication devices UE4 to UE6 as well). When a
communication device that belongs to this group (e.g. UE1) decodes
this RAR message, it determines that this RAR message comprises a
valid random access response (since its selected preamble ID is
included) and proceeds to transmitting Msg3 to the base
station.
[0113] However, when a communication device that does not belong to
this group (e.g. UE4) decodes this RAR message, it determines that
this RAR message was not meant for this communication device (since
its selected preamble ID is not included). Thus UE4 returns to
monitoring for the eCSS in the EPDCCH.
[0114] Beneficially, the timing of the RAR transmissions and the
eCSS are defined such that there is sufficient retuning time
provided after each RAR message and before transmitting a
subsequent eCSS (e.g. there is at least one subframe before each
one of subframes x and y and the end of the preceding RAR
transmission).
[0115] As can be seen, the RAR transmission for the group of
communication devices with identifiers UE4 to UE6 are scheduled via
the eCSS included in subframe y. However, this RAR transmission
uses a different subband to the subband used for the RAR
transmission scheduled via subframe x (although it may use the same
subband). Thus in this example RAR messages (multiplexed, if
applicable) are transmitted on a per group basis in the time domain
(and possibly in the frequency domain as well). It will be
appreciated that communication devices UE4 to UE6 may require a
different CE level (and hence a different number of repetitions) to
the CE level for communication devices UE1 to UE3.
[0116] FIG. 8 illustrates another modification of the random access
procedure in which RAR transmissions are scheduled via the eCSS. In
this case, RAR messages for all scheduled communication devices are
transmitted over the same (albeit dynamically scheduled)
subband.
[0117] In this case, all RAR messages with the same RA-RNTI (but
for different communication devices) and with the same coverage
level are scheduled on the same subband and arranged in sequence
within a time window. This means that the subband for the eCSS and
the subband for the RAR messages may be different, hence scheduling
flexibility can be achieved to some degree. However, the
transmission parameters for RAR messages arranged in a single
sequence need to be the same (signalled by the same DCI
format).
[0118] However, since a potentially large number of RAR messages
need to be transmitted in a single sequence, the RAR transmission
may in some cases exceed the capacity of a single subframe (using 6
RBs only). Therefore, in order to inform the communication devices
that they should continue decoding from the indicated subband after
the first subframe of the RAR transmission, a flag may be included
in (at least) the final RAR message of the subframe to indicate
that there is at least one further message after this message. It
will be appreciated however, that such flag may be included in each
RAR message that is followed by another RAR message (regardless
whether the following RAR message is located in the same subframe
or in the subsequent one).
[0119] In the example shown in FIG. 8, all communication devices
(UE1 to UE6) are being scheduled via the eCSS included in subframe
x. However, the respective RAR messages for communication devices
with identifiers UE1 to UE3 are included in the first part of the
(multiplexed) RAR transmission sequence and RAR message for the
remaining communication devices are included in the second part of
the RAR transmission sequence. It will be appreciated that the RAR
transmission sequence may be repeated in accordance with the CE
level required for the communication devices (UE1 to UE6) scheduled
in this round.
[0120] FIG. 9 illustrates another modification of the random access
procedure in which RAR transmissions are scheduled via the eCSS. In
this case, however, the DCI format also identifies the preamble
range covered in the RAR messages scheduled via that DCI
format.
[0121] For example with 2 bits in the DCI format, four groups (each
group comprising 16 preamble IDs) can be signalled.
[0122] In this example, UE1 (with preamble ID 10), UE2 (with
preamble ID 3), UE3 (preamble ID 12), UE4 (preamble ID 14), UE5
(preamble ID 17), UE6 (preamble ID 19), UE7 (preamble ID 22) and
UE8 (preamble ID 31) have the same RA-RNTI. Assuming that the first
group includes preamble IDs 1 to 16, the second group includes
preamble IDs 17 to 32, the third group includes preamble IDs 33 to
48, and the fourth group includes preamble IDs 48 to 64; then UE1
to UE4 belong to the first group, and UE5 to UE8 belong to the
second group.
[0123] Each communication device is configured to monitor for eCSS
transmissions in the prescribed subframes and determine whether its
selected preamble ID falls within the range identified by the DCI
format. If it is determined that its selected preamble ID falls
within the range identified by the DCI format, then the
communication device is configured to retune its transceiver
(following an appropriate retuning time) to the subband indicated
by the DCI format and decode its associated Msg2 from the base
station's RAR transmission.
[0124] As can be seen, beneficially, there is no need to provide
any retuning time after the RAR transmissions and before the
immediately following eCSS transmission, because only those
communication devices need to monitor the eCSS, at any given time,
that are not yet scheduled (based on their associated preamble ID)
for transmission (e.g. RAR transmission and/or the like).
[0125] FIG. 10 illustrates a case without requiring multiplexing of
multiple RAR messages (or when such multiplexing is not permitted).
In this case, it is beneficial to apply a new RA-RNTI for each
communication device (rather than the RA-RNTI that is derived in
accordance with legacy procedures).
[0126] The legacy RA-RNTI has a range of `1` to `60` and is
determined as follows:
RA-RNTI=1+t_id+10*f_id
where t_id is the index of the first subframe of the transmitted
PRACH
(0.ltoreq.t_id<10); [Math. 1]
and f_id is the index of the transmitted PRACH in frequency domain
of the same subframe
(0.ltoreq.f_id<6). [Math. 2]
[0127] In this modification, however, the RA-RNTI (at least for MTC
devices) is derived by employing the PRACH sequence index as well.
This will prevent using the same RA-RNTI for multiple communication
devices (MTC devices) even if they select the same PRACH resources
(t_id and f_id) for transmitting Msg1, unless also using the same
PRACH sequence index. The value of this `MTC RA-RNTI` or `PRACH
sequence index based RA-RNTI` may be chosen from outside (above)
the legacy RA-RNTI range and may be determined as follows:
RA-RNTI=61+64*f_id+PRA_id
where PRA_id is the transmitted PRACH sequence index
(0.ltoreq.PRA_id<64); [Math. 3]
and f_id is the index of the transmitted PRACH in frequency domain
of the same subframe
(0.ltoreq.f_id<6). [Math. 4]
[0128] Accordingly, if the DCI is masked with such a PRACH sequence
specific RA-RNTI, then only the intended UE(s) (i.e. communication
device(s) using the corresponding PRACH sequence index) will be
able to decode it and receive the associated RAR message (after an
appropriate retuning time). Any other UEs (that use a conventional
RA-RNTI or an RA-RNTI based on a different PRACH sequence index)
will not be able to decode such a DCI format that is not masked
with their own RA-RNTI and hence such UEs skip (tuning to and)
receiving the associated PDSCH. This may result in significant
power savings.
[0129] Beneficially, this approach involving the new RA-RNTI may
also result in reduced power consumption (power saving) at the MTC
device, at least while the MTC device is operating in coverage
enhanced mode.
[0130] FIG. 11 illustrates a case in which the RA-RNTI is
determined based on PRACH (preamble) sequence grouping. In this
case the RA-RNTI is derived using the PRACH sequence group index
(assuming 4 groups) as follows:
RA-RNTI=61+4*f_id+PRA_Group_id
where PRA_Group_id is the index of the PRACH sequence group
(0.ltoreq.PRA_Group_id<4) [Math. 5]
in which the UE's PRACH (preamble) sequence index belongs to. A
possible preamble sequence ID grouping has been described above
with reference to FIG. 9 (although any suitable grouping may be
used).
[0131] Accordingly, if the DCI is masked with such a group-specific
RA-RNTI, then only the intended UEs (i.e. communication device(s)
using a preamble sequence ID from the same group) will be able to
decode it and receive the associated RAR message (after an
appropriate retuning time). Any other UEs (that selected their
respective PRACH sequence index from a different group) will not be
able to decode such a DCI format that is intended for a different
group than their own and hence such UEs skip (tuning to and)
receiving the associated PDSCH. This approach may thus result in
significant power savings.
[0132] Alternatively, the subframe index (t_id) may also be
included in the equation, for example, as follows:
RA-RNTI=61+t_id+64*f_id+PRA_id
where PRA_id is the transmitted PRACH sequence index
(0.ltoreq.PRA_id<64), [Math. 6]
f_id is the index of the transmitted PRACH in frequency domain of
the same subframe
(0.ltoreq.f_id<6) [Math. 7]
and t_id is the index of the first subframe of the transmitted
PRACH
(0.ltoreq.t_id<10). [Math. 8]
[0133] In the above exemplary embodiments, control data (DCI)
transmitted via the eCSS is used for scheduling a (multiplexed)
broadcast transmission, such as RAR or paging message transmission.
However, it will be appreciated that a control-less RAR message may
be used instead. In this case, the number of PRBs is fixed to 6 RBs
(or less). The base station transmits (RAR/paging) messages using a
single TBS (or a limited set of TBS) and the communication devices
are configured to perform a number of blind decodings based on the
TBS. The frequency location or subband for the RAR messages may be
fixed to e.g. the central 6 RBs (although it may also be derived
from PRACH resources). Although in this option the base station's
scheduling flexibility is restricted (as the frequency location may
not be changed dynamically) and the UE's power consumption may
increase (due to blind decoding of all messages), there is no need
for the provision of any retuning time before transmissions (since
there is no control data). Beneficially, when a number of RAR
messages need to be transmitted on the same subband, a queueing
mechanism may also be provided to ensure that RAR messages are
transmitted within their respective detection window (calculated
from Msg1).
[0134] In the above exemplary embodiments, a number of ways are
given for cross-subframe scheduling of broadcast transmissions,
such as RAR (message 2 of the random access procedure) and paging
messages. However, it will be appreciated that the above
embodiments may also be applicable to other messages, for example
message 4 of the random access procedure (even though message 4 is
masked with an identifier (TC-RNTI) that is uniquely associated
with one UE only.
[0135] FIGS. 4 to 11 show three subbands (each subband comprising 6
RBs). However, it will be appreciated that the number of subbands
can be more (or less) than three (e.g. depending on the base
station's system bandwidth).
[0136] In the above exemplary embodiments, the retuning time is
assumed to be (not more than) one subframe in duration. However, it
will be appreciated that a different retuning time (e.g. more than
one subframe) may also be employed.
[0137] In the above description, repetition in time domain is
assumed for all transmissions. However, such repetitions are
omitted in FIGS. 4 to 11 for simplicity.
[0138] A number of exemplary embodiments have been described above,
with reference to FIGS. 4 to 11. It will be appreciated that these
exemplary embodiments are not mutually exclusive and any of the
options may be combined within the same system, either within a
single cell and/or in neighbouring cells. For example, the base
station may be configured to change from one operation mode to
another, e.g. periodically, in dependence on the number/type of MTC
devices in its cell, in dependence on the overall load in the cell,
in dependence on the number of preamble retransmissions (e.g. due
to collision), in dependence on the type of communication (e.g.
random access/paging/broadcast/unicast), and/or the like.
[0139] In the above examples described with reference to FIGS. 10
and 11, the RA-RNTI is calculated without using the subframe index
identifying the subframe in which the preamble prefix (Msg1) was
transmitted. However, it will be appreciated that the index of the
subframe in which Msg1 was transmitted is still considered (by the
base station and the MTC device) at least in determining an
appropriate time window within which Msg2 needs to be
transmitted.
[0140] In the above description, information relating to the PRACH
configuration is signalled via the SIB2. However, it will be
appreciated that the PRACH configuration (at least part of it) may
be signalled via a different system information block, for example,
via one or more SIB specific to reduced bandwidth UEs and/or
coverage enhanced UEs. Alternatively or additionally, some or all
of this information can be obtained by the communication devices in
a different manner--for example the PRACH configuration may be
signalled via system broadcast (e.g. PBCH) and/or via higher layers
(e.g. RRC).
[0141] It will be appreciated that although the communication
system is described in terms of the base station operating as a
E-UTRAN base station (eNB), 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.
[0142] In the above exemplary embodiments, an LTE
telecommunications system was described. As those skilled in the
art will appreciate, the 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.
[0143] In the exemplary embodiments described above, the base
station and the communication device 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.
[0144] 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
un-compiled 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.
[0145] The base station may comprise: a processor configured to
identify at least one subframe in which a broadcast message,
carrying information for at least one communication device, is to
be broadcast; a transmitter configured for: transmitting, in a
control channel, in a frequency subband in at least one subframe
that precedes said at least one subframe in which said broadcast
message is to be broadcast, control information to identify said at
least one subframe in which said broadcast message is to be
broadcast; and broadcasting said broadcast message in said at least
one subframe in which said broadcast message is to be
broadcast.
[0146] The at least one communication device may comprise at least
one machine type communication `MTC` device (e.g. a reduced
bandwidth or low complexity MTC device and/or a coverage enhanced
MTC device).
[0147] If the at least one communication device comprises at least
one coverage enhanced MTC device, the at least one subframe in
which said control information is transmitted may comprise a
plurality of subframes in which said control information is to be
first transmitted and then repeated, and said at least one subframe
in which a broadcast message is to be broadcast may comprise a
plurality of subframes in which said broadcast message is to be
first broadcast and then repeated.
[0148] The broadcast message may carry multiplexed information for
each of a plurality of communication devices. For example, the
broadcast message may carry multiplexed information for each of a
plurality of coverage enhanced machine type communication `MTC`
devices sharing a common coverage enhancement level.
[0149] The processor may be further configured to identify a
frequency subband in which the broadcast message is to be
broadcast. In this case the control information may be arranged to
identify said frequency subband in which said broadcast message is
to be broadcast; and said transmitter may be configured for
broadcasting said broadcast message in said frequency subband in
which said broadcast message is to be broadcast.
[0150] The processor may be further configured to identify at least
one frequency resource (e.g. at least one physical resource block),
within said frequency subband, on which said broadcast message is
to be broadcast; said control information may be arranged to
identify said at least one frequency resource; and said transmitter
may be configured for broadcasting said broadcast message on said
at least one frequency resource.
[0151] The frequency subband in which said broadcast message is to
be broadcast and the frequency subband in which said control
channel is transmitted may be different to one another. In this
case said processor may be configured to identify said at least one
subframe in which said broadcast message is to be broadcast such
that there is at least one further subframe between the at least
one subframe in which said control channel is transmitted and said
at least one subframe in which said broadcast message is to be
broadcast (e.g. between the last subframe in which control
information is repeated and the first subframe in which said
broadcast message is first broadcast).
[0152] The frequency subband in which said broadcast message is to
be broadcast and the frequency subband in which said control
channel is transmitted may be the same. In this case the processor
may be configured to identify said at least one subframe in which
said broadcast message is to be broadcast such that there is no
whole subframe between the, or a last subframe of the, at least one
subframe in which said control channel is transmitted and the, or a
first subframe of said at least one subframe in which said
broadcast message is to be broadcast.
[0153] The broadcast message may carry an indicator that a further
broadcast message will follow in a subframe subsequent to (e.g.
that immediately follows) the at least one subframe in which said
broadcast message is to be broadcast.
[0154] The control information may comprise information for
identifying the at least one device that said broadcast message
carries information for. In this case, the information for
identifying may comprise at least one of: a group identifier for
identifying a group of devices of which said at least one device
that said broadcast message carries information for is a member; at
least one preamble sequence identifier for identifying said at
least one device that said broadcast message carries information
for; and an identifier of a coverage enhancement level associated
with the at least one device that said broadcast message carries
information for.
[0155] The base station may further comprise a receiver for
receiving, from said at least one communication device, a message
carrying a random access preamble, wherein said broadcast message
comprises a message, carrying a random access response `RAR` for
said at least one communication device.
[0156] The control information may comprise information for
identifying the at least one device that said broadcast message
carries information for. For example, the information for
identifying the at least one device may comprise an identifier that
equals 61+64.times.f_id+PRA_id; where fid may be an index of a
frequency resource block on which said message carrying a random
access preamble was received and PRA_id may be a preamble sequence
index. The information for identifying the at least one device may
also comprise an identifier that equals 61+4.times.f_id+PRA_Group
jd; where fid may be an index of a frequency resource block on
which said message carrying a random access preamble was received
and PRA_Group_id may be an index of a preamble sequence group of
which said at least one device that said broadcast message carries
information for is a member. The information for identifying the at
least one device may also comprise an identifier that equals
RA-RNTI=61+t_id+64.times.f_id+PRA_id; where t_id is an index of a
subframe in which said message carrying a random access preamble
was received, fid is an index of a frequency resource block on
which said message carrying a random access preamble was received,
and PRA_id is a preamble sequence index
[0157] The broadcast message may comprise a paging message
broadcast using a paging channel.
[0158] The processor may be further configured to identify a
modulation and coding scheme `MCS` and/or transport block size
`TBS` for said paging message. The control information may be
arranged to identify said MCS and/or TBS.
[0159] In the above exemplary embodiments, machine-type
communication devices and mobile telephones are described. However,
it will be appreciated that mobile telephones (and similar user
equipment) may also be configured to operate as machine-type
communication devices. For example, the mobile telephone 3-1 may
include (and/or provide the functionality of) the MTC module
45.
[0160] Examples of MTC Applications
[0161] It will be appreciated that each communication device may
support one or more MTC applications. Some examples of MTC
applications are listed in the following table (source: 3GPP TS
22.368 V13.1.0, Annex B). This list is not exhaustive and is
intended to be indicative of the scope of machine-type
communication applications.
TABLE-US-00001 TABLE 1 indicates data missing or illegible when
filed
[0162] Various other modifications will be apparent to those
skilled in the art and will not be described in further detail
here.
[0163] 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.
1 INTRODUCTION
[0164] In the current RANI agreements, cross-subframe scheduling is
supported for unicast transmission (i.e. PDSCH for single UE).
However, the scheduling methods for broadcast transmission (i.e.
RAR and Paging) has not been discussed yet.
[0165] In this contribution, we discuss the transmission of RAR
messages and paging for LTE Rel-13 MTC and provide some proposals
at the end.
2 RANDOM ACCESS RESPONSE (RAR) TRANSMISSION
[0166] For MTC, the random access (RA) procedure is the same as
legacy LTE system which involves transmission of four messages
(msg1-4). However, initially, MTC UE should estimate the coverage
level (0-3) based on some criteria for example using downlink RSRP
measurements in order to determine the number of repetitions for
PRACH message 1. Then, UE should select one of the PRACH resources
allocated for that coverage level and start random access
procedure. eNB can determine the coverage level from the PRACH
resource used by the UE as there is one to one mapping between
PRACH resource set and PRACH repetition level. For the random
access response (RAR) message 2, it seems there are two different
ways of scheduling to the UEs as follows:
[0167] Option 1: Control-less RAR message--In this case, the number
of PRBs can be fixed to 6 RBs, single TBS or limited set of TBS can
be used where UE always tries a number of blind decodings. The
frequency location or subband for RAR messages can be fixed to
center 6 RBs or can be derived from PRACH resources. The main
concern is that this option lacks eNB scheduling flexibility as the
frequency location cannot be changed dynamically and it could also
result a higher blocking probability for RAR messages. In addition,
in case a number of RAR messages end up on the same subband, some
kind of queueing will be necessary where UE tries to decode each
RAR message carried by PDSCH in the detection window. Hence, the
power consumption at the UE will be increased significantly.
[0168] Option 2: RAR message on EPDCCH CSS--another option is to
define common search space (eCSS) in EPDCCH to provide dynamic
scheduling for RAR messages where number of PRBs, TBS and frequency
locations, etc. are included in the DCI format. The disadvantage is
the control overhead compare to Option 1 more specifically for
coverage enhanced mode where significant number of repetitions are
needed for eCSS transmission. The advantage is the eNodeB
scheduling flexibility that achieves an efficient system operation
as well as reducing the blocking probability for RAR messages. In
addition, it is possible to multiplex a number of RAR messages
which have same coverage level into a single TBS similar to Rel-8.
If multiple messages are multiplexed, the payload will increase and
as a consequence the number of repetitions in time domain will
increase for a given coverage level. So, in order to get a right
balance, it is beneficial eNB to control the number of messages
that can be multiplexed depending on coverage level. For example,
RAR messages for low complexity MTC UEs in normal coverage can be
multiplexed while enhanced coverage mode (e.g. 5 dB, 10 dB and 15
dB) single RAR message transmission is preferable.
[0169] Furthermore, in order to reduce the power consumption at the
UE, a new MTC RA-RNTI may be necessary at least for coverage
enhanced mode. The legacy RA-RNTI has a range of 1 to 60 and is
determined as follows:
RA-RNTI=1+t_id+10*f_id
where t_id=index of the first subframe of the transmitted PRACH
(0.ltoreq.t_id<0) [Math. 9]
and f_id=index of the transmitted PRACH in frequency domain of the
same subframe
(0.ltoreq.f_id=6). [Math. 10]
[0170] One way is to re-think how RA-RNTI is derived by employing
PRACH sequence index as an RA-RNTI. This will detach the new MTC
RA-RNTI from multiple UEs even if they select same t_id and fid
unless they pick up same PRACH sequence index. The new MTC RA-RNTI
can be placed above the legacy RA-RNTI range and can be determined
as follows:
RA-RNTI=61+64*f_id+PRA_id
where PRA_id=the transmitted PRACH sequence index
(0.ltoreq.PRA_id<64) [Math. 11]
[0171] So, if DCI is masked with sequence-specific RA-RNTI only
intended UE(s) will be able to receive, and other un-intended UEs
will not be able to decode the DCI format and subsequently will
skip the associated PDSCH which will lead a significant power
saving. Therefore, from power saving perspective at the UE, Option
2 is preferable.
[0172] Observation 1: If new MTC RA-RNTI is employed based on PRACH
sequence index, from power saving perspective at the UE, Option 2
(EPDCCH CSS) is preferable for RAR messages.
[0173] Observation 2: For normal coverage, multiple RAR messages
can be multiplexed together under the eNB control, however, for
enhanced coverage mode (e.g. 5 dB, 10 dB and 15 dB), single RAR
message transmission should be supported.
[0174] Proposal 1: EPDCCH CSS should be Used for RA Message 2 and 4
Transmission
[0175] If EPDCCH CSS is adapted for RA messages, time domain
repetition will be necessary for both normal and enhanced coverage
mode. In addition, the scheduled subband index in frequency domain
should be included in the DCI format in order to achieve eNB
scheduling flexibility. Hence, as shown in FIG. 4, dynamic
scheduling via eCSS for RA message 2/4 using cross-subframe
scheduling should be supported for all MTC UEs.
[0176] Proposal 2: Cross-subframe scheduling is supported for RA
message 2 and 4.
3 PAGING TRANSMISSION
[0177] The paging message is variable as the IDs of multiple UEs
can be multiplexed. Therefore, it is desirable to signal TBS in the
DCI format that is transmitted on the eCSS. In addition, for PDSCH
carrying paging message, it is beneficial that the subband index in
frequency location should be selected dynamically from the
available sub-bands by utilizing cross-subframe scheduling as shown
in FIG. 5. This will increase scheduling flexibility at the eNB and
also decrease the blocking probability of the paging messages.
[0178] Proposal 3: EPDCCH CSS should be used for Paging
transmission
[0179] Proposal 4: Cross-subframe scheduling is supported for
Paging transmission.
4 CONCLUSION
[0180] In this contribution, we have discussed the transmission of
RAR messages and paging for LTE Rel-13 MTC and we have the
following observations and proposals.
[0181] Observation 1: If new MTC RA-RNTI is employed based on PRACH
sequence index, from power saving perspective at the UE, Option 2
(EPDCCH CSS) is preferable for RAR messages.
[0182] Observation 2: For enhanced coverage mode (e.g. 5 dB, 10 dB
and 15 dB), single RAR message transmission should be supported.
However, for normal coverage, multiple RAR messages can be
multiplexed together under the eNB control.
[0183] Proposal 1: EPDCCH CSS should be Used for RA Message 2, 4
and Paging Transmission
[0184] Proposal 2: Cross-subframe scheduling is supported for RA
message 2, 4 and Paging transmission
5 REFERENCES
[0185] 1) 3GPP TR 36.888 V12.0.0, "Study on provision of low-cost
MTC UEs based on LTE (Release-12)". [0186] 2) RP-150492, "Revised
WI: Further LTE Physical Layer Enhancements for MTC", Ericsson,
RAN#67 [0187] 3) R1-151555, "Further details of Physical Downlink
Control Channel for MTC", NEC, RAN1#80bis
[0188] The whole or part of the exemplary embodiments disclosed
above can be described as, but not limited to, the following
supplementary notes.
[0189] (Supplementary note 1). A base station for a communication
system in which communication devices communicate via said base
station using radio frames made up of a sequence of subframes and a
frequency band made up of frequency subbands, the base station
comprising: a processor configured to identify at least one
subframe in which a broadcast message, carrying information for at
least one communication device, is to be broadcast;
a transmitter configured for: [0190] transmitting, in a control
channel, in a frequency subband in at least one subframe that
precedes said at least one subframe in which said broadcast message
is to be broadcast, control information to identify said at least
one subframe in which said broadcast message is to be broadcast;
and [0191] broadcasting said broadcast message in said at least one
subframe in which said broadcast message is to be broadcast.
[0192] (Supplementary note 2). The base station according to
Supplementary note 1, wherein said at least one communication
device comprises at least one coverage enhanced machine type
communication `MTC` device, wherein said at least one subframe in
which said control information is transmitted comprises a plurality
of subframes in which said control information is to be first
transmitted and then repeated, and wherein said at least one
subframe in which a broadcast message is to be broadcast comprises
a plurality of subframes in which said broadcast message is to be
first broadcast and then repeated.
[0193] (Supplementary note 3). The base station according to
Supplementary note 1 or 2, wherein said broadcast message carries
multiplexed information for each of a plurality of communication
devices.
[0194] (Supplementary note 4). The base station according to
Supplementary note 3, wherein said broadcast message carries
multiplexed information for each of a plurality of coverage
enhanced machine type communication `MTC` devices sharing a common
coverage enhancement level.
[0195] (Supplementary note 5). The base station according to any
one of Supplementary notes 1 to 4, wherein said processor is
further configured to identify a frequency subband in which said
broadcast message is to be broadcast; wherein said control
information is arranged to identify said frequency subband in which
said broadcast message is to be broadcast; and wherein said
transmitter is configured for broadcasting said broadcast message
in said frequency subband in which said broadcast message is to be
broadcast.
[0196] (Supplementary note 6). The base station according to
Supplementary note 5, wherein said processor is further configured
to identify at least one frequency resource (e.g. at least one
physical resource block), within said frequency subband, on which
said broadcast message is to be broadcast; wherein said control
information is arranged to identify said at least one frequency
resource; and wherein said transmitter is configured for
broadcasting said broadcast message on said at least one frequency
resource.
[0197] (Supplementary note 7). The base station according to
Supplementary note 5 or 6, wherein when said frequency subband in
which said broadcast message is to be broadcast and said frequency
subband in which said control channel is transmitted are different
to one another, said processor is configured to identify said at
least one subframe in which said broadcast message is to be
broadcast such that there is at least one further subframe between
the at least one subframe in which said control channel is
transmitted and said at least one subframe in which said broadcast
message is to be broadcast (e.g. between the last subframe in which
control information is repeated and the first subframe in which
said broadcast message is first broadcast).
[0198] (Supplementary note 8). The base station according to any
one of Supplementary notes 5 to 7, wherein when said frequency
subband in which said broadcast message is to be broadcast and said
frequency subband in which said control channel is transmitted are
the same, said processor is configured to identify said at least
one subframe in which said broadcast message is to be broadcast
such that there is no whole subframe between the, or a last
subframe of the, at least one subframe in which said control
channel is transmitted and the, or a first subframe of said at
least one subframe in which said broadcast message is to be
broadcast.
[0199] (Supplementary note 9). The base station according to any
one of Supplementary notes 1 to 8, wherein said broadcast message
carries an indicator that a further broadcast message will follow
in a subframe subsequent to (e.g. that immediately follows) the at
least one subframe in which said broadcast message is to be
broadcast.
[0200] (Supplementary note 10). The base station according to any
one of Supplementary notes 1 to 9, wherein said control information
comprises information for identifying the at least one
communication device that said broadcast message carries
information for.
[0201] (Supplementary note 11). The base station according to
Supplementary note 10, wherein said information for identifying
comprises at least one of: a group identifier for identifying a
group of devices of which said at least one communication device
that said broadcast message carries information for is a member; at
least one preamble sequence identifier for identifying said at
least one communication device that said broadcast message carries
information for; and an identifier of a coverage enhancement level
associated with the at least one communication device that said
broadcast message carries information for.
[0202] (Supplementary note 12). The base station according to any
one of Supplementary notes 1 to 11, further comprising a receiver
for receiving, from said at least one communication device, a
message carrying a random access preamble, wherein said broadcast
message comprises a message, carrying a random access response
`RAR` for said at least one communication device.
[0203] (Supplementary note 13). The base station according to
Supplementary note 12, wherein said control information comprises
information for identifying the at least one communication device
that said broadcast message carries information for and wherein
said information for identifying comprises an identifier that
equals 61+64.times.f_id+PRA_id; where fid is an index of a
frequency resource block on which said message carrying a random
access preamble was received and PRA_id is a preamble sequence
index.
[0204] (Supplementary note 14). The base station according to
Supplementary note 12, wherein said control information comprises
information for identifying the at least one communication device
that said broadcast message carries information for and wherein
said information for identifying comprises an identifier that
equals 61+4.times.f_id+PRA_Group_id; where fid is an index of a
frequency resource block on which said message carrying a random
access preamble was received and PRA_Group_id is an index of a
preamble sequence group of which said at least one communication
device that said broadcast message carries information for is a
member.
[0205] (Supplementary note 15). The base station according to
Supplementary note 12, wherein said control information comprises
information for identifying the at least one communication device
that said broadcast message carries information for and wherein
said information for identifying comprises an identifier that
equals RA-RNTI=61+t_id+64.times.f_id+PRA_id; where t_id is an index
of a subframe in which said message carrying a random access
preamble was received, fid is an index of a frequency resource
block on which said message carrying a random access preamble was
received, and PRA_id is a preamble sequence index.
[0206] (Supplementary note 16). The base station according to any
one of Supplementary notes 1 to 11, wherein said broadcast message
comprises a paging message broadcast using a paging channel.
[0207] (Supplementary note 17). The base station according to
Supplementary note 16, wherein said processor is further configured
to identify a modulation and coding scheme `MCS` and/or transport
block size `TBS` for said paging message; wherein said control
information is arranged to identify said MCS and/or TBS.
[0208] (Supplementary note 18). The base station according to any
one of Supplementary notes 1 to 17, wherein said at least one
communication device comprises at least one machine type
communication `MTC` device (e.g. a reduced bandwidth or low
complexity MTC device and/or a coverage enhanced MTC device).
[0209] (Supplementary note 19). A communication device for
communicating with a base station using radio frames made up of a
sequence of subframes and a frequency band made up of frequency
subbands, the communication device comprising:
a receiver configured for receiving, in a control channel, in a
frequency subband in at least one subframe, control information to
identify at least one later subframe in which a broadcast message
is to be broadcast; and a processor configured to identify, from
said control information, said at least one later subframe in which
said broadcast message is to be broadcast; wherein said processor
is configured to control said receiver to monitor said at least one
later subframe in which said broadcast message is to be broadcast
for said broadcast message and to receive said broadcast message
when it has been broadcast.
[0210] (Supplementary note 20). A system comprising the base
station according to any one of Supplementary notes 1 to 18 and the
communication device according to Supplementary note 19.
[0211] (Supplementary note 21). A method performed by a base
station in a communication system in which communication devices
communicate via said base station using radio frames made up of a
sequence of subframes and a frequency band made up of frequency
subbands, the method comprising:
identifying at least one subframe in which a broadcast message,
carrying information for at least one communication device, is to
be broadcast; transmitting, in a control channel, in a frequency
subband in at least one subframe that precedes said at least one
subframe in which said broadcast message is to be broadcast,
control information to identify said at least one subframe in which
said broadcast message is to be broadcast; and broadcasting said
broadcast message in said at least one subframe in which said
broadcast message is to be broadcast.
[0212] (Supplementary note 22). A method performed by a
communication device for communicating with a base station using
radio frames made up of a sequence of subframes and a frequency
band made up of frequency subbands, the method comprising:
receiving, in a control channel, in a frequency subband in at least
one subframe, control information to identify at least one later
subframe in which a broadcast message is to be broadcast;
identifying, from said control information, said at least one
subframe in which said broadcast message is to be broadcast; and
monitoring said at least one later subframe in which said broadcast
message is to be broadcast for said broadcast message and receiving
said broadcast message when it has been broadcast.
[0213] (Supplementary note 23). A computer implementable
instructions product comprising computer implementable instructions
for causing a programmable communications device to perform the
method of Supplementary note 21 or 22.
[0214] This application is based upon and claims the benefit of
priority from United Kingdom Patent Application No. 1506151.8,
filed on Apr. 10, 2015, the disclosure of which is incorporated
herein in its entirety by reference.
* * * * *