DESCRIPTION
Title of Invention:
COMMUNICATION SYSTEM
Technical Field:
The present invention relates to mobile communications devices and networks,
particularly but not exclusively those operating according to the 3rd Generation Partnership
Project (3GPP) standards or equivalents or derivatives thereof. The invention has particular
although not exclusive relevance to the Long Term Evolution (LTE) of UTRAN (called Evolved
Universal Terrestrial Radio Access Network (E-UTRAN)).
Background art:
It has been decided, as part of the 3GPP standardisation process, that downlink operation
for system bandwidths beyond 20MHz will be based on the aggregation of a plurality of
component carriers at different frequencies. Such carrier aggregation can be used to support
operation in a system both with and without a contiguous spectrum (for example, a non¬
contiguous system may comprise component carriers at 800MHz, 2GHz, and 3.5GHz). Whilst a
legacy mobile device may only be able to communicate using a single, backward compatible,
component carrier, a more advanced multi-carrier capable terminal would be able to
simultaneously use the multiple component carriers.
Carrier aggregation can be particularly beneficial in a heterogeneous network (HetNet),
even when the system bandwidth is contiguous, and does not exceed 20 MHz because multiple
carriers enable interference management between different power class cells as well as open
access and closed subscriber group (CSG) cells. Long-term resource partitioning can be carried
out by exclusively dedicating carriers to a certain power class of cell (Macro/Pico/CSG).
Further, the need for interference management between different cells operating on
component carriers of the same frequency in co-incident or overlapping geographic areas has led
to the proposal (in Release 11) and development of extension carriers in which as much of the
legacy control and pilot signalling (including Common Reference Signalling) as possible are
removed. In addition to the benefits in terms of interference management, this also helps to
minimise overhead. This means that extension carriers are not generally compatible with Release
10 and earlier mobile communication devices.
More specifically, a multi-carrier capable base station is able to operate at least one of its
carriers as an extension carrier, on which a control channel (e.g. a channel carrying resource
scheduling information such as the Physical Downlink Control Channel (PDCCH)), a Common
Reference Signal (CRS) (sometimes referred to as a Cell-specific Reference Signal), and other
information cannot be transmitted. To allow the use of an extension carrier, at least one further
component carrier of the component carrier set used by the multi-carrier base station must be a
stand-alone carrier that can be used to transmit the scheduling information for the extension
carrier.
Accordingly, when a first base station is operating a component carrier as an extension
carrier, another base station may operate a component carrier of the same frequency to transmit a
control channel, a CRS and other such information more reliably, in the same general geographic
area as the first base station, without significant interference because there is no corresponding
control channel, CRS and other such information on the extension carrier operated by the first
base station.
It is possible that the geographical areas covered by the primary cell and secondary cell
may not be coincident - either by design, or because the range of the first and second component
carriers is different as a result of radio environment conditions. In some cases the primary cell
and secondary cells may be in a different geographical location altogether. Further, as
mentioned above, the primary cell and secondary cells may operate in different frequency bands
than one another. In such cases, despite the fact the primary and secondary cells are controlled
from the same base station, a timing error and carrier frequency drift may, nevertheless, arise
between the primary and the secondary cells.
Disclosure of the Invention:
An exemplary embodiment of the invention therefore aims to provide a mobile
communication system, a mobile communication device, a communication node and associated
methods which overcomes or at least mitigates the above issues.
According to one aspect of the present invention there is provided communication
apparatus for communicating with a plurality of mobile communication devices in a cellular
communication system using a plurality of radio frames, the communication apparatus
comprising: means for operating a communication cell on an associated component carrier;
means for configuring the apparatus to communicate a signal comprising at least one of a
synchronisation signal and a reference signal at a configured relative location within a radio
frame to be transmitted in the communication cell using the component carrier, the configured
relative location being a location within the radio frame relative both to a time range spanned by
the radio frame and to a frequency range spanned by the radio frame; and means for
communicating a signal at the configured relative location within the radio frame; wherein the
configuring means is operable to configure the apparatus to communicate the signal at any of a
plurality of relative locations within the radio frame.
The operating means may be adapted to operate a plurality of communication cells on
respective component carriers. The communicating means may be operable to communicate a
first signal within a first radio frame transmitted in a first of the plurality of cells using a first
component carrier, the first signal being transmitted at a predetermined relative location within
the radio frame relative both to a time range spanned by the first radio frame and to a frequency
range spanned by the first radio frame. The configuring means may be operable to configure the
apparatus to communicate a second signal at a configured relative location within a second radio
frame to be transmitted in a second of the plurality of cells using a second component carrier, the
configured relative location being a location within the radio frame relative both to a time range
spanned by the second radio frame and to a frequency range spanned by the second radio frame.
The communicating means may be further operable to communicate a second signal at the
configured relative location within the second radio frame. The first and second signals may be
of the same type as one another, each comprising at least one of a synchronisation signal and a
reference signal and or another control signal. The configuring means may be operable to
configure the apparatus to communicate the second signal at a configured relative location within
the second radio frame that may be different to the predetermined relative location within the
first radio frame.
Each radio frame may comprise a plurality of subframes spanning a range of different
subframe locations in time; and the configuring means may be operable to configure the
apparatus to communicate the signal, or the second signal, at any of a plurality of relative
locations within the radio frame, which plurality of locations may each comprises a different
subframe location within the range of subframe locations.
Each radio frame may comprise a plurality of slots spanning a range of different slot
locations in time; and the configuring means may be operable to configure the apparatus to
communicate the signal, or the second signal, at any of a plurality of relative locations within the
radio frame, which plurality of locations may each comprise a different slot location within the
range of slot locations.
Each subframe or slot may comprise a plurality of symbols spanning a range of different
symbol locations in time; and the configuring means may be operable to configure the apparatus
to communicate the signal, or the second signal, at a predetermined symbol location within each
subframe or slot in which the signal, or the second signal may be communicated, which
predetermined symbol location may be located within a control region of the subframe or slot.
Each subframe or slot may comprise a plurality of symbols spanning a range of different
symbol locations in time; and the configuring means may be operable to configure the apparatus
to communicate the signal, or the second signal, at any of a plurality of relative locations within
the radio frame, which plurality of locations may each comprise a different symbol location
within the range of symbol locations.
Each radio frame may comprise a plurality of subcarriers spanning a range of different
subcarrier locations in frequency; and the configuring means may be operable to configure the
apparatus to communicate the signal, or the second signal, at any of a plurality of relative
locations within the radio frame, which plurality of locations may each comprise a different
subrange of subcarrier locations within the range of subcarrier locations.
Each radio frame may comprise a plurality of resource blocks spanning a range of
different resource block locations in frequency; and the configuring means may be operable to
configure the apparatus to communicate the signal, or the second signal, at any of a plurality of
relative locations within the radio frame, which plurality of locations may each comprises a
different subrange of resource block locations within the range of resource block locations.
The configuring means may be configured to identify a further relative location within a
further radio frame used by a further communication apparatus to communicate a signal of the
same type as the signal (or the first and second signals) and to configure the signal (or the second
signal) at a configured relative location within an associated radio frame that may be different to
the identified further relative location within a further radio frame.
The configuring means may be operable to identify the further relative location within the
further radio frame by communicating with the further communication apparatus via an X2
interface.
The configuring means may be operable to identify the further relative location within the
further radio frame during an automatic neighbour relation (ANR) procedure.
The apparatus may further comprise means for communicating, to the mobile
communication devices, information for identifying the configured relative location to the
mobile communication devices.
The information for identifying the configured relative location may comprise a
configuration index from which the configured relative location may be derived. The link
between possible configuration indexes and possible configured relative locations may be
represented by a look-up table in a memory of the apparatus. The look-up table may comprise a
link between possible configuration indexes and possible configured relative locations as
follows:
The link between possible configuration indexes and possible configured relative
locations may be represented by one or more equations in a memory of the apparatus. At least
one equation may represent a link between a cell identity (Cell lD) and a configuration index as
follows:
configuration index = (Cell lD mod 5) + 1
The information for identifying the configured relative location may comprise an explicit
indication of the configured relative location. The information for identifying the configured
relative location may comprise a cell identity of the cell in which the signal, or second signal,
may be communicated.
The signal (or each of the first and second signals) may comprise a synchronisation
signal. The signal (or each of the first and second signals) may comprise a primary or secondary
synchronisation signal. The signal (or each of the first and second signals) may comprise a
reference signal. The signal (or each of the first and second signals) may comprise a
demodulation reference signal (DMRS). The signal (or each of the first and second signals) may
comprise a common or cell-specific reference signal (CRS).
The apparatus may comprise a base station.
According to one aspect of the present invention there is provided communication
apparatus for communicating with a plurality of mobile communication devices in a cellular
communication system using a plurality of radio frames the communication apparatus
comprising: means for operating a plurality of communication cells on respective component
carriers; means for communicating a first signal within a first radio frame transmitted in a first
of the plurality of cells using a first component carrier, the first signal being transmitted at a
predetermined relative location within the radio frame relative both to a time range spanned by
the first radio frame and to a frequency range spanned by the first radio frame; and means for
configuring the apparatus to communicate a second signal at a configured relative location
within a second radio frame to be transmitted in a second of the plurality of cells using a second
component carrier, the configured relative location being a location within the radio frame
relative both to a time range spanned by the second radio frame and to a frequency range
spanned by the second radio frame; wherein the communicating means is further operable to
communicate a second signal at the configured relative location within the second radio frame;
wherein the first and second signals are of the same type as one another, each comprising at least
one of a synchronisation signal and a reference signal; and wherein the configuring means is
operable to configure the apparatus to communicate the second signal at a configured relative
location within the second radio frame that is different to the predetermined relative location
within the first radio frame.
According to one aspect of the present invention there is provided a mobile
communication device for communicating with communication apparatus in a cellular
communication system using a plurality of radio frames, the mobile communication device
comprising: means for communicating in a communication cell on an associated component
carrier controlled by the communication apparatus; means for identifying a configured relative
location, within a radio frame, within which configured relative location a signal comprising at
least one of a synchronisation signal and a reference signal is to be transmitted, the configured
relative location being a location within the radio frame relative both to a time range spanned by
the radio frame and to a frequency range spanned by the radio frame; and means for receiving
the signal at the identified configured relative location within the radio frame; wherein the
configured relative location may comprise any of a plurality of relative locations and wherein the
identifying means is operable to determine which of the plurality of relative locations the
configured relative location comprises.
According to one aspect of the present invention there is provided a mobile
communication device for communicating with communication apparatus in a cellular
communication system using a plurality of radio frames, the mobile communication device
comprising: means for communicating in any of a plurality of communication cells, each being
provided on a respective component carrier operated by the communication apparatus; means for
receiving a first signal within a first radio frame transmitted in a first of the plurality of cells
using a first component carrier, the first signal being transmitted at a predetermined relative
location within the radio frame relative both to a time range spanned by the first radio frame and
to a frequency range spanned by the first radio frame; and means for identifying a configured
relative location, within a radio frame, within which location a second signal is to be transmitted,
the configured relative location being a location within the radio frame relative both to a time
range spanned by the radio frame and to a frequency range spanned by the radio frame; wherein
the receiving means is further operable to receive a second signal at the configured relative
location within the second radio frame; wherein the first and second signals are of the same type
as one another, each comprising at least one of a synchronisation signal and a reference signal;
and wherein the identifying means is operable to identify a configured relative location within
the second radio frame that is different to the predetermined relative location within the first
radio frame.
The identifying means may be operable to infer the configured relative location of the
second signal based on timing information obtained the first signal. The identifying means may
be operable to identify the configured relative location from information communicated by the
communication apparatus for identifying the configured relative location.
The information for identifying the configured relative location may comprise a
configuration index from which the configured relative location may be derived.
The link between possible configuration indexes and possible configured relative
locations may be represented by a look-up table in a memory of the mobile communication
device.
The link between possible configuration indexes and possible configured relative
locations may be represented by one or more equations in a memory of the mobile
communication device.
The information for identifying the configured relative location may comprise an explicit
indication of the configured relative location. The information for identifying the configured
relative location may comprise a cell identity of the cell in which the signal, or second signal, is
communicated.
The identifying means may be operable to identify the configured relative location by
conducting a search for signals comprising the at least one of a synchronisation signal and a
reference signal and for identifying the configured relative location from a signal detected during
the search.
The signal (or each of the first and second signals) may comprises a synchronisation
signal and the mobile communication device may further comprise means for synchronising with
the communication apparatus in dependence on the synchronisation signals.
The signal (or each of the first and second signals) may comprises a primary or secondary
synchronisation signal.
According to one aspect of the present invention there is provided a method performed
by communication apparatus for communicating with a plurality of mobile communication
devices in a cellular communication system using a plurality of radio frames the method
comprising: operating a communication cell on an associated component carrier;
configuring the apparatus to communicate a signal comprising at least one of a
synchronisation signal and a reference signal at a configured relative location within a radio
frame to be transmitted in the communication cell using the component carrier, the configured
relative location being a location within the radio frame relative both to a time range spanned by
the radio frame and to a frequency range spanned by the radio frame; and communicating a
signal at the configured relative location within the radio frame; wherein the configuring step
comprises configuring the apparatus to communicate the signal at any of a plurality of relative
locations within the radio frame.
According to one aspect of the present invention there is provided a method performed
by communication apparatus for communicating with a plurality of mobile communication
devices in a cellular communication system using a plurality of radio frames, the method
comprising: operating a plurality of communication cells on respective component carriers;
communicating a first signal within a first radio frame transmitted in a first of the plurality of
cells using a first component carrier, the first signal being transmitted at a predetermined relative
location within the radio frame relative both to a time range spanned by the first radio frame and
to a frequency range spanned by the first radio frame; configuring the apparatus to communicate
a second signal at a configured relative location within a second radio frame to be transmitted in
a second of the plurality of cells using a second component carrier, the configured relative
location being a location within the radio frame relative both to a time range spanned by the
second radio frame and to a frequency range spanned by the second radio frame; and
communicating a second signal at the configured relative location within the second radio frame;
wherein the first and second signals are of the same type as one another, each comprising at least
one of a synchronisation signal and a reference signal; and wherein the configuring step
comprises configuring the apparatus to communicate the second signal at a configured relative
location within the second radio frame that is different to the predetermined relative location
within the first radio frame.
According to one aspect of the present invention there is provided a method performed
by a mobile communication device for communicating with communication apparatus in a
cellular communication system using a plurality of radio frames the method comprising:
communicating in a communication cell on an associated component carrier controlled
by the communication apparatus; identifying a configured relative location, within a radio frame,
within which configured relative location a signal comprising at least one of a synchronisation
signal and a reference signal is to be transmitted, the configured relative location being a location
within the radio frame relative both to a time range spanned by the radio frame and to a
frequency range spanned by the radio frame; and receiving the signal at the identified configured
relative location within the radio frame; wherein the configured relative location may comprise
any of a plurality of relative locations and wherein the identifying means is operable to
determine which of the plurality of relative locations the configured relative location comprises.
According to one aspect of the present invention there is provided a method performed
by a mobile communication device for communicating with communication apparatus in a
cellular communication system using a plurality of radio frames the mobile communication
device comprising: communicating in any of a plurality of communication cells, each being
provided on a respective component carrier operated by the communication apparatus; receiving
a first signal within a first radio frame transmitted in a first of the plurality of cells using a first
component carrier, the first signal being transmitted at a predetermined relative location within
the radio frame relative both to a time range spanned by the first radio frame and to a frequency
range spanned by the first radio frame; identifying a configured relative location, within a radio
frame, within which location a second signal is to be transmitted, the configured relative location
being a location within the radio frame relative both to a time range spanned by the radio frame
and to a frequency range spanned by the radio frame; and receiving a second signal at the
configured relative location within the second radio frame; wherein the first and second signals
are of the same type as one another, each comprising at least one of a synchronisation signal and
a reference signal; and wherein the identifying means is operable to identify a configured relative
location within the second radio frame that is different to the predetermined relative location
within the first radio frame.
Aspects of the invention extend to computer program products such as computer readable
storage media having instructions stored thereon which are operable to program a programmable
processor to carry out a method as described in the aspects and possibilities set out above or
recited in the claims and/or to program a suitably adapted computer to provide the apparatus
recited in any of the claims.
Each feature disclosed in this specification (which term includes the claims) and/or
shown in the drawings may be incorporated in the invention independently (or in combination
with) any other disclosed and/or illustrated features. In particular but without limitation the
features of any of the claims dependent from a particular independent claim may be introduced
into that independent claim in any combination or individually.
Brief Description of the Drawings:
Embodiments of the invention will now be described by way of example only with
reference to the attached figures in which:
Figure 1 schematically illustrates a telecommunication system;
Figure 2 shows a simplified block diagram of a base station for the telecommunication
system of Figure 1;
Figure 3 shows a simplified block diagram of a mobile communication device for the
telecommunication system of Figure 1;
Figure 4 shows an illustration of a typical radio frame used for communication in the
telecommunication system of Figure 1;
Figure 5 shows an illustration of part of a typical subframe of the radio frame used for
communication in the telecommunication system of Figure 1;
Figure 6 shows an illustration of how synchronisation signals may be transmitted in a
primary cell and a secondary cell of the telecommunication system of Figure 1;
Figure 7 shows a simplified flow chart of how a mobile communication device of the
telecommunication system of Figure 1 may operate to determine the location of synchronisation
signalling in the radio frame;
Figure 8 shows a simplified flow chart of how a base station of the telecommunication
system of Figure 1may operate to determine the location of where synchronisation signalling
should be transmitted in the radio frame;
Figure 9 shows an illustration of another example of how synchronisation signals may be
transmitted in a primary cell and a secondary cell of the telecommunication system of Figure 1;
Figure 10 shows an illustration of another example of how synchronisation signals may
be transmitted in a primary cell and a secondary cell of the telecommunication system of Figure
l ; and
Figure 11 shows a simplified flow chart of another example of how a mobile
communication device of the telecommunication system of Figure 1 may operate to determine
the location of synchronisation signalling in the radio frame.
Detailed Description of Exemplary Embodiments:
Overview
Figure 1 schematically illustrates a mobile (cellular) telecommunication system 1 in
which a user of any of a plurality of mobile communication devices 3-1, 3-2, 3-3, 3-4, can
communicate with other users via one or more of a plurality of base stations 5-1, 5-2 and 5-3. In
the system illustrated in Figure , each base station 5 shown is an Evolved Universal Terrestrial
Radio Access Network (E-UTRAN) base station capable of operating in a multi-carrier
environment.
In Figure 1, the base station labelled 5-1 comprises a so called 'macro' base station
operating a plurality of relatively geographically large 'macro' cells 7, 8 using respective
component carriers (CCs) CI, C2, of a component carrier set. In this embodiment, the macro
base station 5-1 operates component carrier CI as a primary component carrier on which a
primary cell (PCell) 7 is provided, and component carrier C2 as a secondary component carrier
on which a secondary cell (SCell) 8 is provided. The PCell 7 has a larger geographical coverage
than the SCell 8. The difference in the size of the PCell 7 and SCell 8 may be by design (e.g. as
a result of using a lower transmit power for component carrier C2) or may result from one or
more radio environmental factors affecting the primary carrier CI and secondary carrier C2 to
different extents (e.g. path loss affecting a lower frequency primary carrier CI to a lesser extent
than a higher frequency secondary carrier C2).
The other base stations 5-2, 5-3 shown in Figure 1, each comprises a so called 'pico' base
station (or possibly so called 'Radio Remote Head (RRH)') operating a plurality of 'pico' cells
9-2, 9-3, 10-2, 10-3, using a component carrier set having component carriers (CCs) CI, C2
corresponding in frequency to those used by the macro-base station 5-1. Each pico base station
5-2, 5-3 operates a respective pico primary cell (PCell) 9-2, 9-3 on component carrier C2 and a
respective pico secondary cell (SCell) 10-2, 10-3 on component carrier CI. Thus, the pico Pcells
9 share substantially the same frequency band as the macro SCell 8, and the pico SCells 10 share
substantially the same frequency band as the macro PCell 7. As seen in Figure 1, the power of
the carriers CI, C2 used to provide the pico cells 9, 10 is set such that the geographical coverage
of the pico PCells 9, of this example, are substantially co-incident with the geographical
coverage of the pico SCells 10.
The power used to provide pico cells 9, 10 is low relative to the power used for the macro
cells 7, 8 and the pico cells 9, 10 are therefore small relative to the macro cells 7, 8. As shown in
Figure 1, in this example the geographical coverage of each of the pico cells 9, 10 falls
completely within the geographical coverage of the macro PCell 7 and overlaps partially with the
geographical coverage of the macro SCell 7.
To alleviate the issue of intercell interference, the component carrier C2 used for the
macro SCell 8 is operated by the macro base station 5-1 as an extension carrier on which the
nature of information that may be transmitted is restricted. Specifically, the component carrier,
when operating as the extension carrier may not be used for transmission of any of the following:
a Physical Downlink Control Channel (PDCCH);
a Physical Hybrid ARQ Indicator Channel (PHICH);
a Physical Control Format Indicator Channel (PCFICH);
a Physical Broadcast Channel (PBCH); or
a Common Reference Signal / Cell-specific Reference Signal (CRS).
Accordingly, the extension carrier is effectively a 'PDCCH-less' carrier that cannot be
operated as a single (stand-alone) carrier, and must therefore be operated a part of a component
carrier set where at least one of the carriers in the set is a stand-alone-capable carrier. The macro
base station 5-1 operates carrier CI as a stand-alone carrier on which the PDCCH is used to
schedule the resources of component carrier C2 to be used for communication purposes by a
mobile communication device 3 when operating in the macro SCell 8.
The respective component carrier CI used for each of the pico SCells 10 is also each
operated as an extension carrier (as described previously) by the associated pico base station 5-2,
5-3. The respective component carrier C2 used for each of the pico Pcells 9 is operated, as a
stand-alone carrier, by the associated pico base station 5-2, 5-3, and is used for cross carrier
scheduling of the resources of component carrier CI to be used for communication purposes by a
mobile communication device 3 when operating in the associated pico SCell 10.
Each base station 5 is also configured to provide signals in each radio frame 210 on the
primary (backwards compatible) component carrier by which the mobile communication devices
3 may achieve synchronisation with the base station 5 for the associated PCell 7, 9. Specifically,
the base station 5 transmits a primary synchronisation signal (PSS) and a secondary
synchronisation signal (SSS) on the primary (backwards compatible) component carrier, at
predetermined fixed locations (in both frequency and time) within each radio frame as set out in
3GPP TS 36.21 1 V10.2.0.
Rather than relying on the signals transmitted on the primary component carrier for
synchronisation with the SCell 8, 10, each base station 5 is also configured to provide separate
synchronisation signals in each radio frame 210 (see Fig. 4) on the secondary (extension)
component carrier by which the mobile communication devices 3 may achieve synchronisation
with the base station 5 for the associated SCell 8, 10. Specifically, the base station 5 also
transmits a primary synchronisation signal (PSS) and a secondary synchronisation signal (SSS)
on the secondary component carrier. Unlike the PSS and SSS transmitted on the primary
component carrier, however, the location of the PSS and SSS within each radio frame is
configurable on a per-base station 5 basis (and a per-carrier basis where multiple secondary
carriers are used). The configurable location of the PSS and SSS is particularly beneficial
because it allows neighbouring base stations 5 and base stations 5 whose cells share a common
geographic area and/or frequency band to avoid inter-cell interference between the PSS/SSS
transmitted by one base station 5 and the PSS/SSS transmitted by another base station 5.
It will be appreciated, however, that reuse of the PSS and SSS in the SCell 8, 10 (even at
different locations in a radio frame) carries with it a risk that a legacy (e.g. release 10 mobile
communication device) may detect it during a cell search procedure and mistake it for a normal
release 10 cell. To avoid this, the structure of the PSS/SSS for the SCell 8, 10 is modified such
that release 10 mobile communication devices will ignore the PSS/SSS whilst maintaining the
required synchronisation performance for release 11 mobile communication devices 3.
Specifically, in this embodiment, the relative positions of the PSS and SSS are swapped
compared with their expected positions (e.g. as transmitted on the primary component carrier).
Base Station
Figure 2 is a block diagram illustrating the main components of the base stations 5 shown
in Figure 1. For clarity, the base stations will be described with reference to the macro base
station 5-1 , but it will be appreciated that each of the pico base stations 5-2, 5-3 may be
configured similarly. The macro base station 5-1 comprises an E-UTRAN multi-carrier capable
base station comprising a transceiver circuit 3 1 which is operable to transmit signals to, and to
receive signals from, the mobile communication devices 3 via at least one antenna 33. The base
station 5-1 is also operable to transmit signals to and to receive signals from: a core network via
a network interface 35; and other base stations 5 in the vicinity via a base station (or so called
'C2') interface. 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 42, a component carrier management module 43, and a synchronisation module
47.
The communication control module 42 is operable to control communication with the
mobile communication devices 3 on the component carriers (CCs) C1, C2, of its component
carrier set and with the core network and other base stations via the network interface 35 and the
X2 interface 36 respectively. The component carrier management module 43 is operable to
manage the use of the component carriers C1, C2 and in particular the configuration and
operation of the component carriers CI, C2 as a backwards compatible standalone carrier for a
PCell 7 or as an extension carrier for an SCell 8. The synchronisation module 47 manages the
transmission of synchronisation signals at appropriate locations in each radio frame 210.
In the above description, the base station 5-1 is 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.
Mobile Communication Device
Figure 3 is a block diagram illustrating the main components of the mobile
communication devices 3 shown in Figure 1. Each mobile communication device 3 comprises a
mobile (or 'cell' telephone) capable of operating in a multi-carrier environment. The mobile
communication device 3 comprises a transceiver circuit 51 which is operable to transmit signals
to, and to receive signals from, the base stations 5 via at least one antenna 53. The operation of
the transceiver circuit 5 is controlled by a controller 57 in accordance with software stored in
memory 59.
The software includes, among other things, an operating system 51, a communication
control module 62, and a synchronisation module 67.
The communication control module 62 is operable for managing communication with the
base stations 5 on the associated component carriers (CCs) CI, C2. The synchronisation module
67 manages synchronisation of the mobile communication device 3 with the radio frame /
subframe timing of the base station 5 for example with the frame / subframe timing of the PCell
7, 9 and the SCell 8, 10. The synchronisation module 67 also manages the identification of the
synchronisation configuration for the SCell 8, 10 such as the location of the PSS/SSS within
each radio frame 210.
In the above description, the mobile communication device 3 is 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.
Synchronisation Signal Configuration
The way in which the synchronisation signals are configured in the present embodiment
will now be described in more detail, by way of example only, with reference to Figures 4 to 6.
Figure 4 illustrates the structure of a radio frame 10 of the type used for communication
by the base stations 5 and mobile communication devices 3 of the communication system 1. As
seen in Figure 4, each base station 5 is configured to transmit control information and data to
associated mobile communication devices using radio frames 210. Each radio frame 210, in this
embodiment, is 10ms long and as seen in Figure 4 comprises a plurality of orthogonal frequency
division multiplexing (OFDM) subframes 230 (in this embodiment ten 1ms subframes which are
indexed '0' through '9' make up a radio frame 210). Each subframe comprises a pair of slots
232a and 232b (in this embodiment 0.5ms long). For the purposes of referencing, the slots 232
are typically referred to by index numbers ranging from '0' to '19' in chronological order (from
left to right on Figure 4) with the first slot 232a of e'ach subframe 230 having an even number
and the second slot 232b having an odd number. Part of the first ('even numbered') slot of each
subframe 230 comprises a so called 'control' region 231 that is generally reserved for the
transmission of control information. The remainder of the first ('even numbered') slot of each
subframe 230 and the second ('odd numbered') slot of each subframe 230 comprises a so called
'data' region 233 that is generally used for the transmission of data, for example in a Physical
Downlink Shared Channel (PDSCH).
Figure 5 shows a resource grid for one of the OFDM subframes 230 of Figure 4. The
resource grid shown is for a resource block (RB) pair 3 10a, 310b (represented by hatched region)
with each RB 310a, 10b of the pair having, for example, a resource grid similar to that
described in section 6.2 of the 3rd Generation Partnership Project (3GPP) Technical Standard
(TS) 36.21 V10.2.0 and shown in Figure 6.2.2-1 of that standard.
As seen in Figure 5, each resource block 310a and 310b is part of a respective slot 232a
and 232b of the subframe 230. Each resource block 310a, 310b comprises a set of resource
elements 335 defined in frequency by 12 subcarrier frequencies (rows) and in time by 7 symbols
(columns). In this embodiment, the control region 231 comprises the resource elements 335 of
the first three OFDM symbols of the first slot 232a of each subframe 230. The remaining
resource elements 335 of the first slot 232a and the resource elements 335 of the second slot
232b form the data region 333.
As described above, each base station 5 is configured to provide synchronisation signals
(PSS/SSS) at particular locations (in frequency and time) in each radio frame 210 to allow the
mobile communication device 3 to achieve synchronisation with the base station 5. The PSS is
used by the mobile communication device 3 to synchronise receipt and transmission of each
symbol, slot and subframe with the corresponding symbol, slot and/or subframe timings of the
base station 5. Further, the PSS is also used by the mobile communication device 3 to identify
other information about the cell to which they relate, for example, cell identity information such
as a physical layer cell identity (PCI). The SSS is used by the mobile communication device 3 to
synchronise receipt and transmission of each radio frame 210 (Fig. 4) with the associated frame
timings of the base station 5. The SSS is also used by the mobile communication device 3 to
identify other information about the cell to which they relate, for example cell group identity
information such as the physical layer cell identity group for the base station 5.
Figure 6 illustrates how the synchronisation signals are configured in the radio frames
210 for the primary cell 7, 9 and the secondary cell 8, 10 respectively.
As seen in Figure 6, in the case of the primary cell 7, 9, each base station 5 always
provides the synchronisation signals (PSS/SSS) in the last two symbols of the first (even
numbered) slot 232a in the first subframe 230 (subframe #0) and in the last two symbols of the
first (even numbered) slot 232a in the sixth subframe 230 (subframe #5). The PSS is transmitted
in the last symbol of the first slot 232a of the first and sixth subframes, whilst the SSS is
transmitted in the second to last symbol of the first slot 232a of the first and sixth subframes 230
(i.e. the last symbol of slot #0 and slot #10).
The PSS and SSS are each allocated the central 62 subcarriers belonging to symbols in
which they are respectively located. The 5 resource elements above and below the
synchronisation signals are not used for transmission. They represent periods of Discontinuous
Transmission (DTX). Thus, the PSS and SSS transmissions each use six resource blocks (with
10 resource elements left unused) and the indexes of the resource blocks (resource block
numbers) within the frequency band covered by the primary component carrier are always the
same.
The sequence d(n) used for the PSS is generated from a frequency-domain Zadoff-Chu
sequence as follows:
where the Zadoff-Chu root sequence index u depends on the PCI and is one of the indices 25, 29
and 34.
The sequence d{Q),..., d{6\) used for the SSS comprises an interleaved concatenation of
two length-3 1 binary sequences. The concatenated sequence is scrambled with a scrambling
sequence given by the PSS.
The combination of two length-3 1 sequences defining the secondary synchronization
signal differs between subframe #0 and subframe #5 according to:
in subframe 0
in subframe 5
in subframe O
in subframe 5
where 0 < n < 30 . The indices m and , are derived from the physical-layer cell-identity group.
Thus, the two PSS transmissions within a radio frame 210 are identical. The two SSS
transmissions within each radio frame 210, however, use different sequences to allow the mobile
communication device 3 to differentiate between the 1st and 2nd transmission thereby allowing
the mobile communication device 3 to achieve frame synchronisation.
As a skilled person will understand, further details on the implementation of the PSS and
SSS may be found in TS 36.21 1 section 6.1 1.1 and 6.1 1.2 respectively.
In this embodiment, in the case of the secondary cell 8, 10, each base station 5 still
provides the synchronisation signals (PSS/SSS) in the last two symbols of the respective first
(even numbered) slots 232a of two different subframes (subframes #n and #n+5, where 'n' is the
index of the first subframe). However, unlike the case of the primary cell 7, 9, the actual
subframes 230 used are configurable so that different base stations 5 can use different subframes
230 for transmitting their synchronisation signals. Further, in this embodiment, the symbol
positions used for the PSS and the SSS are swapped relative to the symbol positions used for the
primary cell 7, 9. Specifically, the PSS is transmitted in the second to last symbol of the first slot
232a of subframe #n and subframe #(n+5), whilst the SSS is transmitted in the last symbol of the
first slot 232a of subframe #n and subframe #(n+5).
Accordingly, one base station 5 is able to use the 1st and 6th subframes 230 (subframes #0
and #5) for synchronisation signals in the associated SCell 8, 10, whilst another base station 5 is
able to use the 2nd and 7th subframes 230 (subframes # 1 and #6) and yet another base station 5 is
able to use the 3rd and 8th subframes 230 (subframes #2 and #7). Thus, interference between the
synchronisation signals transmitted by the different base stations 5 is beneficially avoided.
Further, because the positions used for the PSS and the SSS are swapped relative to the
symbol positions used for the primary cell 7, 9 a legacy mobile communication device 3 (e.g. a
release 10 type device) that is not configured to operate with extension carriers will not
inadvertently detect the PSS and SSS for the secondary cell 8, 0 during a cell search procedure
and will not, therefore, mistake it for a normal release 10 cell.
Identifying Synchronisation Configuration for an SCell
The way in which a mobile communication device identifies the synchronisation
configuration for a particular SCell 8, 10 will now be described, by way of example only, with
reference to Figure 7.
Figure 7 shows a flow chart illustrating one method by which a mobile communication
device 3 may identify the location of the PSS and SSS of an SCell 8, 10.
In this embodiment, when a mobile communication device 3 first enters the PCell 7, 8 of
a base station 5 that operates an SCell 9, 10 at SI, it detects information for identifying the PSS
and SSS configuration of the SCell 8, 10 that is signalled by base station 5 at S2.
Advantageously, in this embodiment, the base station 5 signals a configuration index
from which the location of the synchronisation signals can be derived thereby avoiding
unnecessary signalling overhead. An example of a possible relationship between the
configuration index and indexes of the subframes 230 used for transmitting the PSS and SSS is
illustrated in Table 1 below:
Table 1 : Example of PSS/SSS configuration index
In this embodiment, the link between the configuration index and the indexes of the
subframes 230 used for transmitting the PSS and SSS is represented in the memory of the mobile
communication device 3 and the base station 5 as a look-up table.
On receipt of the configuration information, the mobile communication device 3
determines the location of the PSS and SSS for the SCell 8, 10 at S3. The mobile
communication device 3 is then able to successfully receive and interpret the PSS and SSS on
the secondary component carrier of the SCell 8, 10 and thereby achieve synchronisation with the
frame, subframe, slot and symbol timings of the SCell 8, 10 even if they are different to those of
the PCell 7, 9 by virtue of a timing error or the like.
Selecting Appropriate Synchronisation Configuration
The way in which a base station 5 determines an appropriate PSS and SSS configuration
for the SCell 8, 10 will now be described, by way of example, with reference to Figure 8.
Initially, the base station 5 identifies the radio frame locations (e.g. subframe indices)
being used by nearby base stations 5 (e.g. operating neighbouring or overlapping cells) for
PSS/SSS transmissions. In this embodiment this is achieved by acquiring information
representing the radio frame locations via base station 5 to base station 5 signalling over the X2
interface at S81 and then determining the locations from the acquired information.
The base station 5 then selects, at S82, appropriate radio frame locations for its own
PSS/SSS transmissions in the SCell 8, 10 to avoid or reduce the potential impact of cell to cell
interference between the PSS/SSS being transmitted by the other base stations 5 in the vicinity.
The base station begins transmission of the PSS/SSS in the selected radio frame locations at S83
and, in this embodiment, signals information for use in identifying the radio frame locations
being used at S84.
Modifications and alternatives
A detailed embodiment and has been described above. As those skilled in the art will
appreciate, a number of modifications and alternatives can be made to the above embodiment
and variations whilst still benefiting from the inventions embodied therein.
Referring to Figure 9, for example, in another embodiment in addition to (or as an
alternative to) the subframes 230 used for the PSS and SSS transmissions in the SCells 8, 10
being configurable, the frequencies used (as defined by the indexes of the resource blocks used)
for the PSS and/or SSS transmissions may be configurable thereby providing additional
flexibility to configure the PSS and SSS and thereby enhance protection against cell to cell
interference. Further, in addition to (or as an alternative to) the subframes 230 (and/or
frequency) used for the PSS and SSS transmissions in the SCells 8, 10 being configurable, the
symbols could potentially be configurable.
Referring to Figure 10, in another embodiment in addition to (or as an alternative to) the
subframes 230 (and/or frequency) used for the PSS and SSS transmissions in the SCells 8, 10
being configurable, advantageous use may be made of the fact that the control region is not used
for the control channel and other signalling. Specifically, instead of using the last two symbols
of the even slots in subframes #n and #n + 5, two symbols from the control region (e.g. the first
two symbols) may be used. For example, in FDD, the SSS can be placed on the first OFDM
symbol of subframes #n and #n + 5 (e.g. subframes # 1 and #6) and the PSS can be placed on the
second OFDM symbol of those subframes 230.
Where the base station 5 signals the synchronisation configuration information to the
mobile communication device 3 directly, the signalling may comprise the broadcast of
information for identifying the location of the synchronisation signals (in time and/or frequency)
or may comprise mobile communication device dedicated signalling.
Whilst maintaining the five subframe gap between the two subframes 230 in which the
PSS and SSS are provided in the SCell 8, 10 is advantageous, there may be a different gap (or
even possibly a single subframe could be used). Further although, in above embodiments, a
configuration index is signalled from which the location of the synchronisation signals can be
derived, the time (and/or frequency) location may be signalled explicitly.
Moreover, instead of the base station 5 that transmits the PSS and SSS signalling a
configuration index, the information for identifying the location of the synchronisation signals
may comprise cell identification information transmitted by a base station 5 (e.g. the Cell ID of
an SCell 8, 0 which may be provided as part of a neighbour cell list provided by the base station
5). In this case, the mobile communication device 3 can infer the configuration index for the
SCell 8, 10, and hence the indexes of the subframes used for the PSS and SSS in the SCell 8, 10,
from the Cell ID (alternatively the indexes of the subframes used for the PSS and SSS in the
neighbouring SCell 8, 10 could be determined directly from the Cell ID). For example, the
configuration index (C) could be derived from the Cell ID using the following equation:
C = (Cell lD mod 5) + 1
or directly, where ii and i are the indexes of the first and second subframes respectively as
follows:
i i = (Cell lD mod 5); and
i2 = (Cell_ID mod 5) + 5
The link between the configuration index and the indexes of the subframes 230 used for
transmitting the PSS and SSS may be represented in the memory of the mobile communication
device 3 and/or the base station 5 by an equation, software algorithm or the like, as an alternative
to (or in addition to) a look-up table. For example, the configuration index (C) of the first and
second subframes may be represented by the following equations in the base station 5:
C = 0 if PSS/SSS is not applied on SCell; and
C = i2 + 4
Conversely, the subframe indexes may be represented by the following equations in the
mobile communication device:
PSS/SSS is not applied on SCell if C = 0; and
1 1 = C - 1; and
12 = C - 4 or i2 = i + 5
It will be appreciated that, whilst Table 1 above (and the above equations) only relate to
the derivation and/or encoding of the subframe numbers for the PSS/SSS transmission in the
SCell 8, 10 the same principles could be extended so that the frequencies (e.g. the physical
resource block indexes) used for the PSS/SSS transmission could be derived directly from the
configuration index (and/or Cell ID) as well.
Whilst having the base station 5 inform the mobile communication device 3 of the time
and frequency location of PSS/SSS on SCell 8, 10 directly using PCell communications has
benefits in terms of speed (i.e. faster identification of SCell PSS/SSS location) it requires
additional signalling. Figure 11 shows another method by which a mobile communication
device 3 can identify the synchronisation configuration which, whilst potentially slower, has the
advantage that no additional base station signalling is required.
Referring to Figure 11, in another embodiment as an alternative to (or in addition to) the
information being explicitly signalled by the base station 5 to allow the mobile communication
devices 3 to determine the location of the PSS/SSS within the radio frame (in time and/or
frequency), the mobile communication device may be configured to infer the location of the
PSS/SSS from PSSs/SSSs detected during a search procedure. As seen in Figure 11 for example,
the mobile communication device 3 can engage in a search procedure (SI 1) during which it
detects (SI 2) any PSS/SSS being transmitted by base stations in the vicinity. In this example,
when the search procedure is initiated, the mobile communication device 3 will already be in
possession of the cell identity (Cell ID) of each SCell 8, 10 to which the search procedure relates
(from base station signalling on the primary component carrier in the associated PCell 7, 9 for
example). Accordingly, should the mobile communication device 3 detect a plurality of
candidate PSSs and/or SSSs (for example from neighbouring/overlapping cells) the mobile
communication device 3 is able to determine which of the plurality of candidate PSSs and/or
SSSs belongs to the SCell(s) 8, 10 to which the search procedure relates by comparison of the
known Cell ID(s) with the Cell IDs decoded from the PSS and SSS detected. The mobile
communication device 3 can thus infer the location of the PSS/SSS for the SCell 8, 10 to which
the PSS/SSS belongs (S 13) and synchronise itself with the radio frame/subframe/slot/symbol
timings in the SCell 8, 10 appropriately (S14).
For example, in the PSS/SSS identification procedure of Figure 11, subframe numbers
(indexes) used for PSS/SSS transmission may be inferred based on the reasonable assumption
that the timing error between SCell 8, 10 and the associated PCell 7, 9 will always be much less
than one subframe. Specifically, since the subframe timing of the PCell 7, 9 will already be
known to the mobile communication device from standard PSS/SSS transmissions on the PCell 7,
9, when the PSS/SSS for the associated SCell 8, 10 is detected, the relative difference in the
timing of the PSS/SSS in the SCell 8, 10 and the PSS/SSS in the PCell 7, 9 can be determined to
within an accuracy of one subframe. Accordingly, the subframe index of the PSS/SSS in the
SCell 8, 10 can be determined from the detected position of the PSS/SSS in the SCell 8, 10
relative to the PSS/SSS in the PCell 7, 9.
It will be appreciated, however, that the concept of PSS/SSS with flexible location may
be applied to carriers which are not extension carriers (i.e. which are not associated with a
specific PCell 8, 10). In this case, the mobile communication device 3 may not be able to
determine the subframe numbers used for PSS/SSS from the PSS/SSS transmission alone and,
therefore, the mobile communication device 3 may be unable to establish the subframe and radio
frame timing from the PSS/SSS transmission. However, as discussed above, the existing release
10 PSS/SSS structure allows the UE to determine the Cell ID from the PSS/SSS transmission.
Accordingly, where the PSS/SSS is applied to carriers which are not extension carriers, a fixed
relationship could be maintained between the Cell ID and the time and/or frequency location of
PSS/SSS such that once the Cell ID is known the time/frequency location of PSS/SSS can be
inferred. For example, a configuration index (C) from which the indexes (ii and i2) of the
subframes used for the PSS and SSS may be determined (using any of the methods discussed
above) may be inferred as follows:
C = (CellJD mod 5) + 1
The indexes of the first and second subframes may alternatively (or additionally) be
inferred directly as follows:
11= (CellJD mod 5); and
12 = (CellJD mod 5) + 5
It will be appreciated that whilst, in the above embodiments, the position of the PSS and
SSS for the SCell 8, 10 has been described as having been swapped relative to their expected
positions for the PCell 7, 9, the PSS and/or SSS may be modified in a different way to avoid the
issue of erroneous detection by a legacy mobile communication device. For example, the root
indices of the PSS transmitted on the secondary carrier may be modified so that different
synchronisation sequences are generated. For example, rather than use any of the three possible
PSS signal sequences generated using Zadoff-Chu root sequence indices u = 25, 29 and 34 (as
described earlier), one or more different Zadoff-Chu root sequence indices may be used. In
such cases it is sufficient to modify only the PSS (although the SSS may be modified also) since
a legacy mobile communication device 3 will not search for an SSS if a PSS is not first detected.
In the above embodiments, when the base station 5 identifies the radio frame locations
used for the PSS/SSS transmitted by neighbouring base stations 5, this may be achieved by any
suitable means. For example, if the radio frame location is explicitly linked to cell identity, then
the base station 5 may identify the radio frame locations used for the PSS/SSS transmitted by
neighbouring base stations 5 from the cell identity of those base stations (e.g. transmitted over
the X2 interface). It will be appreciated, however, that information for use in identifying the
radio frame locations used for the PSS/SSS transmitted by neighbouring base stations 5 may be
acquired by other means, for example during an ANR (Automatic Neighbour Relation)
procedure or the like.
It will be appreciated that whilst, in the above embodiments, synchronisation for the
SCell is provided using PSS/SSS on the extension carrier which have a configurable location, in
the case of intra-band carrier aggregation, where the transmission points of PCell and SCell are
collocated (e.g. the PCell and SCell cover the same geographical region), the time and frequency
synchronisation may be based on the PSS/SSS transmitted on the backward compatible carrier.
Accordingly, in the intra band carrier aggregation case where transmission points of PCell and
SCell are collocated, there may be no need to transmit the legacy synchronisation signals
(PSS/SSS) in the subframes on the extension carrier. Nevertheless, in the case of inter band
carrier aggregation (and intra band carrier aggregation where the transmission points of PCell
and SCell are geographically separated) the provision of the PSS/SSS in the radio frames of the
extension carrier is particularly beneficial.
Although extension carriers are intended, primarily, for use by release 11 (and beyond)
mobile communication devices 3 it may be advantageous to provide some way by which legacy
(e.g. release 10 or earlier) mobile communication devices 3 are able to use extension carriers also
(i.e. in the case that a PCell 7, 9 and SCell 8, 10 are in the same frequency band and have
substantially the same geographical location). One way to allow this is to transmit a certain
number of release 10 backward compatible subframes on the extension carrier such that these
subframes can also be used by legacy devices. However, this has the disadvantage that it
requires the definition of dedicated, backwards compatible, subframes having all the control
region signalling required by the legacy device thereby potentially adding to signalling overhead
and potentially resulting in undesirable cell to cell interference.
In a particularly advantageous embodiment of the communication system, in the case that
a PCell 7, 9 and SCell 8, 10 are in the same frequency band and have substantially the same
geographical location, a number of subframes on the extension carrier are configurable as so
called 'Multi-Media Broadcast over a Single Frequency Network' (MBSFN) subframes that have
backwards compatibility with the legacy mobile communication devices. In this embodiment,
therefore, resources of the physical downlink shared channel (PDSCH) of each MBSFN
subframe on the extension carrier may be cross-carrier scheduled from the primary component
carrier (which is operating within the same frequency band as the extension carrier).
Configuring some of the subframes as backwards compatible MBSFN subframes in this way has
the advantage that common reference signals (CRS) are not transmitted in the MBSFN
subframes and hence inter-cell interference and signalling overhead may be reduced.
The idea of providing configurability for the location of synchronisation signalling on the
extension carrier may advantageously be extended to other control/reference signalling. For
example, for extension carriers, the transmission bandwidth of legacy common reference
signalling (CRS) may be reduced to 6 resource blocks (72 subcarriers) transmitted only in the
control region of each subframe on the extension carrier (e.g. restricting the location of the CRS
to the first and second OFDM symbols of each subframe). In order to mitigate the risk of intercell
interference, however, the location of the 6 resource blocks carrying the common reference
signalling may, beneficially, be made configurable in a similar manner to that described for the
PSS/SSS of the above embodiments.
Further, the principles of providing configurability for the location of specific
control/reference/synchronisation signalling on the extension carrier may advantageously be
extended to the case of demodulation reference signals (DMRS). Specifically, unprecoded
legacy DMRS may also be used for maintaining the time and frequency synchronization of the
SCell 8, 10. The bandwidth of unprecoded DMRS patterns may be reduced, for example, to 6
resource blocks in the control region of each subframe on the extension carrier (i.e. on the first
and second OFDM symbols of the subframe). In accordance with this, a new DMRS pattern
may be introduced for the control region of the subframe. Further, in order to mitigate the risk of
inter-cell interference, the location of the 6 resource blocks carrying the unprecoded DMRS may
be made configurable for system bandwidths equal or larger than 12 resource blocks. Moreover,
the 6 resource blocks reserved for carrying the unprecoded DMRS may also be used to transmit
some common control information for all mobile communication devices 3 monitoring the
extension carrier.
It will be appreciated that although the communication system 1 is described in terms of
base stations 5 operating as macro or pico base stations, the same principles may be applied to
base stations operating as femto base stations, relay nodes providing elements of base station
functionality, or other such communication nodes.
In the above embodiments, a mobile telephone based telecommunications system was
described. As those skilled in the art will appreciate, the signalling techniques described in the
present application can be employed in other communications system. Other communications
nodes or devices may include user devices such as, for example, personal digital assistants,
laptop computers, web browsers, etc. As those skilled in the art will appreciate, it is not essential
that the above described relay system be used for mobile communications devices. The system
can be used to extend the coverage of base stations in a network having one or more fixed
computing devices as well as or instead of the mobile communicating devices.
In the embodiments described above, the base stations 5 and mobile communication
devices 3 each include transceiver circuitry. Typically, this circuitry will be formed by dedicated
hardware circuits. However, in some embodiments, part of the transceiver circuitry may be
implemented as software run by the corresponding controller.
In the above embodiments, a number of software modules were described. As those
skilled in the art will appreciate, the software modules may be provided in compiled or uncompiled
form and may be supplied to the base station or the relay station as a signal over a
computer network, or on a recording medium. Further, the functionality performed by part or all
of this software may be performed using one or more dedicated hardware circuits.
Various other modifications will be apparent to those skilled in the art and will not be described
in further detail here.
The following is a detailed description of the way in which the present inventions may be
implemented in the currently proposed 3GPP standards. Whilst various features are described as
being essential or necessary, this may only be the case for the proposed 3GPP standard, for
example due to other requirements imposed by the standard. These statements should not,
therefore, be construed as limiting the present invention in any way.
Introduction
In the last meeting, it has been agreed to introduce at least one new carrier type in
Release 11 with the motivation of enhanced spectral efficiency and improved support of HetNet
and energy efficiency. The conclusion and agreed working assumptions are as follows:
Conclusion:
From a RANI perspective, the main motivations identified for introducing a new carrier
type for carrier aggregation are:
• Enhanced spectral efficiency
· Improved support for HetNet
• Energy efficiency
It is for RAN4 to determine whether there is a need for new RF bandwidths to support
improved bandwidth scalability.
Working assumptions:
- Introduce at least one new carrier type in Rel-1 1 (bandwidth agnostic from a RANI
point of view), with at least reduced or eliminated legacy control signalling and/or
CRS
o at least for the downlink (or for TDD, the downlink subframes on a carrier)
o associated with a backward compatible carrier
o study further:
■ issues of synchronisation/tracking (including whether or not PSS/SSS
are transmitted) and measurements/mobility
" resource allocation methods
" what RSs are required
For FDD a downlink carrier of the new type may be linked with a legacy uplink
carrier, and for TDD a carrier may contain downlink subframes of the new type and
legacy uplink subframes.
From the above working assumptions, the main issue is how to realise the reduction or
elimination of overhead caused by legacy control signalling and common reference signals
(CRS) and to reduce the impact of time-frequency synchronisation as well as mobility
measurements on the new carrier type (i.e. extension carrier) in Release 1.
In this contribution, we discuss some possible solutions for the issues of time-frequency
synchronisations and mobility measurements on the extension carrier in Release 11.
Time frequency synchronisations on the extension carrier
Based on the agreed working assumptions from the last meeting, the extension carrier
should be associated with a backward compatible carrier; therefore, we think that there are two
CA (Communication Apparatus) scenarios where synchronization in time and frequency are
needed for Release 11 UEs.
■ Intra band CA case where transmission points of Pcell and SCell are collocated.
■ Inter band CA case and Intra band CA where transmission points of Pcell and
SCell are geographically separated.
Intra band CA case where transmission points of Pcell and SCell are collocated
In this scenario of intra band CA case where transmission points of Pcell and SCell are
collocated, the time and frequency synchronisation can be derived from synchronisation signals
and reference signals locating on the backward compatible carrier. This means that the carrier
frequency, cell ID and system information are signaled to the UE from the primary cell. In
addition, it has been proposed [2] to enable RRC signaling of downlink cyclic prefix length
(normal/extended) of Scell to the UE and also the UE shall use the synchronization of the Pcell
to acquire/maintain time and frequency synchronization of the Scell.
Proposal 1: Intra band CA case where transmission points of Pcell and SCell are
collocated, the time and frequency synchronisation should be based on the backward compatible
carrier.
Proposal 2: Intra band CA case where transmission points of Pcell and SCell are
collocated, there is no need to transmit the legacy synchronisation signals (PSS/SSS) and
common reference signals (CRS) in the subframes on the extension carrier.
Inter band CA case and Intra band CA case where transmission points of Pcell and SCell
are geographically separated
In this scenario of inter band CA case and intra band CA where transmission points of
Pcell and SCell are geographically separated, there is no mechanism that provides
synchronisation for the SCell for Release 11 UEs as the carrier frequency error and timing error
depend on the propagation channel condition from each transmission point. Therefore, we think
that some kind of known signals are needed for maintaining the time and frequency
synchronization of the Scell. There are several possibilities depending on which signals are to be
transmitted on the extension carrier (i.e. SCell) as follows:
Option-1: Rel-8 PSS/SSS signals transmitted on the extension carrier: Rel-8
PSS/SSS can be used for maintaining the time and frequency synchronization of the Scell. In
this Option-1, the disadvantage is that the location of PSS/SSS is fixed meaning that different
cells transmit on the same location causing significant interference to each other. In FDD, PSS
and SSS signals are always transmitted on subframes 0 and 5 in time domain which are quite
apart, and, therefore, the performance of time and frequency tracking has to be evaluated and
verified for Release 1 UEs.
Option-2: Flexible locations for PSS/SSS signals: Introduce new flexible locations for
PSS/SSS signals for maintaining the time and frequency synchronization of the Scell. The
PSS/SSS signals can be placed in the control region of some subframes in order to avoid intercell
interference of the synchronisation signals. For example, in FDD, SSS can be placed on the
first OFDM symbol of subframes 1 and 6 in time domain and PSS can be placed on the second
OFDM symbol of subframes 1 and 6 in time domain. In addition, it is possible to design
multiple configurations by placing the synchronisation signals of different cells on different
subframes in time domain as shown in the table below.
Table: Different configurations of PSS/SSS signals on different subframes
PSS/SSS Location of PSS/SSS in the subframes 0-9
Configuration index for FDD mode
0 No PSS/SSS exist
1 0, 5
2 1,6
3 2,7
4 3,8
5 4,9
There are two possible alternatives for how UEs find out the location of PSS/SSS signals
as follows:
a) In advance, Pcell informs UE about the location of PSS/SSS by signalling the
time and frequency location explicitly, or by signalling a pre-defined
'configuration index' from which the time and frequency location can be inferred.
An example of the configuration index is shown in the table..
b) Pcell does not need to signal the location of PSS/SSS to the UE, instead UE can
work it out from Cell ID based on an equation: configuration index = (Cell ID
mod 5)+l, where UE knows in advance the Cell ID and an example of the
configuration index is shown in the table.
Option-3: Reduced Release 8 CRS: The transmission bandwidth of the legacy CRS is
reduced to 6RBs transmitted only in the control region of each subframe on the extension carrier
(i.e. keeping CRS locating in the first and second OFDM symbols of the subframe). In order to
avoid inter-cell interference, it is also possible to make the location of 6RBs carrying the CRS
configurable for system bandwidths equal or larger than 12PRBs.
Option-4: Un-precoded DMRS: Un-precoded Rel-10 DMRS can be used for
maintaining the time and frequency synchronization of the Scell. The bandwidth of the unprecoded
DMRS pattern can be further reduced, for example, to 6RBs on the control region of
each subframe on the extension carrier (i.e. on the first and second OFDM symbols of the
subframe). This means introducing a new DMRS pattern on the control region of the subframe
as proposed in [7]. In addition, in order to avoid inter-cell interference, it is also possible to
make the location of 6RBs carrying the un-precoded DMRS configurable for system bandwidths
equal or larger than 12PRBs. These 6RBs carrying the un-precoded DMRS can also be used to
transmit some common control information for all UEs monitoring the extension carrier.
Proposal 3 : For intra band and inter band CA scenarios regardless whether transmission
points of Pcell and SCell are collocated or geographically separated, the carrier frequency, cell
ID, cyclic prefix length and system information of the Scell (Extension carrier) should always be
signaled to the UE from the primary cell.
Proposal 4 : For inter band CA case and intra band CA case where transmission points of
Pcell and SCell are geographically separated, in order to maintain the time and frequency
synchronization of the Extension carrier (Scell), it is proposed to select one of the options 1-4
described above or combination of some of the options.
Backward compatibility with Rel-10 UEs on the Extension carrier
Another issue on the Extension carrier is the backward compatibility with Rel-10 UEs. It
is proposed [3] to_configure backward compatible subframes on the additional carrier type and
these configured subframes contain CRS. However, in order to avoid CRS overhead on the
Extension carrier, it is better to configure backward compatible subframes as MBSFN subframes
that are used for PDSCH transmission instead. This is only applicable to intra band CA case
where transmission points of Pcell and SCell are collocated.
Proposal 5: In order to support backward compatibility with Rel-10 UEs, it should be
possible to configure and cross-carrier schedule for Rel-10 UEs on MBSFN subframes carrying
PDSCH data on the extension carrier in the case of intra band CA where transmission points of
Pcell and SCell are collocated.
Measurements on the Extension carrier
For Rel-1 1 UEs, mobility measurements of the extension carrier could be based on Pcell
when the extension carrier and Pcell are intra band and collocated. This would require no
support of CRS from the extension carrier for the purpose of mobility measurements. In case of
inter band or intra band with geographically separated Pcell and the extension carrier, CSI-RS
and or PSS/SSS signals could be used for mobility measurements. The accuracy of
measurements based on CSI-RS and or PSS/SSS signals would require further study and RAN4
should be involved in these discussions.
Proposal 6 : Use of CSI-RS and or PSS/SSS signals for mobility measurements should be
investigated further.
Conclusion
In this contribution, we have discussed some possible solutions for the issues of timefrequency
synchronisations and mobility measurements on the extension carrier in Release 11.
We have the following proposals:
Proposal 1: For intra band CA case where transmission points of Pcell and SCell
are collocated, the time and frequency synchronisation should be based on the backward
compatible carrier.
Proposal 2: For intra band C case where transmission points of Pcell and SCell
are collocated, there is no need to transmit the legacy synchronisation signals (PSS/SSS)
and common reference signals (CRS) in the subframes of the extension carrier.
Proposal 3: For intra band and inter band CA scenarios regardless whether
transmission points of Pcell and SCell are collocated or geographically separated, the
carrier frequency, cell ID, cyclic prefix length and system information of the Scell
(Extension carrier) are always signaled to the UE from the primary cell.
Proposal 4: For inter band CA case and intra band CA case where transmission
points of Pcell and SCell are geographically separated, in order to maintain the time and
frequency synchronization of the Extension carrier (Scell), it is proposed to select one of the
options 1-4 described in section 2.2 or combination of some of the options.
Proposal 5: In order to support backward compatibility with Rel-10 UEs, it should
be possible to configure and cross-carrier schedule for Rel-10 UEs on MBSFN subframes
carrying PDSCH data on the extension carrier in the case of intra band CA where
transmission points of Pcell and SCell are collocated.
Proposal 6: Use of CSI-RS and or PSS/SSS signals for mobility measurements
should be investigated further.
References
1) RP-1 11115, "LTE Carrier Aggregation Enhancements", RAN#53
2) Rl- 111323, "Remaining details for CA based HetNet in Rel-10," Ericsson and STEricsson.
3) Rl-1 12428, "On need of additional carrier type in Rel-1 1 CA", NTT DOCOMO.
4) Rl-1 12926, "On time and frequency synchronization on additional carrier types",
Ericsson, ST-Ericsson
5) Rl-1 13168, "Initial Discussions on New Carrier Types for LTE Rel-1 1", Renesas
Mobile Europe Ltd.
6) Rl-1 13 186, "Additional Carrier Type for Rel-1 1", LG Electronics
7) Rl-1 2 137, "DL Control channel enhancements with carrier aggregation solutions",
NEC Group.
This application is based upon and claims the benefit of priority from United Kingdom
patent application No. 1119207.7, filed on November 7, 2011, the disclosure of which is
incorporated herein in its entirety by reference.
2013/069579 PCT/JP2012/078551
CLAIMS
Communication apparatus for communicating with a plurality of mobile communication
devices in a cellular communication system using a plurality of radio frames, said
communication apparatus comprising:
means for operating a communication cell on an associated component carrier;
means for configuring said apparatus to communicate a signal comprising at least one of
a synchronisation signal and a reference signal at a configured relative location within a
radio frame to be transmitted in said communication cell using said component carrier,
said configured relative location being a location within said radio frame relative both to
a time range spanned by said radio frame and to a frequency range spanned by said radio
frame; and
means for communicating a signal at said configured relative location within said radio
frame;
wherein said configuring means is operable to configure said apparatus to communicate
said signal at any of a plurality of relative locations within said radio frame.
Communication apparatus as claimed in claim 1 wherein:
said operating means is adapted to operate a plurality of communication cells on
respective component carriers;
said communicating means is operable to communicate a first signal within a first radio
frame transmitted in a first of said plurality of cells using a first component carrier, said
first signal being transmitted at a predetermined relative location within said radio frame
relative both to a time range spanned by said first radio frame and to a frequency range
spanned by said first radio frame;
said configuring means is operable to configure said apparatus to communicate a second
signal at a configured relative location within a second radio frame to be transmitted in a
second of said plurality of cells using a second component carrier, said configured
relative location being a location within said radio frame relative both to a time range
spanned by said second radio frame and to a frequency range spanned by said second
radio frame;
said communicating means is further operable to communicate a second signal at said
configured relative location within said second radio frame;
said first and second signals are of the same type as one another, each comprising at least
one of a synchronisation signal and a reference signal; and
said configuring means is operable to configure said apparatus to communicate said
second signal at a configured relative location within said second radio frame that is
different to the predetermined relative location within said first radio frame.
Communication apparatus according to claim 1 or 2 wherein:
each radio frame comprises a plurality of subframes spanning a range of different
subframe locations in time; and
said configuring means is operable to configure said apparatus to communicate said
signal, or said second signal, at any of a plurality of relative locations within said radio
frame, which plurality of locations each comprise a different subframe location within
said range of subframe locations.
Communication apparatus according to any one of claims 1 to 3 wherein:
each radio frame comprises a plurality of slots spanning a range of different slot locations
in time; and
said configuring means is operable to configure said apparatus to communicate said
signal, or said second signal, at any of a plurality of relative locations within said radio
frame, which plurality of locations each comprise a different slot location within said
range of slot locations.
Communication apparatus according to claim 3 or 4 wherein:
each subframe or slot comprises a plurality of symbols spanning a range of different
symbol locations in time; and
said configuring means is operable to configure said apparatus to communicate said
signal, or said second signal, at a predetermined symbol location within each subframe or
slot in which said signal, or said second signal is communicated, which predetermined
symbol location is located within a control region of said subframe or slot.
Communication apparatus according to claim 3 or 4 wherein:
each subframe or slot comprises a plurality of symbols spanning a range of different
symbol locations in time; and
said configuring means is operable to configure said apparatus to communicate said
signal, or said second signal, at any of a plurality of relative locations within said radio
frame, which plurality of locations each comprise a different symbol location within said
range of symbol locations.
Communication apparatus according to any preceding claim wherein:
each radio frame comprises a plurality of subcarriers spanning a range of different
subcarrier locations in frequency; and
said configuring means is operable to configure said apparatus to communicate said
signal, or said second signal, at any of a plurality of relative locations within said radio
frame, which plurality of locations each comprise a different subrange of subcarrier
locations within said range of subcarrier locations.
8. Communication apparatus according to any preceding claim wherein:
each radio frame comprises a plurality of resource blocks spanning a range of different
resource block locations in frequency; and
said configuring means is operable to configure said apparatus to communicate said
signal, or said second signal, at any of a plurality of relative locations within said radio
frame, which plurality of locations each comprise a different subrange of resource block
locations within said range of resource block locations.
9. Communication apparatus according to any preceding claim wherein said configuring
means is configured to identify a further relative location within a further radio frame
used by a further communication apparatus to communicate a signal of the same type as
said signal (or said first and second signals) and to configure said signal (or said second
signal) at a configured relative location within an associated radio frame that is different
to said identified further relative location within a further radio frame.
10. Communication apparatus according to claim 9 wherein said configuring means is
operable to identify said further relative location within said further radio frame by
communicating with said further communication apparatus via an X2 interface.
11. Communication apparatus according to claim 9 wherein said configuring means is
operable to identify said further relative location within said further radio frame during
an automatic neighbour relation (ANR) procedure.
12. Communication apparatus according to any preceding claim further comprising means
for communicating, to said mobile communication devices, information for identifying
said configured relative location to said mobile communication devices.
13. Communication apparatus according to claim 2 wherein said information for identifying
said configured relative location comprises a configuration index from which said
configured relative location can be derived.
14. Communication apparatus according to claim 13 wherein the link between possible
configuration indexes and possible configured relative locations is represented by a look¬
up table in a memory of the apparatus.
15. Communication apparatus according to claim 14 wherein the look-up table comprises a
link between possible configuration indexes and possible configured relative locations as
follows:
Communication apparatus according to claim 13 or 14 wherein the link between possible
configuration indexes and possible configured relative locations is represented by one or
more equations in a memory of the apparatus.
Communication apparatus according to claim 16 wherein at least one equation represents
a link between a cell identity (Cell lD) and a configuration index as follows:
configuration index = (Cell lD mod 5) + 1
Communication apparatus according to claim 12 wherein said information for identifying
said configured relative location comprises an explicit indication of said configured
relative location.
Communication apparatus according to claim 12 wherein said information for identifying
said configured relative location comprises a cell identity of the cell in which said signal,
or second signal, is communicated.
Communication apparatus according to any preceding claim wherein said signal (or each
of said first and second signals) comprises a synchronisation signal.
Communication apparatus according to claim 20 wherein said signal (or each of said first
and second signals) comprises a primary or secondary synchronisation signal.
Communication apparatus according to any of claims 1 to 19 wherein said signal (or each
of said first and second signals) comprises a reference signal.
Communication apparatus according to claim 1 wherein said signal (or each of said first
and second signals) comprises a demodulation reference signal (DMRS).
Communication apparatus according to claim 2 1 wherein said signal (or each of said first
and second signals) comprises a common or cell-specific reference signal (CRS).
Communication apparatus according to any preceding claim wherein said apparatus
comprises a base station.
Communication apparatus for communicating with a plurality of mobile communication
devices in a cellular communication system using a plurality of radio frames said
communication apparatus comprising:
means for operating a plurality of communication cells on respective component carriers;
means for communicating a first signal within a first radio frame transmitted in a first of
said plurality of cells using a first component carrier, said first signal being transmitted at
a predetermined relative location within said radio frame relative both to a time range
spanned by said first radio frame and to a frequency range spanned by said first radio
frame; and
means for configuring said apparatus to communicate a second signal at a configured
relative location within a second radio frame to be transmitted in a second of said
plurality of cells using a second component carrier, said configured relative location
being a location within said radio frame relative both to a time range spanned by said
second radio frame and to a frequency range spanned by said second radio frame;
wherein said communicating means is further operable to communicate a second signal
at said configured relative location within said second radio frame;
wherein said first and second signals are of the same type as one another, each
comprising at least one of a synchronisation signal and a reference signal; and
wherein said configuring means is operable to configure said apparatus to communicate
said second signal at a configured relative location within said second radio frame that is
different to the predetermined relative location within said first radio frame.
A mobile communication device for communicating with communication apparatus in a
cellular communication system using a plurality of radio frames, said mobile
communication device comprising:
means for communicating in a communication cell on an associated component carrier
controlled by said communication apparatus;
means for identifying a configured relative location, within a radio frame, within which
configured relative location a signal comprising at least one of a synchronisation signal
and a reference signal is to be transmitted, said configured relative location being a
location within said radio frame relative both to a time range spanned by said radio frame
and to a frequency range spanned by said radio frame; and
means for receiving said signal at said identified configured relative location within said
radio frame;
wherein said configured relative location may comprise any of a plurality of relative
locations and wherein said identifying means is operable to determine which of said
plurality of relative locations said configured relative location comprises.
A mobile communication device for communicating with communication apparatus in a
cellular communication system using a plurality of radio frames said mobile
communication device comprising:
means for communicating in any of a plurality of communication cells, each being
provided on a respective component carrier operated by said communication apparatus;
means for receiving a first signal within a first radio frame transmitted in a first of said
plurality of cells using a first component carrier, said first signal being transmitted at a
predetermined relative location within said radio frame relative both to a time range
spanned by said first radio frame and to a frequency range spanned by said first radio
frame; and
means for identifying a configured relative location, within a radio frame, within which
location a second signal is to be transmitted, said configured relative location being a
location within said radio frame relative both to a time range spanned by said radio frame
and to a frequency range spanned by said radio frame;
wherein said receiving means is further operable to receive a second signal at said
configured relative location within said second radio frame;
wherein said first and second signals are of the same type as one another, each
comprising at least one of a synchronisation signal and a reference signal; and
wherein said identifying means is operable to identify a configured relative location
within said second radio frame that is different to the predetermined relative location
within said first radio frame.
A mobile communication according to claim 28 wherein said wherein said identifying
means is operable to infer the configured relative location of said second signal based on
timing information obtained the first signal.
A mobile communication according to claim 27 or 28 wherein said identifying means is
operable to identify said configured relative location from information communicated by
the communication apparatus for identifying said configured relative location.
A mobile communication according to claim 29 wherein said information for identifying
said configured relative location comprises a configuration index from which said
configured relative location can be derived.
A mobile communication according to claim 31 wherein the link between possible
configuration indexes and possible configured relative locations is represented by a look¬
up table in a memory of the mobile communication device.
A mobile communication according to claim 3 1 or 32 wherein the link between possible
configuration indexes and possible configured relative locations is represented by one or
more equations in a memory of the mobile communication device.
34. A mobile communication according to claim 29 wherein said information for identifying
said configured relative location comprises an explicit indication of said configured
relative location.
35. A mobile communication according to any one of claims 29 to 34 wherein said
information for identifying said configured relative location comprises a cell identity of
the cell in which said signal, or second signal, is communicated.
36. A mobile communication according to claim 27, 28 or 29 wherein said identifying means
is operable to identify said configured relative location by conducting a search for signals
comprising said at least one of a synchronisation signal and a reference signal and for
identifying said configured relative location from a signal detected during said search.
37. A mobile communication according to any one of claims 27 to 37 wherein said signal (or
each of said first and second signals) comprises a synchronisation signal and wherein the
mobile communication device further comprises means for synchronising with said
communication apparatus in dependence on said synchronisation signals.
38. A mobile communication according to claim 37 wherein said signal (or each of said first
and second signals) comprises a primary or secondary synchronisation signal.
39. A method performed by communication apparatus for communicating with a plurality of
mobile communication devices in a cellular communication system using a plurality of
radio frames, the method comprising:
operating a communication cell on an associated component carrier;
configuring said apparatus to communicate a signal comprising at least one of a
synchronisation signal and a reference signal at a configured relative location within a
radio frame to be transmitted in said communication cell using said component carrier,
said configured relative location being a location within said radio frame relative both to
a time range spanned by said radio frame and to a frequency range spanned by said radio
frame; and
communicating a signal at said configured relative location within said radio frame;
wherein said configuring step comprises configuring said apparatus to communicate said
signal at any of a plurality of relative locations within said radio frame.
40. A method performed by communication apparatus for communicating with a plurality of
mobile communication devices in a cellular communication system using a plurality of
radio frames the method comprising:
operating a plurality of communication cells on respective component carriers;
communicating a first signal within a first radio frame transmitted in a first of said
plurality of cells using a first component carrier, said first signal being transmitted at a
predetermined relative location within said radio frame relative both to a time range
spanned by said first radio frame and to a frequency range spanned by said first radio
frame;
configuring said apparatus to communicate a second signal at a configured relative
location within a second radio frame to be transmitted in a second of said plurality of
cells using a second component carrier, said configured relative location being a location
within said radio frame relative both to a time range spanned by said second radio frame
and to a frequency range spanned by said second radio frame; and
communicating a second signal at said configured relative location within said second
radio frame;
wherein said first and second signals are of the same type as one another, each
comprising at least one of a synchronisation signal and a reference signal; and
wherein said configuring step comprises configuring said apparatus to communicate said
second signal at a configured relative location within said second radio frame that is
different to the predetermined relative location within said first radio frame.
41. A method performed by a mobile communication device for communicating with
communication apparatus in a cellular communication system using a plurality of radio
frames said method comprising:
communicating in a communication cell on an associated component carrier controlled
by said communication apparatus;
identifying a configured relative location, within a radio frame, within which configured
relative location a signal comprising at least one of a synchronisation signal and a
reference signal is to be transmitted, said configured relative location being a location
within said radio frame relative both to a time range spanned by said radio frame and to a
frequency range spanned by said radio frame; and
receiving said signal at said identified configured relative location within said radio
frame;
wherein said configured relative location may comprise any of a plurality of relative
locations and wherein said identifying means is operable to determine which of said
plurality of relative locations said configured relative location comprises.
42. A method performed by a mobile communication device for communicating with
communication apparatus in a cellular communication system using a plurality of radio
frames said mobile communication device comprising:
communicating in any of a plurality of communication cells, each being provided on a
respective component carrier operated by said communication apparatus;
receiving a first signal within a first radio frame transmitted in a first of said plurality of
cells using a first component carrier, said first signal being transmitted at a predetermined
relative location within said radio frame relative both to a time range spanned by said
first radio frame and to a frequency range spanned by said first radio frame;
identifying a configured relative location, within a radio frame, within which location a
second signal is to be transmitted, said configured relative location being a location
within said radio frame relative both to a time range spanned by said radio frame and to a
frequency range spanned by said radio frame; and
receiving a second signal at said configured relative location within said second radio
frame;
wherein said first and second signals are of the same type as one another, each
comprising at least one of a synchronisation signal and a reference signal; and
wherein said identifying means is operable to identify a configured relative location
within said second radio frame that is different to the predetermined relative location
within said first radio frame.
43. A non-transitory computer program product comprising instructions operable to function
a programmable processor as communication apparatus according to any one of claims 1
to 26 or a communication device according to any one of claims 27 to 38.