COMMUNICATION SYSTEM
Technical Field
The present invention relates to a communication system and to components thereof for
providing communication services to mobile or fixed communication devices. The invention has
particular, but not exclusive, relevance to cell signal measurements and channel state information
reporting in Long Term Evolution (LTE) Advanced systems as currently defined in associated
3rd Generation Partnership Project (3GPP) standards documentation.
Background Art
In a cellular communications network, user equipment (UE) (such as mobile telephones,
mobile devices, mobile terminals, etc.) can communicate with other user equipment and/or
remote servers via base stations. LTE systems include an Evolved Universal Terrestrial Radio
Access Network (E-UTRAN) and an Evolved Packet Core (EPC) network (or simply 'core
network'). The E-UTRAN includes a number of base stations ('eNBs') for providing both userplane
(e.g. Packet Data Convergence Protocol (PDCP), Radio Link Control (RLC), Medium
Access Control (MAC) and PHYsical (PHY) layers) and control-plane (e.g. Radio Resource
Control (RRC)) protocol terminations towards the UE.
Depending on various criteria (such as the amount of data to be transmitted, radio
technologies supported by the mobile telephones, expected quality of service, subscription
settings, etc.), each base station is responsible for controlling the transmission timings,
frequencies, transmission powers, modulations, etc. employed by the mobile telephones attached
to the base station. In order to minimise disruption to the service and to maximise utilisation of
the available bandwidth, the base stations continuously adjust their own transmission power and
also that of the mobile telephones. Base stations also assign frequency bands and/or time slots to
mobile telephones, and also select and enforce the appropriate transmission technology to be
used between the base stations and the attached mobile telephones. By doing so, base stations
also reduce or eliminate any harmful interference caused by mobile telephones to each other or
to the base stations.
In order to optimise utilisation of their bandwidth, LTE base stations receive periodic
signal measurement reports from each served mobile telephone (based on measurement
configurations provided by the E-UTRAN), which include information about the perceived
signal quality on a given frequency band used by (or being a candidate frequency band for) that
mobile telephone. The served mobile telephones carry out measurements on reference signals
that are transmitted at a known (non-zero) power level. By comparing the received power level
to the reference power level, they are able to establish a measure of the signal degradation
between the base station transmitting and the mobile telephone receiving the signal. On the
other hand, interference is usually measured on resource blocks where transmissions of the
serving base station are muted (i.e. set to zero power). That way, any signal that can be detected
by the mobile telephone whilst the base station is known to transmit at zero power can be
classified as interference caused by other transmitters operating in the same frequency band (e.g.
neighbouring base stations and/or other mobile telephones). Depending on the measurement
configurations (which are provided by the E-UTRAN), the mobile telephones generate and send
measurement reports to their serving base stations. The measurement reports may be sent either
periodically or when predefined events occur (e.g. interference gets higher than a predetermined
threshold, signal quality falls below a predetermined level, etc).
These signal measurement reports are then used by the base stations in their decision to
allocate certain parts of their bandwidth to the served mobile telephones and/or to adjust their
transmission power and/or to hand over mobile telephones to other base stations (or other
frequency bands / other radio access technologies (RATs)) when the signal quality does not meet
the established criteria. The handing over of a mobile telephone might be necessary, for example,
when the mobile telephone has moved away from the given base station, and also when a signal
quality / interference problem has arisen.
A so-called Downlink Coordinated Multi-Point (CoMP) transmission/reception feature
was introduced in Rel-1 of the 3GPP standards documentation to improve, for example, the
coverage of high data rates for user equipment, temporary network deployment, cell edge
throughput and/or to increase system throughput. The CoMP feature established techniques for
compatible mobile telephones (and other user equipment) to communicate with multiple
transmission points (TPs), substantially simultaneously. The TPs typically include (any
combination of) base stations (eNBs), remote radio heads (RRHs), relay nodes (R s), and the
like. These techniques are described in, for example, TR 36.819 VI 1.1.0, the contents of which
are hereby incorporated by reference. In summary, CoMP may be used i) to optimise received
signal quality at the mobile telephone by transmitting the same signal from multiple TPs and/or
ii) to increase data throughput by sending different signals (e.g. different parts of the user data)
from different TPs concurrently (but of course without causing interference, e.g. by using
different frequencies/timing/codes/etc).
When multiple transmission points are used by the mobile telephone, it is configured to
measure and report the quality of the signals transmitted by each transmission point and also to
measure and report back any interference experienced so that each transmission point can adjust
its operation accordingly (i.e. to be able to transmit at/near an optimum power level and to keep
interference to a minimum). Since the mobile telephone in this case is located within the
overlapping coverage areas (cells) of multiple transmission points, these transmission points
need to coordinate the transmissions of their reference signals, in order to make it possible to
carry out the above described signal quality and interference measurements. In particular, when
CoMP is used, the different transmission points transmit their respective reference signals at
different times (whilst the other transmission points are muted), one by one, so that signal quality
can be measured effectively by the mobile telephone, for each transmission point. Additionally,
in order for the mobile telephone to able to measure interference caused by other transmitters
than the cooperating transmission points, the base stations need to be muted, temporarily, at the
same time, at least for the duration of the mobile telephone's measurements. Thus, the number
of measurements (to be configured for and performed by the mobile telephone) equals to the
number of transmission points (each one being a hypothetical interfering TP) plus one (for
determining interference caused by other transmitters).
In Release- 11, downlink CoMP has been specified to allow multiple transmission points
(e.g. base stations) to coordinate their downlink data transmissions. In order to support more
efficient utilisation of the downlink resources, the mobile telephone may be configured to report
channel state information (CSI) by measuring a set of non-zero power (NZP) reference signal
(RS or CSI-RS) resources - this set is known as the CoMP measurement set. For example, the
mobile telephone may carry out measurement of a reference signal received power (RSRP) and
report the results of this measurement to the base station which in turn can use the measurement
to adjust its operation and to manage the CoMP measurement set (e.g. to choose a CoMP
measurement set for which CSI feedback is required). The maximum size of the CoMP
measurement set is three NZP CSI-RS resources, selected from all possible CSI-RS resources
(defined as a CoMP Resource Management Set).
The mobile telephone may also be configured to perform one or more interference
measurements (CSI-IM). Each CSI-IM is associated with one interference measurement
resource (IMR), which is a set of resource elements on which interference measurements can be
made.
In a so-called 'CSI process', the E-UTRAN can request the mobile telephone to carry out
a combined measurement on a NZP CSI-RS resource and on an IMR. The mobile telephone
performs the combined measurements on resources indicated by the 'CSI process', and sends a
so-called 'CSI report' to the E-UTRAN, which includes the results of the combined
measurements. The mobile telephone can be configured to perform, in response to a given CSI
process, periodic and/or aperiodic CSI reporting.
A new LTE transmission mode ('Transmission mode 10' or 'TM10') has also been
defined in Rel-12 to provide support for CoMP functionalities. The relevant parameters of
transmission mode 10 are defined in 3GPP TS 36.213 (vl 1.1.0), the contents of which are
incorporated herein by reference. In particular, section 7.1 of TS 36.213 describes scrambling
identities for UE-specific reference signal generation, supported DCI formats and transmission
schemes. Section 7.2 describes that a mobile telephone in transmission mode 10 can be
configured with one or more CSI processes per serving cell (by higher layers). Each CSI process
is associated with a CSI-RS resource (defined in Section 7.2.5) and a CSI-interference
measurement (CSI-IM) resource (defined in Section 7.2.6). A CSI reported by the mobile
telephone corresponds to a CSI process configured by higher layers. Each CSI process can be
configured with or without PMI/RI reporting by higher layer signalling.
In Rel-12, in order to enhance small cell performance, mechanisms for interference
avoidance and coordination between macro and small cells as well as among small cells are
currently being considered. However, since clusters of relatively small cells are typically denser
than scenarios considered for the so-called Enhanced Inter-Cell Interference Coordination
(enhanced ICIC or elCIC) technique in Rel-10, or for the so-called Further Enhanced ICIC
(FelCIC) technique and CoMP in Rel-1 1, these techniques cannot be re-used without added
complexity to the user equipment and/or transmission points.
Furthermore, the carrier aggregation (CA) feature defined for LTE-Advanced supports
transmission bandwidths up to lOOMHz of spectrum by aggregating the resources of two or more
component carriers. When carrier aggregation is used there are a number of serving cells, one
for each component carrier. The radio resources connection is handled by one cell, the primary
serving cell, served by the primary component carrier (PCC), whilst user data may be
communicated via any of the component carriers, primary and/or any secondary component
carrier (SCC). However, the effective coverage of and/or perceived signal qualities offered by
the various serving cells may differ - either due to the different frequencies used in different
cells or due to power planning considerations (and possibly other factors influencing propagation
of transmitted signals). Therefore, the base station configures the mobile telephones it is serving
via its component carriers to carry out and report predetermined signal quality and interference
measurements (i.e. one or more CSI processes, depending on the number of cells to be
measured) so that it can take appropriate corrective actions when signal degradation is
experienced by user equipment within its cell(s).
3GPP has recently made a working assumption (at RANI meeting #71) that for the joint
operation of downlink CoMP and CA, the UE capability for the number of supported CSI
processes is defined as follows:
• Pcsi is the maximum number of CSI processes supported on a component carrier;
• Pcsi is provided per band combination;
• The Pcsi value applies to each component carrier within a band; and
· Pcsi can take a value in {1,3,4}.
In this context, band combination refers to a collection of bands. Therefore, it can be
seen that for a mobile telephone which is capable of performing up to a maximum of four
simultaneous CSI processes in transmission mode 10 (for both single carrier operation and
carrier aggregation), and assuming that there are five bands (component carriers) aggregated, this
means that there is always at least one band in which the mobile telephone cannot process any
CSI processes.
Summary of Invention
Technical Problem
In the case of joint CA and CoMP operation, the total number of CSI processes for CSI
feedback is limited to five from all component carriers. This limitation was introduced in order
to minimise the signalling needed between the base station and served user equipment and
thereby ensure effective utilisation of the radio interface between them. However, since a
maximum of five component carriers can be aggregated per transmission point, this limitation
means that it is not always possible to support CoMP operation when two or more component
carriers are configured. Even in the case of fewer than the maximum number of component
carriers being configured, different CoMP schemes cannot always be supported simultaneously
and/or adequately due to the limited number of CSI feedback processes that are available.
The present invention aims to provide an improved communication system and improved
components of the communication system which overcome or at least alleviate one or more of
the above issues. In particular, the invention aims to provide downlink (DL) CoMP CSI
feedback and IMR mechanisms, improve support for simultaneous CoMP and CA, and/or for
heterogeneous network (HetNet) services. The present invention also aims to reduce complexity
of the user equipment and the number of CSI feedbacks required for CoMP.
Solution to Problem
In one aspect, the present invention provides a network node for controlling coordinated
transmissions, in a communication system comprising at least one mobile device and a plurality
of transmission points which operate at least one cell, the network node comprising: means for
sending, to the at least one mobile device, a signalling message, the signalling message
comprising CSI (Channel State Information) process data that indicates a plurality of combined
measurements to be made by the mobile device, wherein the combined measurement is
associated with a respective different configuration of the plurality of transmission points and the
combined measurement comprises at least one signal quality measurement and at least one
interference measurement for the associated configuration of the plurality of transmission points;
and means for receiving, from the at least one mobile device, measurement results for a selected
one of the plurality of combined measurements and data identifying which one of the plurality of
combined measurements the results relate.
The combined measurement may identify: i) a first set of resource elements on which a
signal quality measurement is to be carried out by the at least one mobile device; and ii) a second
set of resource elements on which an interference measurement is to be carried out by the at least
one mobile device. The first set of resource elements may comprise at least one NZP (non-zero
power) resource element and the second set of resource elements comprises at least one ZP
(zero-power) resource element.
The network node may further comprise means for configuring the plurality of
transmission points in accordance with the CSI process data signalled to the mobile device.
The measurement results received from the at least one mobile device may comprise at
least one of: a CQI (Channel Quality Indicator) a RI (Rank Indicator) and a PMI (Precoding
Matrix Indicator).
The network node may further comprise means for controlling the coordinated
transmissions, by the plurality of transmission points, in dependence upon the measurement
results received from the at least one mobile device.
The data identifying which one of the plurality of combined measurements the results
relates may comprise: data identifying the CSI process ('CSI process id') and data identifying at
least one of a transmission point ('TP id') and an interference measurement resource ('IMR id').
The coordinated transmission points may be configured to coordinate transmissions in
accordance with one or more communication modes selected from the group comprising: i) joint
transmission (JT) mode in which multiple transmission points send data to the mobile device; ii)
CS/CB (Coordinated Scheduling/Beam forming) mode in which the mobile device receives
transmissions from one transmission point, and the transmission points coordinate their
scheduling and/or beam forming decisions to minimise interference between the transmissions;
and iii) DPS (Dynamic Point Selection) mode in which the mobile device receives transmissions
from a transmission point selected from a set of coordinating transmission points.
At least one of the plurality of transmission points may be selected from a group
comprising: i) a base station; ii) a RRH (remote radio head); and a R (relay node). The
network node may comprise a base station operating in accordance with the LTE (long term
evolution) set of standards. At least two cells operated by the plurality of transmission points
may be configured for CA (Carrier Aggregation).
The network node may further comprise means for generating the CSI process data.
In another aspect, the present invention provides a mobile device for a communication
system providing coordinated transmissions via a plurality of transmission points which operate
at least one cell, the mobile device comprising: means for receiving from a transmission point a
signalling message, the signalling message comprising CSI (Channel State Information) process
data that indicates a plurality of combined measurements to be made by the mobile device,
wherein the combined measurement is associated with a respective different configuration of the
plurality of transmission points and the combined measurement comprises at least one signal
quality measurement and at least one interference measurement for the associated configuration
of the plurality of transmission points; and means for sending, to a transmission point,
measurement results for a selected one of the plurality of combined measurements and data
identifying which one of the plurality of combined measurements the results relate.
The mobile device may further comprise a measurement module for obtaining signal
quality measurements and interference measurements of signals received from different
transmission points within the vicinity of the mobile device. The mobile device may further
comprise means for configuring the measurement module in accordance with the CSI process
data signalled by the transmission point.
The mobile device may be selected from a group comprising: i) a mobile telephone; ii) a
mobile terminal; and iii) UE (user equipment).
In yet another aspect, the present invention provides a network node for controlling
coordinated transmissions, in a communication system comprising at least one mobile device and
a plurality of transmission points which operate at least one cell, the network node comprising
transceiver circuitry for: sending, to the at least one mobile device, a signalling message, the
signalling message comprising CSI (Channel State Information) process data that indicates a
plurality of combined measurements to be made by the mobile device, wherein the combined
measurement is associated with a respective different configuration of the plurality of
transmission points and the combined measurement comprises at least one signal quality
measurement and at least one interference measurement for the associated configuration of the
plurality of transmission points; and receiving, from the at least one mobile device, measurement
results for a selected one of the plurality of combined measurements and data identifying which
one of the plurality of combined measurements the results relate.
In yet another aspect, the present invention provides a mobile device for a
communication system providing coordinated transmissions via a plurality of transmission points
which operate at least one cell, the mobile device comprising transceiver circuitry for: receiving
from a transmission point a signalling message, the signalling message comprising CSI (Channel
State Information) process data that indicates a plurality of combined measurements to be made
by the mobile device, wherein the combined measurement is associated with a respective
different configuration of the plurality of transmission points and the combined measurement
comprises at least one signal quality measurement and at least one interference measurement for
the associated configuration of the plurality of transmission points; and sending, to a
transmission point, measurement results for a selected one of the plurality of combined
measurements and data identifying which one of the plurality of combined measurements the
results relate.
In yet another aspect, the present invention provides a method performed by a network
node for controlling coordinated transmissions, in a communication system comprising at least
one mobile device and a plurality of transmission points which operate at least one cell, the
method comprising: sending, to the at least one mobile device, a signalling message, the
signalling message comprising CSI (Channel State Information) process data that indicates a
plurality of combined measurements to be made by the mobile device, wherein the combined
measurement is associated with a respective different configuration of the plurality of
transmission points and the combined measurement comprises at least one signal quality
measurement and at least one interference measurement for the associated configuration of the
plurality of transmission points; and receiving, from the at least one mobile device, measurement
results for a selected one of the plurality of combined measurements and data identifying which
one of the plurality of combined measurements the results relate.
In yet another aspect, the present invention provides a method performed by a mobile
device for a communication system providing coordinated transmissions via a plurality of
transmission points which operate at least one cell, the method comprising: receiving from a
transmission point a signalling message, the signalling message comprising CSI (Channel State
Information) process data that indicates a plurality of combined measurements to be made by the
mobile device, wherein the combined measurement is associated with a respective different
configuration of the plurality of transmission points and the combined measurement comprises at
least one signal quality measurement and at least one interference measurement for the
associated configuration of the plurality of transmission points; and sending, to a transmission
point, measurement results for a selected one of the plurality of combined measurements and
data identifying which one of the plurality of combined measurements the results relate.
The invention also provides a communication system comprising the above described
network node and the above described mobile device.
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 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 mobile telecommunication system of a type to which
the invention is applicable;
Figure 2a illustrates a generic frame structure defined for use in the LTE communication
network;
Figure 2b illustrates the way in which a slot illustrated in Figure 2a is formed of a number
of time-frequency resources;
Figures 3a, 3b and 3c schematically illustrate different mobile telecommunication system
scenarios having multiple, coordinated network transmission points;
Figure 4 is a block diagram illustrating the main components of the base station forming
part of the system shown in Figure 1;
Figure 5 is a block diagram illustrating the main components of a mobile telephone
forming part of the system shown in Figure ;
Figure 6 illustrates an exemplary IMR configuration according to an embodiment of the
present invention; and
Figure 7 is an exemplary timing diagram illustrating a method performed by components
of the mobile telecommunication system of Figure 1 whilst carrying out an embodiment of the
invention.
Description of Embodiments
Overview
Figure 1 schematically illustrates a mobile (cellular) telecommunication system 1
including a mobile telephone 3 (or other compatible user equipment) served via the cells of a
plurality of base stations 5-1 to 5-3. The telecommunication system 1 also comprises a core
network 8. As those skilled in the art will appreciate, whilst one mobile telephone 3 and three
base stations 5 are shown in Figure 1 for illustration purposes, the system, when implemented,
will typically include other base stations and mobile telephones.
The base stations 5 are connected to each other via a so-called X2 interface, and to the
core network 8 via an S1 interface. The core network 8 comprises, amongst other things, a
mobility management entity (MME) 12, a serving gateway (SGW) 14 and a Packet Data
Network (PDN) Gateway (PGW) 16.
As will be understood by those skilled in the art, each base station 5 operates one or more
base station cells (not shown) in which communications can be made between the base station 5
and the mobile telephone 3. A user of the mobile telephone 3 can communicate with other users
and/or remote servers via the base station 5 and the core network 8.
LTE sub-frame data structure
Before discussing the specific ways in which the mobile telephone 3 can communicate
with the multiple transmission points, a brief description will be given of the access scheme and
a general frame structure agreed for LTE communications. An Orthogonal Frequency Division
Multiple Access (OFDMA) technique is used for the downlink to allow the mobile telephone 3
to receive data over the air interface with the base station 5. Different sub-carriers are allocated
by the base station 5 (for a predetermined amount of time) to the mobile telephone 3 depending
on the amount of data to be sent to the mobile telephone 3. These blocks of sub-carriers are
referred to as physical resource blocks (PRBs) in the LTE specifications. PRBs thus have a time
and frequency dimension. The base station 5 dynamically allocates PRBs for each device that it
is serving and signals the allocations for each sub-frame (TTI) to each of the scheduled devices
in a control channel.
Figure 2a illustrates one generic frame structure agreed for LTE communications over the
air interface with the base station 5. As shown, one frame 3 is 10 msec long and comprises ten
sub-frames 15 of 1msec duration (known as a Transmission Time Interval (TTI)). Each subframe
or TTI comprises two slots 17 of 0.5ms duration. Each slot 17 comprises either six or
seven OFDM symbols 19, depending on whether the normal or extended cyclic prefix (CP) is
employed. The total number of available sub-carriers depends on the overall transmission
bandwidth of the system. The LTE specifications define parameters for system bandwidths from
1.4 MHz to 20 MHz and one PRB is currently defined to comprise 12 consecutive subcarriers for
one slot 17 (although this could clearly be different). The transmitted downlink signal comprises
NBW subcarriers for a duration of NsymbOFDM symbols. It can be represented by a resource grid
as illustrated in Figure 2b. Each box in the grid represents a single sub-carrier for one symbol
period and is referred to as a resource element (RE). As shown, each PRB 2 1 is formed from
twelve consecutive sub-carriers and (in this case) seven symbols for each subcarrier; although in
practice the same allocations are made in the second slot 17 of each sub-frame 15 as well.
In the case of carrier aggregation, multiple carriers are provided, each having the frame
structure illustrated in Figures 2a and 2b, but separated in frequency so that they do not interfere.
Some of the resource elements are configured to carry the reference signals used for
signal quality measurements. Similarly, some of the resource elements can be transmitted at
zero power level for facilitating the above described interference measurements. The CSI
process informs the mobile telephone 3 which resource elements of which carriers are currently
configured to carry the NZP CSI-RS and ZP CSI-IM signals to be measured and reported.
In this embodiment, the base stations 5 are arranged to be able to communicate with the
mobile telephone 3 as a number of coordinated transmission points. Optionally, one or more of
the base stations 5 may be configured to provide aggregated component carriers. The
transmission points (TPs) - the base stations 5 in the embodiments, co-operate together to co
ordinate their multi-point transmissions. Typically, different sets of co-ordinating transmission
points will be provided within the communications system. A number of different multi-point
transmission modes are possible, as follows:
1. Joint Transmission (JT). In this case the mobile telephone 3 receives
transmissions from multiple transmission points (TPs) on a time-frequency
resource (such as on a PRB on a sub-frame). These transmissions may be
carrying the same data (such that the signals from each TP can be combined by
the mobile telephone 3 and thereby improve the quality of the received signal) or
different data (such that more data per time-frequency resource is sent to the
mobile telephone 3) from the TPs.
2. Coordinated scheduling/beam forming (CS/CB). In this case the mobile
telephone 3 receives transmissions from only one TP on any one time-frequency
resource, and the TPs co-ordinate their scheduling and/or beam forming decisions
to minimise interference between the transmissions. The transmitting points that
are used are chosen semi-statically - such that they change relatively infrequently.
3. Dynamic Point Selection (DPS). In this case the mobile telephone 3 receives
transmissions on a time-frequency resource from only one TP selected from the
set of co-ordinating transmission points; but the selected TP may change rapidly
(from one sub-frame to another) based on the instantaneous radio channel
conditions between the mobile telephone 3 and the transmission points.
Depending on the number of transmission points, and whether any of the base stations 5
implement carrier aggregation functionality, there are a number of cells that need to be measured
and reported by the mobile telephone 3 in order to assist the serving base station(s) 5 in
optimising signal conditions within the cells of the communication system 1.
In this embodiment, the serving base station 5 (e.g. base station 5-1) configures the
mobile telephone 3 to measure and report the CSI of a set of non-zero power CSI-RS resources
(i.e. the CoMP measurement set). The mobile telephone 3 may also be configured with one or
more interference measurements. Each interference measurement is associated with one CSIinterference
measurement resource (IMR), which is a set of REs on which the mobile telephone
3 is instructed to measure interference.
As specified in the relevant 3GPP standards, a CSI process is identified by a CSI process
index and a serving cell index. The serving cell index identifies the transmission point and a
carrier (i.e. a cell of the base station 5 sending the CSI process to the mobile telephone 3) for
which signal measurements (on NZP CSI-RS) and interference measurements (on ZP IMR)
should be carried out by the mobile telephone 3. E-UTRAN configures at most five CSI
processes across all serving cells (i.e. for up to five component carriers) in order to keep UE
complexity and feedback overhead at a minimum.
However, in this proposal, one CSI process is advantageously associated with multiple
carriers (i.e. multiple TPs and/or component carriers in case of CA) and multiple IMR
configurations. In particular, rather than each base station 5 configuring one signal quality
measurement and one interference measurement per CSI process (i.e. each base station
configuring each CSI process for a single carrier only), in this embodiment, each CSI process
can be associated with multiple transmission points and can specify multiple signal quality and
interference measurements. This allows for an increase of the number of configurations without
requiring an exchange of additional messages between the base stations 5 and the mobile
telephone 3 to configure such additional measurements and also without an impact on the CoMP
throughput performance gain. Increasing the number of configurations for the interference part
of CSI can also improve the interference measurement accuracy and performance. On the other
hand, if only five (or less) configurations are needed, it is possible to implement them using less
signalling thus essentially saving system resources which then can be used to transmit e.g. user
data.
When the mobile telephone 3 reports the results of the measurements to one of the CoMP
transmission points, it identifies which measurement is being reported (rather than just
identifying the CSI process). For example, the mobile telephone 3 may include in the CSI
feedback, reporting information identifying the interference measurement that is being reported
(e.g. an IMR ID) and/or an index of the combination of transmission point (or carrier) and IMR
(TP/IMR index).
The benefit of this approach is that more measurements can be configured using the same
amount of messages and it is also possible to configure measurements for multiple (or even all)
CoMP transmission points (or carriers) by a single transmission point, in one message. Even
when additional measurements are configured for (and carrier out by) the mobile telephone,
since only the results of relevant measurements need to be reported (i.e. carriers on which the UE
is experiencing low signal quality and/or high interference), the amount of information (and the
number of messages) to be sent by the mobile telephone 3 does not increase (significantly) even
when additional measurements have been configured. However, since more interference
measurements can be configured and performed by the mobile telephone 3 compared to methods
using a single IMR measurement per CSI process, the accuracy of measurements is likely to
increase.
On the other hand, if the same amount of measurements are to be configured (i.e. up to
five CSI processes as per current 3GPP requirements), it is possible to configure those
measurements using fewer messages (even in a single message) thus reducing usage of the air
interface resource between the base stations 5 and the mobile telephone 3.
Although not shown on Figure 1, the telecommunication system 1 may also comprise one
or more Remote Radio Heads (RRHs) and/or relay nodes (RNs) in addition to (or instead of any
of) the base stations 5-1 to 5-3. If present, the main difference between 'regular' base stations 5-
1to 5-3 and any RRH or relay node is that RRHs and relay nodes are not connected to the core
network 8 directly. Instead, the RRH is typically connected to a master (or 'donor') base station
by a high speed communication link whilst relay nodes are typically connected to a donor base
station via an air interface. The RRH and the RN may either act just like a remote antenna of the
base station - such that the signals broadcast by the RRH/RN are the same as those broadcast by
its donor base station (e.g. the RRH/RN may use the same cell ID as the 'donor' base station's
cell) or may act as a base station itself serving user equipment within its own cell (which in this
case may have a different cell ID to that of the cell of the 'donor' base station).
CoMP transmission schemes can be generally classified to belong to one (or a
combination) of the following four main scenarios:
1. Homogeneous network with intra-site (i.e. intra base station) CoMP;
2. Homogeneous network with high transmit (Tx) power Remote Radio Heads
(RRHs);
3. Heterogeneous network with low power RRHs within the coverage area of a
macrocell (e.g. a base station cell) where the transmission/reception points created
by the RRHs have different cell identities than the macro cell; and
4. Heterogeneous network with low power RRHs within the coverage area of
macrocell (e.g. a base station cell) where the transmission/reception points created
by the RRHs have the same cell identity as the macro cell.
Figures 3a to 3c schematically illustrate examples of the main CoMP transmission
scenarios for the provision of multiple, coordinated network transmission points.
Figure 3a shows an example for implementing a homogeneous network with intra-site
CoMP (scenario 1). In this case, the middle base station may be configured to perform
coordination of multi-point transmissions (by this and any neighbouring base stations) within the
geographical area defined by the coordinating base station's cells. When transmissions are
coordinated between neighbouring base stations, throughput and/or signal quality along the
common cell edge can be improved.
Figure 3b shows an example for implementing a homogeneous network with high Tx
power RRHs, controlled by a single base station (scenario 2). In this case, the remote radio
heads are connected to the master base station (shown in the middle) via high-speed optical fiber
links. Such arrangement allows the master base station to perform coordination of multi-point
transmissions even beyond the geographical area of its cells.
Figure 3c shows an example for implementing either one of scenario 3 or 4 above. In
this case, a heterogeneous network is shown with low power RRHs within the coverage area of a
macrocell (e.g. a master base station cell). The transmission/reception points created by the
RRHs may have different cell identities than the macro cell (scenario 3) or have the same cell
identity as the macro cell (scenario 4). The remote radio heads are connected to the master base
station (shown in the middle) via high-speed optical fiber links, as above. However, in these
scenarios, rather than extending the coordinated geographical area as above, the number of radio
cells (and hence the available bandwidth) within the geographical area of the master base
station's cell(s) is multiplied.
Relay nodes can be deployed and used to provide additional coverage and/or additional
transmission points in generally the same manner as the RRHs shown in Figure 3b. However,
relay nodes are typically connected to their respective master base stations (called 'donor base
stations') using a wireless link (an air interface) rather than an optical fiber link.
Base station
Figure 4 is a block diagram illustrating the main components of a base station 5 shown in
Figure 1. The base station 5 is a communications node providing services to user equipment 3
within its coverage area. In the embodiments according to the invention, communications
between the various base stations 5 and the user equipment 3 are coordinated. As shown, the
base station 5 includes a transceiver circuit 51 which transmits signals to, and receives signals
from, the mobile telephone 3 via at least one antenna 53. The base station 5 also transmits
signals to and receives signals from the core network 8 and other neighbouring base stations 5
via a network interface 55 (X2 interface for communicating with neighbouring base stations 5
and S1 interface for communicating with the core network 8). The operation of the transceiver
circuit 5 1 is controlled by a controller 57 in accordance with software stored in memory 59. The
software includes, among other things, an operating system 61, a communications control
module 63, a CoMP module 65, a carrier aggregation module 67, and a CSI process
configuration module 69.
The communications control module 63 is operable to control communications between
the base station 5 and the mobile telephone 3, and the core network devices.
The CoMP module 65 is operable to coordinate multi-point transmissions between the
cell(s) of this base station 5 and the mobile telephone 3 served by this base station (and any
further base station). The CoMP module 65 may communicate with corresponding modules of
other base stations to ensure that coordination is maintained between the various base stations
and may also assist the communications control module 63 to carry out control of
communications using CoMP services.
The carrier aggregation module 67 is operable to set up and maintain aggregated carriers
(i.e. primary and secondary component carriers) for communications between the cells of this
base station 5 and the mobile telephones 3 served by the base station 5.
The CSI process configuration module 69 is operable to configure signal quality
indication and interference related measurements and reporting for the mobile telephones 3
served by this base station 5. The CSI process configuration module 69 is also operable to
monitor (e.g. via the CoMP module 65 and the carrier aggregation module 67) whether or not
any cell of the base station 5 is involved in provision of CoMP and/or CA services, and to
configure CSI processes for the mobile telephones 3 accordingly.
Mobile Telephone
Figure 5 is a block diagram illustrating the main components of the mobile telephone 3
shown in Figure 1. As shown, the mobile telephone 3 has a transceiver circuit 31 that is operable
to transmit signals to and to receive signals from a base station 5 via one or more antenna 33.
The mobile telephone 3 has a controller 37 to control the operation of the mobile telephone 3.
The controller 37 is associated with a memory 39 and is coupled to the transceiver circuit 31.
Although not necessarily shown in Figure 5, the mobile telephone 3 may of course have all the
usual functionality of a conventional mobile telephone 3 (such as a user interface 35) and this
may be provided by any one or any combination of hardware, software and firmware, as
appropriate. Software may be pre-installed in the memory 39 and/or may be downloaded via the
telecommunications network or from a removable data storage device (RMD), for example.
The controller 37 is configured to control overall operation of the mobile telephone 3 by,
in this example, program instructions or software instructions stored within memory 39. As
shown, these software instructions include, among other things, an operating system 41, a
communications control module 43, a CSI process module 45, and a measurement module 47.
The communications control module 43 is operable to control the communication
between the mobile telephone 3 and the base station(s) 5. The communications control module
43 also controls the separate flows of uplink data and control data that are to be transmitted to
the base station 5. When CA services are in use, the communications control module 43 is
operable to control communications via the aggregated primary and secondary component
carriers. When CoMP services are in use, the communications control module 43 is operable to
control coordinated communications between the mobile telephone 3 and the multiple
transmission points.
The CSI process module 45 is operable to receive and enforce configurations for signal
quality indication and interference related measurements and reporting to assist the serving base
station(s) 5. The CSI process module 45 is operable to communicate with the corresponding
module (i.e. the CSI process configuration module 69) of the base station 5.
The measurement module 47 is operable to carry out signal measurements to determine
an indication of signal quality / interference experienced by the mobile telephone 3. The
measurement module 47 is also operable to provide the results of such measurements to the
serving base station(s) 5 (via the CSI process module 45 and the transceiver circuit 31).
In the above description, the mobile telephone 3 and the base station 5 are described for
ease of understanding as having a number of discrete modules (such as the communications
control modules, the CoMP module, and the measurement module). 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. These
modules may also be implemented in software, hardware, firmware or a mix of these.
A number of different embodiments will now be described that illustrate how the
invention can be put into effect using the mobile telephone 3 and base stations 5 (as exemplary
transmission points) of Figure 1.
Operation - CSI Association with multiple TP and IMR Configurations
In this embodiment, the mobile telephone 3 is configured to measure interference on an
IMR whilst the base station 5 (the one that is considered to be the interfering TP under that
hypothesis) transmits data symbols on those IMR REs. Within the CoMP coordinating TPs, it is
also possible for the network to transmit non-PDSCH (i.e. non-data) signals on the IMR REs
used by the mobile telephone 3 for interference measurement to generate a precise interference
scenario (PDSCH stands for Physical Downlink Shared Channel, i.e. the main downlink databearing
channel in LTE).
Channel Quality Indication (CQI) comprises information signalled by the mobile
telephone 3 to the serving base station 5 to indicate a suitable data rate (typically a Modulation
and Coding Scheme (MCS) value) for downlink transmissions. CQI is usually based on a
measurement of the received downlink Signal to Interference plus Noise Ratio (SINR) and
information about the mobile telephone's 3 receiver characteristics. Further details about the
CQI can be found in 3GPP TS 36.213, section 7.2.3.
CQI reporting is an important element of LTE and has significant impact on the system
performance. There are two types of CQI reports in LTE: periodic and aperiodic. The periodic
CQI report is carried by either the Physical Uplink Control Channel (PUCCH) or the Physical
Uplink Shared Channel (PUSCH), depending on whether or not the mobile telephone 3 has
uplink data to send in the same subframe as the scheduled periodic CQI report. The aperiodic
CQI report, which may be used to provide a more granular measurement than the periodic one, is
transmitted on the PUSCH.
The granularity of the CQI report can be divided into three levels: wideband, UE selected
subband, and higher layer configured subband. The wideband report provides one CQI value for
the entire downlink system bandwidth. The UE selected subband CQI report divides the system
bandwidth into multiple subbands, then reports one CQI value for the wideband and one
differential CQI value for a set of subbands selected (i.e. preferred) by the mobile telephone 3.
The higher layer configured subband report divides the entire system bandwidth into multiple
subbands, then reports one wideband CQI value and multiple differential CQI values, one for
each subband. This report provides the highest granularity.
PMI (Precoding Matrix Indicator) and RI (Rank Indication) may also be reported by the
mobile telephone 3 together with the CQI report. PMI indicates the codebook (pre-agreed
parameters) the base station 5 should use for data transmission over its multiple antennas 53
based on an evaluation of a received reference signal (e.g. RSRP). RI indicates the number of
spatial transmission layers that the mobile telephone 3 can distinguish. Spatial multiplexing can
be supported only when RI>1. For spatial multiplexing, CQI is reported per codeword.
In order to obtain accurate CQI feedback at the serving base station 5, the mobile
telephone 3 needs to send multiple CQI reports with different interference hypothesis for the
serving TP (e.g. base station 5-1) and for cooperating TPs (e.g. base stations 5-2 and 5-3)
resulting in a significant feedback overhead. Therefore, CQI reports are typically sent every few
milliseconds (approximately every 5-10ms for voice traffic, and possibly more often for other
types of traffic) and for each transmission point (e.g. all of base stations 5-1 to 5-3 and for all
component carriers in case of CA). However, too frequent CQI reporting is wasteful of air
interface resources that would otherwise be used to transmit user data. Consequently, the more
CQI feedback is sent, the less user data can be transmitted over the air interface (although signal
quality may improve).
As shown in Table 1, each CSI process includes one NZP CSI-RS and one IMR for each
TP, hence four CQI feedback reports per component carrier for a CoMP scenario with three TPs
would be sent every 5-10ms. However, for a specific CoMP scheme, such as DPS, DPB or JT,
the CoMP scheduler (i.e. the CoMP module 65) of the base station 5 would only need to know
the full CSI information of one or two of these CSI processes, e.g. the best one or two of the CSI
processes #1, #2, and #3 shown in Table 1. Consequently, the mobile telephone 3 does not need
to send all four possible CQI feedback reports, only the most relevant ones. The mobile
telephone 3 may include in its CQI feedback report the CQI value(s) for the subband
measurement, the wideband measurement, or both.
Table 1 - existing configuration of CSI processes
(3 TPs, e.g. base stations 5-1, 5-2, and 5-3 of Figure 1)
In this embodiment, in order to achieve more accurate CQI per TP for CoMP feedback
without increasing the number of CSI reporting, a single CSI process (i.e. a CSI process set) is
associated with multiple TPs and this single CSI process includes multiple instances of NZP
CSI-RS and multiple instances of IMR where each NZP CSI-RS instance is linked to one TP and
each IMR instance could be linked to one or more TPs.
This scheme can advantageously facilitate vendor specific precoding optimisation
schemes at the transmission point without requiring the mobile telephone 3 to be aware of the
precise precoding matrix. This is particularly useful in scenarios where UE specific elevation
beamforming is required as in the case of some urban scenarios for Release- 12 (e.g. such urban
scenarios may include a mixture of skyscrapers, office buildings and residential buildings, with
some mobile telephones 3 being located at ground level and others distributed at various heights
in the buildings).
Table 2 shows an example of the new CSI process configurations for a mobile telephone
3 in the case of two transmission points. CSI process #0 and CSI process # 1 are designed for
this purpose. In this example, TP2 (e.g. base station 5-2) is transmitting (with some random
weights) using Rank Indicator (RI) set to 1 and Precoding Matrix Indicator (PMI) set to 1, i.e.
RIl/PMI-1, on IMR # 1 and using RI set to 1 and PMI set to 2, i.e. RI1/PMI-2, on IMR #2.
(The reader is referred to 3GPP TS 36.213 Section 7.2 and 7.2.4 for further details of
what the RI and PMI are used for.) The mobile telephone 3 only has to perform interference
measurements on the configured IMR REs. If only a single TP is configured for a given CSI
process, the mobile telephone 3 may send back the best CQI report in the CSI process plus the
corresponding IMR ID with the lowest measured interference (i.e. either IMR # 1 or IMR #2 for
CSI process #0, and either IMR #3 or IMR #4 for CSI process # 1 of this example), i.e. the PMI
that causes the least interference to the reporting mobile telephone 3.
Table 2 - exemplary configuration of CSIprocesses
(2 TPs, e.g. base stations 5-1 and 5-2 of Figure 1)
The primary use case of this scheme is for CQI feedback overhead reduction and to
support CoMP across multiple component carriers. Although this approach requires the mobile
telephone 3 to compute several hypothesis in each CSI process, the complexity of the mobile
telephone 3 is not affected because it is required to carry out the same number of.computations
regardless of whether several hypotheses are defined in one process (as in this embodiment) or
only one hypothesis is defined per CSI process but there are separate CSI processes for each TPs
(i.e. in case each CSI process includes one configuration only). Beneficially, it is also possible
to re-use the PMI value within a particular CSI process among hypotheses that share the same
NZP part so that the common measurements do not have to be repeated for each hypothesis
(because in this case each hypothesis within any CSI process measures the same NZP reference
signal and hence it is likely to give the same result). This can be achieved by configuring an
R PMI reference process. In this context, the reference process refers to the reference PMI/RI
values used for the NZP signal part, not the interference part (i.e. IMR part) shown in Table 2.
One possible way is to re-use the Release- 11 RI/PMI reference process, which can be
configured for a dependent CSI process. A dependent CSI process is expected to be configured
to use the same set of restricted RIs and/or PMIs with codebook subset restriction as the
reference CSI process. As long as the total number of hypotheses remains the same, the
complexity remains fixed and with re-use of PMI within a process complexity of the mobile
telephone 3 can be further limited.
For a given set of hypotheses (where 'hypothesis' means one combination of TP and
IMR), the present proposal reduces reporting overhead (whilst it does not change measurement
complexity). As illustrated by the two examples below, the present proposal (denoted 'Case 2')
achieves a lower reporting overhead than existing methods (denoted 'Case G ) with the same (or
possibly reduced) measurement complexity.
CASE 1 (legacy, 4 CSI processes, 4 hypotheses)
CSIProcess TP IMR
0 # 1 # 1
1 # 1 #2
2 #2 #3
3 #2 #4
CASE 2 (this proposal, 2 CSI processes, 4 hypotheses)
CSIProcess TP IMR
0 # 1 # 1
# 1 #2
1 #2 #3
#2 #4
Table 3 shows an example of a modified CSI process configuration for a mobile
telephone 3 in communication with three transmission points (e.g. base stations 5-1 to 5-3), each
operating two cells (two component carriers, CCs, possibly using carrier aggregation as well). In
this case, multiple NZP CSI-RS and multiple IMRs are configured for each CSI process and each
IMR is linked to multiple TPs. However, despite the relatively high number of configured
measurements, the mobile telephone 3 only needs to feedback a single CQI report for each CSI
process. Advantageously, the mobile telephone 3 sends back the highest CQI report and the
corresponding index of the TP/IMR ID combination.
Signal part Interference Part
IMR Description
(NZP CSI-RS) (ZP CSI-RS)
Interference outside
cooperating set
TP#1, CCO IMR#1
TP1, TP2 and TP3 are muted
(OFF) on Component Carrier 0
Interference outside
CSI
cooperating set
process TP #2, CCO IMR # 1
TP1, TP2 and TP3 are muted
#0
(OFF) on Component Carrier 0
Interference outside
cooperating set
TP #3, CCO IMR # 1
TP1, TP2 and TP3 are muted
(OFF) on Component Carrier 0
Interference outside
cooperating set
TP #1, CC1 IMR #2
TP1, TP2 and TP3 are muted
(OFF) on Component Carrier 1
Interference outside
CSI
cooperating set
process TP #2, CC1 IMR #2
TP1, TP2 and TP3 are muted
#1
(OFF) on Component Carrier 1
Interference outside
cooperating set
TP #3, CC1 IMR #2
TP1, TP2 and TP3 are muted
(OFF) on Component Carrier 1
Table 3 - exemplary configuration of CSIprocesses
(3 TPs, e.g. base stations 5-1, 5-2, and 5-3 of Figure 1)
For any number of coordinated transmission points, the CSI processes may be defined as
follows:
CSI-Process-rl2:
{
CSI-Process-ID Integer
NZP-CSI-RS-ID Multiple Instances
CSI-IM-ID Multiple Instances
}
In the above embodiments, each IMR can be configured independently e.g. with an RIO
'subframeConfig' and an RIO 'resourceConfig', where 'resourceConfig' is for four REs/PRB.
The benefit of the proposal is that accurate per TP CQI for CoMP feedback can be
achieved without increasing the number of CSI reporting signalling. The only additional data to
be exchanged is the index of the selected IMR, i.e. approximately 2-3 bits of data.
An alternative to the above proposal would be to increase the number of CSI processes
according to the number of transmission points / component carriers. However, given the
definition of CSI process and CQI feedback currently used in Rel-1 1, this would result in
significantly larger feedback overhead and increased UE processing complexity.
Operation - CSI-IMR measurement and configuration
The current version of the 3GPP TR 36.213 standard (vl 1.1.0) specifies CQI as follows:
"Based on an unrestricted observation interval in time and frequency, the UE shall derive for
each CQI value reported in uplink subframe n the highest CQI index between 1 and 15".
However, the standard does not specify which CSI-IM REs may be used or how many
IMRs may be used. The set of CSI-IM REs to use for an interference estimate is currently not
specified by 3GPP. Based on the contents of 3GPP document no. Rl-125370, the following
observations can be made:
• the mobile telephone 3 may employ excessive time domain averaging;
• it is not clear how much averaging in frequency is allowed; and
• the absence of RANI guidance on interference leads to inconsistent UE behaviour
and performance loss.
Further, in 3GPP document no. Rl-125051 the following observations are made:
• averaging in time can also degrade the estimation performance; and
• averaging interference over multiple IMRs may significantly increase the CQI
error.
The proposed scheme agrees with the existing requirements for CSI-IMR RE
configuration, i.e. that the IMR measurements for a single CSI process shall be as close to each
other as possible (i.e. a 'time domain requirement') and that the measurement of the interference
part should be within the subband of the signal part (i.e. a 'frequency domain requirement').
The additional IMRs may be configured only on (UE and/or network) selected subbands
and the selected TP/IMR index may only need to be sent whenever there are changes to the
selected TP and/or IMR ID.
The density of the IMR configuration can be reconfigured or reduced in frequency
domain, e.g. within certain selected sub-band. This allows to achieve a reduction of
measurement complexity by reducing the number of IMR measurement to be performed in the
frequency domain.
Figure 6 illustrates an example where each IMR utilizes four REs from two PRBs, e.g.
IMR-1A uses two REs from PRBO and two additional REs from PRBl. In this embodiment, in
accordance with section 7.2.6 of 3GPP TS 36.213 (vl 1.2.0), the mobile telephone is configured
with four CSI-IM resource configurations.
In particular, the following parameters are configured (e.g. using higher layer signalling, e.g.
RRC signalling) for each CSI-IM resource configuration:
• Zero-power CSI RS Configuration (as defined in Table 6.10.5.2-1 and Table
6.10.5.2-2 of 3GPP TS 36.21 1); and
• Zero-power CSI RS subframe configuration (as defined in section 6.10.5.3 of
3GPP TS 36.211).
Summary
In summary, with the embodiments described above, the number of configurable
interference hypothesis was increased without increasing the number of CQI feedback reporting.
Each CSI process may be associated with multiple serving TPs and multiple IMR configurations
with single CQI feedback indicating the corresponding IMR ID with the highest CQI and/or PMI
that causes least interference to the reporting mobile telephone 3.
Figure 7 shows an example timing diagram illustrating a method performed by
components of the telecommunication system 1 when configuring and performing signal quality
and interference related measurements and reporting.
The process begins in step S70.1, in which the base station 5-1 provides information
relating to the possible CSI process configurations to the mobile telephone 3. The CSI process
configurations, including the IMR configuration, are configured by higher layer (e.g. RRC layer)
signalling. However, in this embodiment, the mobile telephone 3 only reports the hypothesis
with the best (one or two) CQI report within each CSI process rather than all of them. Therefore,
the base station 5-1 includes in the CSI process configurations, data identifying each respective
hypothesis (measurement configuration). For example, a hypothesis may be identified using an
index of the transmission points (i.e. a 'TP index') and/or an index of the corresponding
interference measurement resources (i.e. an 'IMR index'). When the mobile telephone 3
subsequently reports the measurement results (e.g. the best CQI report) for a particular CSI
process, the IMR index alone (or in combination with the TP index) may be sufficient to
uniquely identify which measurement configuration (hypothesis) each result relates to. However,
a particular hypothesis may be identified by other methods, e.g. using the CSI index in
combination with the TP index and/or the IMR index as long as the base station 5-1 and the
mobile telephone 3 agree on the method used.
At the end of step S701, the measurement configurations (including the data identifying
each respective hypothesis) are available to the respective modules of the mobile telephone 3
(stored in memory 39) and the base station 5-1 (stored in memory 59).
In step S703, the CSI process configuration module 69 generates and sends (via the
transceiver circuit 51) a 'CSI Process' request message to the corresponding module (CSI
process module 45) of the mobile telephone 3. This message requests the mobile telephone 3 to
perform signal quality and interference measurements and reporting for CoMP services. It does
this by including in this message data identifying the CSI process configurations to be used
during the measurements, such as an identification of the CSI process, an identification of the
resource elements to be measured to obtain a measure of signal quality (of a given TP), and/or an
identification of the IMR(s) to be measured as part of that CSI process.
In response to receiving the CSI process message, the mobile telephone 3 configures, in
step S705, its measurement module 47 in accordance with the received configuration data and
starts monitoring signal conditions as defined therein.
In step S707, the measurement module 47 performs the necessary cell measurements
(CSI measurements) in respect of the resource elements identified in the received configuration
data (i.e. it measures NZP RS resource elements in order to obtain a measure of signal quality
and it measures ZP resource elements in order to obtain a measure of interference). Once the
measurements are completed, in step S709, the CSI process module 45 generates a CSI
measurement report, e.g. as prescribed by the 'CSI Process' request message received at step
S703 and/or in accordance with the specific CoMP scheme being used.
In step S71 1, the CSI process module 45 sends the generated CSI measurement report
(via the transceiver circuit 31) to the base station 5-1 in a CSI report message. This
measurement report includes the results of only those measurements (e.g. one or more CQI
value(s)), performed in step S707, that are considered relevant for the specific CoMP scheme
being used. The measurement report also identifies the corresponding hypothesis for each
measurement result being reported using the agreed identification method for that CSI process,
e.g. TP and/or IMR index. The measurements and the associated reporting procedure (i.e. steps
S707 to S71 1) may be repeated periodically if it has been requested to do so in the preceding CSI
process message. Therefore, a single message at step S703 may trigger multiple, periodic CSI
Reports (i.e. step S71 1 may comprise multiple and/or periodically sent messages). For example,
a new CSI report may be generated and sent when a certain amount of time has passed (or a
prescribed number of sub-frames have been transmitted) since sending a preceding CSI report
and/or whenever the results of the relevant measurements are different to the results informed in
a preceding CSI report.
After it has received the results of the relevant measurements and verified which
measurement configuration they relate to (using the data stored in its memory 59), the base
station 5-1 is operable to control the operation of the CoMP service (as generally shown at S713)
in accordance with the received results. For example, the base station 5-1 may adjust its
transmissions to reduce or eliminate any indicated interference. Furthermore, the base station 5-
1 may also inform the other cooperating transmission points (e.g. base stations 5-2 and 5-3) if
they need to adjust their transmissions in order to achieve better CoMP performance. The base
station 5-1 may either forward the CSI measurement results to the other transmission points or
forward only those parts of the CSI measurement results that are relevant to those transmission
points. Alternatively, the base station 5-1 may provide the required operating parameters for the
other transmission points, thereby effectively acting as a master base station which controls the
operation of other CoMP transmission points as well.
Modifications and Alternatives
Detailed embodiments have been described above. As those skilled in the art will
appreciate, a number of modifications and alternatives can be made to the above embodiments
whilst still benefiting from the inventions embodied therein.
In the above embodiments, the base stations (or RRHs/RNs) are described as
transmission points. However, the term 'transmission point' shall not be construed as being
limited to network nodes that are actually transmitting user data to CoMP enabled mobile
telephones - they may only transmit control data, such as reference signals and the like.
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.
In the embodiments described above, the mobile telephone and the base stations will 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.
This application is based upon and claims the benefit of priority from United Kingdom
patent application No. 1306100.7, filed on April 4, 2013, the disclosure of which is incorporated
herein in its entirety by reference.

CLAIMS
1. A network node for controlling coordinated transmissions, in a communication system
comprising at least one mobile device and a plurality of transmission points which operate at
least one cell, the network node comprising:
means for sending, to the at least one mobile device, a signalling message, the signalling
message comprising CSI (Channel State Information) process data that indicates a plurality of
combined measurements to be made by the mobile device, wherein the combined measurement
is associated with a respective different configuration of the plurality of transmission points and
the combined measurement comprises at least one signal quality measurement and at least one
interference measurement for the associated configuration of the plurality of transmission points;
and
means for receiving, from the at least one mobile device, measurement results for a
selected one of the plurality of combined measurements and data identifying which one of the
plurality of combined measurements the results relate.
2. The network node according to claim 1, wherein the combined measurements identifies:
i) a first set of resource elements on which a signal quality measurement is to be carried out by
the at least one mobile device; and ii) a second set of resource elements on which an interference
measurement is to be carried out by the at least one mobile device.
3. The network node according to claim 2, wherein the first set of resource elements
comprises at least one NZP (non-zero power) resource element and the second set of resource
elements comprises at least one ZP (zero-power) resource element.
4. The network node according to claim 2 or 3, further comprising means for configuring
the plurality of transmission points in accordance with the CSI process data signalled to the
mobile device.
5. The network node according to any of claims 1 to 4, wherein the measurement results
received from the at least one mobile device comprise at least one of: a CQI (Channel Quality
Indicator), a RI (Rank Indicator), and a PMI (Precoding Matrix Indicator).
6. The network node according to any of claims 1 to 5, further comprising means for
controlling the coordinated transmissions, by the plurality of transmission points, in dependence
upon the measurement results received from the at least one mobile device.
7. The network node according to any of claims 1to 6, wherein the data identifying which
one of the plurality of combined measurements the results relates comprises: data identifying the
CSI process ('CSI process id') and data identifying at least one of a transmission point ('TP id')
WO 2014/163169 PCT/JP2014/059904
and an interference measurement resource ('IMR id').
8. The network node according to any of claims 1 to 7, wherein the coordinated
transmission points are configured to coordinate transmissions in accordance with one or more
communication modes selected from the group comprising: i) joint transmission, JT, mode in
which multiple transmission points send data to the mobile device; ii) CS/CB (Coordinated
Scheduling/Beam forming) mode in which the mobile device receives transmissions from one
transmission point, and the transmission points coordinate their scheduling and/or beam forming
decisions to minimise interference between the transmissions; and iii) DPS (Dynamic Point
Selection) mode in which the mobile device receives transmissions from a transmission point
selected from a set of coordinating transmission points.
9. The network node according to any of claims 1 to 8, wherein at least two cells operated
by the plurality of transmission points are configured for CA (Carrier Aggregation).
10. The network node according to any of claims 1 to 9, wherein at least one of the plurality
of transmission points is selected from a group comprising: i) a base station; ii) a RRH (remote
radio head); and a RN (relay node).
1 . The network node according to any of claims 1 to 10, wherein the network node
comprises a base station operating in accordance with the LTE (long term evolution) set of
standards.
12. The network node according to any of claims 1 to 11, further comprising means for
generating the CSI process data.
13. A mobile device for a communication system providing coordinated transmissions via a
plurality of transmission points which operate at least one cell, the mobile device comprising:
means for receiving from a transmission point a signalling message, the signalling
message comprising CSI (Channel State Information) process data that indicates a plurality of
combined measurements to be made by the mobile device, wherein the combined measurement
is associated with a respective different configuration of the plurality of transmission points and
the combined measurement comprises at least one signal quality measurement and at least one
interference measurement for the associated configuration of the plurality of transmission points;
and
means for sending, to a transmission point, measurement results for a selected one of the
plurality of combined measurements and data identifying which one of the plurality of combined
measurements the results relate.
14. The mobile device according to claim 13, further comprising a measurement module for
obtaining signal quality measurements and interference measurements of signals received from
different transmission points within the vicinity of the mobile device.
15. The mobile device according to claim 13 or 14, wherein the combined measurements
identifies: i) a first set of resource elements on which a signal quality measurement is to be
carried out by the at least one mobile device; and ii) a second set of resource elements on which
an interference measurement is to be carried out by the at least one mobile device.
16. The mobile device according to claim 15, wherein the first set of resource elements
comprises at least one NZP (non-zero power) resource element and the second set of resource
elements comprises at least one ZP (zero-power) resource element.
17. The mobile device according to any of claims 13 to 16, wherein the measurement results
comprise at least one of: a CQI (Channel Quality Indicator), a RI (Rank Indicator) and a PMI
(Precoding Matrix Indicator).
18. The mobile device according to any of claims 14 to 17, further comprising means for
configuring the measurement module in accordance with the CSI process data signalled by the
transmission point.
19. The mobile device according to any of claims 1 to 8, wherein the data identifying
which one of the plurality of combined measurements the results relates comprises: data
identifying the CSI process ('CSI process id') and data identifying at least one of a transmission
point ('TP id') and an interference measurement resource ('IMR id').
20. The mobile device according to any of claims 13 to 19, wherein the coordinated
transmission points are configured to coordinate transmissions in accordance with one or more
communication modes selected from the group comprising: i) joint transmission, JT, mode in
which multiple transmission points send data to the mobile device; ii) CS/CB (Coordinated
Scheduling/Beam forming) mode in which the mobile device receives transmissions from one
transmission point, and the transmission points coordinate their scheduling and/or beam forming
decisions to minimise interference between the transmissions; and iii) DPS (Dynamic Point
Selection) mode in which the mobile device receives transmissions from a transmission point
selected from a set of coordinating transmission points.
2 1. The mobile device according to any of claims 13 to 20, wherein at least two cells
operated by the plurality of transmission points are configured for CA (Carrier Aggregation).
22. The mobile device according to any of claims 13 to 21, wherein at least one of the mobile
device is selected from a group comprising: i) a mobile telephone; ii) a mobile terminal; and iii)
UE (user equipment).
23. A network node for controlling coordinated transmissions, in a communication system
comprising at least one mobile device and a plurality of transmission points which operates at
least one cell, the network node comprising transceiver circuitry for:
sending, to the at least one mobile device, a signalling message, the signalling message
comprising CSI (Channel State Information) process data that indicates a plurality of combined
measurements to be made by the mobile device, wherein the combined measurement is
associated with a respective different configuration of the plurality of transmission points and the
combined measurement comprises at least one signal quality measurement and at least one
interference measurement for the associated configuration of the plurality of transmission points;
and
receiving, from the at least one mobile device, measurement results for a selected one of
the plurality of combined measurements and data identifying which one of the plurality of
combined measurements the results relate.
24. A mobile device for a communication system providing coordinated transmissions via a
plurality of transmission points which operate at least one cell, the mobile device comprising
transceiver circuitry for:
receiving from a transmission point a signalling message, the signalling message
comprising CSI (Channel State Information) process data that indicates a plurality of combined
measurements to be made by the mobile device, wherein the combined measurement is
associated with a respective different configuration of the plurality of transmission points and the
combined measurement comprises at least one signal quality measurement and at least one
interference measurement for the associated configuration of the plurality of transmission points;
and
sending, to a transmission point, measurement results for a selected one of the plurality of
combined measurements and data identifying which one of the plurality of combined
measurements the results relate.
25. A method performed by a network node for controlling coordinated transmissions, in a
communication system comprising at least one mobile device and a plurality of transmission
points which operate at least one cell, the method comprising:
sending, to the at least one mobile device, a signalling message, the signalling message
comprising CSI (Channel State Information) process data that indicates a plurality of combined
measurements to be made by the mobile device, wherein the combined measurement is
associated with a respective different configuration of the plurality of transmission points and the
combined measurement comprises at least one signal quality measurement and at least one
interference measurement for the associated configuration of the plurality of transmission points;
and
receiving, from the at least one mobile device, measurement results for a selected one of
the plurality of combined measurements and data identifying which one of the plurality of
combined measurements the results relate.
26. A method performed by a mobile device for a communication system providing
coordinated transmissions via a plurality of transmission points which operate at least one cell,
the method comprising:
receiving from a transmission point a signalling message, the signalling message
comprising CSI (Channel State Information) process data that indicates a plurality of combined
measurements to be made by the mobile device, wherein the combined measurement is
associated with a respective different configuration of the plurality of transmission points and the
combined measurement comprises at least one signal quality measurement and at least one
interference measurement for the associated configuration of the plurality of transmission points;
and
sending, to a transmission point, measurement results for a selected one of the plurality of
combined measurements and data identifying which one of the plurality of combined
measurements the results relate.
27. A communication system comprising the network node of any of claims 1 to 12, and 23,
and the mobile device of any of claims 13 to 22, and 24.
28. A computer implementable instructions product comprising computer implementable
instructions for causing a programmable communications device to perform the method of claim
25 or 26.