Patent ID: 12250698

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Overview

FIG.1schematically illustrates a mobile (cellular) telecommunication system1in which a user of any of a plurality of mobile communication devices3-1to3-7can communicate with other users via one or more of a plurality of base stations5-1,5-2and5-3. In the system illustrated inFIG.1, each base station5shown is an Evolved Universal Terrestrial Radio Access Network (E-UTRAN) base station capable of operating in a multi-carrier environment.

InFIG.1, the base station labelled5-1comprises a so called ‘macro’ base station operating a plurality of relatively geographically large ‘macro’ cells7,8using respective component carriers (CCs) C1, C2, of a component carrier set. In this embodiment, the macro base station5-1operates component carrier C1as a primary component carrier on which a primary cell (PCell)7is provided, and component carrier C2as a secondary component carrier on which a secondary cell (SCell)8is provided. The PCell7has a larger geographical coverage than the SCell8. The difference in the size of the PCell7and SCell8may 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 C1and secondary carrier C2to different extents (e.g. path loss affecting a lower frequency primary carrier C1to a lesser extent than a higher frequency secondary carrier C2).

The other base stations5-2,5-3shown inFIG.1each comprises a so called ‘pico’ base station operating a plurality of ‘pico’ cells9-2,9-3,10-2,10-3, using a component carrier set having component carriers (CCs) C1, C2corresponding in frequency to those used by the macro-base station5-1. Each pico base station5-2,5-3operates a respective pico primary cell (PCell)9-2,9-3on component carrier C2and a respective pico secondary cell (SCell)10-2,10-3on component carrier C1. Thus, the pico Pcells9share substantially the same frequency band as the macro Scell8, and the pico Scells10share substantially the same frequency band as the macro Pcell7. As seen inFIG.1, the power of the carriers C1, C2used to provide the pico cells9,10is set such that the geographical coverage of the pico PCells9, of this example, are substantially co-incident with the geographical coverage of the pico SCells10.

The power used to provide pico cells9,10is low relative to the power used for the macro cells7,8and the pico cells9,10are therefore small relative to the macro cells7,8. As shown inFIG.1, in this example the geographical coverage of each of the pico cells9,10falls completely within the geographical coverage of the macro PCell7and overlaps partially with the geographical coverage of the macro SCell8.

Referring toFIG.2, in which the subframe configuration for the component carriers for each of the cells is illustrated, it will be apparent that there is a potential for relatively high communication interference between the macro PCell7and each of the pico SCells10. The risk of interference is high because the macro PCell7and pico SCells10operate in co-incident geographical regions and use a common component carrier frequency. Further, the strength of communication signals from the macro base station5-1, in the geographical area covered by each pico Scell10, may be comparable to communication signals from the respective pico base station5-2,5-3because of the relatively high power used by the macro base station5-1compared to that used by the pico base stations5-2,5-3. Whilst there is also the potential for some interference between the macro SCell8and each of the pico PCells9, any such interference is likely to be relatively small and restricted to the relatively small geographical region in which the macro SCell8and pico PCells9overlap.

In order to alleviate the issue of interference, the component carrier C2used for the macro Scell8is operated by the macro base station5-1as 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: [0089] a Physical Downlink Control Channel (PDCCH); [0090] a Physical Hybrid ARQ Indicator Channel (PHICH); [0091] a Physical Control Format Indicator Channel (PCFICH); [0092] a Physical Broadcast Channel (PBCH); [0093] a Primary Synchronization Signal (PSS); [0094] a Secondary Synchronization Signal (SSS); or [0095] a Common Reference Signal/Cell-specific Reference Signal (CRS).

The macro base station5-1operates carrier C1for the PCell7as a stand-alone carrier having a Physical Downlink Control Channel (PDCCH), which can be used to schedule the resources of its own component carrier C1(as shown by arrow X). The PDCCH of component carrier C1can also be used to schedule the resources of component carrier C2(‘cross carrier scheduling’) to be used for communication purposes by a mobile communication device3when operating in the macro Scell8(as shown by arrow Y). The PDCCH is transmitted omnidirectionally throughout the cell.

The respective component carrier C1used for each of the pico SCells10is also operated as an extension carrier by the associated pico base station5-2,5-3. The respective component carrier C2used for each of the pico Pcells9is operated, by the associated pico base station5-2,5-3, as a stand-alone carrier having an associated PDCCH for scheduling resources within its own component carrier C2(as shown by arrow X′). This PDCCH can also be used for cross carrier scheduling resources of component carrier C1to be used for communication purposes by a mobile communication device3when operating in the associated pico Scell10(as shown by arrow Y′).

As illustrated inFIGS.1and2, in this embodiment whilst a conventional PDCCH is not provided on the extension carriers, a dedicated Beamformed Physical Downlink Control Channel (BFed PDCCH)4-1,4-2,4-5is provided using the extension component carrier C2of the macro SCell8. The BFed PDCCH4-1,4-2,4-5is directional and can be used selectively to schedule resources of the extension component carrier C2for the macro SCell8(as shown by arrow Z) for specific mobile communication devices3. The BFed PDCCH is used in conjunction with frequency selective scheduling in which the mobile communication device reports the channel state information (CSI) such as channel quality indicator (CQI) for each resource block (RB) or group of RBs in frequency domain of the system bandwidth and the base station selects the best resource blocks to use to schedule the BFed PDCCH for each terminal.

In this exemplary embodiment, a BFed PDCCH is not provided for the extension component carrier C1of the pico SCells10-2,10-3. Instead each pico base station5-2,5-3operates its respective extension component carrier C1as a completely PDCCH-less component carrier as shown inFIG.2.

The PDCCH of the primary component carrier C1, operated by the macro base station5-1, can thus be used for scheduling resources (e.g. as shown by arrow Y) for a mobile communication device3-7, located in the macro SCell8, but which is in geographical close proximity to a pico PCell9-2being operated on the same component carrier C2as the macro SCell8. Accordingly, interference between the macro SCell8and the pico PCell9-2is avoided because, although the macro SCell8and the pico PCell9-2are being operated using same component carrier frequency band (C2), the control information for each cell is transmitted using a different respective component carrier frequency band.

The BFed PDCCH4-1,4-2,4-5of the extension component carrier C2for macro SCell8can be used selectively to schedule resources for a respective mobile communication device3-1,3-2,3-5, operating within the macro SCell8, but which is not geographically close to one of the pico PCells9-2,9-3. Accordingly, where interference is not such a significant risk, the capacity of the PDCCH of the component carrier C1used for the macro Pcell7can, beneficially, be conserved without significantly affecting interference.

For the smaller pico cells in which control channel capacity is not such an issue, the PDCCH of the respective component carrier C2operated by each pico base station5-2,5-3, can be used for the cross carrier scheduling of resources for any mobile communication device3-3,3-4located in the respective pico SCell10-2,10-3. As described above, the pico cells are geographically located entirely within the region covered by the macro PCell7. Accordingly, the absence of a BFed PDCCH, for the component carrier C1operated by each pico base station5-2,5-3, avoids the interference that could otherwise potentially result with the PDCCH of the macro PCell's component carrier C1.

Beamformed Physical Downlink Control Channel (BFed PDCCH)

A possible implementation of a BFed PDCCH will now be described, in more detail.

The beamforming of the BFed PDCCH4-1,4-2,4-5is achieved using a multi-layer beamforming approach that is suitable for a multiple input multiple output (MIMO) based communication system in which the transmitters and the receivers of the signals have multiple antennas. Beamforming is achieved using a precoding technique in which the phase (and possibly gain) of each stream of signals transmitted from each of a plurality of antennas is independently weighted such that the power of each signal stream is focussed in the direction of interest (e.g. that of the mobile communication device for which the BFed PDCCH is intended) to maximise the signal level. Similarly, the power of each stream of signals is minimised in other directions, including directions in which interference is a potential issue (e.g. that of the pico cells9,10).

In order to beamform successfully, the state of the channel is analysed based on Channel State Information (CSI) measured by the mobile communication devices3and reported to the macro base station5-1. The CSI comprises information such as a rank indicator (RI), precoding matrix indicator (PMI), a channel quality indicator (CQI) and/or the like. Based on this information, an appropriate type of beamforming is selected. For example, where full CSI is reliably available a statistical eigenvector beamforming technique may be used. In situations where a more limited CSI is available, an interpolation technique may be used estimate the CSI for beamforming. In situations where no CSI is available the CSI may be estimated blindly at the base station, for example from received signal statistics or uplink signals received from the terminal.

FIG.3shows a resource grid for an orthogonal frequency division multiplexing (OFDM) subframe30for the communication system1ofFIG.1, in which a BFed PDCCH is provided. The resource grid shown is for a resource block (RB) pair each RB having, for example, a resource grid similar to that described in section 6.2 of the 3rdGeneration Partnership Project (3GPP) Technical Standard (TS) 36.211 V10.2.0 and shown in FIG. 6.2.2-1 of that standard.

As seen inFIG.3, the BFed PDCCH transmission is provided in a set of resource elements35in a control region31of the subframe30. The control region31comprises resource elements35of the first three OFDM symbols of the first slot of the subframe30, and spans all twelve subcarrier frequencies of one resource block (RB). The remaining resource elements35of the first slot and the resource elements35of the second slot form a data region33in which the Physical Downlink Shared Channel (PDSCH) is transmitted. A set of UE specific PDSCH demodulation reference signals (DMRS) and UE specific BFed PDCCH DMRS are provided in the data region33and control region31respectively as illustrated.

The DMRS pattern for the BFed PDCCH is different to that used for a legacy PDCCH. In the DMRS pattern shown inFIG.3, PDSCH DMRS for antenna ports7and8are transmitted in resource elements35at three evenly distributed subcarrier frequencies, in each of the last two symbols of the first slot and in each of the last two symbols of the second slot. PDSCH DMRS for antenna ports9and10are also transmitted in resource elements35at three evenly distributed subcarrier frequencies (different to those used for ports7and8), in each of the last two symbols of the first slot and in each of the last two symbols of the second slot. BFed PDCCH DMRS for antenna ports x1and x2are transmitted in resource elements35at three evenly distributed subcarrier frequencies, in each of the first two symbols of the first slot. BFed PDCCH DMRS for antenna ports x3and x4are transmitted in resource elements35at three evenly distributed subcarrier frequencies (different to those used for ports x3and x4), in each of the first two symbols of the first slot.

Macro Base Station

FIG.4is a block diagram illustrating the main components of the macro base station5-1shown inFIG.1. The macro base station5-1comprises an E-UTRAN multi-carrier capable base station comprising a transceiver circuit431which is operable to transmit signals to, and to receive signals from, the mobile communication devices3via a plurality of antennas433. The base station5-1is also operable to transmit signals to and to receive signals from a core network via a network interface435. The operation of the transceiver circuit431is controlled by a controller437in accordance with software stored in memory439.

The software includes, among other things, an operating system441, a communication control module442, a component carrier management module443, a measurement management module445, a control channel management module446, a direction determination module447, a resource scheduling module448, and a beamforming module449.

The communication control module442is operable to control communication with the mobile communication devices3on the component carriers (CCs) C1, C2, of its component carrier set. The component carrier management module443is operable to manage the use of the component carriers C1, C2and, in particular, the configuration and operation of the macro PCell7and macro SCell8and the operation of the secondary component carrier C2for the SCell8as an extension carrier. The measurement management module445communicates with the mobile communication device3to configure the mobile communication device3to initiate measurement of the CSI and to receive and analyse measurement reports received from the mobile communication devices3to assess the channel state for the purposes of beamforming. The direction determination module447determines the directional position of a mobile communication device3, relative to the base station5-1, for beamforming purposes, from the uplink signals that the base station5-1receives from that mobile communication device3. The resource scheduling module448is responsible for scheduling the resources of the primary and extension component carrier C1, C2to be used by the mobile communication devices3operating in the macro cells7,8. The beamforming module449manages the formation of the directional ‘beam’ via which the BFed PDCCH4-1,4-2,4-5is provided to the respective mobile communication devices3-1,3-2,3-5.

In this exemplary embodiment, the control channel management module446determines which control channel to use for scheduling resources of the extension carrier C2of the macro SCell8based on trigger messages received from the mobile communication device3. These trigger messages indicate either that a mobile communication device is within range of a pico base station5-2,5-3or that a mobile communication device3is no longer within range of a pico base station5-2,5-3.

Specifically, if a mobile communication device3has not issued a trigger message indicating that it is within range of a pico base station5-2,5-3, or if it has issued a trigger message indicating that it is no longer within range of a pico base station5-2,5-3, then the control channel management module446determines that the mobile communication device3should receive resource scheduling for the extension carrier C2of the macro SCell8via a BFed PDCCH provided on the extension carrier C2.

If a mobile communication device3has issued a trigger message indicating that it is within range of a pico base station5-2,5-3, then the control channel management module446determines that the mobile communication device3should receive resource scheduling for the extension carrier C2of the macro SCell8via a PDCCH provided on the primary component carrier C1of the macro PCell7.

In the above description, the base station5-1is 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.

Pico Base Station

FIG.5is a block diagram illustrating the main components of a pico base station5-2,5-3shown inFIG.1. Each pico base station5-2,5-3comprises an E-UTRAN multi-carrier capable base station comprising a transceiver circuit531which is operable to transmit signals to, and to receive signals from, the mobile communication devices3via at least one antenna533.

The base station5-2,5-3is also operable to transmit signals to and to receive signals from a core network via a network interface535. The operation of the transceiver circuit531is controlled by a controller537in accordance with software stored in memory539.

The software includes, among other things, an operating system541, a communication control module542, a component carrier management module543, a cell type identifier module547and a resource scheduling module548.

The communication control module542is operable to control communication with the mobile communication devices3on the component carriers (CCs) C1, C2, of its component carrier set. The component carrier management module543is operable to manage the use of the component carriers C1, C2and in particular the configuration and operation of the pico PCell9and pico SCell10and the operation of the secondary component carrier C1for the SCell10as an extension carrier. The cell type identifier module547provides information for identifying the cells controlled by the base station5-2,5-3as pico cells9,10. This information is provided to mobile communication devices3that come within (or close to) the coverage area of the pico Pcell9. In this exemplary embodiment, for example, the cell type identifier module547broadcasts information identifying the cells it controls to be pico cells. The resource scheduling module548is responsible for scheduling the resources of the primary and extension component carrier C2, C1to be used by the mobile communication devices3operating in the pico cells9,10.

In the above description, the base station5-2,5-3is 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

FIG.6is a block diagram illustrating the main components of the mobile communication devices3shown inFIG.1. Each mobile communication device3comprises a mobile (or ‘cell’ telephone) capable of operating in a multi-carrier environment. The mobile communication device3comprises a transceiver circuit651which is operable to transmit signals to, and to receive signals from, the base stations5via at least one antenna653. The operation of the transceiver circuit651is controlled by a controller657in accordance with software stored in memory659.

The software includes, among other things, an operating system661, a communication control module662, a measurement module665, and a cell identification module667, a cell proximity detection module668, and a resource determination module669.

The communication control module662is operable for managing communication with the base stations5on the associated component carriers (CCs) C1, C2. The measurement module665receives measurement configuration information from the base station5-1for the purposes of configuring the mobile communication device3to take measurements of the CSI. The measurement module665manages performance of the measurements of CSI (e.g. for the macro cells7,8), generates associated measurement reports and transmits the generated reports to the macro base station5-1. The measurement module665also determines reference signal received power (RSRP) for the pico cells9,10for use in determining the proximity of the mobile communication device3to the pico cells. The cell identification module667is operable to determine the type of cell, which the mobile communication device3enters, or comes geographically close to, from information provided by the base station5-2,5-3, controlling that cell. In this exemplary embodiment, for example, the cell identification module667is operable to receive the information for identifying the cell type that is broadcast by a pico base station5-2,5-3, and to identify the cell type to be a pico cell from the received information.

The cell proximity detection module668uses the measurements of RSRP from the pico Pcells9to determine the proximity of the mobile communication device3to the pico Pcells9by comparing the RSRP measurement to a predetermined ‘trigger’ threshold663. The trigger threshold is set such that an RSRP above the trigger threshold indicates that the mobile communication device3is in a geographical location that is close enough to a pico Pcell9for there to be a risk of associated control channel interference between the PDCCH on the primary carrier (C2) of the pico PCell9and the BFed PDCCH on the extension carrier C2of the macro SCell8

Hence, if the RSRP measurement exceeds the threshold value, then the mobile communication device3is deemed to be sufficiently close to (or within) the pico cell for there to be a risk of interference between any BFed PDCCH transmitted on the extension carrier C2of the macro SCell8with the PDCCH of transmitted on the extension carrier C2of the pico PCell9. When the trigger threshold663is exceeded, the cell proximity detection module668triggers a message to the macro base station5-1indicating that the mobile communication device is within range of a pico base station5-2,5-3. When the RSRP measurement drops below the trigger threshold663, the cell proximity detection module668triggers a message to the macro base station5-1indicating that the mobile communication device is no longer within range of a pico base station5-2,5-3.

The resource determination module669determines the resources scheduled for use by the mobile communication devices3for communication purposes by decoding the PDCCH and/or BFed PDCCH appropriately.

In the above description, the mobile communication device3is 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.

Operation

FIG.7is a flow chart illustrating typical operation of the communication system1to schedule resources for use by a mobile communication device (MCD)3during communications.

InFIG.7, the exemplary operation scenario begins (at S1) when a mobile communication device3starts operating in the Scell8of the macro base station5-1, in a geographical location that is sufficiently far from the pico Pcells9for there to be little risk of associated control channel to control channel interference. The base station5-1determines the direction of the mobile communication device3relative to the base station at S2and identifies an appropriate precoding matrix (also referred to as a precoding vector) for use in beamforming the BFed PDCCH for that mobile communication device3in the determined direction. The macro base station5-1schedules the resources for the extension carrier C2of the macro SCell8using within-carrier scheduling via the BFed PDCCH (at S3).

In this example, each pico base station broadcasts information for identifying itself to be a pico base station5-2,5-3at S4and the mobile communication device3determines, from this broadcast identity information, that the base station5-2,5-3is a pico base station (at S5). The mobile communication device3identifies the reference signals that it receives from the pico base stations5-2,5-3and then monitors the reference signal received power (RSRP) of these reference signals relative to the predetermined trigger threshold (at S6).

In this example, while the RSRP remains below the trigger threshold, the process in steps S2to S6is repeated via loop L1. When the RSRP increases above the trigger threshold it sends a ‘trigger’ message to the macro base station5-1to indicate that it is in sufficient range of a pico base station5-2,5-3, for control channel interference to be a significant risk at S7. On receipt of the trigger message, the macro base station5-1determines that it should no longer use a BFed PDCCH for that mobile communication device3and schedules the resources for the extension carrier C2of the macro SCell8using cross-carrier scheduling via the PDCCH of the macro PCell's primary component carrier C1at S8.

The mobile communication device3continues to monitor the reference signal received power (RSRP) of the reference signals from the pico base station5-3,5-3relative to the predetermined trigger threshold at S6(via loop L2). While the RSRP remains above the trigger threshold, the process in step S8is repeated via loop L4. When the RSRP drops below the trigger threshold it sends another ‘trigger’ message to the macro base station5-1to indicate that it is no longer in sufficient range of a pico base station5-2,5-3for control channel interference to be a significant risk (at S9via loop IA). On receipt of the further trigger message, the macro base station5-1determines that it can start to use a BFed PDCCH for that mobile communication device3again and schedules the resources for the extension carrier C2of the macro SCell8using within-carrier scheduling via the BFed PDCCH of the macro SCell's extension component carrier C2(at S3) following appropriate direction finding and beamforming (at S2).

Application in a Communication System in which Macro PCell and Pico PCell Use Same Carrier

FIG.8schematically illustrates a further mobile (cellular) telecommunication system81. The telecommunication system81is similar to that ofFIG.1and corresponding parts are given the same reference numerals.

In the telecommunication system81, a plurality of mobile communication devices3-1to3-7can communicate with other users via one or more of a plurality of base stations5-1,5-2and5-3. In the system illustrated inFIG.1, each base station5shown is an Evolved Universal Terrestrial Radio Access Network (E-UTRAN) base station capable of operating in a multi-carrier environment.

InFIG.8, the base station labelled5-1comprises a macro base station operating a plurality of relatively geographically large macro cells7,8using respective component carriers (CCs) C1, C2, of a component carrier set. In this embodiment, the macro base station5-1operates component carrier C1as a primary component carrier on which a primary cell (PCell)7is provided, and component carrier C2as a secondary component carrier on which a secondary cell (SCell)8is provided. The PCell7has a larger geographical coverage than the SCell8.

The other base stations5-2,5-3shown inFIG.8, each comprises a pico base station operating a plurality of ‘pico’ cells9-2,9-3,10-2,10-3, using a component carrier set having component carriers (CCs) C1, C2corresponding in frequency to those used by the macro-base station5-1. In this exemplary embodiment, unlike that shown inFIG.1, each pico base station5-2,5-3operates a respective pico primary cell (PCell)9-2,9-3on component carrier C1and a respective pico secondary cell (SCell)10-2,10-3on component carrier C2.

Thus, unlike the system ofFIG.1, the pico Pcells9share substantially the same frequency band as the macro Pcell7, and the pico Scells10share substantially the same frequency band as the macro Scell8. The geographical coverage of each of the pico cells9,10falls completely within the geographical coverage of the macro PCell7. However, the overlap between the pico cells9and10and the macro SCell8is relatively small.

Referring toFIG.9, in which the subframe configuration for the component carriers for each of the cells is illustrated, it will be apparent that there is a potential for relatively high communication interference between the PDCCH of the macro PCell7and the PDCCH of each of the pico PCells9. In this exemplary embodiment, however, this interference is avoided by using a time domain solution in which the macro base station5-1transmits a PDCCH only in certain subframes and the pico base stations5-2,5-3transmits a PDCCH in other subframes that do not overlap in time with the subframes used by the base station5-1.

More specifically, the macro base station5-1uses a first predetermined set of subframes of a radio frame (in this example even numbered subframes) to transmit a PDCCH and each pico base station5-2,5-3uses a second predetermined set of subframes of a radio frame (in this example odd numbered subframes) to transmit a respective PDCCH. Accordingly, because the PDCCH provided by the macro base station5-1and the pico base stations5-2,5-3, do not overlap the risk of control channel to control channel interference is avoided. The subframes in which a particular base station5does not transmit a PDCCH are also not used for data (e.g. PDSCH) transmission by that base station and, accordingly, are referred to as almost blank subframes (ABS). These ABS may, however, be used for transmission of common/cell-specific reference signals (CRS).

The Potential for any Interference Between the Macro SCell8and Each of the Pico SCells10is Relatively Small

Each base station5operates carrier C1for its PCell7,9as a stand-alone carrier having a Physical Downlink Control Channel (PDCCH), which can be used to schedule the resources of its own component carrier C1(as shown by arrows X and X′). The PDCCH of each component carrier C1can also be used to schedule the resources of component carrier C2(‘cross carrier scheduling’) to be used for communication purposes by a mobile communication device3when operating in the corresponding Scell8,10(e.g. as shown by arrow Y).

The respective component carrier C2used for each of the Scells8,10is operated, by the associated base station5, as an extension carrier (as described previously) on which a BFed PDCCH4-1,4-2,4-3,4-5,4-8can be provided. The BFed PDCCH4-1,4-2,4-3,4-5,4-8is directional and can be used selectively to schedule resources of the extension component carrier C2for each SCell8,10(e.g. as shown by arrows Z and Z′) for specific mobile communication devices3. The BFed PDCCH of each extension component carrier C2can also be used to schedule the resources of the related primary component carrier C1(‘cross carrier scheduling’) to be used for communication purposes by a mobile communication device3when operating in the corresponding Pcell7,9(e.g. as shown by arrow W′).

The BFed PDCCH4-1,4-2,4-3,4-5,4-8of the extension component carrier C2for each SCell8,10can be used selectively to schedule resources for a respective mobile communication device3-1,3-2,3-3,3-5,3-8operating within in the corresponding SCell8,10. Accordingly, the risk of interference in the region in which the macro SCell8and pico SCell10does overlap is significantly reduced because of the geographically localised nature of the BFed PDCCH. The DMRS pattern for the BFed PDCCH is different to that used for a legacy PDCCH.

FIG.10shows another possible subframe configuration for the component carriers for the system ofFIG.8. In the configuration shown inFIG.10, the control region of the subframes provided using component carrier C2used for each SCell8,10is partitioned into a BFed PDCCH region in which the BFed PDCCH is provided, and a PDCCH-less region in which no PDCCH or BFed PDCCH is provided. The regions are generally equal sized and are partitioned such that the BFed PDCCH region for the macro SCell8does not overlap with the BFed PDCCH region for the pico SCell10, thereby reducing the small risk of control channel to control channel interference even further.

Application in a Communication System in which Only the Pico Base Stations Use a BFed PDCCH

FIG.11schematically illustrates a further mobile (cellular) telecommunication system111andFIG.12shows a possible subframe configuration for the component carriers for the system ofFIG.11. The telecommunication system111is similar to that ofFIG.8and corresponding parts are given the same reference numerals.

The communication system is, essentially, the same as that shown inFIG.8except that only the pico base stations5-2,5-3provide a BFed PDCCH and, unlike the system ofFIG.8, the macro base station5-1provides all resource scheduling for the macro SCell8via a PDCCH provided in the primary component carrier C1for the macro PCell7(e.g. as shown by arrow Y inFIG.12).

More specifically, each base station5operates carrier C1for its PCell7,9as a stand-alone carrier having a PDCCH that can be used to schedule the resources of its own component carrier C1(as shown by arrows X and X′). The PDCCH of each component carrier C1can also be used to schedule the resources of component carrier C2(‘cross carrier scheduling’) to be used for communication purposes by a mobile communication device3when operating in the corresponding Scell8,10(e.g. as shown by arrow Y).

The respective component carrier C2used for each of the Scells8,10is operated, by the associated base station5, as an extension carrier as described previously. However, the component carrier C2used for the macro Scell8is not provided with a PDCCH or a BFed PDCCH and so can only be scheduled using the PDCCH provided on the primary component carrier C1. The component carrier C2used for each pico Scell10operated by the associated pico base station5-2,5-3can be provided with a BFed PDCCH4-3,4-8.

The BFed PDCCH4-3,4-8is directional and can be used selectively to schedule resources of the extension component carrier C2for each pico SCell10(e.g. as shown by arrow Z′) for specific mobile communication devices3. The BFed PDCCH of the extension component carrier C2for each pico SCell10can also be used to schedule the resources of the related primary component carrier C1(‘cross carrier scheduling’) to be used for communication purposes by a mobile communication device3(e.g. as shown by arrow W′).

The BFed PDCCH4-3,4-8of the extension component carrier C2for each pico SCell10can thus be used selectively to schedule resources for a respective mobile communication device3-3,3-8operating within the corresponding SCell10. Accordingly, the risk of control channel to control channel interference in the region in which the macro SCell8and pico SCell10overlaps is significantly reduced.

Application in a Single Carrier Communication System

FIG.13schematically illustrates a further mobile (cellular) telecommunication system131,FIG.14shows the configuration of a radio frame for the system131ofFIG.13, andFIG.15shows a number of possible subframe configurations for the system ofFIG.13. The telecommunication system131has similarities to those described earlier and corresponding parts are given the same reference numerals. In the system illustrated inFIG.13, each base station5shown is an Evolved Universal Terrestrial Radio Access Network (E-UTRAN) base station capable of operating in a single-carrier environment.

A major difference between the system131shown inFIG.13and those described earlier is that the telecommunication system131is a single component carrier system which has been adapted in a manner that allows legacy mobile communication devices to use the system as normal (e.g. those defined by the 3rdGeneration Partnership Project (3GPP) release 8, 9 and 10 standards) whilst more advanced mobile communication device can advantageously be scheduled using a BFed-PDCCH.

InFIG.13, the base station labelled5-1comprises a macro base station operating a relatively geographically large macro cell7using a single component carrier C1(e.g. a backwards compatible or ‘legacy’ component carrier). The other base stations5-2,5-3shown inFIG.13each comprises a pico base station operating a pico cell9-2,9-3, using a component carrier C1of the same frequency as the component carrier used by the macro base station5-1.

The power used to provide pico cells9is low relative to the power used for the macro cell7and the pico cells9are therefore small relative to the macro cell7. As shown inFIG.13, in this example the geographical coverage of each of the pico cells9falls completely within the geographical coverage of the macro cell7.

Referring toFIG.14, the configuration of a radio frame140for the communication system113is shown. As seen inFIG.14, and as those skilled in the art will readily understand, each radio frame comprises an E-UTRA radio frame comprising ten subframes142,144, a number of which are reserved for Multi-Media Broadcast over a Single Frequency Network (MBSFN). InFIG.14, the subframes reserved for MBSFN are referred to as MBSFN subframes144.

To allow legacy mobile communication devices to communicate successfully in the system131, the non-MBSFN subframes142comprise legacy E-UTRA subframes having a legacy PDCCH (e.g. as defined in the relevant 3GPP release 8, 9 or 10 standards). Thus, older (e.g. release 8, 9 and 10) mobile communication devices are advantageously able to monitor the legacy PDDCH in the non-MBSFN subframes142.

The MBSFN subframes144are configured with a BFed PDCCH with a corresponding new DMRS pattern, as described previously. Newer (e.g. release11and beyond) mobile communication devices3, such as those shown inFIG.13, are advantageously able to monitor both the legacy PDDCH in the non-MBSFN subframes142and the BFed PDCCH in the MBSFN subframes144.

Referring toFIG.15, there are a number of different options (labelled (a) to (c) inFIG.15) for MBSFN subframe configuration for the system ofFIG.13. In the first option (a), the MBSFN subframes144of both the macro base station5-1and the pico base stations5-2,5-3are provided with the BFed PDCCH. This option has the advantage of simplicity and the fact that beamformed control channels4-1,4-2,4-3,4-5,4-8can be used in both the pico and macro cells7,9.

In the second option (b), the MBSFN subframes144of both the macro base station5-1and the pico base stations5-2,5-3are provided with a partitioned BFed PDCCH region and PDCCH-less region (similar to that described with reference toFIG.10). The regions are generally equal sized and are partitioned such that the BFed PDCCH region for the macro cell7does not overlap with the BFed PDCCH region for the pico cell8. This option reduces the risk of interference and allows beamformed control channels4-1,4-2,4-3,4-5,4-8to be used in both the pico and macro cells7,9.

In the third option (c), the MBSFN subframes144of the of the pico base stations5-2,5-3are provided with a BFed PDCCH region, whilst the MBSFN subframes144of the macro base station5-1are not. This option reduces the risk of interference and allows beamformed control channels4-3,4-8to be advantageously used in the pico cells9(for this option, the macro base station5-1does not use the beamformed control channels labelled4-1,4-2,4-5shown inFIG.13).

Application in a Distributed Antenna System

FIG.16schematically illustrates a mobile (cellular) telecommunication system161in which a user of any of a plurality of mobile communication devices3-1to3-7can communicate with other users via a macro base station and a local antenna15-0at the base station and a plurality of geographically distributed antennas15-1,15-2and15-3. Each distributed antenna15-1to15-3is connected to the base station (for example by a fibre optic link) and the base station5controls reception and transmission via the antenna15. The base station5uses a common cell identity for communications via each antenna15and hence a mobile communication device3being served by any one of the antenna15behaves as if it is operating in a single cell.

InFIG.16, the base station effectively operates, on a first component carrier C1, a single ‘common’ primary cell (PCell)7that comprises a plurality of primary sub-cells7-0to7-3each provided using a different respective antenna15-0to15-3. The base station operates, on a second component carrier C2, an effective secondary cell (SCell)8that comprises a plurality of secondary sub-cells8-0to8-3each provided using a different respective antenna15-0to15-3.

In the example shown, the ‘local’ or ‘master’ primary sub-cell7-0operated via the local antenna15-0has a larger geographical coverage than the ‘local’ or ‘master’ secondary sub-cell8-0operated via the local antenna15-0. The geographical coverage of each of the ‘distributed’ sub-cells7-1to7-3and8-1to8-3operated via the distributed antennas15-1to15-3falls completely within the geographical coverage of the local primary sub-cell7-0and overlaps partially with the geographical coverage of the local secondary sub-cell8-0. The power of the carriers C1, C2used to provide the distributed sub-cells7-1to7-3and8-1to8-3is set such that the geographical coverage of the distributed primary sub-cells7-1to7-3(of this example) are substantially co-incident with the geographical coverage of the distributed secondary sub-cells8-1to8-3. In the example shown the distributed sub-cell7-2,8-2provided using distributed antenna15-2partially overlaps with the distributed sub-cells7-1,7-3,8-1,8-3respectively provided using the other distributed antennas15-1,15-3. It will be apparent, therefore, that there is a potential for relatively high control channel to control channel interference between the sub-cells7,8where they overlap with one another.

In this exemplary embodiment, PDCCH to PDCCH interference on the primary component carrier C2may be avoided by appropriate time domain separation of the sub-frames used to communicate the PDCCH (e.g. with ABS for the other sub-frames as described previously).

Referring toFIG.17, in which the subframe configuration for the component carriers for the distributed cells is illustrated, control channel to control channel interference on the secondary carrier C2is avoided by providing a different control channel (DMRS based PDCCH), each having a different respective DMRS sequence, in the control regions of respective subframes for overlapping distributed secondary subcells8-1to8-3. The DMRS sequence selected for the different DMRS based PDCCHs is selected to be substantially orthogonal.

As shown inFIG.17, a DMRS based PDCCH having a first DMRS sequence (DMRS based PDCCH1) is provided in the control region of subframes communicated in the non-overlapping secondary subcells8-1and8-3provided via antennas15-1and15-3. A DMRS based PDCCH having a second DMRS sequence (DMRS based PDCCH2) is provided in the control region of subframes communicated in the secondary subcell8-2, provided via antenna15-2, that overlaps with the other secondary subcells8-1and8-2, thereby helping to avoid control channel to control channel interference in the regions in which the secondary subcells8overlap.

The structure of each DMRS based PDCCH is, therefore, similar to that of the BFed PDCCH of earlier examples. However, in this embodiment, the new PDCCH is transmitted from a single antenna and is omnidirectional rather than beamformed. The structure of the DMRS based PDCCH is, therefore similar to the BFed PDCCH as transmitted from a single antenna port.

Other 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 and variations whilst still benefiting from the inventions embodied therein.

It will be appreciated that although the macro and the pico base stations5have each been described with particular reference to a different set of modules (as shown inFIGS.4and5) to highlight the particularly relevant features of the different base stations5, the macro and the pico base stations5are similar and may include any of the modules described for the other. For example, each pico base station5-2,5-3may include a measurement management module445, a direction determination module447and/or a beamforming module449as described with reference toFIG.4. Similarly, the macro base station5-1may include a cell type identifier module547as described with reference toFIG.5.

It will be appreciated that although the communication system1is described in terms of base stations5operating 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, home base stations (HeNB), or other such communication nodes.

In the above embodiments, the cell type identifier module has been described as providing information for identifying the cells controlled by the base station5-2,5-3as pico cells9,10and that this information is broadcast to mobile communication devices3that come within or close to the coverage area of the pico Pcell9. It will be appreciated that the information for identifying the cells provided by the base station5-2,5-3may comprise any suitable information such as a specific cell type identifier information element, or a cell identity (Cell ID) from which cell type can be derived. For example, if a HeNB, rather than a pico base station, operates the low power cells9,10, the cell type can be identified from comparing the cell identity provided by the HeNB to a range of Cell IDs known to be allocated to HeNBs.

Further, whilst in the above description it is the mobile communication device that determines whether a particular cell is a pico cell for which control channel interference is a risk, the macro base station could also do this. For example, the macro base station may mandate any mobile communication device configured with a BFed PDCCH, to carry out RSRP measurements and to compare the results with predefined threshold value (e.g. similar to the ‘trigger’ threshold as described). If the results are found to be above that threshold value, the mobile communication device simply reports the measurement to the base station with cell identity information (e.g. the Cell ID) for the cell to which the measurements relate. On receipt of the report, the macro base station (which has access to information identifying the cell IDs for the pico cells in its coverage area) can avoid using a BFed PDCCH for a mobile communication device that is close to a pico cell within its coverage area. In the case of HeNBs, the macro base station is able to identify them, based on their cell IDs, so that the macro base station can avoid using the BFed PDCCH for a mobile communication device that is close to an identified HeNB cell.

Referring to the embodiment described with reference toFIG.1, whilst a BFed PDCCH is not provided for the extension component carrier C1of the pico SCells10-2,10-3, it will be appreciated that such a BFed PDCCH could potentially be provided, albeit at the possible expense of interference between the PDCCH of the macro PCell7and the BFed PDCCH of the pico SCell9. It will also be appreciated that whilst it has not been described in significant detail above, a BFed PDCCH of any of the communication systems could potentially be used for cross carrier scheduling for any component carrier of that system regardless of whether or not a control channel is provided for that component carrier.

Whilst a particular DMRS pattern has been described for the BFed PDCCH any suitable DMRS pattern may be used that is different to that used for a legacy PDCCH.

It will be appreciated that the predetermined trigger threshold may be reconfigurable. Further, the trigger threshold may be adaptive, for example to allow it to change automatically, or semi-automatically, based on prevailing radio conditions. The threshold value, and timing of the trigger message, may vary in dependence on the implementation. The optimum threshold value for different situations may be arrived at based on simulation.

Where a flow chart shows discrete sequential blocks, this is for the purposes of clarity only and, it will be appreciated that many of the steps may occur in any logical order, may be repeated, omitted, and/or may occur in parallel with other steps. For example, referring to step S4of the flow chart ofFIG.7, the pico base stations may broadcast identification periodically, in parallel with the other of the steps shown. Similarly, steps S4and S5need not be repeated every iteration of loops L1and L4. Further, the mobile communication device3may monitor the RSRP of received reference signals continuously in parallel with the other steps.

Although the provision a beamformed PDCCH has been described in detail it will be appreciated that other information, deliberately omitted from transmission on an extension carrier, may also be provided in a beamformed manner on extension carriers. For example a new beamformed Physical Hybrid ARQ Indicator Channel (BFed PHICH) may also be provided on the extension carrier.

Although the terminology used refers to a beamformed PDCCH (BFed PDCCH), any similar terminology may be used appropriately to refer to a new beamformed PDCCH and/or a PDCCH having a modified DMRS (for example ‘Precoded PDCCH’, ‘DMRS-based PDCCH’, ‘Codebook based beamforming PDCCH’).

The beamforming may be codebook based in which a ‘precoding’ vector (for weighting the transmissions from respective antennas) is selected from a set of predefined precoding vectors (the ‘codebook’). In this case the mobile communication device either knows, or is informed of, the precoding vector used. The beamforming may be non-codebook based in which the network applies arbitrary beamforming at the transmitter and the mobile communication device has no immediate means for determining the nature of the beamforming that has been applied. In this case a mobile communication device specific reference signal to which the same beamforming has been applied is transmitted to allow estimation of the channel experienced by the beamformed transmission. The pico and macro base stations may respectively use different beamforming techniques (e.g. the pico base station may use codebook based beamforming or and the macro base station may use non-codebook based beamforming or vice versa).

In the example described with reference toFIG.13, the BFed PDCCH was described as being provided in the MBSFN subframes of a radio frame whilst the legacy PDCCH was placed in other subframes. It will be appreciated that whilst using the MBSFN subframes is advantageous in terms of simplicity of implementation, any appropriate predetermined subframes may be used (for example ABS subframes). In a particularly advantageous scenario for example, the subframes used for BFed PDCCH transmission use MBSFN subframes that are also configured to be ABS subframes. The benefits of this arise because MBSFN subframes are standardised for 3GPP, Release 8 mobile communication devices, and ABS subframes are standardised for 3GPP Release 10 mobile communication devices. Thus, for backward compatibility, Release 8 mobile communication devices are able to interpret MBSFN subframes, and Release 10 mobile communication devices are able to interpret both MBSFN and ABS subframes. Accordingly, having MBSFN subframes carrying the new BFed control channel as a subset of subframes configured for Almost Blank Subframes (ABS) means that the legacy Release 10 mobile communication devices will be able to effectively ignore them as ABS subframes carrying no data, Release 8 mobile communication devices will be able to treat them as MBSFN subframes and newer mobile communication devices, as described for the above embodiments, will be able to treat them as BFed PDCCH carrying sub-frames.

Furthermore, in the example described with reference toFIG.13, by using co-ordinated scheduling in which the macro base station5-1and pico base station5-2,5-3exchange information on when the BFed PDCCH is to be scheduled, collision between the BFed PDCCHs transmitted by those base stations5can be avoided.

In yet another advanced variation of the example described with reference toFIG.13, the macro base station5-1and pico base station5-2,5-3can use the same resource for BFed PDCCHs where orthogonal communication streams are applied based on CSI information exchanged between the macro base station5-1and pico base station5-2,5-3.

In the exemplary embodiments described above, each new control channel having a new DMRS pattern has been described as being provided in a control region of a subframe. It will be appreciated that whilst this is particularly beneficial, the control channel could be provided in a data region of a subframe or partially in a control region and partially in a data region whilst still benefiting from many of the advantages provided by the invention. Nevertheless, despite the fact that there may be a reluctance to reuse a region normally reserved for the existing PDCCH because of the perceived technical difficulties in doing so, providing the new control channel(s) having the new DMRS in the control region, as opposed to the data region does provide some notable advantages. Firstly, for example, decoding a control channel in the region of a subframe reserved as a control region is significantly quicker than decoding a control channel in the region of a subframe reserved as a data region because mobile communication devices look at the control region before the data region. Secondly, for similar reasons, decoding a control channel in the region of a subframe reserved as a control region uses less battery power than decoding a control channel in the region of a subframe reserved as a data region. Further, when no data resources are allocated by the control channel, having the control channel in the control region allows the mobile communication device to ignore the data region completely, with the power and speed advantages that follow from such an arrangement.

In the above exemplary 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 exemplary embodiments described above, the base stations5and mobile communication devices3each include transceiver circuitry. Typically, this circuitry will be formed by dedicated hardware circuits. However, in some exemplary embodiments, part of the transceiver circuitry may be implemented as software run by the corresponding controller.

In the above exemplary embodiments, a number of software modules were described. As those skilled in the art will appreciate, the software modules may be provided in compiled or un-compiled 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.