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    时间：2014-06-05    下载该word文档
    DUAL-MODE BASE STATION
    FIELD OF THE INVENTION This invention relates to apparatus able to transmit and receive both in FDD mode and TDD mode and a method of enabling an apparatus able to transmit and receive both in FDDmode and TDD mode. The invention is applicable to use within a base station in a wireless network. The invention is particularly applicable to implement in-band backhaul in a wireless network containing such a base station. BACKGROUND OF THE INVENTION Mobile telephony systems, include user equipment, such as mobile handsets, have undergone rapid development through a

    number of generations. In the mobile telephony system the user equipment communicates via wireless links to a network of

    base stations connected to a telecommunications network. The initial deployment of mobile telephony systems, using analogue

    modulation for communication, was superseded by second generation digital systems, which are themselves currently being

    superseded by third generation digital systems such as UMTS and CDMA. Third generation standards provide for a greater

    throughput of data than is provided by second generation systems; this trend is continued with the proposal by the Third

    Generation Partnership Project of the so-called Long Term Evolution system, often simply called LTE, which offers

    potentially greater capacity still, by the use of wider frequency bands, spectrally efficient modulation techniques and,

    potentially, the exploitation of spatially diverse propagation paths to increase capacity (Multiple In Multiple Out. Distinct from mobile telephony systems, wireless data access systems have also undergone development. Wireless data access

    systems were initially aimed at providing the "last mile"

    (or thereabouts connection between user equipment at a subscriber's premises and the public switched telephone network

    (PSTN; the user equipment, typically, being a terminal to which a telephone or computer is connected. The WiMax standard


    (IEEE
    802.16 has provided a means for such terminals to connect to the PSTN via high data rate wireless access systems. Whilst WiMax and LTE have evolved via different routes, both can be characterised as high capacity wireless data systems

    that serve a similar purpose, typically using similar technology, and in addition both are deployed in a cellular layout as

    cellular wireless systems. Typically such cellular wireless systems comprise user equipment such as mobile telephony

    handsets or wireless terminals, a number of base stations, each potentially communicating over what are termed access links

    with many user equipments located in a coverage area known as a cell, and a two way connection, known as backhaul, between

    each base station and a telecommunications network such as the PSTN. As the data capacity of cellular wireless systems increases, an increased demand is placed on the capacity of the backhaul,

    the connection that has to convey the wireless-originating traffic to its destination, often in an entirely different

    network. For earlier generations of cellular wireless systems, the backhaul has been provided by one or more connections

    leased from another telecommunications operator (where such a connection exists near to the base station. However,

    increasing data rates increases the number of leased lines required to convey the data. Consequently, the operational

    expense associated with adopting multiple leased lines has also increased, making this a potentially expensive option for

    high capacity systems. As an alternative to leased lines, dedicated backhaul links can be provided by a variety of methods

    including microwave links or optical fibre links. However each of these methods of backhaul has associated costs. Dedicated


    fibre links can be expensive in terms of capital expense due mainly to the cost of the civil works in installation, and

    this problem is especially acute in urban areas. Microwave links also involve the capital expense of equipment and require

    expert installation due to narrow beam widths leading to the requirement for precise alignment of antennas. As an alternative to the provision of a dedicated backhaul link for each individual base station, it is possible to use the

    radio resource of the cellular wireless system to relay backhaul traffic from one base station to another. Typically, the

    base station using the cellular radio resource for backhaul is a small low power base station with an omnidirectional

    antenna known as a relay node. Such a system can be used to extend the area of cellular wireless coverage beyond the area

    of coverage of conventional base stations that are already equipped with a dedicated backhaul. Figure 1 illustrates a conventional in-band wireless cellular network 2; in this instance, base stations, or relays, 4a-4d

    are connected, through wireless channels, to an aggregation node 6. The aggregation node 6 also acts as a base station for

    user terminals and is included in the same cellular planning layout as the base stations 4. The aggregation node 6 is

    connected, for example by a microwave or fibre link 10, to a gateway 12. The gateway 12 is then, in turn, connected to a

    telecommunications network (not shown again, possibly also by using wireless channels. This architecture re-uses the radio

    equipment and spectrum allocation already provided for data links to users, also to provide the backhaul communication

    between a group of base stations.
    It is usual for the channels connecting the base stations 4a-4d to the user equipment terminals and connecting the


    aggregation node 6 to the user equipment terminals to be provided using either a Time Division Duplexing (TDD or a

    Frequency Division Duplexing (FDD system. Often different operators within the same coverage area will have one, or both,

    systems available to user equipment connecting via one of the base stations 4 or 6. In TDD, each channel having a predetermined frequency range is divided into a number of time frames; each frame being

    subdivided into a plurality of timeslots. Some of the timeslots in each frame are designated for uplinking and some are

    designated for downlinking, with each piece of user equipment being allocated particular uplink and downlink timeslots for

    a particular communication session. Of course, different operators will, in general, have different frequency channels

    allocated to them. In FDD, two bands of frequencies are available as communication channels, one for uplink (meaning a data link from the user

    terminal to the base station and the other for downlink (meaning a data link from the base station to the user terminal.

    For a particular communication session with user equipment, the operator will allocate a number of frequency channels from

    the uplink band as an uplink channel and a number of frequency channels from the downlink band as a downlink channel to

    that user equipment.
    The user equipment will then transmit and receive data using those particular frequency channels for the duration of a

    communication session. Different pieces of user equipment may share the same uplink and downlink channels by being assigned

    different spreading codes or OFDM
    sub-carriers to allow their data transmissions to be distinguished.
    Conventionally, a base station and aggregation node in a wireless network will either operate TDD mode or FDD mode. This


    limits the ability of the base stations to serve user equipment supported by different operators. It also restricts the use

    of in-band backhaul within the network. SUMMARY OF THE INVENTION     According to a first aspect of the invention there is provided apparatus comprising: (i an input, for example, as an incoming signal from the base station antenna (ii an output, for example, as an outgoing

    signal to the base station antenna (iii a transmit processor to process data for transmission by the output, (iv a

    receive processor to process data received by the input, (v a duplexer connected to the input and output and including a

    first port and a second port, the duplexer configured to pass data received in a first frequency band between one of the

    input and output and the first port and data received in a second frequency band between one of the input and output and

    the second port; (vi a transceiver switch connected to the transmit processor, receive processor, first port and second port; to

    switcheably connect one of the transmit processor and receive processor to one of the first port and second port. By selectively connecting the transmit and receive processors to the ports in the duplexer the apparatus can allow data to

    be sent and received either in the same time slots (when the apparatus is enabling a base station to operate in FDD mode

    or in different time slots (when the apparatus is enabling a base station to operate in TDD mode.
    The transceiver switch may connect the transmit processor to the second port and switcheably connects the receive processor

    to either the first port or the second port such that the receive processor can process data received either in the first

    set of frequencies or the second set of frequencies. This enables the receive processor to either process data received at


    the same time that data is transmitted (when the base station is operating in FDD mode or only process data received in time slots associated with receiving data (when the base station is operating in TDD

    mode. Data passed from at least one of the first port and second port to the receive processor may be amplified before it is

    passed to the receive processor. This arrangement is advantageous, as it avoids a degradation in receiver sensitivity due

    to the impact of signal loss through the additional components added according to this invention. The transceiver switch may include a circulator connected to the second port and configured to alternately transmit data to

    a pathway connecting the second port and the transmit processor and another pathway connecting the second port and the

    receive processor. This arrangement is advantageous because the use of a circulator is particularly suited to operation in

    high power base station applications, having high reliability and low signal attenuation. The use of a circulator is

    preferable to a high power RF switch which would be expensive using current technologies and likely to degrade the overall

    system performance by introducing loss to the transmitted signal. Optionally, the transceiver switch may connect the receive processor to the first port and switcheably connect the transmit

    processor to either the first port or the second port such that it can pass data to be transmitted either in a first set of

    frequencies or a second set of frequencies. This enables the transmit processor to either cause data to be transmitted at

    the same time that data is received (when the base station is operating in FDD
    mode or only cause data to be transmitted in time slots associated with transmitting data (when the base station is

    operating in TDD mode.     Data passed from the transmit processor to the first port or second port is amplified before it is
    passed to the first or

    second port. The transceiver switch may include a circulator connected to the first port and configured to alternately transmit data to

    the first port from a pathway connecting the first port and the transmit processor and another pathway connecting the first

    port and the receive processor. Preferably, the apparatus further comprises: (i a first frequency synthesiser; (ii a second frequency synthesiser; (iii a synthesiser switch connected to the transmit processor, receive processor, first frequency synthesiser and second

    frequency synthesiser; to switcheably connect one of the transmit processor and receive processor to one of the first

    frequency synthesiser and second frequency synthesiser. The synthesiser switch may connect the transmit processor to the first frequency synthesiser and switcheably connect the

    receive processor to either the first frequency synthesiser or the second frequency synthesiser such that the receive

    processor can process data received either in a first frequency or a second frequency. This means that the transmit and

    receive processor may both operate at the same frequency (when operating in TDD mode or at different frequencies (when

    operating in FDD mode. The synthesiser switch preferably includes a splitter between in the pathway between the first frequency synthesiser and

    the transmit and receive processors such that the first frequency synthesiser can supply data to both the transmit and the

    receive processors when the synthesiser switch is in a first configuration and only the transmit processor when the

    synthesiser switch is in a second configuration. This allows a single synthesiser to drive both the transmit and receive


    processors simultaneously for TDD operation. Alternatively, the synthesiser switch may connect the receive processor to the first frequency synthesiser and switcheably

    connects the transmit processor to either the first frequency synthesiser or the second frequency synthesiser such that the

    transmit processor can process data to be transmitted either in a first frequency or a second frequency. This means that

    the transmit and receive processor may both operate at the same frequency (when operating in TDD mode or at different

    frequencies (when operating in FDD
    mode. The synthesiser switch preferably includes a splitter between the pathway between the first frequency synthesiser and the

    transmit and receive processors such that the first frequency synthesiser can supply a local oscillator to both the

    transmit and the receive processors when the synthesiser switch is in a first configuration and only the receive processor

    when the synthesiser switch is in a second configuration. This allows a single synthesiser to drive both the transmit and

    receive processors simultaneously.

    The apparatus may alternatively, comprise a single frequency synthesiser, the frequency synthesiser being retunable between

    two or more frequencies. This enables the transmit and receive circuits to operate at different frequencies but be driven

    by the same synthesiser. The apparatus may be a base station or may be connectable to a base station to enable a conventional base station to

    operate in either TDD or FDD mode. The apparatus may also be an aggregation node or may be connectable to an aggregation node to operate in either TDD or FDD


    mode. The apparatus is utilised at the base stations 4 or the aggregation node 6 as shown in Figure 1. The data transmitted from

    base station 4 to the aggregation node 6 represents a backhaul uplink, and the data transmitted from aggregation node 6 to

    base stations 4 represents a backhaul downlink. The apparatus described is applied at both nodes, with the TDD timeslots selected at either end of the link so as to allow for both link directions to be transmitted in the same

    frequency band. According to another aspect of the present invention there is provided a telecommunications network including apparatus as

    recited in any of the above paragraphs. BRIEF DESCRIPTION OF THE DRAWINGS As will be understood by one skilled in the art, other aspects and features of the present invention will become apparent

    to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in

    conjunction with the accompanying figures.
    Figure 1 illustrates a cellular wireless network;     Figure 2 illustrates a base station in accordance with the present invention; Figures 3 and 4 illustrate alternative states of the synthesiser switch of the first embodiment; Figures 5 and 6 illustrate alternative states of the transceiver switch of the first embodiment; Figures 7 and 8 illustrate alternative states of the synthesiser switch of the second embodiment; Figures 9 and 10 illustrate alternative states of the transceiver switch of the second embodiment; Figures 11 and 12 illustrate alternative states of the transceiver switch of another embodiment; and Figures 13 and 14

    illustrate alternative states of the transceiver switch of a further embodiment. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Figure 2 illustrates a base station 4 which is enabled to function to selectively use both FDD
    and TDD modes to transmit and receive data. The base station 4 includes an antenna 14 for receiving and transmitting data.

    The base station 4 also includes a downlink synthesiser 16 and an uplink synthesiser 18, the downlink synthesiser 16 being


    tuned to a downlink frequency and the uplink synthesiser 18 being tuned to an uplink frequency. In base station equipment

    with an intermediate frequency architecture, the synthesizer frequencies are those which correspond with radio outputs in

    the desired bands, and the synthesizer outputs may include frequency offsets according to the frequency conversion design

    of the base station.

    A synthesiser switch 20 is provided enabling the downlink synthesiser 16 to be connected to either the transmitter circuit

    22 or the receiver circuit 24 and the uplink synthesiser 18 to be connected to the transmitter circuit 22 or the receiver

    circuit 24. Thus, the base station 4 can both transmit and receive in either the band of frequencies conventionally

    assigned to data uplink or the band of frequencies conventionally assigned for data downlink. Further, there is provided a transceiver switch 26 which enables the transmitter 22 to be connected to either the uplink or

    the downlink port (not shown of a duplexer 28 in the base station 4 and the receiver 24 to be connected to either the

    uplink or the downlink port of the duplexer 28. The duplexer 28 is configured to pass data received at the uplink port to the antenna 14 for transmission in the uplink

    frequency band, and pass data received at the antenna 14 in the uplink frequency band to the uplink port. Additionally, the

    duplexer 28 is also configured to pass data to the antenna 14 for transmission in the downlink frequency band and pass

    data, received at the antenna 14 in the downlink frequency band to the downlink port. By selectively connecting the

    transmitter circuit 22 or the receiver circuit 24 to the relevant port the transceiver switch 26 allows the base station 4

    to receive data or transmit data in either uplink or downlink frequency band.
    A first embodiment of the invention will now be explained in more detail with reference to Figures 3 and 4.

    In this embodiment the in-band backhaul in the base station operates in TDD
    mode using the downlink band of frequencies when transmitting to the aggregation node and receiving data from the

    aggregation node. The base station operates in FDD mode when transmitting data to the downlink and receiving data from the

    uplink user equipment The receiver circuit 24 in the base station must therefore be able to process data received on the

    uplink frequency to process data received from user equipment, and be able to process data received on the downlink

    frequency to process data received from the aggregation node.
    As discussed previously, conventionally, received data is only processed by a base station in an FDD system when it is

    received in uplink frequencies or by a base station in a TDD system when it is received in an uplink timeslot. In order to achieve the additional flexibility the base station of the

    present invention is provided with a synthesiser switch 20 as illustrated in Figure 3.     Considering the synthesiser switch configuration when the base station is operating in FDD mode the synthesiser switch is used to select which synthesiser is feeding data to the receiver circuit 24. When the base

    station is operating in FDD mode the receiver circuit 24 is fed by the uplink synthesiser 18 as illustrated in Figure 3. In

    Figure 3 it can be seen that the uplink synthesiser 18, which operates when data is received in an FDD mode is connected to

    the receiver circuit 24 via the switch 20. Additionally, the downlink synthesiser 16 is connected to the transmitter

    circuit 22 via a splitter in the switch. Thus, the downlink synthesiser 16 permanently feeds data to the transmitter

    circuit 22; however, the switch acts to prevent a connection between the downlink synthesiser 16 and the receiver circuit


    24 when the base station is operating in FDD mode. Hence, in this configuration the transmitter circuit 22 and the receiver

    circuit 24 operate at different frequencies and the base station can operate in FDD mode.

    Conversely, if the base station is to operate in TDD mode, both the transmitter and the receiver circuit 22, 24 operate at

    the same frequency and, thus, are connected to the same synthesiser. To achieve this the switch 20 converts to the

    configuration illustrated in Figure 4. In Figure 4 it can be seen that the transmitter and receiver circuits 22, 24 are

    both connected to, and therefore, driven using the downlink synthesiser 16 and thus, operate on the same frequency. To

    achieve this the switch 20 breaks the connection between the receiver circuit 24 and the uplink synthesiser 18 and connects

    the output of the splitter in the switch 20 to the receiver circuit 20. Thus, both the transmitter and receiver circuits

    22, 24 are fed by the downlink synthesiser and the base station can operate in TDD
    mode. Advantageously, this switched arrangement allows both synthesizers to remain locked to the same frequency at all times,

    such that the frequency outputs are stable. This also avoids degradations of the synthesizer phase noise that would occur

    due to signal cross-coupling if the synthesizer connected to the receiver were to re-tune to the downlink frequency band. In a conventional TDD base station duplexing is performed by switches and/or circulators.
    The duplexor 28 can be replaced by a single frequency band filter. The base station of the embodiment is configured to act both as an FDD and a TDD base station and, hence, may be able to

    process data from the aggregation node in downlink frequencies in addition to those received in uplink frequencies. An

    example of such a switch is the transceiver switch 26 which enables the base station to achieve this is illustrated in


    Figures 5 and 6 and is discussed in more detail below.

    The base station will always transmit in downlink frequencies and thus, the transmitting circuit 22 remains connected to

    the downlink port of the duplexer. To be able to receive data in both uplink and downlink frequencies the receiver circuit

    24 is switchably connected either to the uplink port or the downlink port of the duplexer 28. The duplexer 28 in the base station automatically directs data received in uplink frequencies to the uplink port and data

    received in downlink frequencies to the downlink port. Figure 6 illustrates the base station operating in TDD mode where data received in an uplink frequency is not processed by

    the base station as it is not passed to the receiver circuit and data received in a downlink frequency is processed by the

    receiver circuit.
    In this configuration, data, when received by the antenna 14 is passed to the duplexer 28 which directs the data to its

    downlink port. In Figure 6, the downlink port is connected, via the transceiver switch 26, to the receiver circuit 24 thus

    data received in the downlink frequency band is passed directly to the receiver circuit 24 for processing. Data received in

    the uplink frequency band is not passed to the receiver circuit and, thus, the base station is acting as a TDD base

    station. However, when the base station wishes to act in FDD mode by processing data received in the uplink frequency band the base

    station causes the transceiver switch 26 to change configuration to that illustrated in Figure 5. In Figure 5 the switch

    arrangement is altered such that the uplink output of the duplexer, to which data in the uplink frequency is sent, is

    forwarded to the receiver circuit for processing and hence the base station processes data received in uplink frequencies ,


    typically from the user terminal.

    Preferably, a circulator is used rather than a traditional switch in the transceiver switch to minimise transmitter loss. An alternative embodiment is illustrated in Figures 7 to 10. In this embodiment the transmitter circuit is selectively

    connected to the uplink synthesiser and the relevant port of the duplexer such that the in-band backhaul may operate in the

    uplink frequency band. As in the first embodiment, there is a synthesiser switch 20; however the synthesiser switch 20 selects the synthesiser

    driving the transmitter circuit 22 rather than the receiver circuit. In order for the base station to operate in FDD mode the switch takes the configuration illustrated in of Figure 7. As can

    be seen the downlink synthesiser 16, is connected to the transmitter circuit 22 and the uplink synthesiser 18 is sent

    through a splitter with one copy being forwarded to the receiver circuit 24 and the other copy being passed to an internal

    switching circuit. However, as the internal switching circuit does not connect the uplink synthesiser 18 to the transmitter

    circuit 22, the receiver and transmitter circuit are fed by different synthesisers and, hence the base station can operate

    in FDD mode. Conversely, if the base station is to operate in TDD mode the switch configuration is altered such that the receiver and

    transmitter circuit are both fed by the uplink synthesiser as illustrated in Figure 8. The receiver circuit 24 is

    consistently fed by the uplink synthesiser 18. A transceiver changeover switch is also present in the base station, an example of such a switch is illustrated in Figures

    9 and 10. This switch operates to enable the transmitter circuit 22 to connect to both the uplink and downlink port of the


    duplexer and thereby transmit in both uplink and downlink frequency bands to enable in-band backhaul.

    If data is to be transmitted in downlink frequencies, i.e. to user equipment, and processed by the receiving circuit 24

    when received in uplink frequencies then the switch is configured as illustrated in Figure 9. As can be seen, the switch

    connects the transmitting circuit 22 to the downlink port of the duplexer 28 thereby enabling the transmission of data on

    downlink frequencies. Conversely, if data is to be transmitted to the aggregation node then it will be transmitted in the uplink frequency band.

    In this instance the switch alters to connect the transmitter circuit 22 to the uplink port of the duplexer 28 as

    illustrated in Figure 10. This enables data to be transmitted to the aggregation node using the uplink frequency band thereby enabling in-band

    backhaul on the uplink frequency band. Optionally, the pair of amplifiers shown in Figure 11 and 12 may be replaced by a single amplifier on the transmitter side

    of the switch. This has the disadvantage that the switch is required to operate with high RF power, and also that the power

    output level is similar for both downlink data to user terminals, and for in-band backhaul data. However, if suitable

    switch technology is available, or if amplifiers are developed with high agility in output power level, then a single

    amplifier may be used to reduce cost and complexity. Optionally, the amplifiers of the transceiver switch may be omitted from the transceiver switch of either the first or

    second embodiment. An example, of a transceiver switch omitting the amplifiers is illustrated in Figures 11 and 12.


    Further, the circulator may be replaced by a conventional switch in the transceiver switch of either the first or second

    embodiment. An example, of a transceiver switch omitting the amplifiers is illustrated in Figures 13 and 14. If desired the synthesiser switch and synthesisers of either embodiment may be replaced by a single synthesiser which can

    be retuned between the downlink and uplink frequencies. Although the present invention has been described in relation to a base station, the invention could also be implemented in

    a separate device connectable to a base station and configured to receive data from, and transmit data to an antenna, or

    other component, in a base station.

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