BASE STATION AND METHOD OF OPERATION THEREIN

FIELD OF THE INVENTION

The present invention relates to a base station for use in RF communication, e.g. in a mobile communication system, and a method of operation therein.

BACKGROUND OF THE INVENTION

Mobile stations, ^λ MSs' , such as portable radios, portable telephones and radios carried in moving vehicles, communicate via an infrastructure in a mobile communication system. The infrastructure may include a plurality of interconnected base stations known as ^λ BTSs' (base transceiver stations) , each of which provides communication services to MSs in a particular area or ^λ cell' having the BTS at its centre. Each BTS normally includes a transmitter portion and a receiver portion. Some of the functional components of a BTS serve both the receiver portion and the transmitter portion .

BTSs typically employ at least one transmitted RF signal delivery branch in the transmitter portion and at least one received RF signal delivery branch, often a plurality of such branches, in the receiver portion. Each received RF signal delivery branch typically includes an antenna which picks up input RF signals which have been sent over-the-air and at least one component connected to the antenna to provide front end

processing of the signals. At least one component of the received RF signal delivery branch may require a DC electrical supply for operation. In particular, a low noise amplifier, ^λ LNA' , requires such a supply. The LNA is employed to provide front end amplification of a weak received signal.

A BTS may employ a plurality of base radios and each may include a plurality of receivers. Each of the received RF signal delivery branches may be connected to a plurality of receivers, each included in a different one of a plurality of base radios.

Arrangements employed in the prior art for providing a DC electrical supply to components in multiple received RF signal delivery branches of BTSs have not been ideal since relatively complex cabling configurations have been used to provide an active DC supply as well as a backup supply for use in the event that the active supply fails. Furthermore, configurations for switching between the active DC supply and the backup DC supply in such prior art arrangements have not been simple.

SUMN[ARY OF THE INVENTION

According to the present invention there is provided a base station as defined in claim 1 of the accompanying claims.

According to the present invention in a second aspect there is provided a method of operation as defined in claim 13 of the accompanying claims.

Further features of the invention are as defined in the accompanying dependent claims and in the embodiments of the invention to be described.

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block schematic diagram of an illustrative base transceiver embodying the invention. FIG. 2 is a block schematic diagram of a modified form of base radio for use in the base station of FIG.

1. FIG. 3 is a flow chart of a method of operation embodying the invention.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

FIG. 1 is a block schematic diagram of an illustrative BTS (base transceiver station) 100 embodying the invention. The BTS 100 may be part of an infrastructure of a mobile communication system and may provide RF communication services to MSs (not shown) within a particular geographical area or ^λ cell' of the mobile communication system. The BTS 100 includes a BR 1 (base radio 1) 101, a BR 2 (base radio 2) 102, a BR 3 (base radio 3) 103 and a BR 4 (base radio 4) 104. Each of BR 1 101, BR 2 102, BR 3 103 and BR 4 104, herein collectively referred to as the ^λ BRs' , provides signals

in RF form for transmission and receives signals in RF form. Each of the BRs also processes signals in baseband digital form for inclusion in RF signals to be transmitted and also processes signals in baseband digital form which have been extracted from received RF signals. The RF signals received by each of the BRs may be in a separate channel. For example, each of the channels for received signals may be defined by different carriers (RF carrier frequencies) received by the different BRs, each of the carriers being divided into time slots in a TDMA (Time Division Multiple Access) multiplexing procedure. For example, a TDMA procedure is employed for different carriers by the BTS 100 where the BTS 100 is in a mobile communication system operating in accordance with the TETRA standard as defined by ETSI (European Telecommunications Standards Institute) or another industry standard employing different carrier frequencies.

Each of the BRs has three receivers. Thus, the BR 1 101 has a first receiver Rx 1.1, a second receiver Rx 1.2 and a third receiver Rx 1.3. The BR 2 102 has a first receiver Rx 2.1, a second receiver Rx 2.2 and a third receiver Rx 2.3. The BR 3 103 has a first receiver Rx 3.1, a second receiver Rx 3.2 and a third receiver Rx 3.3. The BR 4 104 has a first receiver Rx 4.1, a second receiver Rx 4.2 and a third receiver Rx 4.3. The receivers Rx 1.1, Rx 2.1 and Rx 3.1 are herein referred to collectively as the ^λ first receivers' . The receivers Rx 1.2, Rx 2.2 and Rx 3.2 are herein referred to collectively as the 'second receivers' . The receivers Rx

3.1, Rx 3.2 and Rx 3.3 are herein referred to collectively as the ^λ third receivers' . Each of the first receivers is connected to a first received RF signal delivery branch 105. Each of the second receivers is connected to a second received RF signal delivery branch 107. Each of the third receivers is connected to a third received RF signal delivery branch 109.

The first received RF signal delivery branch 105 includes an antenna 111, a duplex filter 113 and a LNA 1 (low noise amplifier 1) 115 to which the first receivers are connected. The second received RF signal delivery branch 107 includes an antenna 117, a pre-selector filter 119 and a LNA 2 121 to which the second receivers are connected. The third received RF signal delivery branch 109 includes an antenna 123, a pre-selector filter 125 and a LNA 3 127 to which the third receivers are connected. The duplex filter 113 and the preselector filters 119 and 125 are pass band filters which filter received RF signals to pass only RF frequencies in a required frequency band. The duplex filter 113 also allows RF signals to be transmitted from the antenna 111 in a frequency band different from that of the received signals to be passed to the antenna 111 in a transmit mode . The LNA 1 115, the LNA 2 121 and the LNA 3 127 are collectively referred to herein as the ^λ LNAs' .

In a receive mode, the antenna 111 receives by converting to bound form (guided form along a conductor) an RF signal which has been sent as a radiated over-the- air signal, and delivers the input received signal to

the duplex filter 113, which filters the signal to pass only frequencies in a required pass band. The filtered received signal produced by the duplex filter 113 is delivered to the LNA 1 115. The LNA 1 115 amplifies the filtered received signal and delivers it to each of the first receivers of the BRs. A digital signal is then extracted from the received signal by each of the first receivers and the digital signals are processed in each of BRs. Similarly, the antenna 117 receives by converting to bound form an RF signal which has been sent as a radiated over-the-air signal. The antenna 117 delivers the input received signal to the pre-selector filter 119 which filters the signal to pass only frequencies in a required pass band. The filtered signal produced by the pre-selector filter 119 is delivered to the LNA 2 121. The LNA 2 121 amplifies the filtered signal and delivers the amplified filtered signal to each of the second receivers of the BRs. A digital signal is then extracted from the received signal by each of the second receivers, and the digital signals are processed in each of BRs. Similarly, the antenna 123 receives by converting to bound form an RF signal which has been sent as a radiated over-the-air signal. The antenna 123 delivers the input received signal to the pre-selector filter 125 which filters the signal to pass only frequencies in a required pass band. The filtered signal produced by the pre-selector filter 125 is delivered to the LNA 3 127. The LNA 3 127 amplifies the filtered received signal and delivers the amplified signal to each of the third receivers of the BRs. A

digital signal is then extracted from the received signal by each of the third receivers and the digital signals are processed in each of BRs.

The received signal amplified by the LNA 1 115 is provided to each of the first receivers, the received signal amplified by the LNA 2 121 is provided to each of the second receivers and the received signal amplified by the LNA 3 127 is provided to each of the third receivers, in order to provide reception Miversity' which allows signal reception quality and coverage area provided for a given signal to be enhanced in a known way.

Each of the LNAs draws DC (direct current) electrical energy in operation, as is well known in the art. The DC electrical energy is required for each of the LNAs to provide a bias current for a transistor or other amplifying device employed in the LNA. The bias current may be applied to each of the LNAs as a variable current, e.g. to adjust a dynamic range of the LNA. In the prior art, a supply of DC electrical energy to LNAs in separate received RF signal delivery branches is provided by a separate arrangement unrelated to connections between LNAs and BRs. In the BTS 100 embodying the invention, a DC electrical energy supply to the LNAs is provided in a manner now to be described.

The BTS 100 includes a DC supply source 129 which may be a battery or an adaptor which rectifies and provides voltage conversion of electrical energy from an AC (alternating current) main (mains) supply. The DC supply source 129 is connected via an electronic switch

131 to the receivers Rx 1.1, Rx 1.2 and Rx 1.3 of the BR 1 101. The DC supply source 129 is also connected via an electronic switch 133 to the receivers Rx 2.1, Rx 2.2 and Rx 2.3 of the BR 2 102. The DC supply source 129 is also connected via an electronic switch 135 to the receivers Rx 3.1, Rx 3.2 and Rx 3.3 of the BR 3 103. The DC supply source 129 is also connected via an electronic switch 137 to the receivers Rx 4.1, Rx 4.2 and Rx 4.3 of the BR 4 104. A site controller 141 controls functional operations of the BTS 100. The electronic switches 131, 133, 135 and 135 are controlled by control signals from the site controller 141. The site controller 141 operates the four electronic switches 131, 133, 135 and 137 so that three of those electronic switches are open, i.e. do not allow electrical current to be delivered from the DC supply source 129 to the respective BRs to which they are connected, and a fourth one of those electronic switches is closed, i.e. does allow electrical current to be delivered from the DC supply source 129 to the respective BR to which its is connected.

In FIG. 1 a situation is illustrated in which the electronic switch 137 has been selected by the site controller 141 to be closed. Thus, DC electrical energy is delivered from the DC supply source 129 to the receivers Rx 4.1, Rx 4.2 and Rx 4.3 of the BR 4 104. As described earlier, the receivers Rx 4.1, Rx 4.2 and Rx 4.3 are also connected respectively to the LNA 1 115, the LNA 2 121 and the LNA 3 127. The connections from the receivers Rx 4.1, Rx 4.2 and Rx 4.3 to the LNA 1

115, the LNA 2 121 and the LNA 3 127 are indicated respectively as provided by connectors 143, 145 and 147 respectively in FIG. 1. Although the connectors 143, 145 and 147 are provided primarily as RF connectors to deliver received input RF signals, such connectors are conducting and therefore can conduct DC electrical current to each of the LNA 1 115, LNA 2 121 and the LNA 3 127. The connectors 143, 145 and 147 may for example be coaxial cables and the DC current may be delivered by the conductors of such cables.

One of the BRs has been selected by the site controller 141 to carry a control channel for received input signals. This may for example be a channel on a particular carrier frequency or set of carrier frequencies. System related messages, e.g. to indicate current activity status, are sent from served MSs (not shown) to the BTS 100 on this channel. Conveniently, the same one of the BRs selected to carry the control channel may also be selected to provide a DC electrical supply to the LNAs. Thus, where the BR4 104 has been selected to provide a DC electrical supply to the LNAs as illustrated in FIG. 1, the BR 4 104 may also be selected to carry the control signal. In this way the control logic is simplified. If there is a service problem relating to the BR 4 104, the site controller

141 may detect the fault in a known way and may issue a single control signal indicating that another one of the BRs has to carry the control signal and to provide the DC electrical supply to the LNAs. For example, the BR 3 103 might be the other one of the BRs selected. The

control signal from the site controller 141 is delivered to the electronic switches 131, 133, 135 and 137 to provide changing of the one of the BRs selected for providing DC current supply as well as to provide changing of the control channel allocation in the BRs. The state of each of the electronic switches 131, 133, 135 and 137 is changed by the control signal so that the BR 4 104 no longer provides the DC electrical supply to the LNAs, whereas another selected one of the BRs, e.g. the BR 3 103 instead provides the DC electrical supply to the LNAs .

In the BTS 100 shown in FIG. 1, the electronic switches 131, 133, 135 and 137 are shown as being outside the BRs. However, this is not essential. The electronic switches may, in another embodiment of the invention, be incorporated respectively in the BRl 101, the BR2 102, the BR3 103 and the BR4 104. For example, each one of the electronic switches may be part of a processor of the one of the BRs in which it is incorporated. The same processor may also control and signal processing functions of that BR, e.g. relating to channel allocations in signalling between the BTS 100 and MSs (not shown) served by the BTS and to baseband processing of communication signals. This alternative embodiment of the invention is illustrated in FIG. 2 in respect of the BR 4 104. The BR4 includes a processor 201 which carries out signal processing and control functions of the BR 4 104 as described earlier. The processor 201 incorporates an electronic switch 203 having the same function as the

electronic switch 137 of FIG. 1. The electronic switch 203 is connected to an input connector 205 by which DC electrical energy may be delivered from the DC supply source 129 of FIG. 1. The electronic switch 203 is also connected via an output connector 207 to the receivers Rx 4.1, Rx 4.2 and Rx 4.3 which are the same as the corresponding referenced receivers shown in FIG. 1. A connection 209 from the site controller 141 (FIG. 1) supplies control signals to the processor 201 including signals which operate to change a state of the electronic switch 203. The receivers Rx 4.1, Rx 4.2 and Rx 4.3 have connections 211, 213 and 215 respectively which deliver electronic baseband signals obtained from received input signals by the receivers Rx 4.1, Rx 4.2 and Rx 4.3 to the processor 201 for processing in the processor 201. In addition, the BR4 104 includes a transmitter 217 which receives electronic baseband signals from the processor 201 via a connection 219. The transmitter 217 passes RF signals via the duplex filter 113 to the antenna 111 for conversion from bound to over-the-air radiated form. A combiner (not shown) may be used to combine RF signals produced by the respective transmitters of the BRs for delivery via the duplex filter 113 to the antenna 111. Operation of the processor 201 in the provision of DC electrical supply to the LNAs is as follows. A control signal is sent by the site controller 141 and is received by the processor 201 via the connection 209. The control signal includes an instruction indicating that carrying of the receiver control channel is to be

changed to the BR 104. In response, the processor 201 switches its operation to carry the receiver control channel. The processor 201 may also interpret the received control signal from the site controller 141 as an instruction to provide a DC supply to the LNAs. The processor 201 thereby closes the electronic switch 203. DC electrical energy from the DC supply source 129 (FIG. 1) is thereby supplied via the connector 205 and the connector 207 to the receivers Rx 4.1, Rx 4.2 and Rx 4.3 of the BR 4 and is delivered to the LNAs from the receivers Rx 4.1, Rx 4.2 and Rx 4.3 via the connectors 143, 145 and 147 (FIG. 1) as described earlier.

Where another one of the BRs instead of the BR 4 is selected by the site controller 141 to carry the receiver control channel and to provide a DC supply to the LNAs, a control signal indicating the required change is received from the site controller 141 via the connector 209. In response, the processor 201 opens the electronic switch 203. A processor of another selected one of the BRs, e.g. the BR 3 103, receives a control signal to carry the receiver control channel, and that processor in response switches its operation to carry the receiver control channel and also closes an electronic switch incorporated in that processor, to provide a DC electrical supply to the LNAs.

FIG. 3 is a flow chart summarising a method of operation in the BTS 100 in accordance with an embodiment of the invention. In a step 301, the site controller 141 selects a base radio, e.g. the BR 4 104, to carry the receiver control channel and to provide a

DC electrical supply to the LNAs. The selection may be as a result of a change from these functions being carried out by another one of the base radios, e.g. the BR 3 103. In a step 302, the site controller 141 sends a control signal to the base radios to indicate the selection. In a step 303, the selected base radio receives the control signal sent in step 302. In response, in a step 304, the selected base radio switches its operation to carry the receiver control channel and also closes an electronic switch, e.g. the electronic switch 203, to provide a DC supply to the LNAs via the appropriate connectors, e.g. via the connector 205 and the connector 207.

In the embodiments of the invention which have been described, the provision of a DC electrical supply to the LNAs is achieved by an arrangement which conveniently and beneficially allows the required electrical cabling to be simplified and allows simple and rapid switching to a backup arrangement, already in place and operational for delivery of RF signals, when the previously used arrangement has a service fault. Control logic required to effect the switching to the backup arrangement may also be simplified because the switching can be carried out in conjunction with switching of another function, such as carrying of received signal control channel, carried out by the arrangement .

Although the present invention has been described in terms of the embodiments described above with reference to the accompanying drawings, it is not

intended to be limited to the specific form described in such embodiments. Rather, the scope of the present invention is limited only by the accompanying claims. In the claims, the terms Comprising' or ^λ including' do not exclude the presence of other integers or steps.

Furthermore, although individually listed, a plurality of means, elements or method steps may be implemented by, for example, a single unit or processor. Additionally, although individual features may be included in different claims, these may possibly be advantageously combined, and the inclusion in different claims does not imply that a combination of features is not feasible and/or advantageous. In addition, singular references do not exclude a plurality. Thus references to "a", "an", "first", "second" etc do not preclude a plurality.