ANTENNA DIVERSITY ARRANGEMENT, RF TRANSCEIVER ARRANGEMENT AND METHOD OF OPERATION

FIELD OF THE INVENTION

The present invention relates to an antenna diversity arrangement, an RF transceiver arrangement incorporating the antenna diversity arrangement and a method of operation.

BACKGROUND OF THE INVENTION

Many RF communication terminals use the same antenna for both transmission and reception of RF signals. A switching device such as a T/R

(transmit/receive) switch is usually employed to connect the antenna alternatively to the transmitter and the receiver of the terminal according to whether the terminal is currently in a transmitting or receiving mode .

Some terminals employ two or more antennas instead of one, in order to improve reception in the presence of multi-path fading. Using such multiple antennas is known in the art as providing 'antenna diversity'. Terminals having antenna diversity usually include a further switching device known as an ⁽ antenna selection' switch to make a connection to a selected one of the antennas . The antenna which is selected is the one currently receiving the strongest signal .

Furthermore, terminals operating in more than one frequency band may also include different transmitters to produce signals in the different frequency bands. In these terminals a further switching device known as a diplexer (multiplexer) is usually employed to make a connection to the appropriate selected transmitter. Such terminals usually also include receivers which can receive signals in the different frequency bands. As illustrated later, the transmission losses obtained in the various switching devices in such prior art terminals can be cascaded and the total transmission loss can be unsatisfactorily high. This can produce inefficient operation particularly at the transmitter power amplifier (s) leading to rapid battery drain, reduced power capability and increased heat dissipation.

SUMMARY OF THE INVENTION

According to the present invention in a first aspect there is provided an antenna diversity arrangement as defined in claim 1 of the accompanying claims .

According to the present invention in a second aspect there is provided an RF transceiver arrangement as defined in claim 9 of the accompanying claims .

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

Further features of the invention are defined in the accompanying dependent claims and are disclosed 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 a known RF transceiver arrangement incorporating an antenna diversity arrangement.

FIG. 2 is a block schematic diagram of an RF transceiver arrangement incorporating an antenna diversity arrangement embodying the present invention.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

FIG. 1 shows a known RF transceiver arrangement 100 including a known antenna diversity arrangement for 'use in a RF communication terminal. The transceiver arrangement 100 includes a first transmitter Tx 101 and a second transmitter Tx 103 for transmission of RF signals in different frequency bands. For example, the first transmitter Tx 101 may produce RF signals for transmission in a first band which includes 2.4 GHz and the second transmitter Tx 103 may produce signals in a second band which includes 5.0 GHz. The invention,is not limited to use in these particular bands however. The first transmitter Tx 101 and the second transmitter Tx

103 operate in a known manner and typically include as a last stage an RF power amplifier.

Output RF signals produced alternatively by the first transmitter Tx 101 and the second transmitter Tx 103 (whichever is currently operating) are applied respectively via a transmitter connection 102 and a transmitter connection 104 to a diplexer 107 which is a switching device which connects either the transmitter connection 102 or the transmitter connection 104 to a common transmitter connection 106. A T/R switch 109, operating under the control of a controller 117, is also connected to the common transmitter connection 106. A receiver connection 108 extends from the T/R switch 109 to a dual-band receiver Rx 105. The controller 117 applies control signals to the T/R switch 109 to switch a state of the T/R switch 109 to connect either the common transmitter connection 106 or the receiver connection 108 to a link connection 110 depending on whether the arrangement 100 is in a transmit mode or a receive mode. The link connection 110 is connected in turn to an antenna selection switch 111. The antenna selection switch 111 is connected via an antenna coupling connection 112 to a first dual-band antenna 113 and is connected via an antenna coupling connection 114 to a second dual-band antenna 115. The antenna selection switch 111 has two alternative states selected as described later. In a first selected state, the antenna selection switch 111 connects the link connection 110 to the first antenna 113 via the antenna coupling connection 112 and in a second selected state the

antenna selection switch 111 connects the link connection 110 to the second antenna 115, via the antenna coupling connection 114.

In use, the arrangement 100 has two alternative modes, namely a transmit mode and receive mode, which are applied as selected by a transceiver controller (which may be the controller 117) .

In the transmit mode, either the first transmitter Tx 101 or the second transmitter Tx 103 is selected (by the transceiver controller) to produce an RF signal for transmission. The signal is applied via the connection 102 or 104 as appropriate, the diplexer 107, the connection 106, the T/R switch 109, the connection 110, and the antenna selection switch 111 to either the antenna 113 or the antenna 115 via the connection 112 or the connection 114. Normally, the same antenna is always used for transmission, i.e. antenna diversity is not employed in the transmit mode. Thus, in the transmit mode, the antenna selection switch 111 is fixed in a state in which it connects the link connection 110 to an appropriate selected antenna, i.e. either the first antenna 113 (via the connection 112) or the second antenna 115 (via the connection 115. The selected antenna 113 or 115 sends over the air an RF signal to a remote receiver (not shown) .

In the receive mode, an RF signal is obtained over the air from a remote transmitter (not shown) and is collected by both the first antenna 113 and the second antenna 115. As noted earlier, the antenna selection switch 111 may be set in one of two alternative states,

referred to earlier as the first and second selected states, and the appropriate state in the receive mode is selected by the controller 117 and is indicated to the antenna selection switch 111 by a. signal from the controller 117.

The controller 117 includes a power sampling function which allows sampling in a known manner of the power received by each of the antennas 113 and 115. In order to facilitate operation of the power sampling function, the controller 117 sets the antenna selection switch 111 to be in each of its two possible states for a short predetermined period of time thereby to take samples of signals respectively from the first antenna 113 and the second antenna 115. The controller 117 then selects which of the antennas 113 and 115 is preferred based upon which of the two antennas is currently receiving the better (stronger) signal. Once the preferred antenna has been determined by the controller 117, the antenna selection switch 111 is set in a corresponding state to connect to the selected antenna 113 or 115. The received signal from the appropriate antenna 113 or 115, as selected by the state of the antenna selection switch 111, is thereby delivered via the common link 110, the T/R switch 109 and the connection 108 to the dual-band receiver Rx 105. The receiver Rx 105 can receive signals in two alternative frequency bands, typically the same two bands in which the transmitters Tx 101 and the transmitter Tx 103 can transmit. The dual band receiver Rx 105 processes the received signal in a known manner .

The cascaded transfer losses of the arrangement 100 to transfer a signal between the transmitter Tx 101 or the transmitter Tx 103 to either the first antenna 113 or the second antenna 113 as selected can be significant especially for transmitted signals of high frequency.

For example, where the transmitted signal from the first transmitter Tx 101 has a frequency of 2.4 GHz, typical losses experienced are -0.5 dB at the diplexer 107, -0.6 dB at the T/R switch 109 and -0.6 dB at the antenna selection switch 111 giving a total loss between the first transmitter Tx 101 and an antenna of -1.7 dB . Where the transmitted signal is from the second transmitter Tx 103 and has a frequency of 5.0 GHz, typical losses experienced are -0.8 dB at the diplexer 107, -0.7 dB at the T/R switch 109 and -0.7 dB at the antenna selection switch 111, giving a total loss between the second transmitter 103 and an antenna of - 2.2 dB. These losses are unsatisfactory since they are equivalent to power losses of 32% and 40% respectively between the appropriate transmitter Tx 101 or 103 and the antenna 113 or 115.

FIG. 2 shows an RF transceiver arrangement 200 including an improved antenna diversity arrangement in accordance with an embodiment of the invention. Components of the arrangement 200 shown in FIG. 2 which have the same function as components of the arrangement 100 shown in FIG. 1 are indicated by the same reference numerals. Thus, the arrangement 200 includes the first transmitter Tx 101, the second transmitter Tx 103, the dual-band receiver Rx 105, the first dual-band antenna

113 and the second dual-band antenna 115. In the arrangement 200 an output signal produced for transmission by the first transmitter Tx 101 is applied via a first transmitter connection 202 to a first T/R switch 209; and an output signal produced for transmission by the second transmitter Tx 103 is applied via a second transmitter connection 204 to a second T/R switch 213. The first T/R switch 209 is connectible via a first receiver connection 206 to a receive selection switch 211. The second T/R switch 213 is connectible via a second receiver connection 208 to the receive selection switch 211. The receive selection switch 211 has a single output via a common receiver connection 210 to the dual-band receiver 105. The first T/R switch 209 is connected by an antenna coupling connection 212 to the first antenna 113. The second T/R switch 213 is connected by an antenna coupling connection 214 to the second antenna 115.

The states of the T/R switches 209 and 213 and of the receive selection switch 211 are selected by the controller 217 and applied by control signals from the controller 217.

In use, the arrangement 200 has two modes, a transmit mode and a receive mode, which are selected by a transceiver controller which may be the controller 217 or a separate controller (not shown) .

In the transmit mode, the T/R switch 209 is switched to a state in which the first transmit connection 202 is connected to the antenna coupling connection 212, and the T/R switch 213 is switched to a

state in which the second transmit connection 204 is connected to the antenna coupling connection 214. This allows signals to be delivered from the transmitter Tx 101 to the corresponding first antenna 113 and from the transmitter Tx 101 to the corresponding second antenna 115.

In the transmit mode of the arrangement 200, either the first transmitter Tx 101 or the second transmitter Tx 103 is selected by the transceiver controller to produce an RF signal for transmission, depending on which transmission frequency band is currently to be used. A RF signal produced by the first transmitter Tx 101 is applied via the connection 202, the T/R switch 209 and the connection 212 to the first antenna 113. A RF signal produced by the second transmitter Tx 101 is applied via the connection 204, the T/R switch 213 and the connection 214 to the second antenna 115. When each of the antennas 113 and 115 receives a RF signal for transmission in the transmit mode, it sends the signal over the air to a remote receiver (not shown) .

It is to be noted that, in contrast to the prior art arrangement 100 in which a single T/R switch and a single antenna is used for transmissions from both transmitters, each of the transmitters Tx 101 and Tx 103 in the arrangement 200 has its own dedicated T/R switch and its own dedicated antenna.

In the receive mode of the arrangement 200, a received RF signal in one of two operational frequency bands is obtained over the air from a remote transmitter (not shown) at both the dual-band first antenna 113 and

the dual-band second antenna 115. The signal at the first antenna 113 is applied via the connection 212, the T/R switch 209 and the connection 206 to the receive selection switch 211. The signal at the second antenna 115 is applied via the connection 214, the T/R switch 213 and the connection 208 to the receive selection switch 211. The receive selection switch 211 is set into a selected state, by the controller 217 in a manner similar to that described earlier for the antenna selection switch 111. In a first one of its two states, the receive selection switch 211 connects the connection 206 to the dual-band receiver Rx 105 via the common receiver connection 210. In a second one of its two states, the receive selection switch 211 connects the connection 208 to the dual-band receiver Rx 105 via the common receiver connection 210.

The state of the receive selection switch 211 to be selected in the receive mode is determined by the controller 217 by determining whichever of the antennas 113 and 115 is currently receiving the stronger signal. Like the controller 117 of the prior art, the controller 217 includes a power sampling function which allows sampling in a known manner of the power received by each of the antennas 113 and 115. In order to facilitate use of the power sampling function, the controller 217 sets the receive selection switch 211 to be in each of its two possible states for a predetermined short period of time. The controller 217 then selects which of the antennas 113 and 115 is currently preferred based upon which of these two antennas is currently receiving a

stronger signal. Once the preferred antenna in terms of received signal strength has been determined by the controller 217, the state of the receive selection switch 211 is set accordingly. Either the first antenna 113 if selected is connected via the connection 206 (and the T/R switch 209 and the connection 212) to the common receiver connection 210 by the receive selection switch 211, or the second antenna 115 if selected is connected via the connection 208 (and the T/R switch 213 and the connection 214) to the common receive connection 210 by the receive selection switch 211.

The controller 217 may in practice be a programmed digital signal processor. It may also serve as a controller/processor for the transmitters Tx 101 and 103 and the receiver Rx 105 and possibly other known functions within a terminal incorporating the transceiver arrangement 200.

In contrast to the prior art arrangement 100 shown in FIG. 1, the arrangement 200 embodying the invention beneficially contains only a single switching device in each of the respective signal transmit routes between the transmitter and its corresponding antenna. Thus, between the first transmitter Tx 101 and the first antenna 113 the only switching device is the T/R switch 209, and between the second transmitter Tx 103 and the second antenna 115 the only switching device is the T/R switch 213. As in the prior art arrangement 100, a single dual-band receiver, namely the receiver Rx 105, is employed to process received signals from either the first antenna 113 or the second antenna 115. In contrast to the prior art

arrangement 100, the switching device employed to select the connection from either the first dual band antenna 113 or the second dual band antenna 115 from which received signals are to be delivered, namely the receive selection switch 211, is not included in any route for transmitted signals, i.e. between the first transmitter Tx 101 and the first antenna 113 or between the second transmitter Tx 103 and the second antenna 115. The inventors of the present invention have appreciated that this novel arrangement is possible owing to the fact that antenna diversity, if required, is needed only in the receive mode, not in the transmit mode.

By the arrangement 200 embodying the invention, there is a significant reduction in the transfer loss between each transmitter and its corresponding antenna, i.e. between the first transmitter 101 and the first antenna 113 or between the second transmitter 103 and the second antenna 115. For example, for transmission of signals at a frequency of 2.4 GHz, the transfer loss is reduced to about -0.6 dB, and for transmission of signals at a frequency of 5.0 GHz, the transfer loss is reduced to about -0.7 dB. These losses are equivalent to percentage power losses of about 10% and 13% respectively. Thus, a three fold improvement in the respective transfer losses is obtained by use of the arrangement 200 embodying the invention, compared with the prior art arrangement 100 of FIG. 1.

As a result, several benefits are obtained in a communication terminal incorporating the arrangement 200,

e.g. lower current drain, higher transmission power capability and reduced heat dissipation.

The transceiver arrangement 200 embodying the invention is suitable for use in a RF communication terminal such as a base transceiver terminal or other fixed terminal or in a mobile station such as a portable or vehicle carried radio, a radio telephone, a wireless enabled portable computer and the like. In particular, the arrangement 200 is especially suitable for use in dual- band terminals for use in networks in accordance with IEEE 802.11 standards for WLAN (Wireless Local Area Networks) .