GB2318027A - Mobile transceiver with space diversity transmission and reception - Google Patents

Abstract

Reception of a radio signal by, for example, a car telephone is improved by a phasing technique. Multiple antennae 32-35 are provided at various positions around, in one embodiment, a car, each being connected to transceiver apparatus 40, 41, 48, 47, 49. Phase comparator 40 detects the relative phases of the signals received from a given transmitter. Phase adjuster 48 brings the received signals into phase for combiner 49, the output of which is applied to a normal RF receiver (not shown). A filter 47 may be used to compensate for irregular results originating from phase comparator 40. Signals are also transmitted directionally using the same concept in reverse. The invention may be equally applied to a laptop computer.

Description

Mobile Radio Transceiver The invention relates to mobile radio transceivers, and more particularly though not exclusively to mobile radio telephones..

With the increasing usage of mobile radio systems, system operators are finding that they have to operate with smaller cells to permit greater frequency reuse in order to accommodate the increasing number of users within the available spectrum.

The problems arising from allowing users access on demand can only worsen as more users join networks and existing users make more and longer calls.

The arrival of Faxing, E-mail and Internet access from lap-top computers connected to mobile phones has pushed more demand on mobile networks. There is always a need for improved spectrum use.

There also exists a need to improve the selection of a desired signal from interference in mobile telephony.

Stationary receivers can use highly directional antennae like the multi element Yagi types used for television broadcast reception, or the parabolic dishes used for microwave frequency communications. These must be aimed accurately at the desired transmitter, along the preferred signal path, to achieve a useful result by maximising the desired signal in the presence of unwanted co-channel interference. Directional antennae can be used in mobile radio but only in combination with an electronic tracking device and a mechanical arrangement to keep the antennae pointing in the required direction. Directional antennae are not practical for use in vehicular mobile telephony since vehicles change direction quickly and are subject to pitch and roll due to uneven surfaces or during cornering, accelerating or braking. This, in combination with the fact that the distances between transmitter and receiver are likely to be shorter and the multi- path effects greater than those in say, marine radio, means that tracked directional antennae are completely unsuitable for vehicular telephony.

It is known in vehicular radio systems to have multiple antennae with which to receive a radio signal. These antennae are used to provide combination or selection diversity.

In a selection diversity system a car may have an antenna situated on the roof or wing, as is common, and another located in a rear window or on a rear body panel. Either the receiver of the vehicle's radio system may be connected to both antennae, or a respective receiver may be connected to each antenna The system will determine some characteristic of the signal from each antenna in a sample period and pass to the demodulator of the system the signal which has been determined to be better. The decision may be based on a characteristic such as the signal amplitude or the signal-to-noise ratio. A selection diversity receiver is shown in Fig. 1.

Combination diversity is similar to this but instead of the switch in Figure 1, an adder is used. This adder may be controlled to adjust the level of the signal from each antenna that is passed to the demodulator.

It is also known in radar and in satellite communication systems to use multiple antennae in a phased array to determine the bearing of a transmitter. An arrangement such as that shown in Figure 2 can accurately determine from which direction a signal is received from the phase of the signals received by each antenna. This arrangement enables high sensitivity to transmissions of interest whilst being less sensitive to transmissions from other directions, but the hardware is both complex and expensive.

The present invention provides a receiver arrangement for use in a mobile radio transceiver in which two or more antenna are provided for receiving signals from a transmitter, wherein there are provided means to derive signals representing the relative phases of radio signals received at said two or more antennae from a given transmitter, means utilising the signals so derived to shift the phase of the respective received signals to bring said received signals substantially into phase, and means to combine the phase-shifted signals.

A cellular radio transceiver arrangement in accordance with the invention will now be described by way of example with reference to the accompanying drawings: Fig. 1 is a depiction of a known selection diversity receiver, Fig. 2 is a basic depiction of a known antenna array used in radar direction finding systems, Fig. 3 shows an antenna arrangement for use in the present invention, Fig. 4 shows a block diagram of a receiver in accordance with the present invention, and Fig. 5 shows a block diagram of a transmitter for use in the present invention.

Referring first to Figure 3, a vehicle 31 is provided with four antennae 3235 for receiving radio telephony signals from base station 30. As indecated the transmitted signal waveform will arrive at antenna 32-35 at different moments in time,so that the signals received at each antenna wil be of respective different phases. The difference in phase of signals arriving at any two antennae will be dependent on the distance between them and on the direction or angle of arrival.

The phase difference between two antennae will be: 2sDces e 9= 0 where D is the distance between the antennae, A is the wavelength of the radio signal and 0 is the angle between the base line of the two antennae and the direction of arrival of the signals.

The operation of the phasing combiner will now be described with reference to Figure 4. This Figure shows the phased combination of the signals from the four antennae of Figure 3.

The signals from the antennae 32 - 35 are carried by lines 42 - 45 respectively to a phase comparer 40. The phase comparer 40 detects the relative phases of the signals arriving on lines 42 - 45 and provides a signal on each line 142 - 145 which is representative of the detected relative phase of the signals on the corresponding line 42 - 45.

The filter 47 has the effect of smoothing the phase measurement results and helps to provide a cleaner output from the system. The smoothed phase representative signals on lines 242-245 are passed to phase adjuster 48 where they may be used to adjust the phases of the signals on the lines 42 - 45 so that they are brought substantially into phase with one another. These signals are then combined in combiner 49 and the resultant signal passed to the receiver.

It is clear that the above described arrangement will maximise detection of the desired signal whilst reducing the effect of signals at the same or a similar frequency that originate from a different direction, because these signals will at least partially cancel one another in the combiner 49.

Referring now to Figure 5, the same phase shifts can also be used when transmitting from a mobile unit to the base station in order to minimise the total power required for reliable operation. The signal to be transmitted is passed to phased signal generator 52 where it is to be split for transmission from each antenna. The signals on lines 142 - 145 are based on those originating from the comparer 40 in Figure 4. The signal 51 for each antenna is adjusted in phase by an amount according to the signal present on the corresponding line 142-145, and the phase adjusted signals are then passed to the antennae 32 - 35 where they are transmitted as radio waves. By using the phase measurements derived from signals received from a particular base station, the transmitted signals tend to reinforce one another in the direction of that base station. At the same time, the power levels trransmitted in directions other than that of the base station will tend to be reduced, reducing interference with other users, conserving spectrum and using more efficiently the power source of the car telephone It will be appreciated that the signals transmitted from and received by the mobile unit could originate from and be intended for a lap-top computer or other device capable of using a telephone channel for communication.

Claims (4)

Claims

1. A receiver arrangement for use in a mobile radio transceiver in which two or more antenna are provided for receiving signals from a transmitter, wherein there are provided means to derive signals . representing the relative phases of radio signals received at said two or more antennae from a given transmitter, means utilising the signals so derived to shift the phase of the respective received signals to bring said received signals substantially into phase, and means to combine the phase-shifted signals.

2. A mobile radio transceiver comprising a receiver arrangement in accordance with Clairn 1, means to split a radio signal for transmission by way of at least two of said two or more antennae, and means to adjust the relative phases of the radio signals to be applied to said at least two of said antennae in dependence upon the respective phase representative signals derived in said receiver arrangement.

3. A receiver substantially as described herein with reference to Figure 4 of the accompanying drawings.

4. A transceiver substantially as described herein with reference to Figures 4 and 5 of the accompanying drawings.