GB2332305A

GB2332305A - Signal processing system

Info

Publication number: GB2332305A
Application number: GB9726200A
Authority: GB
Inventors: Paul Howard; Nicholas William Anderson
Original assignee: Motorola Ltd
Current assignee: Motorola Solutions UK Ltd
Priority date: 1997-12-11
Filing date: 1997-12-11
Publication date: 1999-06-16
Anticipated expiration: 2017-12-11
Also published as: GB2332305B; GB9726200D0; GB2332305A9; HK1021258A1

Abstract

A method or means of signal processing, suitable for signals of an adaptive antenna array, which comprises: generating intermediate frequency signals 12, 14 coupled to each of a plurality of antenna elements 10 and combining 18 two or more of the intermediate frequency signals to form one signal which is then processed. The reverse of the above signal processing has also been disclosed. The intermediate frequency signals, which relate to each antenna element 10, may be at different frequencies form one another and bandpass filtering 16 may be used on each of the said signals. Digital processing and filtering 22 may be employed on the combined signal.

Description

1 2332305 SIGNAL PROCESSING SYSTEM

Field of the Invention

The present invention relates to a receiver and/or a transmitter for a communications system using an adaptive antenna array.

M of tJhe Invention In an adaptive antenna array of the type used, for example, in cellular communications systems, it is typical to use one receiver from RF to digital baseband and one transmitter from digital baseband to RF for each element of the array. An example of conventional hardware structure is shown in FIG. 1, in which the receiver hardware circuitry for two of several antenna elements is shown.

The receiver hardware for each antenna element includes a local oscillator and combiner to produce an intermediate frequency and a bandpass filter of known type. Channel selection circuitry includes a second local oscillator coupled to two combiners, of which one receives the second local oscillator signal at a 90- phase shift relative to the other combiner, these producing a baseband signal for use in channel selection in conjunction with associated low pass filters. Two analogue-to-digital converters digitise the filtered signals for subsequent processing by a digital beam former.

It will be apparent that equivalent transmitter circuitry would also be provided for each antenna element. Moreover, any increase in the number of antenna elements in an array would result in a linear increase in the number of hardware components required for the transmitters and receivers. This is costly in terms of number of hardware components which are required for the antenna array. It is also necessary, as a result of different circuit characteristics, to provide some form of continuous calibration to ensure that all the transceivers perform in equivalent manner to one another.

2 Summary of the Invention

The present invention seeks to provide an improved transmitter and/or receiver for an adaptive antenna array.

According to an aspect of the present invention, there is provided a signal processing system for processing signals to be received at an antenna formed of a plurality of antenna elements, including means for generating intermediate frequency signals coupled to each antenna element; signal processing and filtering means; and a signal combiner operable to combine two or more of the intermediate frequency signals from two or more of the plurality of antenna elements for processing together by the signal processing and filtering means.

Combining signals from a plurality of antenna elements prior to processing by some of the hardware components can significantly reduce the amount of hardware required.

Preferably, the means for generating the intermediate frequency signals to be combined are operable to generate the intermediate frequency signals at different frequencies.

Advantageously, the system includes filtering means for filtering the intermediate frequency signals prior to processing by the signal processing and filtering means.

The system may includes an analogue-to-digital converter between the combiner and signal processing and filtering means.

According to another aspect of the present invention, there is provided a method of processing signals received at an antenna formed of a plurality of antenna elements, including the steps of generating an intermediate frequency signal for each antenna element; combining at least two of the intermediate frequency signals to form a combined signal; and processing and filtering the combined signal.

1 3 According to another aspect of the present invention, there is provided a signal processing system for processing signals to be sent by an antenna formed of a plurality of antenna elements, including signal processing means operable to process a combined signal; a signal separator operable to separate from the combined signal a plurality of intermediate frequency signal; and radio frequency generating means coupled to each of the plurality of antenna elements and operable to generate a radio frequency signal from one of the plurality of intermediate frequency signals.

According to another aspect of the present invention, there is provided a method of processing signals to be sent by an antenna formed of a plurality of antenna elements, including the steps of signal processing a combined signal; separating from the combined signal an intermediate frequency signal for at least two of the plurality of antenna elements; and generating a radio frequency signal from the intermediate frequency signal of the at least two of the plurality of the antenna elements.

Brief Dption of the Drawings An embodiment of the present invention is described below, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1 is a block diagram of an example of prior art receiver for an 25 adaptive array;

FIG. 2 is a block diagram of a preferred embodiment of a receiver; and FIG. 3 is a graph of the combined received signal produced by the circuitry 30 of FIG. 2.

Dption of a Preferred xliment 4 For the sake of brevity, only the receiver is described below, although the converse holds for the transmitter, as will be readily apparent to the skilled person.

Referring now to FIG. 2, the receiver circuitry for all the antenna elements of an adaptive antenna array includes a local oscillator 12 and mixer 14 for each antenna element. The RF frequency used by each local oscillator 12 is individual to that branch of the circuitry. For example, the frequency diffierence may be 1 to 2 MHz from one local oscillator to another.

Each branch of the receiver also includes a bandpass filter 16 centred at the relevant local oscillator frequency. A signal combiner 18 produces a combined signal of a type shown in FIG. 3.

Referring to FIG. 3, each antenna element provides a signal within its own frequency band which is frequency shifted relative to the other channels of the other antenna elements. The combined signals can be processed together by the same circuitry. For this purpose, there is provided an analogue-to-digital converter 20 and signal processing and filtering circuitry 22 which operate in a conventional manner, although the signal processing and filtering circuitry 22 is also operable to extract each individual channel signal from the combined signal, to down convert it and pass it to the appropriate digital beam former in the beam former circuitry 24.

Through the use of the above-described scheme, N intermediate frequency chains (where N is the number of antenna elements and thus of channels) have been replaced with a single chain and the number of required analogue-to-digital converters has been reduced from N to 1. In addition, the number of local oscillators and filters required has been significantly reduced. Thus, a considerable saving in the number of hardware components can be achieved.

It will be apparent that the analogue-to-digital converter 20 will need to be of considerably higher resolution and would be used at a much higher sampling rate than the converters used in the prior art receiver circuitry.

1 However, advances in analogue-to-digital and digital-to-analogUe technology and digital processing speeds will provide the necessary technology. In any event, considerable savings in hardware components can be achieved even by combining only some of the channels with one another. One example would be to combine together the circuitry of every two channels.

If the broadband intermediate frequency (IF) is sufficiently "flat" in terms of amplitude response and has a substantially linear phase response, or the responses are known and time invariant, then the only section which needs to be calibrated is that prior to the IF stage. Actual calibration requirements can be determined on a case by case basis by experimentation.

The structure of a transmitter embodying these principles will be readily apparent to the skilled person from the above teachings.

6

Claims

1. A signal processing system for processing signals to be received at an antenna formed of a plurality of antenna elements, comprising means for generating intermediate frequency signals coupled to each antenna element; signal processing and filtering means; and a signal combiner operable to combine two or more of the intermediate frequency signals from two or more of the plurality of antenna elements for processing together by the signal processing and filtering means.

2. A system according to claim 1, wherein the means for generating intermediate frequency signals to be combined are operable to generate the intermediate frequency signals at different frequencies.

3. A system according to claim 1 or 2, including filtering means for filtering the intermediate frequency signals prior to processing by the signal processing and filtering means.

4. A system according to claim 3, wherein the filtering means includes a bandpass filter for each antenna element.

5. A system according to any preceding claim, wherein the signal processing and filtering means is digital; the system including an analogue-to-digital converter between the signal combiner and the signal processing and filtering means.

6. A method of processing signals received at an antenna formed of a plurality of antenna elements, including the steps of generating an intermediate frequency signal for each antenna element; combining at least two of the intermediate frequency signals to form a combined signal; and processing and filtering the combined signal.

7. A method according to claim 6, wherein the intermediate frequency signals have different intermediate frequencies.

1 7

8. A method according to claim 6 or 7, including the step of digitising the combined signal.

9. A method according to claim 6, 7 or 8, including the step of bandpass filtering the intermediate frequency signal for each antenna element prior to combining them.

10. A signal processing system for processing signals to be sent by an antenna formed of a plurality of antenna elements, including signal processing means operable to process a combined signal; a signal separator operable to separate from the combined signal a plurality of intermediate frequency signal; and radio frequency generating means coupled to each of the plurality of antenna elements and operable to generate a radio frequency signal from one of the plurality of intermediate frequency signals.

11. A method of processing signals to be sent by an antenna formed of a plurality of antenna elements, including the steps of signal processing a combined signal; separating from the combined signal an intermediate frequency signal for at least two of the plurality of antenna elements; and generating a radio frequency signal from the intermediate frequency signal of the at least two of the plurality of antenna elements.

12. A signal processing system substantially as hereinbefore described with reference to and as illustrated in FIG. 2 and 3 of the accompanying drawings.

13. A method of processing a signal substantially as hereinbefore described with reference to and as illustrated in FIG. 2 and 3 of the accompanying drawings.