FR2682838A1 - RADIO RECEIVER AND TRANSMITTER PRODUCING DIVERSITY. - Google Patents

Abstract

A radio receiver includes first (10) and second (11) physically spaced antennas to provide diversity and an equalizer (20) to combine components of a received symbol that are separated in time. Signals received at the first and second antennas are combined in a combiner (19) and are coupled to the equalizer. A variable delay means (18) is provided in the reception path of one of the antennas to delay signals received at the level of this antenna with respect to signals received at the level of the other antenna from which it follows that the probability of destructive interference between the signals from the first and second antennas is significantly reduced.

Description

The present invention relates to a radio receiver

  producing a diversity also called "diversity of

  pace "or" diversity antenna "It can for example

  apply to radio transmission systems that use

  feels a digital modulation and that incorporate equalizers for the reduction of the effects of multichannel propagation An example of these systems is constituted by

  The digital mobile radio telephone system

  vention also relates to a radio transmitter producing

diversity.

  The diversity antenna is a technique in which two receiving antennas are used, these

  antennas being physically spaced apart by several lon-

  wavelengths The radio receiver has standard

  only two separate parallel amplification channels to which each antenna is connected. At the end of the reception processing chain, the two signals are applied in a processor which, conventionally, selects either the best signal or phase shifts. then which coherently adds the two signals The reason is that for signals subject to fading (for example for mobile radio systems), the signals on the two antennas are very rarely statistically in a condition of simultaneous fading Consequently, the signal combined in diversity exhibits fading effects

  The conventional dual receiver and diversity combiner, however, add significant additional complexity and it would be desirable to provide a simpler solution.

  For digitally modulated radio systems that incorporate multi-channel EQs (e.g. the

  GSM system), document EP-A-0430481 describes an agent

  diversity cement in which each of two parallel reception chains is connected to one of the two ports of a special two-port equalizer which acts as an integrated equalizer / diversity combiner The arrangement still requires, however, a double

reception chain.

  GB-A-2237706 describes a space diversity system in which signals arriving on

  an antenna or coming from that antenna are re-

  delayed compared to signals arriving on or coming from a second antenna and a Viterbi equalizer is used to combine the signals

delayed and not delayed.

  A problem with the arrangements of prior art

  The reason for this is that the circumstances must be such that the delay of the delay element is, at least occasionally, virtually equal to that of

  real multi-channel separation for pro-

  different pagation, making reception worse

rather than better.

  According to a first aspect of the present invention,

  a radio receiver is proposed and it includes

  first and second physically spaced antennas to produce diversity and an equalizer for combining components of a received symbol which are separated in time, a combiner for combining the signals received at the first and second antennas and for coupling the combined signal to the equalizer and a delay means provided in the reception path of one of the antennas for delaying signals received at this antenna with respect to signals received at the other antenna so as to significantly reduce the probability of interference

  destructive between the signals coming from the pre-

  first and second antennas The invention, in this aspect, is characterized in that the delay means

is variable.

  According to a second aspect of the invention, a transmitter

  radio tor is intended to communicate with a receiver comprising an equalizer for combining components

  of a received symbol which are separated in time, the e-

  transmitter comprising first and second physically spaced antennas to produce diversity, a separator means for separating a signal to be transmitted and for coupling it to the first and second antennas and delay means provided in the channel

  of one of the antennas to delay

  signals transmitted by this antenna by more than a predetermined minimum delay with respect to signals transmitted by

  j 5 the other antenna so as to significantly reduce

  cative the probability of destructive interference between the signals from the first and second antennas, the delay means being a variable delay means. The receiver or transmitter may include means for receiving or transmitting respectively a signal which is divided into discrete frames and the delay between the two signals or between more than two signals may

be changed frame by frame.

  According to a third aspect of the invention, a re-

  radio receiver is proposed and it includes: first and second physically spaced antennas to produce

  diversity; an equalizer to combine components

  time of a received symbol which are separated in time, a combiner for combining the signals received at the first and second antennas and for coupling the combined signal to the equalizer and a delay means provided in the reception channel of the one of the antennas for delaying signals received at this antenna with respect to signals received at

  the other antenna so as to significantly reduce

  cative the probability of destructive interference between the signals from the first and second antennas, characterized by frequency and / or phase shift means for shifting the frequency and / or phase of the signal received at an antenna relative to the frequency and / or phase of the signal

received at the other antenna.

  According to a fourth aspect of the invention, a radio transmitter is provided to communicate with a receiver comprising an equalizer to combine components of a received symbol which are separated in time, the transmitter comprising first and second

  physically spaced antennas to produce a variety of

  sity, a separator means for separating a signal to be transmitted and for coupling it to the first and second antennas and delay means provided in the transmission path of one of the antennas to delay signals transmitted by this antenna more than a predetermined minimum delay with respect to signals transmitted by

  the other antenna so as to significantly reduce

  ficative the probability of destructive interference between the signals from the first and second antennas, the delay means further comprising frequency shift and / or phase shift means for shifting the frequency and / or phase of the signal transmitted to the across an antenna with respect to frequency and / or

  the phase of the signal transmitted through the other antenna. This feature provides improvements when the signals are Doppler shifted.

  The invention, in all its aspects, proposes a very inexpensive and very simple arrangement in which

  diversity can be produced A particular advantage is that diversity can be produced by simply adding a combiner, a delay element and an additional antenna, for example at the RF stage No additional processing is es-

  sensitive to the fact that the signals from the two antennas are combined in addition by the equalizer which

works in its normal way.

  Two antenna signals can be processed by (different) delay line means or a plurality of antennas and delay lines can be used A phased network can be provided and it includes parallel reception channels for diversity and combinations of delay elements in one or more of the receive chains

  chains for additional diversities.

  Multichannel diversity can be ensured through

  to more than two antennas as long as the signals from the antennas are separated from one

the other by a delay.

  The delay means can be analog or

  digital and may exist in the inter- frequency stage

  middle (FI) or in the high frequency (RF) stage.

  In the case of RF processing, the delay means can be in the form of an external unit which can incorporate its own frequency converters, its own IF amplifiers and its own delay means. The delayed and added signal can be validated,

  invalidated or modified according to a certain character-

  detected signal teristics, as described below.

  The problem dealt with by the invention also occurs in a repeater or in a booster which incorporates a delay, the delay in a signal in

  origin of the repeater which can, at least occasionally-

  Also, be virtually equal to the actual multi-channel delay separation for signals from the repeater and a main transmitter, which makes the

  reception worse rather than better.

  According to a fifth aspect of the invention, a repeater is proposed for receiving signals in

  from a main transmitter and for

  transmit, this repeater comprising a delay means for delaying the signals before the retransmission so as to simulate a multi-channel dispersion or spread in the common emission zones of the main transmitter and the

  repeater, the delay means being variable.

  In a repeater or "booster" arrangement where a signal is amplified and re-emitted on the same frequency as that on which it is received, another problem arises and it consists in that a positive loopback occurs from the side emission until

reception side.

  According to a sixth aspect of the invention, an RF booster or repeater is provided for receiving signals from a main transmitter and for

  re-transmit them to a remote receiver which

  carries an equalizer which can equalize pre-

  sensing phase or frequency differences according to a predetermined tolerance, the repeater comprising delay means for delaying signals before their re-transmission so as to simulate multi-channel broadcasting or spreading in the common transmission zones of the main transmitter and repeater and including

  in addition to a frequency shift and / or shift means

  phase link to shift the phase and / or frequency of the signals before re-transmitting a value which

  falls within the tolerance of the remote receiver equalizer.

  Particular embodiments of the invention

  The following are now described by way of examples only, with reference to the drawings, and among these drawings:

  FIG. 1 represents a first embodiment of an improved multi-diversity receiver

  route according to the invention; FIG. 2 represents a phase diagram intended to explain the invention; FIG. 3 represents an embodiment of a diversity receiver according to the invention, the delay means being provided in the RF stage; FIG. 4 represents an extension RF diversity unit according to another embodiment of the invention; FIG. 5 represents a transmitter producing a diversity - according to aspects of the invention; FIG. 6 represents a repeater which uses the invention from the point of view of its fifth and sixth aspects; and FIG. 7 represents the repeater of FIG. 6. In FIG. 1, one can see a part of a radio receiver, for example of the GSM type, which comprises a main reception antenna 10 and a diversity antenna 11 L ' main antenna 10 produces a signal for a main reception channel 12 which includes a front RF amplifier unit 13 including a frequency converter unit (not shown) and an IF stage 14 A number of frequency converter units and IF stages can be used The diversity antenna produces a signal for a diversity reception channel 15 which comprises a front amplifier unit 16 and an IF stage 17 The diversity reception channel 15 also comprises a delay element 18 which may be in the form of a long transmission line, a surface acoustic wave delay line or one or more filters The output of stage FI 14 obtained on the main reception channel 12 and the delay element 18 located on the diversity reception channel are combined in a simple combiner 19 and are passed to a multi-channel equalizer 20 The multi-channel equalizer conforms to the GSM specification and can be for example that described in document EP-A-0318685 or in document EP-A-0343189 The equalizer 20 is of a form

  digital, i.e. the input that arrives at the

  equalizer 20 is the subject of an analog conversion

  digital / digital (A / D) The equalizer uses four times oversampling After equalization, the signal is subject to error coding in an error coder 21, in accordance with the GSM specification, and the result is passed to a voice signal decoder to extract voice signal information and to synthesize a voice signal Analog equalizers

  could also be used.

  The operation of the receiver in FIG. 1 is as follows: A GMSK signal (or any other binary modulated signal) is received at an antenna 10 from a mobile transmitter. At the same time, a signal is received from the transmitter. at the antenna 11 via a different channel Each symbol of the signal

  has a duration of approximately 4 microseconds.

  The signals received at the antennas are amplified and are transposed by lowering the frequency in the front units 13 and 16 as well as in the IF stages 14 and 17 respectively. The signal from

  the antenna 11 is delayed in the delay element 18.

  The delay element delays the signal by at least a fraction of a bit period which is sufficient for the probability of destructive interference between the signals from channels 12 and 15 when combined in combiner 19 is significantly reduced In order to further reduce the probability of destructive interference, the delay introduced by the delay element is made variable. The combiner 19 sums the signals and passes the summed combination to the multi-channel equalizer 20 The equalizer 35 20 performs a digital / analog conversion and applies appropriate delays and appropriate phase shifts to different parts of the signal so as to realign the various components of a symbol in

  time and in phase in a way known in the art

  tive to an interference interference equalization

  symbol The equalizer 22 acts on the separate components of the signal received on channels 12 and 15 (and on all the components introduced by real multi-channel reflections before reaching the antennas 10 and 11) and it corrects the time error and any phase error observed between them The resulting equalized signal is demodulated in order to extract the symbols and it is subjected to error coding in the

error encoder 21.

  In order to reduce the probability of destructive interference at combiner 19, a delay of at least 1/4 bit period is preferred (although smaller delays may suffice) 1/2 bit period is considered being a usable delay A limiting factor is constituted by the bandwidth of the filters in the signal path after the combiner In the GSM system, these filters remove the distinction between two signals separated by less than about a binary period Consequently, a particular delay which is preferably part of

  a range from 1 to 2 binary periods Equali-

  GSM is typically designed to equalize re-

  delays up to 16 microseconds and in theory a delay

  10 to 16 microseconds can be used (i.e.

  say up to 5 binary periods) but some benefits

  these are lost if the signals themselves are subject to

  a multi-channel delay The implementation of an over-

  larger sampling in the equalizer can

allow for shorter delays.

  The operating principle of the equalizer 20 is also shown in relation to FIG. 2 The figure represents a time axis with phasers which represent multiple signals illustrated while

  that their phases revolve around the time axis.

  The time axis is represented according to a stereoscopic visualization so that the time delays and the phases of the different phasers can be seen at the same time. Two symbols Ql and Q 2 are represented out of phase If these symbols have to be summed, the result is obtained. Ql + Q 2 represented We can see that these symbols either can be summed together or can cancel each other with a probability

  equal In contrast, the symbols Q 3 and Q 4 are represented

  felt to be separated in time from a delay d.

  When these symbols are summed in the adder 19, these signals being broadband signals, they cannot cancel each other out The equalizer dephases on the symbol Q 4 to bring it in phase with the symbol Q 3 and it delays the symbol Q 4 so that it coincides with the symbol Q 3 So the two symbols are added and they always produce a larger resulting signal represented as Q 3 + Q 4. The principle is that the multi-channel equalizer coherently combines two or more signals of any phase arriving at a receiver antenna as long as they have a different time delay This is the normal expected function of the equalizer which consists of boost signals that suffer from multichannel propagation In this application, the diversity signal is rendered such that it looks like a delayed multichannel signal, due to the added delay line, and is therefore combined with coherently by the classic multichannel equalizer The delay is made variable so

  to remove the possibility that the delay deliberately intro-

  duit is equal but opposite to the natural propagation delay of the signal between the two antennas No additional phase correction is required and

  provided that the equalizer has been optimized, the improvement

  diversity ration can be at least 3 d B and typically 6 d B for signals subject to fading. The delay line means can be an analog delay line, a digital delay line, an IF delay line or a RF delay line (see below) A transmission line, group circuit, surface acoustic wave circuit or digital circuit can be used (not necessarily exclusively) for the delay line. In a linear receiver as used for the GSM mobile phone system, the delay line and the simple combiner can be installed at the front of the RF section of the receiver. This is shown in Figure 3 In this figure, the elements of figure 1 have the same reference indexes as in figure 1 An RF delay line 25 is connected to the diversity antenna il and the other end of the delay line is connected to a simple RF combiner 26 , as well as an RF connector connected to the main antenna 10 The output of the combiner 26 is passed to the front unit 13 as well as to other

  elements, as shown The arrangement is possible because two or more independent signals can

  can be processed by a linear receiver without mutual interference This means that we can do without the double reception chain A conventional non-diversity receiver 30 (with equalizer) can be used with the diversity components (delay line means and simple combiner) contained in an external expansion unit. The combiner can be a simple signal adder or a hybrid adder. The delay line can operate at RF frequencies or the RF diversity unit can incorporate its own frequency converters so that the delay line can operate at a frequency intermediate, like

shown in figure 4.

  If we refer to this figure, we can see that the elements of Figure 3 are represented with the same reference index Between the diversity antenna 11 and the combiner 26 are provided a first RF filter 30, a mixer 31 , an IF filter 32, a delay element 33, a second mixer 34 and a second RF filter 35 A local oscillator 36 is coupled to the mixers 31 and 34 The mixer 31 and the

  generator 36 operate to transpose by lowering

  frequency signal up to an IF frequency such as 100-200 M Hz At this frequency, an inexpensive and compact delay element 33 can be installed, for example in the form of a surface acoustic wave filter La frequency FI is transposed by increasing the frequency in the mixer 34 and the

  operation of the invention is the same as that of the embodiment of FIG. 3.

  Components 11, 25 and 26 can be

  considered as an extension unit.

  Under certain conditions, when one or more of the diversity signals suffer from real multichannel propagation, it is advantageous to modify the time delay of the delay line for each frame of the modulated signal

  digitally This is achieved using ele-

  switchable delay elements such as for example shown in dotted lines in FIG. 4, the delay element 40 having a delay greater than that of the element 33 and being able to be switched in the IF channel in place of the element 33 Alternatively, in the embodiment of Figure 3, the delay element can be switched from the reception channel of

  diversity on the main reception channel

  ie between points A-A 'and B-B' Combinations

  of these arrangements can be used.

  The switching of the delay element is carried out in response to dispersion information taken from the equalizer 20. As a variant, the switching is

repetitive or pseudo-random.

  In another embodiment of the invention, a small frequency offset of approximately 3 to 5 k Hz is applied to the diversity signal and / or a phase shift of 0-360 is applied This characteristic produces

  improvements when signals are shifted Doppler.

  In the embodiment of FIGS. 1 and 4, the frequency offset is applied in the IF stage, for example by adjusting the injection frequency from an oscillator 36 The frequency offset can be

  rendered to RF level in a way that can be easy-

  implementation by a person skilled in the art The phase shift is implemented by means of a variable capacitance / diode network provided in the RF signal channel or by means of a series of line phase shift elements. transmission This delay element switching technique works in conjunction with the error encoder 21 in a similar manner to the principle

  frequency hopping adopted in the GSM system.

  As with the switching of the delay element, the frequency offset and / or phase shift is made

variable frame by frame.

  The delay, frequency offset and / or

  phase shift can be validated, invalidated or modified according to the characteristics of the signal received as

  signal strength, interference or propagation delay spreading In this way, an adaptive multi-channel enhancement diversity arrangement35 is formed.

  In principle, a variety of multi-channel enhancement can be used at the receivers, at either end of a two-way radio link. For mobile / portable radio telephone systems, it is rarely of interest to have a second antenna system on the mobile or portable unit (i.e. a diversity antenna for the downlink path channel going from the station

to the mobile device).

  FIG. 5 represents an arrangement according to the second aspect of the invention in which a delay element is introduced into the transmitter chain, which validates the use of two transmit antennas at the base station to ensure downlink diversity instead of two antennas

  reception located on the mobile or portable unit.

  The arrangement comprises a transmitter 50, a separator

  simple transmitter 51, a diversity transmitter antenna 53 and a delay element 54 connected between the splitter 51 and the diversity antenna 53 The transmitter communicates with a mobile unit 55 which incorporates a

  multi-channel EQ Additional features

  delay switching, frequency shift and / or phase shift shutters described above may also apply In practice, the delay element 54 is preferably included in the transmission channel before the power amplification signal and two power amplifiers are provided to amplify the primary signal and the delayed signal.30 The transmitter 50 can be a transmitter only and the mobile unit 55 can be a receiver only,

  this unit being provided with a multichannel equalizer specifically added in order to equalize the signals coming from the main antennas and in diversity 52 and 53.

  The principle of the invention can be applied to a booster in order to overcome problems observed at the border of the booster which result from

  multiple natural pathways (from the main cell

  blade and from the booster) This is shown in Figure 6 in which a main cell transmitter 60 is shown as having an emission radius 61 and in the main cell emission radius is a cell booster 62 which has an emission radius 63 The cell booster is typically used to cover a problematic area or "hole" of the cell It has a smaller emission radius than that of the main cell The cell booster simply re-emits the signal 65 which it receives from the main cell transmitter, a shielding being provided to prevent it from re-transmitting its own signal at a point 64 located on the border of the transmission zone of the cell booster, signal 66 from the cell booster can arrive almost simultaneously with signal 67 from the main cell transmitter According to this aspect of the invention, the cell booster introduces a delay into the signal 66 The delay is periodically switched in order to adapt to a possible fading at different points on the emission border of the cell booster. As shown in FIG. 7, the cell booster 62 comprises a receiving antenna 70, a transmitting antenna 75 and a reception / transmission channel which comprises a preamplifier 72 and a power amplifier 74 A delay element is introduced on the side of reception at a position 71 or before the power amplifier, at a position 73 The delay is switched frame by frame by means of a timing circuit 76 It is understood that the variants described above in relation to a diversity of reception and transmission diversity can be implemented For example, there may be more than one reception antenna or more than one transmission antenna In each case, the signal passing through an antenna is delayed relative to the signal

which crosses the other antennas.

Claims (7)

1 radio receiver including   first and second antennas (10, 11) physi-   spaced apart to produce diversity; an equalizer (20) for combining components of a received symbol which are separated in time; a combiner (19) for combining signals received at the first and second antennas (10, 11) and for coupling the combined signal to the equalizer (20); and delay means (18) provided in the reception path (12) of one of the antennas for delaying signals received at this antenna from signals received at the other antenna so as to reduce significantly the probability of destructive interference between the signals from the first and second antennas (10, 11),   characterized in that the delay means comprises a variable delay.   2 radio receiver according to claim 1, characterized in that it comprises means for receiving a signal which is divided into discrete frames and means for varying the delay from one frame to another. 3 radio receiver according to claim 2, characterized in that the equalizer (20) comprises means for indicating a characteristic of the received signal and in that the means for varying the delay varies the delay in response to the characteristic. 4 radio receiver according to claim 3, characterized in that the characteristic is the dispersion of the received signal.   A radio receiver comprising first and second antennas (10, 11) physically spaced to produce diversity; an equalizer (20) for combining components of a received symbol which are separated in time; a combiner (19) for combining signals received at the first and second antennas (10, 11) and for coupling the combined signal to the equalizer (20); and delay means (18) provided in the reception path (12) of one of the antennas for delaying signals received at this antenna from signals received at the other antenna so as to reduce significantly the probability of destructive interference between the signals from the first and second antennas (10, 11), characterized in that the delay means further comprises frequency shift and / or phase shift means for shifting the frequency and / or phase of the signal received at an antenna with respect to the frequency and / or phase of the signal received at the other antenna.   6 Radio receiver according to any one of   previous claims for receiving signals comprising periodic bits, characterized in that   the delay means causes a delay of at least a quarter of a binary period. 7 Radio receiver according to any one of   previous claims for receiving signals comprising periodic bits, characterized in that   the delay means causes a delay of at least one full bit period. 8 Radio receiver according to any one of   previous claims, characterized in that it comprises a primary antenna (10), a plurality   secondary antennas (11) spaced apart to produce diversity and delay means provided in the reception path (15) of each secondary antenna (11), so as to cause the separation in time of signals received at each secondary antenna more than a predetermined minimum delay with respect to signals   received at each other antenna.   9 Radio receiver according to any one of   previous claims, characterized in that the   delay means includes an acoustic wave element of surface.   Radio transmitter for communicating with a receiver having an equalizer for combining components of a received symbol which are separated in time, the transmitter comprising first and second antennas (52, 53) physically spaced to produce diversity, a means of splitter (51) for separating a signal to be transmitted and for coupling it to the first and second antennas (52, 53) and delay means (54) provided in the transmission path of one of the antennas for delaying signals transmitted by this antenna by more than a predetermined minimum delay with respect to signals transmitted by the other antenna so as to significantly reduce the probability of destructive interference between signals from the first and second antennas (52 , 53), characterized in that the delay means (54) is a variable delay means.   11 radio transmitter according to claim 10, characterized in that it comprises means for transmitting a signal which is divided into discrete frames and means for varying the delay from one frame to another. 12 Radio transmitter for communicating with a receiver having an equalizer for combining components of a received symbol which are separated in time, the transmitter comprising first and second antennas (52, 53) physically spaced to produce diversity, a means separator (51) for separating a signal to be transmitted and for coupling it to the first and second antennas (52, 53) and delay means (54) provided in the transmission path of one of the antennas for delaying signals transmitted by this antenna by more than a predetermined minimum delay with respect to signals transmitted by the other antenna so as to significantly reduce the probability of destructive interference between the signals from the first and second antennas ( 52, 53), characterized in that the delay means (54) further comprises frequency shift and / or phase shift means for shifting the frequency and / or the phase of the signal transmitted through an antenna with respect to the frequency and / or phase of the signal transmitted to across from the other antenna.   13 Repeater for receiving signals in   from a main transmitter and for   transmit, characterized in that it comprises a variable delay means for delaying signals before their retransmission so as to simulate a multi-channel spreading   in the main transmitter areas of the main transmitter cipal and repeater.   14 Repeater for receiving pro   coming from a main transmitter and for re-transmitting them to a remote receiver, characterized in that it includes an equalizer making it possible to equalize signals which have phase or frequency differences compared to a predetermined tolerance, the repeater comprising delay means for delaying signals before their retransmission so as to simulate   multi-channel spreading in common emission zones   nes of the main transmitter and the repeater and further comprising a frequency shift means and / or   phase shift to offset the phase and / or frequency of the signals before their re-transmission by a value which is within the tolerance of the equalizer of the remote receiver35.