WO1988002963A1

WO1988002963A1 - Device for receiving broadcasts, television programs or radar echoes

Info

Publication number: WO1988002963A1
Application number: PCT/FR1987/000381
Authority: WO
Inventors: Yvon Fouche; Philippe Elleaume
Original assignee: Thomson-Csf
Priority date: 1986-10-07
Filing date: 1987-10-06
Publication date: 1988-04-21
Also published as: AU8039587A; FR2604843A1

Abstract

Device for receiving broadcasts, television programs or radar echoes. The invention comprises essentially the synchronisation of the clock of a transmitter with a receiver by using the total correlation and/or the local correlation of the signal received by an emission code. The synchronisation allows particularly the provision of a phase reference necessary to the phase modulation transmissions. For the receiver of the radio or television type, the use of an adapted narrow filter (140) makes possible, at the cost of a reduction of the signal/noise ratio, an attenuation of the self-distortion of the signal. The fine analysis of the signal allows an extremely precise synchronisation while the free-synchronisation using convolutioners of the charge coupling device type (130) makes it possible to limit the number of calculations required. The invention may be applied particularly to radio receivers, television receivers or radar receivers.

Description

DEVICE FOR RECEIVING RADIO, TELEVISION OR RADAR ECHOES

The present invention relates to a device for receiving radio, television or radar echo transmissions. The device according to the invention is capable of receiving waves modulated in phase.

The device according to the present invention performs digital signal processing in particular to synchronize a transmission clock with a reception clock. Thus, it is advantageous to perform a pre-synchronization with, for example, a charge transfer device, the analysis of the signal making it possible to determine the phase of the transmitted signal will then only be done around the correlation peak of the code. In addition, the analysis of these correlation peaks, and of its possible asymmetries, allows the reference phase to be deduced with great precision. Advantageously, a filter adapted to the useful part of the signal is used at reception, that is to say a suitable filter which eliminates possible distortions of the signal around the transitions. In this way it is ensured in the event that the bandwidth of the transmission channel is limited, that the distortions will not disturb the reception of the signal.

The main object of the present invention is a receiver characterized in that it includes a clock and a computer capable of synchronizing its clock with a clock of the transmitter by analyzing the received signal.

The present invention also relates to a receiver characterized in that said receiver is a phase modulated wave receiver. The present invention also relates to a receiver characterized in that said computer is capable of correlating the signal with a code and of determining the maximum of the correlation peak by comparing the amplitude of at least two points of the peak . The present invention also relates to a receiver characterized in that the device capable of carrying out the convolution of the signal received by a code comprising a charge transfer device of which certain cells, corresponding to the binary code used, are connected to an output .

The present invention also relates to a receiver characterized in that it comprises an adapted filter whose response curve is of small width making it possible to reduce the passband of the transmission channel. The present invention also relates to a receiver characterized in that said receiver is a receiver of radio broadcasts.

The present invention also relates to a receiver characterized in that said receiver is a receiver of television broadcasts.

The present invention also relates to a receiver characterized by the fact that it comprises a device making it possible, by calculation, to eliminate multiple echoes by subtracting them from the signal or by delaying them so as to put them in modulo phase 2 , with the direct signal.

The invention also relates to a receiver, characterized in that it is capable of eliminating multiple echoes by digital filtering using a filter whose transfer function:

h (t) being the transfer function of the space between the transmitter and the receiver.

The subject of the invention is also a receiver, characterized in that g (t) is determined by carrying out the inverse Fourier transform of the ratio of the Fourier transform of the intercorrelation function of the signal received by the transmission coding and the Fourier transform of the autocorrelation function of the emission code. The present invention also relates to a receiver characterized in that it is capable of displaying images in high resolution.

The present invention also relates to a radar receiver characterized in that it is capable of using the radiation emitted by a separate radar transmitter, to determine the position and / or the speed of the targets.

The present invention also relates to a radar receiver characterized in that it is capable of receiving the radiation coming directly from the radar transmitter as well as the radiation emitted by the transmitter and reflected by a target.

The present invention also relates to a radar receiver characterized in that it comprises a main antenna capable of picking up the electromagnetic radiation reflected by the target and an auxiliary antenna capable of receiving the incident radiation coming directly from the transmitter.

The present invention also relates to a radar receiver characterized in that it comprises a single antenna capable of receiving the radiation coming directly from the transmitter as well as the radiation coming from the transmitter and reflected on the target.

The present invention also relates to a radar receiver characterized in that it comprises at least one mixer capable of combining the radiation coming from the transmitter and the radiation reflected by a target.

The present invention also relates to a radar receiver characterized in that said radar receiver is a monopulse radar receiver.

The present invention also relates to a radar receiver characterized in that it comprises a clock capable of being synchronized with a clock of the transmitter.

The invention will be better understood by means of the description below and the appended figures given as nonlimiting examples among which: - Figure 1 is a diagram illustrating the distortions of the signal; - Figure 2 illustrates the response of a filter adapted according to the invention;

- Figure 3 is a diagram showing the asymmetry of the signal samples received at two different times;

- Figure 4 is a diagram illustrating the information that can be derived from the asymmetry of the signal illustrated in Figure 3;

- Figure 5 is a diagram illustrating the use of three successive correlation peaks;

- Figure 6 is a diagram of a television transmitter;

- Figure 7 is a diagram of a first example of a television receiver according to the invention;

- Figure 8 is a second embodiment of a television receiver according to the invention. - Figure 9 is an embodiment of an amplitude-phase demodulator according to the invention;

- Figure 10 is a flowchart illustrating an example of a program implemented with a device according to the invention;

- Figure 11 is a diagram of a first embodiment of a radar according to the invention;

- Figure 12 is a diagram of a second embodiment of a radar according to the invention;

- Figure 13 is a diagram of a third embodiment of a radar according to the invention; - Figure 14 is a diagram of a fourth embodiment of a radar according to the invention;

- Figure 15 is a diagram of a fifth embodiment of a radar according to the invention;

- Figure 16 is a diagram of a sixth embodiment of a radar according to the invention;

- Figure 17 is a diagram of a seventh embodiment of a radar according to the invention;

- Figure 18 is a diagram of an eighth embodiment of a radar according to the invention. In FIGS. 1 to 18, the same references have been used to designate the same elements. In the description of the patent, the same references have been used to designate the suitable filters as well as their response curves. In FIG. 1, an electromagnetic signal modulated in phase of periods T can be seen. The limitation of the passband of the transmission channel causes, at the phase transitions 20, distortions. Thus, the signal includes periods 31 located around phase transitions 20 comprising distortion and periods 14 located between periods 31 during which it is possible to make phase measurements. Also, it is advantageous to perform phase measurement only during periods 14.

In Figure 2, we can see the response of a filter adapted to the periods. This filter is narrower than a filter adapted to the period T of the signal. For a suitable filter making it possible to collect half the energy of that collected by a suitable filter 23, the signal to noise ratio is reduced by three decibels. On the other hand, the accuracy of the measured phase is very significantly increased. In Figure 3, we can see the amplitude 16 of a signal correlated by a code as a function of time 15: In the example illustrated in Figure 3 we see two points 17 and 18 of different amplitudes. It is possible to deduce from the amplitudes of points 17 and 18 the time corresponding to the maximum sought from the correlation peak.

In FIG. 4, we can see the correlation peak 19 deduced from points 17 and 18. Time 10 corresponds to the maximum of the correlation peak allowing precise synchronization to be obtained. In FIG. 5, we can see the repetition of three similar correlation peaks 11. Using the three similar correlation peaks is equivalent to using a cyclic code. Thus, between the peaks 20, the secondary lobes 32 which disturb the measurement making it possible to determine the instant 10, corresponding to the maximum of the peak making it possible to obtain a very large synchronization, are removed. precision. The use of pseudo-random code of length N makes it possible to obtain peaks 11 of amplitude 2 ^N -1. The synchronization measurement carried out in a zone 22 situated around the central correlation peak 11. In Figure 6, we can see a device for making television programs. Said device comprises, connected in series, a video signal source, for example a television camera 7, an analog-digital converter 6, a phase coding device 2, an amplifier 3 and a transmitting antenna 4. A clock of high precision 5 is connected to the analog-digital converter 6, to the phase coding device 2 and to a pseudo-random code generator 13. The pseudo-random code generator device 13 is connected to the phase 2 coding device and / or at the input of amplifier 3.

Advantageously, a control unit 8 makes it possible to choose, mix, or modify the images that one wishes to emit. Control room 8 makes it possible to exploit the possibilities of the device according to the present invention, in particular the fact that it is possible to separate the physical transmission channel from the transmitted data. Thus, it is for example possible to transmit on the same channel television images, sound, alphanumeric data as well as machine control signals. Control room 8 makes it possible to process, mix and distribute the data to be transmitted between two various channels. In the example illustrated in FIG. 6, the control room 8 is a digital control room. It is therefore located between the output of the analog-digital converter 6 and the input of the phase coding device 2. The control room 8 has inputs allowing it to receive video images from other sources, such as for example other television cameras or VCRs (not shown).

Advantageously, the control room 8 makes it possible to form a plurality of channels transmitted simultaneously on a plurality of carrier waves and / or in time multiplexing. Thus it is possible not to limit transmissions to television images but thus to transmit for example digitized data or sound. In addition, it is possible to distribute the information to be transmitted between the available channels. For example, the information necessary for the transmission of high definition television broadcast is distributed between two transmission channels.

In an alternative embodiment using an analog control room 8, the control room is located between the camera 7 and the input of the analog-digital converter 6.

The television camera 7 makes it possible to obtain a video image. The video image is digitized by the analog-digital converter 6 synchronized by the clock 5. The control room 8 makes it possible to carry out the modifications deemed necessary of the digitized image. The phase 2 coding device converts the digital value of the image to a value of the phase of the signal. For example if the video signal has been digitized on four bits (which corresponds to sixteen levels) the value "4" will correspond to a phase delay of π / 2. The value of four bits has been chosen by way of nonlimiting example, it is understood that digitizations of the video signal comprising a much larger number of bits do not depart from the scope of the present invention. The number of distinct phase levels is limited by the accuracy of the clocks, in particular the transmission clock, phase detectors and that of synchronization, as well as by the signal to noise ratio. However, it should be remembered that the possibilities of clock synchronization remotely, by radio, are limited by the frequency of the carrier waves used and by the theory of relativity.

For proper functioning of the system, it is imperative that on reception it is possible to recreate a phase reference. As we will see later, for this we will use a clock.

The frequency of these synchronizations of the transmission and reception clock is a function of the precision and the stability of these clocks. The transmission clock 5 forming part of a very expensive piece of equipment will advantageously be a clock of very high long-term precision, for example a clock atomic. Depending on the desired precision, the clock 5 will for example be a rubidium or cesium clock or a cesium clock on an atomic jet. The choice of the clock used depends in particular on the distances over which one can be able to transmit.

It is possible to use a quartz oscillator with high short-term stability controlled by an atomic clock with high long-term stability. Enslaving a quartz clock can cause instabilities caused by the dissipation of the energy supplied to the oscillator to force it to take a desired value. To overcome these instabilities, an alternative embodiment comprises two quartz oscillators synchronized alternately on an atomic clock. One synchronizes a quartz oscillator with the atomic clock, simultaneously and until its own synchronization the other quartz oscillator is used as a reference for the emission.

The use of two alternately controlled quartz oscillators is not limited to the transmitter. In the receiver it is advantageous to use two quartz oscillators slaved alternately to the clock of the transmitter.

Advantageously, the synchronization of the transmission clock

5 and a reception clock is obtained by convolution and / or correlation of the signal received by a code, for example pseudo-random. To obtain clock synchronization in this way it is necessary to issue a code.

In a first alternative embodiment, a pseudo-random code generator 13 permanently transmits a code. The pseudo-random code generator 13 is connected to the phase coding device 2. The pseudo-random code generated by the generator 13 is permanently superimposed on the phase coding of the image. For example, the phase coded image is modulated by the pseudo-random code.

This modulation can be of low amplitude. On reception, the correlation of the pseudo-random code generated by a generator 13, by the same code, makes it possible to extract clock synchronization signals. The lower the phase coding modulation by the code generated by the pseudo-random code generator 13, the more it will be necessary to use long codes. Insofar as the coding is known and / or on reception, it is possible to obtain synchronization signals it will be possible, in addition to the phase demodulation of the image, to perform a phase demodulation corresponding to the synchronization code. Thus, the modulation due to the pseudo-random code does not significantly degrade by the signal / noise ratio.

In a second variant embodiment, the synchronization code is transmitted periodically, for example alternately with the data to be transmitted.

Advantageously, in the case of transmission of television programs, the pseudo-random code ensuring synchronization is transmitted during the time intervals which are not used to transmit the signal such as line returns and / or frame returns.

In the case where the coding device is a phase coding device, the transmission amplifier 3 can work in class C in which it has the best efficiency.

In FIG. 7, an exemplary embodiment of a receiver according to the invention can be seen. In the example illustrated in FIG. 7, the receiver is a television receiver capable of viewing images on a cathode ray tube 170 and of emitting sounds through a pair of speakers 181.

The receiver according to the invention comprises, connected in series, an antenna 4, a first microwave amplifier 3, a mixer 80 a second intermediate frequency amplifier 3, a matched filter 140, a mixer 81, an analog-digital converter 6, a demodulator phase amplitude 112, a computer 231, a computer 232, a decoding device 20, digital-analog converters 60, amplifiers 3, a cathode ray tube 170 or loudspeakers 181. On the other hand, the second mixer 81 is connected to a charge transfer device 130 (CCD in English terminology) an interface 122, a computer 23. On the other hand, the computer 23 is connected via a interface 102 to a clock 5, via an interface 101, a device for controlling the synchronization of the scanning of the cathode ray tube 170, by a bus 212 to the analog-digital converter 6, by a bus 211 to the phase amplitude demodulator 112 , by a bus 210 to the computer 231, by a bus 209 to a bus 109 and by a bus 110 to the computer 232.

The analog-digital converter 6 is connected to the phase amplitude demodulator 112 by a bus 107. The phase amplitude demodulator 112 is connected to the computer 231 by a pair of buses 108. The computer 231 is connected to the computer 232 by a bus 109. The computer 232 is connected to the decoding device 20 by a bus 152.

Advantageously, the clock 5 comprises a quartz oscillator 103 controlled by a phase-locked loop 104 (PLL in English terminology). The clock 5 is capable of delivering two frequencies 105 and 106 necessary for the operation of the receiver.

The decoding device 20 is connected to a set of digital-analog converters 60. In the example illustrated in FIG. 7, the receiver comprises five digital-analog converters 60, three connected to the commands of electron guns from a tube to color cathode ray 170 and two connected to speakers 181.

Advantageously, the digital-analog converters 60 are connected to amplifiers 3. On the other hand, the decoding device 20 is connected to a bus 111.

The antenna 4 picks up radio waves. The first amplifier 3 amplifies the waves received. The mixer 81 allows a frequency reduction, ensuring the beats between the waves picked up by the antenna 4 and amplified by the amplifier 3 and a frequency deduced from the clock frequency 5. For example, the signal is demodulated by a frequency equal to the carrier frequency minus the sampling frequency. The sampling frequency is for example equal to 16 MHz. The signal whose frequency has been reduced and amplified by the amplifier 3. Advantageously, the amplifier 3 is an amplifier with automatic gain control. Amplifier receives command

35 gain. The amplifier 3 is connected to a suitable filter 140.

Advantageously, the filter 140 is a filter with a narrow response corresponding to the filter 24 of FIG. 2. The filter 140 is for example produced in the form of a surface acoustic wave filter (SAW in English terminology). The duplexer or mixer 81 beats between the signal and a frequency generated from the clock. Said frequency is for example equal to the intermediate frequency after demodulation by the first mixer 80 minus the sampling frequency divided by four. The analog-digital converter 6 digitizes the signals with for example a sampling frequency of 16 MHz and a resolution of eight bits. The amplitude demodulator 112 will perform phase or phase and amplitude demodulation. It delivers, for example on eight bits on the two buses 108, the real and imaginary value of the signal. In an exemplary embodiment of the device according to the invention, the phase amplitude demodulator 112 supplies with a frequency of 4 MHz the imaginary and real values of the eight-bit signal.

Advantageously, a computer 231 provides digital signal processing for the elimination of multiple echoes.

Indeed, the antenna 4 receives not only the direct signal emitted by the transmitter but also the reflected signals. These signals followed a different path from that followed by the direct signal. Thus it has a delay compared to the direct signal. This delay results in a phase difference. But the reflection is not total, so the reflected signal does not have the same amplitude as the direct signal. The total signal received at each instant is the superposition of the signal direct with reflected signals. Thus at an instant t _i we receive a signal Y _i . t _i - t _{i -1} = 1 / f _e , f _e being the sampling frequency, for example 10 MHz.

At an instant Y _n we receive a signal:

Y _n = a ₀ S ₀ + a ₁ S ₁ + a ₂ S ₂ + ... + a _n S _n Y _{n + 1} = a ₀ S ₁ + a ₁ S ₂ + a ₂ S ₃ + ... + a _n S _{n + 1} Y _{n + 2} a ₀ S ₂ + a ₁ S ₃ + a ₂ S ₄ + ... + a _n S _{n + 2}

Y _{n + 3} = a ₀ S ₃ + a ₁ S ₄ + a ₂ S ₅ + ... + a _n S _{n + 3}

Y _{n + p} = a ₀ S _p + a ₁ S _{p + 1} + ... + a _n S _{p + n}

a ₁ represents the complex amplitude of the first reflected signal, a ₂ of the second reflected signal, a ₃ dur third reflected signal so on, a _n represents the amplitude of the direct signal. The signal can be normalized by setting a _o = 1. The computer 23 supplies, from the data collected from the phase amplitude demodulator 112 the coefficients a _o to a _n . We see that we obtain on reception, a system of equations where after a sufficiently long time it is possible to obtain more equations than unknowns. The computers 232 eliminate the unknowns from the system. Once the coefficient of the equation system is known, the computer 23 performs signal corrections by providing the delay necessary to correct the influence of the reflected signals on the received signal. We can generalize for a continuous transmission signal x (t), without the sampling frequency necessarily being constant.

We receive a signal y (t) y (t) = x (t)

h (t) (1) being the product of convolution and h (t) the function of transfer of space between the transmitter and the receiver.

In the absence of parasitic echo: h (t) = a _o δ (t - t _o ) δ being the Dirac function, at the amplitude of the received signal and t _o the time of arrival at the signal receiver.

In the presence of multiple echoes, the transfer function h (t) becomes: h (t) = Σ a _i δ (t - t _i ) i To get rid of parasitic echoes it is necessary to eliminate in h (t ):

∑ a _i δ (tt _i ). i ≠ o Take the Fourier transform of equation (1):

Y (f) = X (f). H (f)

Y (f) being the Fourier transform of y (t), X (f) the Fourier transform of x (t) and H (f) the Fourier transform of h (t). Let ρ _yx (τ) be the cross-correlation function of y and x: ρ _yx (τ) = <y │x> _τ = ∫y (t)

Now, on reception, we know the coding x (t) used on transmission.

Let Φ _yx (f) be the Fourier transform of ρ _yx (τ)

Φ _yx (f) = Y (f) r

Φ _yx (f) = H (f). | X (f) | ²

Φ _yx (f) = H (f). Φ _xx (f) therefore:

and g (t) the inverse Fourier transform of G (f)

g (t) is the transfer function of a filter that suppresses multiple echoes.

Advantageously, the filter whose transfer function is g (t) is a programmable digital filter.

Advantageously, on transmission, the signal is interrupted by blanks allowing the reception to facilitate the analysis of multiple echoes in order to better eliminate them.

The computer 131 is connected by a bus 109 to the computer 223, the computer 223 determines from the corrected values I and Q of the real and imaginary signal the phase of the signal using the formula: Arc tg (I / Q) = φ

Advantageously, the function Arc tg (I / Q) is tabulated in a memory. In this variant embodiment, the device 223 is a memory, 109 is the address bus of said memory and bus 152 is the data bus of said memory. The computer 232 receives via a bus 110 a phase reference from the computer 23. In the case where the television broadcasts are encrypted, the device according to the invention comprises a decree device 20. The emissions are encrypted for example so as not to make them accessible only to people who have paid a special fee. The decryption device 20 provides, via a digital-analog converter 60 and an amplifier 3. the signals necessary for the operation of the electron guns of a color cathode ray tube 170. The stereophonic sound is obtained from the decryption device 20 via two digital-analog converters 60, two amplifiers 3 and two speakers 181.

Advantageously, there is available at the output of the receiver according to the invention a bus 111. On the bus 111 are available digital data. for example, bus 111 makes it possible to transmit alphanumeric data which, on command, can be displayed on the screen 170, and / or remote control commands. The remote control orders are, for example, the orders to switch on or off the television, to record a video recorder or to switch off the lights. These orders are triggered for example at the beginning or at the end of television broadcasts. Advantageously, these orders are taken into account by the devices for which they are intended only in the event of validation on said devices.

The charge transfer device 130 makes it possible to obtain a pre-synchronization of the clock 5 with a clock 5 of the transmitter. The pre-synchronization makes it possible to carry out only the synchronization of the phase φ by the calculations only around the synchronization peak thus, to very significantly reduce the amount of the calculations carried out by the computer 23. The charge transfer device 130 comprises many cells connected in series. At each clock pulse the signal propagates from each cell to the next cell. At each clock pulse, the first cell receives signals present on the input of the charge transfer device. Likewise, at each clock pulse the value of the charge present in the last cell is available at the output of the charge transfer device. To carry out the convolution of a signal by a digital code, the cells corresponding to the value 1 of a binary code are connected to the output of the device 130. the t cells corresponding to 0 of the binary code are not connected to the outside of the charge transfer device 130.

The charge transfer device acts as a transverse filter. The voltage will be maximum at the output of the charge transfer device 130 when the cells connected to said output will include charges corresponding to the maximum amplitude of the signal. Thus, to obtain synchronization at a given time, it suffices to send, taking into account the delay introduced by the processing, the signal modulated according to the same code as that contained in a charge transfer device 130.

The delay between the introduction of the signal into the charge transfer device 130 and the obtaining of the synchronization peak on its output corresponds mainly to the time necessary for the signals to reach the last cell and is therefore substantially equal to the number of cells that multiplies the time corresponding to a clock cycle. It is obvious that to obtain the finest possible synchronization it is necessary to use long codes and therefore a charge transfer device comprising a large number of cells.

In an alternative embodiment the charge transfer device 130 are removable from the television receiver. Insofar as to operate the television receiver according to the invention, it is necessary to obtain a presynchronization using a charge transfer device comprising a code corresponding to the program code, it is possible to reserve all or part of the transmissions to the owner of control cards comprising the charge transfer device whose code corresponds to the received emission. Thus, it is possible to issue control cards comprising a charge transfer device, for toll programs which are billed for the payment of the television fee, or to a public selected for reception of specialized transmissions for example, to the doctor. for medical shows. In this case, 11 is advantageous to transfer from said card comprising a charge transfer device 130 the codes to the computer 23 allowing it to establish phase synchronization. Interfaces make it possible to adapt the signals between the various elements of the television receiver. The computer 23 is a signal processor of the transverse filter type. The computer 23 includes for example processors produced by the company "Texas Instruments" under the reference TMS 320 C 25, by the company MOTOROLA under the reference 56000 or by the company THOMSON-CSF under the reference TS 68 930. The computer 23 provides the correlation calculation of the signal received by a code just around the correlation peak, performs the analysis of the signal on samples of the signal 17 and 18 of FIGS. 3 and 4 allowing it to determine the maximum of the correlation peak, the phase is deduced of reference allowing the slaving of the clock 5 and the determination of the value of the phase of the emissions and phase modulations; determine the coefficients necessary for the phase amplitude demodulator 112 and for the computer 231 allowing the elimination of multiple echoes; and adapt the decoding to the quality of reception. Advantageously, on transmission, to obtain emissions in phase modulation, a pseudo-random binary sequence repeated three times is transmitted. Thus a cyclic code is simulated, in the absence of parasitic echoes, the presence of a secondary lobe between the peaks of the signal is avoided. The parasitic echoes cause 1 appearance of peaks of small amplitude between the peaks 11. On reception, the synchronization obtained by the charge transfer device 130 makes it possible to make a fine analysis of the central peak while devoting to this operation only means of processing of reasonable calculations. Synchronization is obtained for example by an analysis of the differential measurement type of two successive samples of the signal in the vicinity of the central peak. If the two samples have the same amplitude, the middle of correlation peak 10 is exactly in the middle against the samples. In the general case of the amplitude ratio is deduced the position of the middle of the correlation peak.

In alternative embodiments of the device according to the present invention, an interpolation or the method of least squares (LMS in English terminology) is used to determine the maximum of peaks.

In a simplified variant of the device according to the invention, synchronization is carried out by sending pulses which can be used directly without correlating the code of the incident signal. Advantageously on transmission, the information to be transmitted is divided into two groups, the information necessary for obtaining an image of average quality, and the additional information, making it possible to pass from the quality of average image to the image. in high resolution. In a first alternative embodiment, line returns and frame returns are used during which it is not necessary to transmit information constituting an Image for transmitting service information and sound. In a second variant embodiment, the information necessary for obtaining the image and receiving sound is transmitted simultaneously to the image. Examples of digital distribution of information are given by way of non-limiting example:

- two most significant bits of the medium resolution image, two least significant bits of the information necessary for switching to high resolution; this variant corresponds to an embodiment capable of working even with a low signal-to-noise ratio;

- two most significant bits of the medium resolution image, one bit for the sound, two bits for the additional information making it possible to reach the high resolution; - three bits for medium definition television, three bits of additional high definition information;

- five medium definition image bits, one sound bit and five bits of additional information making it possible to switch to high definition; this variant corresponding to the embodiments intended to operate with a good signal to noise ratio. On reception, by analyzing the multiple echoes, the computer 23 determines whether the least significant bits making it possible to obtain a high resolution image are transmitted correctly, and perform the switching by buses 110 of the computer 232 making it possible to obtain either the medium or high resolution. Advantageously, in addition to this automatic control, the high definition medium definition passage is accessible to the user of the television receiver according to the invention. Advantageously, the clock 5 comprises two quartz oscillators synchronized alternately. During synchronization of a quartz oscillator 103 the second oscillator serves as a time base and phase reference. (In FIG. 7, a single quartz oscillator 103 has been illustrated). The invention is not limited to the use of quartz oscillators the use of other types of oscillators such as for example oscillators ceramic or atomic oscillators is not beyond the scope of the present invention.

Radio broadcast receivers do not depart from the scope of the present invention. The radio broadcast receiver does not include a display screen 170. In an alternative embodiment of the device according to the invention, the same receiver makes it possible to receive radio broadcasts as well as television broadcasts.

In Figure 8, we can see an alternative embodiment of the device according to the invention. The device illustrated in FIG. 8 comprises a single bus 120 making it possible to connect the computer 23 to the analog-digital converter 6, to the phase amplitude demodulator 112, to the computer 231, to the phase determination device 232. In FIG. 8, the tube cathode ray 170, the speakers 181, the digital-analog converter 60 and the amplifier 3 have not been shown. a bus 121 symbolizes the availability of information in digital form, whatever their future uses. In FIG. 9, one can see an exemplary embodiment of a phase amplitude demodulator 112 usable in a device according to the present invention.

The example illustrated corresponds to the case where the sampling frequency f _e is equal to four times the band B. Other embodiments corresponding for example to f _e = 6B or f _e = 8B do not depart from the scope of the present invention.

The principles of the phase amplitude demodulator 112 consist in sampling the signals on the carrier. For this it is necessary that the passband of their intermediate frequency is adapted to the useful band of the signal so as not to deteriorate the signal to noise ratio.

The circuit 112 includes a processing circuit 920 which makes it possible to restore the real part I of the signal. It also includes a 940 processing circuit which allows to restore the imaginary part Q of the signal. Each of these two circuits performs filtering and subsampling.

The series of samples x _n , n = 0, 1.. . N, is received at the input of each of the circuits 920 and 940. These two circuits perform digital filtering and subsampling.

Let y _{n be} the signal at the output of these circuits, the filtering and sub-sampling operation on the samples x _n is obtained by performing the following operations:

N-1 y _n = ∑ h _u . x _4n-u (1) u = 0 where h _u represents the complex coefficients of the digital filter produced.

Note that a sample y _n corresponds to the sample x _4n . The filtering and sampling operation represented by equation (1) can be simplified by noting that if we consider u past samples and u future samples, the complex coefficient h _n to apply for a given sample among the u past samples is equal to the conjugate of h _n, that is to say h * _n , to be applied to the corresponding future sample over time. The operation therefore consists in fact in performing the following function:

u = + N / 2

Y _n = ∑ x _{4n - u.} h _u u = - N / 2 either:

0 + N / 2 Y _n = Σ x _4n-u . h _u + Σ x _{4n + u} . h _u u = - N / 2 u = 0

With: h _u = h _u *

To simplify understanding we take an example in which u = 0, 1, 2, 3; h _u = a _u + jb _u and h _-u = h _u * hence h _-u = a _u - jb _u

y _n = x _4n-3 (a _u - jb _u ) + x _{4n + 3} (a _u - jb _u )

is :

N / 2 y _n = ∑ (x _{4n-u + x4n + u} ) (a _u ) + (x _{4n + u}

_{x4n- u)} (b _u ) u = 0

either for the previous example:

The circuit 921 makes it possible to carry out the function (x _4n-u + x _{4n + u} ), that is to say the summation of the samples considered as past and of the samples considered as future. The circuit

941 makes it possible to carry out the function (x _{4n + u} - x _4n-u ), that is to say the difference of these same samples.

The circuit 922 makes it possible to memorize the 2u real elements, that is to say that it will carry out the operation:

+ N / 2

Σ (x _4n-u + x _{4n + u} ) (a _u )

0

The circuit 942 makes it possible to memorize the 2u imaginary elements, that is to say that it will perform the operation:

+ N / 2

Σ ((x _{4n + u} - x _4n-u ) (b _u )

0 The output of circuit 922 delivers a digital signal in quadrature with the signal at the output of circuit 942.

The circuit - 921 advantageously comprises a plaice 925 first in, first out (FIFO in English terminology) which successively receives the samples x _n , these samples are stored in a RAM 24 RAM in English terminology) which will constitute the memory containing future samples (+ 4 samples at a given time). A sequential circuit 925 for example of the programmable logic network type (PLA in English terminology) makes it possible to address the memory. These samples are put in a register 926 which stores them to transmit them to a stack 927 of the type of the first in-first out type (FIFO in English terminology) on the one hand and to an adder 928 on the other hand.

The stack 927 successively introduces the samples which were in the memory 924 in order to re-enter them in a random access memory 929. The memory 929 makes it possible to store the "future" samples which become "past". A sequential circuit 930 makes it possible to address this memory 929. The data read from memory 929 are stored in a register 931 which restores them to an input of the adder 928 at the same time as register 926 restores the data stored in it. other input of the adder. The adder 928 therefore receives successively at each input the future and past samples (x _4n-u and x _{4n + u} ) in order to add them up and deliver to the output successively the samples resulting from the sum.

The circuit 922 includes an accumulator multiplier circuit 931 (MAC). This circuit 931 comprises a multiplier 932 which receives the output signal of the adder 928 and the data stored in a programmable read only memory (PROM in English terminology) 933 which stores the real coefficients a _u filter. This memory 933 is controlled by a programmable logic network sequencer 934. This adder is associated with an accumulator 936 for perform the sum of 2u elements and deliver a sample which is stored in a register 937.

The circuit 941 consists of the circuits referenced 951 to 950. The circuits 943 to 947, 949 and 950 are identical to circuits 923 to 927, 929 and 930 respectively, that is to say that they provide the same function in view of the same result. Only the 948 differs since it is a subtractor which makes it possible to make the difference between the "future" samples and the "past" samples. Circuit 942 is made up of. the circuits referenced 951 to 957. The circuits 51 to 57 are respectively identical to the circuits (931) to (937), they provide the same function for the same result. However, the programmable read-only memory 953 does not contain the real coefficients of the filter but the complex coefficients b _u of the filter. Register 957 delivers quadrature samples with the output samples from register 937.

The phase amplitude demodulator makes it possible to carry out an amplitude-phase demodulation of a signal on carrier f _i by using a sampling frequency f _e which can be much lower than the carrier frequency since this frequency f _e is equal to 4B, in a preferred embodiment and B being generally very small compared to fi (the ratio can range from 1 to 50 for example). In FIG. 10, we can see a flow diagram of a program allowing the computer 23 to determine the position of the middle of the synchronization peak.

In 501 the computer 23 receives the first synchronization interruption. The computer 23 stores the time of the first synchronization.

In 502 the computer 23 receives the second synchronization interruption. In 502 the time of the second synchronization is stored in a memory.

In 503, the time elapsed between the two synchronizations obtained in 502 and in 501 is calculated. The duration separating two successive synchronizations, obtained with the device at charge transfer 130 are substantially equidistant over time. Thus the computer 23 can predict the time of the next synchronization.

In 504 the computer 23 verifies that one is in the correlation window during which the measurements can be made.

If not we go to 505.

In 505 either we exit this program, or we return to 504 while waiting to be in the correlation window.

If yes, we go to 506. In 506 we carry out the signal amplitude acquisitions. We go to 507. In 507 we check if the measured points are symmetrical.

If yes, we go to 509. In 509 we calculate the top of the correlation peak corresponding to the middle between the acquisition point. We are going to 510.

If not, go to 508. In 508, the correlation peak is calculated. We are going to 510.

In 510, the clock synchronization is carried out on the new phase reference. We're going to 511.

In 511 the date of the next synchronization is calculated.

We are going to 512.

In 512 we leave this program.

In FIG. 11, an exemplary embodiment of a radar receiver according to the invention can be seen. The use of a radar receiver that does not have a transmitter or whose transmitter does not work has many advantages:

- a receiver being only passive is much more difficult to detect; - has a low cost price;

- the use of emitter in continuous wave (CW in English terminology) makes it possible to reduce the peak power of the emitter and promotes the use of transistorized emitter;

- the separation of the reception of the emission makes it possible to optimize the waveguides of the transmitter to transmit high powers for example of the order of a few megawatts and the receiver waveguides for low powers, for example of the order of a few microwatts;

- sometimes can be much closer to the target and therefore receive a stronger reflected signal. It is for example possible to use a single antenna ensuring the illumination of the battlefield for a plurality of radars. This antenna can be either omnidirectional, or, for example, a 3D electronic scanning antenna with great spatial agility successively illuminating all the targets to be tracked by a plurality of receivers. On the other hand, it is possible to use the radiation emitted by a friend or even an enemy radar to track a target. By way of non-limiting example of application of the device according to the invention, it is possible to cite the use of a conventional type radar (transceiver) on an important building such as an aircraft carrier, and plurality of small buildings equipped only with receivers. For example, speedboats can thus more effectively protect the aircraft carrier, in particular against anti-ship missiles. Speedboats standing far from the aircraft carrier, for example at a distance of between 5 and 35 kilometers, have more time to react by destroying a missile. In addition, the speedboat not being targeted by a missile, the crew will be able to react with more composure. It should be noted that the speedboats are still under the electronic and physical protection of the aircraft carrier. It is known to produce multistatic radars comprising separate transmitters and receivers. However, the transmitter and the receiver had to be fixed. Any movement would distort target position acquisitions. In addition, the Doppler treatment was only approximate because the radiation received was not coherent.

By analogy, the radar receiver according to the present invention allowing the movements of transmitters and receivers is called multidynamic radar. To obtain an effective radar receiver and in particular to be able to make an operation allowing a good resolution in speed by Doppler analysis of the received signal, it is imperative to obtain a good synchronization between the transmitter and the receiver. In the example illustrated in FIG. 11, the correlation is obtained by convolution and / or correlation of the signal emitted by a code. Once synchronization has been established, the direct signal from the transmitter is eliminated by the calculations. The device of FIG. 11 comprises connected in series a receiving antenna 4, an amplifier 3, a mixer 80, an amplifier 3, a receiver 639, an operating device 635, a display device 170. At the output of the second amplifier 3 are connected in parallel with a charge transfer device 130, a correlator 131. The output of the charge transfer device 130 is connected, through an interface 122 to the correlator 131. The correlator 131 is connected to a clock 5. The clock is connected on the one hand to a local oscillator 82 and on the other hand to the receiver 139. The local oscillator 82 is connected to the mixer 80. When receiving the direct signal emitted by the radar, the device has charge transfer 130 and / or the correlator 131 make it possible to obtain fine synchronization of the clock 5 with the clock of the transmitter. Establishing this fine synchronization implies knowing the code used for the transmission. Thus only friendly buildings can use (parasitically) the radiation emitted by a radar. In addition, knowledge of the code allows elimination by direct radiation calculations. However in certain circumstances the direct radiation being preponderant it is imperative to use an amplifier with ur limit. This limiter amplifier is for example the second amplifier 3. By having a phase just inside each pulse it is possible to carry out conventional Doppler treatments, which until now were only possible, with transceiver radars. In addition the use of frequent synchronization allows at any time to compensate for the relative displacements of the transmitter relative to the receiver.

In FIG. 12, an exemplary embodiment of the radar receiver according to the invention can be seen, making it possible to receive messages from the radiation emitted by a radar. It is imperative in radar, to increase the resolution to perform pulse compressions. Thus, the transmitted signal is coded. Insofar as several codings are possible, the choice of coding makes it possible to carry out the transmission of information. Thus, the same radiation can be used both for target detection and for the transmission of information. Since the radiation from a radar is very powerful, this type of transmission is extremely difficult to interfere with. On the other hand, it should be noted that the interference will have to illuminate the receiver to be of any efficiency. This condition may be very difficult to fulfill on a battlefield, the passive receiver being difficult to detect. The device illustrated in FIG. 12 comprises, in addition to the devices in FIG. 11, a decoder 20 connected to the receiver 639. The decoder 20 is connected to a display device such as for example a cathode ray tube 171 or a bus. The bus can be connected, for example, to a computer, printer or remote control. As well as it is possible to display a transmitted message or to execute a remote control command. Advantageously, the decoder 20 is connected to the radar operating device 637. Thus, the transmitter can transmit information relating to a target which it itself tracks. In this way it is possible to designate the priority targets, and to allow the receiver to hang a tracking window more quickly on said target. In addition, the comparison of the target positions and speed acquired by the transmitter (insofar as it also includes a receiver) and the receivers makes it possible to test the correct operation or the calibration of the receivers. In addition, the transmitter is likely to warn the receivers of a next change in the coding used. Only the code numbers and the date of the change are transmitted. The secret codes themselves are stored at the transmitter and receiver levels.

In the case of upward (from receivers to the transmitter) or horizontal (between receivers) transmission, conventional means of communication are used. However, it is imperative not to allow the identification of receivers, which are also entirely passive. Frequency evasion radio transmitters are used, for example.

It is imperative to guarantee the confidentiality at least for a few tens of minutes of the information transmitted which, if not, risks reducing the effectiveness of the defense. For example, in addition to coding the information, the positions are indicated with respect to a secret hideout chosen arbitrarily.

In FIG. 13, an exemplary embodiment of the device according to the invention can be seen comprising a code generator 13. The code generator 13 transmits a code to the correlator 131. at each clock cycle. shift register some cells of which will be looped through an Or-exclusive door on its input allows the generation of very long codes. Thus it is extremely easy to use identical very long codes on the transmitter and on the receiver.

In FIG. 14, an exemplary embodiment of a monopulse radar receiver according to the invention can be seen. The radar receiver comprises an antenna 4 comprising 4 sources, for example of the 646 horn type. Thus it is possible to perform the sum and the difference in both planes. The use of monopulse capable of measuring deposit: the deposit comprising only two cones is not outside the scope of the present invention. Each horn 642 is connected to an amplifier 3. Each amplifier 3 is connected to a mixer 80. The mixer 80 is connected to a magic Te 633. The magic Te delivers on three outputs the sum 631 of the four horns, the vertical difference 632 and the horizontal difference 630. The sum channel 631 and the different channels 632 and 630 are connected to a receiver 634. The receiver 634 is connected to an operating device radar 637. The radar operating device is connected to a display device 170. On the other hand, the output of the mixers 80 is connected, on each channel, to a charge transfer device 130 and / or a computer 23 The charge transfer device and / or the computer 23 are connected to clocks 5. The clocks 5 are connected to local oscillators 82 to the receiver 643 and to the radar operating device 637 by lines 638. The local oscillators 82 are connected to the mixer 80.

Insofar as by carrying out the tracking, the reflector 4 moving, the device of FIG. 14 includes synchronization with the emission clock on each channel of the monopulse means. Advantageously, the operating device ensures, via a line 640 and a servomechanism 641, the pursuit of the targets. The computer 23 is illustrated in the variant embodiment in FIGS. 14 and 18 performs the correlation calculation.

In FIG. 15, an exemplary embodiment of the radar receiver according to the invention can be seen. The example in FIG. 15 comprises a receiver comprising a main antenna 4 ensuring the tracking of the target and an antenna 1004 receiving the direct signal coming from the transmitter. Insofar as the transmitter uses coherent radiation, the treatments carried out approximate the holography.

The device according to the invention comprises a main antenna 4 and an amplifier 3 connected to a first input of a mixer 1080 as well as a second auxiliary antenna 1004 and a limiting amplifier 1003 connected to the second input of said mixer 1080. The output of the mixer 80 is connected to the receiver 634. The receiver 639 is connected to the radar operating device 137 and the operating device 637 is connected to the display device 170. The size and therefore the gain of the auxiliary antenna 1004 is adapted to the amplitudes of the signal that it is capable of picking up.

In FIG. 16, an exemplary embodiment of a radar receiver according to the invention can be seen comprising a main antenna 4, an auxiliary antenna 1004 and the clock synchronization device 5.

The device comprises connected in series an auxiliary antenna 1004, a limiter amplifier 1003, a mixer 80. At the output of the mixer 80 are connected in parallel a mixer 1080, a charge transfer device 130, a correlator 131. charge transfer 130 is connected via an interface 122 to the correlator 131. The correlator 131 is connected via an interface 1220 to a clock 5. The clock 5 is connected to. two local oscillators 82, a radar receiver 634, an operating device 637. Each local oscillator 82 is connected to one of the inputs of a mixer 80. The main antenna 4 is connected to the other input d one of the mixers 80 via an amplifier 3. the outputs of the two mixers 80 are connected to the inputs of the mixer or duplexer 1080. The output of the mixer or duplexer 1080 is connected to the radar receiver 634. The output of the radar receiver 634 is connected to the input of the radar operating device 637. The radar operating device 637 is connected to a display device 170.

The amplifier 1003 is a limiter amplifier eliminating the risk of saturation of the receiver 634.

The association of the processing of the signal reflected by the target by the direct signal received by the antenna 1004 with the use of synchronized clocks makes it possible to carry out all the fine processing both within each radar recurrence and the comparison. of signals belonging to successive recurrences. Measuring the variation of the echo position within a recurrence allows the 637 operating system to do a fine Doppler analysis. Signal processing reflected by the target by the direct signal carried out in an alternative embodiment of the device illustrated in FIG. 16, after a frequency reduction.

In FIG. 17, an exemplary embodiment of a monopulse radar receiver according to the invention can be seen. The radar device comprises on the one hand an antenna 4 comprising four sources or receivers 642, for example of the horns type. Each source is connected to an amplifier 3. Each amplifier 3 is connected to a first input of a mixer 80. On the other hand the device includes an auxiliary antenna

1004 connected to a limiting amplifier 1003 connected to the second inputs of the four mixers 80. The four outputs of the mixers 80 are connected to a magic Te 633. The magic Te delivers on outputs 631, 632 and 630 steals sum and two ways differences. The sum channel and the two difference channels are connected to the radar receiver 634. The radar receiver 634 is connected to the radar operating device 637. The radar operating device (637) is connected to a display device 170. The antenna 4 tracks one or more targets, while antenna 1004 is pointed towards the radar transmitter. The antenna 1004 receives either radiation from the main lobe of an antenna, for example omnidirectional, or energy from a secondary lobe. In FIG. 18, an alternative embodiment of a monopulse radar receiver according to the invention can be seen. The device comprises an antenna 4 comprising 4 sources or receivers 642 of the horn type. Each source is connected to an amplifier 3. Each amplifier 3 is connected to a first input of a mixer 80.

On the other hand the system includes an auxiliary antenna 1004 connected to a limiting amplifier 1003. The output of the amplifier 1003 is connected on the one hand to a charge transfer device 130 and on the other hand to a computer 23 by l 'through an interface 1221. The charge transfer device 130 is connected to the computer 23 through a interface 122. The computer 23 is connected to the clock 5 through an interface 1220. The clock 5 is connected to a local oscillator 82. The local oscillator 82 is connected to the second inputs of the four mixers 80. The outputs of the four 80 mixers are connected to a magic Te 633, the magic Te allows to obtain a sum channel 631 and two difference channels 632 and 630. The sum channel and the difference channels are connected to the receiver 134. The receiver is connected to the device radar operation 637. The radar operation device is connected to a display device 170. The clock 5 is connected to the receiver 634 to the operation device 637.

The device illustrated in FIG. 18 allows very fine operation on radiation reflected by the targets as long as one receives direct radiation from the emitter. In addition, for a fixed receiver and transmitter it is possible to continue performing a fine processing during interruptions of the links between the transmitter and the receiver.

In this case, the clock 5 continues to provide the phase reference necessary for the proper functioning of the system. However, it is imperative that the transmitter has a coherent radiation source.

Likewise, for a radar transmitter whose movement relative to the receiver is slow as a function of the wavelength used, the clock 5 makes it possible to continue to perform fine processing, in particular Doppler processing during short-term absences of direct link between transmitter and receiver.

The invention applies to the production of receivers, in particular of receivers requiring knowledge of the phase of the signal received.

The invention is not limited to the use of a single transmitter. It is possible to use a plurality of transmitters.

Receivers thus have the option of either choosing the transmitter allowing them to pursue the target with maximum efficiency. In addition, it is possible for a receiver to compare (or correlate) the echoes returned by a target from a plurality of transmitters. This makes it possible to obtain more precise and more reliable data. If, for example, the standard deviation from the mean a measurement is very large, this measurement is eliminated. The result will be the average of the results obtained from the other transmitters. Each transmitter uses a different coding and / or frequency:

The invention applies mainly to the production of a radio or television receiver intended for emissions in phase modulation as well as to the radar receiver using direct radiation coming from a transmitter as well as radiation coming from the same reflected transmitter. by a target.

Claims

1. Receiver, characterized in that it comprises a clock (5) and a computer (23) capable of synchronizing its clock (5) with a clock (5) of the transmitter by carrying out the analysis of the received signal.

2. Receiver according to Claim 1, characterized in that the said receiver is a phase modulated wave receiver.

3. Receiver according to claim 1 or 2, characterized in that said computer (23) is capable of performing the correlation of the signal by a code and of determining the maximum of the correlation peak by comparing the amplitude of at minus two points (17 and 18) of the peak (19).

4. Receiver according to one of the preceding claims, characterized in that the device (130) capable of convolving the signal received by a code comprising a charge transfer device (130) including certain cells, corresponding to the code binary used, are connected to an output.

5. Receiver according to claim 1, 2, 3 or 4, characterized in that it comprises a filter (140) adapted whose response curve (24) is of small width making it possible to reduce the passband of the transmission channel .

6. Receiver according to claim 1, 2, 3, 4 or 5, characterized in that said receiver is a receiver of radio broadcasts.

7. Receiver according to one of the preceding claims, characterized in that the said receiver is a receiver TV shows.

8. Receiver according to one of the preceding claims, characterized in that it comprises a device making it possible, by calculation, to eliminate multiple echoes by subtracting them from the signal or by delaying them so as to put them in modulo phase 2, with the direct signal.

9. Receiver, according to claim 8, characterized in that it is capable of eliminating multiple echoes by digital filtering using a filter whose transfer function:

10. Receiver according to claim 9, characterized in that g (t) is determined by carrying out the transform of

Inverse Fourier of the ratio of the Fourier transform of the intercorrelation function of the signal received by the transmission coding and of the Fourier transform of the autocorrelation function of the emission code.

11. Receiver according to claim 7, 8, 9 or 10, characterized in that it is capable of displaying images in high resolution.

12. Radar receiver according to claim 1, 2, 3, 4, 5, 8, 9 or

10, characterized in that it is capable of using the radiation emitted by a separate radar transmitter, to determine the position and / or the speed of the targets.

13. Radar receiver according to claim 12, characterized by the fact that it is capable of receiving radiation coming directly from the radar transmitter as well as the radiation emitted by the transmitter and reflected by a target.

14. Radar receiver according to claim 13, characterized in that it comprises a main antenna (4) capable of picking up the electromagnetic radiation reflected by the target and an auxiliary antenna (1004) capable of receiving the incident radiation coming directly from the 'transmitter.

15. Radar receiver according to claim 13, characterized in that it comprises a single antenna (4) capable of receiving the radiation coming directly from the transmitter as well as the radiation coming from the transmitter and reflected on the target.

16. Radar receiver according to claim 14, characterized in that it comprises at least one mixer (80, 1080) capable of combining the radiation coming directly from the transmitter and the radiation reflected by a target.

17. Radar receiver according to claim 12, 13, 14, 15 or 16, characterized in that said radar receiver is a monopulse radar receiver.

18. Radar receiver according to claim 12, 13, 14, 15, 16 or 17, characterized in that it comprises a clock (5) capable of being synchronized with a clock of the transmitter.