FR2877167A1 - ULTRA WIDE BAND RADIO FREQUENCY TRANSMISSION METHOD AND DEVICE - Google Patents

Abstract

This device for radiofrequency transmission of binary data (ci) in a transmission channel comprises: a signal generator adapted to generate, for each binary data item (ci), a pulse signal (pi) of shorter duration than the duration of said binary datum (ci); - means for multiplying said pulse signal (pi) by at least one periodic signal of variable frequency (fj) specific to said transmission device, said variable frequency (fj) being greater than the frequency of said signal impulse (pi); and - means for transmitting the pulse signal (pi.fj) resulting from said multiplication.

Description

The present invention is in the field of

  radio frequency pulsed transmission of spread spectrum ultra high bandwidth (UWB) broadband binary data with frequency diversity.

  The invention more particularly relates to a device and a transmission method and a device and a method for receiving such data.

  We will first describe, with reference to Figures 1 to 3, a transmitter and a spread spectrum radio receiver that use a pulse transmission broadband (UWB), these devices are known to those skilled in the art.

  The conventional information data transmitter b 1, shown in FIG. 1, comprises direct sequence spread spectrum (DS-SS) direct spread spectrum means of these information data b; to obtain binary data c.

  In known manner, these spreading means DS-SS are mainly constituted by a multiplier 11 of the binary data b; by pseudo-random PN code.

  The conventional transmitter 1 also comprises a pulse signal generator 20 adapted to provide a pulse signal q; from each binary data c; at the outlet of the spreading means 10.

  This q Gaussian pulse signal and duration approximately equal to 0.2 ns is shown in Figure 2a.

  In known manner, the conventional transmitter 1 also comprises a power amplifier 30 and an antenna 40 for transmitting pulse signals q; in the transmission channel.

  The transmitting antenna 40 which acts as a bandpass filter, derives the amplified Gaussian signal q; and emits an electromagnetic wave in the form of pulse signals e ;.

  Figure 2b shows the shape of the emitted pulse signals e; in the case of a conventional pulsed transmitter 1 to very broadband (UWB). The spectrum of the emitted signal e; is shown in Figure 2c.

  The conventional transmitter of Figure 1 is also used for CDMA multiple access techniques.

  Those skilled in the art will understand that the spectrum of the emitted signal e; is much larger than the spectrum of information data b ;, which characterizes in particular a spread spectrum device.

  If the duration of a pulse signal q; is of the order of 0.2 ns, and the antenna 40 is a bandwidth antenna of 3 to 11 GHz, the spectrum of the signal transmitted by the antenna 40 and measured at -10 dB is 3.1 to 7 GHz. Thus, the emitted signal e; has a spectrum that falls within the frequency range [3.1, 10.6 GHz] reserved for UWB communications.

  In Figure 2c is also shown, in relative units, the form of the spectral mask allowed for UWB communications. By definition, a signal is considered to be very broadband (UWB) if the width of its spectrum at -10 dB is greater than 500 MHz. The width of the spectrum of the signal e; being 3.9 GHz, this signal e; transmitted by the antenna is of the UWB type.

  These emitted signals e; can be received by the conventional receiver 2 known to those skilled in the art and shown in Figure 3a.

  This conventional receiver has a receiving antenna 40 which also acts as a bandpass filter and derives the transmitted signal e.

  At the output of the receiving antenna 40, a received signal r is obtained; having the shape shown in Figure 3b. The receiving antenna 40 of FIG. 3a at the same bandwidth as the transmitting antenna 40 of FIG.

  This conventional receiver 2 comprises a low noise amplifier 50 adapted to deliver the received signals r; and amplified to a pulse signal detector 60.

  In a manner known to those skilled in the art, the pulse signal detector 60 mainly comprises a filter adapted to detect the shape of the received signal r 1, and to output a signal c; which is an estimator of the binary data c; provided at the input of the pulse signal generator 20 of the conventional transmitter 1. It is also possible to make the matched filter 60 as a correlator.

  The estimated signal c; is provided simultaneously at the input of a synchronization unit 62 and a multiplier 61 similar to the multiplier 11 of the conventional transmitter 1.

  In a manner known to those skilled in the art, the synchronization unit 62 is adapted to generate, from the estimated signal, the pseudo-random code PN identical to that supplied at the input of the multiplier 11 of the conventional transmitter 1 for the spreading the information data b ;.

  The PN pseudo-random code is provided at the input of the multiplier 61 which generates, by multiplying the estimated signal c; by the PN pseudo-random code, an intermediate signal supplied as input to an integrator 70.

  In a known manner, this integrator 70 makes it possible to obtain the information data item b.

  Those skilled in the art will understand that the assembly formed by the synchronization unit 62, the multiplier 61 and the integrator 70, constitutes a DS-SS despreading means 21 of the estimated signal 6;

  Of course, the synchronization block 62 knows the pseudo-random code PN used on transmission, this PN code being generated at the receiver 2 in a manner synchronous with the PN code on transmission.

  The transmission system constituted by the conventional transmitter 1 and receiver 2 described above has two major drawbacks: Firstly, the shape of the spectrum of the transmitted signal e shown in FIG. 2b depends directly on the shape of the Gaussian impulse signal q; of Figure 2a. Of course, this disadvantage is all the more critical because the Gaussian pulse must be generated at frequencies of the order of GHz where it is extremely difficult to control the shape of the signals obtained.

  In Figure 2c we also see that the spectrum of e; does not completely fill the authorized UWB spectral mask, so the emission can not be performed with the maximum power allowed and the emission is not optimal.

  Second, the detector 60 of the transmitted pulse signal must know the shape of the received signal r, this shape being able to vary in particular according to the type and orientation of the transmit and receive antennas 40, and the physical characteristics of the transmission channel. . In the case where the propagation channel between the transmitter and the receiver is of the fast fading type (frequency selective), the form of the received signal r; will be highly affected by the characteristics of the channel.

  In addition, the detection is all the more difficult because it is performed on a received pulse r; very high frequency.

  The invention solves these disadvantages.

  For this purpose, and according to a first aspect, the invention is directed to a device for radiofrequency transmission of binary data in a transmission channel comprising a signal generator adapted to generate, for each binary data, a pulse signal of shorter duration than the duration of said binary data, means for multiplying this pulse signal by at least one periodic signal of variable frequency specific to the transmission device, wherein said variable frequency is greater than the frequency corresponding to the duration of the pulse signal, and means for transmitting the pulse signal resulting from this multiplication.

  In the case of a UWE3 system, the duration of the pulse signal making it possible to obtain a 500 MHz frequency band must be less than 4 ns, ie about twenty times longer than the Gaussian pulse duration of the conventional system of FIG. 2a. .

  The pulse signal used in the invention is therefore much easier to generate than the high frequency Gaussian pulse of the conventional transmitter.

  In addition, the pulse signal according to the invention is multiplied by a periodic signal of variable frequency specific to the transmission device, which allows, on average, to occupy the entire spectrum by varying this frequency in the range of 3.1 to 10.6 GHz without it being necessary to precisely adjust the shape of the pulse signal of the transmitting device.

  In other words, these periodic signals of variable frequencies make it possible to carry out a spectral smoothing. It will also be noted that this variable signal does not in itself carry information, which distinguishes the transmission device according to the invention from a conventional frequency hopping spread spectrum device FH-SS (Frequency Hopping Spread Spectrum).

  Advantageously, the variable frequency used by the transmission device being specific to the transmitter, the signal receiving device does not need to know the variable frequency used.

  In a preferred embodiment, the pulse signal is multiplied by several variable frequency signals.

  The transmission device then comprises means for summing the resultant pulse signals of these multiplications, these transmission means being adapted to transmit the pulse signal obtained by this summation. In this case the pulse signal is transmitted over several frequency bands and there is a frequency diversity. This frequency diversity makes it possible to effectively overcome the problems of propagation of radio signals in the case of frequency-selective channels.

  Preferably, the variable frequencies used are random, which makes it possible to improve the spectral smoothing.

  Preferably, the binary data transmitted by the device according to the invention are obtained by spectral spreading of information data.

  This characteristic advantageously makes it possible, as in the case of a conventional spread spectrum method, to transmit the information data over the entire spectrum in a manner that is difficult to detect, these data being seen as noise by a third party system. not knowing the pseudo-random spreading code.

  In a preferred embodiment of the invention, the time difference between two consecutive pulse signals is greater than the delay depth of the multiple paths in the transmission channel.

  The skilled person will understand. that this characteristic advantageously allows to get rid of an equalizer in the receiver.

  Correlatively, the invention relates to a method of radiofrequency transmission of binary data in a transmission channel, this method comprising, for each binary data: a step of generating a pulse signal of shorter duration than the duration of said binary data; a step of multiplying this pulse signal by at least one periodic signal of variable frequency specific to the transmission method, this variable frequency being greater than the frequency corresponding to the duration of the pulse signal; and a step of transmitting the signal resulting from this multiplication step.

  The particular advantages of the transmission method being identical to those of the transmission device mentioned above, they will not be recalled here.

  Other aspects and advantages of the present invention will appear more clearly with the aid of the description of the particular embodiment which will follow, this description being given solely by way of nonlimiting example and with reference to the appended drawings in which: FIG. 1, already described, represents, schematically, a conventional transmitter of the state of the art; FIG. 2a, already described, represents an intermediate Gaussian pulse signal used by the emitter of FIG. 1; FIG. 2b, already described, represents the shape of the pulse signal emitted by the antenna of the transmitter of FIG. 1; FIG. 2c, already described, represents the frequency spectrum corresponding to the transmitted signal of FIG. 2b; FIG. 3a, already described, represents a conventional receiver known from the state of the art; FIG. 3b, already described, represents the form of a signal received at the output of the reception antenna of the receiver of FIG. 3a; FIG. 4 represents a transmission device according to the invention in a preferred embodiment; FIG. 5a represents the shape of a pulse signal used in the transmission device of FIG. 4; FIG. 5b shows the pulse signal used in the transmission device of FIG. 4 multiplied by a periodic signal used in the transmission device of FIG. 4; FIG. 5c represents the pulse signal used in the transmission device of FIG. 4 multiplied by several periodic signals of variable frequencies; FIG. 5d represents the average frequency spectrum corresponding to several signals of the type of that of FIG. 5c; and FIG. 6 represents, in flowchart form, the main steps of a transmission method according to the present invention.

  Fig. 4 shows an information data transmission device b; according to the invention in a preferred embodiment.

  The transmitter 100 comprises spreading means 10 identical or similar to those of the conventional transmitter 1 described above with reference to FIG.

  These spreading means 10 are thus adapted to generate binary data c; by DS-SS spectral spreading of the information data b;

  The transmission device 100 according to the invention comprises a pulse generator 120 adapted to generate, for each binary data c i, a pulse signal p; of duration Ti such as that shown in solid lines in Figure 5a.

  In this same FIG. 5a, the Gaussian pulse signal q, used in a conventional UWB transmitter and previously described with reference to FIG. 2a, is shown in dashed line, for comparison purposes.

  In the embodiment described here, it thus appears that the pulse signal p; of the invention is a square signal of duration approximately twenty times greater than that of the Gaussian signal q; of a conventional UWB system.

  Those skilled in the art will readily understand that this pulse signal p; is much easier to generate and control than the pulse signal q; of the prior art.

  In the preferred embodiment described here, the transmission device 100 comprises several multipliers 125 adapted to multiply the pulse signal p; by periodic signals of variable frequencies fi, fi2 ... end, these variable frequencies being specific to the transmission device 100. The frequencies fi are chosen greater than the frequency corresponding to the duration Ti of the pulse p; : fi> 1 / Ti.

  FIG. 5b represents the amplitude of the signal thus obtained at the output of the multiplier 125.

  In this embodiment, the transmission device 100 comprises means 126 for summing the signals at the output of the multipliers 125.

  FIG. 5c represents the sum signal; obtained at the output of the summing means 126. This signal is obtained with four periodic signals of frequencies f.

  The transmission device 100 comprises a power amplifier 30 and an antenna 40 which are identical or similar to those of the conventional transmitter 1 previously described in FIG. 1, for transmitting, in the transmission channel, the signal s; obtained at the output of the summing means 126.

  FIG. 5d represents the average spectrum of the sum signal; corresponding to a pulse signal q1 multiplied by four periodic ro signals of random variable frequencies fi1, fj2, fj3 and fi4.

  s; The frequencies fi1, fj2, fia and fi4 are in the frequency band in which the spectrum of the emitted signal s is to be found. In the example described here, the frequencies f1, fj2, fia and fi4 are in the UWB band. Since for each pulse signal pi the frequencies f vary, the spectrum of the sum signal s; also varies.

  In FIG. 5d, representing the average spectrum of the signal s, it is clear that the spectrum of the signal sum s; effectively occupy all the spectral mask given for UWB communications.

  As for each pulse signal pi the frequencies fi vary, the spectrum of the sum signal s; also varies. In Figure 5d is shown the average spectrum of the signal if. It is clear that the spectrum of the signal sum s; effectively occupy all the spectral mask given for UWB communications.

  The transmitter 100 makes it possible to carry out a pulsed transmission on an adjustable frequency band according to the frequencies f 1.

  Those skilled in the art will understand that the invention facilitates the use of the UWB legislated band from 3.1 to 10.6 GHz and reception at the receiver 2.

  According to the invention, the variable frequencies used specific to the transmission device carry no information. They are used simply for the spread of the spectrum of the pulse pi, the positioning of the spectrum of the pulse p; in the band defined by the legislation, to make an optimal occupation of the spectrum as well as a spectral smoothing.

  With the aid of the pulse width p, the number of variable frequencies, and the bands occupied when these frequencies vary, the width of the spectrum of the sum signal can be precisely adjusted; as well as the location of the spectrum of the sum signal if in the frequency domain and in particular on the band reserved for UWE4 communications.

  In addition, the jump of the variable frequencies, generating a frequency diversity, minimizes the fading phenomena due to the propagation channel. It is well known that frequency diversity increases the reliability of the link.

  The filtering and derivation introduced by the receiving antenna does not affect the sum signal si. Indeed, the signal sum if being formed of several signals of variable frequencies f; their derivation is equivalent to a simple time shift.

  In the preferred embodiment described herein, the time difference D between two consecutive p-pulse signals is greater than the multipath delay depth in the transmission channel.

  In practice, this time difference D is defined once and for all during the production of the device, as a function of the maximum time spread (or maximum depth of delays) of the intended use environment between a transmitter and a receiver.

  The signal emitted by the transmission device 100 according to the invention can be received by a conventional receiver 2 as described above in FIG. 4, since the pulse detector 60 is programmed to detect the envelope of the sum signal. s ;.

  FIG. 6 represents the main steps E10 to E50 of a method for transmitting an information data item according to the invention in a preferred embodiment.

  This method comprises a first step E10 during which a DS-SS spectral spreading of the information datum b; is performed to obtain a binary data item c. i0

  This step consists, in known manner, in multiplying the information data item b; by a pseudo-random code PN known from the reception device 2.

  The spreading step E10 is followed by a step E20 during which a pulse signal p is generated for the binary data c; , of duration i ;, this duration being shorter than the duration of the binary data c.

  In the preferred embodiment described herein, the time difference between two consecutive pulse signals p ;, p; +1 is greater than the maximum depth D of the multipath delays in the transmission channel.

  the step E20 of generating the pulse signal p; is followed by a step E30 during which the pulse signal p is multiplied; by several periodic signals of frequencies fi: wire, 12 .., variable end.

  It will be recalled that it is not necessary that the frequencies of these periodic signals be known to the receiver. In the preferred embodiment described herein, the frequencies of these periodic signals are randomly selected.

  This step E30 of multiplications is followed by a step E40 during which the summation of the pulse signals obtained during the preceding step E30 is carried out, then by a step E50 during which the transmission channel is transmitted in the transmission channel. , the signal obtained during the preceding summing step E40.

Claims (8)

  1 - Device for radiofrequency transmission of binary data (c i) in a transmission channel comprising a signal generator adapted to generate, for each binary data item (c i), a pulse signal (pi) of shorter duration (Ti) that the duration of said binary data (c;), this device being characterized in that it further comprises: means for multiplying said pulse signal (pi) by at least one periodic frequency signal (fi) variable specific to said device transmission, said variable frequency (fi) being greater than the frequency (1 / i;) of said pulse signal (p;); and means for transmitting the pulse signal (p; .fi) resulting from said multiplication.   Transmitting device according to claim 1, characterized in that: said multiplication means are adapted to multiply said pulse signal (p;) by several variable frequency signals (fi) specific to said transmitting device, said variable frequencies ( fi) being greater than the frequency (1 / i;) of said pulse signal (pi); in that it comprises: means for summing the pulse signals (p; .fi) results of said multiplications; and in that: said transmitting means being adapted to transmit the pulse signal (s; = Ep; .fi) result of said summation.   3 transmission device according to claim 1 or 2, characterized in that said variable frequency (fi) is random.   4 - transmission device according to any one of claims 1 to 3, characterized in that the frequency of said periodic variable frequency signal varies during the multiplication of said pulse signal (p;).   5 - Transmitting device according to any one of claims 1 to 4, characterized in that said binary data (c;) are obtained by spectral spreading of information data (b;).   6 - Transmission device according to any one of claims 1 to 5, characterized in that the time difference between two pulse signals (pi, p; .i) consecutive is greater than the maximum depth of the delays of the multiple paths in said transmission channel.   7 - Method for radiofrequency transmission of binary data (c i) in a transmission channel, this method comprising, for each binary data item (c i): a step of generating a pulse signal (pi) of duration (i i) shorter than the duration of said binary data (c;); this method being characterized in that it further comprises: a step of multiplying said pulse signal (pi) by at least one periodic frequency signal (fi) variable specific to said transmission method, said variable frequency (fi) being greater at the frequency (1 / i;) of said pulse signal (pi); and.   a step of transmitting said pulse signal (p; .fi) resulting from said multiplication step.   8 transmission method according to claim 7, characterized in that during said multiplication step, said pulse signal (pi) is multiplied by several frequency signals (fi) variable specific to said transmitting device, said variable frequencies (fi) being greater than the frequency (1 / r) of said pulse signal (pi); in that it comprises: a step of summing the pulse signals (p; .f;) results of said multiplications; and in that during said transmitting step, the pulse signal 25 (s; = Ep; .fi) is output from said summing step.   9 - A transmission method according to claim 7 or 8, characterized in that, during said multiplication step, a periodic signal of frequency (fi) variable random.   Transmitting method according to any one of claims 7 to 9, characterized in that the frequency (fi) of the variable frequency periodic signal is varied during the multiplication of said pulse signal (pi).   11 - Transmission method according to any one of claims 7 to 10, characterized in that it comprises a step of obtaining said binary data (c;) by spectral spread of information data (b;).   12 - Transmission method according to any one of claims 7 to 11, characterized in that the time difference between two pulse signal generation steps is greater than the maximum depth of the multipath delays in said transmission channel.