Electronic part of CRPA antenna of an anti-jamming device for a GNSS receiver, associated anti-jamming processing method and navigation system

Abstract

Electronic part of CRPA antenna of an anti-jamming device for a GNSS receiver, associated anti-jamming processing method and navigation system The present invention relates to an electronic part (17) of CRPA antenna (15) of an anti-jamming device (10) for a GNSS receiver (12), comprising: - M inputs (21) configured to receive elementary signals from an array antenna (15) comprising M elementary antennas, M being strictly greater than 1; - a processing module (22) configured to apply anti-jamming processing to the M elementary signals and produce M cleaned output signals; - an output module (23) configured to deliver the M cleaned output signals to the GNSS receiver (12). Figure for abstract: Figure 1

Description

Title of the invention: Electronic part of CRPA antenna of an anti-jamming device for a GNSS receiver, associated anti-jamming processing method and navigation system

[0001] The present invention relates to an electronic part of a CRPA antenna of an anti-jamming device for a GNSS receiver.

[0002] The present invention also relates to an associated anti-jamming processing method.

[0003] The present invention finally relates to an associated navigation system. The navigation system notably comprises an anti-jamming device.

[0004] More particularly, the technical field of the invention is that of anti-jamming devices based on controlled pattern antenna networks for GNSS receivers (from the English "Global Navigation Satellite System" or "Satellite Positioning System" in French). This type of antenna is also known by the English acronym CRPA (for "Controlled Radiated Pattern Antenna" or "Controlled Pattern Antenna" in French).

[0005] An anti-jamming device generally comprises an antenna array, cables and a CRPA antenna electronic part. Such a device is configured to provide a GNSS signal partially or totally free of interfering signals initially present in the useful band of the satellite signals. This then allows the GNSS receiver connected to the output of such an anti-jamming device to operate and provide a navigation solution correctly. The GNSS signals are in the L1, E6, L2 and E5 bands with widths between 40 MHz and 20 MHz.

[0006] In a manner known per se, the electronic part of the CRPA antenna uses several types of algorithms to mitigate interference while retaining useful GNSS signals. The choice of algorithm is a compromise between performance and complexity. Performance is characterized in terms of interference mitigation, convergence time and signal delay. Complexity translates into development cost, recurring cost, and power consumption (and therefore thermal problem).

[0007] A commonly used technique to mitigate interference is to create holes in the antenna pattern in the direction of the jammers. This is called hole formation or "Null steering". This technique is easy to implement because it works blindly, i.e. it does not need to know a priori the direction of the satellites in antenna reference. The direction of the jammers in antenna reference is determined implicitly using the received signals, by looking for the linear combination of the M antenna channels which minimizes the total power. To preserve the useful satellite signals, a coefficient equal to 1 is imposed on one of the M antenna channels (chosen arbitrarily) via a fixed constraint vector C common to all the satellites.

[0008] This technique nevertheless has the disadvantage of not taking advantage of the multiplicity of antenna channels to increase the gain in the direction of the satellites (we speak of beamforming), which further improves the resistance to jamming. Typically, with a 4-channel antenna, it is still possible to gain up to 6 dB on the signal-to-noise ratio, or even more if the satellite direction falls into a hole in the antenna pattern. To do this, we impose as a constraint no longer a unit gain on one of the M antenna channels (i.e. an imposed coefficient equal to 1) but a unit gain on a linear combination of the M channels corresponding to the maximum gain in the direction of the satellite via a constraint vector C specific to each satellite.

[0009] However, beam formation assumes:

[0010] - to carry out in parallel as many antenna treatments as there are satellites tracked since we have a different constraint vector per satellite;

[0011] - to know the direction of the satellites in antenna reference to calculate the coefficients of the satellite constraint vector.

[0012] These two conditions are difficult to meet because:

[0013] - firstly, antenna processing is very resource intensive hardware (due to the bandwidth of GNSS signals, several tens of MHz); and

[0014] - secondly, if we know the direction of the satellites in terrestrial reference thanks to in ephemerides and almanacs, we generally do not know the angular position of the antenna in relation to the terrestrial reference point (unless we have inertial aid which is expensive).

[0015] The present invention aims to remedy these drawbacks and to propose a way of using all of the antenna channels, while allowing moderate use of hardware resources.

[0016] To this end, the invention relates to an electronic part of a CRPA antenna of an anti-jamming device for a receiver, comprising:

[0017] - M inputs configured to receive elementary signals from an antenna network comprising M elementary antennas, M being strictly greater than 1;

[0018] - a processing module configured to apply anti-jamming processing to the M elementary signals and produce M cleaned output signals;

[0019] - an output module configured to deliver the M cleaned output signals to the GNSS receiver.

[0020] According to other advantageous aspects of the invention, the electronic part comprises one or more of the following characteristics, taken in isolation or in all technically possible combinations:

[0021] - the processing module comprises:

[0022] - a filtering component comprising for each of the M inputs, a bank of band-pass filters configured to decompose each elementary signal received by this input into P sub-bands to obtain P sub-sampled signals;

[0023] - a computing component configured to apply the anti-jamming processing to the M sub-sampled signals of each sub-band, and produce M cleaned sub-sampled signals at output per sub-band;

[0024] - a summing component comprising M banks of adding filters, each bank of adder filters being configured to receive P cleaned sub-sampled signals and to sum all of these cleaned sub-sampled signals to form a corresponding cleaned signal;

[0025] - the calculation component comprises P calculation units, each calculation unit being associated with one of the P sub-bands and configured to apply in the corresponding sub-band the anti-jamming processing to the M sub-sampled signals, to obtain M linear combinations of cleaned sub-sampled signals by applying a vector of complex weighting coefficients;

[0026] each bank of adder filters being configured to receive a linear combination of cleaned sub-sampled signals from each calculation unit;

[0027] - the vector of complex weighting coefficients is determined from a constraint vector determined for each of the M entries;

[0028] - each constraint vector comprises M components, one component of which constant associated with the corresponding input and zero components for the other inputs;

[0029] - the bandpass filter banks form polyphase filters;

[0030] - each computing unit is configured to implement a type of processing RLS;

[0031] - RLS type processing is configured to directly provide the M linear combinations of subsampled signals associated with the M constraint vectors, without inversion of an intercorrelation matrix between different signals.

[0032] The invention also relates to a navigation system comprising:

[0033] - a GNSS receiver;

[0034] - a CRPA antenna;

[0035] - an electronic part as defined previously.

[0036] According to other advantageous aspects of the invention, the system comprises one or more of the following characteristics, taken individually or in all technically possible combinations:

[0037] - the GNSS receiver is configured to demodulate for each tracked satellite the M cleaned output signals from the electronic part and to perform a linear combination of the M demodulated signals so as to maximize the power of the useful satellite signal in the discriminators of the tracking loops;

[0038] - the GNSS receiver is configured to determine the direction of arrival of the signal from each satellite tracked from the M demodulated signals so as to determine the complex coefficients which maximize the useful satellite signal power of the linear combination;

[0039] - the GNSS receiver is configured to improve the convergence speed of the estimators of the direction of arrival of satellite signals using inertial measurements;

[0040] - the GNSS receiver is configured to determine a decoy indicator from of the direction of arrival of satellite signals;

[0041] - the GNSS receiver is configured to determine for each tracked satellite the complex coefficients of the linear combinations of the M signals demodulated using analog antenna patterns of the M elementary antennas.

[0042] The invention also relates to an anti-jamming processing method for a GNSS receiver, the method comprising the following steps:

[0043] - receive M elementary signals from an array antenna comprising M elementary antennas, M being strictly greater than 1;

[0044] - apply anti-jamming processing to the M elementary signals and produce M cleaned output signals;

[0045] - deliver the M cleaned output signals to the GNSS receiver.

[0046] These characteristics and advantages of the invention will appear on reading the description which follows, given by way of non-limiting example, and made with reference to the appended drawings, in which:

[0047] - [Fig.l] [Fig.l] is a schematic view of a navigation system according to the invention, the system comprising in particular an anti-jamming device and a GNSS receiver;

[0048] - [Fig.2] [Fig.2] is a detailed schematic view of a processing module of the anti-jamming device of [Fig.l];

[0049] - [Fig.3] [Fig.3] is a detailed schematic view of a hardware part of the GNSS receiver of [Fig.l]; and

[0050] - [Fig.4] [Fig.4] is a detailed schematic view of a software part of the GNSS receiver of [Fig.l].

[0051] [Fig.l] illustrates a navigation system 10 according to the invention. This navigation system 10 comprises an anti-jamming device 11 and a GNSS receiver 12.

[0052] The GNSS receiver 12 has a GNSS signal receiver capable of determining a navigation solution from the received GNSS signals, which come from one or more global satellite navigation systems (such as the GPS system or the GALILEO system). In a manner known per se, each global satellite navigation system forms a constellation of satellites and is capable of providing one or more navigation services. For example, the GPS system provides different navigation services, such as for example “PPS” or “M code” services. The same is true for the GALILEO system which provides for example “PRS” and “OS” services.

[0053] To receive the GNSS signals, the GNSS receiver 12 is connected to the anti-jamming device 11 making it possible to receive all the radiofrequency signals S available according to a given frequency range, and to extract GNSS radiofrequency signals therefrom, designated by “Sm” in [Fig.l], by cleaning them from the jamming radiofrequency signals, designated by “b” in [Fig.l]. The jamming radiofrequency signals b come, for example, from one or more jamming sources 13 arranged in the vicinity of the GNSS receiver 12. These jamming sources 13 can be introduced voluntarily or involuntarily.

[0054] To do this, the anti-jamming device 11 comprises an antenna network 15, also called a CRPA antenna, and an electronic part of the CRPA antenna 17, hereinafter referred to simply as “electronic part 17”. The antenna network 15 is capable of receiving an input signal on each channel and transmitting these input signals to the electronic part 17.

[0055] The antenna array 15 comprises M elementary antennas arranged on a base according to a known configuration. In the example of [Fig.l], the number M is equal to 4. Each elementary antenna is connected to the electronic part 17 by an antenna channel and is capable of delivering to this part 17 received radiofrequency signals, hereinafter called elementary signals. The input signal Se delivered to the electronic part 17 by the antenna array 15 is therefore composed of M elementary signals.

[0056] As can be seen in [Fig.l], the electronic part 17 comprises M inputs 21 configured to receive elementary signals from the antenna array 15, a processing module 22 configured to process the received elementary signals to generate M cleaned output signals Sm (index m varying between 1 and M), and an output 23 configured to deliver the M cleaned output signals Sm to the GNSS receiver 12.

[0057] In particular, in the example of [Fig.l], each input 21 is connected to one of the elementary antennas of the antenna array 15 and provides the processing module 22 with digitized elementary input signals, brought back to baseband and sampled at the frequency Fe, represented by complex numbers. Furthermore, in the example of the same [Fig.l], the output 23 of the electronic part 17 is connected to the GNSS receiver 12 by M transmission channels. In this case, the output 23 therefore provides the M cleaned output signals Sm to M processing channels of the GNSS receiver, as will be explained later.

[0058] The processing module 22 is capable of processing the received radiofrequency signals to extract therefrom GNSS radiofrequency signals exempted totally or at least in part from the jamming radiofrequency signals. In particular, the processing module 22 is capable of receiving the elementary signals received by the antenna array 15 with a sampling frequency Fe which is for example between 20 MHz and 80 MHz, and advantageously equal for example to 50 MHz. Advantageously, the processing module 22 is capable of processing the received radiofrequency signals corresponding to B GNSS bands such as for example the L1, E6 and L2 bands.

[0059] Preferably, the processing module 22 has an entirely hardware structure formed of one or more programmable logic circuits of the FPGA (Field-Programmable Gate Array) or ASIC (Application-Specific Integrated Circuit) type.

[0060] The processing module 22 is illustrated in more detail in [Fig.2] illustrating an exemplary embodiment of this module. Thus, as can be seen in this figure, the processing module 22 comprises a filtering component 31, a calculation component 32 and a summation component 33.

[0061] The filtering component 31 advantageously comprises M banks of P sub-sampling bandpass filters. This filtering component 31 thus makes it possible to carry out a space-frequency processing of the SFAP type (from the English “Space Frequency Adaptive Processing”).

[0062] Each filter bank is connected to one of the M inputs 21 and capable of receiving each elementary signal, digitized and brought back to baseband, coming from this input to decompose it into P sub-bands, that is to say to obtain P sub-sampled signals Si, ..., SP. The number P is greater than or equal to 1, advantageously strictly greater than 1. Advantageously, the number P is equal to a power of 2 and preferably, can be chosen equal to 8 or 16.

[0063] Advantageously, each filter bank is implemented according to the technique known as “polyphase filters” and described in particular in application FR 21 07910. This means that instead of using P bandpass filters in parallel working at the frequency Fe, the sampling frequency of each sub-band is reduced by factor P. This allows the filter bank to be produced with a single multiplexed FIR filter (working at the frequency Fe) having a number of coefficients reduced by the factor P. The FIR filter (from the English "Finite Impulse Response Filter") is a finite impulse response filter, known per se. In addition, the P outputs of the multiplexed FIR filter produced at the frequency Fe / P are connected to an FFT operator (from the English "Fast Fourier Transform") allowing a fast Fourier transformation of the vector made up of these P outputs to be carried out and to find at the output the equivalent of a sub-sampled digital filter bank.

[0064] The calculation component 32 makes it possible to process all of the sub-sampled signals Si, ..., SP formed by the M filter banks by applying a method for calculating the complex weighting coefficients corresponding to these sub-sampled signals.

[0065] According to the invention, the calculation component 32 comprises P calculation units SAPi, ..SAPp, each calculation unit SAPi, ..., SAPP being adapted to apply in the corresponding sub-band an anti-jamming treatment to the sub-sampled signals coming from the M inputs, to obtain M linear combinations of cleaned sub-sampled signals.

[0066] In particular, each calculation unit SAPi, ..., SAPP is capable of calculating M output signals Ssapp m using the following formula:

[0067] c -w 'h* LJ 'ASAPp mm

[0068] WHERE

[0069] hj is the row vector containing the M complex samples received at time 1 from the M antenna channels in the sub-band p after the corresponding input filter bank, at each period Te of sub-sampling of the sub-bands:

[0070] h / =[ Svl(l.Te) Sv2(J.Te) ... S^LTe')]

[0071] is the vector of complex weighting coefficients for each output m.

[0072] This vector of complex weighting coefficients can be calculated as:

[0073] W^PCj

[0074] where:

[0075] Cm is the constraint vector common to all sub-bands and is equal to 1 in position m and to 0 otherwise;

[0076] P is the inverse of the intercorrelation matrix Rxx (of dimensions M x M) given by the formula:

[0077] Rxx = HtH t L

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[0092] l, M To calculate the vector, each SAPh calculation unit ..SAPP is for example configured to implement an RLS method (i.e. a recursive least squares method or "Recursive Least Square" in English, often replaced by the acronym RLS) for calculating complex weighting coefficients per sub-band. According to the RLS method, it is not necessary to recalculate the inverse of the matrix Rxx to update the vector Wm each time a row is added to the matrix Se, which saves computations. Thus, according to the RLS method, rather than calculating the inverse of the matrix Rxx at the end of each integration interval of Rxx, the inverse Rxxn 1 is updated at each sampling period of the received signals. As an alternative to the RLS method, the gradient method or LMS (Least Mean Square) can be used. This method has the advantage of simplicity without the disadvantage of longer convergence time. This LMS recursive method uses a less expensive formula in terms of the number of operations: ^„,= «'„,.(- / <(11,.^,.!). h / OR 1: time index; : recalibration coefficient, between 0 and 1, typically equal to 0.1; h,.h'm: scalar product between the row vector h / and the column vector / 4. Regardless of the method used, to take into account each constraint vector Cm we force the component m to 1: “ 1 Advantageously, the computing component 32 entirely has a single hardware component, such as a logic circuit, for example of the FPGA (Field-Programmable Gate Array) type. In such a case, the architecture of the computing component 32 may have a “pipeline” architecture. In this case, this architecture has consecutive layers which are connected together by flip-flops allowing the transmission between these layers of data resynchronized on the clock of the logic circuit. The summing component 33 comprises M interpolator filter banks adding the Ssapp signals m- Each interpolator filter bank adding has for example a multiplexed FIR filter and allows to sum the signals Ssapp m (index p varying between 1 and P) to provide a cleaned output signal Sm at the frequency Fe. In other words, the summing component 33 provides M cleaned output signals S m (index m varying between 1 and M) at the frequency Fe.

[0093] With reference to [Fig. 3], the GNSS receiver 12 comprises a hardware part 41 and a software part 42. The hardware part 41 is for example formed of one or more programmable logic circuits. The software part 42 is implemented using at least one or more processors and a RAM.

[0094] The hardware part 41 comprises, for each satellite n tracked (n varying between 1 and N), M demodulators making it possible to demodulate in parallel the M cleaned output signals Sm coming from the anti-jamming device 11 and thus, to make the direction of arrival of the satellite signals observable thanks to the phase shifts between the M antenna channels at the output of the correlators.

[0095] In particular, each demodulator makes it possible to demodulate the associated Stn signal with at least three correlators per signal, called advance, punctual and delay correlators, thanks to three shifted versions of a spreading code generated in the channel.

[0096] The correlation consists of multiplying the signal received Sm by the demodulator m with a local carrier e'^ and a local code , A and integrating over intervals of ^^code) consecutive times.

[0097] In particular, by denoting by Zimn( q) a complex correlation on the interval [ tq, tq+T ] between the broadband signal Sm and the local signal consisting of a local carrier and the local code of the satellite (code specific to satellite n), this correlation can be written: 100981 =J[li] ti+T)S„,(ï).exp( -2>ÿ(O

[0099] where

[0100] index i: advance, punctual or delayed track, i = A, P or R;

[0101] Index m: output signal of the anti-jamming device 11, m = 1 to M;

[0102] Index n: demodulated satellite, n = 1 to N;

[0103] Index q: integration interval [tq, tq+T] = [tq, tq+i];

[0104] T: integration time.

[0105] The software part 41, illustrated in more detail in [Fig.4], makes it possible to carry out for each tracked satellite 5 linear combinations with complex coefficients of the M demodulated channels at the output of the correlators: - A “reconstituted advance” channel resulting from the linear combination of the complex outputs “ZAmn” of the M advance correlators with the coefficients Kmn(o,a),

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[0117] - A “reconstituted point” channel resulting from the linear combination of the complex outputs “ZPmn” of the M point correlators with the coefficients Kmn(ChC0 , - A “reconstituted delay” channel resulting from the linear combination of the complex outputs “ZR mn” of the M delay correlators with the coefficients Km n(o,a); - A “delta site” channel resulting from the linear combination of the complex “ZPmn” outputs of the M point correlators with the KAsitem coefficients n(o,a); - A “delta azimuth” channel resulting from the linear combination of the complex outputs* ZPmn” of the M point correlators with the KAazimut m coefficients The "reconstructed punctual" channel is used for the tracking loop of the carrier phase of the satellite signal. The three reconstructed advance, punctual and delay channels are used for the tracking loop of the satellite signal code phase via the code discriminator. The “delta site” and “delta azimuth” channels are used to iteratively estimate the angles o and a of elevation and azimuth maximizing the power of the satellite signal after linear combination of the “reconstructed point” path using two tracking loops, in elevation and in azimuth. The parameters o and a are the estimated elevation and azimuth angles of the direction of arrival of the satellite signal, in antenna reference. The M coefficients Kmn(o,a) aim to maximize the satellite signal power in the estimated direction of arrival of the satellite signal given by the elevation and azimuth angles o and a. The M coefficients KAsitemn(o,a) aim to estimate the correction to be made to the elevation angle to achieve maximum power. The M coefficients KAazimutmn(o,a) aim to estimate the correction to be made to the azimuth angle to achieve maximum power. Subsequently, we denote: - the vectors connecting the center of the antenna reference frame to the phase centers of the M channels antennas: 1 way antenna m Y ■ antenna channel m 7 • . ^antenna channel m for m = 1 to M - the direction vectors pointing in the direction of the N satellites: sat n for n = 1 to N 1 sat n 7 '-'sat n 2 + y 2 + 7 sat n ' sat n '-'sat n

[0118] - the direction vectors pointing in the estimated direction ((?,«):

[0119] / ua, a cosia cr ) ” sini aa ) CO^ cr ) •

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[0123] o: elevation angle of the estimated direction of arrival of the satellite signal; a: azimuth angle of the estimated direction of arrival of the satellite signal; - the vector of coefficients of the linear combination giving the maximum satellite power in the estimated direction (o,a): / K-fa , a ) '

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[0138] Km(a , et) = ex pi -2jn . r,,^ , a) / 2 ) with = {rm, u} scalar product; - the vector of coefficients of the linear combination indicating the correction to be made to the estimated elevation angle: 1 & K / \ )= - the vector of coefficients of the linear combination indicating the correction to be made to the estimated azimuth angle: * A azimuth ,ü j- ,aj The two derivatives are calculated using analytical formulas giving Km as a function of (o,a). The five above-mentioned combinations are written in the following form: for reconstructed advance, punctual and late tracks: ZAn = £4(0,a). ZAln + K2(o,a). ZA2n + ... + KM(o,a). ZAMn Zp n = Ki(o,a). ZP1 n + K2(o,a). ZP 2 n + ... + KM(o,a) . ZP M n ZRn = £1(0,a). ZRln + K2(o,a). ZR2n + ... + KM(o,a). ZRMn for reconstructed delta tracks: ZAcode n ZA - ZR ZA siïe n — KAsite 1 n(O,Ct). Zp 1 n + KAsite 2 • Zp 2 n "I" • • • "H KAsite m(O,CI). Zp mn ZAazimut n KAazimut 1 n(o,a) . Zp | n + KAazimut2n(O,Ct). Zp2n + ...+ KAazimutjyi(O,Q) . Zpjy[n This allows the following discriminators to be determined: - carrier phase discriminator:

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[0159] ZP j Zp 2 ^PM. ^carrier angle( Zp n ) - code discriminator: Dcode = Real part [ ZAcoden / ZPn ] = Real part [ ZAcoden. conjugate( ZPn ) ] / II ZPn II2 - site and azimuth discriminators: Dsite = Real part [ ZAsiten / ZPn ] = Real part [ ZAsiten. conjugate ( ZPn ) ] / Il ZPn II2 Dazimut = Real part [ ZAazimutn / ZPn ] = Real part [ ZAazimutn. conjugate ( ZPn ) ] / Il ZPn II2 Furthermore, the elevation and azimuth discriminators can be justified as follows: - We seek to maximize 11 \ 77* 112 with ZP- K(a,a)Z P = K^a).Z Pl + Æ2((7, a). Z P 2 + ... + a). Z P M (dot product) - We calculate the derivative with respect to the parameters o and a: 11 K(&, a)ZP 11 = Real part [ a )zP).(k((t, a )Z^ ] 11 a )ZP 11 = Real part [ 2.^ (a)Z^ a )ZP) ] 11 K(a, a)ZP 11 = Real part [ 2^y|(tr, (K(a, a)Zp) ] 11 k( <j, a)^|p="Partie" réelle [ 2. z&azimuf. conjugué( zp ) ] È 11 K(a, a)Z^ 112 = 2. Dazimut When we are close to the maximum, the derivative indicates the correction to be made to approach the maximum (gradient method). To estimate the elevation and azimuth angles, software part 42 uses the gradient method: &H+1 ~ <7 n + W ■ ^site ^«+1 — + ^azimuth The choice of the value of the recalibration gain is the result of a compromise between convergence speed (to limit the drag with respect to the dynamics of the evolution of the angles due to the carrier) and precision (filtering of the measurement noise). In some embodiments, it is possible to take into account, in the linear combinations of the directional beams, the analog antenna patterns of the M channels. This is particularly the case for a multi-channel antenna with close phase centers, due to coupling phenomena which distort the diagrams.

[0160] In this case, the software part 42 multiplies the coefficients by complex gains which depend on the channel m and the assumed direction of arrival of the satellite signal: [°161 ] K^a, a) = exp( - . rmu(a, a) I à) .Gvoie mtenne m(a, a)

[0162] fi („■ n ): complex gain (module and phase) of channel m of the antenna '-Tvoie antenna m\u ' w / in the direction (g- q.

[0163] The values ​​of the complex gains can be stored in tables as a function of the elevation and azimuth angles (i.e. M tables).

[0164] It is also possible to take the diagram into account in the calculation of 07) and da J

[0165] The two derivatives of the complex gains can also be tabulated (which requires having 3 x M tables) or calculated by finite difference between two discretization points.

[0166] In some embodiments, the software portion 42 also uses angular velocity information from an inertial unit in estimating the elevation and azimuth angles, in order to improve the performance thereof.

[0167] In such a case, it is assumed that there is an inertial unit whose axes are aligned with those of the antenna and provide angular increments around the X, Y, Z axes, at the calculation period of the estimators, noted cox, «y, «z-

[0168] We can then estimate a priori the variations in the elevation and azimuth angles at the calculation period of the estimators, noted da and do in the following way:

[0169] da = coz

[0170] and

[0171] do = cox sin(a) + coY cos(a).

[0172] This information can be used to assist elevation and azimuth estimators in the following ways: cr„+1 = tJn + fi- ^site + (ÙJX • sin(a) + my.co^a)).A t

[0173] = an+ji. D^+üoAi

[0174] Finally, the software part 42 can also use the elevation and azimuth angle estimates to determine a decoy indicator.

[0175] In particular, when the GNSS receiver 12 receives the signals from an authentic GNSS constellation, these come from completely distinct directions in space. On the other hand, when the signals received come from a decoy, these all come from a single direction (that of the decoy's transmitting antenna).

[0176] We can therefore determine a likelihood criterion for a decoying situation by comparing the sites and azimuths of all the channels tracked.

[0177] An example criterion is: "if, for any pair (i, j) of satellites tracked, | cri - cj | < threshold and \cd- aj | < thresholds then declare a decoy situation".

[0178] This then makes it possible to detect deception even in the presence of jamming because the anti-jamming processing is done upstream.

[0179] A navigation method implemented by the navigation system 10 will now be explained.

[0180] This method is implemented during operation of the anti-jamming device 10 with the frequency Fe, corresponding to the sampling frequency Fe mentioned previously.

[0181] This navigation method comprises an initial anti-jamming processing phase during which an anti-jamming processing method is implemented by the anti-jamming device 11.

[0182] During an initial step of this anti-jamming processing method, the inputs 21 of the electronic part 17 receive the M elementary signals received by the antenna network 15. These elementary signals are then transmitted to the processing module 22 after digitization, passage to baseband and sampling at the frequency Fe.

[0183] During a following step of the anti-jamming processing method, the filtering component 31 of the processing module 22 receives these elementary signals, brought back to baseband and digitized, then decomposes them into P sub-bands and sub-samples them at the frequency Fe / P, using M digital filter banks, thus forming the sub-sampled signals Si, ..., Sp, as explained previously.

[0184] During a following step of the anti-jamming processing method, the calculation component 32 applies an anti-jamming processing and forms in each sub-band p M linear combinations of cleaned sub-sampled signals Ssafp m-

[0185] In a subsequent step of the anti-jamming processing method, the summing component 33 receives the M output signals Ssapp m in each sub-band and provides M resulting wideband signals Sm. These signals are cleaned of interference.

[0186] In a subsequent step of the anti-jamming processing method, output 23 transmits the resulting M signals Sm to the GNSS receiver 12.

[0187] The navigation method further comprises a phase of processing the cleaned signals.

[0188] During this phase, the GNSS receiver 12 processes these cleaned signals to first determine the direction of arrival of the satellite signals and then a corresponding navigation solution.

[0189] It is therefore understood that the present invention has a certain number of advantages.

[0190] In particular, the invention makes it possible to carry out complete antenna processing with hole formation and beam formation in order to make the most of a multi-channel antenna while being resource-efficient since it does not require multiplying the anti-jamming processing and it is autonomous in determining the direction of the satellites.

[0191] For this, the invention proposes to carry out in the antenna processing not N beams in the direction of the N tracked satellites, but M linear combinations with for each one the constraint of having one of the M coefficients of the linear combination equal to 1. Given that M is strictly less than N, this makes it possible to save resources while ensuring complete processing of all the antenna channels.

[0192] The invention further proposes to carry out M linear combinations in each of the P sub-bands and to reconstitute at the output of a processing (SFAP for example) M wideband signals each associated with one of the M antenna channels using M banks of interpolating summing filters.

[0193] A combination of the M wideband signals after antenna processing is carried out further in the GNSS receiver, satellite axis by satellite axis depending on the direction of the satellites, after demodulation of the spreading codes specific to each satellite. In particular, for each tracked satellite, the M wideband signals are demodulated in parallel so as to make the direction of arrival of the satellite signal observable. A linear combination is sought which maximizes the power of the satellite signal after demodulation.

Claims

Claims

1. Electronic part (17) of CRPA antenna (15) of an anti-jamming device (10) for a GNSS receiver (12), comprising: - M inputs (21) configured to receive elementary signals from an array antenna (15) comprising M elementary antennas, M being strictly greater than 1; - a processing module (22) configured to apply an anti-jamming processing to the M elementary signals and produce M cleaned output signals; - an output module (23) configured to deliver the M cleaned output signals to the GNSS receiver (12).

2. Electronic part (17) according to claim 1, in which the processing module (22) comprises: - a filtering component (31) comprising for each of the M inputs (21), a bank of bandpass filters configured to decompose each elementary signal received by this input into P sub-bands to obtain P sub-sampled signals; - a calculation component (32) configured to apply the anti-jamming processing to the M sub-sampled signals of each sub-band, and produce M cleaned sub-sampled signals at output per sub-band; - a summing component (33) comprising M banks of adder filters, each bank of adder filters being configured to receive P cleaned sub-sampled signals and to sum all of these cleaned sub-sampled signals to form a corresponding cleaned signal.

3. Electronic part (17) according to claim 2, in which the calculation component (32) comprises P calculation units (SAPb ..., SAPp), each calculation unit (SAPb ..., SAPP) being associated with one of the P sub-bands and configured to apply in the corresponding sub-band the anti-jamming processing to the M sub-sampled signals, to obtain M linear combinations of cleaned sub-sampled signals by applying a vector of complex weighting coefficients; each bank of adder filters being configured to receive a linear combination of cleaned sub-sampled signals from each calculation unit (SAPi, ..., SAPP).

4. Electronic part (17) according to claim 3, in which the vector of complex weighting coefficients is determined from a constraint vector determined for each of the M inputs.

5. Electronic part (17) according to claim 4, in which each constraint vector comprises M components including a constant component associated with the corresponding input and zero components for the other inputs.

6. Electronic part (17) according to any one of claims 2 to 5, in which the banks of bandpass filters form polyphase filters.

7. Electronic part (17) according to any one of the preceding claims taken in combination with claim 3, in which each calculation unit (SAPi, ..., SAPP) is configured to implement RLS type processing.

8. Electronic part (17) according to claim 7 taken in combination with claim 4, in which the RLS type processing is configured to directly provide the M linear combinations of sub-sampled signals associated with the M constraint vectors, without inversion of an intercorrelation matrix between different signals.

9. Navigation system (10) comprising: - a GNSS receiver (12); - a CRPA antenna (15); - an electronic part (17) according to any one of the preceding claims.

10. Navigation system (10) according to claim 9, in which the GNSS receiver (12) is configured to demodulate for each tracked satellite the M cleaned output signals from the electronic part (17) and to perform a linear combination of the M demodulated signals so as to maximize the power of the useful satellite signal in the discriminators of the tracking loops.

11. The navigation system (10) of claim 10, wherein the GNSS receiver (12) is configured to determine the direction of arrival of the signal of each tracked satellite from the M demodulated signals so as to determine the complex coefficients which maximize the useful satellite signal power of the linear combination.

12. The navigation system (10) of claim 11, wherein the GNSS receiver (12) is configured to improve the convergence speed of the estimators of the direction of arrival of the satellite signals using inertial measurements.

13. The navigation system (10) of claim 11 or 12, wherein the GNSS receiver (12) is configured to determine a decoy indicator from the direction of arrival of the satellite signals.

14. Navigation system (10) according to any one of claims 10 to 13, in which the GNSS receiver (12) is configured to determine for each tracked satellite the complex coefficients of the linear combinations of the M demodulated signals using analog antenna patterns of the M elementary antennas.

15. Anti-jamming processing method for a GNSS receiver (12), the method comprising the following steps: - receiving M elementary signals from an array antenna (15) comprising M elementary antennas, M being strictly greater than 1; - applying anti-jamming processing to the M elementary signals and producing M cleaned output signals; - delivering the M cleaned output signals to the GNSS receiver (12).

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