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

Abstract

Electronic CRPA Antenna Part of an Anti-Jamming Device for a GNSS Receiver, Anti-Jamming Processing Method, and Associated Navigation System. The present invention relates to an electronic CRPA antenna part (17) (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 the abstract: Figure 1

Description

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

[0003] The present invention also relates to an associated navigation system. The navigation system includes, in particular, an anti-jamming device.

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

[0005] An anti-jamming device generally comprises an antenna array, cables, and an electronic CRPA antenna component. Such a device is configured to provide a GNSS signal that is partially or completely free of the jamming 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 function and provide a proper navigation solution. The GNSS signals are in the L1, E6, L2, and E5 bands with bandwidths ranging from 40 MHz to 20 MHz.

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

[0007] A commonly used technique for mitigating interference consists of creating 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 operates blindly, meaning it does not need to know the antenna-referenced direction of the satellites a priori. The antenna-referenced direction of the jammers is determined implicitly from the received signals, by searching The linear combination of the M antenna channels 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 satellites.

[0008] This technique, however, has the drawback of not taking advantage of the multiple antenna paths to increase the gain in the direction of the satellites (this is called beamforming), which further improves resistance to interference. Typically, with a 4-way antenna, it is still possible to gain up to 6 dB in the signal-to-noise ratio, or even more if the satellite direction falls within a gap in the antenna pattern. To achieve this, the constraint is no longer a single gain on one of the M antenna paths (i.e., an imposed coefficient equal to 1), but a single gain on a linear combination of the M paths corresponding to the maximum gain in the direction of the satellite via a constraint vector C specific to each satellite.

[0009] However, beam formation presupposes:

[0010] - to perform in parallel as many antenna processing operations as there are satellites being tracked since we have a different constraint vector per satellite;

[0011] - to know the direction of the satellites in antenna coordinates in order 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, which is several tens of MHz); and

[0014] - secondly, if the direction of the satellites in a terrestrial reference frame is well known thanks to In ephemerides and almanacs, the angular position of the antenna relative to the terrestrial reference frame is generally not known (unless one has an inertial aid which is expensive).

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

[0016] To this end, the invention relates to an electronic CRPA antenna part 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 M elementary signals and produce M cleaned output signals;

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

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

[0021] - the processing module includes:

[0022] - a filtering component comprising, for each of the M inputs, 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;

[0023] - a computing component configured to apply anti-jamming treatment to the M subsampled signals of each subband, and produce M cleaned subsampled output signals per subband;

[0024] - a summation component comprising M banks of adding filters, each bank of adder filters being configured to receive P cleaned downsampled signals and to sum all of these cleaned downsampled 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-interference 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 downsampled signals cleaned from each computing unit;

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

[0028] - each constraint vector comprises M components, one of which is a component 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 undersampled signals associated with M constraint vectors, without inversion of a cross-correlation 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 above.

[0036] According to other advantageous aspects of the invention, the system comprises one or more of the following features, 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 in order 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 in such a way as to determine the complex coefficients that 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 the satellite signals;

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

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

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

[0044] - apply an anti-interference treatment to the M elementary signals and produce M output signals cleaned up;

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

[0046] These features and advantages of the invention will become apparent from the following description, given by way of non-limiting example, and made with reference to the accompanying drawings, on which:

[0047] - [Fig. 1] [Fig. 1] is a schematic view of a navigation system according to the invention, the system including 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 the [Fig.l];

[0049] - [Fig.3] [Fig.3] is a detailed schematic view of a material part of the GNSS receiver of the [Fig. 1]; and

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

[0051] Figure 1 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 originate from one or more global navigation satellite systems (such as the GPS or GALILEO systems). Each global navigation satellite system, as is known, 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 "PPS" or "M-code" services. The same is true for the GALILEO system, which provides, for example, "PRS" and "OS" services.

[0053] To receive GNSS signals, the GNSS receiver 12 is connected to the anti-jamming device 11, which receives all available radio frequency signals S within a given frequency range and extracts GNSS radio frequency signals, designated by "Sm" in [Fig. 1], by removing the radio frequency jamming signals, designated by "b" in [Fig. 1]. The radio frequency jamming signals b originate, for example, from one or more jamming sources 13 located in the vicinity of the GNSS receiver 12. These jamming sources 13 may be introduced intentionally or unintentionally.

[0054] To this end, the anti-jamming device 11 comprises an antenna array 15, also called a CRPA antenna, and an electronic CRPA antenna component 17, hereafter referred to simply as the "electronic component 17". The antenna array 15 is capable of receiving an input signal on each channel and transmitting these input signals to the electronic component 17.

[0055] The antenna array 15 comprises M elementary antennas arranged on a base in a known configuration. In the example of [Fig. 1], the number M is equal to 4. Each elementary antenna is connected to the electronic section 17 by an antenna channel and is capable of delivering received radio frequency signals, hereafter referred to as elementary signals, to this section 17. The input signal Se delivered to the electronic section 17 by the antenna array 15 is therefore composed of M elementary signals.

[0056] As can be seen in [Fig.1], 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. 1], 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, basebanded and sampled at the frequency Fe, represented by complex numbers. Furthermore, in the same example of [Fig. 1], the output 23 of the electronic part 17 is connected to the GNSS receiver 12 via M transmission channels. In this case, the output 23 therefore provides the M cleaned output signals Sm to the M processing channels of the GNSS receiver, as will be explained later.

[0058] The processing module 22 is capable of processing received radio frequency signals to extract GNSS radio frequency signals that are totally or at least partially free of interference radio frequency 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 that is, for example, between 20 MHz and 80 MHz, and advantageously equal to, for example, 50 MHz. Advantageously, the processing module 22 is capable of processing received radio frequency signals corresponding to GNSS bands such as, for example, the L1, E6, and L2 bands.

[0059] Preferably, the processing module 22 has a hardware structure consisting entirely 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], which shows an example of an 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 subsampling bandpass filters. This filtering component 31 thus makes it possible to perform 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 is capable of receiving each elementary signal, digitized and basebanded, from that input in order 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, perhaps chosen to be equal to 8 or 16.

[0063] Advantageously, each filter bank is implemented using the technique known as "polyphase filters" and described in particular in French patent application FR 21 07910. This means that instead of using P parallel bandpass filters operating at frequency Fe, the sampling frequency of each sub-band is reduced by The P factor allows the filter bank to be implemented with a single multiplexed FIR filter (operating at frequency Fe) with a reduced number of coefficients in terms of the P factor. The FIR (Finite Impulse Response Filter) is a filter with a finite impulse response, known in itself. Furthermore, the P outputs of the multiplexed FIR filter, produced at frequency Fe / P, are connected to an FFT (Fast Fourier Transform) operator, which performs a fast Fourier transform on the vector of these P outputs, resulting in the equivalent of an undersampled digital filter bank.

[0064] The calculation component 32 allows the processing of all the subsampled signals Si, ..., SP formed by the M filter banks by applying a method of calculating the complex weighting coefficients corresponding to these subsampled signals.

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

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

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

[0068] WHERE

[0069] hj is the line 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 sub-sampling period Te 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 stress 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 cross-correlation matrix Rxx (of dimensions M x M) given by the formula:

[0077] Rxx = HtH t L

[0078]

[0079]

[0080]

[0081]

[0082]

[0083]

[0084]

[0085]

[0086]

[0087]

[0088]

[0089]

[0090]

[0091]

[0092] l, M To calculate the vector, each SAPh ..SAPP computing unit is configured, for example, to implement an RLS method (i.e., a recursive least squares method, 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 calculations. Thus, according to the RLS method, rather than calculating the inverse of the matrix Rxx at each end of the Rxx integration interval, we update the inverse Rxxn 1 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 offers the advantage of simplicity without the drawback of a longer convergence time. This recursive LMS method uses a formula that is less expensive in terms of the number of operations: ^„,= «'„,.(- / <(11,.^,.!). h / OR 1: time index; : registration coefficient, between 0 and 1, typically equal to 0.1; h,.h'm: dot product between the row vector h / and the column vector / 4. Regardless of the method used, to account for each constraint vector Cm, the component m is forced to 1: “ 1 Advantageously, the computing component 32 consists entirely of a single hardware component, such as a logic circuit, for example, an FPGA (Field-Programmable Gate Array). In such a case, the architecture of the computing component 32 can be a "pipelined" architecture. This architecture features consecutive layers connected by flip-flops, allowing the transmission of resynchronized data between these layers, synchronized to the logic circuit's clock. The summing component 33 comprises M banks of Ssapp m signal interpolating and summing filters. Each bank of interpolating and summing filters For example, it presents a multiplexed FIR filter and allows the summation of the Ssapp m signals (index p varying between 1 and P) to provide a cleaned output signal Sm at the frequency Fe. In other words, the summation component 33 provides M cleaned output signals Sm (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 random access memory.

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

[0095] In particular, each demodulator allows the Stn signal associated with at least three correlators per signal, called lead, point and delay correlators, to be demodulated by means of three offset 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 Sm signal 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 delay lane, i = A, P or R;

[0101] Index m: signal at output 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 perform for each tracked satellite 5 linear combinations with complex coefficients of the M demodulated channels at the output of correlators: - A "reconstituted advance" path resulting from the linear combination of the complex "ZAmn" outputs of the advance M correlators with the coefficients Kmn(o,a),

[0106]

[0107]

[0108]

[0109]

[0110] [YES]

[0112]

[0113]

[0114]

[0115]

[0116]

[0117] - A "reconstituted point" path resulting from the linear combination of the complex outputs "ZPmn" of the point correlators M 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" path resulting from the linear combination of the complex outputs "ZPmn" of the M point correlators with the coefficients KAsitem n(o,a); - A "delta azimuth" channel resulting from the linear combination of the complex outputs* ZPmn" of the M point correlators with the coefficients KAazimut m The "reconstructed point" channel is used for the tracking loop of the carrier phase of the satellite signal. The three reconstituted advance, punctual and delay paths are used in the tracking loop of the satellite signal code phase via the code discriminator. The "delta site" and "delta azimuth" methods are used to estimate iteratively. the angles o and a of site and azimuth maximizing the power of the satellite signal after linear combination of the "reconstituted point" path thanks to two tracking loops, in site and azimuth. The parameters o and a are the estimated site and azimuth angles of the direction of arrival of the satellite signal, in antenna reference frame. The M coefficients Kmn(o,a) aim to maximize the power of the satellite signal in the estimated direction of arrival of the satellite signal given by the site and azimuth angles o and a. The M coefficients KAsitemn(o,a) aim to estimate the correction to be made to the site angle to achieve the maximum power. The M coefficients KAazimutmn(o,a) aim to estimate the correction to be made to the azimuth angle to reach the maximum power. Subsequently, we note: - the vectors connecting the center of the antenna 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 ) •

[0120]

[0121]

[0122]

[0123] o: site angle of the estimated arrival direction of the satellite signal; a: azimuth angle of the estimated arrival direction 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) '

[0124]

[0125]

[0126]

[0127]

[0128]

[0129]

[0130]

[0131]

[0132]

[0133]

[0134]

[0135]

[0136]

[0137]

[0138] Km(a , et) = ex pi -2jn . r,,^ , a) / 2 ) with = {rm, u} dot product; - the vector of coefficients of the linear combination indicating the correction to be applied to the estimated site angle: 1 & K / \ )= - the vector of coefficients of the linear combination indicating the correction to be applied to the estimated azimuth angle: * A azimuth ,ü j- ,aj The two derivatives are calculated using the analytical formulas giving Km as a function of (o,a). The five aforementioned combinations can be written in the following form: for reconstructed advance, punctual and delay 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 routes: 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 us to determine the following discriminators: - Carrier phase discriminator:

[0139]

[0140]

[0141]

[0142]

[0143]

[0144]

[0145]

[0146]

[0147]

[0148]

[0149]

[0150]

[0151]

[0152]

[0153]

[0154]

[0155]

[0156]

[0157]

[0158]

[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, site and azimuth discriminators can be justified as follows: - We seek to maximize 11 \ 77* 112 with ZP- K(a,a)ZP= K^a).ZPl + Æ2((7, a). ZP 2 + ... + a). ZP 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 get closer to the maximum (gradient method). To estimate the site and azimuth angles, software component 42 uses the gradient method: &H+1 ~ <7 n + W ■ ^site ^«+1 — + ^azimut The choice of the recalibration gain value comes from a compromise between convergence speed (to limit the lag with respect to the dynamics of angle evolution due to the carrier) and accuracy (filtering measurement noise). In certain 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 phase centers are close together, due to coupling phenomena that distort the diagrams.

[0160] In this case, the software part 42 multiplies the coefficients by complex gains that 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 (magnitude and phase) of channel m of the antenna '-Tvoie antenne 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 site 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 part 42 also uses angular velocity information from an inertial measurement unit in the estimation of elevation and azimuth angles, in order to improve the performance of the latter.

[0167] In such a case, it is assumed that an inertial measurement unit is available 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, denoted cox, y, z-

[0168] We can then estimate a priori the variations in angle of site and azimuth at the calculation period of the estimators, denoted 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 site and azimuth estimators in the following way: 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 exploit the site angle and azimuth estimates to determine a decoy indicator.

[0175] In particular, when the GNSS receiver 12 receives signals from a genuine GNSS constellation, these signals originate from entirely distinct directions in space. In contrast, when the received signals originate from a decoy, they all originate from a single direction (that of the decoy's transmitting antenna).

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

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

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

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

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

[0181] This navigation method includes 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-interference processing method, the inputs 21 of the electronic part 17 receive the M elementary signals received by the antenna array 15. These elementary signals are then transmitted to the processing module 22 after digitization, baseband conversion and sampling at the frequency Fe.

[0183] In a subsequent step of the anti-interference processing, the filtering component 31 of the processing module 22 receives these elementary signals, brought down to baseband and digitized, then decomposes them into P sub-bands and subsamples them at the frequency Fe / P, by means of M digital filter banks, thus forming the subsampled signals Si, ..., Sp, as explained previously.

[0184] In a subsequent step of the anti-interference processing, the computing component 32 applies anti-interference processing and forms in each sub-band p M linear combinations of cleaned subsampled signals Ssafp m-

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

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

[0187] The navigation method further includes 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 number of advantages.

[0190] In particular, the invention makes it possible to carry out a complete antenna processing with hole formation and beam formation in order to make the best use of a multi-way antenna while being economical in resources since it does not require multiplying the anti-interference processing and it is autonomous in determining the direction of the satellites.

[0191] To this end, the invention proposes to perform in the antenna processing not N beams in the direction of the N satellites being tracked, but M linear combinations with each of the constraint of having one of the M coefficients of the linear combination equal to 1. Since M is strictly less than N, this saves resources while ensuring complete processing of all the antenna channels.

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

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

Claims

Demands

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 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); wherein 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 that input into P sub-bands to obtain P downsampled signals;- a calculation component (32) configured to apply anti-interference processing to the M subsampled signals of each subband, and produce M cleaned subsampled output signals per subband; - a summation component (33) comprising M banks of summing filters, each bank of summing filters being configured to receive P cleaned subsampled signals and to sum all of these cleaned subsampled signals to form a corresponding cleaned signal.

2. Electronic part (17) according to claim 1, wherein the computing component (32) comprises P computing units (SAPb ..., SAPp), each computing unit (SAPb ..., SAPP) being associated with one of the P sub-bands and configured to apply in the corresponding sub-band the anti-interference 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 summing filters being configured to receive a linear combination of cleaned sub-sampled signals from each computing unit (SAPi, ..., SAPP).

3. Electronic part (17) according to claim 2, wherein the vector of complex weighting coefficients is determined from a constraint vector determined for each of the M inputs.

4. Electronic part (17) according to claim 3, wherein each constraint vector comprises M components including a constant component associated with the corresponding input and zero components for the other inputs.

5. Electronic part (17) according to any one of claims 1 to 4, wherein the bandpass filter banks form polyphase filters.

6. Electronic part (17) according to any one of the preceding claims taken in combination with claim 2, wherein each computing unit (SAPi, ..., SAPP) is configured to implement RLS-type processing.

7. Electronic part (17) according to claim 6 taken in combination with claim 3, wherein the RLS-type processing is configured to directly provide the M linear combinations of subsampled signals associated with the M stress vectors, without inversion of a cross-correlation matrix between different signals.

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

9. Navigation system (10) according to claim 8, wherein 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 tracking loop discriminators.

10. Navigation system (10) according to claim 9, wherein the GNSS receiver (12) is configured to determine the direction of arrival of the signal from each tracked satellite from the M demodulated signals so as to determine the complex coefficients that maximize the useful satellite signal power of the linear combination.

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

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

13. Navigation system (10) according to any one of claims 9 to 12, wherein the GNSS receiver (12) is configured to determine for each tracked satellite the complex coefficients of linear combinations of the M demodulated signals using analog antenna patterns of the M elementary antennas.

14. An anti-interference 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-interference processing to the M elementary signals and producing M cleaned output signals; - delivering the M cleaned output signals to the GNSS receiver (12); wherein the anti-interference processing is performed by a processing module (22) comprising: - 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 that input into P sub-bands to obtain P sub-sampled signals;- a calculation component (32) configured to apply anti-interference processing to the M subsampled signals of each subband, and produce M cleaned subsampled output signals per subband; - a summation component (33) comprising M banks of summing filters, each bank of summing filters being configured to receive P cleaned subsampled signals and to sum all of these cleaned subsampled signals to form a corresponding cleaned signal.

Images