RECEIVER OF RADIO NAVIGATION SIGNALS WITH A COMPUTER OF A CORRELATION POWER INDICATOR

Description

TECHNICAL FIELD

[0001] The present invention relates to a radio navigation signal receiver. STATE OF PRIOR ART

[0002] Radio navigation refers to the use of radio signals emitted by GNSS satellites for positioning or navigation.

[0003] In this text, the term GNSS, short for "Global Navigation Satellite System," is a generic term encompassing all satellite navigation systems. These systems comprise several distinct systems, such as GPS (Global Positioning System) and Galileo, operated by different countries or regions.

[0004] Generally, several frequency bands are allocated for transmitting GNSS signals. GNSS signals are built on the same signal model, namely one or more sinusoidal carrier frequencies on which different phase-modulated binary signals are carried, containing the information necessary for navigation. There can be several types of binary signals carried by the GNSS carriers: a navigation message containing several parameters necessary for the receiver to calculate its position (time of transmission of the message, satellite ephemeris, constellation status, etc.), a pseudo-random code allowing the identification of the transmitting satellite and the performance of pseudo-range measurements, possibly with a rectangular subcarrier for certain signals using BOC (Binary Offset Carrier) modulation.The pseudo-random codes used in GNSS signals are PRN (Pseudo-Random Noise) codes composed of binary elements called "bribes." Each satellite is associated with one or more unique PRN codes—referred to as codes in the rest of this text. Generally speaking, pseudo-random codes, or codes, are nearly orthogonal binary codes that allow satellites to transmit simultaneously in the same frequency band.

[0005] In the field of metrology, degraded GNSS signals can be used. In particular, atmospheric sounding is studied using GNSS radio occultation. In this application, it is sometimes difficult to remain synchronized with degraded GNSS signals and therefore to perform measurements with them.

[0006] A well-known, conventional solution involves using a GNSS receiver equipped with closed tracking loops. Signal reception channels are then fitted with nested code loops and carrier loops to perform pseudo-range measurements on the code and carrier of the signal. In most GNSS receivers, the code loop is assisted by the carrier loop. However, this solution is not satisfactory for such degraded signals because the loops can lose connection, particularly the carrier loop, which is the most sensitive.

[0007] Another solution, when the receiver's motion is known, is to provide Doppler velocity assistance for the carrier loop, which in turn assists the code loop. This is particularly relevant for a receiver in space orbit, as described in the patent "Method for autonomously reducing the acquisition and tracking thresholds of carriers received in orbit" (FR2746232B1). Furthermore, this document describes the possibility of fully opening the carrier loop if the Doppler velocity assistance is of sufficient quality. In this case, the system operates in what is called "open carrier loop" mode; only the code loop remains closed, and only the code pseudo-range measurement is performed.

[0008] In the case of radio occultation, the measurement of interest is the carrier phase measurement. Thus, the architecture described above is used, with the addition of the outputs of the correlators of the synchronous code channel of the received code (called "Prompt" in the English-language literature, referred to as "main" in the remainder of the patent) to extract the error between the received carrier and the carrier replica generated from the injected Doppler velocity model. This then allows the carrier phase measurement to be reconstructed. This reconstruction can be performed during post-processing, possibly carried out on the ground with a short delay. This is the case, for example, on the METOP and COSMIC missions.A necessary condition for carrier phase measurement to be possible is that the code loop remains correctly locked onto the signal correlation peak, which is difficult to achieve in the presence of signals whose delay and / or amplitude can vary greatly in the case of a strong tropospheric delay. DESCRIPTION OF THE INVENTION

[0009] The present invention aims to provide a radio navigation signal receiver, enabling the resolution of all or part of the problems presented above.

[0010] Specifically, one goal is to provide a solution that meets the following objective: to allow robust continuation of the degraded GNSS signal code and to obtain a measurement of the degraded GNSS signal carrier phase over an extended range.

[0011] This goal can be achieved using a radio navigation signal receiver, comprising: a radio frequency stage to produce a GNSS signal Sr(t), from an incident GNSS signal; a generator of a carrier replica signal Srep(t), the carrier replica signal Srep(t) being an estimate of the carrier of the GNSS signal Sr(t); a mixer of the carrier replica signal Srep(t) with the digitized GNSS signal Sr(t), configured to obtain a baseband signal Sbb(t);a code position control loop comprising: a code replica signal generator including a code integrator configured to deliver, as input to a code generator, an estimated code position, the code generator comprising on the one hand a main code replica signal generator SC R(L) (t) delivering on output a main code replica signal SC R(L) (t) and on the other hand a plurality of leading and lagging code replica signal generators SC R(k) (t) each having a code lag or lead offset with respect to the main code replica signal SC R(L) (t); each replica of the plurality being indexed by an integer index between 1 and n; a plurality of correlators capable of computing a correlation function: between the main code replica signal SC R(L) (t) and the baseband signal Sbb(t) in order to produce a main correlation over a coherent integration time Tic;between each of the leading and lagging code replica signals SC R(k) (t) and the baseband signal Sbb(t) in order to produce lead and lag correlations over the coherent integration time Tic; each plurality correlator being indexed by an index; a correlation power indicator calculator configured to: determine correlation powers from the main correlation (50) and from the lead and lag correlations; and determine a maximum correlation power from the correlation powers so as to obtain a primary index kmax corresponding to the index of the correlator showing the maximum correlation power;a correction calculator configured to determine an adjusted code frequency, as a function of the primary index kmax, as a function of an index L corresponding to the correlator processing the main code replica signal SC R(L) (t), as a function of an operating period T fb and as a function of an adjustable gain; the code snippet frequency control being the sum between the adjusted code frequency from the correction calculator and a carrier aid signal from a physical model multiplied by a scaling factor, the physical model corresponding to a Doppler aid or a fine velocity aid, the code position control loop comprising an output delivering at least the main correlation.

[0012] Some preferred but not exhaustive aspects are as follows.

[0013] In an implementation of the radio navigation signal receiver, the adjacent index correlators process SC R(L) (t), SC R(k) (t) code replica signals separated from each other by a constant value d of a snippet of the GNSS signal code.

[0014] In an implementation of the radio navigation signal receiver, the plurality of correlators comprises an odd number of correlators, the number of code replica signals leading relative to the main code replica signal SCRP(t) and the number of code replica signals lagging SC R(k) (t) relative to the main code replica signal SCRP(t) being equal.

[0015] In an implementation of the radio navigation signal receiver, the incident GNSS signal being endowed with a transmitted carrier frequency and a code rate, receiver in which the scaling coefficient is equal to the ratio of the code rate to the carrier frequency.

[0016] In an implementation of the radio navigation signal receiver, the code position delivered by the code integrator corresponds to the code position of the primary replica.

[0017] In an implementation of the radio navigation signal receiver, the code position delivered by the code integrator corresponds to the code position of the primary code replica translated by a constant gap.

[0018] In an implementation of the radio navigation signal receiver, the code position delivered by the code integrator corresponds to a code position of the most advanced code replica.

[0019] In an implementation of the radio navigation signal receiver, the carrier replica signal Srep(t), the baseband signal Sbb(t), the main correlation and the lead and lag correlations are complex; The correlation power indicator calculator is configured to determine correlation powers also from complex correlations from secondary correlators; a complex conjugate calculator, capable of calculating a complex conjugate from the main complex correlation, is arranged at the output of the main complex correlation so as to deliver the complex conjugate of the main correlation; and the secondary correlators are arranged so that each of the main complex correlation and the leading and lagging complex correlations is correlated to the complex conjugate of the main correlation over the operating period T fb; the output of the secondary correlators constituting the input of the complex correlation power indicator calculator.

[0020] In an implementation of the radio navigation signal receiver, the operating period T fb corresponds to a non-coherent integration time T nc.

[0021] In an implementation of the radio navigation signal receiver, the non-coherent integration time T nc is equal to a multiple of the coherent integration time Tic of the main correlation.

[0022] In an implementation of the radio navigation signal receiver, the operating period T fb corresponds to a coherent integration time.

[0023] In one implementation, the radio navigation signal receiver's plurality of correlators comprises a number greater than or equal to three correlators.

[0024] In one implementation of the signal receiver, the digitized GNSS signal Sr(t) has an intermediate carrier frequency fi, the input frequency control of the carrier replica signal generator being obtained from the Doppler frequency of the signal Sr(t) estimated by the external model and the frequency fi.

[0025] In an implementation of the signal receiver, the digitization of the signal Sr(t) is real at intermediate frequency fi, and the mixer of the carrier replica signal Srep(t) with the digitized GNSS signal Sr(t) is capable of processing the real digitization of the signal Sr(t).

[0026] In an implementation of the signal receiver, the digitization of the signal Sr(t) is complex in intermediate frequency fi, and the mixer of the carrier replica signal with the digitized GNSS signal Sr(t) is capable of handling the complex digitization of the signal Sr(t).

[0027] In an implementation of the signal receiver, the code position control loop includes: a plurality of correlators capable of computing a complex correlation function: between the main code replica signal and the baseband signal in order to produce a main complex correlation over a consistent integration time; between each of the leading and lagging code replica signals and the baseband signal in order to produce complex leading and lagging correlations over the consistent integration time; each correlator of the plurality being indexed by an index; a correlation power indicator calculator configured to: determine correlation powers from the main complex correlation and from the lead and lag complex correlations; and determine a maximum complex correlation power from the correlation powers so as to obtain a primary index corresponding to the index of the correlator showing the maximum complex correlation power; a correction calculator configured to determine an adjusted code frequency, as a function of the primary index (kmax), as a function of an index corresponding to the correlator processing the main code replica signal, as a function of an operating period and as a function of an adjustable gain;the code snippet frequency control being the sum between the adjusted code frequency from the correction calculator and a carrier aid signal from the physical model multiplied by a scaling coefficient, the code position control loop comprising an output delivering at least the main complex correlation.

[0028] In a signal receiver implementation, the baseband signal is complex. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Other aspects, objectives, advantages, and features of the invention will become clearer upon reading the following detailed description of preferred embodiments thereof, given by way of non-limiting example, and made with reference to the accompanying drawings in which: there figure 1 illustrates a schematic view of an example of a radio navigation signal receiver according to the invention; the figure 2illustrates a schematic view of a further example of a radio navigation signal receiver according to the invention where a conjugate complex calculator is arranged at the output of the main complex correlation and where a plurality of secondary correlators are arranged such that each of the main complex correlation and the leading and lagging complex correlations is correlated to the conjugate complex of the main correlation, the output of the secondary correlators constituting the input of the complex correlation power indicator calculator. DETAILED DESCRIPTION OF SPECIFIC IMPLEMENTATION METHODS

[0030] On the Figures 1 And 2In the appendices and throughout the description, identical or similar functional elements are identified by the same reference numerals. Furthermore, the various elements are not drawn to scale in order to prioritize the clarity of the figures and facilitate understanding. Moreover, the different embodiments and variants are not mutually exclusive and can, on the contrary, be combined.

[0031] In the rest of the description, unless otherwise stated, the terms "approximately", "about", "roughly" and "in the order of" mean "within 10%".

[0032] In general and in the rest of the text, a signal having a complex value or called complex, is a signal having a phase component which corresponds to the real part and a quadrature component which corresponds to the imaginary part.

[0033] Throughout the text, the term "period" is homogeneous with a time and can be used in an equivalent way.

[0034] In all embodiments of the invention and as illustrated in the Figures 1 And 2 The radio navigation signal receiver 10 includes a radio frequency stage E1. The radio frequency stage E1 may include, for example, one or more antennas, filtering, amplification, frequency translation, digitization elements, and automatic gain control.

[0035] The radio frequency stage E1 produces a digitized or analog GNSS signal Sr(t), dependent on the time t, at a sampling frequency Fe typically between 1 and 50 MHz, from the incident GNSS signal. The digitized GNSS signal Sr(t) thus comprises a frequency band of the digitized signal. The digitized GNSS signal Sr(t) can be real or complex. The carrier frequency of the digitized signal is generally lowered to an intermediate frequency fi. fi can be close to zero or even equal to zero; in this case, the digitization is said to be baseband.

[0036] In the rest of the text, the signals indicated with (t) are dependent on time t.

[0037] Between receiving the signal and performing measurements on the digitized signal, the radio navigation signal receiver 10 must carry out several steps to extract the necessary information. In particular, acquisition and tracking steps are performed to synchronize the receiver with the navigation signals.

[0038] In the text, the terms "physical model" correspond to a Doppler aid or a fine velocity aid.

[0039] The radio navigation signal receiver 10 also includes a carrier replica signal generator E2, Srep(t), to form a local replica of the carrier. This carrier replica signal, Srep(t), is a complex signal, represented by a complex value and generated at a rate Fe. The carrier replica signal, Srep(t), consists of an estimate of the carrier of the input signal. This signal is defined by: Srep(t) = ej.φ(t)t, where φ(t) is the phase of this carrier replica signal, Srep(t). The phase of the carrier replica signal is obtained by integrating a frequency control input to a carrier integrator 40. The carrier integrator 40 is a pure integrator of the digitally controlled oscillator (NCO) type.

[0040] In one example, the generator E2 of a complex carrier replica signal Srep(t) at the same sampling rate Fe, of which a phase φ(t) is obtained by integrating, with a carrier integrator 40, a frequency control at the input of the carrier replica signal generator E2, the frequency control at the input of the carrier replica signal generator E2 being obtained from at least one Doppler frequency of the signal Sr(t) estimated by a physical model 41, the generator E2 comprising a device 40a capable of generating the complex carrier replica signal Srep(t) from the output of the carrier integrator 40.

[0041] In an example implementation of the radio navigation signal receiver 10, the generator E2 includes a device 40a capable of generating the complex carrier replica signal Srep(t) from the output of the carrier integrator 40.

[0042] The radio navigation signal receiver 10 further includes a mixer 47 of the carrier replica signal Srep(t) with the digitized GNSS signal Sr(t). The output signal of the mixer 47 is a baseband signal Sbb(t), sampled at a rate Fe. The baseband signal Sbb(t) and the carrier replica signal Srep(t) are complex.

[0043] In an implementation of the radio navigation signal receiver 10, the digitization of the Sr(t) signal is complex.

[0044] In another implementation of the radio navigation signal receiver 10, the digitization of the Sr(t) signal is real.

[0045] The mixer 47 of the carrier replica signal Srep(t) with the digitized GNSS signal Sr(t) is designed to be capable of processing the actual or complex digitization of the signal Sr(t) according to the following Math. 1 equation: Sbb t = Sr t × Srep t

[0046] To perform code tracking, the radio navigation signal receiver 10 includes a code position control loop E4. The code position control loop E4 can also be called code tracking.

[0047] The E4 code position control loop includes firstly an E4a code replica signal generator operating at the Fe rate.

[0048] The E4a code replica signal generator includes, in particular, a code 45 integrator and a code 43 generator.

[0049] The code integrator 45 is a pure integrator of the type of digitally controlled oscillator (or NCO / "Numerically controlled oscillator" according to Anglo-Saxon terminology) which delivers, for example, a so-called main code position at the rate of the sampled signal Fe. This code integrator 45 is configured to deliver, as input to a code generator 43, an estimated code position, such as the position τ(t) of the main code or, depending on the implementations, of any other code replica, typically the most advanced replica. For this it receives as input a frequency command of the code fragments consisting of the sum between the frequency from the code loop, a bias 80 of constant code rate and generally equal to the product RC GNSS and a carrier aid signal from the Doppler model 41 multiplied by a scaling coefficient 44 called K = RC GNSS / f GNSS where RC GNSS is the code rate transmitted by the GNSS and f GNSS is the carrier frequency.

[0050] The code generator 43 includes a SC RP(t) master code replica signal generator 43a delivering at output a signal, for example real, of SC RP(t) master code replica.

[0051] The code generator 43 also includes a plurality of signal generators 43b, for example, real, leading and lagging code replica signals. Another notation for the code replica signals is: SC R(k) (t) where the index k is the replica rank. Each of the leading code replica signals SC R(k) (t) has a different and stepped code lead, that is, offset, arbitrarily or discretely depending on the chosen implementation, relative to the main code replica signal SC RP (t). Each of the lagging code replica signals SC R(k) (t) has a lagging code position, that is, has a different and stepped code delay, arbitrarily or discretely, relative to the main code replica signal SC RP (t).

[0052] Thus, the plurality of 43b code replica signal generators (leading and lagging) may include at least two code replica signal generators, for example, one leading and one lagging. To optimize the operation of the radio navigation signal receiver 10, the plurality of 43b code replica signal generators (leading and lagging) may include three or more code replica signal generators, with, in a non-limiting example, at least two leading and at least two lagging code replica signal generators.

[0053] L is defined as the rank of the main code replica, that is: SC RP t = SC R L t ,

[0054] Throughout the text, the terms SC RP (t) and SC R(L) (t) are equivalent.

[0055] The positions (advance if positive value, delay if negative value) of the replicated signals with respect to the counter from the integrator of code 45 are noted Δτ k.

[0056] An SC code replica R(k) (t) is ahead if: Δτ k > Δτ L.

[0057] A code replica SC R(k) (t) is lagging if: Δτ k < Δτ L. In another example of the implementation of the radio navigation signal receiver 10, each of the main code replica signals SC RP (t) and the leading and lagging SC R(k) (t) are separated from each other by a constant value d expressed in snippets of the GNSS signal code. In other words, the interval between two adjacent code replicas is identical. In the case where the code integrator 45 corresponds to the leading replica, the position differences Δτ k between each code replica SC R(k) (t) and the output of the code integrator 45 are: Δτ 1 ; Δτ 2 ; … ; Δτ L , ; … ; Δτ n − 1 ; Δτ n = − n − 1 d ; − n − 2 d ; … ; − n − L d ; … ; d ; 0

[0058] In another example, the number of lag code replica signals SC R(k) (t) is equal to the number of lead code replica signals SC R(k) (t). In this example, the index L of the lead replica is: L=(n+1) / 2, the total number of replicas being odd in this case.

[0059] If these last two cases are combined, then the positional differences of the code replicas in the case where code integrator 45 corresponds to the main replica are: Δτ 1 ; … ; Δτ L − 1 ; , Δτ L , ; Δτ L + 1 ; … ; Δτ n = − n − 1 d / 2 ; … ; − d ; 0 ; d ; … ; n − 1 d / 2 .

[0060] The E4 code position control loop further comprises the same plurality n of E4c correlators. In one embodiment, one correlator among the plurality of E4c correlators includes a mixer and a summing junction with reset. The mixers and summing junctions together constitute E4c correlators capable of performing complex correlation functions known to those skilled in the art. By complex correlation, it is understood that the in-phase and quadrature parts of the signals are processed during the correlation. The in-phase parts of the correlation are denoted with an index I: CI(k) (t), and the quadrature parts are denoted with an index Q: CQ(k) (t).

[0061] Each of the main code replica signals SC R(L) (t) and the leading and lagging SC R(k) (t) undergoes a complex correlation operation over a period called the coherent integration time, equal to Tic, with the baseband signal Sbb(t). Tic typically has a value between 1 and a few tens of milliseconds.

[0062] The result of the complex correlation C(k)(t) with the replica of order k, at time t, is given by the following Math. 3 equation: C k t j = C I k t j + jC Q k t j = ∑ t = t j − T ic + T e t S r t × S rep t × SC R k t

[0063] T e represents the interval between 2 digitized samples: T e = 1 / Fe.

[0064] The main complex correlation 50 also noted C (L) (tj ) is also called the “Prompt” correlation point or the “synchronous” correlation.

[0065] Correlators are also arranged between each of the SC R(k) (t) code replica signals and the baseband signal Sbb(t) in order to produce 51 leading correlations, also denoted C (k) (T j ) and called "leading" correlation points, over a consistent integration time Tic.

[0066] Correlators are also arranged between each of the SC delay code replica signals R(k) (t) and the baseband signal Sbb(t) to produce delay correlations 51, also denoted C (k) (tj) and called "Delay" correlation points, following the coherent integration time Tic.

[0067] In another example, the E4c plurality of mixers and correlators includes an odd number of mixers and the same odd number of E4c correlators.

[0068] In one example, advantageously, the number of SC code replica signals R(k) (t) leading the SC master code replica signal R(L) (t) is equal to the number of SC code replica signals R(k) (t) lagging behind the SC master code replica signal R(L) (t).

[0069] The E4 code position control loop also includes a correlation power indicator calculator E4d. This is configured to determine an indicator representing the power or a power-related quantity such as a correlation amplitude. Here, it is configured to determine correlation powers from the main complex correlation 50 and from the various lead and lag complex correlations 51, or from complex correlations derived from secondary correlators 71.

[0070] Determining a correlation power using the E4d correlation power indicator calculator involves calculating the square of the modulus of each complex correlation. In this case, it involves calculating the square of the modulus of a complex correlation linked to a correlator with a given index k. Equation Math. 4 describes the calculation of a correlation power, here called Power_Corr(k), where k corresponds to a correlator index. Equation Math. 4 is as follows: Power Corr k = C I k + jC Q k 2 = C I k 2 + C Q k 2

[0071] The E4d correlation power indicator calculator is also configured to determine a maximum correlation power between each of the correlation powers calculated as described in the previous paragraph. This yields a primary index corresponding to the index of the correlator showing the maximum power, which, in the following example, is called kmax.

[0072] The E4 code position control loop also includes a correction calculator E4e. The correction calculator E4e is configured to determine a code frequency correction calculated at each iteration of the loop. The code frequency is thus adjusted with a correction established as a function of the position deviation of the primary index replica: Δτ kmax(t) and the index L: ΔτL(t), denoting the replica of the main code SC R(L)(t). The frequency correction δ also depends on an operating period Tfb of the loop and a gain, here called G for the example, which can be modulated to optimize the loop's operation. A nominal value of G is equal to 1. The frequency correction δ is then expressed in the following Math. 5 equation: δ = Δ τ kmax − Δ τ L × G T fb

[0073] In the case where the code replicas are spaced at a regular interval d expressed in code fragments, the position of the replica signal having the best correlation with the main code replica signal SC R(L) (t) is obtained by performing (kmax-L)xd, and the frequency correction δ of the code integrator 45 becomes: δ = kmax − L × d × G T fb

[0074] Frequency corrections δ are applied to the code integrator 45 during the following operating period T fb until a new frequency correction is calculated from the correlator outputs at the operating period T fb.

[0075] T fb corresponds, in an implementation, to a coherent integration time.

[0076] Advantageously, the loop's operating period will be equal to the coherent integration time of the following correlator: Tfb = Tic. Once fed back to the code integrator 45, such a frequency correction from the correlation power indicator calculator E4d and the correction calculator E4e advantageously makes the correlation of the received signal's code more robust, enabling carrier phase measurement on the outputs of the main complex correlation 50. Indeed, conventional closed-loop techniques cannot track highly disturbed signals, for example, for use in radio occultation or navigation in harsh environments. Thus, the E4 code position control loop includes an output 60 delivering the main complex correlation 50 at each loop iteration. This output 60 is, as illustrated in the... Figures 1 And 2, placed before the determination of correlation power. The main correlation 50 and the parameters of the signals from which it originates are thus transmitted for further processing either in real time or in delayed time, for example in terrestrial radio-occultation data processing stations.

[0077] The input frequency control of generator E2 is the sum of the Doppler frequency of the signal Sr(t) estimated by an external model 41 and the frequency fi.

[0078] Thus, the tracking remains stable and the extraction of the carrier phase is ensured. This is essential in applications such as radio occultation.

[0079] More generally, the code integrator 45 can be configured to receive as input the code clip frequency command, this code clip frequency command being the sum of the adjusted code frequency from the correction computer E4e, a carrier aid signal from the physical model 41 multiplied by a scaling factor 44, and, optionally, the constant code rate bias 80 mentioned above. Thus, the radio navigation signal receiver 10, and in particular its code position control loop E4, can be configured to deliver the code clip frequency command as input to the code integrator 45.

[0080] In a further example of implementation illustrated on the figure 2The radio navigation signal receiver 10 includes a conjugate complex calculator 70. The conjugate complex calculator 70 is capable of calculating a conjugate complex from the main complex correlation 50 or from the SC R(L)(t) main code replica signal. The conjugate complex calculator 70 is arranged at the output of the main complex correlation 50 so as to deliver the conjugate complex of the main correlation 50 or of the SC R(L)(t) main code replica signal. The secondary correlators 71 are arranged so that each of the main complex correlation 50 and the leading and lagging complex correlations 51 is correlated to the conjugate complex 70 of the main correlation 50 or to the conjugate complex 70 of the SC R(L)(t) main code replica signal.These secondary correlators 71 then perform an inconsistent integration whose period t nc is an integer multiple of the coherent integration time T ic of the main correlators 50 such that: t nc = N xt ic . The output of the secondary correlators 71 then constitutes the input of the complex correlation power indicator calculator E4d.

[0081] In an implementation, the operating period t fb of the code loop will advantageously be worth the consistent integration time: T fb = T nc.

[0082] This architecture is advantageous because it allows for extending the total integration time and increasing the signal-to-noise ratio.

Claims

1. A radio navigation signal receiver (10), comprising: - a radio frequency stage (E1) for producing a GNSS signal (Sr(t)), from an incident GNSS signal; - a generator (E2) of a carrier replica signal (Srep(t)), the carrier replica signal (Srep(t)) being an estimate of the carrier of the GNSS signal (Sr(t)); - a mixer (47) of the carrier replica signal (Srep(t)) with the digitized GNSS signal (Sr(t)), configured to obtain a baseband signal Sbb(t); - a code position control loop (E4) comprising: - a code replica signal generator (E4a) comprising a code integrator (45) configured to deliver, at the input of a code generator (43), an estimated code position, the code generator (43) comprising, on the one hand, a generator (43a) of main code replica signal (SCR(L)(t)) delivering at the output a main code replica signal (SCR(L)(t)) and, on the other hand, a plurality of generators (43b) of early and late code replica signals (SCR(k)(t)) each having a code delay or advance offset relative to the main code replica signal (SCR(L)(t)); each replica of the plurality being indexed by an integer index between 1 and n; - a plurality of correlators (E4c) capable of calculating a correlation function: - between the main code replica signal (SCR(L)(t)) and the baseband signal Sbb(t) in order to produce a main correlation (50) over a coherent integration time (Tic); - between each of the early and late code replica signals (SCR(k)(t)) and the baseband signal (Sbb(t)) in order to produce early and late correlations (51) over the coherent integration time (Tic); each correlator of the plurality being indexed by an index; - a correlation power indicator calculator (E4d) configured to: - determine correlation powers from the main correlation (50) and from the early and late correlations (51); and - determine a maximum correlation power from the correlation powers so as to obtain a primary index (kmax) corresponding to the index of the correlator showing the maximum correlation power; - a correction calculator (E4e) configured to determine an adjusted code frequency, as a function of the primary index (kmax), as a function of an index (L) corresponding to the correlator processing the main code replica signal (SCR(L)(t)), as a function of an operating period (Tfb) and as a function of an adjustable gain; the code chip frequency command being the sum of the adjusted code frequency derived from the correction calculator (E4e) and a carrier aid signal derived from a physical model (41) multiplied by a scaling coefficient (44), said physical model (41) corresponding to a Doppler aid or a fine velocity aid, the code position control loop (E4) comprising an output (60) delivering at least the main correlation (50).

2. The radio navigation signal receiver (10) according to claim 1 wherein the adjacent index correlators process code replica signals (SCR(L)(t)), (SCR(k)(t)) separated from each other by a constant value d of a chip of the GNSS signal code.

3. The radio navigation signal receiver (10) according to any one of claims 1 or 2 wherein the plurality of correlators (E4c) comprises an odd number of correlators, the number of early code replica signals relative to the main code replica signal (SCRP(t)) and the number of late code replica signals (SCR(k)(t)) relative to the main code replica signal (SCRP(t)) being equal.

4. The radio navigation signal receiver (10) according to any of claims 1 to 3, the incident GNSS signal being provided with an emitted carrier frequency and a code rate, in which receiver the scaling coefficient (44) is equal to the ratio of the code rate to the carrier frequency.

5. The radio navigation signal receiver (10) according to any of claims 1 to 4, wherein the code position delivered by the code integrator (45) corresponds to the code position of the main replica.

6. The radio navigation signal receiver (10) according to any of claims 1 to 5, wherein the code position delivered by the code integrator (45) corresponds to the code position of the main code replica translated by a constant offset.

7. The radio navigation signal receiver (10) according to claim 6, wherein the code position delivered by the code integrator (45) corresponds to a code position of the earliest code replica.

8. The radio navigation signal receiver (10) according to any one of claims 1 to 7, wherein the carrier replica signal (Srep(t)), the baseband signal Sbb(t), the main correlation (50) and the early and late correlations (51) are complex; wherein the correlation power indicator calculator (E4d) is configured to determine correlation powers also from complex correlations derived from secondary correlators (71); wherein a complex conjugate calculator (70), capable of calculating a complex conjugate from the main complex correlation (50), is arranged at the output of the main complex correlation (50) so as to deliver the complex conjugate of the main correlation (50); and wherein the secondary correlators (71) are arranged so that each of the main complex correlation (50) and the early and late complex correlations (51) is correlated to the complex conjugate (70) of the main correlation (50) over the operating period (Tfb); the output of the secondary correlators (71) constituting the input of the complex correlation power indicator calculator (E4d).

9. The radio navigation signal receiver (10) according to claim 8, wherein the operating period (Tfb) corresponds to a non-coherent integration time (Tnc).

10. The radio navigation signal receiver (10) according to claim 9, wherein the non-coherent integration time (Tnc) is equal to a multiple of the coherent integration time (Tic) of the main correlation.

11. The radio navigation signal receiver (10) according to any of claims 1 to 8, wherein the operating period (Tfb) corresponds to a coherent integration time.