Method for detecting false synchronization of a receiver with a satellite, corresponding receiver and corresponding computer program product

Description

[0001] The present invention relates to a method for detecting false synchronization of a receiver with a satellite.

[0002] The present invention also relates to an associated receiver and computer program product.

[0003] The method according to the invention is implemented after a phase of acquiring a navigation signal from a satellite.

[0004] Such a satellite is part of a global satellite positioning system also known by the English acronym GNSS (for « Global Navigation Satellite System »).

[0005] Generally speaking, a GNSS system is composed of a plurality of satellites allowing a mobile receiver to determine its position in a terrestrial reference frame, its speed and the time.

[0006] There are currently several GNSS systems, including the GPS system, the GLONASS system and the GALILEO system, which are expected to be put into operational service soon.

[0007] The satellites of such a GNSS system are capable of emitting electromagnetic signals including navigation information.

[0008] Each navigation information generally includes data relating to the time of transmission by the satellite of the corresponding signal and the current position of the satellite. In particular, the data relating to the current position of the satellite generally contains the almanac giving a rough position of the satellite and the ephemeris giving the exact current position of the satellite.

[0009] Navigation information is carried by a carrier wave and modulated by a spreading code specific to each satellite. Thus, the signals are emitted by the satellites using a spread spectrum technique.

[0010] The receiver is able to receive the signals emitted by the satellites and to extract the navigation information from them, in particular to determine the distance to the satellite that emitted the corresponding signal. This distance, also called pseudo-distance, is determined by analyzing the propagation time of the corresponding signal.

[0011] To determine its position, speed and time, the receiver implements digital processing of navigation information from at least three different satellites.

[0012] In practice, to get a more precise position, the receiver needs navigation information from at least four different satellites.

[0013] More precisely, to acquire navigation information from a given satellite, the receiver implements two phases processing the signals from this satellite.

[0014] During an initial phase, called in the state of the art, acquisition phase, the receiver generates a local signal containing in particular a local spreading code presenting the image of the satellite spreading code.

[0015] Since the receiver initially does not know its position, the local signal is not synchronized with the received signal. This means in particular that the local signal is shifted in carrier frequency from the received signal by a value called the Doppler value, and that the spreading code of the received signal is delayed from the local spreading code by a value called the delay value.

[0016] Then, the receiver searches for a peak in the correlations between the local signal and the received signal by trying different Doppler and delay values.

[0017] When a peak is detected, the receiver determines the Doppler and delay values ​​corresponding to this peak and from these values, launches a next phase, called in the state of the art, the tracking phase.

[0018] During the tracking phase, the receiver regularly updates the Doppler and delay values, and extracts the navigation information from the signal emitted by the satellite using in particular the local spreading code and the determined Doppler and delay values.

[0019] At the end of the acquisition phase, the receiver is considered to have synchronized with the satellite or to have "locked" to the satellite.

[0020] This means in particular that the receiver was able to find the Doppler and delay values ​​relative to this satellite to initiate the tracking phase.

[0021] Sometimes the receiver synchronizes its local signal corresponding to the searched satellite with the signal received from another satellite, which leads to an erroneous distance measurement, and therefore potentially to false positioning.

[0022] In this case, it is a false synchronization or a false "hook".

[0023] This happens, for example, when the correlation between the local signal and the signal received from the searched satellite gives less energy than the correlation with the signal received from another satellite, due to a high received power difference.

[0024] There are various state-of-the-art methods to avoid such false synchronization.

[0025] Thus, a conventionally used method is to check the consistency between the satellite position calculated from the ephemeris contained in the navigation information and that calculated from the almanac, which contains the satellite identifiers, unlike the ephemeris. Inconsistency between these values ​​therefore means false synchronization.

[0026] However, this method is not entirely satisfactory. In particular, it requires collecting all the ephemeris contained in the navigation information, which is relatively time-consuming. In practice, this can take up to two minutes.

[0027] It is therefore understood that this penalizes the operation of the receiver, in particular following masking of the satellite and re-acquisition, and does not ensure continuity of service.

[0028] There is also a known method for detecting false synchronization described in document FR 3 043 790 which uses the algebraic properties of spreading codes. This then makes the implementation of this method dependent on the spreading codes used.

[0029] We also know a method for detecting false synchronization described in document FR 3 047 567 which consists of comparing the power of the signals received on several correlation channels.

[0030] Finally, we know a method for detecting false synchronization described in US 2011 / 103432 A1.

[0031] The present invention aims to improve the methods and in particular to detect false synchronization quickly, efficiently and independently of the spreading codes used.

[0032] For this purpose, the invention relates to a method for detecting false synchronization in accordance with claim 1.

[0033] According to further advantageous aspects of the invention, the detection method comprises one or more of the features of claims 2 to 7.

[0034] The invention also relates to a computer program product comprising software instructions which, when implemented by computer equipment, implement a method as defined above.

[0035] The invention also relates to a receiver implementing the procedure as defined above.

[0036] These characteristics and advantages of the invention will appear on reading the description which follows, given solely as a non-limiting example, and made with reference to the appended drawings, in which: [ Fig 1 ] there figure 1 is a schematic view of a global satellite positioning system and a receiver according to the invention; [ Fig 2 ] there figure 2 is a detailed view of the receiver of the figure 1 ; And [ Fig 3 ] there figure 3 is a flowchart of a detection method implemented by the receiver of the figure 2 .

[0037] In fact, it has been represented on the figure 1 , a global positioning system 10 by satellites of the GNSS type (from the English " Global Navigation Satellite System »). This global system 10 is for example the GALILEO system.

[0038] In reference to this figure 1 , the positioning system 10 comprises a plurality of satellites Sat n arranged in different orbits around the Earth for which the positioning system 10 is set up.

[0039] The total number of satellites Sat n is for example equal to 30.

[0040] The index n corresponds to an identifier of each satellite Sat n and varies for example between 1 and 30.

[0041] Each satellite Sat n is capable of emitting electromagnetic signals S towards a part of the Earth's surface 14 that it is currently flying over.

[0042] In particular, satellites Sat n are arranged so that at least four satellites Sat n are capable of emitting electromagnetic navigation signals S to substantially every point on the Earth's surface 14.

[0043] The current position of each satellite Sat n is characterized by the ephemerides relating to this satellite or by its almanac.

[0044] As is known, the ephemeris allows to determine the exact position of the satellite Sat n while the almanac gives a rough position.

[0045] Each signal S emitted by each of the satellites Sat n includes a data channel containing navigation information.

[0046] In particular, such a signal S comprises navigation information modulated by a data spreading code C n d ϕ c satellite-specific Sat n having emitted this signal.

[0047] The modulated navigation information is carried by a carrier wave exp ( -jϕ p ) according to a technique known per se.

[0048] Each signal S emitted by each of the satellites Sat n further comprises a pilot channel comprising a pilot spreading code C n p ϕ c satellite-specific Sat n having emitted this signal.

[0049] Each navigation information includes in particular the transmission time of the corresponding signal, the ephemeris and the satellite almanac Sat n at the time of emission of signal S.

[0050] Each data spreading code C n d ϕ c or pilot C n p ϕ c presents a pseudo-random type binary code, also known in the state of the art by the English acronym PRN (for “ Pseudo Random Noise » ) .

[0051] Each data spreading code C n d ϕ c or pilot C n p ϕ c is a periodic code with a denoted code period L c and expressed in an integer number of reference units.

[0052] The reference unit is for example a chip whose duration is denoted T chip and expressed in seconds.

[0053] A "chip" is a reference unit corresponding to a slot of a pseudo-random code.

[0054] Over the duration of each reference unit, or chip, the spreading code takes a constant value equal to either +1 or -1.

[0055] Data spreading codes C n d ϕ c or pilot C n p ϕ c are characterized by their autocorrelation functions R n,n determined respectively by the following formulas: R n , n τ = 1 L c ∫ 0 L c C n d u C n d u + τ du , R n , n τ = 1 L c ∫ 0 L c C n p u C n p u + τ du .

[0056] In particular, at point τ = 0, called the reference point, the autocorrelation function R n,n takes its maximum value V max . For τ ≤ -T chip And τ ≥ T chip, the autocorrelation function R n,n takes very small V values ​​in front of V max , that's to say, V ≪ V max .

[0057] Data spreading codes C n d ϕ c or pilot C n p ϕ c corresponding to the satellites Sat n different, are quasi-perpendicular. In other words, the inter-correlation function R n,j between each pair of different spreading codes C n d ϕ c And C i d ϕ c Or C n p ϕ c And C i p ϕ c takes values V negligible in front of V max , the inter-correlation functions R n,j for these codes being determined respectively by the following formulas: R n , j τ = 1 L c ∫ 0 L c C n d u C j d u + τ du , R n , j τ = 1 L c ∫ 0 L c C n p u C j p u + τ du .

[0058] Each data spreading code C n d ϕ c allows the navigation information emitted by the satellite to be modulated Sat n .

[0059] Each signal from a satellite Sat n is demodulated using a spreading code which is the local image C n d ϕ cloc data spreading code C n d ϕ c or the local image C n p ϕ cloc of the pilot spreading code C n p ϕ c corresponding to this satellite.

[0060] These signals are demodulated using various techniques for transmitting complex type signals known per se.

[0061] In the technique known as CDMA (Code Division Multiple Access), each complex signal is transmitted via two carrier waves at the same frequency and synchronously. In this case, the composite spreading code is the sum of the data spreading codes. C n d ϕ c and pilot C n p ϕ c correspondents.

[0062] According to the exemplary embodiment described below, the positioning system 10 is the GPS system (from the English “ Global Positioning System » ) .

[0063] Of course, other examples of implementation are also possible.

[0064] The S signals emitted by at least some of the satellites Sat n are received by a receiver 20.

[0065] The receiver 20 is for example a portable electronic device.

[0066] The receiver 20 is capable, for example, of moving on the earth's surface 14 or in the vicinity thereof with a variable speed.

[0067] The receiver 20 is capable of receiving signals S from satellites Sat n , and to extract from these signals S navigation information to deduce its current position, current speed and time as will be explained later.

[0068] Receiver 20 is illustrated in more detail in the figure 2 .

[0069] So, with reference to this figure 2 , the receiver 20 comprises an antenna 22, an acquisition module 24, a tracking module 26, a detection module 28, a control module 30 and hardware resources.

[0070] The modules 24, 26, 28 and 30 are presented for example in the form of software which is implemented by the hardware resources provided for this purpose, such as a processor, a RAM, a ROM, etc. The hardware resources are for example powered by a battery.

[0071] In particular, the read-only memory of the receiver 20 is capable of storing images of the data spreading codes C n d ϕ c and possibly pilot C n p ϕ c of each satellite Sat n .

[0072] Antenna 22 is capable of receiving signals S r electromagnetic signals corresponding to the S signals emitted by satellites Sat n when these are within an area of ​​its visibility.

[0073] The control module 30 is capable of controlling the operation of the modules 24, 26 and 28.

[0074] The acquisition module 24 is capable of implementing a signal acquisition phase S r according to techniques known per se.

[0075] The tracking module 26 is capable of implementing a signal tracking phase. S r according to techniques known per se.

[0076] Finally, the detection module 28 is capable of implementing a convergence phase, transient between the acquisition phase and the tracking phase. The convergence phase notably comprises a method for detecting false synchronization according to the invention. This method will be described in detail later.

[0077] The operation of receiver 20 will now be explained.

[0078] At each start of the receiver 20, the control module 30 initiates a plurality of acquisition channels for all of the satellites. Sat n . Each of these channels allows the acquisition of navigation information from the satellite Sat n to which it is associated, when this satellite Sat n is within the visibility range of antenna 22.

[0079] The operation of the receiver 20 on each acquisition channel is substantially similar. Thus, only the operation of the receiver 20 on one channel will be explained below.

[0080] This channel is associated for example with the satellite Sat n , subsequently said to be the sought-after satellite. It is further assumed that the satellite Sat n is located within the range of visibility of the antenna 22 and that this satellite is capable of transmitting navigation signals.

[0081] Receiver 20 generates a local data signal S loc d comprising a local carrier wave exp ( -jϕ ploc ) and a local data spreading code C n d ϕ cloc corresponding to a local image of the data spreading code C n d ϕ c of the satellite sought.

[0082] The local data signal S loc d depending on the time tis then written in the following form: S loc d t = exp − jϕ ploc t . C n d ϕ cloc t , with j 2 < = -1.

[0083] Receiver 20 further generates a local pilot signal S loc p comprising a local carrier wave exp ( -jϕ ploc ) and a pilot local spreading code C n p ϕ cloc corresponding to a local image of the driver spreading code C n p ϕ c of the satellite sought.

[0084] The local pilot signal S loc d as a function of time t is then written in the following form: S loc p t = exp − jϕ ploc t . C n p ϕ cloc t , with j 2 < = -1.

[0085] Then, the control module 30 launches the execution of the acquisition phase which is then implemented by the acquisition module 24.

[0086] In particular, during the acquisition phase, the acquisition module 24 determines a Doppler value and a delay value of the received signal. S r relative to the local data signal S loc d or pilot S loc p .

[0087] The Doppler value corresponds to the frequency shift of the local carrier wave exp(-jϕ ploc ) relative to the carrier wave exp ( -jϕ p ) of the signal S r received.

[0088] The delay value corresponds to the delay of the pilot spreading code C n p ϕ c of this received signal with respect to the pilot local spreading code C n p ϕ cloc .

[0089] The delay values ​​are determined using known techniques which include the calculation of correlations of three types.

[0090] A first type of correlation, called punctual, consists of calculating correlations between the received signal S r and the local data signal S loc d or pilot S loc p .

[0091] A second type of correlation, called advance, consists of calculating correlations between the received signal S r and a signal corresponding to the local data signal S loc d or pilot S loc p in which the local spreading code C n d ϕ cloc + d ou C n p ϕ cloc + d is shifted forward by one value d between 0 and T chip .

[0092] A third type of correlation, called delay, consists of calculating correlations between the received signal S r and a signal corresponding to the local data signal S loc d or pilot S loc p in which the local spreading code C n d ϕ cloc − d ou C n p ϕ cloc − d is shifted back by the same value d .

[0093] At the end of the acquisition phase, the receiver 20 synchronizes the local data signal S loc d or pilot S loc p with the S signal emitted by the satellite Sat n searched using the determined Doppler and delay values.

[0094] Then, the control module 30 launches the execution of the convergence phase and in particular the method for detecting a false synchronization. This method is notably implemented by the detection module 28.

[0095] The convergence phase performs a control of the delay value of the local spreading code C n d ϕ cloc Or C n p ϕ cloc and the Doppler value of the local carrier wave exp ( -jϕ ploc) , on the received signal S r , thanks to code and carrier tracking loops, thanks in particular to the three types of correlation mentioned above.

[0096] This transitional phase allows the local spreading code to be precisely matched C n d ϕ cloc Or C n p ϕ cloc and the local carrier wave exp ( -jϕ ploc ) with the spreading code C n d ϕ c Or C n p ϕ c and the carrier wave exp ( -jϕ p ) of the received satellite signal S r .

[0097] Furthermore, the detection method implemented during this phase makes it possible to detect a false synchronization of the corresponding acquisition channel with a satellite. Sat p other than the satellite sought Sat n .

[0098] In particular, during a false synchronization, the Doppler and delay values ​​determined by the acquisition module 24 correspond to the signal S emitted by a satellite Sat p other than the satellite Sat n research.

[0099] We can then understand that in this case, the signals S loc d Or S loc p and S cannot be synchronized properly. So this is false synchronization and false locking.

[0100] When the detection module 28 detects a false synchronization, the control module 30 launches the acquisition phase again.

[0101] When the detection module 28 does not detect false synchronization, the control module 30 launches the tracking phase which is then implemented by the tracking module 26.

[0102] In particular, during the tracking phase, the tracking module 26 regularly updates the Doppler and delay values, which allows it to demodulate the received signal. S r and extract the corresponding navigation information. It then transmits this information to the control module 30.

[0103] Finally, the control module 30 consolidates all of the information acquired by all of the acquisition channels and deduces the position of the receiver 20, its speed and the time.

[0104] The process of detecting a false synchronization will now be explained in detail with reference to the figure 3 presenting a flowchart of its stages.

[0105] In particular, this method comprises steps 110, 120 and 130 each corresponding to a criterion of a false synchronization. These criteria are then compared with predetermined thresholds during step 140 which then makes it possible to conclude whether a false synchronization has taken place or not.

[0106] Steps 110 to 130 are independent of one another and can therefore be implemented in parallel or consecutively. In a particular embodiment, at least some of these steps are implemented using results of previous calculations carried out in particular during the acquisition phase.

[0107] Furthermore, in the embodiment described below, the three steps 110 to 130 are implemented and the three criteria are therefore compared with the corresponding thresholds during step 140.

[0108] According to another exemplary embodiment, only two steps among steps 110 to 130 are implemented and the two criteria obtained are therefore compared with the corresponding thresholds during step 140.

[0109] According to yet another exemplary embodiment, only one step among steps 110 to 130 is implemented and the criterion obtained is therefore compared with the corresponding threshold during step 140.

[0110] Before implementing steps 110 to 140, the detection module 28 determines a plurality of correlation intervals which are for example the same for all of these steps.

[0111] Each correlation interval is thus called a reference interval and will subsequently be identified by the index m varying between 1 and N, N being the total number of reference intervals over the duration of the convergence phase.

[0112] For example, the reference intervals have roughly the same duration. T which is equal to, for example, 20 ms. This duration T will subsequently be called the reference value.

[0113] In step 110, the detection module 28 determines a first value v 1 corresponding to the anisotropy of the covariance matrix between the pilot and data channels.

[0114] In particular, during this step 110, the detection module 28 first determines a plurality of pilot channel point correlations Z p ( m ) and a plurality of point correlations data path Z d ( m ).

[0115] These punctual correlations Z p ( m ) And Z d ( m ) are determined as follows: Z p m = 1 T ∫ mT , m + 1 T S loc p ∗ t . S r t , Z d m = 1 T ∫ mT , m + 1 T S loc d ∗ t . S r t , Or S loc p , S loc d And S r correspond respectively to the local pilot signal, local data signal and received signal, as explained previously; and X * means conjugate of the complex number X .

[0116] Then, the detection module 28 determines a covariance P pp one-off correlations pilot route Z p ( m ), a covariance P dd point correlations data path, a covariance P pd pilot channel point correlations and data channel point correlations and reference power P ref .

[0117] These values ​​are defined as follows: P pp = 1 N ∑ m = 1 , … , N Z p m × Z p m ∗ = 1 N ∑ m = 1 , … , N Z p m 2 , P dd = 1 N ∑ m = 1 , … , N Z d m × Z d m ∗ = 1 N ∑ m = 1 , … , N Z d m 2 , P pd = Re 1 N ∑ m = 1 , … , N Z p m × Z p m ∗ , P ref = 1 N ∑ m Z p m . exp − jθ m . ϵ m 2 , Or Re [X] means real part of the complex number X ; ε ( m ) = ±1 is the secondary code of the pilot channel; and θ ( m ) is the estimate of the phase of the complex number Z p ( m) performed using the carrier phase loop.

[0118] Finally, the detection module 28 determines the first value v 1 as follows v 1 = P pp − P dd 2 + 4 P pd 2 P ref N 2 σ 2 , Or σ l< is the variance of the noise of ( P pp - P dd ) and 2 P pd .

[0119] The first value v 1 follows a χ 2 law with two degrees of freedom.

[0120] In step 120, the detection module 28 determines a second value v 2 using a plurality of partial correlations pilot path Z pp ( m,p ).

[0121] Each partial correlation pilot path Z pp ( m,p ) corresponds to a point correlation on an integration interval of length equal to a fraction of the reference value T between the received signal S r and the local pilot signal S loc p .

[0122] In the notation Z pp ( m,p ) ,the number p determines the type of partial correlation. The number p varies between 1 and P , the number P meaning the number of fractions of the reference interval which, in the example described, is equal to 4. Furthermore, these fractions all have the same duration which is then equal to T / 4.

[0123] So , each partial correlation pilot path Z pp ( m, p ) is determined as follows: Z pp m p = 1 T ∫ mT + p − 1 T / 4 , mT + pT / 4 S loc p * t . S r t dt .

[0124] Finally, the second value v 2 is determined using the following relationship: v 2 = Sum P P ref σ 2 , Or Sum P = I pp 1 − M 2 + I pp 2 − M 2 + I pp 3 − M 2 + I pp 4 − M 2 , M = 1 4 ∑ p = 1 , … , 4 I pp p , I pp p = 1 N ∑ m = 1 , … , N Re Z pp m p . ϵ m , and where the values ε ( m ) And P ref are defined previously; and σ 2< is the variance of the noise of each of the functions I pp ( p ).

[0125] The second value v 2 follows a law of χ 2 with three degrees of freedom.

[0126] Alternatively, it is possible to determine the second value v 2 also using partial data path correlations which are determined in a manner analogous to that used to determine the pilot path partial correlations.

[0127] In this case, the second value v 2 is determined as follows: v 2 = Sum P + Sum d P ref , where the value Sum d is determined in a manner analogous to that of the value Sum p but using partial correlations data path.

[0128] In step 130, the detection module determines a third value v 3 based on a plurality of shifted correlations pilot path Z pd ( m,τ ) .

[0129] In particular, each pilot path shifted correlation Z pd ( m, τ ) corresponds to a shifted correlation between the received signal S r and a shifted local signal S loc dp corresponding to the local pilot signal S loc p in which the local image of the pilot spreading code C n p ϕ cloc is shifted by an integer number of chips.

[0130] Thus, each correlation shifted pilot path Z pd ( m,τ ) is determined as follows: Z pd m τ = 1 T ∫ mT + m + 1 T S loc pd * t τ . S r t , Or S loc pd t τ = exp − jϕ ploc t . C n p ϕ cloc t + τ , with j 2< = -1 and τ = kT chip , where the number k varies between -K And K and is different from 0, the number K meaning the maximum number of shifts used in one direction.

[0131] In the example described, four types of shifted correlations corresponding respectively to k = +2, +1, -1 and -2 are determined. These correlations are said to be very advanced or very delayed depending on the sign of k .

[0132] According to other exemplary embodiments, only very advanced correlations or very delayed correlations are used.

[0133] The third value v 3 is determined as follows: v 3 = I p + 1 2 + I p + 2 2 + I p − 1 2 + I p − 2 2 P ref σ 2 , Or I p + k p = 1 N ∑ m = 1 , … , N Re Z pd m kT chip . ϵ m , Or the values ε ( m ) And P ref are defined previously; and σ 2< is the variance of the noise of each of the functions I p+k (p).

[0134] The third value v 3 follows a χ 2 law with four degrees of freedom.

[0135] Alternatively, as in the previous case, it is possible to use data channel shifted correlations. In this case, the values I p+k ( p ) for the data channel shifted correlations will be determined in a manner analogous to that used to determine these values ​​for the pilot channel shifted correlations.

[0136] In step 140, the detection module 28 analyzes the values ​​v 1 , v 2 and v 3 to detect false synchronization.

[0137] In particular, when at least one of these values v 1 , v 2 and v 3 exceeds a predetermined threshold for this value, the detection module 28 detects a false synchronization.

[0138] It is therefore understood that the present invention presents a certain number of advantages.

[0139] Indeed, the invention makes it possible to detect a synchronization phase with a satellite independently of the type of spreading codes used.

[0140] This detection is carried out with a high probability, which makes the invention particularly effective.

[0141] Furthermore, the invention has particular advantages when the overall system 10 is the GALILEO system and when, in particular, the receiver according to the invention is used to receive so-called “open” signals from the L1 band.

[0142] It is known in this case that the data spreading or pilot codes used are periodic at 4 milliseconds.

[0143] Thus, there is no need to recalculate the partial correlations during step 120 when the number P is equal to 4, that is to say when the partial correlations are calculated over a quarter of the reference interval, i.e. 1 millisecond, because these correlations have already been calculated over time intervals of 1 millisecond, corresponding to an integration time commonly used in the satellite channels of the receivers.

[0144] Finally, it was observed that the data spreading codes or pilot of said signals exhibit particular properties. In particular, their autocorrelations are zero or almost zero at -2 chip, -1 chip, +1 chip and +2 chip around the main autocorrelation peak. This then makes the third value v 3 particularly representative of a false collision when K = 2.

Claims

1. A method for determining a wrong synchronization of a receiver (20) with a satellite during a phase for acquiring a navigation signal coming from this satellite, the satellite belonging to a global navigation satellite system (10); the navigation signal comprising a data channel including an item of navigation information modulated by a data spreading code specific to this satellite and carried by a carrier wave, and a pilot channel including a pilot spreading code specific to this satellite and carried by a carrier wave; during the acquisition phase, the receiver (20) being able to receive the navigation signal, called received signal, transmitted by the satellite, to generate a local data signal including a local image of the data spreading code and a local image of the carrier wave, and to generate a local pilot signal including a local image of the pilot spreading code and the local image of the carrier wave; the method being implemented after the acquisition phase during a convergence phase and comprising at least one of the following steps: - determining (110) a plurality of periodic pilot channel correlations each corresponding to a periodic correlation on a reference interval of duration equal to a reference value between the received signal and the local pilot signal, and a plurality of periodic data channel correlations each corresponding to a periodic correlation on one of the reference intervals between the received signal and the local data signal, and determining a first value as a function of these periodic correlations; - determining (120) a plurality of partial pilot channel correlations each corresponding to a periodic correlation on an interval of duration equal to a fraction of the reference value between the received signal and the local pilot signal, and determining a second value as a function of these partial correlations; - determining (130) a plurality of shifted pilot channel correlations each corresponding to a shifted correlation on one of the reference intervals between the received signal and a shifted local signal corresponding to the local pilot signal in which the local image of the pilot spreading code is shifted by an integer number of reference units, and determining a third value as a function of these shifted pilot channel correlations; the convergence phase further comprising the following step: - determining (140) a wrong synchronization when at least one of the values among the first value, the second value and the third value, when such a value is determined, exceeds a predetermined threshold; the first value being determined based on covariances between the periodic pilot channel correlations and the periodic data channel correlations.

2. The method according to claim 1, wherein the first value is determined as follows: v 1 = P pp − P dd 2 + 4 P pd 2 P ref / N 2 σ 2 , where v1 is the first value; N is the number of pilot channel periodic correlations equal to the number of data channel periodic correlations; Ppp is the covariance of the pilot channel periodic correlations; Pdd is the covariance of the data channel periodic correlations; Ppd is the covariance of the pilot channel periodic correlations and the data channel periodic correlations; Pref is a reference power determined as a function of the pilot channel periodic correlations; and σ2 is the variance of the noise of (Ppp - Pdd) and 2Ppd.

3. The method according to any one of the preceding claims, wherein, during the step for determining (120) a plurality of pilot channel partial correlations, P types of partial correlations are determined, a partial correlation of a given type being determined on a predetermined fraction of one of the reference intervals.

4. The method according to claim 4, wherein the second value is determined as follows: v 2 = Sum P P ref σ 2 , where Sum P = ∑ p = 1 , … , P I pp p − M 2 , M = 1 P ∑ p = 1 , … , P I pp p , I pp p = 1 N ∑ m = 1 , … , N Re Z pp m p . ϵ m , where v2 is the second value; N is the number of partial correlations; ε(m) is the secondary code of the pilot channel 1 or - 1 ; Zpp(m,p) is a partial correlation of a type p, the number p being inclusively between 1 and P; Pref is a reference power determined as a function of the pilot channel periodic correlations; Re[X] is the real part of a complex number X ; and σ2 is the variance of the noise of each of the functions Ipp(p).

5. The method according to any one of claims 1 to 3, wherein the second value is further determined as a function of a plurality of data channel partial correlations each corresponding to a periodic correlation over an interval of duration equal to a fraction of the reference value between the received signal and the local data signal.

6. The method according to any one of the preceding claims, wherein each shifted pilot channel correlation is determined by using the local image of the pilot spreading code advanced or delayed by one or two reference units.

7. The method according to any one of the preceding claims, wherein the third value is determined as follows: v 3 = ∑ k ∈ E I p + 2 k P ref σ 2 , where I p + k p = 1 N ∑ m = 1 , … , N Re Z pd m kT chip . ϵ m , where v3 is the third voltage, N is the number of shifted correlations; ε(m) is the secondary code of the pilot channel, its values being equal to 1 or - 1 ; E is a subset of the set {- K, ..., - 1,1,...K}, where K is the maximum number of shifts used in one direction; Zpd(m,kTchip) is a correlation advanced by k reference units when k > 0 and delayed by k reference units when k < 0; Pref is a reference power determined as a function of the pilot channel periodic correlations; and σ2 is the variance of the noise of each of the functions Ip + k(p).

8. A computer program product comprising software instructions which, when implemented by a piece of computer equipment, carry out the method according to any one of the preceding claims.

9. A receiver (20) including a detection module (28) configured to carry out the method according to any one of claims 1 to 7.