Method of factorisation of pseudorange dating in an assisted GNSS system.

The present invention relates to a method for calculating the position of a mobile device based on:<ul id="ul0001" list-style="dash" compact="compact"><li>the knowledge of spreading code phases of several satellites in view,</li><li>the knowledge of a precise or approximate time reference corresponding to the measurement of these code phases,</li><li>reconstituting the pseudo-distances from the time reference, an approximate position of the mobile device to be positioned, as well as code phases.</li></ul>

In the field of mobile telephony, it is becoming more and more necessary to be able to locate mobile devices.

For this, it is known to associate, within this type of mobile devices usually comprising a mobile radio telephone receiver, of the GSM mobile phone type (Global System for Mobile Communications), a GNSS (Global Navigation Satellite System) receiver such as a receiver of the Global Positioning System (GPS), GLONASS or GALILEO type by which the mobile device receives emissions from satellites to know its position. In this way, in the event of a traffic accident for example or for any other positioning need, the mobile device can calculate and transmit its position.

The determination of the position of such a receiver can be done as follows: a plurality of satellites continuously transmits a dated signal to the receiver. The synchronized receiver on the satellite clock can then measure the propagation time of this signal and deduce a distance separating it from a particular satellite. From three satellites, such a receiver is able to triangulate to determine its position. Each measurement of propagation time represents the radius of a sphere centered on a particular satellite, the receiver being located on this sphere. With two distance measurements, the position of a receiver is on a circle formed by the intersection of two spheres. A third simultaneous measurement reduces the two-point intersection, one of which is far away in space and is easily isolated.

However, the clock of the receiver is affected by a ΔT bias because it is not totally synchronous with the GPS system. Indeed, the atomic clocks of the GPS satellites have a very high level of precision but the accuracy of the GPS receiver, more rudimentary, is fatally much less precise. This ΔT clock bias is therefore the time difference between the receiver clock and the satellite clock and can reach several seconds. It results in an error in the measurement of the GPS signal propagation time and, consequently, in a c.ΔT error on the satellite-receiver distances, where c is the speed of light. This error is found on all the distances measured by the receiver. Since the distances are not perfect because they are tainted by a time bias, they are called pseudo-distances. The time bias, a priori unknown, must then be determined.

There is therefore a third unknown in three dimensions (three satellites) and it is necessary to measure at least one additional distance, thus to have at least four satellites, to solve a system of four equations with four unknowns.

The signal emitted by each satellite is a pseudo-random signal modulated in phase; the GPS receiver must then acquire this signal. Both the satellite and the receiver transmit the pseudo-random signal (the receiver generates a replica) at the same moment (time set on the GPS system's general clock). The receiver then delays the start of this broadcast until its signal is superimposed with that coming from the satellite. The determination of this delay is done by a correlation technique of the two signals. The value of this delay is thus the time taken by the signal to propagate from the satellite to the user. This type of measurement requires an immense precision (better than 100 nanoseconds) since the time taken by the signal to make such a path is of the order of 1 / 20th of a second. However, since the clock of the GPS receiver is never fully synchronized with that of the satellites, the receiver will have to constantly adjust its clock by successive approximations to achieve the maximum correlation of the two signals. The acquisition of the signal therefore requires a very important time scan by the receiver.

In the context of "Assisted-GPS" (Assisted Global Positioning System), the position calculation process uses a mobile receiver capable of receiving and processing GNSS signals as well as communicating with a cellular network, and a server. support data in charge of disseminating data to assist the processing of GNSS signals made in the mobile. One of the operating modes, known as "MS-Assisted" (MS for "Mobile Station" in English or mobile station), is for the server to broadcast help data to the measurement of pseudo-distances on the GPS signals, these measurements being then sent back to the server which calculates the position. The object of such a mode of operation is:<ul id="ul0002" list-style="dash" compact="compact"><li>minimize the amount of support data,</li><li>reduce the operating threshold (in terms of signal-to-noise ratio) of the receiver,</li><li>reduce the computing power required to process GNSS signals.</li></ul>

Indeed the main idea of ​​"Assisted GPS" or "Assisted-GNSS" consists of:<ul id="ul0003" list-style="dash" compact="compact"><li>to prevent the receiver from demodulating the ephemerides of the satellites contained in the signals coming from the satellites, which favors the time necessary for calculating the first point as well as the operating threshold,</li><li>provide the receiver with a prelocalisation, an idea of ​​the time and the Doppler effect of the satellites, so as to speed up the operation.</li></ul>

Nevertheless, in this mode of operation, typically called "MS-Assisted", the mobile must return to the server the pseudo-distances.

In order to minimize the traffic and because the position of the mobile is a priori known to the uncertainty of the size of the cell, it is possible to return only spreading code phase information. Typically, in the context of the GPS SPS (Standard Positioning Service), the spreading code having a periodicity of 1ms, the mobile returns, to the server, the position measurements of the beginning of a spreading code length in a millisecond data usually referenced to the beginning of a millisecond hour GPS system. The system time is then used to deduce by the server the position of the satellites at the time of transmission of the signal allowing the server to triangulate the position of the user.

The most immediate mode of operation aimed at a saving in processing by the mobile receiver is represented in FIG. 1. Suppose that the mobile has access to the navigation system's time, in this case represented here as an example that of the GPS under the reference 1. Several methods can be put in place to achieve this:<ul id="ul0004" list-style="dash" compact="compact"><li>maintenance of time on a specific local clock,</li><li>synchronization on an external source itself synchronized on GPS.</li></ul> This is the case when the receiver is connected to a synchronized mobile network on the GPS.

To position itself, the receiver must measure the distance that separates it from each satellite in view. The distance measurement is done by multiplying the difference between the date of transmission and the date of reception of the signal coming from the satellite. To do this the satellite signal encloses a date information ("Time of Week" or TOW). This dating information is contained in a date message that has a periodicity of a few seconds, typically 6 seconds in the GPS. The dating information is relayed to a shorter repetitiveness by the very structure of the signal and more specifically by the repetitions of the spreading codes (hereinafter, for the sake of brevity, the spreading code is called code). This information taken independently of the date information contained in the navigation message is ambiguous because it repeats with a certain periodicity. This structure is represented in 1. In the case of GPS L1, the spread codes have a repeatability of 1ms. They are respectively represented as 2 for a signal received from a first SV Observ satellite. # 1 (for "Visible Satellite Observed # 1), 3 for a signal received from a second SV Observ satellite. # 2 (for "Visible Satellite Observed # 2), and 4 for a signal received from an nth SV Observ satellite. #nsat (for "Visible Satellite Observed #nsat).

In the case of assistance shown in Figure 1, ie where the mobile has access to an external synchronization source (reference 1, GPS system clock), it is not necessary to resolve the positioning to read the date of transmission of the TOW signal on the message. It suffices to measure the code phase of each satellite ie measuring the time between the beginning of a receive code period, referenced from 6 to 8 (measured in number of bits or chips in English) and the millisecond transition on the GPS time scale (reference 1).

The knowledge :<ul id="ul0005" list-style="dash" compact="compact"><li>a prelocation,</li><li>the GPS date at which the measurement is made,</li></ul> allows:<ul id="ul0006" list-style="dash" compact="compact"><li>to calculate the approximate position of the satellites at the moment of the emission of the signal,</li><li>to deduce the approximate user-satellite distance,</li></ul> and therefore clear the ambiguity to 1 ms on the emission dates.

At the end of this process, the satellite-user distance measurement is known unambiguously.

The amount of information transmitted is then reduced because only one hourly reception time reference.

This device is particularly attractive when the mobile access time GPS, typically in a GPS synchronized mobile phone network, type IS95. This is not the case in a GSM asynchronous telephony network. In GSM network, the GPS system time can be found by reading on the GPS message received the "Time of Week" (TOW) field on satellites, but this has several drawbacks:<ul id="ul0007" list-style="dash" compact="compact"><li>this forces the mobile receiver to demodulate a GPS message, which has an impact on the calculation time of the point,</li><li>Data demodulation requires a higher received signal strength than simply detecting a code start.</li></ul>

Another way could be to maintain a local clock GPS time at the mobile, but it supposes to have had access to the information once to reset the local clock. On the other hand, the local clock of the receivers being of limited quality, an error of several tens of ms can appear on this dating, which causes an error at the level of the server during the calculation of the position of the satellites and consequently a error on the resolution of the user's position.

The present invention proposes for this purpose a method for minimizing the synchronization search complexity on the GPS.

In a first implementation, it is proposed to locate the code phase measurements, no longer with respect to the date of the GPS system, but with respect to the date received in a particular GPS signal. The advantage of this method is to minimize the demodulation number of TOW. Indeed, for this, it is sufficient to identify the code transition date on only one received signal, in other words, it is sufficient to demodulate a received signal. The advantages are then:<ul id="ul0008" list-style="dash" compact="compact"><li>a minimization of the computing load for the mobile,</li><li>a much lower level of satellite receive power than would be required for demodulation of all TOWs.</li></ul>

The subject of the invention is therefore a method for calculating the position (or the point) of a mobile device, the method implementing:<ul id="ul0009" list-style="dash" compact="compact"><li>a help data server for providing help with resolving the point of the mobile device,</li><li>said mobile device comprising means of communication with the server via a cellular radio-telephone network, said device comprising means for receiving positioning signals from a satellite positioning system (GPS, GNSS) ,</li></ul> the process comprising the following steps:<ul id="ul0010" list-style="dash" compact="compact"><li>following the reception of the positioning signals, the device sends to the server a set of code phases corresponding to the acquired satellites, these code phases being dated by a single date information corresponding to the time of emission of one of the phases code,</li><li>the server derives from this information the transmission hours corresponding to these code phases as well as the pseudo-distances,</li><li>the server resolves the point.</li></ul>

The subject of the invention is also a method for calculating the position (or point) of a mobile device, the method implementing:<ul id="ul0011" list-style="dash" compact="compact"><li>a help data server for providing help with resolving the point of the mobile device,</li><li>said mobile device comprising means of communication with the server via a cellular radio-telephone network, said device comprising means for receiving positioning signals from a satellite positioning system (GPS, GNSS) ,</li></ul> the process comprising the following steps:<ul id="ul0012" list-style="dash" compact="compact"><li>said mobile device sends to the server a set of code phases corresponding to the acquired satellites, these code phases being measured with respect to the beginning of millisecond slots maintained by a local clock, the code phases being dated with respect to one hour of program,</li><li>the server deduces from these code phases and the associated transmission time the pseudo-distances,</li><li>the server calculates the position of said mobile device.</li></ul>

The invention also relates to a method for calculating the position (or point) of a mobile device, said device comprising means for receiving positioning signals from a satellite positioning system (GPS, GNSS), characterized in that, to avoid reading the issue date <i>T</i>_<i>e</i> on positioning signals, the following function is minimized by a non-linear technique:<maths id="math0001" num=""><img file="EP1560037A2_D0001.tif" /></maths> where Xu, Yu, Zu represents the position of the mobile device, ΔT represents the clock error committed on the pseudo-distance measurement,<i>T</i>_<i>e</i> represents the date of issue of the positioning signals.

According to one embodiment, the step of minimizing said function <i>f</i> establishes symmetrically on the date of receipt <i>T</i>_<i>r</i> positioning signals instead of the date of issue <i>T</i>_<i>e</i>.

According to one embodiment, said minimization step is performed by computing means of the mobile device.

According to one embodiment, said method implementing:<ul id="ul0013" list-style="dash" compact="compact"><li>a help data server for providing help with resolving the point of the mobile device,</li><li>said mobile device comprising means of communication with the server via a cellular radio-telephone network,</li></ul> the step of minimizing said method is performed by means of calculating the server.

The invention and the advantages thereof will appear more clearly on reading the following description of the preferred embodiments, given purely by way of non-limiting examples, with reference to the appended drawings in which:<ul id="ul0014" list-style="dash" compact="compact"><li>FIG. 1, already described, relates to the standard dating of the code phases,</li><li>FIG. 2 relates to an embodiment coding information from the mobile to the server,</li><li>Figures 3 and 4 relate to measurements made on the TOW field with identical transmissions for all satellites.</li></ul>

Figure 2 illustrates the method according to a first embodiment of the invention. A first signal from a first satellite is acquired (reference 9). The dating of the code phases on this first signal 12 is performed by demodulation of the TOW. A time reference is then deduced. The measurement of the code phases of the other signals received is then made with respect to this reference time respectively at 13 and 14.

Said method uses the following elements:<ul id="ul0015" list-style="dash" compact="compact"><li>at least one radio navigation satellite,</li><li>at least one mobile device,</li><li>at least one assistance server for improving the acquisition of satellite data by the mobile device,</li></ul> said method comprising the following steps:<ul id="ul0016" list-style="dash" compact="compact"><li>reception by the mobile device of the satellite data,</li><li>estimation by the mobile device of the code phases of the GPS signals (or by GNSS extension),</li><li>dating the code phases by the time of emission with respect to one of the satellites, typically the loudest in view,</li><li>transmission to the server of said code phases and dating,</li><li>estimation by the server of the pseudo-distances associated with each of the code phases.</li></ul>

Said estimation method is also characterized in that: the server, by the knowledge of the position of the mobile obtained by an information of the network, position of the base cell for example, derives a date of issue of the code phases not affected by the dating transmitted in the help message.

Concretely in the example of Figure 2, the dating pivot is taken on the satellite 1. The message returned to the server is then constituted by: <tables id="tabl0001" num="0001"><table frame="none"><tgroup cols="1" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="157.50mm" /><tbody valign="top"><row><entry namest="col1" nameend="col1" align="center">TOW: transmission time extracted from satellite message 1 in the following list, TOW is an integer of ms</entry></row><row><entry namest="col1" nameend="col1" align="center">Satellite phase code 1 = 0</entry></row><row><entry namest="col1" nameend="col1" align="center">Satellite phase code 2, with the origin of the satellite code transition 1, between 0 and 1024 chips</entry></row><row><entry namest="col1" nameend="col1" align="center">...</entry></row><row rowsep="0"><entry namest="col1" nameend="col1" align="center">Satellite phase code n, with the origin of the satellite code transition 1, between 0 and 1024 chips</entry></row></tbody></tgroup></table></tables> The server knows the ephemerides of the satellites. The calculation steps at the server level are then as follows:<ul id="ul0017" list-style="dash" compact="compact"><li>calculating the positions of the satellites at the time TOW referenced in the message from the mobile,</li><li>distance calculation <i>d</i>_<i>TOW</i>(<i>k</i>_<i>sat</i>,<i>MS</i>) separating the satellite <i>k</i>_<i>sat</i> from the position a priori of the mobile (approximate position obtained by information of the cell) at the date TOW.</li><li>estimated travel time <i>t</i>_<i>TOW</i>(<i>k</i>_<i>sat</i>,<i>MS</i>) = <i>d</i>_<i>TOW</i>(<i>k</i>_<i>sat</i>,<i>MS</i>) /<i>c</i> where is the speed of light.</li><li>application of the different corrections:<img file="EP1560037A2_D0002.tif" />_<i>OW</i>(<i>k</i>_<i>sat</i>,<i>MS</i>) <i>= t</i>_<i>TOW</i>(<i>k</i>_<i>sat</i>,<i>MS</i>) - Δ<i>b</i>_<i>ksat</i> - Δ<i>I</i>_<i>ksat</i>, where Δ<i>b</i>_<i>ksat</i> corresponds to the clock correction of the satellite ksat and <i>.DELTA.I</i> corresponds to the sum of the ionospheric and tropospheric corrections.</li><li>estimate of the transmission time of each code phase addressed in the list <i>T</i>_{<i>Program</i>}(<i>k_sat</i>) = <i>TOW-E</i>[<img file="EP1560037A2_D0003.tif" />_<i>TOW</i>(<i>k</i>_<i>sat</i>,<i>MS</i>) -<img file="EP1560037A2_D0004.tif" />_<i>TOW</i>(1,<i>MS</i>)] or <i>E</i>[.] means the whole part.</li><li>removal of ambiguity:</li></ul><maths id="math0002" num=""><img file="EP1560037A2_D0005.tif" /></maths> where Rc is the chip rate (1.023Mchips / s in the case of GPS), then <i>T</i>_{<i>program</i>}(<i>k</i>_<i>sat</i>) = <i>T</i>_{<i>program</i>}(<i>k_sat</i>) -1<i>ms</i>,<maths id="math0003" num=""><img file="EP1560037A2_D0006.tif" /></maths> where Rc is the chip rate (1.023Mchips / s in the case of GPS), then <i>T</i>_{<i>program</i>}(<i>k</i>_<i>sat</i>) <i>= T</i>_{<i>program</i>}(<i>k</i>_<i>sat</i>) 1<i>ms</i> ,<ul id="ul0018" list-style="dash" compact="compact"><li>estimates of pseudoranges:<maths id="math0004" num=""><img file="EP1560037A2_D0007.tif" /></maths></li><li>Standard resolution of the mobile position by solving the following system:<maths id="math0005" num=""><math display="block"><mrow><mtext>∥</mtext><mtext mathvariant="italic">Pos</mtext><mtext>_</mtext><mtext mathvariant="italic">sat</mtext><mtext>(</mtext><msub><mrow><mtext mathvariant="italic">k</mtext></mrow><mrow><mtext mathvariant="italic">sat</mtext></mrow></msub><mtext>,</mtext><msub><mrow><mtext mathvariant="italic">T</mtext></mrow><mrow><mtext mathvariant="italic">Issued</mtext></mrow></msub><msub><mrow><mtext></mtext></mrow><mrow><mtext>sin</mtext></mrow></msub><mtext>(</mtext><mtext mathvariant="italic">ksat</mtext><mtext>) -</mtext><mtext mathvariant="italic">Pos</mtext><mtext>_</mtext><mtext mathvariant="italic">MS∥</mtext><mtext> = ρ (</mtext><mtext mathvariant="italic">k</mtext><mtext>_</mtext><mtext mathvariant="italic">sat</mtext><mtext>) +</mtext><mtext mathvariant="italic">cΔClock</mtext></mrow></math><img file="EP1560037A2_D0008.tif" /></maths> or <i>ΔClock</i> is the clock unknown.</li></ul>

Thanks to the invention, in an asynchronous network of the GSM type, it is possible for the assistance data server in "MS-Assisted" mode to resolve the position of the mobile without committing any error and while transmitting in the sense " only one time reference in multiples of ms and one set of code phases.

Advantageously, the device takes advantage of the server-side knowledge of the ephemerides of the satellites and the approximate position of the mobile so that the mobile has, at any time, need to know this information.

The present invention may also be implemented, in a slightly different manner, by reporting to the server a code phase measurement with respect to the MS millisecond start maintained on a local clock. The TOW field designates the start time of each code period on which the measurement is made, as shown in Figure 3. The local clock 15 of the receiver serves as a time reference. The code periods of each satellite in visibility (SV for "Satellite Visible") are represented from 17 to 19. The measurements made by the GPS receiver consists in measuring the code phases of the code periods transmitted synchronously on each satellite. Thus, the measurement returned by the receiver to the mobile corresponds to the date of transmission (example 142 ms in FIG. 3, under the reference 20) and the time elapsed between the beginning of each period and the millisecond transition of the clock. local, referenced respectively 16 for the satellite 1, 21 for the satellite 2, 22 for the satellite N.

The resolution of the point is then naturally because the beginning of the code period all correspond to the same transmission time, but are naturally not received at the same time. The server by a calculation similar to the previous estimates the difference in number of milliseconds to add to each code phase to deduce the pseudo-distances.

A second implementation aimed at reducing the need for demodulation of the signal time information and therefore aimed at limiting the processing at the receiver level is proposed hereinafter. The procedure is shown in FIG. Clock information is used by the receiver 23. This information is not necessarily synchronous with the GPS system. The receiver measures the code phases of the satellites in visibility with respect to a millisecond edge of the synchronization information 28 to 30 respectively for the satellites 1 to N. The information inferred from these measures is as follows: <tables id="tabl0002" num="0002"><table frame="none"><tgroup cols="1" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="157.50mm" /><tbody valign="top"><row><entry namest="col1" nameend="col1" align="center">TOW: Received date measured on an internal clock</entry></row><row><entry namest="col1" nameend="col1" align="center">Satellite phase code 1, with as origin the millisecond transition of the receiver's internal clock reference, between 0 and 1024 chips</entry></row><row><entry namest="col1" nameend="col1" align="center">Satellite phase code 2, with as origin the millisecond transition of the internal clock reference of the receiver, between 0 and 1024 chips</entry></row><row><entry namest="col1" nameend="col1" align="center">...</entry></row><row rowsep="0"><entry namest="col1" nameend="col1" align="center">Satellite phase code n, with as origin the millisecond transition of the internal clock reference of the receiver, between 0 and 1024 chips</entry></row></tbody></tgroup></table></tables>

The pseudo-distances are then calculated in the same way as presented in the first implementation

Conventionally, it is known that the resolution of the user position is given by the resolution of the following system:<maths id="math0006" num=""><img file="EP1560037A2_D0009.tif" /></maths> or    d (x, y) is the distance between x and y,    ρ_<i>k</i> denotes the pseudo-distance between the satellite k in visibility and the user,

<i>DT</i> is the clock error on the pseudo-distance measurement.

Classically, the issue date <i>T</i>_<i>e</i> is known perfectly by reading on the satellite signal. The system of equations is then classically linearized to be reduced to a linear system:<maths id="math0007" num=""><img file="EP1560037A2_D0010.tif" /></maths> or<maths id="math0008" num=""><math display="block"><mrow><mtext mathvariant="italic">d</mtext><mtext>(</mtext><msub><mrow><mtext mathvariant="italic">T</mtext></mrow><mrow><mtext mathvariant="italic">e</mtext></mrow></msub><mtext>,</mtext><msub><mrow><mtext mathvariant="italic">k</mtext></mrow><mrow><mtext mathvariant="italic">sat</mtext></mrow></msub><mtext>) = </mtext><msqrt><mtext>(</mtext><msub><mrow><mtext mathvariant="italic">X</mtext></mrow><mrow><mtext mathvariant="italic">s</mtext></mrow></msub><mtext>(</mtext><msub><mrow><mtext mathvariant="italic">T</mtext></mrow><mrow><mtext mathvariant="italic">e</mtext></mrow></msub><mtext>) - </mtext><msub><mrow><mtext mathvariant="italic">X</mtext></mrow><mrow><mtext mathvariant="italic">u</mtext></mrow></msub><msup><mrow><mtext>)</mtext></mrow><mrow><mtext>2</mtext></mrow></msup><mtext> + (</mtext><msub><mrow><mtext mathvariant="italic">Y</mtext></mrow><mrow><mtext mathvariant="italic">s</mtext></mrow></msub><mtext>(</mtext><msub><mrow><mtext mathvariant="italic">T</mtext></mrow><mrow><mtext mathvariant="italic">e</mtext></mrow></msub><mtext>) -</mtext><msub><mrow><mtext mathvariant="italic">Y</mtext></mrow><mrow><mtext mathvariant="italic">u</mtext></mrow></msub><msup><mrow><mtext>)</mtext></mrow><mrow><mtext>2</mtext></mrow></msup><mtext> + (</mtext><msub><mrow><mtext mathvariant="italic">Z</mtext></mrow><mrow><mtext mathvariant="italic">s</mtext></mrow></msub><mtext>(</mtext><msub><mrow><mtext mathvariant="italic">T</mtext></mrow><mrow><mtext mathvariant="italic">e</mtext></mrow></msub><mtext>) - </mtext><msub><mrow><mtext mathvariant="italic">Z</mtext></mrow><mrow><mtext mathvariant="italic">u</mtext></mrow></msub><msup><mrow><mtext>)</mtext></mrow><mrow><mtext>2</mtext></mrow></msup></msqrt></mrow></math><img file="EP1560037A2_D0011.tif" /></maths>

In this case, the mobile does not read the date of transmission on the satellite signal. This issue date becomes an unknown.

For this purpose, the present invention also provides a method for resolving the issue date as an additional unknown. The problem therefore has 5 unknowns: (<i>X</i>_<i>u</i>,<i>Y</i>_<i>u</i>,<i>Z</i>_<i>u</i>,<i>DT</i>,<i>T</i>_<i>e</i>). To solve the problem, it is proposed to minimize the following function:<maths id="math0009" num=""><img file="EP1560037A2_D0012.tif" /></maths>

The minimization techniques to be implemented are non-linear techniques, known per se, of the Newton or other type.

According to another embodiment, and in a symmetrical manner, the step of minimizing said function <i>f</i> is established on the date of receipt <i>T</i>_<i>r</i> positioning signals instead of the date of issue <i>T</i>_<i>e</i>.

This technique can be implemented either by the calculation means of the mobile or by the calculation means of the server.

We will note, in addition, that the description of the invention has emphasized the different steps of the process according to the invention, however, it is obvious that the various elements used in this process include the means necessary for carrying out the invention, so the mobile and the server include, in addition to the calculation means mentioned above, respectively means of communication for the exchange of signals between the mobile and the server, means for receiving the positioning signals (GPS, GNSS etc.). In addition, the mobile comprises means for transmitting the code phases and the server comprises means for receiving said code phases.

In particular, the invention has been described in the context of a GPS system but it may act of another GNSS system such as a GLONASS or GALILEO type system.