RU2574604C2 - Method for locating terminal on surface of coverage area by means of communication network using communication satellite with multi-beam antenna - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: terminal performs uplink transmission of a message incorporated into a modulated signal to a communication satellite with a multi-beam antenna at a frequency shared by at least three different uplink beams such that said message is received by said communication satellite with a multi-beam antenna via said multi-beam antenna with three different amplitudes; said communication satellite with a multi-beam antenna performs downlink transmission of three modulated signals incorporating said message, each of the first, second and third signals corresponding to a different beam from among said three beams; a terrestrial receiver receives said first, second and third signals; a terrestrial computer determines the amplitudes of the message sent by the terminal incorporated into said first, second and third signals; the location of the terminal is determined from the amplitudes of said message from said first, second and third signals.

EFFECT: high accuracy of locating a terminal on the surface of a coverage area.

10 cl, 9 dwg

Description

The present invention relates to a method for determining the location of a terminal on the surface of a coverage area by means of a communication network for creating radio frequency channels. The mapping method is applied more specifically to a network using a satellite containing multiple beams, referred to as a communication satellite with a multipath antenna. This type of satellite allows multiple beams to be used on board the satellite to cover geographic areas or cells, instead of one wide beam.

Numerous methods are known for locating terminals on the surface of a given coverage area.

The most famous of these is the global positioning system (GPS), which operates by calculating the distance that separates the terminal containing the GPS receiver and several satellites. Such a system nevertheless creates a certain amount of difficulties.

First of all, the system obviously assumes that the terminal contains a GPS receiver and, therefore, does not cover a universal communication terminal.

Moreover, sometimes it is important to know, in a certain way, the position of the terminal in relation to the service center, in contrast to the terminal itself (usually in the case of a vehicle parked by a company). In this case, the GPS terminal transmits its position to the company via communication networks. Such a solution may nevertheless have certain disadvantages, since the terminal user can fake the transmitted GPS data (for example, using a GPS emulator).

Another well-known solution is to use an OmniTRACS ™ service. The unit installed in the vehicle measures the data sent by the “hub” type ground station through several communication satellites, then transmits the measurements made by satellite, ground station or NOC type center (network operation center), which will process the measurements and will determine the position of the vehicle.

In addition to the significant cost of such a system (associated, in particular, with the presence of a technological unit provided with a controlled antenna), once again, fake transmitted information may be provided, NOC is not provided by any means to complete the determination of the position of the vehicle or terminal.

Basically, the methods of limited cost, known today, for determining the position of the terminal in relation to the service center, are based on information measured and then sent by the terminal itself and it is impossible for the service center to establish the authenticity of this information, and thus the position terminal calculated from the specified information.

In this regard, the present invention is directed to providing an economical method for determining the location of a terminal on the surface of a coverage area by means of a communication network, the location is determined in a certain way (i.e., without likely forgery by the user of the terminal) and during the use of the communication terminal.

To this end, the invention provides a method for determining the location of a terminal on the surface of a coverage area by means of a communication network for installing radio frequency channels, the network comprising a communication satellite comprising a plurality of beams, referred to as a communication satellite with a multipath antenna, said communication satellite with a multipath antenna, comprising a multipath antenna, a coverage area consisting of a plurality of cells, wherein each cell is associated with at least one beam for communication with a satellite to which a frequency band is assigned, at Ohm, the specified method includes the following steps, in which:

- the terminal transmits, via the ground-to-board communication channel, a message included in the modulated signal to the specified satellite at a frequency separated by at least three different beams in the ground-to-board communication channels such that the message is received by the specified communication satellite with a multipath antenna using the specified multipath antenna with three different amplitudes;

- said communication satellite with a multipath antenna transmits three modulated signals including the indicated message via the onboard-ground communication channel, wherein each of the first, second and third signals corresponds to a different beam from among the three beams;

- ground receiving means receives said first, second and third signals;

- ground-based computing means determine the amplitudes of the message sent by the terminal contained in the indicated first, second and third signals;

- determine the location of the terminal from the amplitudes of the specified message in the specified first, second and third signals.

A terminal is used to indicate a terminal that can be stationary, transportable, such as a decoder, or mobile.

In accordance with the invention, preferably three beams are used, dividing the same frequency into transmission; the message transmitted by the terminal is received by the multi-beam antenna of the satellite with three different amplitudes; three signals including the specified message corresponding to these three amplitudes and containing the same payload (amount of information) are transmitted via a downlink to a ground receiving means (usually a ground station) that will detect a message in each of the three signals and determine based on this, the amplitude. The data on these amplitudes makes it possible to position the terminal in the service area using the connection between the message amplitudes in the received signals and the Q factors related to the position of the terminal with respect to each of the cells corresponding to three beams.

It should be noted that thanks to the invention, the determination of the position of the terminal occurs without adaptation of the terminal, which can be a conventional communication terminal. Moreover, the terminal does not perform any specific calculations to determine its position.

Moreover, to implement the method in accordance with the invention requires a single communication satellite with a multipath antenna; the specified satellite can be used both to implement the method in accordance with the invention, and to provide communication.

It should be noted that the terminal does not interfere in determining its position; therefore, the terminal user cannot fake the position of the latter.

The method in accordance with the invention may also include one or more of the features below, considered individually or in accordance with any technically possible combinations thereof:

- the specified signal, including the specified message transmitted by the terminal (and, thus, the three indicated signals received by the multipath antenna), is modulated in accordance with the broadband protocol;

- said message included in said first signal is received by said ground receiving means with a greater amplitude than said message included in second and third signals, said method comprising the following steps:

ο demodulation with the indicated ground-based means of computing the indicated first signal so as to recover the following information related to the message:

■ message payload;

■ parameters of radiation and / or coding of the specified message;

ο the use of the specified information related to the message to search for the specified message, respectively, in the indicated second and third signals by means of the indicated ground-based computing means (the use of the specified information makes it possible to speed up the search, in comparison with the usual search, in which this same information would not be available);

- the specified signal, including the specified message transmitted by the terminal, is modulated in accordance with the broadband protocol and the specified recovered radiation and / or encoding parameters contain a binary broadband sequence;

- said ground computing means finds said message, respectively, in said second and third signals by means of a correlation operation;

- transmission through the communication channel "board-to-ground" through the specified communication satellite with a multipath antenna of the three specified modulated signals, including the specified message, occurs at three different frequencies;

- the method in accordance with the invention includes the step of determining at least two of the three differences in the amplitudes of the message included in the specified first, second and third signals;

- the method in accordance with the invention includes:

ο stage of determining the curves, which are the difference in the quality factors corresponding to the specified differences of the amplitudes;

ο the step of determining the location of the specified terminal corresponding to the intersection of the specified curves;

- these terrestrial receiving means periodically receive messages through one or more reference terminals, the exact position of which is known (for example, contained in the message itself), while the specified position (s) allows you to correct the lines of the quality factor used to determine the position of the specified terminal;

- determination of the three differences in the amplitudes of the message included in the specified first, second and third signals;

- information retrieved by the specified ground computing means in the specified first signal, contains the initial part of the specified message.

Other characteristics and advantages of the invention will become apparent from the description, which is given in this regard below by way of illustration and in no way limitation, with reference to the accompanying figures, including:

- in FIG. 1 is a simplified schematic diagram of a multi-path network for implementing the method in accordance with the invention;

- in FIG. 2 shows the various steps of a method in accordance with the invention;

- in FIG. 3 shows a number of lines of Q factors corresponding to the first ray of the coverage zone;

- in FIG. 4 shows a number of lines of Q-factors corresponding to the second ray of the same coverage area of FIG. 3;

- in FIG. 5 shows a series of Q-factor lines corresponding to the third ray of the same coverage area of FIG. 3;

- in FIG. 6 is a series of lines depicting the difference in the Q factors of FIG. 3 and 4;

- in FIG. 7 is a series of lines depicting the difference in the Q factors of FIG. 4 and 5;

- in FIG. 8 is a series of lines showing the difference in the quality factors of FIG. 3 and 5;

- in FIG. Figure 9 shows the coverage area, as well as the lines of differences in the Q factors calculated from a comparison of the Q factors for the three values of the difference in amplitudes determined by the method in accordance with the invention in the specific example described below.

In all figures, ordinary elements have the same reference numerals.

In FIG. 2 shows various steps of a method 200 for determining the location of a terminal in a communication network in accordance with the invention. Said method 200 may, for example, be implemented through a communication network, such as network 100 shown in FIG. one.

The specified network 100 contains:

- at least one main ground station 102, such as a ground communications gateway;

- NOC or Network Operation Center 105;

- a plurality of mobile terminals, of which only one T is represented here by way of illustration;

- communication satellite 103 with a multipath antenna.

The communication satellite 103 with a multi-beam antenna is a satellite of the "transparent" type (ie, provided with a transparent payload), the payload of which consists essentially of converting the frequency of the signals received at the satellite level before amplification for retransmission to the downlink . In other words, the method in accordance with the invention is applied to this type of transparent satellite and not to “regenerative” type satellites (that is, provided with a regenerative payload), whose payload demodulates and re-modulates the signals on board the satellite.

In the case of a high speed broadband satellite communication system 10, satellite 103 is used in a bi-directional manner, in other words simultaneously for:

- relaying information transmitted by the main ground station 102 to the T terminals: this first channel of type point-to-group points is a direct channel;

- relaying to the ground station 102 information transmitted by the ground terminals T: this second point-to-group point channel is a reverse channel.

The primary ground station 102 is connected to the NOC 105 (typically via the Internet). NOC 105 is a network management system that enables the operator to control and manage all network components.

In the return channel, the modulated signals are sent to the communication satellite 103 with the multipath antenna via the uplink LMR channel by the terrestrial terminal T. The signals sent by the terrestrial terminal T are then processed at the satellite level 103, which, using the on-board equipment, amplifies them, leading them to appropriate frequency, then retransmits them from the satellite dish (s) through the downlink LDR channel in the form of a beam or multiple beams to a ground station (s) 102.

A forward channel including uplink LMA channels and downlink LDA channels of the ground station (s) 102 to the ground terminals T operates identically in the opposite direction of communication. In the context of the present invention, the forward channel is not applicable.

Satellite 103 covers the coverage area in which the ground terminals T are located, divided into elementary coverage areas or cells. The configuration of the network 100, as shown in FIG. 1, applies a method referred to as a frequency reuse method: this method allows the same frequency range to be applied several times in the same satellite system in order to increase the overall system power without increasing the established bandwidth.

For each cell, it is possible to use at least one frequency band of the corresponding part of the available bandwidth. Each frequency band is associated with a beam of a communication satellite 103 with a multipath antenna. Three cells A, B and C are presented in this document, terminal T, as shown, is located in cell A. Each of the cells is individually irradiated with a beam (which will also be denoted by the corresponding reference position A, B and C of the antenna) of the multi-beam antenna of satellite 103.

Basically, the antenna gain of each beam is high inside the corresponding cell and decreases outside the cell. Therefore, the terminal T will be better “heard” by satellite 103 on the beam corresponding to cell A than on the rays corresponding to cells B and C (satellite 103 is provided with a multi-beam antenna that scans various beams corresponding to different cells). Each frequency band can be divided into many frequency channels. The ground terminal T will thus use a frequency channel for transmission; this same terminal T will also function in a certain time period (time interval).

A cell spans a surface ranging from a hundred or so kilometers to several thousand kilometers (i.e., a whole country). When confirming that the beam covers a cell (or corresponds to a cell), this means that part of the satellite’s multipath receiving antenna is concentrated on this cell so that the resulting Q factor is greater than the specified threshold S. Usually expressed in dB / K, Q factor, denoted by G / T, corresponds to the ratio of the gain of the receiving antenna in the direction of the terminal to the equivalent noise temperature of the receiving system. S (T, A) will subsequently assign a Q / T figure of merit associated with the cell (equally assigning beam A) to the position of terminal T; in a more general sense, S (Y, X) (expressed in dB / K) will hereinafter be assigned the Q / T figure of merit associated with cell X (beam X) for position Y of the terminal. This figure of merit includes the figure of merit of the receiving satellite antenna (which depends on the geographical location of the terminal), on the amplifier on board the satellite, on the receiving antenna of the ground station, on its amplifiers and cables up to the input of the demodulator. It should be noted that among all the factors that contribute to the overall G / T, only the G / T of the multipath antenna on board the satellite changes in accordance with the geographical position of the terminal.

These coding and modulation methods for communication of the system are selected so that the threshold value of S guarantees a sufficient level of quality of service, the specified level of quality of service is not guaranteed if the terminal is located in a position where the quality factor is below the threshold value of S (the terminal in this case is considered to be outside beam coverings). It is almost obvious that the figure of merit is gradually reduced when the terminal leaves the cell. The cell coating is represented by a series of lines (or figures) of successive and essentially concentric Q factors, while the Q factors are identical in all respects of each line and decrease as one moves away from the center of the cell. The exact configuration can be very complex and depend on how the antenna is formed (reflectors, beamforming network, etc.).

In FIG. Figure 3 shows a series of LA lines of the Q factors corresponding to the first beam A, in the coverage area of Europe.

In FIG. 4 shows a number of lines of LB Q-factors corresponding to the second beam B in the coverage area of Europe.

In FIG. 5 shows a series of lines of LC Q-factors corresponding to the third C beam in the coverage area of Europe.

In FIG. 3-5, the transition from one line to another occurs in accordance with a step of 1 dB / K, the line bypassing the zone of the smallest diameter contains the highest figure of merit, it should be understood that the decrease in the figure of merit from the center of the cell to its outer part is continuous .

As an example, it should therefore be noted that in these figures 3-5 the city of Rome is covered by three beams A, B and C with different Q factors, respectively 8.7 dB / K for beam A (Fig. 3), 6, 5 dB / K for beam B (FIG. 4) and -5 dB / K for beam C (FIG. 5). The lines LA1, LB1, and LC1 passing through Rome are represented by dotted lines for illustrative purposes only.

Thus, it should be noted that the data of the three Q-lines LA1, LB1 and LC1 of the Q-factors allow determining the position of the terminal transmitting from Rome and located at the intersection of these three lines. This result will be advantageously applied by the method in accordance with the invention.

In what follows, a hypothesis will be proposed that cells A, B, and C, shown schematically in FIG. 1 correspond to the figure of merit shown in FIG. 3, 4 and 5.

A method 200 for determining the location of a terminal on the surface of a coverage area (here Europe) via a communications network 100, the same as in FIG. 1 is carried out as follows.

This paper will hypothesize that three cells A, B, and C (corresponding to beams A, B, and C) are associated with the same frequency band and that the ground terminal T is located in cell A. Terminal T, for example, is located in Rome

The main ground station in this case contains three demodulators / de-correlators 116A, 116B, and 116C adapted to demodulate signals originating from cells A, B, and C, respectively.

Modulations are carried out, for example, in accordance with the asynchronous multiple random access protocol with a band propagating by modulation of the SPREAD ALOHA type using interference mitigation techniques. Such a protocol, for example, is described in document US2010 / 0054131 (del Rio Herrero et al.).

In the case of FIG. 1, a terminal T located in a cell will be “heard” at a certain power by a demodulator 116A, at a lower power by a demodulator 116B, and even less power by a demodulator 116C. It should be noted that the city of Rome is covered by three rays A, B and C with decreasing Q factors (Fig. 3-5).

Moreover, it should be noted that here is one ground station 102 containing three demodulators, but it is also possible to have three ground stations located in different places.

In accordance with the first step 201 of the method 200 in accordance with the invention, the terminal T transmits via an uplink LMR channel a message included in the modulated SM signal to satellite 103 at a frequency belonging to frequency bands separated by three beams A, B and C.

The method in accordance with the invention preferably employs coding and modulation selected to obtain a very low threshold value S (as described above). This is equivalent to expanding a cell compared to a commonly used communication system, so that the emitted SM signal can be reconstructed in three different cells.

According to step 202, said SM signal including a message transmitted by the terminal is received by the multi-beam antenna of satellite 103; the message included in the SM signal is received with three different amplitudes depending on whether it is received by the parts of the antenna corresponding to beams A, B and C, respectively; the antenna contains one or more reflectors, as well as a beam forming a network intended for the inputs of the satellite repeater. As was already revealed above, the amplitude of the message included in the signal received by beam A will be the largest, the amplitude of the message included in the signal received by beam B will be weaker, and the amplitude of the message included in the signal received by beam C will be the weakest out of three. Thus, it should be considered that from one signal including a message sent by terminal T, there are, at the satellite level, three signals including this same message, but with different amplitudes.

According to step 203, signals including a copy of the message with three different amplitudes are then processed at satellite level 103, which, using its on-board equipment, outputs them and modulates them to a suitable frequency (in this case, three different frequencies for each of the signals) amplifies them, then transmits through the LDR downlink these three signals S1, S2 and S3, modulated to different frequencies and including the specified message from the satellite’s antenna (s) to the ground station 102; each of the three signals S1-S3 includes a copy of one message sent by the terminal T and received by the satellite along with the three beams A, B and C. The three signals S1-S3 may also contain signals coming from other terminals, as well as interference and noise.

In accordance with step 204, it will be easy to understand that the demodulator 116A (beam A) receives the signal from the terminal T with more power than the demodulators 116B (beam B) and 116C (beam C).

Since the energy potential of the communication channel corresponding to signal transmission along the beam is good, the demodulator 116A is able to process this signal and restore information corresponding to the message transmitted by the terminal. This information contains the message payload, as well as the terminal identifier, signal phase, time setting (i.e., sampling frequency related to the clock of the ground station 102) of the message in the received signal; the demodulator 116A, in search of a message, will also determine the binary broadband sequence. The binary information contained in the electronic signal is, for example, extracted by two operations, often performed in a common way, the first frequency transpose operation uses a carrier locally generated by the PLL (phase-locked loop) oscillator-type circuits with the ability to transpose the signal into the frequency band of the modulating signals, and a second operation, consisting, for example, in sampling a signal to perform a compression step using pseudo-random binary sequences, a gene integrability locally by binary sequence generator and to demodulate the despread signal; the demodulator thus generates several binary sequences, then performs a correlation operation. To restore the message information, the demodulator must generate the same spreading sequence that is used in the radiation and multiply it by the received signal, while the information encoded by this sequence is thus restored by the correlation operation (compression).

According to step 205, provided with the full data of the message sent by the terminal T, as well as the transmission parameters (i.e., the binary broadband sequence), each of the demodulators 106B and 106C is able to find the message transmitted by the terminal T in the corresponding received signals S2 and S3. To accomplish this, each of the demodulators 106B and 106, separately from the transposition and sampling frequencies, performs a correlation operation simplified by the data of the message payload, the initial part of the message, and the binary broadband sequence. The fact of knowing the message greatly simplifies the search for a message in the signal by demodulators 106B and 106C, which receive a signal with a significantly lower signal-to-noise ratio than the demodulator 106A. Moreover, it should be noted that the demodulator 106A can also transmit information related to the sample size in order to enable the demodulators 106B and 106C to save time during the correlation operation (i.e., have a time window available in which the message is located and where demodulators 106B and 106C can go directly to the search). Another way to improve the signal-to-noise ratio may be to use a noise suppression method for signals originating from each cell A, B, and C (intercell interference suppression). To do this, for each cell, the ground station 102 restores a “clean” signal (ie, a noiseless signal) from the information recovered from the message, then extracts the specified “clean” signal from the received signal. The new received signal, in turn, is demodulated by a demodulator of the corresponding cell (116A, 116B or 116C). This operation may be repeated for other packages. Its principle of operation is to regenerate interference using a signal evaluated in the output of the current stage. This interference is then extracted from the received signal, and the resulting signal contains the input of the next step. The operation can be performed by grouping several packets together (for example, ten packets are demodulated before reconstructing the signal for extraction).

Thus, after step 205, the ground station 102 was provided with complete message data sent by the terminal T and its position using signals received from the three beams A, B and C.

In accordance with step 206, the ground station 102 will determine the amplitudes P (T, A), P (T, B) and P (T, C) at which it received the message inside signals S1-S3, corresponding respectively to the rays A, B and C. Each of the amplitudes P (T, A), P (T, B) and P (T, C) corresponds respectively to the powers in which the message transmitted by the terminal T along the corresponding beams A, B, and C were received by ground station 102. Various methods for determining amplitudes, for example, are described in the following. x documents: “Analysis of a DS / CDMA successive interference cancellation scheme using correlations” (P. Patel, J. Holtzman, Global Telecommunications Conference IEEE 1993, GLOBECOM '93, Houston, Texas, USA, November 29 - December 2, 1993, pp. 76-80, volume 1), “Analysis of a simple successive interference cancellation scheme in a DS / CDMA system IEEE Journal on Selected Areas in Communications” (P. Patel, J. Holtzman, June 1994 city, volume 12, ed. 5, p. 796-807), “Practical Implementation of Successful Interference Cancellation in DS / CDMA Systems” (K. Pedersen, T. Kolding, I. Seskar, J. Holtzman, ICUPC'96, Cambridge, Mass., P. 321 -325). It should be noted that the various steps described can be performed using computing tools included in the ground station 102 or in the network control center NOC 105.

It should also be noted that the calculations are not necessarily performed in real time; usually, correlation operations can be performed after the information necessary for these operations has been stored, depending on the nature of the requested service.

Based on the hypothesis that the same ground station 102 receives all three signals (and so that they have the same communication channel energy potential), it can be shown that P (T, A) is proportional to the EIRP ( equivalent isotropically radiated power) of the transmission of the terminal T and indicators S (T, A) of the quality factor of the rays in the position of the terminal; the same output is suitable for P (T, B) and P (T, C). Since the EIRP is the same in all cases, being one signal transmitted by the terminal, one then has the following three relations of independent EIRP of the transmission terminal:

P (T, A) - P (T, B) = S (T, A) - S (T, B).

P (T, B) - P (T, C) = S (T, B) - S (T, C).

P (T, A) - P (T, C) = S (T, A) - S (T, C).

It should be noted that S (Y, X) (expressed in dB / K) represents the G / T figure of merit associated with cell X for the location of terminal Y.

In accordance with method step 207, three differences P (T, A) - P (T, B), P (T, B) - P (T, C) and P (T, A) - P (T, C) are calculated )

It should be noted that if the EIRP of the terminal were known, it would be possible to directly calculate its figure of merit from the amplitude adopted for each beam. The data of these quality factors enable, by placing oneself on the corresponding line of the quality factor, (see Figs. 3-4) to determine the location of terminal T using only two rays. Nevertheless, the EIRP of the terminal is rarely known with accuracy: it may differ depending on the type of terminal used, depending on the conditions; in addition, the user can try to make her change to change her alleged position. Therefore, the method in accordance with the invention preferably applies the difference in the amplitudes determined in accordance with step 206 for distribution according to the EIRP by calculating the difference in the Q factors associated with two cells for the same terminal T.

The values below are information given for illustrative purposes only. Suppose that the following amplitudes are calculated by demodulators corresponding to the specific EIRP used by the terminal T:

P (T, A) = - 145.4 dBW

P (T, B) = - 147.6 dBW

P (T, C) = - 159.1 dBW.

The following values are displayed based on which are independent of the EIRP terminal:

P (T, A) - P (T, B) = S (T, A) - S (T, B) = 2.2 dB

P (T, B) - P (T, C) = S (T, B) - S (T, C) = 11.5 dB

P (T, A) - P (T, C) = S (T, A) - S (T, C) = 13.7 dB.

It should be noted that the mapping of the lines of the Q-factors, as shown in FIG. 3-5, is, moreover, known (i.e., the line of the Q factor corresponds to the line of the coverage zone for a given beam on which the Q factor contains the same value).

From these lines, it is thus possible to construct lines representing the difference between the figure of merit corresponding to the first ray and the figure corresponding to the second ray. By way of illustration, FIG. 6 represents several DAB lines representing the difference in the Q factors between FIG. 3 and FIG. 4. FIG. 7 represents several DBC lines representing the difference in the Q factors between FIG. 4 and FIG. 5. FIG. 8 represents several DAC lines representing the difference in the Q factors between FIG. 3 and FIG. 5.

According to method step 208, knowing the values of the difference between the Q factors associated with beams A, B and C for the location of terminal T, it is possible to determine the difference lines in the Q factors corresponding to the three values P (T, A) - P (T, B ) = 2.2 dB, P (T, B) - 20 P (T, C) = 11.5 dB and P (T, A) - P (T, C) = 13.7 dB.

FIG. 9 represents the coverage area, as well as the lines of the difference in the quality factors calculated from the Q-factors plotted on the map for the three values of the difference in amplitudes of 2.2 dB, 11.5 dB and 13.7 dB.

According to step 209, it should be inferred based on this position of the terminal T, as located at the intersection of these three lines of difference in quality factors. It should be noted that two lines of difference sufficiently determine the position, while the third serves to clarify the result. On the other hand, the method in accordance with the invention requires the determination of at least three amplitudes in order to achieve the determination of these differences.

Moreover, it should be noted that the assumption was made that the same ground station 102 receives all three signals (and thus that one contains the same energy potential of the communication channel), so the following three relations are checked:

P (T, A) - P (T, B) = S (T, A) - S (T, B).

P (T, B) - P (T, C) = S (T, B) - S (T, C).

P (T, A) - P (T, C) = S (T, A) - S (T, C).

As mentioned above, the method in accordance with the invention is also applied when several ground stations are applied in such a way that three signals transmitted by the satellite are not received by the same ground station.

In this case, suppose that the existence of the reference terminal R is ideally localized in the coverage area and differs from the terminal T, as is known, with good accuracy:

- Q factors S (R, A), S (R, B) and S (R, C) associated with the position of the ground terminal R with respect to cells A, B and C;

- powers P (R, A), P (R, B) and P (R, C) at which the message transmitted by terminal R is received by various ground stations 102A.

The normalized power ratio of terminal T and reference terminal R is the same, regardless of cell A or B; normalized power is set by the ratio between the received power and the quality factor; when the received power and the quality factor are expressed in dB, this ratio is expressed by the difference: P (Y, X) - S (Y, X); therefore, one then contains the relation:

P (T, A) - S (T, A) - (P (R, A) - S (R, A)) = P (T, B) - S (T, B) - (P (R, B ) - S (R, B)).

One derives from this difference S (T, A) - S (T, B), estimated by the relation:

S (T, A) - S (T, B) = P (T, A) - P (T, B) + P (R, A) - S (R, A) - P (R, B) + S (R, B).

Differences S (T, B) - S (T, C) and S (T, A) - S (T, C) are calculated in a similar way. Once differences are obtained, the remainder of the method in accordance with the invention is identical.

The assumption is that the ground station knows in sufficient detail the mapped coverage for various beams (i.e., knows the G / T figure of merit for all points within the service area). These mappings are typically constructed during a test phase called the satellite’s IOT (orbit test). The G / T values for the position may vary for various reasons (satellite movements, thermal effects on reflectors or other components of the satellite). This is likely to result in a loss in the accuracy of the location obtained by the method of the invention. To reduce the resulting error, it is possible to use one or several reference terminals that can be used: these reference terminals, which are controlled by the service operator, are thus “reliable” and calculate their exact position by means of (for example, GPS, EGNOS), in addition to the method in accordance with the invention; reference terminals periodically send “control” messages. For each received message, the ground station knows the exact position of the reference terminal that sent it (for example: the position is fixed and already known; it is communicated through any communication network; it is contained in the control message). By measuring the control message, the ground station will be able to dynamically correct coverage maps in areas corresponding to the positions of the reference terminals and, by interpolation, in the remainder of the coverage area so as to reduce the error in determining the location of the method.

The method in accordance with the invention makes it possible, regardless of the terminal and its power (including for a terminal that does not have high-performance computing means), to determine with good accuracy the location of the terminal on the surface of the coverage area (in this regard, it should be noted that the method does not allow determining the height which the terminal is located). Positioning is performed at the NOC or ground station (s) level, and it can be changed due to erroneous terminal behavior. The method finds particularly interesting application in the case of the construction of certain mobile terminals (usually in the case of transportation of hazardous materials or animals and rescue operations), but also in the case of location of fixed terminals (usually decoders, the use of which is limited to a given territory and for which I would like to check the presence of specified territory). Preferably, in combination with a standard positioning system (eg, GPS), which may have better accuracy, the method according to the invention makes it possible to verify that the position determined by the terminal is genuine (within a certain error interval).

Obviously, the invention is not limited to the embodiment that has been described.

The invention can thus be applied to various types of communication networks using a communication satellite with a multipath antenna, such as a satellite operating in the S, K or X frequency band.

Claims (10)

1. The method (200) for determining the location of the terminal (T) on the surface of the coverage area by means of a communication network (100) for establishing radio frequency connections, the network (100) comprising a communication satellite (103) containing a plurality of beams, referred to as a multipath communication satellite an antenna, wherein said communication satellite with a multipath antenna comprises a multipath antenna, wherein said coverage area consists of a plurality of cells (A, B, C), wherein each cell is associated with at least one beam (A, B, C) for satellite communications (103), which a frequency band, said method comprising the steps of:
- said terminal (T) transmits, via ground-to-board communication channel (201), a message included in a modulated signal including a message to said satellite (103) at a frequency separated by at least three different beams (A, B, C) in the communication channels "ground-to-board", such that the specified message is received using the specified communication satellite through the specified multipath antenna (103) with three different amplitudes;
- the specified communication satellite (103) with a multi-beam antenna transmits (202, 203) via a board-to-ground communication channel of three modulated signals including the specified message, each of the first, second and third signals (S1, S2, S3) corresponds to another ray (A, B, C) from among these three rays;
- ground receiving means (204) receives said first, second and third signals (S1, S2, S3);
- ground-based calculation means (102, 116A, 116B, 116C, 105) determine (205, 206) the amplitudes (P (T, A), P (T, B), P (T, C)) of the message sent by the terminal in said first, second and third signals (S1, S2, S3);
- determine (207, 208, 209) the location of the indicated terminal (T) from the indicated amplitudes (P (T, A), P (T, B), P (T, C)) of the specified message contained in the indicated first, second and third signals. 2. The method (200) according to the preceding paragraph, characterized in that said modulated signal including said message transmitted by said terminal is modulated in accordance with a broadband protocol. 3. The method (200) according to one of the preceding paragraphs, characterized in that said message included in said first signal (S1) is received using said ground receiving means with a larger amplitude (P (T, A)) than that of said messages included in the second and third signals (S2, S3), while this method includes the following steps, in which:
- demodulate (204) the indicated ground-based means (102, 166A) of the calculation of the specified first signal (S1) so as to restore information related to the message:
• message payload;
• parameters of radiation and / or coding of the specified message;
- apply (205) the specified information related to the message to search for the specified message, respectively, in the indicated second and third signals (S2, S3) by the indicated ground-based calculation means (102, 116B, 116C). 4. The method (200) according to the preceding paragraph, characterized in that said signal including said message transmitted by said terminal is modulated in accordance with a broadband protocol, and said recovered radiation and / or encoding parameters comprise a binary broadband sequence. 5. The method (200) according to claim 4, characterized in that said ground-based computing means (102, 116B, 116C) find said message in said second and third signals, respectively, by means of a correlation operation. 6. The method (200) according to the preceding paragraph, characterized in that the transmission (202, 203) of the three indicated modulated signals (S1, S2, S3), including the specified message, via the air-to-ground communication channel via the specified satellite (103) Communication with a multipath antenna occurs at three different frequencies. 7. The method according to the preceding paragraph, characterized in that it includes step (207), which determines at least two of the three differences in amplitudes (P (T, A), P (T, B), P (T, C)) the specified message included in the specified first, second and third signals (S1, S2, S3). 8. The method according to the preceding paragraph, characterized in that it includes:
- step (208), which determines the curves representing the difference in the quality factors corresponding to the specified difference in amplitudes;
- step (209), which determines the location of the specified terminal (T) corresponding to the intersection of these curves. 9. The method according to the preceding paragraph, characterized in that the said ground-based receiving means periodically receive messages through one or more reference terminals, the exact position of which is known, and the indicated position (s) allows correcting the quality factor lines used to determine the position of the indicated terminal. 10. The method according to one of paragraphs. 7-9, characterized in that it determines three differences in the amplitudes (P (T, A), P (T, B), P (T, C)) of the specified message included in the specified first, second and third signals (S1, S2 , S3).

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