Method for correcting frequency offset of a signal transmitted between a transmitter and a receiver of a wireless communication system

Abstract

A method of wireless communication between a transmitter and a receiver in relative motion with respect to each other is proposed. The method uses an array of elements for transmitting and / or receiving electromagnetic signals, each weighted by a coefficient (Ck) to form a resulting signal associated with a setpoint radiation pattern in the far field. The method comprises a frequency shift correction relating to a Doppler effect of said resulting signal between the transmitter and the receiver. Said correction comprises: acquiring (320) the relative motion data; determining (340) a phase template of said pattern from said motion data; determining (360), for each element of the array, the complex value of the coefficient (Ck) from said pattern. Said correction further comprises applying (380), to each electromagnetic signal to be transmitted and / or received, said associated coefficient (Ck). Figure for abstract: Fig.3.

Description

Title of the invention: Method for correcting the frequency offset of a signal transmitted between a transmitter and a receiver of a wireless communication system Technical field

[0001] The present invention relates generally to the field of radiofrequency antennas, and in particular to a method for correcting the frequency offset of a communication signal transmitted from a transmitter to a receiver.

[0002] In satellite communication systems, it is known to use solutions for compensating (or correcting) the Doppler effect of a communication signal transmitted between a transmitter and a receiver of the system, in the method of demodulating exchanged information. The known solutions require estimation, correction, implementation of acquisition and tracking loops, or communication with third-party infrastructures, to correct the frequency offset of a transmitted signal. Correcting the frequency offset of a transmitted signal consists of maintaining the state of frequency alignment between the frequency of the signal transmitted at transmission and the frequency of the signal transmitted at reception.

[0003] Such solutions are for example described in US patent 10,862,577 B2 and in the article “Angular partitioning to yield equal Doppler contributions” by O. Norklit and RG Vaughan, IEEE Trans. Veh. Technol., 48(5), pages 1437-1442, 1999.

[0004] These solutions and their implementations are however very costly in terms of time and resources and require a significant computing load and energy consumption, which is particularly critical in space applications associated with devices with reduced or constrained payloads, such as user equipment on the ground or small satellites in orbit.

[0005] There is thus a need for a wireless communication system capable of improving the correction of the frequency offset of a communication signal transmitted between a transmitter and a receiver of the system. Summary of the invention

[0006] To this end, a method of wireless communication between a transmitter and a receiver in relative motion with respect to each other in a wireless communication system is proposed, the method using an array of elements Ek for transmitting and / or receiving electromagnetic signals of the wireless communication system, each electromagnetic signal transmitted and / or received by an element of the array of elements being weighted by a weighting coefficient to form a signal resulting from the electromagnetic signals transmitted from the transmitter to the receiver, the resulting signal being associated with a far-field setpoint radiation pattern. The method comprises correcting a frequency shift relating to a Doppler effect of the resulting signal, the frequency shift corresponding to a difference between the frequency of the resulting signal at the transmitter and the frequency of the resulting signal at the receiver. The frequency shift correction step of the method comprises at least the following steps:

[0007] - acquire relative motion data between the transmitter and the receiver;

[0008] - determine a phase template $ of the set radiation pattern at from relative motion data;

[0009] - determine, for each element of the network, the complex value of the coefficient weighting from the set radiation pattern e(^) of the resulting signal.

[0010] The frequency offset correction step of the method further comprises a step of applying, to each electromagnetic signal to be transmitted and / or received, the associated weighting coefficient, so as to correct the frequency offset between the transmitter and the receiver.

[0011] In some embodiments, all or part of the steps of the method may be implemented on a communications satellite platform placed in orbit of the communications system.

[0012] In embodiments, all or part of the steps of the method may be implemented during the calibration of a satellite communication platform of the communication system, before the launch and placing in orbit of the space platform.

[0013] Advantageously, the relative motion data may be fixed and the method may comprise an analog implementation, in the satellite communication platform, of the unique application of the weighting coefficients to the electromagnetic signals to be transmitted and / or received.

[0014] The relative motion data may be variable and the method may comprise a digital implementation, in the communications satellite platform, of the dynamic application of the weighting coefficients to the electromagnetic signals to be transmitted and / or received.

[0015] According to some embodiments, the method may comprise determining one or more lists of weighting coefficients to be applied based on different predetermined relative motion data.

[0016] The communication satellite platform can be positioned at an altitude z and pointed at the nadir, and the phase template 0 can be defined by the expression ¢( e, z ) = ^.( ( R. + z ) x COS0 - ( + z)We ) • o*9 «* between the transmitter and receiver relative to the nadir, 2 is the wavelength of the carrier for transmitting and / or receiving electromagnetic signals, and Re is the Earth's radius.

[0017] Advantageously, the complex values ​​of the excitation coefficients of the elements of the network Ek can be determined by applying optimization calculations of the setpoint radiation pattern A) of the resulting signal further defined from a non-constant amplitude template A.

[0018] The invention also provides a wireless communication system comprising a transmitter and a receiver in relative motion with respect to each other, the communication system further comprising an array of elements for transmitting and / or receiving electromagnetic signals, each electromagnetic signal transmitted and / or received by an element of the array of elements being weighted by a weighting coefficient to form a signal resulting from the electromagnetic signals transmitted from the transmitter to the receiver, the resulting signal being associated with a setpoint radiation pattern in the far field, the system comprising a correction device configured to correct a frequency shift relating to a Doppler effect of the resulting signal, the frequency shift corresponding to a difference between the frequency of the resulting signal at the transmitter and the frequency of the resulting signal at the receiver. The correction device is configured to:

[0019] - acquire relative motion data between the transmitter and the receiver;

[0020] - determine a phase template 'l' of the setpoint radiation pattern E((})), at from relative motion data;

[0021] - determine, for each element of the network, the complex value of the coefficient weighting from the set radiation pattern e(^) of the resulting signal.

[0022] The correction device is further configured to apply, to each electromagnetic signal to be transmitted and / or received, the associated weighting coefficient, so as to correct the frequency offset between the transmitter and the receiver.

[0023] In embodiments, the wireless communication system may include a communication satellite platform and at least one wireless communication terminal, and the transmitter may be the communication satellite platform and the receiver may be a wireless communication terminal.

[0024] In other embodiments, the wireless communication system may include a communication satellite platform and at least one wireless communication terminal, and the transmitter may be a wireless communication terminal and the receiver may be the communication satellite platform.

[0025] Embodiments of the invention improve data transmission performance of wireless satellite communications.

[0026] They also make it possible to provide an affordable solution in terms of hardware complexity to implement and energy consumption on board the communication satellite, in particular for small satellites with limited computing power, communicating with ground terminals also with very limited computing power, for example in low-power Internet of Things (or loT) applications via satellite or 5G communication via satellite.

[0027] They also make it possible to simplify the signal processing protocol transmitted at the transmitter and / or receiver level and to reduce the connection time of a terminal to a satellite in a wireless communication system.

[0028] The embodiments of the invention advantageously provide a simple solution for passive compensation of the Doppler effect of a transmitted signal by proposing an RF satellite antenna, comprising a conventional structure of an array of elements, managing a transmission channel, between the satellite and any terminal located in a coverage area and being by construction devoid of apparent Doppler effect. Description of the figures

[0029] Other characteristics, details and advantages of the invention will emerge from reading the description given with reference to the appended drawings given by way of example.

[0030] [Fig.l] [Fig.l] is a diagram showing a wireless communication system, according to embodiments of the invention.

[0031] [Fig.2] [Fig.2] is a diagram showing a communication payload of the communication satellite platform of the wireless communication system, according to embodiments of the invention.

[0032] [Fig.3] [Fig.3] is a flowchart showing steps of correcting the frequency offset of a signal transmitted between a transmitter and a receiver of the wireless communication system, according to embodiments of the invention.

[0033] Identical references are used in the figures to designate identical or similar elements. For reasons of clarity, the elements shown are not to scale. Detailed description

[0034] [Fig.l] schematically represents a wireless communication system 1 comprising a set 10 of N wireless communication terminals 10-n and a communication satellite platform 20, according to embodiments of the invention. The wireless communication system 1 is an infrastructure non-terrestrial network communication applied to the space field of communications.

[0035] A 10-n wireless communication terminal (also called an 'end station') refers to a user equipment UE (acronym for 'user equipmenf' in English) configured to transmit and receive data through the system 1. The number N of terminals in the system is a positive integer greater than or equal to 1. The parameter 'n' refers to an index associated with any wireless communication terminal in the system, and is an integer between 1 and N.

[0036] The communications satellite platform 20 (also referred to as a 'space platform' or 'satellite') may be any type of communications satellite in orbit above the Earth's surface configured to serve a coverage area associated with the set 10 of wireless communications terminals 10-n. The communications satellite platform 20 may be deployed at various altitudes z, in different orbits around the Earth. For example and without limitation, the communications satellite platform 20 may be disposed in a circular orbit at an altitude of 35,786 km from the surface. In other exemplary embodiments, the space platforms may be disposed in a medium Earth orbit (MEO) closer to the Earth's surface, in a low Earth orbit (LEO), or in so-called highly elliptical orbits (HEO).

[0037] In the wireless communication system 1, the communication satellite platform 20 is geomobile so as to be in relative motion with respect to each of the wireless communication terminals 10-n of the set 10. In particular, the communication satellite platform 20 is arranged in an orbit defined according to an orbital period other than 24 hours.

[0038] The wireless communication system 1 comprises a transmission channel 30 of one or more links established between the set 10 of communication terminals and the space platform 20. The transmission channel 30 is associated with a set of frequencies located in the radio frequency (RF) domain so that the links, uplink or downlink, made through the transmission channel 30 correspond to the transmission of radio frequency signals. For example and without limitation, such a set of frequencies may correspond to an “X-band” type RF band typically between 8 GHz and 12 GHz, to a “Ku-band” type RF band typically between 12 GHz and 18 GHz, to a “K-band” type RF band typically between 18 GHz and 27 GHz, or to a “Ka-band” type RF band typically between 27 GHz and 40 GHz.

[0039] When transmitting a signal (or RF signal), the wireless communication system 1 can be defined as comprising a transmitter E of the signal and a receiver R of the signal.

[0040] In embodiments, the transmitter E may be the satellite communication platform 20 and the receiver R may be one of the wireless communication terminals 10-n.

[0041] Alternatively, the transmitter E may be one of the wireless communication terminals 10-n and the receiver R may be the communication satellite platform 20.

[0042] In the wireless communication system 1, the transmitter E and the receiver R are therefore in relative motion with respect to each other. The distance d between the transmitter E and the receiver R thus varies over time, that is to say during the transmission of a signal. Thus, the transmission of such a signal, from the transmitter E to the receiver R, undergoes a Doppler effect (also called the Doppler-Fizeau effect) corresponding to a frequency shift observed between the frequency of the signal transmitted at transmission (or signal emitted by the transmitter E, denoted SE) and the frequency of the signal transmitted at reception (or signal received by the receiver R, denoted SR). The transmitted signal SE can be defined from a first set of transmission frequencies f E (or set of transmission wavelengths 2£), and the received signal SR can be defined from a second set of reception frequencies fR (or set of reception wavelengths ^r).The frequency shift due to the Doppler effect, noted A / (or wavelength shift, noted A4), corresponds to the difference between the first set of transmission frequencies fE and the second set of reception frequencies fR.

[0043] [Fig. 2] schematically represents the communication payload of the communication satellite platform 20 comprising a radiofrequency communication satellite antenna 210 for acquiring and / or transmitting RF signals (also called 'RF antenna') and a module 230 for processing and / or generating RF signals, according to embodiments of the invention.

[0044] The RF antenna 210 of the satellite 20 comprises an array of K radiating elements Ek, each element Ek being configured to transmit and / or acquire an electromagnetic signal sk. The number K of radiating elements is a positive integer greater than or equal to 2. The parameter 'k' designates an index associated with any radiating element of the RF antenna, and is an integer between 1 and K.

[0045] The satellite communication platform 20 may consist of a plurality of faces. The RF antenna 210 of the satellite 20 may thus be arranged on one of the faces of the satellite facing the Earth.

[0046] The array of radiating elements may be of any topology. For example and without limitation, each radiating element Ek may be a printed element and / or have a horn shape having an opening oriented towards a common direction d, defined by the transmitter E and the receiver R, as shown in [Fig. 1].

[0047] Advantageously, the array of radiating elements may have a substantially planar structure, defined in a plane (X,Y) associated with an orthonormal reference frame (X,Y,Z). Thus, the array of the RF antenna 210 mounted on board the satellite 20 may generally extend in the plane (X,Y), according to a 2D matrix of radiating elements as shown schematically in [Fig.2] for example.

[0048] In the embodiments where the transmitter E is the satellite communication platform 20 (also called 'transmission mode'), the signal resulting from the K electromagnetic signals sk emitted by the elements Ek corresponds to the emitted signal SE.

[0049] Alternatively, in the embodiments where the receiver R is the satellite communication platform 20 (also called 'reception mode'), the signal resulting from the K electromagnetic signals sk received by the elements Ek corresponds to the received signal SR.

[0050] In the transmission mode, the space platform 20 can be configured to generate each of the K electromagnetic signals sk to be transmitted before transmission. Thus, the module 230 can comprise a unit 232 for producing K electromagnetic signals sk to be transmitted from information to be transmitted and predetermined instruction information for producing electromagnetic signals to generate the signal SE to be transmitted.

[0051] In reception mode, the space platform 20 can be configured to process each of the K electromagnetic signals sk received. Thus, the module 230 can comprise a unit 234 for analyzing the K electromagnetic signals sk received from predetermined setpoint information for processing electromagnetic signals to generate the received signal SR.

[0052] Those skilled in the art will understand that the module 230 for processing and / or generating RF signals may comprise other conventional elements such as one or more digital / analog conversion units, one or more carrier frequency conversion units, one or more distribution units through error correction matrices, one or more amplification units, one or more filtering units, one or more recombination units through error correction matrices, one or more multiplexing units, one or more frequency demultiplexing units, and / or one or more antenna array beamforming units, etc.

[0053] In order to correct the frequency shift due to the Doppler effect between the frequency of the transmitted signal SE and the frequency of the received signal SR, associated with the same signal to be transmitted from the transmitter E to the receiver R, the wireless communication system 1 comprises a correction device 40.

[0054] The correction device 40 comprises a module 250 for acquiring position and orientation data from the communications satellite 20. Such data, associated with the data relating to the orbital period of the satellite 20 (i.e. its speed), correspond to the relative movement data defined between the transmitter E and the receiver R.

[0055] In embodiments, the module 250 may be configured to collect the altitude z and / or attitude data of the space platform 20 at a time 1 during the mission of the satellite 20, i.e. while the space platform 20 is already in orbit. As shown in [Fig. 2], the communication payload of the communication satellite platform 20 may comprise such a module 250 for acquiring position and orientation data of the communication satellite 20.

[0056] According to certain embodiments, the module 250 can be configured to determine, before the launch and placing in orbit of this space platform, the altitude 2 and / or attitude data of the space platform 20 during the mission of the satellite 20.

[0057] As used herein, the notion of “attitude” of the space platform also designates the orientation of the RF antenna 210 defined for example with respect to the Z axis of the orthonormal reference frame (X,Y,Z). In particular, if the Z axis of the RF antenna 210 is directed towards the center of the Earth, then the RF communication satellite antenna 210 is pointed at the nadir. The attitude control of the space platform consists of controlling the orientation in space of the platform and / or the RF antenna, and in particular the so-called pitch, roll and / or yaw movements.

[0058] The correction device 40 further comprises means 402 for calculating weighting coefficients Ck of the electromagnetic signals sk. The weighting coefficients Ck are complex coefficients, also called hereinafter 'complex excitation coefficients'. In transmission mode, each weighting coefficient Ck is applied to an electromagnetic signal sk to be transmitted, before the transmission of said signal. In reception mode, each weighting coefficient Ck is applied to a received electromagnetic signal sk, after acquisition of said signal.

[0059] The weighting coefficients Ck are applied to the electromagnetic signals sk so as to correct the frequency shift due to the Doppler effect, for example via a unit 236 for applying the Doppler effect correction of the module 230 for processing and / or generating RF signals of the space platform 20, as shown in [Fig.2].

[0060] The space platform 20 may comprise for each radiating element Ek of the network a specific reception path and / or a specific transmission path. The separation between the reception and transmission paths thus induces a separation of the unit 236 for applying the Doppler effect correction associated with complex excitation coefficients Ck (R) for each radiating element Ek in reception and complex excitation coefficients Ck (E) for each radiating element Ek in transmission. To facilitate understanding of the invention and for simplification, the remainder of the description will be made mainly with reference to weighting coefficients Ck associated with a single unit 236 for applying the Doppler effect correction, as shown in [Fig.2].

[0061] The unit 236 for applying the Doppler effect correction, implementing the application of the weighting coefficients Ck, may be a Beamformer (or BFN for Beamforming Network) type architecture. Such an architecture may be an analog and / or digital implementation on the space platform 20.

[0062] The electromagnetic signals sk each associated with a radiating element Ek are thus weighted by the weighting coefficients Ck to form (or reconstitute) in the far field the resulting signal (i.e. a useful coherent signal), corresponding to the transmitted signal SE or to the received signal SR. The weighting coefficients Ck provide a gain (or an amplitude) and a phase shift, i.e. a complex multiplicative factor or a complex weighting respectively, to each electromagnetic signal sk.

[0063] As used herein, the term 'far field' refers to a sufficiently large distance from a transmitting or receiving antenna such that the radiation pattern (i.e., electric field) of a resulting RF signal transmitted or received by such an antenna has evolved until it stabilizes due to diffraction. In addition, far field may also refer to the electric field profile of an RF signal at a distance greater than the Fraunhofer distance.

[0064] The calculation means 402 are adapted to calculate (or optimize) the phase shift adjustments of the weighting coefficients Ck and the amplitude adjustments of the weighting coefficients Ck so that the real radiation pattern of the resulting signal in the far field is as close as possible to a setpoint radiation pattern E associated with a radiation template to be satisfied.

[0065] For example and without limitation, such calculation means 402 may use CMA type calculation algorithms (acronym for 'Conjugale Match Algorithm' in English), or conventional beamforming algorithms (or 'Conventional beamforming algorithm' in English).

[0066] In embodiments, the calculation means 402 of the payload of the satellite 20 for calculating the K potential complex values ​​of weighting coefficients Ck can use windowing type calculation algorithms (or ' Windowing' in English) applied, typically during an RF communications satellite antenna design stage, for example in the context of limiting (or weighting) amplitude oscillation of the RF signal in the coverage area.

[0067] In order to correct the frequency shift due to the Doppler effect, the correction device 40 comprises a module 404 configured to determine, from the relative motion data, a phase template of the far-field reference radiation pattern associated with the resulting signal to be transmitted or acquired. Such a phase template corresponds to the radiation template to be satisfied, used by the calculation means 402 to optimize the weighting coefficients Ck.

[0068] Advantageously, the communication payload of the communication satellite platform 20 may further comprise a memory 270 configured to record (i.e. capable of collecting, storing and communicating) for example relative movement data, determined phase template information and / or calculated weighting coefficient Ck data.

[0069] [Fig. 3] represents steps of correcting the frequency offset of a signal transmitted from the transmitter E to the receiver R in relative motion with respect to each other, during a wireless communication method, according to embodiments of the invention.

[0070] The correction device 40 is configured to apply the steps of correcting frequency shift relative to a Doppler effect.

[0071] In embodiments, all or part of the steps of the method may be implemented on the communication satellite platform 20 placed in orbit of said communication system. For example and without limitation, the communication satellite platform 20 may comprise the correction device 40, as shown in [Fig.2].

[0072] According to certain embodiments, all or part of the steps of the method may be implemented during the calibration of the communications satellite platform 20, before the launch and placing in orbit of this space platform. For example and without limitations, the correction device 40 may be a device, partially external to the communications satellite platform 20, used in a center on Earth (also called 'ground segment', and not shown in the figures) to calibrate the communications satellite platform 20.

[0073] As shown in [Fig.3], the method comprises a step 320 consisting of determining or collecting the relative movement data between the transmitter E and the receiver R.

[0074] In step 340, a phase template (1>, of the setpoint radiation pattern EÔjj) in the far field associated with the resulting signal to be transmitted or acquired is determined. The determination of such a phase template <l>is performed from the relative motion data collected in step 320.

[0075] In step 360, for each element of the network, the complex value of a weighting coefficient Ck is determined (or calculated) from the reference radiation pattern E(^) carried out in step 340.

[0076] The method further comprises a step 380 consisting of applying, to each electromagnetic signal sk to be transmitted and / or received, the weighting coefficient Ck determined in step 360 so as to correct the signal frequency shift between the transmitter E and the receiver R due to the Doppler effect.

[0077] In certain embodiments, the calculation means 402 can be associated with calibration means external to the communications satellite platform 20, implemented before the launch of the space platform 20 and its placing in orbit.

[0078] For example and without limitations, in the embodiment where the space platform 20 is stable after deployment of the RF antenna 210 on its orbit not requiring adjustment (i.e. the satellite 20 is in a stable orbit, for a constant altitude z and an attitude, in particular of the RF antenna 210, also constant), the steps of correcting the frequency offset of the signal transmitted from the transmitter E to the receiver R can thus be implemented only once, during the calibration of the RF antenna 210 in the center on Earth, to determine K weighting coefficients Ck to be applied. In this case, the architecture of the unit 236 for applying the Doppler effect correction can be an analog implementation on the space platform 20 so that the application of the weighting coefficients Ck is executed in a unique (or fixed or static) manner.Step 320 may thus consist of determining (or collecting) the constant altitude z and attitude of the satellite 20 during its mission. In this case, in step 340, the phase template $ may be determined from the constant altitude z and attitude.

[0079] Alternatively, in the embodiment where the altitude z and / or the attitude of the space platform 20 is variable during the mission of the satellite 20, the step 380 of applying the weighting coefficients Ck can be implemented directly during the mission in the communication satellite platform 20, and as a function of the variations in altitude z and / or attitude of the space platform 20. The architecture of the unit 236 for applying the Doppler effect correction can thus be a digital implementation on the space platform 20 so that the application of the weighting coefficients Ck is dynamic.

[0080] In embodiments where the altitude z and / or the attitude of the space platform 20 is variable, the steps 320 and 340 of correcting the frequency offset may be implemented during the calibration of the RF antenna 210 (for example via calibration means external to the communication satellite platform 20). For example and without limitation, the method may comprise a sub-step 322 consisting of calculating (or determining or interpolating) a plurality of lists of different potential altitude data z and / or different potential attitude data of the satellite 20 previously defined. In step 340, a phase template 4' may be determined from each of the altitude data z and / or potential attitude data previously defined to form lists of potential phase templates 45.

[0081] Advantageously, the step 360 of correcting the frequency offset can also be implemented during the calibration of the RF antenna 210, so that for each previously defined altitude z and / or potential attitude data (i.e. for each determined potential phase template 0), the associated potential complex values ​​of weighting coefficients Ck are determined (for example calculated or interpolated).

[0082] The method may then comprise a sub-step 362 consisting of recording such lists of potential complex coefficients in a memory, such as for example in the memory 270 of the communication payload of the communication satellite platform 20. In the memory, each list of potential complex coefficients is associated (and linked) to potential specific altitude z and / or attitude data.

[0083] Advantageously, the method may comprise a sub-step 382, ​​implemented during the mission of the satellite 20, consisting of collecting the altitude z and / or attitude data of the space platform 20 at a time 1 (for example via the module 250 of the communication payload of the communication satellite platform 20). This sub-step 382 may be triggered in response to a modification and / or an altitude z correction and / or attitude correction instruction of the satellite 20. Such a correction instruction may be transmitted from a control center on Earth or determined by a position control module of the space platform 20 (not shown in the communication payload in FIG. 2).The method may comprise for example a sub-step 384, consisting of collecting the K potential complex values ​​of weighting coefficients Ck from the set of lists of potential complex coefficients, as a function of the altitude z and / or attitude data determined from the satellite 20 at an instant. The K potential complex values ​​of weighting coefficients Ck collected are then the values ​​to be applied, respectively to each electromagnetic signal sk received or to be transmitted by . a radiating element Ek. ​​The memory 270 can then be configured to transmit the collected values ​​to the unit 236 for applying the Doppler effect correction.

[0084] In other embodiments where the altitude z and / or the attitude of the space platform 20 is variable, the steps of correcting the frequency offset of the signal transmitted from the transmitter E to the receiver R can be implemented on board the space platform 20 comprising the calculation means 402, as shown in [Fig.2],

[0085] For example and without limitation, the frequency offset correction method may be triggered in response to a correction instruction possibly issued by a control center on Earth or in response to a modification of the altitude and / or attitude of the satellite 20.

[0086] Advantageously, step 320 of the frequency offset correction method can be implemented via the module 250 to collect the altitude z and / or attitude data of the space platform 20 at an instant f. Steps 340 and 360 can then be implemented respectively by the module 404 for determining the phase template of the setpoint radiation pattern E(([)) in the far field from the collected altitude z and / or attitude data and by the calculation means 402 of the payload of the satellite 20 to calculate the K potential complex values ​​of weighting coefficients Ck associated as a function of the optimization of the radiation pattern of the resulting signal with respect to the setpoint radiation pattern in the far field.These potential complex calculated values ​​can also be recorded in lists of complex coefficients (for example in the memory 270 of the communication payload of the communication satellite platform 20) which can be used subsequently. The calculation means 402 can in particular be configured to transmit the calculated values ​​to the unit 236 for applying the Doppler effect correction.

[0087] In embodiments where a space platform 20 is at an altitude z and an RF communications satellite antenna 210 is defined according to a 2D array of radiating elements, pointed at the nadir, the phase template <l>can be defined by the following expression (01):

[0088] ^0,z)=^r.((Re+z)x cos0- \)r2 - (Re + z)2si n2() ) (01)

[0089] In the preceding equation (01), Re corresponds to the Earth radius and 0 corresponds to the angle between the transmitter E and the receiver R with respect to the nadir as shown in FIG. 1. In particular, the maximum angle G associated with the phase mask $ is associated with the coverage area of ​​the communication satellite 20 for the set 10 of wireless communication terminals 10-n.

[0090] In equation (01), the parameter 2 designates the wavelength of the carrier (or carrier wave) for transmitting and / or receiving electromagnetic signals at the RF communication satellite antenna 210. Thus, in transmission mode, 2 corresponds to the transmission wavelength and in reception mode, A corresponds to the reception wavelength 2^.

[0091] In other embodiments where the space platform 20 is at altitude z and the RF communication satellite antenna 210 is defined according to a 2D matrix of radiating elements, pointed in any direction, the phase mask can be defined by the following expression (02):

[0092] ^(e,z)=^r.((Re+z)y <cos(B+eQ)-^Re2-(Re+z)hm2(e+60) )(02)

[0093] Dans l’équation (02) précédente, correspond à l’angle de dépointage de la direction de la matrice 2D d’éléments rayonnants par rapport au nadir dans le plan de l’orbite de la plateforme spatiale 20.

[0094] The use of a phase template <l>for the optimization of the radiation pattern of the resulting signal with respect to the set radiation pattern Ei(4>) in the far field, and the determination of complex values ​​of weighting coefficients allow the wireless communication system 1 to carry out a transmission of RF signals undergoing an apparently zero Doppler effect. The relative movement between the transmitter E and the receiver R is notably compensated in the form of a phase shift in the direction d of each radiating element Ek (i.e. dependent on the pointing direction). In other words, the natural scrolling h, as shown in FIG. 1, of the RF communication satellite antenna 210 with respect to the wireless communication terminals 10-n, combined with the induced phase shift in the direction d of each radiating element Ek makes it possible to substantially compensate for the Doppler effect during the signal transmission between the transmitter E and the receiver R.

[0095] In embodiments, the method for correcting the frequency offset may further comprise a step of determining a non-constant amplitude template A of the target radiation pattern a) to optimize the radiation pattern associated with the resulting signal to be transmitted or acquired. As a result, the target radiation pattern may be defined by the following expression (03):

[0096] £(¢, A) =A(0, v?) xexp(ÿ(0, z)) (03)

[0097] In equation (03), the parameter V' corresponds to the azimuth angle around the nadir as shown in [Fig.l].

[0098] The use of a phase template makes it possible to constrain in phase the radiation pattern of the resulting signal in the far field to apply compensation for the Doppler effect. The use of an amplitude template A makes it possible to better control the far field so as not to present oscillations in the radiation pattern of the resulting signal in the far field, which would affect the balance of the downlinks and uplinks between the transmitter E and the receiver R.

[0099] Those skilled in the art will understand that the method, according to the embodiments of the invention, can be implemented in various ways by hardware, software, or a combination of hardware and software, in particular in the form of program code that can be distributed as a program product, in various forms. The program code can be distributed using computer-readable media, which can include computer-readable storage media and communication media. The methods described in the present description can be implemented in particular in the form of computer program instructions executable by one or more processors in a computer computing device. These computer program instructions can also be stored in a computer-readable medium.

[0100] The invention is not limited to the embodiments described above as a non-limiting example. It encompasses all the variant embodiments that may be envisaged by those skilled in the art. In particular, those skilled in the art will understand that the invention is not limited to the different steps of the method and to the different modules and units of the wireless communication system described as non-limiting examples.< / l> < / l> < / l>

Claims

Claims

1. A method of wireless communication between a transmitter and a receiver in relative motion with respect to each other in a wireless communication system, the method using an array of elements (Ek) for transmitting and / or receiving electromagnetic signals of said wireless communication system, each electromagnetic signal transmitted and / or received by an element (Ek) of the array of elements being weighted by a weighting coefficient (Ck) to form a signal resulting from said electromagnetic signals transmitted from the transmitter to the receiver, said resulting signal being associated with a far-field radiation pattern, the method comprising a correction of a frequency shift relating to a Doppler effect of said resulting signal, the frequency shift corresponding to a difference between the frequency of said resulting signal at said transmitter and the frequency of said resulting signal at said receiver,characterized in that the frequency offset correction step comprises at least the following steps consisting of: • acquiring (320) relative motion data between said transmitter and said receiver; • determining (340) a phase template 0 of a setpoint radiation pattern e(^) in the far field, from said relative motion data; • determining (360), for each element of the network (Ek), the complex value of the weighting coefficient (Ck) so that the radiation pattern of said resulting signal in the far field is as close as possible to said setpoint radiation pattern e(^) associated with said template to be satisfied; the frequency offset correction step further comprising a step consisting of applying (380), to each electromagnetic signal to be transmitted and / or received, said associated weighting coefficient (Ck), so as to correct said frequency offset between the transmitter and the receiver.,

2. A communication method according to claim 1, wherein all or part of the steps of the method are implemented on a communications satellite platform (20) placed in orbit of said communications system.

3. Communication method, according to claim 1 or 2, in which all or part of the steps of the method are implemented during the calibration of a communication satellite platform (20) of said communication system, before the launch and placing in orbit of said space platform (20).

4. Communication method, according to claim 3, wherein said relative motion data are fixed and the method comprises an analog implementation, in the communication satellite platform (20), of the unique application of the weighting coefficients (Ck) to the electromagnetic signals to be transmitted and / or received.

5. Communication method, according to claim 2 or 3, wherein said relative motion data are variable and the method comprises a digital implementation, in the communication satellite platform (20), of the dynamic application of the weighting coefficients (Ck) to the electromagnetic signals to be transmitted and / or received.

6. A communication method, according to claim 5, wherein the method comprises determining one or more lists of weighting coefficients (Ck) to be applied based on different predetermined relative motion data.

7. Communication method, according to one of claims 2 to 6, in which said communication satellite platform (20) is positioned at an altitude z and pointed at the nadir, and in which said phase template $ is defined by the expression: ¢(0, z) (Re+z) xcos0-^2- ( + ^)2.sin20 )' 6 being the angle between the transmitter and the receiver relative to the nadir, 2 being the wavelength of the carrier for transmitting and / or receiving electromagnetic signals, and Re being the Earth radius.

8. Communication method, according to one of the preceding claims, in which said complex values ​​of said excitation coefficients Ck of the elements of the network (Ek) are determined by applying optimization calculations of the setpoint radiation pattern A) of said resulting signal further defined from a non-constant amplitude template A.

9. Wireless communication system (1) comprising a transmitter and a receiver in relative motion with respect to each other, the communication system further comprising an array of elements (Ek) for transmitting and / or receiving electromagnetic signals, each electromagnetic signal transmitted and / or received by an element (Ek) of the array of elements being weighted by a weighting coefficient (Ck) to form a signal resulting from said electromagnetic signals transmitted from the transmitter to the receiver, said resulting signal being associated with a far-field radiation pattern, the system comprising a correction device (40) configured to correct a frequency shift relating to a Doppler effect of said resulting signal, the frequency shift corresponding to a difference between the frequency of said resulting signal at said transmitter and the frequency of said resulting signal at said receiver,characterized in that the correction device (40) is configured to: • acquire (320) relative motion data between said transmitter and said receiver; • determine (340) a phase template 0 of a setpoint radiation pattern in the far field, from said relative motion data; • determine (360), for each element of the network (Ek), the complex value of the weighting coefficient (Ck) so that the radiation pattern of said resulting signal in the far field is as close as possible to said setpoint radiation pattern e(^) associated with said template to be satisfied; the correction device (40) being further configured to apply (380), to each electromagnetic signal to be transmitted and / or received, said associated weighting coefficient (Ck), so as to correct said frequency offset between the transmitter and the receiver.,

10. A communication system according to claim 9, wherein said wireless communication system (1) comprises a communication satellite platform (20) and at least one wireless communication terminal (10-n), and wherein said transmitter is the

11. communication satellite platform (20) and said receiver is a wireless communication terminal (10-n). The communication system of claim 9, wherein said wireless communication system (1) comprises a communication satellite platform (20) and at least one wireless communication terminal (10-n), and wherein said transmitter is a wireless communication terminal (10-n) and said receiver is the communication satellite platform (20).

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