Space system and method for wireless communication by transmitting radiofrequency and optical signals via return path

Abstract

A communication satellite (20) is provided, configured to transmit an optical signal, through an optical transmission channel, in response to the reception of at least one modulated and encoded radio frequency signal. The satellite comprises: a unit (212) for applying soft demodulation to said at least one received radio frequency signal, and providing N intermediate demodulated data frames B1-n, each frame B1-n comprising a set of digitized soft values; a unit (232) for applying an error correction code to said frames B1-n, and providing N encoded intermediate demodulated data frames B2-n; a unit (234) for interleaving said N frames B2-n, and providing M interleaved data frames I2-m; and a unit (236) for applying, to each frame I2-m, an optical carrier modulation so as to form said optical signal. Figure for the abstract: [Fig.3]

Description

Title of the invention: Space system and method for wireless communication by transmission of radiofrequency and optical signals by return path Technical field

[0001] The present invention relates generally to the space field of communications, and in particular to a wireless communication system and method using, for the return path, optical signal transmissions.

[0002] In recent years, new telecommunications services requiring increased throughput have developed significantly, following the strong competition in the field of terrestrial communication networks. In particular, to meet the need to reduce the digital divide aimed at providing all users with the same quality of service, wherever they are, including users who cannot be connected to the terrestrial network, the transmission capacity requirements of satellite operators have become very significant and have required the deployment of improved very high throughput systems (or HTS / VHTS / UHTS for High / Very High / Ultra High Throughput Systems according to the corresponding English expression).

[0003] However, these capacity demands are such that today traditional satellite wireless communication technologies are reaching their limits. Indeed, such technologies based on the transmission of radiofrequency (RF) waves are experiencing saturation of the usable RF spectral bands, are subject to strong regulatory constraints, and have significant limitations. In this context, optical technologies, capitalizing on the developments in very high-speed terrestrial fiber optic telecoms, constitute a promising alternative for the transmission of very high-speed data for a wide range of applications, such as megaconstellations of telecom satellites, very high-capacity geostationary satellites, high-speed satellite-user point-to-point links, the transmission of large volumes of observation data from satellites to the ground, etc.In addition, these optical technologies allow access to wide frequency bands that are less congested than RF and unlicensed signals, to achieve very high data rates and to reduce the size of on-board and ground terminals.

[0004] However, satellite links for wireless optical communications through the atmosphere are subject to more adverse propagation effects than radiofrequency links. Indeed, the composition of the layers of the atmosphere and the turbulence of the atmosphere induce significant degradations on an optical signal and generate deep fades, thus interrupting the transmission of services for several milliseconds.

[0005] There are solutions for wireless communication satellite systems using optical technologies and, in particular, signal interleaving methods to overcome this problem of fading of optical signals.

[0006] In particular, so-called "regenerative" satellite architectures have been proposed in a wireless communications system using, for the return channel, the complete regeneration of the data from the demodulation and decoding function of the RF signal transmitted by service user equipment. However, such a regenerative architecture has the disadvantage of requiring a very complex implementation on board the satellite. Indeed, regenerative architectures are difficult to implement given the complexity of RF signal reception processing and the very large number of RF carriers to be considered in the case of a deployment of VHTS systems.

[0007] So-called "transparent" satellite architectures are also envisaged in a wireless communications system using, for the return channel, the direct digitization of the RF carriers transmitted by service user equipment. However, such digitization requires the use of a high sampling frequency according to the Nyquist criterion and a very high number of quantization bits, for example greater than about ten bits per sample. Due to such oversampling, the transparent architecture has the disadvantage of a large expansion of the spectral occupation of the signals transmitted on the optical link in the downlink, in order to be able to transmit the high throughput of the digitized RF carriers. The use of a wide optical spectral band also induces the implementation of a greater number of equipment such as high-power optical amplifiers or multiplexers, for example on board the satellite.

[0008] These transparent and regenerative architectures thus present almost inevitable drawbacks which slow down their deployment in the short and medium term.

[0009] There is thus a need for an improved satellite wireless communication system using optical technologies. Summary of the invention

[0010] The present invention improves the situation by proposing a communication satellite configured to transmit an optical signal, through an optical transmission channel, in response to the reception of at least one modulated and encoded radiofrequency signal. The satellite comprises:

[0011] - a flexible demodulation unit configured to apply demodulation flexible to at least one received radio frequency signal, which provides a plurality of N intermediate demodulated data frames B, each intermediate demodulated data frame B, „ comprising a set of digitized soft values;

[0012] - an encoding unit configured to apply an error correcting code to the intermediate demodulated data frames Bbn, which provides a plurality of N encoded intermediate demodulated data frames B2 n;

[0013] - an interleaving unit configured to interleave the N data frames demodulated intermediate encoded B2_n, which provides M interleaved data frames I2m; and

[0014] - an optical carrier modulation unit configured to apply, to each interleaved data frame I2 _ m, a modulation on optical carrier so as to form the optical signal.

[0015] In embodiments, for each intermediate demodulated data frame Bbn, the digitized soft values ​​may be defined according to a Gaussian distribution. The error correcting code applied by the encoding unit may take into account the Gaussian distribution of the digitized soft values ​​of the frames Bi n.

[0016] Advantageously, for each frame of intermediate demodulated data Bbn, each quantization bit of the digitized soft values ​​can be associated with an importance index. The error correcting code applied by the encoding unit can take into account the importance index of the bits of the digitized soft values ​​of the frames Bi n.

[0017] The present invention further provides a communication station configured to receive, through an optical transmission channel, an optical signal associated with a plurality of initial data frames T0_q. The communication station comprises:

[0018] - a demodulation unit configured to demodulate the received optical signal, which provides M frames of demodulated interleaved data I*2_ m ;

[0019] - a deinterlacing unit configured to deinterlace the M frames of demodulated interleaved data I*2.m, which provides a plurality of N frames of deinterleaved data B*2.n;

[0020] - a decoding unit configured to apply a reciprocal function of a error correcting code to the deinterleaved B*2.n data frames, thereby providing a plurality of N decoded B*in data frames, each B*in frame comprising a set of digitized soft values; and

[0021] - a decoding unit configured to apply a decoding function of digitized soft values ​​to the set of N decoded data frames B*in, which provides a plurality of N regenerated data frames T*On, each frame of regenerated data T*on corresponding to a reconstructed frame of initial data T()-n*

[0022] In embodiments, the reciprocal function of the error correcting code applied by the decoding unit may take into account a Gaussian distribution of the soft values ​​of the generated decoded data frames B*bn.

[0023] Advantageously, the reciprocal function of the error correcting code applied by the decoding unit can take into account an importance index associated with each bit of the soft values ​​of the generated decoded data frames B*in.

[0024] The embodiments of the invention thus provide a wireless communication system comprising a communication satellite and a communication station, connected by an optical transmission channel. The communication station is configured to receive the optical signal from the communication satellite, through the optical transmission channel, the reciprocal function being the reciprocal function of the error correcting code applied by the communication satellite.

[0025] In some embodiments, the communication satellite may further comprise a soft-value frame compression unit and the communication station may further comprise a soft-value frame decompression unit.

[0026] Further provided is a method for transmitting an optical signal, the method being implemented in a communications satellite connected to an optical transmission channel. The method comprises the steps of:

[0027] - receive at least one modulated and encoded radiofrequency signal;

[0028] - applying soft demodulation to at least one received radiofrequency signal to determine a plurality of N intermediate demodulated data frames B, each frame Bbn comprising a set of digitized soft values;

[0029] - apply an error correcting code to the demodulated data frames intermediates B, „ to determine a plurality of N frames of encoded intermediate demodulated data B2 „;

[0030] - apply an interleaving function to the demodulated data frames encoded intermediates B2 _n to determine M interlaced data frames I2 m;

[0031] - apply optical carrier modulation to each data frame interlaced I2 _ m, which provides the optical signal; and

[0032] - transmit the optical signal through the optical transmission channel.

[0033] There is also provided a method for receiving an optical signal, the method being implemented by a communication station connected to an optical transmission channel. The method comprises the steps of:

[0034] - receive the optical signal associated with a plurality of initial data frames To q, through the optical transmission channel;

[0035] - apply demodulation to the received optical signal, which provides M frames of demodulated interleaved data I*2 m;

[0036] - apply a deinterlacing function to the interlaced data frames demodulated I*2 m, which provides a plurality of N frames of deinterleaved data B*2n;

[0037] - apply a reciprocal function of an error correcting code to the frames of deinterleaved B*2_n data, which provides a plurality of N frames of decoded B*in data, each B*in frame comprising a set of digitized soft values; and

[0038] - apply a digitized soft value decoding function to all of the N decoded data frames B*in to determine a plurality of N regenerated data frames TVn, each regenerated data frame T*on corresponding to a reconstructed frame of initial data TO n.

[0039] The embodiments of the invention make it possible to improve wireless satellite communication, in terms of data transmission performance for the return path, and occupied optical spectral band.

[0040] They make it possible to obtain an affordable solution, in terms of hardware complexity to implement, mature technological accessibility that can be spatialized today, and energy consumption (resources in digital processing for memory storage for example) on board the satellite, thus transferring a large part of this complexity to the ground communication station.

[0041] They also make it possible to implement a data interleaving solution on board the satellite and to compensate for optical channel turbulence.

[0042] The use of optical technologies and wavelengths, in the wireless communication system according to the embodiments of the invention, makes it possible to take advantage of the absence of optical frequency regulation, the accessible high speeds, the wide availability and the reduced cost of ground-proven optical components corresponding to the benefit of terrestrial telecom research and development efforts. It also allows a reduction in the mass / consumption of optical equipment, the possible synergy with terrestrial networks, and the possible synergy with photonic payloads on board the satellite. Description of figures

[0043] Other characteristics, details and advantages of the invention will emerge on reading the description given with reference to the appended drawings given by way of example.

[0044] [Fig.l] [Fig.l] is a diagram showing a wireless communication system, according to embodiments of the invention.

[0045] [Fig.2] [Fig.2] is a diagram showing a wireless communication device, according to embodiments of the invention.

[0046] [Fig.3] [Fig.3] is a diagram showing a satellite comprising a wireless communication payload, according to embodiments of the invention.

[0047] [Fig.4] [Fig.4] is a diagram showing a communication station, according to embodiments of the invention.

[0048] [Fig.5] [Fig.5] is a flowchart showing the steps of the wireless communication method implemented by the wireless communication payload, according to embodiments of the invention.

[0049] [Fig.6] [Fig.6] is a flowchart representing the steps of the wireless communication method implemented by the communication station, according to embodiments of the invention.

[0050] 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

[0051] [Fig.l] schematically represents a wireless communication system 1 comprising a set of elements communicating with each other, according to embodiments of the invention.

[0052] The wireless communication system 1 is a non-terrestrial network (or NTN for Non-Terrestrial Networks according to the corresponding English expression) communication infrastructure applied to the space domain of communications. By way of illustration, the system 1 may comprise a set 10 of Q wireless communication terminals 10-q, a satellite communication platform 20 and an associated communication station 30.

[0053] The set 10 corresponds to the wireless communication terminals served in the coverage area of ​​the communication satellite platform 20. A wireless communication terminal 10-q (also called 'terminal station' or 'client device') designates a user equipment UE (acronym for 'user equipmenf') configured to transmit and receive data through the system 1. The user equipment, used by an end user, is configured to consume and / or create a service via one or more heterogeneous access communication networks based on a variety of access technologies, standards and protocols. The number Q of terminals in the system is a positive integer greater than or equal to 1. The parameter 'q' denotes an index associated with any wireless communication terminal in the system, and is an integer between 1 and Q.

[0054] 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-q. According to the implementation of the invention, the wireless communications system 1 may comprise one or more space platforms 20 configured in one or more constellations to provide global, national, supranational, or regional coverage for sets of wireless communications terminals. The one or more space platforms 20 may be deployed at different altitudes in various orbits around the Earth to facilitate service coverage over different geographic areas.In some exemplary embodiments, the space platforms may be disposed in a geosynchronous or geostationary Earth orbit (GSO or GEO) at an altitude of 35,786 km from the Earth's surface with an orbital period of 24 hours. In other exemplary embodiments, the space platforms may be disposed, for example, 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).

[0055] The communication station 30 may be a service gateway switching node (or 'gateway node' for Gateway station according to the corresponding English expression) which may be coupled to one or more terrestrial communication networks (not shown in the figures). Such a gateway node 30 thus forms a gateway between the non-terrestrial network communication infrastructure and any type of network or combination of terrestrial communication networks.

[0056] As used herein, the term "service" refers to telephone services, data services, or any other service offered by access network providers to users or subscribers via user equipment. For example, and without limitation, the services may be satellite communications (voice, data, text, video, and / or Internet), land mobile satellite services, maritime mobile satellite services, multimedia broadcasting services, navigation and global positioning services, etc.A service may be constructed from a first generation (IG), second generation (2G), third generation (3G), fourth generation (4G), or fifth generation (5G) cellular communications protocol, a high-speed packet access (or HSPA for High Speed ​​Pocket Access according to the corresponding English expression), high-speed downlink packet access (or HSDPA for High Speed ​​Downlink Packet Access) or uplink packet access. high-speed (or HSDPA for High Speed ​​Uplink Packet Access), an Internet of Things (or loT for Internet of Things) protocol, a digital video broadcasting protocol by satellite communication (or DVB-S for Digital Video Broadcasting - Satellite according to the corresponding English expression), DVB-S second generation (or generation (or DVB-S2), DVB-S2 extension communication (or DVB-S2X), DVB-S by return channel (or DVB-RCS), DVB-RCS second generation (or DVB-RCS2), etc.Examples of user equipment may thus include satellite phones, multi-mode terminals for non-terrestrial network communication, terrestrial cellular communication or Wi-Fi communication, as well as connected vehicles (manual and / or autonomous), network or local gaming consoles, media players, and any portable device such as smart watches, laptops, tablets, mobile phones, IoT sensors, or augmented reality, virtual reality or mixed reality devices, etc.

[0057] The wireless communication system 1 comprises a first transmission channel 40 (commonly called a user link) of one or more links, established between the set 10 of communication terminals and the space platform 20, as well as a second transmission channel 50 (commonly called a feeder link) of one or more other links, established between the space platform 20 and the associated communication station 30. In the remainder of the description, the transmission channel 50 will also be called an 'optical channel'.

[0058] Each transmission channel 40 or 50 comprises uplinks (or UL for uplink in English) and downlinks (or DL ​​for downlink in English). The UL and DL links of the same transmission channel are carried out in the same frequency band or in different frequency bands. For the first transmission channel 40, the UL links correspond to the transfer of data from the 10-q terminals to the space platform 20, and the DL links correspond to the transfer of data from the space platform 20 to the 10-q terminals. For the second transmission channel 50, the UL links correspond to the transfer of data from the communication station 30 to the space platform 20 and the DL links correspond to the transfer of data from the space platform 20 to the communication station 30.Finally, the links between the communication station 30 and the terminals 10-q, via the space platform 20, also called 'round-trip' communications, comprise a forward path and a return path. The forward path corresponds to the UL links between the communication station 30 and the space platform 20, associated with the DL links between the space platform 20 and the terminals 10-q. Similarly, the return path, as shown in [Fig.l], corresponds to the UL links between . the 10-q terminals and the space platform 20, associated with the DL links between the space platform 20 and the communication station 30.

[0059] According to embodiments of the present invention, the wireless communication system 1 comprises the use of a first set of frequencies or frequency bands 4, to carry out the UL links through the first transmission channel 40 for the transfer of data from the terminals 10-q to the space platform 20. The wireless communication system 1 also comprises the use of a second set of frequencies or frequency bands 42 to carry out the DL links through the second transmission channel 50 for the transfer of data from the space platform 20 to the associated communication station 30. The embodiments of the invention make it possible to process the information transfers along the return path of a wireless communication system 1.

[0060] Advantageously, the first set of frequencies is in the radio frequency (RF) domain so that the UL links made through the first transmission channel 40 correspond to the transmission of radio frequency signals. For example and without limitation, the first set of frequencies 4] may correspond to an “X-band” type RF band typically between 8 GHz and 12 GHz, to an “K-band” type RF band typically between 22.5 GHz and 27 GHz, or to an “Ka-band” type RF band typically between 27 GHz and 40 GHz.

[0061] Advantageously, the second set of frequencies 42 is located in the optical domain so that the DL links made through the second transmission channel 50 correspond to the transmission of signals called optical signals. In particular, the second set of frequencies 42 may correspond to a wavelength or to an interval of wavelengths located in the infrared (IR) and near and far infrared domains. For example and without limitation, the second set of frequencies 42 may correspond to the wavelength of 1550 nm.

[0062] Each device 10-q of the wireless communication system 1 is therefore configured to generate one or more radiofrequency communication signals constructed from a communication protocol. Such radiofrequency communication signals are then radiofrequency signals modulated and encoded from data to be transmitted.

[0063] The communication protocol used to form such radiofrequency communication signals can be, for example, defined according to the DVB-RCS2 (Digital Video Broadcasting - Retum Charnel via Satellite - Second Generation) multimedia content transmission standard established by the ETSI standardization body. (European Telecommunications Standards Institute according to the corresponding Anglo-Saxon expression).

[0064] For example, each wireless communication terminal 10-q may comprise a signal generation module 110-q as shown schematically in [Fig.2], and a radiofrequency NTN transmitter 120-q not shown in the figures.

[0065] In embodiments, the signal generation module 110-q may comprise an initial data encoding unit 112-q configured to apply a first error correcting code to an initial data frame To q so as to determine an encoded data frame T iq

[0066] As used herein, the term 'data frame' refers to data packets comprising sets of values ​​or bits (i.e., consecutive digital elements) specified according to a communication protocol.

[0067] A Forward Error Correction code (or FEC code) refers to a technique, in information theory, for detecting and correcting errors affecting data transmitted over a noisy channel. The principle of this technique is the addition (or concatenation), at a transmitter, of redundancy information to the data frame to be transmitted. This redundancy information is then used by a receiver to check and correct errors in the received data frame. Examples of known FEC codes are Reed Solomon codes, used in digital communications, low-density parity-check codes (LDPC), or Turbo codes.

[0068] For example and without limitation, the first error correcting code may be a concatenation of the initial data frame To q with a first redundancy frame T; to form the encoded data frame Ti. q. The first redundancy frame T; then corresponds to a set of parity bits, that is to say a set of bits calculated with respect to the information bits of the initial data frames To q.

[0069] The signal generation module 110-q may also comprise a data modulation unit 114-q on RF carrier configured to apply an amplitude and / or phase modulation of a radiofrequency signal, depending on the encoded data frame Ti q so as to form a radiofrequency communication signal to be transmitted via the radiofrequency NTN transmitter 120-q through the first transmission channel 40. Thus, each frame Ti _ q modulated on an RF signal and transmitted by a terminal of the set 10 comprises a redundancy of one or more redundancy frames T;.

[0070] An error correcting code thus makes it possible to detect and correct errors generated during the transmission of the data To q through the first transmission channel 40 via RF signals.

[0071] [Fig. 3] schematically represents the communication payload of the satellite communication platform 20 comprising an RF signal processing module 210 and an optical signal generation module 230, according to embodiments of the invention.

[0072] The space platform 20 is configured to receive in UL link a signal Si equivalent to a modulated and encoded radiofrequency signal Si.q or a signal Si resulting from an aggregation of several modulated and encoded radiofrequency signals Si.q. The space platform 20 is also configured to transmit in DL link an optical communication signal S2.

[0073] The space platform 20 is also configured to apply soft demodulation to each of the received signals Si. q to determine a plurality of N intermediate demodulated data frames Bi n. The optical communication signal S2 is then generated (or produced) from at least two of the N intermediate demodulated data frames Bi n.

[0074] The number N of data frames demodulated by the space platform 20 is a positive integer greater than or equal to 2. The parameter 'n' designates an index associated with any demodulated data frame, and is an integer between 1 and N. Each received radio frequency signal corresponds to a radio frequency communication signal transmitted by one of the devices 10-q of the set 10 of the wireless communication system 1. Those skilled in the art will understand that N data frames demodulated by the space platform 20 may be previously defined from a single or several radio frequency communication signals. For example and without limitation, a received modulated and encoded radio frequency signal may be associated with a data frame modulated on the RF signal, or a radio frequency signal may comprise a plurality of data frames to be processed.

[0075] It should be noted that the optical communication signal S2 can correspond to a set of optical communication sub-signals.

[0076] The communication payload may also include one or more data storage memories, for example associated with the different units of the radiofrequency signal processing chain to produce the optical signals.

[0077] Advantageously, the space platform 20 may comprise an uplink antenna (not shown in the figures), operating in the first set of frequencies configured to receive the modulated and encoded radiofrequency signal(s) Si.q from wireless communication terminals 10-q. The Space platform 20 may also include a downlink antenna (not shown in the figures), also called an optical terminal or telescope, operating in the second set of frequencies configured to transmit the optical signal S2 to the communication station 30.

[0078] The RF signal processing module 210 comprises a unit 212 for flexible demodulation of the plurality of received RF signals configured to determine a plurality of N intermediate demodulated data frames B,

[0079] Thus, the RF soft demodulation unit 212 is adapted to apply a soft RF demodulation to the modulated and encoded RF signal or plurality of received RF signals, to determine, for each bit associated with each encoded data frame Tbn (or Tbn), a soft value (also called metric value) taking into account the probability of induced noise affecting the RF signal through the first transmission channel 40.

[0080] As used herein, the term 'soft value' refers to a value that is not a hard binary value, such as a '0' or a '1'. In particular, the application of soft RF demodulation induces the determination of log-likelihood ratio (or LLR) values. Each LLR value is a real value and corresponds to a ratio between the probability for a bit to have a value equal to 0 taking into account the received signal and the probability for this same bit to have a bit value equal to 1 taking into account the received signal.

[0081] The RF soft demodulation unit 212 is also adapted to quantize on a certain number of bits each soft value (or LLR value) determined to generate the intermediate demodulated data frame B,

[0082] In particular, an intermediate demodulated data frame Bbn may comprise LLR values ​​coded on a limited number of bits. For example, the LLR values ​​may be coded on less than ten bits.

[0083] In some embodiments, the RF signal processing module 210 may also include a soft-value frame compression unit 214 configured to reduce the size of the plurality of N intermediate demodulated data frames Bbn before being processed by the optical signal generation module 230.

[0084] For example and without limitations, the compression unit 214 may implement an algorithm for quantizing and compressing the LLR value data, defined from different optimization procedures. Such a procedure may be the minimization of the bit error rate between the values ​​of the so-called original LLRs and the values ​​of the so-called reconstructed LLRs by the RF soft demodulation unit 212. A such procedure can also be the maximization on the mutual information between the values ​​of the original LLRs and the values ​​of the reconstructed LLRs.

[0085] The modulated and encoded radiofrequency signals passing through the first transmission channel 40 undergo propagation errors or interference when passing through the atmosphere, according to the Gaussian channel model. As a result, the flexible RF demodulation of RF signals induces a distribution of LLR values ​​defined according to a Gaussian distribution. Advantageously, the compression unit 214 can implement a frame compression algorithm taking into account such a Gaussian distribution of the LLR values.

[0086] For example and without limitations, the compression unit 214 can implement an algorithm taking into account the Gaussian distribution of the LLR values ​​to define non-uniform quantization levels of the LLR value data so as to minimize the quantization noise from one end to the other of a frame of intermediate demodulated data Bbn to be compressed.

[0087] Such an RF signal processing module 210 according to the embodiments of the invention significantly reduces the implementation complexity of the payload linked to the processing of RF signals on a satellite compared to the spatializable technological maturity of a complex regenerative architecture. Such an RF signal processing module 210 also allows a significant gain in terms of memory storage of the different frames during the processing of the intermediate demodulated data frames (i.e. digitized LLR) to produce the optical signals.

[0088] The optical signal generation module 230 comprises an intermediate demodulated data encoding unit 232 configured to apply a second error correcting code to the plurality of N intermediate demodulated data frames Bi n so as to determine a plurality of N encoded intermediate demodulated data frames B2 _n.

[0089] For example and without limitations, the second error correcting code consists of performing a concatenation of an intermediate demodulated data frame Bi n with a second redundancy frame B; to form an encoded intermediate demodulated data frame B2 _n. The second redundancy frame B; then corresponds to a set of parity bits, that is to say a set of bits calculated with respect to the information bits of the intermediate demodulated data frames B,

[0090] Advantageously, the application of the second error correcting code at the level of the encoding unit 232 can take into account the Gaussian distribution of the LLR values ​​induced by the soft RF demodulation of RF signals.

[0091] Furthermore, the digitization of an LLR value over a number K of bits may induce the association of each k-th bit with an importance index, k being an integer between 1 and K. In particular, the first bit of a digitized LLR value may have the highest importance index and the last bit of a digitized LLR value may have the lowest importance index. In other words, the bits associated with the largest (i.e. strong) importance indices represent the parts of the frame (i.e. of the bit stream) that are most critical or important in the frame decoding process. Thus, these parts may benefit from a higher protection order than the bits associated with the lowest importance indices.Advantageously, for each frame of intermediate demodulated data Bbn, the application of the second error correcting code and / or the application of frame compression can also take into account the importance index of each bit of each of the LLR values ​​of the frame.

[0092] For example and without limitations, the second error correcting code can apply to the bits with high importance indices a more robust protection, and therefore more costly in terms of the number of redundancy bits, and to the bits with low importance indices a lighter protection, i.e. associated with a redundancy comprising a small number of redundancy bits.

[0093] For example and without limitations, the encoding unit 232 can implement an algorithm for unequal protection of the bits of a frame against errors, taking into account hierarchical modulation codes or multi-level error correcting codes.

[0094] The optical signal generation module 230 also comprises a data interleaving unit 234 configured to apply an interleaving function to all of the N encoded intermediate demodulated data frames B2 _n, so as to determine a plurality of M interleaved data frames I2 m.

[0095] The number M of interleaved data frames is a positive integer greater than or equal to 1. The parameter 'm' denotes an index associated with any interleaved data frame, and is an integer between 1 and M. The number M may be determined for example from the number N of encoded intermediate demodulated data frames and / or the size of each of these frames. In embodiments, the number M may be equal to the number N.

[0096] An interleaving function uses techniques for interleaving (or mixing) bits between different data frames. In particular, certain so-called 'temporal' interleaving techniques have been developed to counteract optical channel fading experienced by optical signals. An example of an interleaving function may correspond to a so-called 'row-column' interleaving. Such an interleaving function uses a 'block interleaver' filling, row by row, a data matrix of N rows and M columns with input bits or symbols defined from the N intermediate encoded demodulated data frames B2. The interleaving function then determines the M interleaved data frames I2 m using the contents of each column of the resulting data matrix.

[0097] It should be noted that the application of an interleaving function, even if it only lasts a few milliseconds, involves the memory storage of all the N B2 data frames to be interleaved. Thus, a significant gain is obtained, in terms of storage by using LLR values ​​coded on less than ten bits, which makes it possible to obtain communications dedicated to very high speed services by limiting the expansion of the optical band.

[0098] The optical signal generation module 230 also comprises an optical carrier modulation unit 236 configured to apply modulation to an optical signal so as to form an optical communication signal S2 to be transmitted via the downlink telescope through the second transmission channel 50. For example and without limitation, such modulation may be phase modulation, amplitude modulation, frequency modulation, or any combination of modulations, such as phase and amplitude modulation. Optical carrier modulation is applied according to an encoding of the plurality of M interleaved data frames I2 m on the optical signal.

[0099] The modulation of the optical signal can be carried out, for example and without limitations, from an amplitude and phase shift keying modulation (or APSK for Amplitude and Phase-Shift Keying according to the corresponding English expression), a quadrature amplitude modulation (or QAM for Quadrature Amplitude Modulation according to the corresponding English expression), a modulation from the family of phase shift modulations (or PSK for Phase-Shift Keying according to the corresponding English expression) such as a BPSK modulation (Bi or 2-PSK with two possible phase values), a QPSK modulation (Quad or 4-PSK with four possible phase values), or even a DPSK modulation (Differential-PSK).

[0100] The use of a flexible RF signal demodulation unit 212 in the satellite processing module 210 allows the use of a reduced spectral bandwidth on the optical channel. By way of illustration, for LLR values ​​represented on less than ten bits, the width of the spectral bandwidth occupied by the signal S2 can be reduced up to 8 times compared to the spectral bandwidth occupied by an optical signal emitted by a digital transparent architecture.

[0101] In embodiments, the signal S2 may be transmitted to the communication station 30 from a space-based or airborne optical signal relay platform.

[0102] [Fig.4] schematically represents a communication station 30 comprising an optical signal processing module 310 and a data reconstruction module 330, according to embodiments of the invention.

[0103] The communication station 30 is configured to receive the resulting signal S2 transmitted by the space platform 20 in DL link, and to reconstruct the initial data frames TO n.

[0104] Advantageously, the communication station 30 comprises a telescope (not shown in the figures), operating in the second set of frequencies 22, configured to receive the optical signal S2 coming from the space platform 20.

[0105] The optical signal processing module 310 comprises a demodulation unit 312 configured to demodulate the received optical signal S2 to determine a plurality of M demodulated interleaved data frames I*2_ m.

[0106] The demodulation applied by the unit 312 can be defined as a function of the modulation of the optical signal applied by the communication payload of the space platform 20, before the transmission of the optical signal S2. Each demodulated interleaved data frame I*2_ m then corresponds to the associated interleaved data frame I2. m taking into account the fading of the optical channel undergone by the optical signal.

[0107] The optical signal processing module 310 also comprises a data deinterleaving unit 314 configured to apply a deinterleaving function to the set of M demodulated interleaved data frames I*2_m, so as to determine a plurality of N deinterleaved data frames B*2_n.

[0108] The deinterleaving function uses techniques for reordering bits from the different data frames. Each deinterleaved data frame B*2.n then corresponds to the associated encoded intermediate demodulated data frame B2„, taking into account the fading of the optical channel experienced by optical signals.

[0109] Advantageously, the deinterlacing function applied by the unit 314 can be defined as a function of the interlacing applied by the communication payload of the space platform 20 before the transmission of the optical signal S2.

[0110] The optical signal processing module 310 also comprises a unit 316 for decoding transmitted data configured to apply a decoding function to all of the N deinterlaced data frames B*2.n, so as to determine a plurality of N decoded data frames B*i n.

[0111] The decoding function implemented in the unit 316 can be defined as a function of the encoding of intermediate demodulated data (i.e. quantized LLR values) of the communication payload of the space platform 20 corresponding to the error correcting code considered in the module 232. Each decoded data frame B*in then corresponds to the associated intermediate demodulated data frame B, „ taking into account the fading of the optical channel undergone by optical signals.

[0112] For example and without limitation, the decoding function implemented in unit 316 may be a reciprocal function of the concatenation function of the second redundancy frame B; applied to the deinterleaved data frames B*2 n-

[0113] Advantageously, such a decoding function can be implemented by taking into account the expected Gaussian distribution of the LLR values ​​found for each frame of decoded data B*in

[0114] Furthermore, such a decoding function can be implemented by taking into account the importance index of each bit of each of the LLR values ​​found for each decoded data frame B*i n.

[0115] In embodiments where the RF signal processing module 210 of the space platform 20 comprises a soft-value frame compression unit 214, the data reconstruction module 330 may comprise a soft-value frame decompression unit 332 configured to reconstruct the LLR components of the decoded and advantageously compressed B*in data frame.

[0116] For example and without limitation, the soft-value frame decompression unit 332 may be defined as a function of the compression applied by the compression unit 214 of the space platform 20.

[0117] Furthermore, the data reconstruction module 330 may comprise a soft decoding unit 334 configured to apply a decoding function to all of the N decoded data frames B*in (which may optionally be decompressed), so as to determine a plurality of N regenerated data frames T*On- The LLR values, thus recovered at the output of the module 316 (or optionally 332), feed the decoding algorithm of the first error correcting code of the soft decoding unit 334, the first error correcting code having been implemented at the level of the data encoding module 112-q of the signal generation module 110-q of the wireless communication terminal 10-q.

[0118] Each regenerated data frame T*on (or T*oq) then corresponds to the associated initial data frame TO n (or To q) reconstituted (i.e. regenerated) taking into account the fading of the optical channel undergone by the optical signal(s) and the losses suffered by radio frequency signals. Such decoding implemented for example in the form of iterative soft decoding allows sufficient code gain or redundancy to reconstruct the initial data frames TO n from the LLR values ​​reconstructed at the output of the module 310.

[0119] The algorithm used for decoding coded binary data may be, for example, an FEC decoding algorithm corresponding to the type of error-correcting codes used in the 110-q module (i.e., a Viterbi algorithm, a so-called 'BCJR' algorithm, a belief propagation algorithm, a turbo-decoding algorithm, etc.).

[0120] [Fig.5] is a flowchart representing the steps of the transmission process of optical signals, implemented by the communication satellite 20 (and in particular by the communication payload of the space platform), according to embodiments of the invention.

[0121] In step 500, one or a plurality of modulated and encoded radio frequency signals is received by the communications satellite 20.

[0122] In step 510, a soft demodulation of the received RF signal(s) is applied to determine N intermediate demodulated frames B,

[0123] In step 520, a compression of the N intermediate demodulated frames B, „ can be applied.

[0124] In step 530, an encoding of the N intermediate demodulated frames B, „ is applied to determine N encoded intermediate demodulated frames B2 _n, the applied encoding corresponding to a function associated with a second error correcting code.

[0125] In step 540, an interleaving of the N encoded intermediate demodulated frames B2 _n is applied to determine M interleaved frames I2 _m.

[0126] In step 550, modulation on one or more optical carriers of the M interlaced frames I2.m is performed to determine a (resulting) optical signal S2.

[0127] In step 560, the optical signal S2 is transmitted by the communication satellite 20, via the optical transmission channel.

[0128] The modulation, encoding, and compression operations are implemented according to the embodiments described above.

[0129] [Fig.6] is a flowchart representing the process of receiving the or optical signals, implemented by the communication station 30, according to embodiments of the invention, in order to reconstruct the initial data frames associated with the received optical signals.

[0130] In step 600, the optical signal S2 (resulting), transmitted by the communication satellite 20, via the optical transmission channel, is received by the communication station 30.

[0131] In step 610, a demodulation of the received optical signal S2 is applied to determine M demodulated interlaced frames I*2. m.

[0132] In step 620, a deinterlacing of the M demodulated interlaced frames I*2 _ m is applied to determine N deinterlaced frames B*2 _n.

[0133] In step 630, a decoding of the N deinterlaced frames B*2 „ is applied to determine N decoded frames B*i _n. Such applied decoding may correspond to a reciprocal function of the second error correcting code implemented at the level of the communication satellite 20.

[0134] In step 640, a decompression of the N decoded frames B*i „ can be applied.

[0135] In step 650, a decoding of the N decoded frames B*i „ is applied for determine N regenerated data frames T*o n- Such applied decoding may correspond to a reciprocal function of the first correcting code implemented at a 10-q wireless communication terminal.

[0136] The demodulation, decoding, and decompression operations are implemented according to the embodiments described above.

[0137] Those skilled in the art will understand that the wireless communication elements of the system, 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 in the form of 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. For example, the digital processes of the methods of the invention can be implemented on FPGAs or ASICs.These computer program instructions may also be stored in a computer-readable medium.

[0138] The invention is not limited to the embodiments described above as non-limiting examples. It encompasses all the variant embodiments that may be envisaged by those skilled in the art. In particular, those skilled in the art will easily understand that the invention is not limited to the different modules of the space platform and the communication station, described as non-limiting examples.

[0139] Furthermore, those skilled in the art will readily understand that the present invention can be implemented in any NTN architecture involving equipment other than satellites operating at various altitudes lower than so-called 'typical' satellite altitude deployments, depending on the implementation, allocation spectrum, and / or service coverage. For example and without limitation, such equipment may be one or more airborne or space vehicles configured for communications such as high-altitude or low-altitude platform stations, aircraft systems or unmanned aerial vehicles (also called drones), etc.

Claims

Claims

1. Communication satellite (20) configured to transmit an optical signal, through an optical transmission channel, in response to the reception of at least one modulated and encoded radio frequency signal, characterized in that said satellite (20) comprises: - a soft demodulation unit (212) configured to apply a soft demodulation to said at least one received radio frequency signal, thereby providing a plurality of N intermediate demodulated data frames B, each intermediate demodulated data frame Bbn comprising a set of digitized soft values; - an encoding unit (232) configured to apply an error correcting code to said intermediate demodulated data frames Bi n, thereby providing a plurality of N encoded intermediate demodulated data frames B2 _n;- an interleaving unit (234) configured to interleave said N frames of encoded intermediate demodulated data B2 n, which provides M frames of interleaved data I2 m; and - an optical carrier modulation unit (236) configured to apply, to each frame of interleaved data I2 _ m, a modulation on optical carrier so as to form said optical signal.;

2. Communication satellite (20), according to claim 1, wherein, for each intermediate demodulated data frame B, n, the digitized soft values ​​are defined according to a Gaussian distribution, and wherein said error correcting code applied by said encoding unit (232) takes into account said Gaussian distribution of the digitized soft values ​​of the frames Bi n.

3. Communication satellite (20), according to one of claims 1 or 2, in which, for each frame of intermediate demodulated data Bbn, each quantization bit of the digitized soft values ​​is associated with an importance index, and in which said error correcting code applied by said encoding unit (232) takes into account the said importance index of the bits of the digitized soft values ​​of the Bi n frames.

4. Communication station (30) configured to receive through an optical transmission channel an optical signal originating from a satellite and associated with a plurality of initial data frames T0- q, characterized in that said communication station (30) comprises: - a demodulation unit (312) configured to demodulate said received optical signal, thereby providing M demodulated interleaved data frames I*2 m; - a deinterleaving unit (314) configured to deinterleave the M demodulated interleaved data frames I*2 m, thereby providing a plurality of N deinterleaved data frames B*2_n; - a decoding unit (316) configured to apply a reciprocal function of an error correcting code to said deinterleaved data frames B*2_n, which provides a plurality of N decoded data frames B*in, each B*in frame comprising a set of digitized soft values;and - a decoding unit (334) configured to apply a digitized soft value decoding function to the set of N decoded data frames B*in, which provides a plurality of N regenerated data frames T*On, each regenerated data frame T*On corresponding to a reconstructed frame of initial data Tn;

5. 1 0-n* Communication station (30), according to claim 4, wherein said reciprocal function of said error correcting code applied by said decoding unit (316) takes into account a Gaussian distribution of the soft values ​​of the generated decoded data frames B*in.

6. Communication station (30), according to one of claims 4 or 5, wherein said reciprocal function of said error correcting code applied by said decoding unit (316) takes into account an importance index associated with each bit of the soft values ​​of the generated decoded data frames B*in.

7. Wireless communication system (1) comprising a communication satellite (20) according to one of claims 1 to 3, and a communication station (30) according to one of claims 4 to 6, connected by an optical transmission channel, and in that the communication station (30) is configured to receive said optical signal from the communication satellite, through said optical transmission channel, said reciprocal function being the reciprocal function of the error correcting code applied by the communication satellite.

8. A wireless communication system (1) according to claim 7, wherein said communication satellite (20) further comprises a soft-value frame compression unit (214) and said communication station (30) further comprises a soft-value frame decompression unit (332).

9. A method for transmitting an optical signal, the method being implemented in a communication satellite (20) connected to an optical transmission channel, the method comprising the steps of: - receiving (500) at least one modulated and encoded radio frequency signal; - applying (510) a soft demodulation to said at least one received radio frequency signal to determine a plurality of N intermediate demodulated data frames B, „ , each frame Bbn comprising a set of digitized soft values; - applying (530) an error correcting code to said intermediate demodulated data frames Bbn to determine a plurality of N encoded intermediate demodulated data frames B2 _n; - applying (540) an interleaving function to said encoded intermediate demodulated data frames B2.n to determine M interleaved data frames I2 m; - applying (550) an optical carrier modulation to each interleaved data frame I2. m, which provides said optical signal; and - transmitting (560) said optical signal through said optical transmission channel.

10. A method of receiving an optical signal from a satellite, the method being implemented by a communication station (30) connected to an optical transmission channel, the method comprising the steps of: - receiving (600) said optical signal associated with a plurality of initial data frames T0- q, through said optical transmission channel; - applying (610) a demodulation to said received optical signal, thereby providing M demodulated interleaved data frames i*2- m; - applying (620) a deinterleaving function to said demodulated interleaved data frames I*2 m, thereby providing a plurality of N deinterleaved data frames B*2 n; - applying (630) a reciprocal function of an error correcting code to said deinterleaved data frames B*2 n, which provides a plurality of N decoded data frames B*i_n, each frame B*in comprising a set of digitized soft values;and - applying (650) a digitized soft value decoding function to the set of N decoded data frames B*in to determine a plurality of N regenerated data frames T*on, each regenerated data frame T*on corresponding to a reconstructed frame of initial data To-n-;