Data processing method for generating soqpsk-stc signals, and for processing such signals

Abstract

The invention relates to a data processing method, the method comprising: encoding (S104, S202) a pilot bit sequence according to space-time block coding, so as to produce a first encoded pilot bit sequence and a second encoded pilot bit sequence; encoding (S104, S203) a data stream according to space-time block coding, so as to produce a first encoded stream and a second encoded stream; modulating (S106, S206) a first pilot-inserted encoded stream according to an SOQPSK modulation scheme so as to produce the first signal, the first pilot-inserted encoded stream resulting from periodic insertion of the first encoded pilot bit sequence into the first encoded stream; and modulating (S107, S207) a second pilot-inserted encoded stream according to the SOQPSK modulation scheme so as to produce the second signal, the second pilot-inserted encoded stream resulting from periodic insertion of the second encoded pilot bit sequence into the second encoded stream.

Description

[0001] DESCRIPTION

[0002] TITLE: Data processing method for generating SOQPSK-STC signals, and for processing such signals

[0003] DOMAIN OF INVENTION

[0004] The present invention relates in particular to a processing method for generating signals modulated according to the SOQPSK modulation scheme.

[0005] STATE OF THE ART

[0006] In the context of MISO communication, it is known to emit two SOQPSK-STC signals, which are then received in superposition by a receiver.

[0007] A conventional SOQPSK-STC signal pair is generated as follows:

[0008] • an input data stream is encoded using STC (spatiotemporal block) encoding, which produces a first encoded stream and a second encoded stream.

[0009] • a first sequence of pilot bits is inserted periodically into the first encoded stream, so as to produce a first piloted stream.

[0010] • The first driven stream is modulated according to the SOQPSK (Shaped Offset Quadrature Phase Shift Keying) modulation scheme, so as to produce one of the two SOQPSK-STC signals.

[0011] • Similarly, a second sequence of pilot bits is periodically inserted into the second encoded stream, so as to produce a second driven stream.

[0012] • The second driven stream is modulated according to the SOQPSK modulation scheme, so as to produce the other of the two SOQPSK-STC signals.

[0013] During propagation through a communication channel between a transmitter and a receiver, each SOQPSK-STC signal is attenuated, phase-shifted, and temporally and frequency-shifted by the combined effect of the propagation channel and the transmitter's movement. The pilot bit sequences inserted by the transmitter serve precisely to detect these shifts at the receiver end, in order to resynchronize the two received signals and thus allow their demodulation.

[0014] Such synchronization works correctly when the signal-to-noise ratio (SNR) on the receiver side is relatively high (typically 10 dB), and when the time offset between the two SOQPSK-STC signals induced by the communication channel (also called differential delay) remains small (typically less than 1 / 4 of a "bit time"). But synchronization performance degrades sharply when the SNR becomes low and when the time offset becomes too high.

[0015] DESCRIPTION OF THE INVENTION

[0016] One aim of the invention is to provide a pair of signals using the SOQPSK-STC modulation scheme, which are easier to synchronize on the receiver side in the case of low SNR and in the case of large differential delay.

[0017] A data processing method is proposed for this purpose, the method comprising:

[0018] • encode a sequence of pilot bits according to a block spatio-temporal coding, so as to produce a first encoded sequence of pilot bits and a second encoded sequence of pilot bits;

[0019] • encode a data stream using block-based spatio-temporal coding, so as to produce a first encoded stream and a second encoded stream;

[0020] • modulate a first driven and encoded stream according to an SOQPSK modulation scheme so as to produce the first signal, the first driven and encoded stream resulting from a periodic insertion of the first encoded driver bit sequence into the first encoded stream; and

[0021] • modulate a second driven and encoded stream according to the SOQPSK modulation scheme so as to produce the second signal, the second driven and encoded stream resulting from a periodic insertion of the second encoded driver bit sequence into the second encoded stream.

[0022] In the proposed method, the pilot bit sequence is also STC-encoded. The two encoded pilot bit sequences are nearly orthogonal, making them highly resistant to the differential delay discussed in the introduction. The consequences are a higher probability of detection and improved resistance to differential delay. The proposed method, constituting a first objective, may also include the following optional features, taken alone or in combination.

[0023] Preferably, the pilot bit sequence is one of the p0 and p1 sequences as defined in IRIG 106-20 dated June 20, 2020, prepared by the Telemetry Group. Preferably, the method comprises: periodically inserting the pilot bit sequence into the data stream so as to produce a piloted stream; then encoding the pilot stream using block-time spatio-coding, so as to produce the first and second encoded piloted streams. Preferably, the encoding of the pilot bit sequence and the encoding of the data stream are performed separately; the first encoded bit sequence is periodically inserted into the first encoded stream after the data stream has been encoded; and the second encoded pilot bit sequence is periodically inserted into the second encoded stream after the data stream has been encoded.

[0024] Preferably, the block space-time coding used to encode the pilot bit sequence is different from the block space-time coding used to encode the data stream.

[0025] A second object consists of a data processing device comprising:

[0026] • an encoder configured to encode a sequence of pilot bits according to a block spatio-temporal coding, so as to produce a first encoded sequence of pilot bits and a second encoded sequence of pilot bits;

[0027] • an encoder configured to encode a data stream according to a spatio-temporal block coding, so as to produce to obtain a first encoded stream and a second encoded stream;

[0028] • a first modulator configured to modulate a first driven and encoded stream according to an SOQPSK modulation scheme so as to produce the first signal, the first driven and encoded stream resulting from an insertion of the first encoded bit sequence into the first encoded stream: and

[0029] • a second modulator configured to modulate a second driven and encoded stream according to the SOQPSK modulation scheme so as to produce the second signal, the second driven and encoded stream resulting from an insertion of the second encoded bit sequence into the second encoded stream.

[0030] A third object consists of a signal processing method comprising:

[0031] • to obtain a signal resulting from the transmission by a transmitter to a receiver of a first signal and a second signal, both modulated according to a SOQPSK modulation scheme,

[0032] • correlate the signal with a first pilot signal so as to produce a first correlation signal, the first pilot signal resulting from the application of the SOQPSK modulation scheme to a first encoded pilot bit sequence, the first encoded pilot bit sequence resulting from a block spatiotemporal coding applied to a pilot bit sequence,

[0033] • correlate the signal with a second pilot signal so as to produce a second correlation signal, the second pilot signal resulting from the application of the SOQPSK modulation scheme to a second encoded pilot bit sequence, the second encoded pilot bit sequence also resulting from the block spatiotemporal coding applied to the pilot bit sequence,

[0034] • determine a frame start index in the signal using the first correlation signal and the second correlation signal.

[0035] Preferably, the method constituting the third object comprises: detecting a first peak in the first correlation signal, detecting a second peak in the second correlation signal, and estimating a differential delay between the first signal and the second signal, both modulated according to the SOQPSK modulation scheme, from a time gap between the first peak and the second peak.

[0036] Preferably:

[0037] • The first correlation signal is derived from the modulus of a first complex correlation signal normalized using a norm of the obtained signal and a norm of the first pilot signal.

[0038] • The second correlation signal is derived from the modulus of a second complex correlation signal normalized using the norm of the obtained signal and a norm of the second pilot signal.

[0039] • The process also includes:

[0040] o identify a first peak in the first correlation signal,

[0041] to estimate a first complex gain of a propagation channel between the transmitter and the receiver by normalizing a complex value of the first complex signal in a sample where the first peak has been identified, using the norm of the first pilot signal,

[0042] o Identify a second peak in the second correlation signal, o Estimate a second complex gain of the propagation channel by normalizing a complex value of the second complex signal in a sample where the second peak has been identified, using the norm of the second pilot signal. A fourth object consists of a signal processing device comprising:

[0043] • an input to obtain a signal resulting from the transmission by a receiver to a receiver of a first signal and a second signal, both modulated according to a SOQPSK modulation scheme,

[0044] • a detector configured for:

[0045] o correlate the signal with a first pilot signal so as to produce a first correlation signal, the first pilot signal resulting from the application of the SOQPSK modulation scheme to a first encoded pilot bit sequence, the first encoded pilot bit sequence resulting from block spatiotemporal coding applied to a pilot bit sequence, o correlate the signal with a second pilot signal so as to produce a second correlation signal, the second pilot signal resulting from the application of the SOQPSK modulation scheme to a second encoded pilot bit sequence, the second encoded pilot bit sequence also resulting from block spatiotemporal coding applied to the pilot bit sequence,

[0046] • determine a frame start index in the signal using the first correlation signal and the second correlation signal.

[0047] DESCRIPTION OF THE FIGURES

[0048] Other features, purposes and advantages of the invention will become apparent from the following description, which is purely illustrative and not limiting, and which should be read in conjunction with the accompanying drawings on which:

[0049] Figure 1 schematically illustrates a MISO communication system according to one embodiment.

[0050] Figure 2 schematically illustrates an emitter that forms part of the system in Figure 1.

[0051] Figure 3 schematically illustrates a data processing device according to a first embodiment.

[0052] Figure 4 is a flowchart of steps in a processing procedure implemented by the processing device in Figure 3.

[0053] Figure 5 schematically illustrates a data processing device according to a second embodiment.

[0054] Figure 6 is a flowchart of steps in a processing procedure implemented by the processing device in Figure 5.

[0055] Figure 7 schematically illustrates a receiver that forms part of the system in Figure 1.

[0056] Figure 8 is a flowchart of steps of a process carried out by the receiver of Figure 7. Figure 9 details sub-steps implemented by a pilot decoder according to one embodiment.

[0057] Figure 10, Figure 11, Figure 12 and Figure 13 represent probability of detection curves obtained using several methods in different situations.

[0058] Across all figures, similar elements bear identical references.

[0059] DETAILED DESCRIPTION OF THE INVENTION

[0060] With reference to Figure 1, a MISO (Multiple Input Single Output) radio communication system comprises a transmitter 1 and a receiver 3.

[0061] Transmitter 1 is configured to emit two s0 signals,

[0062]

[0063] with SOQPSK (Spectrally Efficient Offset Quadrature Phase Shift Keying) modulation.

[0064] The two signals s0,

[0065]

[0066] have the same bit rate. In the embodiment shown in Figure 1, the transmitter 1 is an aircraft or a launcher.

[0067] The channel used for the transmission of the two aforementioned signals to receiver 3 can be characterized in particular by the following parameters:

[0068] • h0, h: complex gains of the channel seen respectively by the signals s0,

[0069]

[0070] • T0, Ti: propagation delay between the transmitting and receiving antennas;

[0071] For example, the signals could be telemetry signals during flight tests or for launchers (Ariane, etc.).

[0072] Receiver 3 is designed to receive a signal r resulting from the two signals s0,

[0073]

[0074] transmitted in parallel according to the MISO principle. The received signal r is of the following form (the parameters h, T and fO depend on time):

[0075] r

[0076]

[0077] (t) = [h o s o (t - T0) + h^tt - TJ] e ]27lfot + w(t) where w is a Gaussian white noise, and f0 is a "common" baseband frequency gap, the non-common part being taken into account by the phases of the parameters h0 and h1.

[0078] 1) Issuer and process implemented by the issuer

[0079] With reference to Figure 2, the transmitter 1 comprises a data processing device 10 for generating the two signals s0, and two antennas 12, 14 for emitting these two signals s0 respectively

[0080]

[0081] The data processing device 10 can be implemented in several ways.

[0082] Figure 3 shows a first embodiment of the data processing device 10, which includes: a pre-encoder 100, a multiplexer 102, an encoder 104, a first modulator 106 and a second modulator 107.

[0083] The pre-encoder 100 is configured to apply a forward error correction (FEC) code to an input data stream. Specifically, the pre-encoder 100 can apply a prior art low-density parity-check (LDPC) encoding to the input data stream. The pre-encoder is an optional feature of the processing device 10.

[0084] The multiplexer 102 is configured to insert a pilot bit sequence p into a stream produced by the pre-encoder 100. The pilot bit sequence p is stored in a memory 101.

[0085] The driver bit sequence p comprises N bits. For example, N = 128.

[0086] Encoder 104 is configured to apply STC (spatiotemporal block) coding to a stream produced by the multiplexer. As is known, the encoder produces two encoded streams.

[0087] The first modulator 106 is configured to modulate according to an SOQPSK modulation scheme one of two encoded streams produced by the encoder 104, so as to produce the signal s0.

[0088] The second modulator 107 is configured to modulate according to an SOQPSK modulation scheme the other of the two encoded streams produced by the encoder 104, so as to produce the signal Si.

[0089] We will now describe a process implemented by the emitter 1 according to a first embodiment with reference to figure 4. This process is implemented when the data processing device 10 conforms to the first embodiment shown in figure 3.

[0090] The data processing device 10 receives an input data stream to be processed (i.e., communicated to the receiver 3). In an optional step S100, the pre-encoder 100 applies (if present) FEC coding to the input data stream, so as to produce a pre-encoded stream. This step is known from the prior art.

[0091] In an S102 step, the 102 multiplexer periodically inserts the pilot bit sequence p into the pre-encoded stream, so as to produce a piloted stream.

[0092] The resulting driven stream from this S102 step comprises a succession of blocks alternating between the driver bit sequence p and blocks of M bits from the pre-encoded data stream. For example, M = 3200. In other words, the same driver bit sequence is present in the driven stream in a periodic arrangement (every N+M bits).

[0093] The pilot bit sequence is, for example, the pilot bit sequence denoted "pO" and / or the pilot bit sequence denoted "p1" in the IRIG 106-20 standard dated June 20, 2020, and prepared by the Telemetry Group. These sequences are as follows:

[0094] PO - 1010100010001101 1001 1010110 1 01 00

[0095] 11011 1000 10000000100 1001 0 1000 11 1

[0096] 11 10 0 0 10 10 0 10 10 0 00 0 00 10 0 0 11 10 1 1

[0097] 0010 1 0 11 01 0 1 00 11 01 1 00 0 10 00 1 0 10 1

[0098] Pi 1 11 00 0 11 1 10001 11 0 11 10 1 1 1011000 0 1

[0099] 111100000111000000 1 10110101111 0 01111101011011000000111000001111

[0100] 1 00 11 1110111 1 11 00 1111 1 1 1

[0101] These sequences have autocorrelation properties that can be advantageously exploited by receiver 3, as will be seen later. However, it is possible to use other values ​​for the driver bit sequence p, having analogous properties. In an S104 step, encoder 104 applies STC (spatiotemporal block coding) to the driven stream, so as to produce two driven and encoded streams: a first driven and encoded stream, and a second driven and encoded stream.

[0102] The first controlled and encoded stream comprises a succession of blocks alternating between a first encoded pilot bit sequence p0', which is derived from sequence p, and encoded blocks of M bits which are derived from the M-bit blocks of the controlled stream. In other words, the first encoded pilot bit sequence p0' is present in the first controlled stream according to the same periodic arrangement as the controlled stream provided by the multiplexer (every N+M bits).

[0103] Similarly, the second driven and encoded stream comprises a succession of blocks alternating between a second encoded driver bit sequence p1', which is also derived from sequence p, and blocks of M bits derived from the M-bit blocks of the driven stream. In other words, the second driver bit sequence p1' is present in the second driven stream in the same periodic arrangement as the driven stream provided by the multiplexer (all N+M bits).

[0104] Although their notations are similar, the p0' and p1' sequences are different from the pO and p1 sequences discussed in IRIG 106-20; as stated above, the first encoded pilot bit sequence pO' and the second encoded pilot bit sequence p1' result from an STC encoding applied to the pilot bit sequence p, the contents of which may or may not be those of either the pO and p1 sequences.

[0105] The STC encoding used by the encoder is orthogonal or quasi-orthogonal.

[0106] The steps described above ultimately show that the first driven and encoded stream results from an insertion of the first encoded driver bit sequence into the first encoded stream, and that the second driven and encoded stream results from an insertion of the second encoded driver bit sequence into the first encoded stream.

[0107] In an S106 step, the first modulator 106 modulates the first driven and encoded stream according to an SOQPSK modulation scheme so as to produce the s0 signal.

[0108] In a step S107, the second modulator 107 modulates the second stream driven and encoded according to the SOQPSK modulation scheme so as to produce the signal Si.

[0109] In a transmission stage, antennas 12 and 14 emit the s0 and s0 signals.

[0110]

[0111] in parallel. The orthogonality or near-orthogonality of the applied STC coding has the advantage of mitigating interference between the two antennas 12, 14.

[0112] Figure 5 shows a second embodiment of the processing device comprising: a pre-encoder 200, a first encoder 202, a second encoder 203, a first multiplexer 204, a second multiplexer 205, a first modulator 206 and a second modulator 207.

[0113] The pre-encoder 200 is configured to apply a FEC encoding, for example, the prior art LDPC, to an input data stream. It is identical to the pre-encoder 100. As in the first embodiment, the pre-encoder 200 is an optional component.

[0114] The first encoder 202 is configured to apply STC (block space-time encoding) to the driver bit sequence p. The first encoder 202 produces two encoded driver bit sequences. The driver bit sequence p is stored in memory 201.

[0115] The second encoder 203 is configured to apply STC (spatiotemporal block) coding to a stream produced by the pre-encoder 200. In a manner known per se, the second encoder 203 produces two encoded streams.

[0116] The first multiplexer 204 is configured to insert one of the two encoded pilot bit sequences into one of the two encoded streams produced by the second encoder 203. Similarly, the second multiplexer 205 is configured to insert the other of the two encoded pilot bit sequences into the other of the two encoded streams produced by the second encoder 203.

[0117] The first modulator 206 and the second modulator 207 are respectively identical to the first modulator 106 and the second modulator 107 described previously.

[0118] We will now describe a second emission method implemented by emitter 1 with reference to figure 6, when the processing device conforms to the second embodiment shown in figure 5.

[0119] The data processing device receives an input data stream to be processed.

[0120] In step S200, pre-encoder 200 applies LDPC encoding to the input data stream, producing a pre-encoded stream. This step is similar to step 100. In step S202, first encoder 202 applies first STC encoding to the previously discussed pilot bit sequence p. This step produces a first pilot sequence encoded p0” and a second pilot sequence encoded p1”.

[0121] The first STC encoding used by the first 202 encoder is orthogonal or quasi-orthogonal.

[0122] In step S203, the second encoder 203 applies a second STC (block space-time encoding) to the pre-encoded stream, producing two encoded streams: a first encoded stream and a second encoded stream. The second STC encoding used by the second encoder 203 is orthogonal or quasi-orthogonal. It should be noted that the second STC encoding may be identical or different from the first STC encoding.

[0123] In an S204 step, the first 204 multiplexer periodically inserts into the first encoded stream the first encoded pilot bit sequence p0” (from p), so as to produce a first driven and encoded stream.

[0124] In an S205 step, the second multiplexer periodically inserts into the second encoded stream the second encoded pilot bit sequence p1” (also from p), so as to produce a second driven and encoded stream.

[0125] Ultimately, the first driven and encoded stream resulting from a periodic insertion of the first encoded driver bit sequence into the first encoded stream, and the second driven and encoded stream resulting from a periodic insertion of the second encoded driver bit sequence into the second encoded stream, as was already the case in the first embodiment.

[0126] In an S206 step, the first modulator 206 modulates the first driven and encoded stream according to an SOQPSK modulation scheme so as to produce the s0 signal.

[0127] In an S207 step, the second modulator 207 modulates the second driven and encoded stream according to the SOQPSK modulation scheme so as to produce the signal Si.

[0128] In a transmission stage, antennas 12, 14 emit the s0 signals

[0129]

[0130] and in parallel. It should be noted that steps 200 and 203 of the process are common steps with the process mentioned in the introductory section.

[0131] It should be noted that the S202 step implemented by the 202 encoder can be a preliminary step: the encoded pilot bit sequences p0” and p1” can be stored in a memory of the processing device, and then used in several successive implementations of the S204 step.

[0132] It should be noted that the two controlled and encoded streams produced by the processing devices according to the first and second embodiments are identical when the STC encodings they implement are identical. A difference between these two embodiments lies in the order of the periodic insertions and the STC encodings implemented. But in both cases, a "seed" sequence p is encoded by STC at a certain stage to generate the pair of pilot sequences (pO'; p1') or (pO"; p1"), according to embodiment 1 or 2 respectively, before multiplexing with an encoded stream and SOQPSK modulation. 2) Receiver and process implemented by the receiver

[0133] With reference to Figure 7, the receiver 3 comprises an antenna 30, a sampler 32 and a signal processing device 34.

[0134] Antenna 30 is suitable for receiving the r signal resulting from the two s0 signals,

[0135]

[0136] emitted by transmitter 1, in parallel according to the MISO principle on antennas 12 and 14.

[0137] Sampler 32 is configured to sample the signal into a sampled signal, which is denoted r k and which is supplied to the processing device 34.

[0138] The signal processing device 34 includes a detection filter 340, a frequency synchronizer 342, a driver detector 344, a demodulator / decoder 346 and a post-decoder 348.

[0139] The 340 detection filter is known from the prior art.

[0140] The frequency synchronizer 342 is configured to estimate the frequency f0, which is the "common" baseband frequency deviation generated by the propagation channel between transmitter 1 and receiver 3, and to produce from the signal it receives a frequency-corrected signal, in which the term e ;27r / °fe is removed. Thus, the correction applied by the frequency synchronizer is a multiplication by the term e _;27r / ofe The pilot detector 344 is configured to detect pilot sequences in the signal it receives. Another function performed by the pilot detector is to estimate the aforementioned channel parameters, namely the complex gains h0, h and the propagation delays T0, Tl.

[0141] The 346 demodulator / decoder is configured to demodulate the corrected signal using SOQPSK demodulation. Furthermore, the demodulator / decoder is configured to perform STC decoding, which is a reciprocal processing of the STC encodings performed by the transmitter. To perform these operations, the 346 demodulator / decoder relies on the channel parameters estimated by the pilot detector. The 346 demodulator / decoder is known from the prior art.

[0142] The post-decoder 348 is configured to decode an error-correcting code, inversely to the pre-encoder 100 or 200, according to a method known in the prior art. The post-decoder 348 is an optional component, present when transmitter 1 includes the pre-encoder 100 or 200. The signal processing device 34 also includes a memory storing the first pilot bit sequence encoded p0' or p0” and the second pilot bit sequence encoded p1' or p1”.

[0143] With reference to Figure 8, a process implemented by receiver 3 comprises the following steps.

[0144] In what follows, we will consider that the sequences memorized by receptor 3 are pO' and p1', it being understood that they can be replaced by the sequences pO” and p1” discussed previously.

[0145] In step S300, the receiver antenna 30 receives the signal r resulting from the two signals s0 and Si respectively emitted in parallel by transmitter 1, as discussed previously. In sampling step S302, the sampler samples the signal r into the signal r k discussed previously.

[0146] The sampled signal r k is written:

[0147] r k = r(kT ech ) = [h o s o (kT ech - e0T ech ) + h^tkT^ - e ]27Tf ° kT ^ + w(kT ech )

[0148]

[0149] = [h o s o ,k- £o + e' 2nf “ k + w k

[0150] where T is a period such that: T ecfl =

[0151]

[0152] e0 = and e1 = where F ech is the frequency Tech ec h T e ch

[0153] sampling.

[0154] Next, the signal processing device implements the following steps based on the signal r k .

[0155] In an S340 stage, the 340 detection filter maximizes the signal-to-noise ratio (SNR) and minimizes inter-symbol interference (ISI) in the signal r k according to a method known from the prior art. This step aims to minimize the term w k .

[0156] In a step S342, the frequency synchronizer 342 produces a frequency-corrected signal from the signal supplied by the detection filter 340 according to a known method, to remove the e term i2nf ° kTech in the signal.

[0157] The frequency-corrected signal can be written in the form of a sample vector, as follows:

[0158] r test ~ { r k-Np > r k-Np + l > ■ ■ ■ > r k}

[0159] The pilot detector 344 implements a step S344 called "pilot detection" in Figure 8, but which includes substeps shown in Figure 9. In a substep S400, the pilot detector 344 implements a cross-correlation between the frequency-corrected signal r test and a first pilot signal Po This cross-correlation produces a first complex correlation signal C0( / c) as follows:

[0160] >

[0161] G) (To) ' ^test (0 *

[0162]

[0163] i

[0164] The first pilot signal s Po , is a signal modulated according to the SOQPSK modulation scheme. It was obtained by SOQPSK modulation applied to the first encoded pilot bit sequence p0' stored by receiver 3 (the sequence p0' itself resulting from the STC encoding applied to the sequence p). This preliminary step is performed by receiver 3.

[0165] The 344 pilot detector calculates a first normalized real correlation signal from the first complex correlation signal, as follows:

[0166] 1

[0167] LQ (To) = > I Co (fc) |

[0168] VSkl^estW I 2 J Lk | S Po , (fc) |

[0169]

[0170] 2

[0171] Here, we see that the first correlation signal L Q (k) is normalized according to the standard of signal r test passed to the input of the pilot detector 344 and the standard of the first pilot signal s Po ,(k). More precisely, the magnitude of the signal C0( / c), denoted |C0( / c)|, is divided by the product of the two aforementioned norms, which are respectively VSfcl r test(k)l 2 et JHk\s Po ,(k)\ 2 .

[0172]

[0173] In step S403, the driver detector 344 detects a first peak in the first correlation signal L0( / c). We denote k0 the sample of the signal supplied to the driver detector 344 in which the peak was detected.

[0174] To detect the first peak, the pilot detector compares the first correlation signal L Q (k) with a first correlation threshold denoted L o We have L0( / c0) > C o - In step S405, the pilot detector 344 calculates an estimate

[0175]

[0176] of the complex gain h0 as follows:

[0177] > 1

[0178] ho = : 72 ^o(^o)

[0179]

[0180] Sk|s Po ,(A:) |

[0181] Here we see that the complex gain h0 is estimated by normalizing the complex value C0( / c0) using the norm of the first pilot signal s

[0182]

[0183] Po ( / c). More precisely, the complex value C0( / c0) is divided by the square of the norm of the first pilot signal.

[0184] Similarly, in an S400 step, the pilot detector 344 implements a cross-correlation between the frequency-corrected signal and a second pilot signal s Pi This cross-correlation produces a first complex correlation signal C^k) as follows:

[0185] Cj( / c) * -> P1 / (0

[0186]

[0187] i

[0188] The second pilot signal s Pi , is modulated according to the SOQPSK modulation scheme. The second pilot signal Pi This results from SOQPSK modulation applied to the second encoded pilot bit sequence p1' stored by receiver 3 (p1' itself resulting from STC encoding applied to sequence p). This preliminary step is performed by receiver 3.

[0189] The 344 driver detector calculates a second normalized real correlation signal from the first complex correlation signal, as follows:

[0190] 1

[0191] AiÇfc) = - - - = IQC / c)!

[0192] y / lk\rtestW\ 2 J Ek | s P1 , (k) 1 2

[0193]

[0194] Here, we see the second correlation signal

[0195]

[0196] is normalized according to the signal standard r test eï the standard of the second pilot signal s Pi ,( / c). More precisely, the magnitude of the signal C / c), denoted I / c)!, is divided by the product of the two aforementioned norms, which are respectively j£ k \r test (k)\ 2 and JSk|s P1 ,( / c)| 2 .

[0197]

[0198] In step S402, the driver detector 344 detects a first peak in the first correlation signal L0( / c). We denote k0 the sample of the signal supplied to the driver detector 344 in which the peak was detected.

[0199] To detect the first peak, the 344 pilot detector compares the second correlation signal with a first correlation threshold denoted L. We have LjX / q) > L.

[0200] In step S404, the pilot detector 344 calculates an estimate

[0201]

[0202] of the complex gain h as follows:

[0203] > 1

[0204] Tïi = ■ -J Ci (Ai)

[0205]

[0206] Sk|s P1 ,(A)|

[0207] Here we see that the complex gain h is estimated by normalizing the complex value C^k^ using the norm of the second pilot signal s Pi / ( / c). More precisely, the complex value / q) is divided by the square of the magnitude of the second pilot signal. The pilot detector 344 also calculates an estimated Ar of the differential delay T0-T 1; based on a time difference between the detected samples k0 and k. The driver detector proceeds as follows:

[0208] AT = Ae T ech = +(k0- / q) T ech

[0209] The sign of the estimated differential delay is dictated by the pilot sequence that is detected first, hence the ±.

[0210] It should be noted that the orthogonality of the two STC-encoded pilot signals from the p-seed sequence is sufficiently high that it is possible to derive information about the time delays and channel gains directly from the L0(k) correlation signals and

[0211]

[0212] This is a consequence of the STC coding applied to the "seed" sequence p.

[0213] The two normalized real correlation signals L0(k) and L^k) are also used to detect a frame start index in the signal r k according to a method known from the prior art, in a step S408.

[0214] The method for detecting a frame start index in the signal r k Step S408 may involve a finite state machine. Preferably, the finite state machine locks the start-of-frame index after N consecutive identical detections to reduce detection errors. The state machine also allows the start-of-frame index estimation to be released after M consecutive erroneous detections. This locking and unlocking scheme ensures the stability of the driver detector and its robustness against channel noise fluctuations.

[0215] The metrics used to dimension the parameters N and M of the finite state machine correspond to the false unlock probabilities Pf U and false lockout probabilities Pfi. These probabilities can be directly expressed as a function of the false alarm probabilities Pf a and Pd detection according to the following relationships:

[0216] Pfl = (Pfa)” Pfu = (1 - Pd) M

[0217] The probabilities of false alarms P fa and P detection d depend directly on the correlation properties of the pilot signals used.

[0218] Returning to Figure 8, the process continues with a step S346 during which the demodulator / decoder 346 demodulates the signal r testusing the SOQPSK modulation scheme and applies STC decoding. The result of this step is supposed to correspond to the transmitter's input stream which has undergone STC encoding. Then, in an optional S348 step performed when the post-decoder is present, the 348 post-decoder decodes the stream generated by the demodulator / decoder.

[0219] Comparative results with the IRIG-106 standard process

[0220] Figures 10, 11, 12, and 13 illustrate the advantages on the receiver side 3 of STC encoding to the upstream pilot bit sequences by the transmitter 1. Each of these figures superimposes three curves, each representing the detection probability P d depending on the first threshold L o(which in this example is equal to the second threshold L. Two of the curves are obtained via the method described above, by choosing p = p0 or p = p. The third curve is obtained via the method described in the IRIG-106 standard, in which the pilot bit sequences are not STC encoded on the transmitter side. These figures correspond to the following situations:

[0221] Figure Signal-to-noise ratio Differential delay

[0222] 7 -1 dB Zero

[0223] 8.2 dB Zero

[0224] 9 -1 dB Non-zero

[0225] 10.2 dB Non-zero

[0226]

[0227] We observe that in all cases the probability of detection P d is improved with the proposed process, compared to the process of the IRIG-106 standard. This improvement is particularly significant when there is a substantial differential delay (as reflected in Figures 12 and 13).

[0228] Of course, we can substitute the encoded sequences p0” and p1” for the sequences p0’ and p1’ in the process described above implemented by the receiver 3.

Claims

DEMANDS 1. Data processing method, the method comprising: • encode (S202) a sequence of pilot bits according to a block spatio-temporal coding, so as to produce a first encoded sequence of pilot bits and a second encoded sequence of pilot bits; • encode (S203) a data stream according to a spatio-temporal block coding, so as to produce a first encoded stream and a second encoded stream; • modulate (S206) a first driven and encoded stream according to an SOQPSK modulation scheme so as to produce a first signal, the first driven and encoded stream resulting from a periodic insertion of the first encoded driver bit sequence into the first encoded stream; and • modulate (S207) a second driven and encoded stream according to the SOQPSK modulation scheme so as to produce a second signal, the second driven and encoded stream resulting from a periodic insertion of the second encoded driver bit sequence into the second encoded stream.

2. A method according to the preceding claim, wherein: • the encoding (S202) of the pilot bit sequence and the encoding (S203) of the data stream are performed separately; • the first encoded bit sequence is periodically inserted (S204) into the first encoded stream after the data stream encoding; and • the second encoded pilot bit sequence is periodically inserted (S205) into the second encoded stream after the data stream encoding.

3. A method according to any one of the preceding claims, wherein the block space-time coding used to encode the pilot bit sequence is different from the block space-time coding used to encode the data stream.

4. Data processing method, the method comprising: • periodically insert (S102) a sequence of pilot bits into a data stream so as to produce a piloted stream; • encode (S104) the driven stream according to a block spatio-temporal coding, so as to produce a first driven and encoded stream and a second driven and encoded stream; • modulate (S106) the first driven and encoded stream according to an SOQPSK modulation scheme so as to produce a first signal; and modulate (S107) the second driven and encoded stream according to the SOQPSK modulation scheme so as to produce a second signal.

5. A method according to any one of the preceding claims, wherein the pilot bit sequence is one of the pO and p1 sequences as defined in IRIG 106-20 dated June 20, 2020, prepared by the Telemetry Group.

6. Data processing device (10) comprising: • an encoder (202) configured to encode a sequence of pilot bits according to a block spatio-temporal coding, so as to produce a first encoded sequence of pilot bits and a second encoded sequence of pilot bits; • an encoder (203) configured to encode a data stream according to a spatio-temporal block coding, so as to produce to obtain a first encoded stream and a second encoded stream; • a first modulator (206) configured to modulate a first driven and encoded stream according to an SOQPSK modulation scheme so as to produce a first signal, the first driven and encoded stream resulting from an insertion of the first encoded bit sequence into the first encoded stream: and • a second modulator (207) configured to modulate a second driven and encoded stream according to the SOQPSK modulation scheme so as to produce a second signal, the second driven and encoded stream resulting from an insertion of the second encoded bit sequence into the second encoded stream.

7. Data processing device (10) comprising: • a multiplexer (102) configured to periodically insert a sequence of pilot bits into a data stream so as to produce a piloted stream; • an encoder (104) configured to encode the driven stream according to a spatio-temporal block coding, so as to produce a first driven and encoded stream and a second driven and encoded stream; • a first modulator (106) configured to modulate the first stream driven and encoded according to an SOQPSK modulation scheme so as to produce a first signal; and • a second modulator (107) configured to modulate the second stream driven and encoded according to the SOQPSK modulation scheme so as to produce a second signal.

8. Signal processing method (34) comprising: • obtaining a signal from the transmission by a transmitter to a receiver of a first signal and a second signal, both modulated according to an SOQPSK modulation scheme, • correlate the signal with a first pilot signal so as to produce a first correlation signal, the first pilot signal resulting from the application of the SOQPSK modulation scheme to a first encoded pilot bit sequence, the first encoded pilot bit sequence resulting from a block spatiotemporal coding applied to a pilot bit sequence, • correlate the signal with a second pilot signal so as to produce a second correlation signal, the second pilot signal resulting from the application of the SOQPSK modulation scheme to a second encoded pilot bit sequence, the second encoded pilot bit sequence also resulting from the block spatiotemporal coding applied to the pilot bit sequence, • determine a frame start index in the signal using the first correlation signal and the second correlation signal.

9. A method according to the preceding claim, comprising • detect an initial peak in the first correlation signal, • detect a second peak in the second correlation signal, • estimate a differential delay between the first signal and the second signal, both modulated according to the SOQPSK modulation scheme, from a time difference between the first peak and the second peak.

10. A method according to claim 8 or claim 9, wherein: • The first correlation signal is derived from the modulus of a first complex correlation signal normalized using a norm of the obtained signal and a norm of the first pilot signal. • The second correlation signal is derived from the modulus of a second complex correlation signal normalized using the norm of the obtained signal and a norm of the second pilot signal. • The process also includes: • identify a first peak in the first correlation signal, • Estimate a first complex gain of a propagation channel between the transmitter and the receiver by normalizing a complex value of the first complex signal in a sample where the first peak has been identified, using the norm of the first pilot signal, • Identify a second peak in the second correlation signal, • Estimate a second complex gain of the propagation channel by normalizing a complex value of the second complex signal in a sample where the second peak has been identified, using the norm of the second pilot signal.

11. Signal processing device comprising: • an input to obtain a signal resulting from the transmission by a receiver to a receiver of a first signal and a second signal, both modulated according to a SOQPSK modulation scheme, • a detector configured for: • correlate the signal with a first pilot signal so as to produce a first correlation signal, the first pilot signal resulting from the application of the SOQPSK modulation scheme to a first encoded pilot bit sequence, the first encoded pilot bit sequence resulting from a block spatiotemporal coding applied to a pilot bit sequence, • correlate the signal with a second pilot signal so as to produce a second correlation signal, the second pilot signal resulting from the application of the SOQPSK modulation scheme to a second encoded pilot bit sequence, the second encoded pilot bit sequence also resulting from the block spatiotemporal coding applied to the pilot bit sequence, • determine a frame start index in the signal using the first correlation signal and the second correlation signal.

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