Abstract: A go-back-N automatic repeat request method for use on a duplex installation having noisy return channels. When an acknowledge signal (ACK) is not correctly received, it is assumed to be positive until the Nth successive incorrectly received acknowledgement, which is treated as a negative acknowledgement, thereby ensuring that blocks are repeated even if acknowledgements are degraded by jamming.

Abstract: A method and apparatus for coherent demodulation for phase shift keyed signals including:a phase estimation stage based on a sequence of reference symbols transmitted at the start of each block of data anda second order phase-locked loop stage.

Abstract: A method and apparatus for sequential decoding using the stack algorithm. A stack is used which is small in size and which has a leaky bottom. A counter stores the total count of nodes observed so as to abandon decoding if this count exceeds a fixed value. A comparator continuously compares the metric at the top of the stack with the largest metric lost from the bottom of the stack as stored in a memory. A small memory stores the path scanned through the logic tree, thereby directly providing the decoded block.

Abstract: A method of detecting a disturbing signal for demodulating digital data, wherein, on the modulated signal transposed into baseband, the disturbing signal is detected by periodically inserting known signals by means of a fixed guard time delay ((R+I)T.sub.s) applied to the received signal prior to demodulation, and wherein said method includes: a step of estimating the square of the modulus of the cross-correlation of the received referenced signal and of the expected signal at a determined instant when the reference signal is assumed to be present; a step of estimating the square of the correlation of the received signal at the same instant, of multiplying by a coefficient which represents the square of the threshold for the estimated correlation coefficient, and of multiplying by the number of reference symbols used in a reference burst; and a step of comparing with each other the two quantities obtained simultaneously during the preceding two steps.

Abstract: Enough room is provided in a transmitted frame to receive a plurality (n) of useful information blocks, thereby making it possible to catch up any excessive lateness (r) which may arise due to successive repeats. The decoder (2) provides a confidence flag (3) to the controlling microprocessor (5). The command block (COM) from the decoder includes an indication of the number of useful blocks that are transmitted in the frame. This block is advantageously applied to an HDLC component (8).

Abstract: A method of establishing an inverse pilot sequence for deinterleaving as used in digital transmission, with the interleaving being performed by means of a transmit register and a pilot sequence. Each portion (2 5 1 4 3 6) of the inverse pilot sequence is obtained from the preceding portion (3 1 6 5 4 2) of the inverse pilot sequence and from the two corresponding portions (2 6 1 5 4 3, 4 1 3 6 5 2) of the pilot sequence, with the k-th element of the N-th portion of the inverse pilot sequence being determined by observing the rank of the k-th element in the (N-1)-th portion of the pilot sequence in the N-th portion of the pilot sequence, and then in selecting the element to be found at this rank in the (N-1)-th portion of the inverse pilot sequence.

Abstract: A psuedo-random interleaving method suitable for use in transmitting digital data. A pseudo-random pilot sequence is used for simultaneously reading from and writing to a vector of size Tv.gtoreq.Tc.times.Lm, the pilot sequence satisfying a minimum distance law Lm, except when blocking occurs. Deinterleaving is performed symmetrically by means of an inverse pilot sequence suitable for reconstituting successive code words.