Alcatel Transmission Par Faisceaux Hertziens

Alcatel Telspace

Alcatel Transmission Par Faisceaux Hertziens A.t.f.h.

Alcatel N.v.

Philippe Sadot

Marc Darmon

Bertrand Thebault

Jacques Eudes

Marc Pontif

Andre Bazet

Sami Harari

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.

Method of automatically requesting retransmission in a duplex digital

Method of coherent demodulation for phase shift keying and a device for

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).

Method and apparatus for digital data transmission with automatic repeat

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. The invention also relates to apparatus for implementing the method. The invention is particularly applicable to digital radio beams.

Method of detecting a disturbing signal for a digital data demodulator,

In a circuit for decoding convolutional codes for executing the survivor path storage and reverse scanning stage of a Viterbi algorithm, decoding consists in reverse scanning a plurality of paths of a trellis representing a diagram of the possible transitions resulting from encoding by an encoder comprising .nu. flip-flops, each node of the trellis being represented by a word on N=2.sup..nu. bits. The circuit selects from a plurality of possible survivor paths that which has the lowest metric, so as to reconstitute the trellis path actually determined by the encoding process and to recover the sequence of information bits that caused this path to be adopted. The circuit comprises a memory storing a plurality of said words of N=2.sup..nu. bits and, connected to the output of said memory, a cascade of .nu. groups of 2-in-1 multiplexers progressively combining the 2.sup..nu. outputs of the memory into a single output, a D flip-flop being provided at the output of each multiplexer. The final single flip-flop delivers sequentially the information bits representing the required path and the select signal of each multiplexer is the output signal of said final flip-flop.

Circuit for decoding convolutional codes for executing the survivor path

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.

Method of establishing an inverse pilot-sequence for deinterleaving as

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.

Interleaving method for a digital transmission system

A method of detecting erasures in a digital radio link conveying a signal which is encoded prior to modulation and transmission of the signal by means of an error correcting code having a low covering radius which signal is demodulated and decoded, after which a flag signal is generated whenever the error correcting capacity of said decoding is exceeded, and said capacity-exceeded flag signal is integrated in order to obtain an erasure flag signal.

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Paris, France

Philippe Sadot