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 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: 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: 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.

Abstract: A method of recovering the carrier for modulation having a large number of states, the method being wherein the demodulated constellation is brought to the monotonic range of a conventional estimator, with sufficient accuracy to enable autonomous operation on this new criterion. The invention also provides apparatus for implementing the method. The invention is particularly applicable to digital ratio beam transmission.

Abstract: An agile microwave filter tunable by ferrite is constituted as a filter having dielectric confinement resonators and as a result comprises an evanescent mode waveguide and resonant cylinders placed in the waveguide. In addition, the cylinders are made of ferrite and means are provided for applying an adjustable magnetic field thereto, thereby enabling the center frequency of the filter to be shifted.

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 digital signal receiver comprises receiver and demodulator means producing from the received signal a succession of complex elements. It produces sequences of successive complex elements consisting of conjugate elements of homologous elements used at the transmitting end. The sequences so used at the receiving end are synchronized to the homologous sequences used at the transmitting end. The complex elements obtained at the output of the demodulator are multiplied by a corresponding sequence of successive complex elements so produced and synchronized. The resultant complex elements appearing during the duration of an information symbol are summed over said duration to produce an estimate of the original information symbols used at the transmitting end. The complex elements obtained at the output of the demodulator are analyzed to identify a marking introduced at the transmitting end.

Abstract: A device for measuring bending movements of an antenna support mast, wherein the device being comprises: at least two sets of sensors separated by a determined distance d and fixed to the mast in the vicinity of the free end of the mast; and a processor for processing the signals by the sensors; the processor including means for memorizing the signals. The invention is particularly applicable to radio beam links.

Abstract: The invention provides a digital radio link receiving device consisting of a microwave frequency part with a device for signal downconversion to an intermediate frequency, an intermediate frequency part limited to direct demodulation of the signal at intermediate frequency, and a baseband part responsible for processing the signal.

Abstract: The invention provide a digital method of correcting non-linearity in a transmission chain, in which the effects of amplifier non-linearities are compensated by applying predistortion in baseband prior to modulation, with the signal being processed digitally in real time. The invention also provides apparatus for implementing the method. The invention is particularly applicable to radio beams for conveying digital signals.

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.

Abstract: A non-intrusive diagnostic system for a transmission channel for a digital modem is appllied to a demodulator-regenerator, and, in each of the channels (14, 15) for the signals demodulated into baseband, it includes an analog-to-digital converter (16, 17) which is clocked by a clock signal at a frequency equal to a multiple of the symbol rate (H), said multiple being not less than twice said rate.

Abstract: A self-adaptive equalizer circuit for a receive using differential demodulation, and in particular for a receiver using a plurality of paths in diversity (1, 2). For each diversity path (1, 2) there is a self-adaptive filter (18, 19) placed before the differential demodulation. The coefficients (CO to Cn) of the filter are updated at each instant KT, where T is the symbol rate period, using the formula:Ci(k)=Ci(k-1)-.mu.. y(k-1). x(k-1)* . e(k)where .mu. is a real number much less than 1, e.g. equal to 0.001, where Ci(k) is the value given to the coefficient (Ci) at instant kT; Ci(k-1) is the value taken by the same coefficient Ci at the instant (k-1)T; y(K-1) is the output signal from the self-adaptive filter, the symbol being sampled at the symbol rate of period T; x(k-i)* is the complex conjugate value of the sample x(k-i) present in the filter at said instant kT and relating to the coefficient Ci; and e(k) is the above-mentioned error at the instant kT.

Abstract: A method of measuring the signature of digital transmission equipment, in which the measurement can be performed during operation without adding special apparatus, and in which: the digital filtering on transmission is varied in order to simulate multiple paths; and the depth of fading is varied at each of a plurality of frequencies until a predetermined error rate is obtained. The invention also provides apparatus for implementing the method. The invention is particularly suitable for use with digital radio links.