Abstract: A search method for acquisition of time synchronization between a spreading sequence of a receiver and a spreading sequence of a transmitter, the receiver receiving a spread signal and demodulating the signal using the spreading sequence of the receiver includes a test step consisting in measuring the energy of the demodulated signal by integrating the demodulated signal during a time interval Tobs.sub.i and comparing that energy with a threshold value to determine if the threshold value is exceeded, for a given hypothesis as to the time shift between the spreading sequences, and modifying the time shift hypothesis if the threshold value is not exceeded and incrementing the value of a counter. Steps a and b are repeated until the value of the counter reaches a predetermined value. When the predetermined value is reached, the time interval Tobs.sub.i is replaced with a time interval Tobs.sub.i+1, with Tobs.sub.i+1 =m.Tobs.sub.i and m>1, and the process resumes at step a replacing Tobs.sub.i with Tobs.sub.

Abstract: In a method of detecting reference symbols in a digital data stream constituted by successive frames, each frame contains R reference symbols and I information symbols, and the R reference symbols are uniformly spaced apart in the digital data stream. The received signal is sampled with a period T.sub.e =T.sub.s /N.sub.e, where N.sub.e is an integer not less than 2, and T.sub.s is the symbol time. A cross-correlation is calculated, with each calculated cross-correlation supplying a magnitude I.sub.n equal to: ##EQU1## where x.sub.n+dNe represents the sample received at instant n+dN.sub.e, S*.sub.d,k represents the complex conjugate of the reference symbol of index d, k .epsilon. {0, . . . , R-1} and represents frame index, r=R/q, where q is an integer not less than 1. The cross-correlations are summed over M frames so as to form energy levels J.sub.M,d equal to: ##EQU2## where m is the frame index, M is the number of sums performed, and d .epsilon. {0, . . . , N.sub.e (R+1)-1}.

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 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.