Derangement detector in a receiver of a system for data transmission by means of phase modulation of a carrier

Claim 1

A derangement detector in a receiver of a system for data transmission by means of n-phase modulation of a carrier, the receiver comprising a phase discriminator including a calculating unit having input means for receiving digital signals having signal samples occurring at a rate equal to the data symbol rate, said digital signals being representative of the in-phase and quadrature components of a received passband signal at each sampling instant and of the in-phase and quadrature components of a reference carrier at the preceding sampling instant, said calculating unit comprising means for calculating during a first interval of each period samples x 1 and x 1 of signals representative of the in-phase and quadrature components of a signal derived from the passband signal by a phase rotation over an angle equal and opposite to the phase of the reference carrier at the preceding sampling instant, the phase discriminator reproducing the transmitted phase jumps from said signal samples x 1 and x 1 , said phase discriminator further comprising means for increasing during a second interval of each sampling period the phase of the reference carrier by a first additional phase equal to the phase variation of the transmitted carrier corresponding to the phase jump reproduced during said first interval, the derangement detector further comprising (a) a circuit means coupled to said calculating unit for detecting the sign of one of the signal samples x 2 and x 2 supplied by the calculating unit during said second interval, (b) means coupled to said calculating unit for increasing during a third interval of each sampling period the phase of the reference carrier by said first additional phase and also by a second additional phase whose magnitude is equal to π/n and whose sign is opposite to the sign detected by said sign detection circuit, (c) a calculating circuit means coupled to said calculating unit for producing a quantity |x 3 |-kx 3 from the signal samples x 3 and x 3 supplied by the calculating unit during said third interval, where k is a predetermined positive coefficient having a value smaller than tan (π/p), and (d) a circuit means coupled to said calculating circuit for supplying alarm pulses at a negative sign of said quantity |x 3 |-kx 3 .