Method of reducing phase noise at the receiver end of a data transmission system

Apparatus for reducing phase noise at the receiver end of a data transmission system for transmitting multi value symbols at a modulation rate 1/.DELTA.T, the system including, at the receiver end, a decision circuit for supplying an estimate of the originally transmitted symbols on the basis of the symbols actually received, and means prior to the decision circuit for putting the received symbols into complex form y.sub.k with an in-phase component y'.sub.k and a quadrature component y".sub.k, said apparatus for reducing phase noise comprising means for generating a complex phase noise correction coefficient m.sub.k and means for performing complex multiplication of the received symbol in complex form times the complex correction coefficient to obtain a phase noise reduced symbol in complex form for application to the decision circuit, the complex phase noise correction coefficient m.sub.k being generated by said means according to an equation having the form:

• m.sub.k+1 =[m.sub.k -.lambda.(v.sub.k -a.sub.k)y*.sub.k ] exp [-if.sub.k (.epsilon..sub.j)]
• where:
• .lambda. is a real coefficient;
• y*.sub.k is the complex conjugate of the symbol received at instant k.DELTA.T+t.sub.o (where t.sub.o is the instant taken as the origin of time measurements);
• v.sub.k is the symbol applied to the decision circuit at said instant;
• a.sub.k is the estimated value of the received symbol;
• .epsilon..sub.j is an error signal derived from the phase difference between the symbol applied to the decision circuit and the symbol estimated by the decision circuit at instant j.DELTA.T+t.sub.o ;
• and
• F.sub.k (.epsilon..sub.j) is a linear function of at least the error signals .epsilon..sub.j.