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

摘要

Data in the form of multi-value symbols is transmitted at a symbol rate 1/ DELTA T. At the receiver a decision circuit supplies estimates of the transmitted symbols on the basis of the received symbols. The present invention concerns compensating phase noise after equalization, if any, of the received symbols and before application of the received symbols to the decision circuit (38, 39). The received symbols are in complex form with in-phase and quadrature components yk' and yk'' respectively. Phase noise is compensated by complex multiplication in a multiplier (36) of the received symbols by a complex coefficient mk mk+1=[mk- lambda (vk-ak)yk*]exp[-iFk( epsilon j)] where: lambda is a real coefficient; yk* is the complex conjugate of the symbol received at instant k DELTA T+to (where to is the instant taken as the origin of time measurements); vk is the symbol applied to the decision circuit at said instant; ak is the estimated value of the received symbol; epsilon 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+to; and Fk( epsilon j) is a linear function of at least the error signals epsilon j. The invention is particularly applicable to quadrature modulation systems, but if only one channel is transmitted the quadrature channel can be simulated using the Hilbert transform of the one channel.