Equalizer for complex data signals

摘要

In a data receiver (40) for a quadrature-amplitude-modulated signal s(t) having symbol interval T, line samples (sk) are formed at a sampling frequency n/T which is at least equal to the Nyquist frequency. With the sampling being performed at this rate, the functions conventionally provided by individual bandpass filter (12), phase splitter (14) and equalizer (22) circuits are performed by a single transversal filter equalizer (122). Tap coefficients for the transversal filter equalizer are derived in a decision-directed manner. The tendency of the tap coefficient values to drift is suppressed by adding energy to the received signal at frequencies within the band (0-n/2T) Hz at which the received signal has negligible energy.