An adaptive QAM linearizer using data postdistortion

Abstract

An adaptive Volterra linearizer for reducing channel nonlinearities in QAM data transmission systems is described and its performance is evaluated. The linearizer is implemented as a modem receiver digital circuit which employs two read-only memories that are programmed to cancel either third or fifth order nonlinearities. The memory outputs are scaled by adaptive coefficients which minimize the channel nonlinearity. In a 64-QAM digital radio system, the linearizer is shown to reduce nonlinear residual error rates by five orders of magnitude.