Intersymbol interference cancellation for 16QAM transmission through nonlinear channels

This paper presents a method for the cancellation of Intersymbol Interference (1%) produced in a typical nonlinear channel with memory. It has been specifically targeted for 16QAM constellations, however could be readily adapted to other modulation schemes. The cancellation method uses a model for the nonlinear channel to predict the IS1 component and then subtract this component from the received signal. There are several equalization techniques presented in the literature for the compensation of nonlinear distortion, such as Maximum Likelihood Sequence Detection (MLSD) [l], Volterra equalization [Z] and RAM based Decision Feedback Equalizer ( D E ) algorithm [3]. Each of these approaches suffer from an exponential growth in complexity with increasing memory. This limits their ability to compensate for signals with small excess bandwidth. The complexity of the technique presented here for IS1 cancellation increases linearly with the amount of memory in the system. This approach does not require a training sequence to he sent and makes an estimate of the channel parameters from the structure of the received signal. This allows the IS1 canceller to track changes in the channel conditions.