Comparison of algorithms for use in adaptive adjustment of digital data receivers

The adaptive technique employs a predetection filter ahead of either a near-maximum-likelihood detector or a nonlinear equaliser, which itself can be considered as a degenerate form of a near-maximum likelihood detector. The authors address in particular the problem of adjusting the tap coefficients of the predetection filter, a process that involves computing the complex roots of complex-valued polynomials. The adjustment technique requires an estimate of the sampled impulse response of the channel over which data is to be transmitted, and involves the location of the roots of the Z-transform of the channel´s sampled impulse response that lie outside the unit circle in the Z-plane. Although the results of the study were obtained using computer-simulation methods, the practical problems of modem implementation, brought about by the need to use finite accuracy, limited speed digital-signal-processing techniques, are considered when attempting to rank the suitability of the algorithms for the particular application of high-speed data communications.<>