Mitigation of multipath effects in broadband wireless systems using quantized state adaptive equalization methods

Broadband wireless systems are currently in a rapid evolutionary phase in terms of development of various technologies, development of various applications, deployment of various services and generation of many important standards in the field. Among the many factors to be considered in the design of these systems, the key factor has been the bandwidth utilization efficiency offered by orthogonal frequency division multiple accessing (OFDM) techniques. However, in severe multipath environments, which may occur, for example, in indoor environments especially for the high-speed data links, the proper operation of the OFDM link requires techniques such as adaptive equalization to overcome the intersymbol interference caused by multipath propagation and channel fading. This paper presents simulation results on the performance of various equalizer algorithms when applied to the OFDM link operating in such a severe multipath environment. The algorithms that are compared include the recursive least squares (RLS) and quantized state (QS) algorithms. While the RLS algorithms are more familiar to the engineers in this field, a set of a number of algorithms termed QS algorithms have also been invented earlier by the first author of this paper and have certain advantages in terms of computational efficiency and numerical robustness. A number of simulation examples are presented showing the bit error rates achieved with the adaptive equalizer algorithms.