Joint multipath delay and direction tracking for CDMA array systems

A novel H ^∞ type approach is proposed for tracking the time varying multipath uplink spatio-temporal channel of an asynchronous direct sequence CDMA array system. The proposed approach utilises a bank of novel spatio-temporal preprocessors to deal with the problem of coherent multipath. The signal vector at the output of each of these pre-processors is partitioned into two sub vector signals which provide the starting point for the formation of a parallel bank of ´state-space´ H^∞ type linear combiner matrices. These linear combiner matrices can then be used to obtain estimates of the transformed noise subspaces, upon which the evaluation of a MUSIC-type cost function can be used. This cost function employs the transformed spatio-temporal manifold vectors, and provides jointly the delays and directions of the incident multipath rays associated with the desired user. The proposed approach is able to track extreme multipath channels in which the directions, delays and number of paths vary on a symbol by symbol basis. The theoretical framework is supported by computer simulation studies.