Maximuma posteriori decorrelating discrete-time rake receiver

Recently, a discrete-time version of the rake receiver has been proposed, as an alternative to the conventional continuous-time rake receiver, to overcome the need for complex path searching and tracking procedures. This discrete-time version is able to tackle diffuse multipath channels, avoiding by the way any required knowledge on the delays associated to the most significant channel paths. Unfortunately, it has been found to be very sensitive to channel estimation quality and leads to a significant degradation in performance in practice. To reduce this degradation, we propose and investigate in this paper an optimum structure of this discrete-time rake receiver, according to the maximuma posteriori criterion. Derived from an uncorrelated version of the discrete-time channel, provided by the Karhunen-Loève orthogonal expansion theorem, this structure requires for its operation more or less precise estimates of the discrete-time channel statistics. Consequently, for a precise characterization and evaluation of the enhancement in performance provided by this new structure, we propose to use both perfect and estimated statistics of the discrete-time channel. The estimated statistics, derived in conformity with the maximum likelihood criterion, are carried on a symbol-by-symbol basis. The performance of this new structure is evaluated through theoretical and simulation results and compared to that of the conventional discrete-time rake receiver with perfect and estimated discrete-time channel state information. In this evaluation, a diffuse multipath Rayleigh fading propagation channel with classical Doppler power spectrum and exponentially decaying multipath intensity profile is used.