An adaptive space–time receiver for high‐capacity communications systems based on multichannel multirate DS‐CDMA

Abstract

AbstractThe capacity of wireless communications systems based upon Direct‐Sequence Code Division Multiple Access (DS‐CDMA) is severely reduced by Multiple Access Interference (MAI), especially at higher bit rates. Therefore, methods aimed at limiting the MAI are mandatory solutions in order to face the ever‐growing number of subscribers of next‐generation wireless systems. Smart Antennas are a promising technology for improving the performance of high‐capacity mobile communications systems, because they are able to increase the Signal to Interference plus Noise power Ratio (SINR) of the received signals by dynamically adapting the equivalent array beam pattern in order to track the movements of the users within the cell. Moreover, Spatiotemporal RAKE receivers, representing the synergy between beamforming techniques and RAKE receiver structures, are one of the best candidates for the realization of high‐capacity multichannel (CDMA) wireless systems, due to their ability in exploiting both the spatial and temporal diversity inherently offered by wireless channels.This paper is focused on the structure of a Spatiotemporal RAKE receiver for the uplink of multichannel DS‐CDMA systems. Its main feature is the capability of coherently combining the multipaths of the useful signal across both space and time, while simultaneously reducing the MAI. A blind and adaptive beamforming algorithm realizing such a Spatiotemporal RAKE receiver is presented. It exploits the knowledge and the synchronization of the scrambling code uniquely assigned to an addressed user, requiring neither estimates of the spatiotemporal propagation channel nor training or pilot sequences. Its design philosophy consists in the maximization of the SINR at the beamformer output, and it is based upon an orthogonal projection of the received signal onto the linear space generated by the spreading code of the desired user.Computer simulations show the effectiveness of the Spatiotemporal receiver, in terms of convergence speed, SINR gain and bit error probability. Copyright © 2002 John Wiley & Sons, Ltd.