Joint space-multipath-Doppler RAKE receiving in DS-CDMA systems over time-selective fading channels

Diversity technology is an effective technique to combat channel fading. The conventional RAKE receiver improves the performance of a system through temporal diversity combination of delayed replicas of the same desired signal. The diversity idea behind the RAKE receiver is now extending from time domain to frequency domain (Doppler shift) and space domain (antenna array beamforming). As is well known, fast fading results in a Doppler spread, and the system performance degrades under these time-selective channels. The joint multipath-Doppler RAKE proposed by A. M. Sayeed (see Sayeed et al., 1998; Sayeed and Aazhang, B., 1998; Bhashyam, S. et al., 2000), achieves diversity gains on the time-frequency domain. By combining adaptive antennas with RAKE receivers, space-time 2D RAKE simultaneously exploits space-time diversity. We propose a new receive structure in which the above two 2D RAKE are combined together, providing a joint space-multipath-Doppler three dimensional (3D) RAKE. Although the computation complexity increases a little, the 3D RAKE matched filter output provides a maximum SINR estimate of the signal by optimally combining the desired signals from different paths, different antenna elements and with different Doppler frequency. Numerical simulations illustrate the effectiveness of this novel scheme.