Optimal Rake Receiver for CDMA Communications Using Time-Frequency Analysis

RAKE receiver that is used in both uplink and downlink in CDMA and W-CDMA mobile communications systems is tapping the received signal several times in order to reduce the multipath fading. The conventional rake receiver considers only the time delays due to the arrival of the replicas of the original signal and neglects the effects of Doppler shifts due to the mobility of the receiver which proves to have a significant effect specially at high speed movement of the mobile receiver. At rake fingers the received signal is correlated with the local spread signature and summed to increase the energy of the transmitted signal to provide a bitter correct decision rule for the transmitted binary bits. In this paper instead of the tapping scheme that is used in the classical rake receiver we consider obtaining first an estimate of the channel parameters such as delays, Doppler shifts and attenuation factors who then were adoptively employed into the rake receiver. Our propose channel estimation scheme is based on using the joint time-frequency analysis of the received signal via the discrete evolutionary transform DET. The channel impulse response obtained from the time-frequency kernel leads to the spreading function of the channel which provides a good estimate of all channel parameters required for rake receiver.