Pre-Rake schemes for TDD multi-carrier/DS-CDMA

This paper proposes pre-Rake combining schemes for TDD multi-carrier DS/CDMA in the reverse link. Pre-Rake diversity in the reverse link could effectively exploit the channel information of MC/CDMA in the forward link, without significant complexity increase, because the channel estimation part, which is usually the most complex and power-consuming part in a Rake receiver, in this case is the channel estimation used by the receiver to demodulate the received signal. Since MC/DS-CDMA uses several subcarriers, several pre-Rake schemes could be considered. In the first scheme, pre-Rake combining is done after the multi-carrier symbol is converted into time domain signal, the structure of this type of pre-Rake is similar with that used in a single carrier DS/CDMA system. In the second scheme, pre-Rake is performed in each subcarrier of MC/DS-CDMA, prior to MC modulation. The latter scheme is more flexible when the channel condition and the delay profile of each subcarrier is different one to another. The performance of the proposed system is compared using computer simulation.