Interference free decision feedback channel estimation technique for M-ary orthogonal DS/CDMA systems

We consider interference free decision feedback channel estimation (DFCE) for M-ary orthogonal modulation in direct sequence/code division multiple access (DS/CDMA) systems. The proposed DFCE uses the maximum combiner output in a RAKE receiver as the decision feedback information, enabling M-ary orthogonal signals to be demodulated coherently and a RAKE receiver to use a maximal ratio combining (MRC) scheme. Under multiuser environments, a multistage parallel interference cancellation (PIC) scheme is combined with the DFCE in order to cancel the interference. Accurate knowledge of the channel coefficient estimated by the proposed DFCE is used to regenerate the signal of each user for the multistage PIC scheme. According to the results of our simulations, the performance of coherent demodulation using the proposed system is significantly improved in comparison with conventional noncoherent demodulation.