MUI-free receiver for a synchronous DS-CDMA system based on block spreading in the presence of frequency-selective fading

We discuss a synchronous direct-sequence code-division multiple-access (DS- CDMA) system based on block spreading in the presence of frequency-selectiv e fading, Note that block spreading, which is also known as chip interleavi ng, refers to a spreading of a data block sequence, which is obtained by di viding a data symbol sequence into consecutive blocks. For such a system, w e develop a simple new receiver that completely removes the multiuser inter ference (MUI) without using any channel information thence, the name MUI-fr ee receiver). The MUI-free operation is obtained by the use of a shift-orth ogonal set of code sequences on which this receiver is based. Within the fr amework of the MUI-free receiver, we further present a subspace determinist ic blind single-user channel estimation algorithm, As a benchmark for the M UI-free receiver and the corresponding subspace deterministic blind single- user channel estimation algorithm, we consider the linear multiuser equaliz er and the corresponding subspace deterministic blind multiuser channel est imation algorithm developed by Liu and Xu for a standard synchronous DS-CDM A system in the presence of frequency-selective fading, We show that the co mplexity of the MUI-free receiver using the corresponding subspace determin istic blind single-user channel estimation algorithm is much smaller than t he complexity of the linear multiuser equalizer using the corresponding sub space deterministic blind multiuser channel estimation algorithm. We furthe r show that the performance of the MUI-free receiver is comparable with the performance of the linear multiuser equalizer. This is for the case in whi ch the channels are known as well as for the case in which the channels are estimated with the corresponding subspace deterministic blind channel esti mation algorithm.