The performance of a multistage quasi-orthogonal minimum output energy multiuser detector for convolutionally coded CDMA systems in multipath environment

This work presents the performance of the multistage quasi-orthogonal minimum output energy (QOMOE) multiuser detector (MuD) for a convolutionally coded synchronous CDMA system. The QOMOE detector minimizes the output variance with respect to the component equivalent to the quasi-orthogonal component to the desired user´s signature waveform, then the solution is the linear minimum mean square error (LMMSE) transformation. The multistage QOMOE receiver employs maximal-ratio combiner (QOMOE-MRC) for detection, and feeds a soft decision Viterbi decoder. A comparison is made among multistage detectors with first stage QOMOE-MRC, matched filter (MF-MRC), decorrelator-MRC, LMMSE-MRC and blind adaptive-MRC detector, in a frequency flat Rayleigh fading channel. Analysis and simulation results show that the multistage QOMOE-MRC can obtain better performance than other used detectors.