ROOT-MUSIC BASED JOINT IDENTIFICATION AND TIMING ESTIMATION OF ASYNCHRONOUS CDMA SYSTEM OVER RAYLEIGH FADING CHANNEL

An efficient algorithm is proposed to identify the active users and ex tracting their respective timing information in asynchronous direct se quence CDMA (DS-CDMA) communication system over Rayleigh fading channe l. The joint identification and timing estimation algorithm is derived by performing discrete Fourier transform (DFT) on the observation vec tor and exploiting the uniqueness and nullity characteristics of the r oot-MUSIC test polynomial. The root-MUSIC based algorithm is shown to be asymptotically near-far resistant. Compared to the maximum a poster iori (MAP) or maximum likelihood (ML) based multiuser timing estimator , the complexity is greatly reduced by separating the multi-dimensiona l optimization problem into several polynomial rooting problems. Moreo ver: we characterize the dependence of system performance with respect to signature sequence length, number of active users, window size, de sired user's signal-to-noise ratio(SNR) and crosscorrelation property of the code structure. The analytical results reveal that under the un correlated Rayleigh Fading model, the root-MUSIC timing estimator tend s to achieve the Cramer-Rao lower bound (CRLB) at interesting signatur e sequence length and desired user's SNR.