DS-CDMA system with joint channel estimation and MAP detection in time-selective fading channels

In this paper, maximum a posteriori (MAP) detection is applied to a direct- sequence code-division multiple-access (I)S-CDMA) system jointly with ident ification and estimation of time-selective Fading channels. By sampling the outputs of the matched filter and combining antenna array elements, strong and time-varying multiple-access interference (MAI) is characterized and s uppressed instantaneously. The decision statistics for MAP detection are ob tained from the conditional probability density function of prediction erro r. The prediction is accomplished by approximating the fading channel with a constrained nonlinear state model. Unknown parameters such as auto-regres sive (AR) process coefficients, noise covariance matrices, and the antenna array vector are estimated based on received sample vectors only. Also, dif ferential modulation is applied to eliminate the need for pilot insertion. Through computer simulations, near-optimum bit error rates (BERs) are found .