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Iterative multiuser detection and pilot aided channel estimation for coded CDMA systems over fading channels

We consider two iterative multiuser detection (MUD) schemes at the base station using code division multiple access (CDMA) signaling over a Rician fading channel. These two iterative MUD both employ soft interference cancellation (SIC) to eliminate the multiple access interference (MAI) from other users. After SIC, two filtering methods, one is based on matched filtering (MF) and the other one is based on the criterion of minimum mean-squared error (MMSE), are utilized to suppress residual interference. The forward error correction codes considered in this paper are convolutional codes and the BCJR decoding algorithm is used for acquiring the reliability of coded symbols. Since channel state information (CSI) can not be known perfectly at the receiver in practical situations, the effect of channel estimation error on system performance needs to be investigated. We modify the pilot aided demodulation (PAD) channel estimation scheme by taking advantage of iterative processing so that the accuracy of channel estimates can be improved as the number of iterations grows. Numerical results show the performance of the proposed MUD can achieve the single user bound with perfect CSI. The penalty when the CSI is estimated from the iterative PAD is about 2-3 dB which depends on the channel loads.