An efficient blind adaptive receiver based on parallel interference cancellation for asynchronous DS-CDMA systems

Abstract

In this paper, we propose a modified linear parallel interference cancellation (PIC) structure using the blind adaptive minimum mean output-energy (MMOE) algorithm for direct-sequence code-division multiple-access (DS-CDMA) systems. Our aim is to improve both the convergence speed and the bit error rate (BER) performance of the conventional blind adaptive MMOE receiver in asynchronous AWGN channels. The proposed receiver structure makes use of the available knowledge of all users' spreading codes (i.e., at the base-station) to cancel multiple access interference (MAI) using a combined adaptive MMOE-PIC algorithm. It is shown that the proposed algorithm can significantly reduce the long training period requirement of the conventional adaptive MMOE receiver due to both the asynchronous transmission and the near-far problem. The BER of the proposed system is evaluated using the Gaussian approximation. Moreover, the performance of the proposed algorithm is compared with the conventional blind trained method. Both numerical and theoretical results show that the proposed receiver performs close to the standard minimum mean-squared error (MMSE) receiver whereas the adaptive MMOE detector suffers from a higher BER due to the imperfect filter coefficients.