Blind adaptive multiuser detection using linear parallel interference cancellation for CDMA systems

We consider the application of parallel interference cancellation (PIC) schemes to improve both convergence speed and bit error rate (BER) performance of blind adaptive minimum mean output-energy (MMOE) detectors for direct-sequence code-division multiple-access (DS-CDMA) systems in near-far environments. The approach taken is to make use of the available knowledge of spreading codes for all users (i.e., at the base-station) to cancel multiple access interference (MAI) using a combined adaptive MMOE-PIC algorithm. The BER of the proposed system is evaluated using the Gaussian approximation. Simulation results show that the Gaussian approximation yields a precise evaluation at BER levels that are of practical interest. Moreover, it is shown that for a 10 user system with a severe near-far scenario and binary phase shift keying (BPSK) transmission, a 4-stage adaptive MMOE-PIC receiver does not need a training period for convergence to be reached. Furthermore, the proposed receiver is shown to attain a steady-state BER performance close to the standard minimum mean-squared error (MMSE) receiver while the adaptive MMOE detector suffers from a higher BER due to the imperfect filter coefficients.