Improving soft interference cancellation for CDMA systems

The optimum receiver to detect the bits of multiple CDMA users has exponential complexity in the number of active users in the system. Previous work showed that the successive and parallel soft interference cancellers correspond to nonlinear programming relaxations of the optimum multiuser detection problem. We use this approximation method combined with the slowest descent approach to improve the performance of soft interference cancellers. The aim is to achieve a performance closer to the performance of the optimum receiver without significantly compromising the low complexity of the resulting receiver. We derive the resulting detectors and evaluate their performance. Results show that they can achieve near-optimum performance and outperform several previously proposed multiuser detectors.