Enhancing near-far resistance for linear CDMA detectors

Near-far resistance is one of the most important performance measures in a CDMA multiuser communication system, especially when power control is difficult to implement, such as in an ad hoc wireless network. The optimum multiuser detector can achieve the optimum near-far resistance. But due to its high computational complexity, the optimum detector is impractical to implement. Cost-effective suboptimum detectors, i.e., linear detectors, are more practical to implement. However, the optimality in near-far resistance is generally lost. We examine the structural differences of the channel matrix between the optimum and the suboptimum detectors. A transmission scheme is then proposed that almost restores the near-far resistance of the suboptimum detectors to that of the optimum one, at least theoretically. Computer simulations are performed to verify the theoretical findings.