ASYMPTOTIC EFFICIENCY OF LINEAR MULTIUSER DETECTORS.

Demodulation of data streams transmitted synchronously by several users over a Gaussian multiple-access channel is considered. Each user modulates a different signal from a linearly independent signal set. The asymptotic efficiency criterion is used to evaluate the performance of different detection rules. The two currently most important detectors are presented and compared: the optimum multiuser detector whose complexity is exponential in the number of users, and the single-user detector whose performance degrades rapidly as the multiuser interference energy increases. In contrast, a memoryless linear transformation on the matched filter outputs of the receiver is proposed, and shown to guarantee a high lower bound on the asymptotic efficiency, which is independent of signal energies, while the time-complexity per bit is linear in the number of users. An algorithm which finds the best linear transformation is given, along with sufficient conditions on the signal energies and cross-correlations to ensure optimum asymptotic efficiency of the proposed detector.