Multistage detection in asynchronous codedivision multipleaccess communications
Abstract
A multiuser detection strategy for coherent demodulation in an asynchronous codedivision multipleaccess system is proposed and analyzed. The resulting detectors process the sufficient statistics by means of a multistage algorithm based on a scheme for annihilating successive multipleaccess interference. An efficient realtime implementation of the multistage algorithm with a fixed decoding delay is obtained and shown to require a computational complexity per symbol which is linear in the number of users K. Hence, the multistage detector contrasts with the optimum demodulator, which is based on a dynamic programming algorithm, has a variable decoding delay, and has a software complexity per symbol that is exponential in K. An exact expression is obtained and used to compute the probability of error is obtained for the twostage detector, showing that the twostage receiver is particularly well suited for nearfar situations, approaching performance of singleuser communications as the interfering signals become stronger. The nearfar problem is therefore alleviated. Significant performance gains over the conventional receiver are obtained even for relatively highbandwidthefficiency situations.
 Publication:

IEEE Transactions on Communications
 Pub Date:
 April 1990
 Bibcode:
 1990ITCom..38..509V
 Keywords:

 Bit Error Rate;
 Code Division Multiple Access;
 Error Analysis;
 Real Time Operation;
 Spread Spectrum Transmission;
 Algorithms;
 Bandwidth;
 Cross Correlation;
 Matched Filters;
 Matrices (Mathematics);
 Probability Density Functions;
 Communications and Radar