Constant modulus algorithm (CMA) for CDMA communications systems

Abstract

Blind adaptive multiuser detection based on the constant modulus algorithm (CMA) has received a lot of attention recently. In the blind detectors proposed previously, the CMA is applied to the output of the chip match filters. In this paper, we consider the use of the CMA at the output of a bank of filters matched to the signature waveforms of each user. For simplicity, a synchronous code division multiple access (CDMA) system is adopted. The convergence performance of the blind detector is also analyzed and the results indicate that the CMA does not have the stable undesired equilibrium, which has been proven to exist for the practical Godard Algorithm with the finite tap equalizer when used in intersymbol interference (ISI) channels. However, the permutation ambiguity and the phase ambiguity occur. To avoid the permutation and phase ambiguities, some constraints are introduced into the CMA and their validity is also proven by analysis and simulations. When the CMA for each user converges to the desired solution, the blind detector is approaching to the decorrelating detector.