Blind Equalization Based on Modified Constant Modulus Algorithm

Abstract: Future services demand high data rate and quality. Thus, it is necessary to define new and robust algorithms to equalize channels and reduce noise in communications. Now a days, new equalization algorithms are being developed to optimize the channel bandwidth and reduce noise, namely, Blind Channel Equalization. Conventional equalizations minimizing mean-square error generally require a training sequence accompanying the data sequence. Considering the fact that blind equalizers do not require pilot signals to recover the transmitted data. The constant modulus algorithm (CMA) is one widely used algorithm for blind equalization of QAM signals. The algorithm exhibits slow convergence rate and large steady state mean square error and the phase-blind nature in comparison with the algorithms used in conventional data-aided equalization schemes. In this paper, a variable step size modified constant modulus algorithm is proposed. The proposed algorithm can speed up convergence rate and decrease steady state mean square error and correct phase error and frequency offset at the same time. The simulation results demonstrate the effectiveness of the proposed algorithm in improving convergence rate and reducing steady state mean square error. Finally, a comparison of the simulation results of LMS and CMA for the test channels is provided, for different iteration rate.

Keywords: (Blind Equalization, CMA, LMS, MMA)