On the Use of Joint Error-Norms Adaptive Algorithm in QPSK (DS-CDMA) System

The concept of using joint error norms adaptive algorithm and the resulting least mean switched error (LMSE) algorithm in the adaptation process of the DFE receiver´s structures of asynchronous QPSK (DS-CDMA) is investigated. The performance measure is in-terms of bit error rate (BER) and mean square error (MSE) and for various step-sizes, over AWGN and Gaussian mixture type impulsive channels. The proposed algorithm consists of applying the Least Mean Fourth (LMF) algorithm and switching to the Least Mean Square (LMS) algorithm when the absolute value of error is greater than one. The MSE and BER performances of using the LMSE show that the optimum step-size for the LMF algorithm is 1×10^-6 while for the NLMS is kept constant at 0.01. Also the performance of the proposed algorithm was examined against the standard NLMS algorithm and it provides fast convergence rate, lower ground noise floor, and similar BER.