Soft output decision feedback equalizer using variable step-size algorithm for turbo coded DS/CDMA systems

This paper presents a new variable step-size algorithm on soft output adaptive decision feedback equalizer for turbo coded direct-sequence code division multiple access (DS/CDMA) systems. The proposed adaptive equalizer utilizes a performance of the system or by means of bit error rate to control the adaptation process of the equalizer and the new structure is based on the decision feedback equalizer. By this method, the performances of the proposed adaptive equalizer cooperate with the attractive log-maximum a posteriori (Log-MAP) algorithm of turbo decoder for the DS/CDMA system. It provides a good statistical in non-stationary channel condition scenario. The simulation results are shown the superior bit error rate performances of the proposed adaptive equalizer over other equalizers such as the finite impulse response equalizer and conventional decision feedback equalizer.