An adaptive pilot symbol-aided MMSE receiver in fading channels

Realistic direct sequence code division multiple access (DS/CDMA) channels are severely time-varying. Standard minimum mean squared error (MMSE) receivers have various problems in tracking the rapidly changing channel characteristics in fading environments. In addition, they require a training sequence for their adaptation. This paper presents a constrained MMSE receiver with a modified MMSE criterion. The constrained MMSE receiver is adaptively implemented using the orthogonal decomposition-based least mean square (LMS) algorithm. In order to improve the accuracy of the reference signal and channel estimates, a pilot symbol-aided scheme is employed. It also makes the proposed MMSE receiver not require any separate training sequence. The simulation results show that the proposed MMSE receiver provides significant performance improvements in bit error rate (BER) over the conventional matched filter (MF) receiver and the currently available MMSE receivers, and is insensitive to the speed of Rayleigh fading