Applications of Adaptive LMS Algorithm for Detection of CDMA Signals

Abstract:
The well known matched filter maximum likelihood receiver (MF-ML) for the code
division multiple access (CDMA) system uses a bank of matched 􀂿lters followed by a
threshold detector for detection of users’ transmitted symbols [1]. The performance of
the MF-ML receiver degrades in presence of multipath and multiple access
environments. In this paper, an application of the least mean square (LMS) adaptive
algorithm is presented by replacing the bank of matched 􀂿lters by a bank of adaptive
minimum mean square error (MMSE) 􀂿lters. This formal replacement has signi􀂿cant
conceptual consequences and provides improvement by several performance measures.
The advantages of the proposed adaptive MMSE-ML receiver over the ML-MF receiver
are: 1) ability to perform joint synchronization, channel parameter estimation, and signal
detection where the signal is sent over an unknown, slowly time-varying, frequencyselective
multipath fading channel; and 2) signi􀂿cantly improved bit error rate (BER)
performance in a multicultural mobile communications environments. Numerical results
showing the BER performance of the MMSE-ML receiver in a multipath channel
environment is presented, the results are compared with the performance of the
conventional (ML-MF).