An adaptive maximum likelihood receiver for asynchronous CDMA systems

A modification of the maximum likelihood (ML) [1] receiver for asynchronous CDMA channels is proposed. Instead of the matched filter (MF) bank as the generator of sufficient statistics for maximum likelihood detection, a bank of minimum mean squared error (MMSE) filters is used. The proposed adaptive MMSE-ML receiver is suitable for CDMA systems in frequency selective multipath fading channels. It is shown that in a single cell environment the bit error rate performance of the proposed receiver is similar to the conventional MF-ML receiver with known channel parameters. The advantages of the proposed MMSE-ML receiver over the MFML receiver are: 1) ability to perform joint synchronization, channel parameter estimation and signal detection where the signal is sent over unknown, slowly time varying frequency selective multipath fading channel, and 2) significantly improved performance in multicellular environments.