Transmitter-based Joint Nonlinear Multiuser Interference Cancellation and Multipath Diversity Combining for DS/CDMA Systems

 A nonlinear transmitter-based multiple access interference (MAI) cancellation technique, Tomlinson-Harashima transmitter precoding (THP), is proposed for Direct Sequence (DS) Code-Division Multiple Access (CDMA) systems with or without multipath fading. This zero forcing (ZF)-based transmitter precoding method minimizes the mean square error at the receiver. It is suitable for the downlink since the receiver is as simple as the single user matched filter receiver. For frequency-selective fading channels, by combining THP with diversity techniques, we develop two specific designs, PreRAKETHP and multipath decorrelating THP (MDTHP), which provide desired performance-complexity trade-off. It is shown that THP designs outperform linear transmitter (Tx)-based methods and both linear and nonlinear receiver (Rx)-based decorrelating approaches. The nonlinear precoders have better performance for the weaker users. Therefore, they reduce total transmit power relative to linear precoders. In addition, in rapidly varying multipath fading channels, THP aided by the long range channel prediction (LRP) method achieves almost the same performance as when the channel state information is perfectly known at the transmitter. Index Terms  Code-division multiple access, diversity methods, multiuser detection, Tomlinson-Harashima precoding, transmitter precoding. 1 This work was supported by NSF grant CCR-0312294 and ARO grant DAAD 19-01-1-0638 1