Transmitter-Based Multiple Access Interference Rejection and Diversity Techniques for Code-Division Multiple Access Systems
NORTH CAROLINA STATE UNIV AT RALEIGH DEPT OF ELECTRICAL ENGINEERING
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For the downlink of direct sequence code-division multiple access DS-CDMA systems, transmitter Tx-based multiple access interference MAI cancellation techniques, termed multiuser precoding, and Tx-based diversity techniques can significantly increase system capacity while remaining low complexity at mobile stations MS. We have proposed novel linear and nonlinear decorrelating precoding algorithms. Hybrid transmitter designs were developed to combine MAI cancellation and diversity techniques. We have also analyzed the important duality between Tx-based multiuser precoding and receiver Rx-based multiuser detection. The class of decorrelating precoding techniques is simple, efficient and satisfies the minimum mean square error MMSE criterion. The nonlinear decorrelating Tomlinson-Harashima precoding THP inherently outperforms linear MAI cancellation methods. For frequency-selective fading channels, we developed the THP with Pre-RAKE combiner PreRAKETHP and Multipath Decorrelating THP MDTHP designs. While the PreRAKETHP is the optimal THP design by both ZF and MMSE criteria, it is computationally complex because the MAI cancellation filters depend on the instantaneous channel gain coefficients and therefore need to be updated frequently. In the MDTHP, the precoding filter is independent of the channel state information CSI. The MDTHP is simpler than PreRAKETHP at the expense of moderate performance loss.
- Electrical and Electronic Equipment
- Radio Communications
- Numerical Mathematics