Multipath combining/cancelling DS spread spectrum detection

The additional dimensionality and bandwidth of direct-sequence spread spectrum signaling can be used to provide multiple access and exploit multipath in wireless communication. However, the severely spread channels that will be encountered in broadband wireless applications, combined with bandwidth limitations, motivates the use of additional receiver processing to provide improved performance at moderate spreading gains. Spread spectrum with simultaneous RAKE combining and ISI cancellation is explored. A received signal model is presented that captures the general time-varying multipath/multi-user case. Linear detectors are studied; in particular, results are shown for a correlation detector supplying tentative decisions to a RAKE detector working in tandem with a decision feedforward/feedback structure. The performance of this method is compared with both classical RAKE detection and a RAKE performance bound. The results show significant gains for typical multipath channels and suggest directions for further study of joint spread-spectrum and symbol-rate receiver processing.