Performance of active codes detection algorithms for the downlink of TD-SCDMA system

TD-SCDMA (time division synchronous CDMA) systems employ joint detection algorithms both in uplink and in downlink. For the downlink, mobile stations (MS) usually have no information about other users, so we have to determine active codes beforehand to simplify joint detection processing. We introduce two kinds of active code detection algorithms, data power judgement and channel power judgement, which are related to the omnidirectional system and the beamforming (smart antenna) system, respectively. We describe their basic theory first, and then simulate their performance in the downlink of a TD-SCDMA system. Theory analyses and simulation results demonstrate that both active code detection algorithms can improve the system performance compared to non-detection; channel power judgement has a simpler structure and better performance than data power judgement.