Effect of HARQ Gain for a Smart Antenna System and a Diversity Antenna System in a TD-SCDMA System

This paper presents a performance analysis of a beam forming smart antenna array system and a diversity antenna array system operating in a time division synchronous code division multiple access (TD-SCDMA) signal environment which adopts Hybrid Automatic Request (HARQ). Performance analysis was based on a receiver structure proposed in this paper which combined the HARQ with a smart antenna system or a diversity antenna system. When there was no HARQ, the diversity system outperformed the smart antenna system by about 4.2 dB for a given Frame Error Rate (FER) if the number of antenna elements was set to six for both the receiving systems. However, the performance difference was reduced to 2 dB when HARQ was appended in the receiver, as HARQ gain can be exploited more efficiently in a smart antenna system. Comparing the 6-antenna beamforming system with the 2-antenna diversity system (which is more realistic than a 6-antenna diversity receiver in practice), we found that the former outperforms the latter by 3 dB due to the contribution of HARQ gain. Performance analysis is shown in terms of FER and the required system complexities in a TD-SCDMA mobile communication system.