Downlink Site Diversity with Frequency-Domain Equalization for a DS-CDMA Cellular System

In DS-CDMA high speed wireless signal transmissions, the bit error rate (BER) performance with coherent rake combining degrades due to inter-path interference (IPI) caused by a severe frequency-selective fading. The use of frequency-domain equalization (FDE) can significantly improve the BER performance. However, the local average received signal power slowly varies due to path loss and shadowing loss according to the movement of a mobile user. This variation degrades the link capacity particularly when the user is located close to the cell edge. To improve the link capacity, the well-known site diversity can be used in conjunction with FDE. In this paper, we present downlink site diversity with FDE for a DS-CDMA cellular system and derive the MMSE weight for site diversity combining. The downlink capacity is evaluated by computer simulation and compared to the case with coherent rake combining. Then it is shown that the link capacity with FDE is better than that with coherent rake combining.