On the downlink capacity of TDD CDMA systems using a pre-RAKE

The pre-RAKE technique for the downlink transmission in TDD-based CDMA wireless systems has been shown to provide greater capacity and a simpler receiver design at the mobile receiver. Nevertheless this technique is very affected by fast changing channels, since it relies on uplink channel measurements for the downlink transmission. In this paper a semi-analytical approach to the performance, including channel coding is presented. Furthermore we analyse the pre-RAKE performance including its behaviour with changing channels. Finally we show that the pre-RAKE maximises the correlation between the received and the desired signal, and this demonstration provides us the means to obtain an instant power control at bit level that improves performance significantly.