A chip level decision feedback equalizer for CDMA downlink channel with the alamouti transmit diversity scheme

Abstract

In commercial wideband code division multiple access (W-CDMA), the transmitted signal in the downlink channel is spread by orthogonal codes. However, frequency selective fading destroys the orthogonality, which causes multiple access interference (MAI). Although the RAKE receiver can exploit path diversity, it does not restore the orthogonality and suppress the MAI. As a result, CDMA becomes an interference limited system. The equalization followed by despreader can be adopted to restore the orthogonality and then to suppress the MAI, without significantly increasing the complexity. In this paper, we propose to apply a chip level decision feedback equalizer (DFE) with the Alamouti transmit diversity scheme to restore the orthogonality of the received spreading sequences. Theoretical and simulation results show significant performance gains compared to the chip level linear equalizer (LE) and the RAKE receiver.