Pilot-aided adaptive chip equalizer receiver for interference suppression in DS-CDMA forward link

In the forward link of DS-CDMA systems; the multipath propagation channel destroys the orthogonality of the spreading codes and therefore causes multi-user interference (MUI). Ideal non-adaptive Zero-Forcing (ZF) and MMSE chip equalizer receivers have been proposed to restore the orthogonality and suppress the MUI in DS-CDMA systems employing aperiodic scrambling codes. However, these receivers can only deal with slow fading multipath channels. Practical adaptive implementations of the chip equalizer receiver that can track fast fading multipath channels, are not straightforward, since no continuous training chip sequence is available. In this paper we propose a new pilot-aided adaptive fractionally-spaced chip equalizer receiver that is well-suited for fast fading multipath channels. By exploiting the presence of a continuous pilot signal in forthcoming third generation cellular and LEO satellite communication systems, it continuously updates at the symbol rare using a simple NLMS or a more advanced PLS adaptive scheme. The proposed receiver outperforms the RAKE receiver with perfect channel knowledge over a wide range of normalized Doppler spreads, with a complexity that is still independent of the number of users.