An improved signature waveform estimation approach in synchronous CDMA systems

Synchronous-CDMA (S-CDMA) techniques are protected against co-channel interference by employing orthogonal codes. In an actual mobile radio environment, however, multipath may cause the orthogonality of S-CDMA signals to suffer from the increased cross correlation. In this scenario, multiuser detection is imperative to recover the orthogonality of the code. Liu and Xu (see Proc. 29th Asilomar Conf. on Signals, Systems and Computers, 1996) have proposed a blind-estimation scheme that provides closed-form estimates of the signature waveforms by exploiting the structure information of the data output. The approach is deterministic in the sense that noise or signal statistics are not required for the estimation. However the estimation utilizes only users' code information. We present a modified method that uses the known information of the pulse shaping filter as well as code information to improve the signature waveform estimates. We then extend this approach to overloaded systems by employing smart antennas.