Blind channel and carrier offset estimation in multiuser CDMA

The problem of CDMA multiuser detection in the presence of a small residual carrier is considered in this paper. Subspace-based approaches are employed for channel estimation and signal demodulation. The channel response and carrier offset are estimated separately in order to avoid the computational complexity of joint estimation of two parameters. The simulation results show that the separate estimation approach results in lower BER than a previous subspace-based joint estimation algorithm does for a large range of carrier offsets which are generally considered in practical applications. Adaptive channel estimation in a time-variant channel is also considered. A novel adaptive algorithm for subspace estimation, namely the normalized orthogonal Oja (NOOja) algorithm, is used to track the channel variations with time. The NOOja algorithm is applicable for both signal and noise subspace tracking and offers advantages of better orthogonality and numerical stability than previous tracking algorithms without any significant increase in computational complexity. It is shown that the NOOja algorithm exhibits good tracking performance in a time-variant channel