Fast blind channel and carrier offset estimation in multiuser CDMA

The problem of CDMA multiuser detection in the presence of a small residual carrier offset is considered, with subspace-based approaches being employed for channel estimation and signal demodulation. The channel response and the carrier offset are estimated separately to avoid the complicated computation in the joint estimation of two parameters. The simulation results show that the separate estimation approach results in lower BER than does a previous subspace-based joint estimation algorithm for a large range of carrier offsets that 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 NOOja algorithm, is used to track the channel variations. The NOOja algorithm offers a set of advantages as compared to similar algorithms in the literature; in particular, it can be used for both signal and noise subspace estimation and has a very low computational complexity as compared to the batch eigendecomposition techniques.