Subspace adaptive detection for asynchronous multiuser CDMA with frequency domain channel response and delay estimation

Channel estimation, particularly delay estimation in an asynchronous CDMA channel, is essential for most receivers. The correlated time domain data sequence becomes asymptotically uncorrelated in the frequency domain. By taking the discrete Fourier transform (DFT) of the received signals, we can take advantage of this asymptotical property to simplify the estimation algorithm. The proposed scheme can jointly estimate the path delay and the complex channel response with lower computational complexity. Furthermore, having such estimates, it is possible to use an adaptive subspace MOE (minimum output energy) detector, previously implemented in synchronous channels, for asynchronous multiuser CDMA. By simulation, it was shown that this scheme can provide comparable performance to that obtained with a Wiener filter.