Multiuser channel estimation for CDMA systems over doubly selective fading channels

In this paper, a pilot assisted minimum mean square error multiuser channel estimation algorithm is proposed for quasi-synchronous CDMA systems. The doubly selective multiuser fading channel is represented as a time-varying chip-spaced tapped delay line filter with correlated filter taps. The multiuser channel tap coefficients at pilot symbol positions are estimated under the MMSE criterion with the help of the channel tap correlation matrix, which can be jointly estimated with the filter tap timing with a novel iterative method. Simulations show that the channel tap correlation is critical to the performance of the channel estimation, and the channel taps at different delays cannot be assumed uncorrelated for systems experiencing doubly selective fading.