Channel acquisition for wideband CDMA signals

The problem of initial acquisition of the channel parameters of a wideband CDMA signal received in a multipath fading environment with multiaccess interference is considered. Since the signal is wideband, the fading is frequency selective and the parameters of interest are the (complex) gains and delays in the corresponding tapped delay line model for the channel. The scenario considered is one where a single new user is to be acquired on the reverse link by the base station, and where the channel parameters of the interfering users are known, Following a minimum mean squared error (MMSE) strategy for suppressing the multiaccess interference, the parameter estimation problem is posed in a maximum likelihood framework. To reduce complexity, the solution is implemented in two stages: first, the estimated tap delays are restricted to be at chip spacings; second, the number of taps is reduced by allowing for arbitrary spacing between them. The performance of the proposed techniques is studied through numerical simulations. It is shown that significant gains can be obtained by exploiting the structure of the interference and acquiring the channel parameters jointly.