Maximum-likelihood channel estimation using the spreading matrix in fast time-variant frequency selective channels

The text at hand presents a principal method for parametric maximum-likelihood channel estimation in fast time-variant frequency selective channels. These channels occur in mobile communications at very high velocities. We approach the problem by estimating the spreading function, which is limited in delay and Doppler frequency and therefore lends itself to sampling. A training sequence is assumed to be transmitted in parallel to the data sequence. The estimation is carried out in the time domain and derived for direct sequence spread spectrum systems as well as unspread systems. The estimation of the spreading coefficients results in an improved channel estimation by reconstruction of the impulse response. As an application, the channel estimator is tested in a UMTS terrestrial radio access (UTRA) frequency division duplex (FDD) uplink multiuser environment, where the multiple users are assumed to be totally asynchronous.