Direct semi-blind symbol estimation for multipath channels

A number of recent papers have treated the problem of channel estimation when known training data are present. The unknown part of the signal is typically estimated in an independent step, where the channel inverse or the Viterbi algorithm is applied to the received data. In this paper a technique is presented for directly estimating the unknown symbols in a block of data that also contains training information. An unstructured estimate of the channel can also be obtained that exploits the finite alphabet property of the transmitted signal. The proposed method is implemented in the frequency domain, and works best in situations where the transmitted symbols act to convert the linear convolution of the channel into circular convolution (as with a cyclic prefix in multicarrier systems). However reasonable results are still obtained asymptotically even without this constraint.