Channel estimation with superimposed pilot sequence

For the purpose of various synchronization tasks (including carrier phase, time, frequency, and frame synchronization), one may add a known pilot sequence, typically a pseudo-noise sequence, to the unknown data sequence. This approach is known as a spread-spectrum pilot technique or as a superimposed pilot sequence technique. In this paper, we apply the superimposed pilot sequence technique for the purpose of channel estimation (CE). We propose and verify a truly coherent receiver based on the Viterbi algorithm, which is optimal in the sense of per-survivor processing. We also suggest a generic low-cost receiver structure based on reduced-state sequence estimation. Among the distinct advantages compared to conventional pilot-symbol-assisted CE are (i) a lack of bandwidth expansion and (ii) a significantly improved performance in fast fading environments. The proposed Viterbi receiver may also be used as an alternative receiver for pilot-symbol-assisted CE.