Phase-tracking viterbi demodulator

Abstract

The maximum-likelihood sequence estimation reception system, where the transmitted signal sequence is decided by the maximum likelihood using Viterbi algorithm, from the modulated signal, such as the phase modulated convolution-coded signal, TCM, and CPM, is considered to be very interesting because of its excellent signal-to-noise ratio (SNR) versus error rate performance. Such a system assumes the coherent detection of the received signal in order to realize excellent performance. The reception system, which is expected to follow the carrier with a large offset and a low SNR, has been difficult to realize due to the difficulty of satisfying the requirement. This paper proposes the following system. The phase-locked loop is provided corresponding to each survival path in the Viterbi algorithm used in the estimation of the maximum-likelihood sequence estimation. The phase-locked loop is selected in parallel to the selection of the survived path. In other words, the phase synchronization and the (maximum-likelihood) sequence estimation are simultaneously achieved. The system is discussed in detail, and it is shown that a stable coherent detection can be realized for a very low SNR.