A carrier recovery scheme used for synchronous serial two-dimensional data transmission system is investigated. A decision-directed observation vector, formulated at baseband, permits use of this technique to arbitrary two-dimensional modulation schemes. The imphasis here is on obtaining carrier tracking loops based on the decision-directed observations, which would perform well even when the dynamics of the actual phase jitter model is unknown. Several specific state estimation formulations are discussed in detail from this point of view. Among the nonlinear observation models considered are those associated with a constant phase offset, a linear phase model and a piece-wise linearity in the phase jitter. Also, attempt has been made to compare the performance of the state estimation techniques with that of the conventional fixed gain phase-locked loops.
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