Kurtosis DPLL AND PTCM decoder for non-linearly amplified 16-QAM

We describe a non-decision directed kurtosis-based digital phase lock loop (DPLL) algorithm for 16-QAM carrier recovery in the presence of non-linear amplification. A constellation rotation (with respect to locked phase) allows each of the trellis decoder's set-partitions to be fully confined to the received vector quadrants. Transponder characteristic variations may be automatically tracked by adapting the TCM decoder's metric LUT based on 4 dominant maxima in a 2-D histogram of quadrant data