Interplay of Probabilistic Shaping and the Blind Phase Search Algorithm
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Probabilistic shaping (PS) is a promising technique to approach the Shannon limit using typical constellation schemes. However, the impact of PS on the chain of signal processing algorithms of a coherent receiver still needs further investigation. In this work we study the interplay of PS and phase recovery using the blind phase search (BPS) algorithm, which is currently a de-facto standard in optical communications systems. We first investigate a supervised phase search (SPS) algorithm as a theoretical upper bound on the BPS performance, assuming perfect decisions. It is shown that PS influences the SPS algorithm, but its impact can be alleviated by moderate noise-rejection window sizes. On the other hand, BPS is affected by PS even for long windows because of correlated erroneous decisions in the phase recovery scheme. The simulation results also showed, for investigated constellations, that the capacity-maximizing shaping is near to the worst-case situation for BPS, causing potential implementation penalties.
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