Interplay of Probabilistic Shaping and the Blind Phase Search Algorithm

• Published in: Journal of lightwave technology Vol. 36; no. 22; pp. 5096 - 5105
• Main Authors: Mello, Darli A. A., Barbosa, Fabio Aparecido, Reis, Jacklyn Dias
• Format: Journal Article
• Language: English
• Published: New York IEEE 15.11.2018; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Algorithms; Analytical models; Coherent optical communications; Computer simulation; Constellations; Decision theory; Decisions; Modulation; Optical fiber communication; Phase noise; phase recovery; Probabilistic logic; probabilistic shaping; Recovery; Search algorithms; Signal processing; Signal processing algorithms; Signal to noise ratio; Upper bounds
• ISSN: 0733-8724; 1558-2213
• DOI: 10.1109/JLT.2018.2869245

Probabilistic shaping (PS) is a promising technique to approach the Shannon limit using a typical constellation geometries. However, the impact of PS on the chain of signal processing algorithms of a coherent receiver still needs further investigation. In this paper, we study the interplay of PS and phase recovery using the blind phase search (BPS) algorithm, which is widely used 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 show that the capacity-maximizing shaping is near to the BPS worst-case situation for square-QAM constellations, causing potential implementation penalties.