Performance of Subcarrier PSK Systems Using PSAM Maximum Likelihood Estimation in Lognormal Turbulence Channels

Abstract

In order to increase throughput and improve system performance for free space optical communications, we consider a pilot-symbol assisted modulation (PSAM) subcarrier phase shift keying (PSK) system with maximum likelihood (ML) phase estimation. Using the phase error probability density function of ML estimation phase error, we study the error rate performance of the subcarrier PSK system with carrier phase error in lognormal turbulence channels. Results reveal the differences between the imperfectly synchronized system and the perfectly synchronized system, and how the performances are influenced by the pilot symbol length. An analytical expression of asymptotic signal-to-noise ratio penalty is derived and verified with numerical results.