Average error performance in Subcarrier PSK FSO links over weak turbulence channels with spatial jitter and phase noise

Free space optical (FSO) communication systems or point-to-point optical wireless communication links via light, have recently emerged as a very promising and commercially viable laser technology that comes up to the growing demands for larger available bandwidth, huge data rates and higher security level transmissions in a both energy-efficient and cost-effective manner. However, their performance is adversely affected by atmospheric turbulence, pointing errors and phase noise effects when Subcarrier Intensity Modulation (SIM) based on M-PSK modulation formats are employed. In this work, the error performance of a FSO link using SIM based on M-PSK scheme is investigated over weak turbulence conditions along with the presence of pointing errors. The turbulence-induced fluctuations are emulated through the mathematically simple and compact Gamma distribution model that is very accurate for weak turbulence conditions, while the effect of phase noise is modeled by the suitable Tikhonov distribution. Under these assumptions, novel approximate closed-form expressions for the average SEP are derived which are accurate enough over a wide SNR range. Finally, proper numerical results are presented and validated by Monte Carlo simulations.