Performance analysis of QPSK in free-space optical communications channel with phase compensation error

Performance of free-space optical (FSO) links employed quadrature phase shift keying (QPSK) modulation with phase compensation error over Gamma-Gamma turbulent channel is investigated in this paper. By considering the key factors of weather condition, additional noise and phase noise, the closed-form expressions of symbol error rate (SER) are derived by employing the hyper-geometric functions substitution method. Numerical results show that for FSO system, SER must be the trade off between transmission distance and weather condition, but it suffers more from the weather condition. The effects of imperfect phase compensation on system performance are also studied. Phase noise, which is described by phase compensation error variance parameter σ_Δφ², will lead to great degradation to system SER. Increased system signal to noise rate (SNR) helps to increase the system tolerance to σ_Δφ² and the maximum tolerable σ_Δφ² is around 10° for all weather conditions.