Coherent free-space optical transmission with diversity combining for Gamma-Gamma atmospheric turbulence

The error rate performance of coherent free-space optical transmission is studied for Gamma-Gamma turbulent environments. The moment generating function of Gamma-Gamma distributed irradiance is obtained, along with a closed-form expression for the characteristic function for the square root of Gamma-Gamma distributed irradiance. Biterror rate expressions are presented for binary phase-shift keying multiple-input multiple-output free-space optical transmission with maximum ratio combining and equal gain combining receptions. These coherent optical systems are shown to greatly improve the system error rate performance.