Performance enhancement of free space optical satellite uplink with transmitter spatial diversity technique

In this paper, the performance analysis of a Free Space Optical (FSO) satellite link from Earth to Geostationary Earth Orbit (GEO) satellite is carried out by considering atmospheric turbulence effects. It is observed that spatial diversity is a feasible option at the transmitter side and not at the receiver side. Further, increasing aperture diameter improves the performance due to higher received power (and not because of aperture averaging) and the improvement with increase in aperture diameter is higher at lower ground turbulence levels. For transmitter spatial diversity, the arrangement of transmitters in order to minimize correlation between the received beams is discussed. Initially, we see that there is considerable improvement in link performance by increasing the number of transmitters and the law of diminishing returns sets in with further increase in the number of transmitters. The expression of capacity with outage is derived. It is observed from the results that the maximum achievable capacity increases and the corresponding outage probability reduces with an increase in the number of transmitters for the same average received signal to noise ratio.