Generalized frequency division multiplexing (GFDM) can be a desirable option for free space optical communication systems since it has several advantages such as good spectral efficiency, low peak-to-average power ratio (PAPR) and low co-channel interference. In this paper, we present the performance improvement of GFDM over FSO links by employing maximum ratio transmission (MRT) technique. The asymptotic and closed form expressions for both symbol error probability and outage probability are derived for GFDM over gamma-gamma channel model. The theoretical results are verified with the Monte-Carlo simulations. Moreover, the impact of turbulence levels and weather conditions are also explored.