It is well known that free space laser system performance is limited by atmospheric turbulence. Most theoretical
treatments have been described for many years by Kolmogorov's power spectral density model because of its
simplicity. Unfortunately several experiments have been reported recently that show the Kolmogorov theory is
sometimes incomplete to describe atmospheric statistics properly, in particular, in portions of the troposphere and
stratosphere. In this paper, using a non Kolmogorov spectrum and following same procedure already used for horizontal
path analysis, we extend free space optical system performance analysis to uplink and downlink paths. Our non
Kolmogorov spectrum uses a generalized exponent instead of constant standard exponent value 11/3 and a generalized amplitude factor instead of constant value 0.033. Therefore, in non-Kolmogorov weak turbulence, we carry out, for a uplink and a downlink paths, analysis of Long Term Beam Spread, Scintillation index, Probability of fade, mean SNR and mean BER as variation of the spectrum exponent.