Performance of Free Space Optical (FSO) communication system is affected by atmospheric turbulences and pointing errors. These effects can easily be mitigated by adapting natural system parameters such as wavelength. In this paper, considering effects of pointing error and atmospheric turbulence, two optimization models are presented on FSO communication system. In Model 1, the normalized transmitter power is objective function, Bit Error Rate (BER) is equality subjective. In Model 2 normalized transmitter power is equality subjective, the BER is objective function. In both of them the normalized wavelength is variable parameter. These models were previously investigated using numerical methods; in the sense that they were solved asymptotically. From this point of view, this paper regenerated these models and solved them by a completely different analytical method, and derived a new exact solution. Comparing exact and asymptotic methods shows some interesting results; the asymptotic method achieves BER=10^(-9), but the presented new exact method achieves BER=10^(-13), which is a significant difference. It means that even at the worst case scenario such as pointing error, it is possible to have a very good performance by only the transmitting wavelength a bit. Proposed models are practical and obtained results show that this system is cost and power effective.