Free Space Optics is the technology which implies the line-of-sight link for the transfer of data between two distant points. The beam of light is used to provide optical connection that can transmit and receive data. The performance of the modulation techniques-Binary Phase Shift Keying (BPSK) and Quadrature Phase Shift Keying (QPSK) are studied in the Nakagami channel and the Rician Channel. The QPSK modulation provides double data rate than the BPSK modulation technique. The certain impairments associated with the FSO system are also studied in this paper. The effect of scintillation index and Free Space Path Loss (FSPL) are also considered in this paper.