Comparison of modulation formats for free space optics with SelC diversity

In the present work, a comparative analysis of different modulation formats in free space optical turbulent media with and without spatial diversity technique is presented. The channel modelling is done with gamma-gamma distribution and the modulation formats used for comparison are ASK, BPSK, QPSK and FSK. Selection combining diversity technique is employed at the receiver and bit-to-bit comparison is used to estimate the error performance i.e. BER. The four modulation formats are employed on the FSO link in the presence as well as absence of diversity. The comparison is done on the basis of the performance matrices like BER, input optical power, SNR and the minimum received power obtained. The result shows BPSK as the suitable format in presence as well as absence of diversity. Also with diversity the requirement of SNR to achieve the same BER is reduced by 7 dB.