Improving power efficiency of OFDM based FSO system using linear companding transform

Radio on Free Space Optics — RoFSO is cost effective and efficient in transferring high data rate that can be compared with optical fiber transmission. OFDM based FSO can further increase the data rate and at the same time can overcome the drawbacks of atmospheric turbulence of the free space like scintillation effect that has been considered in this paper. OFDM based FSO is an emerging solution for “last mile” broadband connectivity where deployment of fiber is not possible. Besides this it is also possible to use FSO for Inter chip connectivity, interplanetary communication etc. Using OFDM in optical domain must be power efficient so that the amount of DC bias added to the OFDM signal to make it unipolar is less. Performance of the PSK baseband modulated OFDM based FSO system with three different Linear Companding Transform-LNST, ALCT and CLCT is studied. The comparative study shows that, of the three transforms, CLCT performs better providing 20% power efficiency. Also it has the flexibility in the choice of number of subcarrier for transmission, as the PAPR remains same for change in number of subcarrier. 2 — 5 dB performance of CLCT companded OFDM is better than the other two transforms.