Modulation techniques used in earth-to-satellite and inter-satellite free space optical links

Abstract

Bit error rate expressions for OOK, PPM, DPPM, PAPM and DAPPM have been derived for Earth-to-satellite and satellite-to-Earth optical links. Threshold detection for OOK, DPPM, DAPPM and optimal detection for PPM and PAPM have been employed. The numerical results have been compared. It is found that for uplink: the performance of PPM is the best followed by that of DPPM, PAPM, OOK and DAPPM and for downlink the performance of PPM is the best followed by DPPM, OOK, DAPPM and PAPM. The difference in performance between the schemes is not much for uplink as compared to downlink. Since the bandwidth requirement of PPM is the largest, more bandwidth efficient schemes can be used at the cost of slightly higher transmitted power in the case of uplink. This study will be useful for modulation scheme selection for optical satellite links.