On the Performance of Downlink Optical Communication via Relaying in the Presence of Pointing Errors

We investigate the error performance of a satellite-to-ground optical link between a low-earth orbit (LEO) satellite and an optical ground station (OGS) in which a geostationary orbit (GEO) satellite is used as a relay. We perform a bit-error probability (BEP) analysis by taking the atmospheric turbulence effects and pointing errors into account. We use pulse position modulation (PPM) and consider both decode-and-forward (DF) and amplify-and-forward (AF) relaying schemes. Results show that for small pointing errors DF scheme outperforms AF scheme in terms of bit error rate (BER) performance. We also demonstrate that error control coding can significantly improve error performances especially for high pointing errors.