Performance of Optical Space Shift Keying Over Gamma–Gamma Fading With Pointing Error

Optical space shift keying (OSSK) is a multiple transmit aperture based scheme which attains improved spectral efficiency in optical wireless communication (OWC). In addition to atmospheric turbulence (AT), pointing error (PE), which originates due to vibrations or building sway, has potential to deteriorate the performance of OWC link. This paper discusses the effect of AT and PE jointly on the performance of OSSK scheme. An analytical framework is proposed for evaluating average bit error rate (ABER), coding gain, and diversity order of OSSK scheme. It is found by analysis that for low PE, error performance of OSSK in weak AT condition is poorer than that in strong and moderate AT conditions. However, for high PE, the trend is the reverse. ABER, coding gain, and diversity order for pulse amplitude modulation (PAM) over AT and PE are also derived in order to compare its performance with the same rate OSSK scheme. The analysis shows that OSSK is less sensitive to PE severity as compared to PAM. Also, the diversity order of OSSK is independent of AT and PE, whereas the diversity order of PAM depends on both AT and PE, which makes OSSK a suitable modulation scheme for the practical scenario.