Effect of Synchronization Error on Optical Spatial Modulation

This paper examines the effect of synchronization error on the performance of spatial modulation (SM) technique in optical wireless communication (OWC) systems. SM exploits the deployment of multiple transmitters by encoding user information on their spatial domain. In most works related to SM, a perfect synchronization among these multiple transmitters is assumed. However, synchronization error can result from multipath propagation in OWC channel, and clock jitter and variation in propagation delay of each transmitter. Synchronization error degrades system performance and hence the need to investigate its effect. Using union bound technique, and defining synchronization errors as timing offsets in the received signals, we derive the symbol error rate for space shift keying (SSK), generalized SSK (GSSK), SM, and generalized SM (GSM) schemes, and we validate our analysis with tightly matched simulation results. Results show that degradation in performance increases with synchronization error. While SSK is tolerant for a small range of synchronization error, GSSK, SM, and GSM are significantly impaired. Our results also demonstrate the dependence of SM on channel gain values. We observe that the lower the channel gain of the transmitter in which synchronization error occurs, the lesser the impact of the synchronization error on the system performance.