Marked Multi-Layer Optical Spatial Pulse Position Modulation

The existing optical spatial modulation has some problems, such as low transmission rate, low transmitter utilization rate and undesirable bit error rate performance. A marked multi- layer optical spatial pulse position modulation (MMLOSPPM) scheme is proposed by employing the layered spatial structure and combining pulse position modulation (PPM). The timeslot of each PPM symbol is extended to distinguish layers, and the correctness of the first detection layer and its modulation symbol is improved. Besides, the theoretical bit error rate expression of the MMLOSPPM system is derived under the Gamma-Gamma turbulence model and is verified by Monte Carlo method. The simulation results show that when the spectral efficiency is 3/2 bit.s(-1).Hz(-1), the transmission rate of (5x4-2-2) MMLOSPPM is 3 bpcu (bit per channel use) better than that of (4x4-2) spatial PPM (SPPM) system and (3x4-2) generalized SPPM (GSPPM). When given the same transmission rate, the (5x4- 2-2) MMLOSPPM system requires 2 and 11 fewer lasers than that of (7x4-4) GSPPM and (16x4-4) SPPM system respectively, and MMLOSPPM gains the best bit error rate performance in the high signal to noise ratio (SNR) region (SNR is greater than 28 dB).