Theoretical Analysis of Optical Spatial Multiple Pulse Position Modulation

This paper proposes an advanced multi-pulse multi-light emitting diodes (LEDs) modulation technique to improve the efficiency for indoor visible light communication systems. The technique is referred to as spatial multiple pulse position modulation (SMPPM), and it is developed by combining a high spectral efficiency space shift keying (SSK) with a high energy efficiency multiple pulse position modulation (MPPM). During a symbol transmission, multiple active pulse slots and active LED indices are utilized as two degrees of freedom to modulate information which in turn provides the balance between the complexity, achievable spectral efficiency and energy efficiency. The analytical expression for symbol error rate (SER) of SMPPM in a multiple input multiple output system with multi-path propagation from reflection is derived theoretically using union bound technique and validated by means of Monte-Carlo simulations. Error performance of SMPPM is then evaluated extensively for different transceiver parameters and pulse configurations. Error rate distribution in a typical indoor workspace is plotted and analyzed. The SMPPM system achieves significantly higher spectral efficiency with respect to the conventional MPPM, SSK and spatial pulse position modulation (SPPM).