A PPM-based four-dimensional modulation scheme for visible light communications

This paper presents a four-dimensional (4-D) modulation scheme combined pulse position modulation (PPM) with four-color (RGBA) light-emitting diode (LED) in a visible light communication (VLC) system. In the proposed scheme, multi-LED selection is used within a symbol interval in order to decrease the cross-talk between each LED and make sure that each LED works in its linear area. Based on the maximal minimum Euclidean distance criteria, the constellations of the new 4-D modulation are constructed under the constraints of the optical power and the illumination. Moreover, the theoretical symbol error rate (SER) of the proposed scheme with maximal likelihood (ML) detection is also analyzed. Finally, we simulate the proposed scheme under both the additive white Gaussian noise channel and the practical optical channel measured from our VLC prototype. The simulation results verify the correctness of our theoretical analysis and reveal that the proposed 4-D modulation scheme outperforms the traditional color shift keying (CSK) in term of the SER.