Channel Capacity of Hybrid Dimmable MPPM for Visible Light Communications

In this paper, variable multi-pulse pulse position modulation (VMPPM) that combines a new dimming control method using pseudo-orthogonal codes with MPPM is proposed. Proposed VMPPM can improve the channel capacity of conventional variable rate MPPM (VR-MPPM) because new dimming control method can reduce degradation of the error rate performance. In VMPPM, r slots are selected from n MPPM slots and codes for data are generated in each selected r slot according to source data log2 (n r) + r [bit/frame]. Additionally, VMPPM can represent the dimming percentage of n - r + 1 stages by using the empty n-r slots. Moreover, we have presented hybrid dimmable MPPM (HD-MPPM) that combines proposed VMPPM with VR-MPPM to enhance the channel capacity of VR-MPPM. In this paper, the channel capacity of HD-MPPM is investigated through theoretical analysis. In addition, the channel capacity of HD-MPPM is compared with that of VR-MPPM by taking into account the human eye response. Consequently, HD-MPPM can enhance the channel capacity of VR-MPPM at the high dimming percentage. Especially, when the ratio of electrical signal power per bit to noise is 0 dB and -5 dB, HD-MPPM can improve the channel capacity about 15 [bit/channel use] and about 20 [bit/channel use], respectively, at the perceived light is 80%.