Current Optics and Photonics

Optical Society of Korea (한국광학회)
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Dimmable Spatial Intensity Modulation for Visible-light Communication: Capacity Analysis and Practical Design

  • Kim, Byung Wook (Department of ICT Automotive Engineering, Hoseo University) ;
  • Jung, Sung-Yoon (Department of Electronic Engineering, Yeungnam University)
  • Received : 2018.09.06
  • Accepted : 2018.11.14
  • Published : 2018.12.25
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Abstract

Multiple LED arrays can be utilized in visible-light communication (VLC) to improve communication efficiency, while maintaining smart illumination functionality through dimming control. This paper proposes a modulation scheme called "Spatial Intensity Modulation" (SIM), where the effective number of turned-on LEDs is employed for data modulation and dimming control in VLC systems. Unlike the conventional pulse-amplitude modulation (PAM), symbol intensity levels are not determined by the amplitude levels of a VLC signal from each LED, but by counting the number of turned-on LEDs, illuminating with a single amplitude level. Because the intensity of a SIM symbol and the target dimming level are determined solely in the spatial domain, the problems of conventional PAM-based VLC and related MIMO VLC schemes, such as unstable dimming control, non uniform illumination functionality, and burdens of channel prediction, can be solved. By varying the number and formation of turned-on LEDs around the target dimming level in time, the proposed SIM scheme guarantees homogeneous illumination over a target area. An analysis of the dimming capacity, which is the achievable communication rate under the target dimming level in VLC, is provided by deriving the turn-on probability to maximize the entropy of the SIM-based VLC system. In addition, a practical design of dimmable SIM scheme applying the multilevel inverse source coding (MISC) method is proposed. The simulation results under a range of parameters provide baseline data to verify the performance of the proposed dimmable SIM scheme and applications in real systems.

Keywords

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FIG. 1. Example of the total Nt = 16 LED array’s blinking sequence, based on the spatial intensity modulation (SIM) scheme with a 50% target dimming level ((8+ 6 +8 +10) / 4 /16×100 = 50%).

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FIG. 2. Optimal turn-on probabilities maximizing the entropy, when (a) Nt = 4 and (b) Nt = 8.

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FIG. 3. Binary tree of multilevel Huffman encoding ( Nt = 4, ζD = 0.775)

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FIG. 4. Practical turn-on probabilities maximizing the entropy using multilevel inverse source coding, when (a) Nt = 4 and (b) Nt = 8.

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FIG. 5. Achievable dimming level of the SIM scheme, when (a) Nt = 4 and (b) Nt = 8.

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FIG. 6. Entropy versus the dimming ratio.

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FIG. 7. Dimming capacity versus SNR, when the dimming level is (a) 48% and (b) 72%.

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FIG. 8. Dimming capacity, depending on both SNR and dimming ratio.

TABLE 1. Example of multilevel Huffman coding ( Nt = 4, ζD = 0.775 )

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TABLE 2. Example of multilevel inverse source coding ( Nt = 4, ζD = 0.781)

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