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Open Access Publications from the University of California

Physical Layer Characteristics and Techniques for Visible Light Communications

  • Author(s): Cui, Kaiyun
  • Advisor(s): Xu, Zhengyuan
  • et al.
Abstract

With the rapid development of semiconductor lighting technologies, the light emitting diodes (LEDs) are promising to eventually replace traditional incandescent and fluorescent lamps for their high energy efficiency, environmental friendliness, and long lifetime. Visible light communication (VLC) utilizing lighting LEDs as transmitters has been an emerging research area since its first proposal. Ubiquitous communication coverage will become possible with wide deployment of lighting LEDs.

This thesis studies physical layer characteristics of VLC systems based on either indoor LED lighting or outdoor LED traffic signaling infrastructure. Advanced communication techniques are proposed to cope with LED bandwidth limitations and grant multiple accesses. Their performance is comprehensively analyzed in typical lighting and signaling environments. Firstly, communication link issues are studied. A conversion method from photometric parameters for illumination to radiometric parameters for communication is developed. Two typical VLC links, the line-of-sight (LOS) link and non-line-of-sight (NLOS) diffuse link, are characterized both experimentally and numerically. Some optional reverse link provisions are evaluated for a full duplex system. Different noise sources and background interferences are analyzed, and dominant noises are identified under typical application scenarios. With identified signal propagation and noise characteristics, link performance is then evaluated. Secondly, transceiver design techniques to increase the data rate are proposed, including digital pre-equalization techniques and the optical orthogonal frequency division multiplexing (O-OFDM) whose peak to average power ratio (PAPR) issue is investigated. Thirdly, the capacity of the multiple-input multiple-output (MIMO) VLC system exploring inherent multiple LED transmitters and multiple photodetectors is evaluated. The effects of some system parameters involved in non-imaging and imaging transceivers are analyzed. Finally, a combined wavelength-division and code-division multiple access (WD-CDMA) scheme for indoor VLC scenario is proposed. Its performance is analyzed theoretically and then evaluated using the Monte-Carlo simulation.

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