Optical wireless and visible Light Communications

LED lamps have recently become the technology of choice for lighting in many environments, from indoor office spaces to outdoor vehicular use. These LED lamps can be modulated at relatively high speeds, opening up the possibility to use them to provide simultaneously illumination and data transmission, so-called visible light communications (VLC). One of the most compelling applications for VLC is in large unobstructed indoor spaces where many users desire concurrent high-speed connectivity, such as conference centers and classrooms; Wi-Fi fails here because of its limited spectrum re-use. Other promising applications include indoor geo-location, vehicle-to-anything (V2X) communications, indoor positioning, and transmission inside airplane cabins. In our research we consider modulation, signal processing, user tracking, and resource allocation for this new optical communications modality

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Advanced Modulation and Coding for Optical Communication Systems

Optical channels offer a tremendous opportunity for high-throughput data transfer. Yet with this opportunity come some fundamental challenges. Novel modulation and coding schemes are needed to access and exploit the optical bandwidth resources, and to survive the deleterious effects of the optical medium. In our work we develop higher-order modulation techniques suitable to optical (visible, IR, and UV) systems. We explore the potential benefits of using error control coding on the system performance, with particular emphasis on LDPC codes. We also consider the use of multiple transceivers (single technology and hybrid RF/optical) to establish more robust and higher performance MIMO communication systems.

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Cross-Layer Design and Optimization of Optical Networks

The dramatic increase in throughput demands on transport systems has propelled the development of all-optical networks. These networks can provide tremendous capacity when they are designed with their own limitations in mind, such as coarse wavelength granularity and physical impairments. In this research we consider the holistic design of optical networks that include the interdependence of three network layers: the traffic grooming layer, the lightpath management layer, and the physical fiber layer.

The network is first viewed from the top-down, where sub-wavelength circuit requests arrive with specific quality of service requirements. Current traffic grooming approaches are altered to incorporate their dependence on the lightpath management and physical layer constraints. The system is then examined from the bottom-up, so that the quality of transmission and efficiency of resource utilization can be optimized as the higher layer protocols evolve. Total capacity is measured from an information theoretic view point and system optimization uses ideas from game theory.

The results of the research are practical algorithms for improved capacity and survivability of future optical networks as well as providing a quantitative proof of their superiority. The enhancement of network capability will help satisfy our society’s ever-increasing need for information. It encourages the development of applications that require significant bandwidth. It also stimulates cross-fertilization of ideas from the two fields of networking and communications. When fully tested, the algorithms and software will be made publicly available via this web-site.

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