24,664 research outputs found
A review of communication-oriented optical wireless systems
This article presents an overview of optical wireless (OW) communication systems that operate both in the short-
(personal and indoor systems) and the long-range (outdoor and hybrid) regimes. Each of these areas is discussed
in terms of (a) key requirements, (b) their application framework, (c) major impairments and applicable mitigation
techniques, and (d) current and/or future trends. Personal communication systems are discussed within the context
of point-to-point ultra-high speed data transfer. The most relevant application framework and related standards are
presented, including the next generation Giga-IR standard that extends personal communication speeds to over 1
Gb/s. As far as indoor systems are concerned, emphasis is given on modeling the dispersive nature of indoor OW
channels, on the limitations that dispersion imposes on user mobility and dispersion mitigation techniques. Visible
light communication systems, which provide both illumination and communication over visible or hybrid visible/
infrared LEDs, are presented as the most important representative of future indoor OW systems. The discussion on
outdoor systems focuses on the impact of atmospheric effects on the optical channel and associated mitigation
techniques that extend the realizable link lengths and transfer rates. Currently, outdoor OW is commercially
available at 10 Gb/s Ethernet speeds for Metro networks and Local-Area-Network interconnections and speeds are
expected to increase as faster and more reliable optical components become available. This article concludes with
hybrid optical wireless/radio-frequency (OW/RF) systems that employ an additional RF link to improve the overall
system reliability. Emphasis is given on cooperation techniques between the reliable RF subsystem and the
broadband OW system
Free-Space Quantum Key Distribution
Based on the firm laws of physics rather than unproven foundations of
mathematical complexity, quantum cryptography provides a radically different
solution for encryption and promises unconditional security. Quantum
cryptography systems are typically built between two nodes connected to each
other through fiber optic. This chapter focuses on quantum cryptography systems
operating over free-space optical channels as a cost-effective and license-free
alternative to fiber optic counterparts. It provides an overview of the
different parts of an experimental free-space quantum communication link
developed in the Spanish National Research Council (Madrid, Spain).Comment: 22 pages, 15 figure
Internet of Things-aided Smart Grid: Technologies, Architectures, Applications, Prototypes, and Future Research Directions
Traditional power grids are being transformed into Smart Grids (SGs) to
address the issues in existing power system due to uni-directional information
flow, energy wastage, growing energy demand, reliability and security. SGs
offer bi-directional energy flow between service providers and consumers,
involving power generation, transmission, distribution and utilization systems.
SGs employ various devices for the monitoring, analysis and control of the
grid, deployed at power plants, distribution centers and in consumers' premises
in a very large number. Hence, an SG requires connectivity, automation and the
tracking of such devices. This is achieved with the help of Internet of Things
(IoT). IoT helps SG systems to support various network functions throughout the
generation, transmission, distribution and consumption of energy by
incorporating IoT devices (such as sensors, actuators and smart meters), as
well as by providing the connectivity, automation and tracking for such
devices. In this paper, we provide a comprehensive survey on IoT-aided SG
systems, which includes the existing architectures, applications and prototypes
of IoT-aided SG systems. This survey also highlights the open issues,
challenges and future research directions for IoT-aided SG systems
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