The exponential traffic growth, demand for high speed wireless data communications, as well as incessant deployment of innovative wireless technologies, services, and applications, have put considerable pressure on the mobile network operators (MNOs). Consequently, cellular access network performance in terms of capacity, quality of service, and network coverage needs further considerations. In order to address the challenges, MNOs, as well as equipment vendors, have given significant attention to the small-cell schemes based on cloud radio access network (C-RAN). This is due to its beneficial features in terms of performance optimization, cost-effectiveness, easier infrastructure deployment, and network management. Nevertheless, the C-RAN architecture imposes stringent requirements on the fronthaul link for seamless connectivity. Digital radio over fiber-based common public radio interface (CPRI) is the fundamental means of distributing baseband samples in the C-RAN fronthaul. However, optical links which are based on CPRI have bandwidth and flexibility limitations. Therefore, these limitations might constrain or make them impractical for the next generation mobile systems which are envisaged not only to support carrier aggregation and multi-band but also envisioned to integrate technologies like millimeter-wave (mm-wave) and massive multiple-input multiple-output antennas into the base stations. In this paper, we present comprehensive tutorial on technologies, requirements, architectures, challenges, and proffer potential solutions on means of achieving an efficient C-RAN optical fronthaul for the next-generation network such as the fifth generation network and beyond. A number of viable fronthauling technologies such as mm-wave and wireless fidelity are considered and this paper mainly focuses on optical technologies such as optical fiber and free-space optical. We also present feasible means of reducing the system complexity, cost, bandwidth requirement, and latency in the fronthaul. Furthermore, means of achieving the goal of green communication networks through reduction in the power consumption by the system are considered.

Toward an Efficient C-RAN Optical Fronthaul for the Future Networks: A Tutorial on Technologies, Requirements, Challenges, and Solutions

The main drawback of photovoltaic (PV) laser power converters based on GaAs material is the low output voltage, which is often insufficient to power electronic circuits directly. Aside from the use of a dc-dc converter in combination with a single PV converter, it is possible to boost the voltage by the monolithic serial interconnection of several converter segments on a single chip, often called multiple converters. Another novel approach introduced in this paper is a multijunction PV cell, where several subcells of the same material are stacked onto a substrate and interconnected by interband tunnel diodes. This paper explores a tandem GaAs-GaAs converter and compares the results with a 2-V multiple PV converter under monochromatic laser illumination. In addition, 4-V multiple PV converters with maximum monochromatic efficiencies (810 nm) of up to 50.1% at 51.6 W/cm2 and 6-V converters are investigated. Thereby, the fabrication technology of the devices is outlined and the influence of inhomogeneous illumination on the performance of these energy converters is discussed.

High-Voltage GaAs Photovoltaic Laser Power Converters

This article provides an overview of current efforts in reducing energy consumption in passive optical access networks. Both ITU-T and IEEE standardized PONs are considered. The current solutions proposed by standardization authorities, industry, and academia are classified based on the layer they address in the standardized architectures: physical layer, data link layer, and hybrid. Then, the article provides answers to major questions, such as where, when, and how to reduce PON energy consumption in TDM PONs by means of a quantitative evaluation. Results show that to reduce energy consumption, ONUs must be provided with physical devices that are not only power-efficient but also provide improved services (e.g., fast synchronization) to upper layers. For this latter purpose, novel physical ONU architectures are proposed to speed up the synchronization process and enable effective data link layer solutions. Finally, the feasibility of switching ONUs to low power mode in idle slots is assessed through a testbed implementation.

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Energy efficiency in passive optical networks: where, when, and how?

The integration of photonic components on silicon chips creates the challenge of achieving a uniform and efficient architecture. Here, the authors demonstrate on-chip light-emitters, photodetectors, photovoltaic power supply and optical data link, all based on InGaAs nanoresonators grown on silicon.

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Nanophotonic integrated circuits from nanoresonators grown on silicon

Optically powered networks are demonstrated. Heterogeneous subscribers having widely varying needs with respect to power and band-width can be effectively controlled and optically supplied by a central of-fice. The success of the scheme relies both on power-efficient innovative hardware and on a novel low-energy medium access control protocol. We demonstrate a sensor network with subscribers consuming less than 1 microW average power, and an optically powered high-speed video link transmitting data at a bitrate of 100 Mbit/s.

Optically powered fiber networks

An optically powered camera sensor link is demonstrated. Power and data are transmitted over a 62.5-?m multimode glass fiber. Uncompressed video with 640 × 480 pixels resolution is streamed continuously at 100 Mb/s as soon as the fiber is illuminated with sufficient optical power. No energy has to be stored at the sensor location in batteries with limited capacities and lifetimes. Inexpensive fiber optics and low-power state-of-the-art electronics are used to make >100 mW available at sites which have no direct access to an electrical network. There is a complete electrical isolation between the remote camera unit and a base station.

An Optically Powered Video Camera Link

Blade condition monitoring systems with fiber-optic sensors attract much attention because they are resistant to lightning strikes, a major issue with increasing blade lengths. However, fiber-optic sensor systems are more complex and more expensive than their electronic counterparts. We describe a new blade condition monitoring system, which combines the lightning safety of optical fibers with the reliability and cost-effectiveness of electronic sensors. The optical fibers transport data from the blades to the hub, and in addition, they provide the electrical power for operating the sensor units in the blades. To achieve full protection against lightning-induced electromagnetic fields, an appropriate shielding of the sensor units is required. We present results on the reliability of a newly developed prototype based on optically powered sensors. In a field trial, the unit monitored successfully the blade vibrations of a 1.5 MW wind turbine for a period of 23 months. Copyright © 2016 John Wiley & Sons, Ltd.

Reliable and lightning‐safe monitoring of wind turbine rotor blades using optically powered sensors

We implemented an optically powered video camera connected to a base station at 200 m distance. Power and 100-Mbps data-channel are multiplexed at 810 nm and 1310 nm into a standard 62.5 µm multimode fiber.

Optically Powered Video Camera Link

The present invention relates to a rotor blade (5) for a power plant (1), particularly for a wind power plant (1) or a water power plant, wherein – the rotor blade (5) comprises an electrically operable sensor device (9) and wherein – the electrically operable sensor device (9) is provided with energy and/or operated by irradiating electromagnetic radiation, and to a power plant, and to a use

C. Klamouris

Papers

Optically powered fiber networks

An Optically Powered Video Camera Link

Reliable and lightning‐safe monitoring of wind turbine rotor blades using optically powered sensors

Optically Powered Video Camera Link

Rotor blade, power plant, and use