Power-over-fiber (PoF) is a novel power transmission technology that uses optical fibers, instead of the traditional copper wires, to deliver electrical power to feed remote sensors or electrical devices. Research on the PoF systems has been receiving extensive attention due to the advantages of fiber optic systems compared to the conventional power supply systems. Optical fibers are less bulky and lightweight, robust to electromagnetic interference (EMI) and electric sparks, resistant to corrosion and to extreme weather. Optical fiber installation is less susceptible to explosive and hazardous environments and presents a minimal security risk. Moreover, a single optical fiber can simultaneously transmit highspeed data and deliver electrical power to remote places. This paper experimentally demonstrates a PoF system using offthe- shelf components to feed microelectronics for low-power applications. The optical system consists of a 1550nm Pigtailed Laser Diode, an InGaAs photodetector for the optical to electrical conversion, and both Single-Mode (SM) and Multi-Mode (MM) optical fibers are tested. Experimental results show that data signal and power signal can be successfully transmitted simultaneously using an optical communication link. Analysis of the electrical-to-optical (E/O) conversion efficiency of the laser source, optical-to-optical (O/O) efficiency of the optical fibers, and optical-to-electrical (O/E) conversion efficiency of the receiver are also presented. Moreover, the System Energy Efficiency (SEE) is studied, and the effects of signal data-rate on the SEE are investigated.
KEYWORDS: Free space optical communications, Optical testing, Signal detection, Free space optics, Telecommunications, Signal processing, Signal to noise ratio, Prototyping, Transmitters, Optical communications
Multi-point free space optical communication (FSOC) has been identified as a valuable and promising technology for meeting high-capacity and -density demands of future space and terrestrial communication networks. FSOC’s point-topoint nature has boosted extensive research on technologies and methods that support multi-user optical networks. An FSOC system platform is essential for fully characterizing, testing, and evaluating state-of-the-art, multi-user prototypes and technologies developed by both businesses and academic communities. This paper presents an experimental FSOC testbed that demonstrates next generation FSO systems and allows cognitive, multi-point communication. These systems provide a significant improvement over those with currently hampered with single-user limitations. The FSOC testbed is multi-node, modular, and high-speed with real-time ability to test O-PHY modules and O-MAC schemes. The testbed consists of multiple, independently tunable optical transmitters and receivers that can be configured to emulate various communication scenarios (e.g., point-to-point (P2P), point-to-multipoint (P2MP), and multi-point-to-multipoint (MP2MP). At the receiver side, a cognitive controller performs real time, blind processing of received signals for identifying the number of concurrent transmissions. Accordingly, the controller drives an optical switch to route detected signals to pre-defined paths. Given that a single-user transmission is detected on multiple paths, diversity combining will be performed to improve received signal-to-noise ratio (SNR). If multiple-user transmissions are identified, signals are routed into separate high-speed photodetectors for processing. The work described below details hardware components integrated in the platform, as well as software development for the cognitive controller. Furthermore, this work provides an experimental demonstration of the testbed capabilities for single-user and multiple-user scenarios.
A methodology based on convolutional neural network (CNN) is proposed for joint classification of transmitting user number and modulation format in a multiuser free-space optical communication (FSOC) link. The proposed methodology relies on amplitude information of received mixed signal. In-phase and quadrature components of users that are sharing time and bandwidth resources transmitting into the same optical wireless access point and interfering within each other are analyzed. The proposed approach utilizes the constellation diagrams of the received mixed symbols to generate image data sets that are fed into CNN input. The designed CNN model with three convolutional layers was tested for: varying image resolutions, image-data set size, varying number of received symbols, and atmospheric turbulence to identify optimal parameters and processing time for system design and implementation. The results indicate that the CNN model can blindly and accurately identify the communicating device number and their optical modulation format with classification accuracy up to 100% for various SNRs. Moreover, the CNN demonstrated robustness against atmospheric turbulence and suggested immunity to additive noise. Therefore, the proposed methodology proved to be a promising and feasible solution for practical implementation of an intelligent optical wireless receiver for aerial and terrestrial FSOC links.
Increasing usage and higher demand for wireless traffic are causing a critical need for increased bandwidth and capacity communication networks. Accordingly, multipoint free-space optical communication (FSOC) links are beginning to draw significant attention as a valuable and promising solution for satisfying new network requirements. Extensive interest has focused on investigating and developing hardware design solutions to perform multiuser FSOC. However, to meet the low size, weight, and power needs of this technology, we propose using a robust and solid signal-processing method, namely independent component analysis (ICA), to implement an optical multiple access technique. A high-speed, multipoint free space optical system composed of two independent users and two receiving sensors is introduced. FastICA and joint approximate diagonalization of eigenmatrices algorithms are exploited for multiuser detection, and extensive analysis of power ratio, data rate difference, computational complexity, achievable system capacity, turbulence generation accuracy, and turbulence severity effects on signal reconstruction is performed. Experimental results demonstrate that ICA provides suitable source separation for all tested configurations. Additionally, transmission parameters that maximize signal reconstruction performances were identified.
Free Space Optical (FSO) multi-user communication provides high aggregate bandwidth and link robustness attributable to spatial diversity. The primary challenge for this technology is interference among multiple users at the receiver. A non-orthogonal multiple access (NOMA) technique multiplexes numerous users in the power domain at the same time and frequency resource. Thus, different users simultaneously transmit their signals with various power levels. The receiver then decodes user data individually from the overlapped signal using successive interference cancellation (SIC). This paper reports the use of NOMA in an FSO link with two users and details an investigation of the effects of power allocation and channel estimation on the user’s signals demodulation accuracy. Analysis of varying data rate and system capacity gain are explored. Experimental results indicate that accurate channel estimation and optimum power allocation ratio can improve the accuracy of signal reconstruction. Difference in data rate tested proved negligible to signal demodulation quality.
Free Space Optical (FSO) communication is widely recognized for its powerful features, especially when compared to other wireless technologies utilized in point-to-point communication links. Although current literature focuses primarily on point-to-point transmission, multi-user FSO systems are beginning to draw significant attention. The primary objective in a multi-user communication system is to estimate individually transmitted signals from received signals, namely Blind Source Separation (BSS). A solution to the BSS problem in an FSO multi-user communication link is proposed. A multi-point FSO system composed of two independent transmitters operating at different wavelengths and a dual path fiber bundle receiver was used. The FastICA algorithm was exploited for multi-user detection. Experimental results demonstrate that this method can separate original transmitted signals from their received mixtures. Effects of signal power, data rate, misalignment error, and turbulence severity on signal separation are also explored to define the working range for achieving best performance.
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