Weather effects on FSO network connectivity

The use of relays is one of the most promising methods for mitigating impairments of the performance of free-space optical (FSO) systems and extending their limited transmission range. However, several factors contribute to significant link performance degradation. Most severe is the influence of the adverse atmospheric conditions that frequently appear, thus making the design of strongly connected networks a demanding issue. In this paper, we consider a multiple-hop FSO network, where the nodes are distributed at fixed positions on a given path-link. We take account of the most critical weather phenomena, i.e., fog, rain, and snow, and derive analytical expressions for the node isolation probability, assuming a suitable path loss model. Next, we find the number of transceivers for a given path-link in order to achieve reliable performance. We also examine the reverse case; i.e., we find the total service length for a known number of FSO transceivers. The effect of the prime FSO modulation formats is also considered. The addressed analytical framework offers significant insights into the main factors that degrade the performance of FSO networks. It constitutes a valuable tool for telecom researchers to design such networks in practice. © 2009-2012 OSA

Optimal Trade-Off between Depth and Coverage for a Vertical UOWC Link

The optimal trade-off between coverage and depth for a vertical underwater optical wireless communication (UOWC) link is thoroughly investigated in this letter. In the scenario under consideration, the optical transmitter is mounted at a fixed position on the sea surface and illuminates a subsea area through a Lambertian radiation pattern. A generic path loss expression is considered with a simplified extinction coefficient, and the most critical parameter values are taken into account. Then, a tractable mathematical formula relating the coverage radius with depth is readily extracted. The analysis of the coverage issues discussed herein takes on a particular research interest due to the rapid growth of UOWC networks nowadays. © 1989-2012 IEEE

Exploring the Random Location Problem Inside a Truncated Conic Shape: Application in UAV Communications

More often than not, transmitters (Txs) in wireless networks operate using directional radiation patterns where the main radiation lobe creates a three-dimensional conic-shaped volume. In this context, any receiver (Rx) placed inside it can establish a strong communication link. Since the Rx location is not always known, it is desirable to investigate its random position effect to describe the link performance in a reliable manner. As in most cases, Rxs lie far away from the apex where the Tx is placed, we investigate the random location problem inside a truncated conic shape where the cone arises as a limiting case. To this end, we deduce a set of statistical metrics, including the random distance from the apex to a random point position. As an application, we focus on the outage performance of an unmanned aerial vehicle (UAV) communications scenario susceptible to Nakagami- m fading and derive novel closed-form expressions for the composite model. © 1972-2012 IEEE

Node isolation probability for serial ultraviolet UV-C multi-hop networks

Non-line-of-sight optical wireless transmission, operated in the unlicensed ultraviolet UV-C band, has been recently suggested as an alternative means of communication. However, due to limited coverage, relayed UV-C networks need to be deployed in order to supply communication services at large distances. In this paper, we consider a serial multi-hop UV-C network where the nodes are distributed at fixed positions on a given service interval. We adopt a suitable path loss model and derive analytical expressions for the node isolation probability assuming on-off keying and pulse position modulation formats. Moreover, we investigate the node density required to achieve connectivity for several geometrical transceiver configurations. The numerical results of this paper are of significant value for telecom researchers working toward a flexible UV-C network deployment in practice. © 2009 OSA

Using a HAP network to transfer WiMAX OFDM signals: Outage probability analysis

Transferring wireless broadband services across extremely far distances on Earth is usually implemented nowadays either by ground-based or satellite communications. Terrestrial networks require, however, heavy installation and maintenance costs, whereas satellite networks suffer from excessively high power requirements. An alternative but highly challenging solution is to employ a network consisting of high-altitude platforms (HAPs). In this paper, we propose a way of delivering WiMAX traffic using a serial multi-hop HAP network configuration. HAPs are located at specific locations in the stratosphere, pick up the traffic from the Earth region they cover, and communicate with each other using optical links. In such a configuration, we determine the WiMAX quality of service by evaluating the outage probability for the entire HAP network. The overall performance is examined by using a channel model that takes into account laser path loss and pointing error effects. The findings of the present study indicate that the consideration of specific network and channel model parameters is crucial toward the design and implementation of future multi-hop HAP networks. © 2009-2012 OSA

A Tractable Model for Turbulence- and Misalignment-Induced Fading in Optical Wireless Systems

Composite models for the combined effect of both scintillation- and misalignment-induced fading in terrestrial optical wireless systems are often expressed in terms of higher order special functions, making, thus, the performance evaluation of such links quite complicated. In order to overcome this problem, we propose the mixture Gamma distribution as an accurate approximation of the turbulence effect. Then, a tractable mixture distribution is deduced, for the statistical description of the composite scintillation/pointing error effects. Some statistical metrics of the new model are also derived in closed form, which provides insight information for the system design. © 2016 IEEE

Connectivity issues for ultraviolet UV-C networks

This paper focuses on the connectivity issues of a non-line-of-sight (NLOS) optical wireless network operating in the ultraviolet UV-C spectral region. NLOS UV-C transmitters have a limited effective coverage and, hence, a dense node distribution is required in order to efficiently cover a large geographical area. Under this assumption, the concept of connectivity is more than important since it provides a strong indication of the network reliability and robustness. In the present study, we consider transmission with onoff keying and pulse position modulation schemes assuming both Gaussian and Poisson noise and adopt an effective experimental path loss model. Then, we evaluate the k-connectivity properties in terms of several network parameters. More precisely, we present and analyze the trade-off between node density and the degree of k-connectivity against other parameters (i.e.,transmitted power, supported data rate, and error probability). The derived results are depicted using appropriate figures and tables and constitute the theoretical basis for the design and implementation of a reliable UV-C network in practice. © 2011 Optical Society of America

Impact of a Randomly Placed Terminal on LiFi Performance

The ambitious goal of light-fidelity (LiFi) technology to provide seamless user mobility in indoor environments requires strong link connections to confront any stochasticity that possibly comes out. In this context, a robust LiFi network should effectively address the spatial random terminal locations inside its coverage volume. In contrast with the previously published works dealing mainly with randomness in two dimensions, the present study aims to provide a more realistic framework by treating the problem in the three-dimensional space. In view of the foregoing, a LiFi configuration is adopted where a terminal lies at a random position inside its truncated conic coverage volume at a distance from the transmitter. Some key statistics for a distance-related metric and the channel gain, including the probability density function, are derived in the first place. The investigation is then headed on the performance analysis of the LiFi link by providing closed-form expressions of the outage probability and the average bit error rate for on-off keying assuming indirect modulation/direct detection at the receiver. A multiuser scenario with several users placed inside the coverage volume is examined as well. A series of numerical results is also depicted to provide valuable insights into how the random terminal placement affects the link performance. © 1972-2012 IEEE