On the Terminal Location Uncertainty in Elliptical Footprints: Application in Air-to-Ground Links

Wireless transmitters (Txs) radiating directionally downwards often generate circular footprints on the ground. In certain scenarios, using elliptical cells can offer increased flexibility for providing user coverage, owing to the unique network characteristics. For instance, an elliptical footprint can be produced when a practical directional antenna with unequal azimuth and elevation half-power beamwidths is used in high-speed railway networks. Another common scenario involves the production of an elliptical footprint when an airborne Tx radiates at an angle by tilting its directional antenna by a few degrees. This paper aims to investigate, for the first time, the association between the random user location within an elliptical coverage area and the performance of a wireless communication link by considering these scenarios. We assume an unmanned aerial vehicle (UAV) as a Tx, although a tall cellular base station tower could also be employed without losing generality. To better understand the impact of random location, we derive relevant distance metrics and investigate the outage probability of the link for the two scenarios, taking both random terminal location and fading impairments into account. The findings may provide valuable insights into the performance of similar wireless systems.Comment: 23 pages, 11 figure

IEEE Access special section editorial: optical wireless technologies for 5G communications and beyond

Wide bandwidth and dense spatial reuse are of extreme importance for future wireless communication networks, including 5G and beyond. In particular, these properties are important to enable future wireless networks to cope with the explosive increase in the demand for high data-rate communications. Optical wireless communications (OWC) is a promising technology for achieving this goal due to the abundant reusable license-free optical spectrum. This potential of OWC attracted significant global attention both from communications and optoelectronics viewpoints, and continues to do so

Underwater Optical Wireless Communication Systems: A Concise Review

Underwater optical wireless communications (UOWC) have gained a considerable interest during the last years as an alternative means for broadband inexpensive submarine communications. UOWC present numerous similarities compared to free space optical (FSO) communications or laser satellite links mainly due to the fact that they employ optical wavelengths to transfer secure information between dedicated point‐to‐point links. By using suitable wavelengths, high data rates can be attained. Some recent works showed that broadband links can be achieved over moderate ranges. Transmissions of several Mbps have been realized in laboratory experiments by employing a simulated aquatic medium with scattering characteristics similar to oceanic waters. It was also demonstrated that UOWC networks are feasible to operate at high data rates for medium distances up to a hundred meters. However, it is not currently available as an industrial product and mainly test‐bed measurements in water test tanks have been reported so far. Therefore, extensive research is expected in the near future, which is necessary in order to further reveal the “hidden” abilities of optical spectrum to transfer broadband signals at higher distances. The present work summarizes the recent advances in channel modeling and system analysis and design in the area of UOWC

Optimization models for misalignment fading mitigation in optical wireless links

We consider a free-space optical (FSO) channel model affected by misalignment fading (pointing error) effects. Assuming intensity modulation/direct detection (IM/DD) with on-off keying BOOK), new closed form expressions for the bit-error rate (BER) and the outage probability are presented. Furthermore, four optimization models are formulated and solved taking into account various metrics such as the beamwidth, the electrical signal-to-noise ratio, the normalized jitter, the BER, and the outage probability. The results obtained can be a useful outcome for FSO system designers in order to limit pointing error effects and achieve, thus, an optimum performance

Performance Analysis of a Laser Ground-Station-to-Satellite Link With Modulated Gamma-Distributed Irradiance Fluctuations

The performance of a ground-station-to-space laser uplink with a Gaussian-beam wave model subject to turbulence and beam wander effects is the topic of the present study. The modulated gamma distribution is used to describe the combined effect of the above two deteriorating factors. At first, a versatile expression of the above probability density function is deduced. We then derive novel closed-form expressions for its cumulative distribution function and the moment-generating function. The scintillation index and the probability of fade are hence readily evaluated. The analysis is completed with the evaluation of the bit error rate assuming heterodyne detection with differential phase-shift keying. In order to attain an adequate error rate target, we incorporate diversity at the satellite receiver. A proper simulation scenario is adopted, and numerical results are provided to verify the accuracy of the derived expressions

Coded Free-Space Optical Links over Strong Turbulence and Misalignment Fading Channels

The performance of optical wireless systems deteriorates to a large extent from the presence of turbulence and pointing error effects. To meet the typical bit error rate (BER) targets for reliable communications within the practical ranges of signal-to-noise ratio, error control coding schemes are often proposed. This paper investigates the error performance for convolutional coded on-off keying free-space optical systems through symbol by symbol interleaved channels characterized by strong turbulence and/or pointing error effects. We consider several channel types and derive exact analytical expressions for the pairwise error probability. These expressions are applied to obtain upper bounds on the BER performance using the transfer function technique

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