Light-Emitting Diodes. (Monographs in Electrical and Electronic Engineering.) By A. A. Bergh and P. J. Dean. Pp. viii+591. (Clarendon: Oxford; Oxford University: London, 1976.) £22.

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Light-emitting diodes

Femtocells, despite their name, pose a potentially large disruption to the carefully planned cellular networks that now connect a majority of the planet's citizens to the Internet and with each other. Femtocells - which by the end of 2010 already outnumbered traditional base stations and at the time of publication are being deployed at a rate of about five million a year - both enhance and interfere with this network in ways that are not yet well understood. Will femtocells be crucial for offloading data and video from the creaking traditional network? Or will femtocells prove more trouble than they are worth, undermining decades of careful base station deployment with unpredictable interference while delivering only limited gains? Or possibly neither: are femtocells just a "flash in the pan"; an exciting but short-lived stage of network evolution that will be rendered obsolete by improved WiFi offloading, new backhaul regulations and/or pricing, or other unforeseen technological developments? This tutorial article overviews the history of femtocells, demystifies their key aspects, and provides a preview of the next few years, which the authors believe will see a rapid acceleration towards small cell technology. In the course of the article, we also position and introduce the articles that headline this special issue.

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Femtocells: Past, Present, and Future

In this chapter we deal with the following nonlinear fractional programming problem: 

$$P:\mathop{{\max }}\limits_{{x \in s}} q(x) = (f(x) + \alpha )/((x) + \beta )$$

where f, g: R n → R, α, β ∈ R, S ⊆ R n . To simplify things, and without restricting the generality of the problem, it is usually assumed that, g(x) + β + 0 for all x ∈ S,S is non-empty and that the objective function has a finite optimal value.

Nonlinear Fractional Programming

Visible Light Communication (VLC) is an emerging field in Optical Wireless Communication (OWC) which utilizes the superior modulation bandwidth of Light Emitting Diodes (LEDs) to transmit data. In modern day communication systems, the most popular frequency band is Radio Frequency (RF) mainly due to little interference and good coverage. However, the rapidly dwindling RF spectrum along with increasing wireless network traffic has substantiated the need for greater bandwidth and spectral relief. By combining illumination and communication, VLC provides ubiquitous communication while addressing the shortfalls and limitations of RF communication. This paper provides a comprehensive survey on VLC with an emphasis on challenges faced in indoor applications over the period 1979–2014. VLC is compared with infrared (IR) and RF systems and the necessity for using this beneficial technology in communication systems is justified. The advantages of LEDs compared to traditional lighting technologies are discussed and comparison is done between different types of LEDs currently available. Modulation schemes and dimming techniques for indoor VLC are discussed in detail. Methods needed to improve VLC system performance such as filtering, equalization, compensation, and beamforming are also presented. The recent progress made by various research groups in this field is discussed along with the possible applications of this technology. Finally, the limitations of VLC as well as the probable future directions are presented.

LED Based Indoor Visible Light Communications: State of the Art

Providing ubiquitous connectivity to diverse device types is the key challenge for 5G and beyond 5G (B5G). Unmanned aerial vehicles (UAVs) are expected to be an important component of the upcoming wireless networks that can potentially facilitate wireless broadcast and support high rate transmissions. Compared to the communications with fixed infrastructure, UAV has salient attributes, such as flexible deployment, strong line-of-sight (LoS) connection links, and additional design degrees of freedom with the controlled mobility. In this paper, a comprehensive survey on UAV communication towards 5G/B5G wireless networks is presented. We first briefly introduce essential background and the space-air-ground integrated networks, as well as discuss related research challenges faced by the emerging integrated network architecture. We then provide an exhaustive review of various 5G techniques based on UAV platforms, which we categorize by different domains including physical layer, network layer, and joint communication, computing and caching. In addition, a great number of open research problems are outlined and identified as possible future research directions.

UAV Communications for 5G and Beyond: Recent Advances and Future Trends

For the current 5G era, the deployment of small cells in residential and commercial areas plays an imperious preamble in improving network coverage and the quality of service (QoS) Major technical problems associated with the mass deployment of small cells, such as femtocells are interference management and QoS provisioning These are important for service-providing operators because the system capacity and achievable data rates mainly depend on interference Future generation wireless networks will use autonomous and distributed architecture for ameliorating the efficacy and flexibility of communication systems In this paper, we propose a game theory-based model along with dynamic channel allocation and self-optimizing power control scheme for resolving priority-based access exposure by applying the concept of primary and secondary users It is expected that the consumers will experience better QoS with reduced interference levels, and the service-providing operators will be able to increase their revenue, while ensuring optimal price for the consumers We assimilated extensive numerical results to demonstrate the efficacy of our proposed model

Game-Based Approach for QoS Provisioning and Interference Management in Heterogeneous Networks

With the swift evolution of wireless technologies, the demand for the Internet of Things (IoT) security is rising immensely. Elliptic curve cryptography (ECC) provides an attractive solution to fulfill this demand. In recent years, Edwards curves have gained widespread acceptance in digital signatures and ECC due to their faster group operations and higher resistance against side-channel attacks (SCAs) than that of the Weierstrass form of elliptic curves. In this paper, we propose a high-speed, low-area, simple power analysis (SPA)-resistant field-programmable gate array (FPGA) implementation of ECC processor with unified point addition on a twisted Edwards curve, namely Edwards25519. Efficient hardware architectures for modular multiplication, modular inversion, unified point addition, and elliptic curve point multiplication (ECPM) are proposed. To reduce the computational complexity of ECPM, the ECPM scheme is designed in projective coordinates instead of affine coordinates. The proposed ECC processor performs 256-bit point multiplication over a prime field in 198,715 clock cycles and takes 1.9 ms with a throughput of 134.5 kbps, occupying only 6543 slices on Xilinx Virtex-7 FPGA platform. It supports high-speed public-key generation using fewer hardware resources without compromising the security level, which is a challenging requirement for IoT security.

https://www.mdpi.com/1424-8220/20/18/5148/pdf

Design and Implementation of High-Performance ECC Processor with Unified Point Addition on Twisted Edwards Curve.

In recent times, optical wireless communications (OWC) have become attractive research interest in mobile communication for its inexpensiveness and high-speed data transmission capability and it is already recognized as complementary to radio-frequency (RF) based technologies. Light fidelity (LiFi) and optical camera communication (OCC) are two promising OWC technologies that use a photo detector (PD) and a camera, respectively, to receive optical pulses. These communication systems can be implemented in all kinds of environments using existing light-emitting diode (LED) infrastructures to transmit data. However, both networking layers suffer from several limitations. An excellent solution to overcoming these limitations is the integration of OCC and LiFi. In this paper, we propose a hybrid OCC and LiFi architecture to improve the quality-of-service (QoS) of users. A network assignment mechanism is developed for the hybrid system. A dynamic link-switching technique for efficient handover management between networks is proposed afterward which includes switching provisioning based on user mobility and detailed network switching flow analysis. Fuzzy logic (FL) is used to develop the proposed mechanisms. A time-division multiple access (TDMA) based approach, called round-robin scheduling (RRS), is also adopted to ensure fairness in time resource allocation while serving multiple users using the same LED in the hybrid system. Furthermore, simulation results are presented taking different practical application scenarios into consideration. The performance analysis of the network assignment mechanism, which is provided at the end of the paper, demonstrates the importance and feasibility of the proposed scheme.

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Fuzzy Based Network Assignment and Link-Switching Analysis in Hybrid OCC/LiFi System

In this paper, we consider the current status and technical issues involved in the use of optical camera communication (OCC)/visible light communication (VLC) technologies in vehicular communication systems. Hybrid spatial phase-shift keying was introduced in IEEE 802.15.7-2018 as the standard hybrid modulation scheme for vehicular OCC/VLC systems. We herein propose a functional communication system architecture for vehicular systems based on this hybrid waveform, and we also present state-of-the-art research work on an artificial intelligence (AI)-based vehicular OCC system. Every AI module within the proposed system architecture is discussed in detail. Finally, our experimental procedures and results are analyzed to evaluate the performance of the proposed system over a complex channel model in a vehicular environment. We effectively employed the popular You Only Look Once version 2 object detection algorithm for real-time region-of-interest tracking in city driving (at a vehicular velocity of around 30 km/h and highway night driving (at a vehicular velocity of > 60 km/h) scenarios. Moreover, our novel neural-network-based decoder and AI-based error correction proved effective in improving the data decoding accuracy, resulting in a best-case reduction of 2.2 and 9.0 dB, respectively, in the signal-to-noise ratio needed to achieve the desired bit error rate of 10
 -4
 in a vehicular OCC/VLC system.

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Deep Learning for Optical Vehicular Communication

The satisfaction level of femtocell users depends on the availability of requested bandwidth. But, the xDSL line that can be used for the backhauling of femtocell traffic cannot always provide sufficient bandwidth due to the inequality between the xDSL capacity and demanded bandwidth of home applications, like IPTV, PC, Wi-Fi, and others. A Service Level Agreement (SLA) between xDSL and the femtocell operator (mobile operator) to reserve some bandwidth for the upcoming femtocell calls can increase the satisfaction level for femtocell users. In this paper, we propose a SLA negotiation procedure for femtocell networks. The Bandwidth Broker controls the allocated bandwidth for femtocell users. Then, we propose the dynamically reserved bandwidth scheme to increase the femtocell user's satisfaction level. Finally, we present our simulation results to validate the proposed scheme.

Yeong Min Jang

Papers

Game-Based Approach for QoS Provisioning and Interference Management in Heterogeneous Networks

Design and Implementation of High-Performance ECC Processor with Unified Point Addition on Twisted Edwards Curve.

Fuzzy Based Network Assignment and Link-Switching Analysis in Hybrid OCC/LiFi System

Deep Learning for Optical Vehicular Communication

Dynamic SLA negotiation using bandwidth broker for femtocell networks