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

This paper proposes software-based scheme for unidirectional communications of OCC system. Proposed scheme based on over-sampling technique will solve fully effects of exposure to the unidirectional OCC system where there is no synchronization. These schemes do not consider mitigating flicker, and then they are suitable for both global shutter and rolling shutter OCC system.

Asynchronous scheme for unidirectional optical camera communications (OCC)

Orthogonal Frequency-Division Multiplexing (OFDM) is different from a single-carrier modulation, which is a digital multi-carrier modulation scheme. It has proceeded in broadband wireless or broadband wired communication as an effective settlement with Inter-Symbol Interference which occurred due to a multipath fading. In the Light Fidelity Technique, the OFDM modulation is well-known and widely employed; however, the using of OFDM modulation with Optical Camera Communication is difficult to employ. To increase data rate, the researchers consider to use multi-LED to transmit data but the effect among LEDs needs to consider. This paper presents the Multiple Input Multiple Output OFDM OCC system according to the effect of the rolling shutter. The proposed scheme according to OFDM deploys a rolling-shutter effect to transmit signal at a high rate with more than 2 LEDs. Based on the theoretical of the Rolling OFDM scheme, we propose a novel scheme architecture with technical details of the system architecture.

Rolling MIMO-OFDM for Optical Camera Communication System

In this article, we introduce an image sensor–based optical vehicular communication system for performing vehicular condition resolution adaptively in the spatial domain and the temporal domain. To...

Adaptive spatial-temporal resolution optical vehicular communication system using image sensor

In recent times, the electric power management based on customers’ demand has drawn significant attention of smart-grid (SG) governors. The SG requires real-time management of dynamic load to maintain the quality of service (i.e., balance between supply and demand) by interfacing with users. In this paper, we propose an approach to respond to the active demand (AD) based on user-defined energy-management policy. An algorithm is also proposed for the smart-controller device (SCD) modeled with the load aggregator and connected to the customers. The total contracted load and the user ADs are determined based on area, load, and phase classification, which specify the individual energy consumption. The proposed scheme is implemented in MATLAB/Simulink using the load-information of the IEEE 30-bus system, and the feasibility is assessed in IEEE 13 and IEEE 34 node test feeder systems. By applying the customer’s controlled SCD device both the deficiency and redundancy of generation in terms of grid controllable load have been improved that lead the maximization of generation and distribution services. The voltage regulation and power factor of the particular area have been enhanced by integrating appropriate distributed generation and power factor improvement devices. The results garnered from the performance analysis show that the proposed scheme can optimize power generation based on the user-defined demand.

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Power Flow Management With Demand Response Profiles Based on User-Defined Area, Load, and Phase Classification

Unlike visible light communication (VLC), optical camera communication (OCC) utilizes an image sensor as receiver. In this paper, we will discuss trade-off communication distance and data rate which occurs when using rolling shutter camera. Beside we proposed comparison and an improvement to over data frame format.

Yeong Min Jang

Papers

Asynchronous scheme for unidirectional optical camera communications (OCC)

Rolling MIMO-OFDM for Optical Camera Communication System

Adaptive spatial-temporal resolution optical vehicular communication system using image sensor

Power Flow Management With Demand Response Profiles Based on User-Defined Area, Load, and Phase Classification

Trade-off Communication distance and Data rate of Rolling shutter OCC