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

Time-of-Flight (ToF) camera has become an attractive source of applications in location-based services, autonomous navigation, object localization for robotic manipulation, ego-motion estimation, etc. Besides, these services demand centimeter level accuracy to provide the required services. Though ToF cameras can provide high accuracy in location-based services with high frame rates (approx. 30 fps), they are facing some problems like multipath interference (MPI), internal scattering, motion blur, etc. The interferences inherent to ToF camera can influence the measurements by several centimeters. In this paper, we formulate a model to mitigate MPI and light scattering problems through a combination of scale-invariant feature transform (SIFT) and iterative closest point (ICP). We use SIFT algorithm for image features extraction and ICP for error correction during estimation. Finally, we present simulation results to prove the scalability and flexibility of our proposed algorithm for both MPI and light scattering mitigation.

Interference mitigation technique for Time-of-Flight (ToF) camera

This paper proposes a novel method of training and applying a neural network to act as an adaptive decoder for a modulation scheme used in optical camera communication (OCC). We present a brief discussion on trending artificial intelligence applications, the contemporary ways of applying them in a wireless communication field, such as visible light communication (VLC), optical wireless communication (OWC) and OCC, and its potential contribution in the development of this research area. Furthermore, we proposed an OCC vehicular system architecture with artificial intelligence (AI) functionalities, where dimmable spatial 8-phase shift keying (DS8-PSK) is employed as one out of two modulation schemes to form a hybrid waveform. Further demonstration of simulating the blurring process on a transmitter image, as well as our proposed method of using a neural network as a decoder for DS8-PSK, is provided in detail. Finally, experimental results are given to prove the effectiveness and efficiency of the proposed method over an investigating channel condition.

A Novel Neural Network-Based Method for Decoding and Detecting of the DS8-PSK Scheme in an OCC System

In this paper, Smart LED lighting system based on continuous human tracking data using US(UltraSonic) sensor and IR(Infared) sensor is proposed. LED Control of On-Off is determined by the output based on human tracking data using US or IR sensor. However existing LED control system is impossible to detect continuously by using separately for each sensor. And the efficiency of the existing system is low. Therefore this paper proposes the solution of the continuous human tracking and the efficiency. And it leads the direction of the implementation for LED smart lighting system by implementing the hardware based on proposed system. And we demonstrated the usefulness of the proposed system.

Smart LED lighting system implementation using human tracking US/IR sensor

There are several existing Low Power Wide Area Network (LPWAN)-technologies competing to provide M2M connectivity and secure niche in the Internet of Things (IoT) universe. Most of well-known LPWAN approaches are quite recognizable thanks to sizable marketing efforts though most of it practically is not the right choice for the robust long-range and large-scale networks. We have compared the famous LPWAN technologies to provide a complete overview of the different perspective. From the comparison, the considering candidate to be used in the Smart Cities Application is then revealed based on its advantages.

Low Power Wide Area Network Technologies for Smart Cities Applications

The requirements in terms of service quality such as data rate, latency, power consumption, number of connectivity of future fifth-generation (5G) communication is very high. Moreover, in Internet of Things (IoT) requires massive connectivity. Optical wireless communication (OWC) technologies such as visible light communication, light fidelity, optical camera communication, and free space optical communication can effectively serve for the successful deployment of 5G and IoT. This paper clearly presents the contributions of OWC networks for 5G and IoT solutions.

Yeong Min Jang

Papers

Interference mitigation technique for Time-of-Flight (ToF) camera

A Novel Neural Network-Based Method for Decoding and Detecting of the DS8-PSK Scheme in an OCC System

Smart LED lighting system implementation using human tracking US/IR sensor

Low Power Wide Area Network Technologies for Smart Cities Applications

Opportunities of Optical Spectrum for Future Wireless Communications