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

The upcoming fifth generation (5G) and beyond communications introduce numerous immerging technological systems. With the rising number of users, meeting the data rate demand utilizing radio frequency (RF) spectrum is becoming extremely difficult, even for 5G communications. For this reason, researchers have shifted to visible spectrum as an alternative to the RF spectrum. Visible spectrum can provide huge channel capacity as a result the network traffic jam can be solved for future communication networks. Visible light communication (VLC) system is done by this visible spectrum. VLC is mainly an indoor communication system. VLC has a high channel capacity over RF communication. The major concern of this VLC system is when the users are far from light source or remote areas, the signal strength becomes poor and data rate received by users is comparatively low. Reconfigurable intelligent surface (RIS) is a brand new technology for 5G and beyond communications. It allows to maintain high signal strength, better network security, and helps to provide seamless connectivity with high data rate. RIS creates a great impact on VLC system. RIS uses its intelligent beamforming to allow it to get better signal strength and seamless connection to users in remote areas or far from the source. This article combines the RIS technology with VLC and performance analysis between RIS-assisted VLC over traditional VLC. Research finding clearly shows that the overall performance of RIS-assisted VLC is much higher than the current VLC system.

Integration of Reconfigurable Intelligent Surface and Visible Light Communication Systems for 5G and Beyond Communications

Recently, video broadcast/multicast over wireless networks has created a significant interest in the field of wireless communication. However, the wireless resources have limitations to broadcast/multicast many video sessions at the same time with the best quality. Hence, during the video transmission through wireless networks, it is very important to make the best utilization of the limited bandwidth. When the system bandwidth is not sufficient to allocate the demanded bandwidth for all of the active broadcasting/multicasting video sessions, instead of allocating equal bandwidth to each of them, our proposed scheme allocates bandwidth per video session based on popularity of the video program. Using the mathematical and simulation analyses, we show that the proposed scheme maximizes average user satisfaction level. The simulation results also indicate that a large number of subscribers can receive a significantly improved quality of video. To improve the video quality for large number of subscribers, the only tradeoff is that a very few subscribers receive slightly degraded video quality.

Popularity based Bandwidth Allocation for Video Broadcast/Multicast over Wireless Networks

In this paper, we propose and analyze the flicker cancellation scheme using an optimum line coding for LED-ID (light emitting diode-identification) systems The flicker is a visible fading between cycles displayed on video displays, especially the refresh interval on LED based lighting appliances LED light fixtures may appear to flicker at the lowest settings, but only when the dimmer control is moved The proposed line coding schemes have a lot of advantages such as synchronization and mitigation of noise at the receiver From the simulation results, it is confirmed that the proposed line coding scheme achieves better performance The results of this paper can be applied to design and implementation of LED-ID systems for indoor wireless home networks

Performance of flicker cancellation scheme for LED-ID systems

LED-ID (Light Emitting Diode-Identification) network is envisioned to be the next generation indoor wireless communication medium by which simultaneously high speed data transmission, identification, and illumination are possible. In spite of being extremely promising, it suffers from much impairment. Signals having different propagation paths can suffer from delays, and phase shifts which will eventually result interference. The probability of interference is also increased when communication links are established between a tag and several readers. Therefore it is necessary to reduce the interference in LED-ID network to ensure quality of service. It is possible to avoid interference by knowing the information about readers prior to assign the available spectrum. In this paper, we have proposed dynamic spectrum decision using cognitive radio concept. The simulation results justify that the proposed scheme is better than the conventional scheme.

Interference Minimization Using Cognitive Spectrum Decision for LED-ID Network

In semiconductor industry, concentration of particulate matter in cleanroom is important to maintain as it can damage the wafer die in the manufacturing process. The environment in semiconductor industry is well maintained where the temperature and humidity are always stable. Hence, it is not possible to use other features to predict the PM2.5 concentrations. In this paper, we present a modified attention Seq2Seq BiLSTM model for predicting the PM2.5 concentration. Based on the proposed model, short term (60 minute ahead, 90 minute ahead, and 120 minute ahead) PM2.5 concentration predictions was built. The proposed model also compared with Seq2Seq LSTM, Seq2Seq BiLSTM, and attention Seq2Seq LSTM models where the proposed model outperformed those models by achieving lowest RMSE, MAE, and MAPE values in all prediction time length.

Yeong Min Jang

Papers

Integration of Reconfigurable Intelligent Surface and Visible Light Communication Systems for 5G and Beyond Communications

Popularity based Bandwidth Allocation for Video Broadcast/Multicast over Wireless Networks

Performance of flicker cancellation scheme for LED-ID systems

Interference Minimization Using Cognitive Spectrum Decision for LED-ID Network

Short-term PM2.5 Prediction using Modified Attention Seq2Seq BiLSTM