High-Speed Indoor Optical Wireless Links Employing Fast Angle and Power Adaptive Computer-Generated Holograms With Imaging Receivers

In this paper, we introduce an adaptive optical wireless system that employs a finite vocabulary of stored holograms. We propose a fast adaptation approach based on a divide and conquer methodology resulting in a number of adaptation algorithms: fast angle adaptive holograms (FAA-Holograms), fast power adaptive holograms (FPA-Holograms), and fast angle and power adaptive holograms (FAPA-Holograms) and evaluate these in mobile optical wireless (OW) systems in conjugation with imaging reception. The ultimate goal is to improve the signal-to-noise ratio (SNR), to reduce the effect of intersymbol-interference (ISI), to speed up the adaptation process, and to eliminate the need to calculate the hologram in real-time at each transmitter and receiver location. The system operates at high data rates under the impact of multipath dispersion, background noise and mobility. At a data rate of 2.5 Gb/s and under eye safety regulations, the proposed FAPA-Holograms offers around 20 dB SNR in the presence of background shot noise, receiver noise, multipath dispersion, and mobility. Simulation results show that the proposed system, FAPA-Holograms, can reduce the time required to identify the optimum hologram position from 80 ms in the original beam angle and power adaptive line strip multibeam system (APA-LSMS) to about 13 ms

The green ICT initiative: an IEEE-wide focus building upon ComSoc's leadership

This month's President's Page is devoted to the IEEE Green Information and Communications Technology (ICT) initiative. By its very nature, Green ICT is a theme, not only of interest but also offering numerous opportunities, for virtually every IEEE Society and Council. Through this initiative, ComSoc seeks an IEEE-wide outreach to achieve even greater recognition for IEEE's mission of advancing technology for humanity

Performance Evaluation of Multi-gigabit Indoor Visible Light Communication System

This paper presents a performance evaluation of a mobile multi-gigabit visible light communication (VLC) system in two different environments. The VLC channel characteristics and links were evaluated under the diverse situations of an empty room and a room with very strong shadowing effects resulting from mini cubicle offices. RGB laser diodes (LDs) were used to mitigate the low modulation bandwidth of conventional transmitters (light emitting diodes, LEDs) in the VLC system. In addition, an angle diversity receiver (ADR) was introduced to mitigate intersymbol- interference (ISI). Furthermore, a delay adaptation technique was used to further reduce the effect of ISI and multipath dispersion. The combination of delay adaptation and ADR (DAT ADR system) added a degree of freedom to the link design, which resulted in a VLC system that has the ability to provide high data rates (i.e. 5 Gbps) in the considered harsh indoor environment. Our proposed system used a simple on-off keying (OOK) modulation format and it was able to provide data rates of 5 Gbps and a bit-error-rate (BER) of 10-3 in the worst case scenario in the considered realistic indoor environment

Mobile Multi-Gigabit Visible Light Communication System in Realistic Indoor Environment

The main challenges facing high data rate visible light communication (VLC) are the low-modulation bandwidth of the current transmitters (i.e., light emitting diodes), the intersymbol interference (ISI) caused by the multipath propagation and cochannel interference (CCI) due to multiple transmitters. In this paper, for the first time, to the best of our knowledge, we propose, design, and evaluate the use of laser diodes (LDs) for communication as well as illumination. In addition, we propose an imaging receiver for a mobile VLC system to mitigate ISI. A novel delay adaptation technique is proposed to mitigate CCI, maximize the signal to noise ratio, and reduce the impact of multipath dispersion under user mobility.The proposed imaging system is able to provide data rates of 5 Gb/s in the worst-case scenario.The combination of a delay adaptation approach with an imaging receiver (DAT imaging LD-VLC system) adds a degree of freedom to the link design, which results in a VLC system that has the ability to provide higher data rates (i.e., 10 Gb/s) in the considered harsh indoor environment.The proposed technique (delay adaptation) achieves significant improvements in the VLC channel bandwidth (more than 16 GHz) over an imaging system in the worst-case scenario.The VLC channel characteristics and links were evaluated under diverse situations including an empty room and a room with very strong shadowing effects resulting from minicubicle offices

Dynamic Spectrum Leasing for Bi-Directional Communication: Impact of Selfishness

In this paper, we propose a beamforming-based dynamic spectrum leasing (DSL) technique to improve the spectral utility of bi-directional communication of the legacy/primary spectrum users through the help of colocated secondary users. The secondary users help for a time interval to relay the data between two primary terminals using physical layer network coding and beamforming to attain bi-directional communication with high spectral utility. As a reimbursement, the secondary users, cognitive radios (CRs) in our case, get exclusive access to the primary spectrum for a certain duration. We use Nash bargaining to determine the optimal division of temporal resources between relaying and reimbursement. Moreover, we consider that a fraction of secondary nodes can act selfishly by not helping the primary, yet enjoy the reimbursement time. We measure the utility of the DSL scheme in terms of a metric called time-bandwidth product (TBP) ratio quantifying the number of bits transmitted in direct communication versus DSL. We show that if all secondary nodes act honestly, more than 17-fold increase in the TBP ratio is observed for a sparse CR network. However, in such a network, selfish behavior of CR nodes can reduce the gain by more than a factor of 2

Analysis of dynamic spectrum leasing for coded Bi-directional communication

In this paper, we aim to present a cooperative relaying based two way wireless communication scheme which can provide both spectral and energy efficiency in future wireless networks. To this end, we propose a novel network coding based Dynamic Spectrum Leasing (DSL) technique in which the cognitive secondary users cooperatively relay the primary data for two-way primary communication. In exchange for the relaying services, the primary grants exclusive access to the secondary users for their own activity. We model the random geometry of the ad hoc secondary users using a Poisson point process. We devise a game theoretic framework for the division of leasing time between the primary cooperation and secondary activity phases. We demonstrate that under these considerations and employing network coding, DSL can improve the number of bits that are successfully transmitted by 54% as compared to un-coded direct two way primary communication. Also the energy costs of the proposed DSL scheme are more than 10 times lower. Employing DSL also enables the cognitive users to get reasonable time for their own transmission after increasing the primary spectral and energy efficiency