A PE-ACO-OFDM (Position-Encoded Asymmetrically Clipped Optical Orthogonal Frequency Division Multiplexing) signaling scheme for intensity modulation and direct detection is introduced in this paper,where the anti-asymmetry characteristics of ACO-OFDM are exploited to improve the rate of data transmission.This is achieved by reducing the symbol duration of the ACO-OFDM signal,where only the first half of ACO-OFDM is used to transmit the ACO-OFDM data symbol after inverting its negative samples to positive ones.In addition,encoded ACO-OFDM samples are combined with every ACO-OFDM symbol to allow the receiver to identify the position of the inverted samples.Simulation results are introduced,and it is shown that the data rates of PE-ACO-OFDM improve by 33% compared with ACO-OFDM,when a 256-quadrature amplitude modulation scheme is considered as the encoded constellation order.It is also shown that the signal to noise ratio of the proposed PE-ACO-OFDM is higher by almost 1 dB compared with the traditional ACO-OFDM.
Practical VLC (Visible Light Communication) systems are expected to leverage the lighting infrastructure in order to deliver data to devices in a lighting field.These devices can be static or quasistatic (e.g.,laptops or IoT devices); however,it is becoming clear that the preponderance of wireless data consumption is dominated by handheld mobile devices which will exhibit varying physical orientations and 3D dynamics.Because free-space optical and visible light communications are primarily line of sight,transmitter radiation patterns and receiver field of view are very important for predicting the data performance.Given dynamic emission characteristics,there is an opportunity to adapt to the receiver.The caveat of dynamic VLC systems is that the quality and distribution of the resulting illumination must be considered as part of the dual goal of providing high quality lighting.In this paper we investigate the impact of device orientation and mobility on static and then dynamic lighting emission under a multi-cell lighting model.From a source standpoint we consider the performance of beam control through angular control and beam focus for one or more sources in a lighting array.Analysis and simulation demonstrate that dynamic beam and luminaire control can increase the AP coverage range by 12.8X under a 1.67 m ceiling height.Furthermore,the use of multiple sources tracking device orientation and position can mitigate off-angle performance degradation by increasing redundancy in the number of available connections.Our proposed techniques,when applied in concert,successfully mitigate common concerns about the viability of VLC and indoor FSO (Free Space Optical Communication) methods related to signal occlusion and device dynamics.
Data transmission with RGB LEDs is attracting significant research interest in VLC (Visible Light Communication).We consider the power optimization under brightness and communication requirements for RGB LEDs,and model the color constraint using the MacAdam ellipse instead of a fixed point in the chromaticity diagram.Then an optimization problem is formulated to determine the transmission power consumption and the corresponding coordinates in the chromaticity diagram.We propose a novel two-step algorithm to solve the optimization problem with lower implementation complexity.Numerical results show that the proposed approach shows the same performance as the optimal solution using a brute-force method,and requires the lower power consumption using MacAdam ellipse instead of merely a fixed point in the chromaticity diagram.
In this paper,we propose an EADO-OFDM (Enhanced Asymmetrically Clipped DC Biased Optical Orthogonal Frequency Division Multiplexing) method for IM/DD (Intensity-Modulated DirectDetection) optical systems,in which the AV-DCO-OFDM (Absolute Valued DC Biased Optical OFDM) symbols on the even subcarriers and ACO-OFDM (Asymmetrically Clipped Optical OFDM) symbols on the odd subcarriers are combined for simultaneous transmission.Moreover,we discuss the PDF (Probability Density Function) and electrical SNR (Signal to Noise Ratio) of the symbols,which are utilized to estimate the BER (Bit Error Ratio) performance and overall performance of EADO-OFDM.The Monte Carlo simulation results have validated the theoretical analysis and have also confirmed the EADO-OFDM is attractive considering the following benefits.Firstly,EADO-OFDM is more energy efficient compared to the power-efficient DCO-OFDM (DC Biased Optical OFDM),since the required DC bias is smaller when appropriate constellation size combinations are chosen.In addition,EADO-OFDM performs better than the conventional ADO-OFDM (Asymmetrically Clipped DC Biased Optical OFDM),because the absolute value operation causes no clipping distortion.
OCC (Optical Camera Communication) has been proposed in recent years as a new technique for visible light communications.This paper introduces the implementation and experimental demonstration of an OCC system.Phase uncertainty and phase slipping caused by camera sampling are the two major challenges for OCC.In this paper,we propose a novel modulation scheme called undersampled differential phase shift on–off keying to encode binary data bits without exhibiting any flicker to human eyes.The phase difference between two consecutive samples conveys one-bit information,which can be decoded by a low-frame-rate camera receiver.Error detection techniques are introduced to enhance the reliability of the system.We present the hardware and software design of the proposed system,which is implemented with a Xilinx FPGA and a Logitech commercial camera.Experimental results demonstrate that a bit-error rate of 10?5can be achieved with 7.15 mW received signal power over a link distance of 15 cm.
In this work,we consider employing the NOMA (Non-Orthogonal Multiple Access) technique in downlink VLC (Visible Light Communication) for performance enhancement.In particular,focusing on a typical NOMA scenario with two users,we optimize the power allocation strategies under both sum-rate maximization and max-min fairness criteria,where practical optical power and QoS (Quality of Service)constraints are included.As our main contribution,we achieve optimal power allocation solutions in semi-closed forms via mathematical analysis,which,to the best of our knowledge,have not been reported in literature.Simulation results demonstrate that NOMA can provide remarkable performance gains over OMA (Orthogonal Multiple Access) in the context of VLC downlinks.
This paper introduces infrastructure-to-vehicle and vehicle-to-vehicle communications using VLC.A VLC coupled with a high-speed image sensor is introduced (i.e.,image sensor communication).The high-speed image sensors provide eyes for autonomous and connected vehicles.VLC imparts data reception capability to image sensors with necessary functions,which can then be provided to autonomous and connected vehicles.In this paper,some of our research on coupling VLC to high-speed image sensors is introduced,including our key findings:the basics of ISC,a vehicle motion model,and range estimation.
Indoor wireless communication networking has received significant attention along with the growth of indoor data traffic.VLC (Visible Light Communication) as a novel wireless communication technology with the advantages of a high data rate,license-free spectrum and safety provides a practical solution for the indoor high-speed transmission of large data traffic.However,limited coverage is an inherent feature of VLC.In this paper,we propose a novel hybrid VLC-Wi-Fi system that integrates multiple links to achieve an indoor high-speed wide-coverage network combined with multiple access,a multi-path transmission control protocol,mobility management and cell handover.Furthermore,we develop a hybrid network experiment platform,the experimental results of which show that the hybrid VLC-Wi-Fi network outperforms both single VLC and Wi-Fi networks with better coverage and greater network capacity.
Data centers are crucial elements in modern information technology.In order to implement the next generation of data centers,new challenges must be overcome.These include reducing the energy consumption,increasing the data rates,reducing the communication latency,increasing the flexibility and scalability,and reducing the maintenance time and cost.One promising way for meeting these challenges is to employ multichannel optical wireless communication as part of the data center hybrid communication network.In this paper,we analyze three technologies that could be used in this context:MIMO(Multiple-in-Multipleout),multiplexing through orbital angular momentum of light,and direct modulation through the large number of modes associated with orbital angular momentum.Our results indicate that these technologies could provide an innovative and flexible means of meeting the challenges of the next generation of data centers.
Recently,FSO(Free-Space Optical Communication)has received a lot of attention thanks to its high data-rate transmission via unbounded unlicensed bandwidth.However,some weather conditions lead to significant degradation of the FSO link performance.Based on this context and in order to have a better understanding of the capabilities of FSO communication in a coastal environment,the effects of temperature and humidity on an FSO system are investigated in this study.An experiment is conducted using an open source FSO system that achieves a transmission rate of 1 Gbit/s at a distance of 70 m.Two new mathematical models are proposed to represent the effects of temperature and humidity on our developed FSO system operating at a wavelength of 1 550 nm.The first model links the FSO attenuation coefficient to the air temperature in coastal regions,while the second model links the FSO attenuation coefficient to the humidity and the dew-point temperature.The key finding of this study is that FSO links can achieve maximum availability in a coastal city with normal variations in temperature and humidity.
As Internet access widens,IDS (Intrusion Detection System) is becoming a very important component of network security to prevent unauthorized use and misuse of data.An IDS routinely handles massive amounts of data traffic that contain redundant and irrelevant features,which impact the performance of the IDS negatively.Feature selection methods play an important role in eliminating unrelated and redundant features in IDS.Statistical analysis,neural networks,machine learning,data mining techniques,and support vector machine models are employed in some such methods.Good feature selection leads to better classification accuracy.Recently,bio-inspired optimization algorithms have been used for feature selection.This work provides a survey of feature selection techniques for IDS,including bio-inspired algorithms.
Millimeter wave (mm-wave) communication is widely considered to be a promising technique for 5G (Fifth Generation) cellular systems.Owing to the high path loss of mm-wave channels,5G networks could employ a heterogeneous structure that consists of an MBS (Macro Base Station) and numerous SBSs (Small Base Stations).In this paper,we analyze the coverage and rate performance of an mm-wave heterogeneous network.Using user beam selection,we derive analytical expressions for the coverage probabilities of the SBSs and MBS.Furthermore,the average achievable rate for a typical user is also investigated.It is shown that the analytical results closely follow those of the simulations with marginal differences.
Thanks to the recent advances in SIS (Space Information Science) and increasingly mature technologies,network simulations have attracted much attention,which play vital roles in research on validation of the correctness of SIN’s (Space Information Network) solutions.In this paper,we constitute an architecture of a hardware-in-the-loop simulation system,where we use a server to act as a real satellite of SINs.Moreover,we model the channel of the satellite network relying on real cables and servers by referring to the Corazza model.Furthermore,based on the data of real weather events,we propose a coordinate mode for reducing LEO’s (Low Earth Orbit) communication delay and validate the efficiency of our proposed method on simulation platform by simplifying the problem to a shortest path problem.
In FSO (Free-Space Optical) communications,performance of the communication systems is severely degraded by atmospheric turbulence.PPM (Pulse Position Modulation) is widely used in FSO communication systems owing to its high power efficiency.In this paper,we present a combination of the BMST (Block Markov Superposition Transmission) technique and the PPM scheme to improve the reliability of the transmission over FSO links.Based on analyzing an equivalent system,a lower bound on the bit-error-rate of the proposed scheme is presented.Extensive simulations are performed which show that the BMST-PPM system performs well under a wide range of turbulence conditions and improves the performance of the basic code.Simulation results also show that,the performance of the system with the sliding-window detection/decoding algorithm matches well with the lower bound in the low-error-rate region.