367 research outputs found
Analysis and design of three-stage concatenated color-shift keying
Visible Light Communication (VLC) relies on abundant unlicensed bandwidth resources. As an attractive high-data-rate modulation scheme designed for VLC, Color Shift Keying (CSK) assisted modulation is analysed. We commence our study from an uncoded M-CSK scheme relying on the joint Maximum Likelihood (ML) Hard-Detection (HD) of three colors, when communicating over an AWGN channel, where both empirical and analytical results are provided. We invoke EXtrinsic Information Transfer (EXIT) charts for designing a Maximum A-posteriori Probability (MAP) based Soft-Detection (SD) aided iterative receiver jointly detecting the three colors. Based on the EXIT characteristics of M-CSK, we design different signal labeling strategies for diverse color constellations and detection schemes, which are capable of achieving a substantially improved Bit Error Ratio (BER) performance. Thus, given a fixed transmission power, a CSK system using our proposed signal labeling is capable of increasing the reliable data transmission distance by about 30%
Cascaded PLC-VLC channel using OFDM and CSK techniques
Abstract: This paper puts in Cascade the power line communications (PLC) channel and the visible light communications (VLC) channel, in order to use the PLC channel as backbone for the VLC channel. This combination is suitable for applications in which hybrid PLC-VLC systems are needed. We investigate the behaviour of the cascaded channels for a full link transmission. Quadrature phase shift keying combined with orthogonal frequency division multiplexing (QPSK-OFDM) is used over the PLC channel and color shift keying (CSK) is deployed over the VLC channel to convey the information. Cascaded channel variances are analyzed. Complete simulated bit error rate (BER) is analyzed and presented for multiple scenarii that could occur in the two channels
Segmental analysis of the transmission in CSK systems based on the Euclidean distance
Abstract: This article presents a segmental analysis of the transmission in colour shift keying (CSK). The Euclidean distance is fractionally studied to find the distance limits between the observed and the expected points. Practical segmental characterisation of the CSK receiver is presented to verify the Voronoi segmentation over the CSK channel and confirm crosstalk and correlation between the red, green and blue channels based on the threshold selection
DC-Informative Joint Color-Frequency Modulation for Visible Light Communications
In this paper, we consider the problem of constellation design for a visible
light communication (VLC) system using red/green/blue light-emitting diodes
(RGB LED), and propose a method termed DC-informative joint color-frequency
modulation (DCI-JCFM). This method jointly utilizes available diversity
resources including different optical wavelengths, multiple baseband
subcarriers, and adaptive DC-bias. Constellation is designed in a high
dimensional space, where the compact sphere packing advantage over lower
dimensional counterparts is utilized. Taking into account multiple practical
illumination constraints, a non-convex optimization problem is formulated,
seeking the least error rate with a fixed spectral efficiency. The proposed
scheme is compared with a decoupled scheme, where constellation is designed
separately for each LED. Notable gains for DCI-JCFM are observed through
simulations where balanced, unbalanced and very unbalanced color illuminations
are considered.Comment: submitted to Journal of Lightwave Technology, Aug. 5th 201
Inter-building PLC-VLC integration based on PSK and CSK techniques
Abstract: This paper presents the implementation of an integration technique used to combine power line commu- nications (PLC) and visible light communications (VLC) channels in inter-building scenarios. It considers the narrow band PLC (NBPLC). Phase-shift keying (PSK) is used to convey the information over the PLC link and colour shift keying (CSK) technique is used on the VLC link. The colour wheel method is exploited to map PSK symbols to colours.We define a parameter x, which represents different magnitudes of the PSK complex symbol observed over the PLC channel. x is adjusted to an optimal value to meet the requirement of the CSK design. The bit error rate (BER) is analysed and the performance of the system is presented for multiple values of the modulus of the detected PSK symbol. A practical implementation is performed to verify the PSK-CSK mapping method. The impact of the sun’s rays on the red-green-blue (RGB) symbols is analysed and the interference source is highlighted
Enhanced Optical Wireless Channel For Indoor And Intravehicle Communications: Power Distribution And Signal To Noise Ratio Analysis
Visible light communication—(VLC) provides wide bandwidth and high security
capabilities for free space optical communication. This thesis presents the key concepts,
underlying principles and practical applications of visible light communications. In
particular, this thesis focuses on the received power distribution pattern and signal to noise
ratio for line-of-sight indoor and vehicular applications. Several methods are used to
modify the SNR and power distribution levels. It is shown that in the absence of
obstruction, the optical footprint is nearly circular and offers a platform for large- scale
deployment in commercial environments, which is similar to micro and Pico cells.
By studying various kinds of commonly used VLC channel analysis: diffuse and
line of sight channels, a simple improved indoor and intra-vehicular VLC transmission
model for power distribution and SNR is presented. Employing optical wireless
communications within the vehicle not only enhances user mobility, but also alleviates
radio frequency interference, and lowers system cost through the utilization of license free
spectrum. Moreover, a solution to increase the received power by changing the semi angle
at half power is presented. The simulation results show the improved received power
distribution and SNR. A VLC system, based on color-shift-keying (CSK) modulation and
code-division multiple-access (CDMA) is presented. CSK–CDMA VLC system is used to
enhance the VLC system capacity and mitigate single color light interference, which allows
multiple users to access the network
Physical Layer Defenses Against Primary User Emulation Attacks
Cognitive Radio (CR) is a promising technology that works by detecting unused parts of the spectrum and automatically reconfiguring the communication system\u27s parameters in order to operate in the available communication channels while minimizing interference. CR enables efficient use of the Radio Frequency (RF) spectrum by generating waveforms that can coexist with existing users in licensed spectrum bands. Spectrum sensing is one of the most important components of CR systems because it provides awareness of its operating environment, as well as detecting the presence of primary (licensed) users of the spectrum
Joint Constellation-Labeling Optimization for VLC-CSK Systems
In this letter, we have optimized the joint constellation-labeling for a finite number of signals in visible light communication (VLC) systems with color-shift keying (CSK) modulation by maximizing the pragmatic mutual information (PMI). First, an equivalent parallel channel model of the VLC-CSK system is constructed. Then the PMI is derived to be the objective function of the newly formulated joint constellation-labeling optimization problem of the VLC-CSK system. Simulated annealing (SA) algorithm and modified interior point method (MIPM) are adopted to solve the joint constellation-labeling optimization problem. Simulation results show that the proposed methods improve the PMI performance compared to the existing constellation-labeling scheme of signals, especially in the low signal-to-noise ratio (SNR) region. Besides, it can been seen that the MIPM saves a large amount of computational time compared to the SA algorithm while achieving the same performance improvement
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