Color Shift Keying Modulation Research Articles

Camera-Based Channel Modeling and Symbol Error Rate Analysis of CSK Modulation for Outdoor OCC Systems

A camera with an image sensor is an important alternative device to a photodiode-based receiver of visible-light communication in outdoor scenarios. The intrinsic color separation capability of a camera qualifies color shift keying (CSK) modulation as an intuitive solution to enhance the achievable data rate. The symbol error rate (SER) of CSK modulation is considerably important to system design and performance evaluation, and has not been extensively investigated for outdoor optical camera communication systems from the viewpoint of camera-based channel and image processing-based demodulation. In this study, a two-level channel model is proposed to characterize CSK transmission in a single pixel and in the entire image. A general framework of SER analysis for arbitrary CSK constellations was proposed by directly calculating the upper bounds from the empirical distribution of the noise light in the CIE 1931 color space. Through numerical simulations, the influence of the image detector on CSK demodulation was evaluated. The results indicated that an accurate target region is important for maintaining the SER, and an enlarged target region is beneficial when the maximum ratio combination and selective combination algorithms are used in pixel combination.

Performance evaluation of IEEE 802.15.7 CSK modulation under blue shift effect of optical receiver filters

In recent years, the use of light-emitting diodes (LEDs) in lighting, which has higher energy efficiency and longer-lasting environmentally friendly lighting compared to conventional lighting devices, has accelerated the development of a promising new technology for short-range wireless optical transmission called visible light communication (VLC). Besides other applications, VLC switches the LEDs at very high speeds to simultaneously realize indoor lighting and data transmission. But the intensity and color of the lighting may vary because of data transmission. Color shift keying (CSK) modulation defined in the IEEE 802.15.7 VLC standard guarantees constant light intensity and color. The CSK receiver uses a band-pass optical filter to separate the light channels. However, the transition band of optical filters shifts towards the blue wavelength depending on the incidence angle of the light which is called the blue shift effect. In this paper, the performance of the CSK receiver is investigated for the first time under the blue shift effect in the case of single and multiple transmitter LED cells. The numerical results show that the blue shift effect significantly decreases system performance. To eliminate the distorting effect, various methods and an adaptive equalizer-based CSK receiver are proposed. The proposed structures provide notable improvement.

Constellation Design for Single Photodetector Based CSK With Probabilistic Shaping and White Color Balance

Research and development of Li-Fi (Light Fidelity) in Internet-of-things (IoT) has created significant interest among researchers. The low-cost version of standard color shift keying (CSK) modulation scheme having single photodetector (PD) at the receiver can become an alternative to on-off keying (OOK) in IoT sensor networks as an M -ary CSK modulation scheme provides log 2 M times more data rate than that of OOK. This work revolves around optimizing the constellation points of single PD based CSK (CSK-1PD) to achieve a more power-efficient modulation scheme. The optimization has been done with and without average white tone constraint for uniform and non-uniform (exponential, Maxwell-Boltzmann, Pareto) source distributions. The constellation design strategy is based on maximizing the minimum distance among the differently distributed symbols. In the case of non-uniform distributions, the constellations points have been optimized by geometrically shaping the points based on their probabilistic shaping (PS). The optimized constellation points (OCPs) of CSK-1PD without white tone constraint provide higher signal-to-noise ratio (SNR) gain at forward error correction (FEC) limit symbol error rate (SER) as compared with strict white tone constraint. Further, the strict white tone constraint has been relaxed by considering the whole white light region in the CIE 1931 chromaticity diagram as white tone. The OCPs for uniform data with relaxed white tone constraint achieves SNR gain similar to without white tone constraint. However, for probabilistically shaped symbols, the SNR gain achieved from OCPs improves from strict white tone constraint but remains less than the without white tone constraint. A novel method to utilize an additional RGB LED at the transmitter side has been proposed and designed to maintain any white tone light in the white light region without degrading the maximum achieved SNR gain.

Design and Implementation of a Multi-Colour Visible Light Communication System Based on a Light-to-Frequency Receiver

Colour-shift keying (CSK) is a visible light communication (VLC) modulation scheme used in the existing IEEE 802.15.7 standard. In CSK, information is transmitted by changing the light intensities of the RGB LEDs. In this work, a low-complexity VLC system is proposed using CSK modulation and a novel receiver based on a light-to-frequency (LTF) converter. At the receiver, CSK symbols are interpreted and decoded in terms of frequencies, which are processed by a counter module of a generic microcontroller, thus avoiding the use of analog-to-digital converters (ADCs), which results in a low-cost VLC system. The main contributions of this work are summarized in the following key points: (1) A low-complexity receiver for CSK modulation is introduced; (2) A particle swarm optimization (PSO) algorithm for CSK constellation design is suggested considering the restrictions of the LTF based receiver; (3) Experimental and theoretical validation is perfomed for the proposed multi-colour VLC system. The results show that this system can provide a transmission speed of 100 kbps using a 4-CSK-LTF constellation for a symbol error rate (SER) of 10 − 4 and a signal to noise ratio (SNR) around 35 dB. These results suggest that the analysed system could find applications on those scenarios where low transmission speeds and ease of deployment are the goals.

Fast-adaptive color-collaborative constellation designs for multicolor multiple-input multiple-output visible light communications systems.

A fast-adaptive color-collaborative signal constellation (CCSC) is proposed for chromaticity-changeable multicolor multiple-input multiple-output (MIMO) visible light communications (VLC) systems. The design of CCSC aims at developing the constellation to minimize the average optical power with shaping-based lattice code. For multicolor VLC signals, we arrive at the fact that the optimum shape of the constellation bounding region is an inequilateral N-D simplex. With the densest lattice-packing structure, detailed design steps of CCSC are fully elaborated by lattice construction, effective point selection, and chromaticity adjustment. As CCSC has a low complexity, its constellation structure can adapt quickly to changeable chromaticity demands. Simulation results show that the performance of CCSC is better than enhanced standard color shift keying (CSK) and is close to iterative CSK modulation based on numerical search.

On the Mutual Information of VLC Systems Employing Color-Shift Keying

In visible light communication (VLC), color-shift keying (CSK) is an intensity modulation scheme that transmits data through the variation of color with fixed optical intensity. The mutual information of a CSK modulation scheme is investigated in this letter. An expression for the mutual information of the VLC system is first derived. However, the expression is not in a closed form and its value can only be obtained by numerical simulations. To overcome this issue, an approximation for the mutual information is then obtained on the basis of Jensen’s inequality. The approximation is in a closed form, which brings convenience for analyzing the system performance and optimizing the mutual information. Numerical results show that the approximation is accurate in both low and high signal-to-noise ratio (SNR) regimes, and approaches the real value well for in-between SNR values.

Experimental validation of a single‐photodiode receiver for VLC systems using color shift keying modulation

ABSTRACTThis letter reports the first experimental results obtained from a recently proposed single‐photodiode receiver for visible light communications (VLC) using color shift keying (CSK) modulation. This novel detection scheme has the potential to reduce the implementation cost by two‐thirds compared to the CSK‐based receiver structure introduced in the VLC IEEE 802.15.7 standard. A proof of concept is performed to demonstrate its practical feasibility and advantages towards the deployment of VLC systems. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:428–432, 2017

Hierarchical Colour-Shift-Keying Aided Layered Video Streaming for the Visible Light Downlink

Colour-shift keying (CSK) constitutes an important modulation scheme conceived for the visible light communications (VLC). The signal constellation of CSK relies on three different-color light sources invoked for information transmission. The CSK constellation has been optimized for minimizing the bit error rate, but no effort has been invested in investigating the feasibility of CSK aided unequal error protection (UEP) schemes conceived for video sources. Hence, in this treatise, we conceive a hierarchical CSK (HCSK) modulation scheme based on the traditional CSK, which is capable of generating interdependent layers of signals having different error probability, which can be readily reconfigured by changing its parameters. Furthermore, we conceived an HCSK design example for transmitting scalable video sources with the aid of a recursive systematic convolutional (RSC) code. An optimization method is conceived for enhancing the UEP and for improving the quality of the received video. Our simulation results show that the proposed optimized-UEP 16-HCSK-RSC system outperforms the traditional equal error protection scheme by $\sim 1.7$ dB of optical SNR at a peak signal-to-noise ratio of 37 dB, while optical SNR savings of up to 6.5 dB are attained at a lower PSNR of 36 dB.

Symbol error rate analysis for colour‐shift keying modulation in visible light communication system with RGB light‐emitting diodes

The symbol error rate (SER) is investigated for colour-shift keying (CSK) modulation in visible light communication system with red/green/blue LEDs. A new concept of pseudo signal-to-noise ratio is proposed to illustrate the relationship between the signal power and the noise power since the traditional electrical signal-to-noise ratio fails to capture the properties of CSK signals. The authors map the three-dimensional (3D) signal space of CSK signals to a 2D plane because the decision region of constellations in 2D space is easy to analyse and is proved to be equivalent to that of 3D signal space. The symbol error probability for a certain constellation is calculated as the summation of the probabilities of the received signals lying outside the decision region. As the SER is formulated as the weighted sum of error probabilities for all constellations, an analytical expression for SER is derived for certain constellation distribution. Moreover, a general formula for 22n -CSK modulation is derived by exploiting the distribution regularity of 4CSK and 16CSK. The SER expression for CSK modulation is evaluated approximately using the numerical Gaussian formula. Simulation results show that the analytical expression can predict SER performance accurately.

Merging Color Shift Keying and Complementary Pulse Position Modulation for Visible Light Illumination and Communication

The ever increasing need to be able to take advantage of broadband services without the need to increase the electromagnetic pollution, has led the scientific community, in recent years, to look for alternatives to the use of a radio frequency communication. From this, it stems the need of budding paradigm of visible light communications. In the context of the activities of the IEEE 802.15.7 Task Group, a new modulation format named Color Shift Keying (CSK), based on sending signals spaced in the domain of the wavelength able to both support the communication and the illumination of indoor environments has been tackled. In this paper, a transmission scheme based on the use of the CSK modulation which also makes use of a modulation format that descends from the Pulse Position Modulation (PPM) has been proposed. The aim of this contribution is also proposing the receiver architecture for that kind of transmission and then evaluate its performance in terms of Bit Error Rate (BER) of Transmission Rate by performing also comparisons with the literature. The proposed scheme is robust with respect to optical interference and presents high rate and low BER at the cost of a bit complexity increasing with respect to other approaches.

Combined CSK and pulse position modulation scheme for indoor visible light communications

The use of pulse-coded signals over each colour component on a colour shift keying (CSK) modulation is explored. This codification improves the time-synchronisation recovery capability on the IEEE 802.15.7 PHY III standard and reduces the overall system complexity. Different symbol codification rates are studied so as to improve the symbol error rate while minimising the effect over the throughput of the whole system.