Colour Shift Keying Constellation 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.

Design of Multilevel Reed–Solomon Codes and Iterative Decoding for Visible Light Communication

This paper proposes multilevel Reed–Solomon (MRS) codes and their iterative multistage soft decoding (IMSD) for visible light communication (VLC), realizing both high decoding performance and transmission spectrum efficiency. The proposed IMSD algorithm decodes the MRS codes level-by-level through iterating either hard decisions or extrinsic information of RS coded bits. Each level RS decoding is realized by cascading the adaptive belief propagation (ABP) algorithm that produces the extrinsic information and the Berlekamp–Massey (BM) algorithm that estimates the codeword. The earlier level decoding provides better a priori information for the later ones. A complexity reducing IMSD (CR-IMSD) algorithm is also proposed to facilitate the decoding. This paper further investigates a joint design of color-shift keying (CSK) constellation and the MRS code, optimizing the decoding performance. The CSK constellation is designed by considering both the set partitioning (SP) criterion and the harmonic mean of constellation’s minimum squared Euclidean distance (MSED). The MRS codes are further designed using the capacity and the equal error probability rules. Our simulation results show that the IMSD algorithm achieves significant iterative decoding gains. The performance of the designed MRS code is 0.3 dB away from the capacity limit at the bit error rate (BER) of 10−9.

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.

Adaptive multi-color shift keying constellation design for visible light communications considering lighting requirement

In visible light communications (VLCs), light-emitting diodes (LEDs) are utilized for communication and lighting simultaneously. Therefore, in VLC systems, it is necessary to jointly consider communication quality and lighting level. For multi-color VLC systems, although optical filters are used on the receiving end, there is still multi-color crosstalk inevitably. In this work, an adaptive multi-color constellation design framework of color shift keying (CSK) modulation is established for VLC systems based on multi-color LEDs, with consideration of the channel state information. To achieve joint communication and illumination, we optimize the Euclidean distance of received signal with signal amplitude constraint, chromaticity constraint and luminance constraint. Further, with the linear approximation of Taylor series, a constellation design is attained to control multi-color crosstalk. The numerical results show that our proposed adaptive constellation design has better symbol error rate (SER) performance than CSK constellation design.

Constellation Design Enhancement for Color-Shift Keying Modulation of Quadrichromatic LEDs in Visible Light Communications

Quadrichromatic light-emitting diode (QLED) cluster is a four-color solid-state apparatus suitable for simultaneous illumination and communications. Unlike traditional red/green/blue (RGB) LEDs, its extra color provides not only one new wavelength-division multiplexing data channel but also better color quality in illumination. Taking full consideration of the high quality of color rendering index (CRI) requirement with tunable color temperature (CT), this paper investigates the constellation design of color shift keying (CSK) to maximize the minimum pairwise Euclidean distance (MED) for communication performance optimization. Beyond existing works, maintaining a high-level CRI with a specified CT complicates our design optimization problem. We propose to transform the CRI requirement into a set of linear constraints on one of the LED source composition while jointly incorporating the CT constraints. Both simulation results and prototype CSK communication testbed measurements based on commercial multicolor LEDs (LUMILEDS Luxeon C) illustrate that, under the same luminous flux and CT conditions, our proposed flux independent CSK constellation for QLEDs can significantly enhance the MED, bit error rate, and illumination color qualities.

Digital Color Shift Keying With Multicolor LED Array

Color shift keying (CSK) is a visible light communication (VLC) intensity modulation scheme, which is outlined in IEEE 802.15.7, that transmits data imperceptibly through the variation of the color emitted by red, green, and blue light-emitting diodes (RGB LEDs). In this paper, digital CSK (DCSK) is presented, which represents CSK symbols by digitally controlled multiple multicolor LEDs to avoid the effect of LED nonlinearity. By using this scheme, the DCSK system using nine RGB LEDs can transmit IEEE 802.15.7 CSK constellations with an error-vector-magnitude (EVM) performance on an x-y chromaticity of 3%. The bit-error-rate (BER) evaluation of both the conventional and the proposed DCSK system shows that the DCSK system achieves similar BER to that of CSK with a linear variable current driver including predistortion, with taking into account optical wireless channels including the LED response, undesired color shift, and channel crosstalk by the practice characteristics of RGB LEDs, RGB bandpass filters, and photodiodes.

PSK to CSK mapping for hybrid systems involving the radio frequency and the visible spectrum

This paper presents an efficient technique to map phase shift keying (PSK) signalling to colour shift keying (CSK) constellation, to establish a full link in hybrid systems involving the radio frequency (RF) and the visible spectrum. It fits in systems combining (first link) wireless communication technologies such as the wireless fidelity (WiFi) or wired communication technologies such as power line communications (PLC) to visible light communications (VLC) technology (second link). On the first link, PSK technique is used to convey the information, while, on the second link, a technique based on colour variation is deployed. WiFi standards targeted are those that employ PSK as sub-carrier modulation techniques (IEEE 802.11a/11g/11n). The PSK complex constellation observed at the output of the first link is converted into colours using the hue-saturation-value/intensity (HSV/I) colour models. The constant lighting required in VLC corresponds with the coordinate I of the HSI and the colour constraint is met by assigning adequate current intensities to the red-green-blue LEDs (RGB-LEDs) used. The design meets the requirements of CSK constellation design outlined in IEEE 802.15.7. The performance of the system is analysed through bit error rate curves obtained by simulations, for binary PSK (BPSK) and quadrature PSK (QPSK), 8PSK and 16PSK constellations. The results show that as the constellation size increases, the performance of the system decreases.

Multi‐colour LED specified bipolar colour shift keying scheme for visible light communications

Colour shift keying (CSK) can achieve significant performance gains in multi-colour visible light communications (VLCs). Existing CSK constellations are designed within the positive domain which satisfies the requirement of non-negative optical intensity modulations. A scheme is proposed to incorporate spatial modulation with a CSK design by grouping LEDs. In this way, the CSK constellation is optimised within the entire real domain and hence achieves a larger minimum Euclidean distance so as to enhance the bit error rate (BER) performance. Simulation results show a noticeable performance gain by the proposed scheme compared with traditional CSK under ideal light-of-sight optical channels. Further, by experimental tests, an even more pronounced BER gain is achieved by the proposed scheme over real VLC channels.

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.

Improved performance of colour shift keying using voronoi segmentation for indoor communication

We analyze the performance of IEEE 802.15.7 standard colour shift keying (CSK) modulation for visible-light indoor wireless optical communication system. Judiciously combining the available wave lengths for red, green and blue LEDs indoor wireless communication at constant intensity can be made with the energy efficient next generation lighting system. Design of multilevel CSK constellation for high bit rate transmission is a challenging problem. In this work, Voronoi segmentation is employed for decoding $$M$$ -CSK constellation and system performance is evaluated. Monte Carlo simulation shows superiority of our method over the other existing CSK constellation decoding in terms of better received SNR and symbol error rate. Inter symbol interference (ISI) is the chief source of degrading performance in communication with 2D LED chip. Simple linear equalization by LMS and RLS is found suitable to mitigate ISI and provide improved symbol error rate performance and increased field of view in the receiver.

Design and Implementation of Color-Shift Keying for Visible Light Communications

Color-shift keying (CSK) is a visible light communication intensity modulation scheme, outlined in IEEE 802.15.7, that transmits data imperceptibly through the variation of the color emitted by red, green, and blue light emitting diodes. An advantage of CSK is that the power envelope of the transmitted signal is fixed; therefore, CSK reduces the potential for human health complications related to fluctuations in light intensity. In this work, a rigorous design framework for high order CSK constellations is presented. A key benefit of the frame work is that it optimizes constellations while accounting for crosstalk between the color communication channels. In addition, and unlike previous approaches, the method is capable of optimizing 3-D constellations. Furthermore, a prototype CSK communication system is presented to validate the performance of the optimized constellations, which provide gains of 1-3 dB over standard 805.15.7 constellations.