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Abstract
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.
... Furthermore, a 2 × 2 optical SM based structure is proposed in [11] to solve the DC bias penalty issue by introducing two light emitting diodes (LEDs) to send negative and positive signals. Using the advantage of different wavelengths in the visible band is another promising solution to enhance the spectrum efficiency by means of multi-channel communication [12][13][14][15][16]. ...
... Using a = a T a and after some algebra, (14) can be simplified as ...
... In other words, after the calculation of the MAP estimates ofx k, R andx k, I for all (m, n) ∈ {(1, 3) , (1, 4) , (2, 3) , (2, 4)} that considers all possible active LED scenarios, the conditional MAP estimator of the GLIM-OFDM scheme decides on the most likely active LED pair (m,n) and corresponding estimates ofx k, R andx k, I (x MAP k,R ,x MAP k, I ) by calculating the MAP estimation metric given by (14) for all four scenarios. The / combiner then calculates the estimate of the complex OFDM signal x k aŝ ...
Visible light communications (VLC) is a promising and uncharted new technology for the next generation of wireless communication systems. This paper proposes a novel generalized light emitting diode (LED) index modulation method for multiple-input-multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) based VLC systems. The proposed scheme avoids the typical spectrum efficiency losses incurred by time and frequency domain shaping in OFDM signals. This is achieved by exploiting spatial multiplexing along with LED index modulation. Accordingly, real and imaginary components of the complex time domain OFDM signals are separated first, then resulting bipolar signals are transmitted over a VLC channel by encoding sign information in LED indexes. As a benchmark, we demonstrate the performance analysis of our proposed system for both analytical and physical channel models. Furthermore, two novel receiver designs are proposed. Each one is suitable for frequency-flat or selective channel scenarios. It has been shown via extensive computer simulations that the proposed scheme achieves considerably better bit error ratio (BER) vs. signal-tonoise- ratio (SNR) performance than the existing VLC-MIMOOFDM systems that use the same number of transmit and receive units (LEDs and photo diodes (PDs)). Compared with the singleinput single-output (SISO) DC biased optical OFDM (DCOOFDM) system, both spectral efficiency and DC bias can be doubled and removed respectively simply by exploiting a MIMO configuration.
... To design such a constellation so as to maximize the minimum of all pair-wise distances among the constellation's M alphabets, the following optimization is to be solved: 1 [4], [10], [14], [15], [17], [20], [23], [29] S := arg max ...
... This paper investigates how the constellation's maximized d min would be affected by the prior choice of this operating color c. Numerous references [4], [9], [10], [13]- [15], [17], [20], [29] have previously investigated constellation design for color shift keying, but none has studied how the preset operating color c would affect the maximized minimum-distance d min , at various constellation sizes M . This paper's key finding is this elegant approximation: ...
Color-shift keying (CSK) is a type of visible light wireless communication where a visible color is preset and is to appear constant during the human vision’s “critical flicker fusion threshold” (CFF) and “critical color fusion threshold” (CCF). This paper is first in the open literature to systematically investigate how CSK’s largest achievable “minimum distance” (dmin) would vary with the preset chromaticity and with the constellation size (M). This paper discovers this elegant approximation: The best dmin 1:921M�0:5985 �2:736M�0:645( ˜x2 + ˜y2)0:7802(log2 M)�0:436 , where ( ˜x; ˜y) refers to the preset chromaticity’s displacement (in a twodimensional space) from the case of all LEDs emitting with an equal intensity.
... So far a number of methods have been proposed in the direction of transmitting the data using visible light spectrum in an indoor environment [6][7][8][9][10][11]. In this context, white LED evolves as a potential illuminant for the highspeed short-range line of sight data transmitter. ...
In recent time of looming RF spectrum crisis, visible light communication using lighting infrastructure emerged as a potential alternative at an indoor environment. This paper addresses the setback associated with ambient light interference in an indoor VLC system to ensure joint communication and illumination performance inside an office room. A novel VLC architecture with suitable WLED luminaire arrangement is presented to minimize the dispersion of signal to interference plus noise ratio (SINR) across the room. Luminaires are categorized in two groups' viz. data transmitting illuminants and illuminants for lighting purpose. The first group is dedicated to transmit data as well as serves the purpose of illumination. The other set creates only ambient illumination to achieve quality lighting attributes. The proposed forward error corrected receiver configuration discards the ambient light noise originated by the illuminants that serve the ambient illumination. Tail biting convolutional encoder and viterbi decoder are used at the encoding section of the transmitter and decoding section of the receiver respectively to improve bit error rate. Results obtained through MATLAB simulation shows better average BER in the order of 10-8 measured at uniformly distributed twenty-five grid points over the working plane. At the same time achieved average horizontal illuminance with good uniformity comply with ISO recommendation.
... Color-shift keying (CSK), uses different combinations of the RGB color bands to convey information, keeping the transmitted signal power at a fixed level. As a result, CSK signals have low intensity fluctuations compared to CIM, which reduces the flicker in the optical signal[66]. ...
... There are a few works in the literature addressing the optimization or promotion of CSK. Some researchers have studied the optimal constellation design [8][9][10][11]. In [2] and [12] two independent enhanced CSK modulation schemes are introduced which use four color bands instead of the triple colors used in the existing IEEE 802.15.7 CSK physical layer standard. This system has enhanced the minimum Euclidean distance between the symbols with the cost of using an additional LED. ...
Recently, visible light communication (VLC) has got increasing attention in the field of indoor wireless communications. VLC has the obligation of lighting besides data communications. The IEEE 802.15.7 task group proposed a VLC modulation format named color shift keying in which data symbols are defined based on the diffused light wavelength. This paper presents a new modulation scheme for indoor wireless visible light communication system named non-uniform time slot modulation (NUTS). The NUTS modulation scheme defines the feeder signals of red, green and blue LEDs as rectangular pulses with appropriate width and their positions. In this method, the time axes of all the three light sources (channels) are slotted to some non-uniform durations that all symbols are spanned over these slots as orthogonal dimensions. The proposed scheme has some advantages with respect to other approaches such as low bit error rate and high bit rate. Furthermore, it provides appropriate synchronization capability. Besides, in the design of NUTS modulation scheme it has been tried to deliberate all practical constraints, as far as possible.
The new era of the Internet of Things has spawned research into multifunctional photodetectors. Herein, the intriguing features of dual-polarity and flexibility are creatively embraced in Sb2Se3/ZnO bilayer photodetectors. The current reversal, with respect to the incident wavelengths, originates from the synergy of photovoltaic and photo-thermoelectric effects. An unprecedented polarity-double-flipping phenomenon was discovered at a critical thickness of the ZnO capping layer. The dual-polarity response is tailorable, as it is critically dependent on the band alignment, light penetration depth, and interfacial properties of the heterostructure. The optimal device has superior overall performance in terms of the response bandwidth, responsivity, detectivity, and response speed. The flexible devices can withstand 600 bending cycles with only a 4.38% degradation in the performance and a well-localized polarity-flipping wavelength. This study shows that the Sb2Se3/ZnO photodetector has excellent potential for use in bipolar signal communications in wireless, filterless, and wearable optoelectronic systems. It also paves the way for the design and optimization of flexible dual-polarity photodetectors from arbitrary hetero-assemblies.
This chapter discusses the health issues associated with underlying technologies of 5G and 6G. It is mostly dedicated to the investigation of the short-term and long-term influence of different types of electromagnetic radiation on various human health aspects. Both the physics of wave propagation and medical research studies are discussed. Potential health issues associated with VLC are also discussed in this chapter.
Abstrct
Self-powered photodetectors (PD) have great potential applications in visible light communication (VLC) systems due to their unique advantages such as energy saving and low cost, where color shift keying (CSK) is widely utilized to meet the requirements of non-negative light intensity modulation. However, at least two PDs with filters are needed to decode the optical signals, greatly increasing the device cost and complicating the communication system. Here, we report a new type of dual-polarity response PD with an adjustable polarity switching wavelength, where the output signals are positive and negative in long and short wavelength regions, respectively. The dual-polarity response is a consequence of the competition between photovoltaic (PV) effect of ZnO NWs/Sb2Se3 film p-n junction and pohtothermoelectric (PTE) effect of Sb2Se3 thin film. As compared with current PDs in CSK systems, our PD can work without any filter and one PD can realize the function of two traditional PDs. This new PDs have the potential applications in optical communication systems and filterless color discrimination.
We consider an indoor visible light communication (VLC) system in which an arbitrary
number of light emitting diodes (LEDs) are transmitting the information to the
users. Due to the circular field of view (FOV) of the LED transmitters, there is always
a trade-off between the coverage and interference at the receiving end. Any approach
to increase the coverage area increases the overlapping area of two or more FOVs
resulting in severe interference at the receiver. In this paper, we propose a method
which simultaneously reduces the interference due to multiple sources in an indoor
VLC system and improves the coverage area. The signal to interference ratio
SIR based approach is used for analyzing the outage and error performances. Specifically,
the effect of the proposed method is investigated on various performance metrics
such as signal-to-interference ratio, coverage probability and bit-error rate. The effect
of ambient light on system performance is also incorporated in the analysis.
The Visible Light Communication (VLC) can provide data transmission via the illumination Light Emitting Diodes (LED). This paper introduces a new model to analyze the Bit Error Rate (BER) of Binary Phase Modulation (BPM) in VLC for an arbitrary modulation depth and data duty cycle while taking into account both the Gaussian and signal-dependent shot noise. The impact of the driver design on the BER and its impact on ripple, have not been considered in detail before. We compare two different LED driver schemes, namely directly adapting the driver control loop and binary shunting. We address data rate, BER and power efficiency, for which we propose to use the Extra Energy Per Symbol (EEPS) above unmodulated light. We further introduce an analysis of the effect that (truncated) ripple interference has in the (matched or other) filter of the receiver. Ripple causes a harmful interference in VLC and thus a BER expression is derived to include its effect. Two approximations are proposed to model the ripple interference and their accuracies are compared by simulations. A low-pass filtering is proposed to alleviate the impact of ripple interference in VLC system.
In order to achieve diversity gain of multi-color LED channels in visible light communication systems, we present an innovative method which transmits inversely interleaved signal combinations, yielding real signals for optical orthogonal frequency division multiplexing (OOFDM). The proposed scheme transmits two groups of signals carrying the same information through two different color LED channels. Since the Hermitian symmetry is no longer needed, the data rate remains the same as conventional OOFDMs like DC-biased optical OFDM (DCO-OFDM) and asymmetrically clipped optical OFDM (ACO-OFDM), while diversity gain of over 2 dB is achieved at the bit error rate (BER) of 10 −5 compared to the conventional OOFDMs, which is verified by experimental simulations.
In this paper, a novel layer-by-layer bit allocation algorithm is proposed, which can effectively reduce the system complexity. Meanwhile, this algorithm complexity is lower than Chow algorithm and Greedy algorithm under the same resources allocation performance.
In this paper, we propose a novel high dimensional constellation design
scheme for visible light communication (VLC) systems employing red/green/blue
light emitting diodes (RGB LEDs). It is in fact a generalized color shift
keying (CSK) scheme which does not suffer efficiency loss due to a constrained
sum intensity for all constellation symbols. Crucial lighting requirements are
included as optimization constraints. To control non-linear distortion, the
optical peak-to-average-power ratio (PAPR) of LEDs is individually constrained.
Fixing the average optical power, our scheme is able to achieve much lower
bit-error rate (BER) than conventional schems especially when illumination
color is more "unbalanced". When cross-talks exist among the multiple optical
channels, we apply a singular value decomposition (SVD)-based pre-equalizer and
redesign the constellations, and such scheme is shown to outperform
post-equalized schemes based on zero-forcing or linear
minimum-mean-squared-error (LMMSE) principles. To further reduce system BER, a
binary switching algorithm (BSA) is employed the first time for labeling high
dimensional constellation. We thus obtains the optimal bits-to-symbols mapping.
In this paper, a generalised technique for spatial modulation (SM) is presented. Generalised spatial modulation (GSM) overcomes in a novel fashion the constraint in SM that the number of transmit antennas has to be a power of two. In GSM, a block of information bits is mapped to a constellation symbol and a spatial symbol. The spatial symbol is a combination of transmit antennas activated at each instance. The actual combination of active transmit antennas depends on the random incoming data stream. This is unlike SM where only a single transmit antenna is activated at each instance. GSM increases the overall spectral efficiency by base-two logarithm of the number of antenna combinations. This reduces the number of transmit antennas needed for the same spectral efficiency. The performance of GSM is analysed in this paper, and an upper bound on the bit-error-ratio (BER) performance is derived. In addition, an algorithm to optimise the antenna combination selection is proposed. Finally, the performance of GSM is validated through Monte Carlo simulations. The results are compared with traditional SM. It is shown that for the same spectral efficiency GSM performs nearly the same as SM, but with a significant reduction in the number of transmit antennas.
In this letter, we derive the optimal detector for the so-called spatial modulation (SM) system introduced by Mesleh et al. in (Mesleh, 2006). The new detector performs significantly better than the original (~ 4 dB gain), and we support our results by deriving a closed form expression for the average bit error probability. As well, we show that SM with the optimal detector achieves performance gains (~ 1.5 - 3 dB) over popular multiple antenna systems, making it an excellent candidate for future wireless communication standards.
In this paper, we propose a new joint beamformer and offset design method for visible light communication (VLC) with multiple red/green/blue light emitting diodes (RGB LED). We take into account key practical lighting constraints including optical power, color illumination, non-negativeness, CRI and LER, and formulate a non-convex optimization problem to minimize the system mean squared error (MSE). We resort to approximation methods to relax a non-convex constraint into a convex one, and propose a way to relax the original problem into a simple version, which is solvable by the standard water-filling method. Simulation results are provided to illustrate performance of the proposed method for different color illumination scenarios. Also, the relationship between channel cross-talks and optimized offset allocation is observed.
This paper presents a new color shift keying (CSK) modulation format for wireless visible light communication (VLC), based on four colors instead of the three colors used in the existing IEEE 802.15.7 CSK physical layer standard. The new four color system uses a novel intensity modulation and direct detection approach to realize a four-dimensional signaling scheme that uses the available color and signal spaces efficiently. The bit error rate evaluation of both the existing and proposed system shows that the new four color scheme achieves a significant 4.4-dB electrical SNR gain over the three color scheme for an additive white Gaussian noise channel. The performance of existing and proposed CSK systems is examined over a range of dispersive optical wireless channels including the channel crosstalk and insertion losses, which reveals that the four color CSK scheme is more power efficient and reliable than the three color scheme for a particular amount of delay spread that the optical wireless channel may have.
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.
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.
Light-emitting diodes (LEDs) have the potential to replace traditional devices in a variety of lighting applications, offering the possibility of simultaneous modulation for communications. One modulation method, color-shift keying (CSK), has been recently proposed specifically for red/green/blue (RGB) LEDs. We examine the design of CSK signaling constellations for an additive white Gaussian noise channel, incorporating the common requirement that the RGB LED outputs a specific, possibly time-varying, perceived color. In particular, we equate this design problem to that of disk packing and employ modified billiards algorithms that rely on the “thermodynamic” settling of the disks to obtain constellation points with good minimum distance. Simulation results are presented that illustrate the design approach.
Visible light communication refers to shortrange optical wireless communication using visible light spectrum from 380 to 780 nm. Enabled by recent advances in LED technology, IEEE 802.15.7 supports high-data-rate visible light communication up to 96 Mb/s by fast modulation of optical light sources which may be dimmed during their operation. IEEE 802.15.7 provides dimming adaptable mechanisms for flicker-free high-data-rate visible light communication.
In this letter we consider the design of multi-dimensional compact constellations that minimize the average symbol energy for a given minimum Euclidian distance between constellation points. We formulate the constellation design as a non-convex quadratically constrained quadratic programming. We propose a simple and efficient optimization method, which offers good solutions for small to medium sized constellations.