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Combining Illumination Dimming Based on Pulse-Width Modulation With Visible-Light Communications Based on Discrete Multitone
Journal of Optical Communications and Networking
Abstract and Figures
In the field of indoor wireless networks, visible-light communications is garnering increasing attention. One of the type of emitters used in this technology is white light-emitting diodes, which can synergistically provide both illumination and data transmission. Discrete multitone modulation is attractive for visible-light communications. One of the issues to be addressed in these synergetic use cases is how to incorporate light dimming while not corrupting the communication link. In this paper, the performance of a visible-light communication system combining pulse-width modulation for dimming and discrete multitone for data transmission was investigated. Performance indicators were addressed, i.e., the signal-to-interference ratio due to dimming and the achievable bit-error ratio in the absence of additional noise. By aid of simulations it was shown that practical communication is only feasible when the line rate of the dimming modulation is at least twice the frequency assigned to the largest multitone subcarrier frequency. The results demonstrate that under this constraint and when using a suitably modified demodulation scheme, dimming does not influence the data transmission.
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... In contrast, PWM-based approaches maintain a fixed current while varying the duty cycle of signal pulses, making them more commonly used for dimming control [14]. These schemes mainly prioritize efficient data transmission, especially when reducing the duty cycle, and they often employ high-efficiency modulation formats [15], [16], [17], [18], [19]. For example, discrete multi-tone was combined with PWM in [15], but this method imposes a limit on the system data rate. ...
... These schemes mainly prioritize efficient data transmission, especially when reducing the duty cycle, and they often employ high-efficiency modulation formats [15], [16], [17], [18], [19]. For example, discrete multi-tone was combined with PWM in [15], but this method imposes a limit on the system data rate. In pursuit of enhanced spectral efficiency (SE), we proposed integrating variable M-ary quadrature amplitude modulation (M-QAM) orthogonal frequency division multiplexing (OFDM) with PWM [16] and multipulse position modulation (MPPM) [17] for dimming control, respectively. ...
... For instance, at a duty cycle of 0.5, the achievable data rate with OOK in both VL and IR link is stable at 10 Mb/s. However, 15 Mb/s at the same dimming level. Therefore, the hybrid scheme not only maintains data rates but also has the potential to increase them. ...
Implementing dimming control in visible light communication (VLC) systems often involves a trade-off that reduces data rates. To address this, we propose a hybrid visible light (VL)/Infrared (IR) communication scheme that leverages pulse amplitude modulation (PAM) symbols in both VL and IR spectra, alternating them within pulse width modulation (PWM) “ON” and “OFF” slots. By efficiently using PWM “OFF” slots, the achievable data rate drop due to dimming is mitigated without affecting illumination. To ensure synchronization during the switch between VL and IR links, we design real-time dimming control state machines at both ends of the link, enhancing link stability. Additionally, we develop an adaptive hybrid frame structure that dynamically adjusts the length of transmitted information as the duty cycle continuously changes, ensuring uninterrupted communication. Experimental results from implementation using field-programmable gate arrays (FPGA) demonstrate real-time transmission under precise full-range dimming control, dynamically ranging from 1 to 0 with a resolution of 0.0053, maintaining a consistent 10 Mb/s data rate at bit error rates (BERs) lower than 3.4×10
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and 20 Mb/s at BERs lower than 7.0×10
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within a link range of 0.53 m without light concentration at the transmitter. Compared to baseline VLC, our system achieves a 100% data rate improvement at a duty cycle of 0.5, and supports stable data transmission even in low-light conditions.
... LED arrays based on GaN are proposed in [4] for illumination and high-speed visible light communication. Combined illumination dimming on PWM and visible light communication based on a discrete multitone signal can be found in [5]. The optimization of the illumination performance of trichromatic white LEDs and the characterization of the modulation bandwidth for communication applications are addressed in [6]. ...
... Ref. [7] shows a study of illumination and communication using organic LEDs. So far, in [1][2][3][4][5][6][7], different concepts of light data transmission and LED technologies are mentioned. Ref. [8] shows several modulation concepts and a high dynamic current source for LED light and data transmission applications. ...
Three LED drivers which can be used for illumination, but whose main task is the transmission of information (data) via the light of the LEDs, are explored in this paper. The converter circuits need no capacitors for the energy transformation and avoid an inrush current. The lack of necessity of electrolytic capacitors reduces cost and space. Dimming the illumination is also easy to achieve. The control concept of the converters and the generation of pulsing of the LEDs for transmitting the information (data) are explained. The converters can also be expanded to more stages to drive more LEDs with different types of information. All three converters are explained in detail; all presented circuits are built up and simulated with LTSpice. Several data transmission concepts are applied and demonstrated through simulations.
... By utilizing a high PWM frequency, a range of dimming levels can be achieved spanning from 0% to 100% [37]. However, the PWM method presented in [38] had its limitation, capping the data rate at 4.8 Kbps. In response to these limitations, researchers in [39] combined PWM with Discrete Multitone (DMT) to enable both communication and dimming control, resulting in a higher data rate than that of [37]. ...
We explore the use of smartphones to decode data transmitted from LEDs to smartphone cameras in visible light communication (VLC) applied to indoor positioning applications. The LEDs—modified to enable rapid on-off keying—transmit identification codes or optically encoded location data imperceptible to human perception. Equipped with a camera, the smartphone employs a single framed image to detect the presence of the luminaires in the image, decode their transmitted identifiers or locations, and determine the smartphone’s position and orientation relative to the luminaires. The camera captures and processes images continuously. The following fundamental issues are addressed in this research: (i) analyzing the camera parameters on smartphones that affect data decoding results; (ii) exploiting the rolling shutter effect of the CMOS image sensor to receive multiple bits of data encoded in the optical communication line with a single frame shot; (iii) advancing research in developing algorithms to process data from multiple LEDs simultaneously. We conduct experiments to evaluate and analyze feasibility, as well as the challenges of the design, through scenarios varying in distance, transmission frequency, and data length.
... There are two types of OFDM modulation: DCO-OFDM and ADC-OFDM (Khalid et al., 2012;Ntogari et al., 2011;Elgala et al., 2007). Another multi-carrier scheme is the CSK. ...
This work presents a general and introductory review of visible light communication. Visible light communication or VLC refers to wireless communications using a spectral range from 380 to 780 nm for the transmission of information. This part of the optical-electromagnetic range presents some advantages to current wireless radio frequency technologies, as well as several challenges to its development and application. Different visible light communication systems have been developed for indoor, outdoor, domestic, and industrial fields where the luminaire performs two tasks: general lighting and data transmission, since this type of communication has important and valuable applications. Recently, research has been performed to improve each functional block’s performance that composes this kind of communication system. The incursion VLC poses challenges such as LED bandwidth limited by the carrier lifetime, the LED-Driver Linearity, it’s up-link; the general lighting infrastructure to the internet; and the dimming and general lighting performance. It is concluded that the incursion of Visible Light Communication into the already extended spectrum of wireless communications systems will complement and make it less harmful to our environment as international regulation has helped to improve this technology substantially.
... To cope with the congestion of radio frequency (RF) spectrum, it is obligatory to guarantee the obtainability of new-fangled spectrum. The illumination is substitute technologies to entice the candidate for the upcoming local area networks [1]. The bandwidth of wireless fidelity (Wi-Fi) is constrained with 50-100 Megabits per Second (Mbps). ...
In modern homes, the home automation is more preferable to ensure safety and security. Lots of devices can be interconnected in home automation through wireless technologies. The overhead of data communication increases with increasing data transmission through local wireless network like wireless fidelity from the devices used in indoors. Spatial reprocess is not able to meet the current needs with accumulative traffic demand in existing communication technique. The paper focuses the need of visible light communication in future era in home automation system. The sustainable materials in light emitting diodes requires less power than normal forms of lightning. It consumes less energy and impacts positive effect in the environment. Also it has reduced emission effect and supports eco-friendly environment. The proposed work is the usage of Light Fidelity (Li-Fi) with unipolar OFDM (DC biased Optical OFDM (DCO-OFDM)) method to support data transmission with enhanced Signal to Noise Ratio (SNR), data rate and reduced Bit Error Rate (BER) in the home automation system.
... In [19], a variable pulse amplitude and position modulation scheme was proposed for a dimmable VLC system. Ntogari et al. [20] proposed PWM dimming with discrete multitone signals to transmit data over a VLC channel. In [21], the authors proposed a combination of PPM and PWM to control the dimming level. ...
Visible light communication (VLC) is considered a new technology for interconnecting devices in 5G and beyond. VLC can provide additional bandwidth for communicating devices which can help to reduce the radio frequency bandwidth congestion. In this work, we aim to maximize the bandwidth usages for VLC. The proposed modulation technique can impose more bits due to the combined utilization of both pulse height and width changes. Moreover, we subdivide the single bit duration to impose more bits for data transmission. The proposed modulation is capable of transmitting more bits by utilizing fewer optical pulses than other traditional modulation techniques such as multilevel modulation, on-off keying, pulse width modulation, pulse position modulation, pulse amplitude modulation, and multiple pulse position modulation. We have evaluated the theoretical bit error rate (BER) expression in terms of average signal to noise ratio and compared the experimental BER performance for the proposed system. The experimental results demonstrate that the proposed modulation technique can achieve a communication distance of 3 m in an indoor environment.
... It is mandatory to ensure the availability of a new spectrum as the congestion in the spectrum is increased. The solution is alternate technologies to attract the candidate for the future local area networks [1]. The Wi-Fi challenges are its availability, capacity, security, and efficiency. ...
The paper focuses on the need for optical communication in future eras. Spatial reprocess cannot meet the present conditions with increasing traffic demand in Radio Frequency (RF) communication. The frequency spectrum in traditional methods of wireless communication has been saturated. Visible Light Communication (VLC) and Internet-of-Things (IoT) integration will open up many indoor applications in the near future. Light Emitting Diodes (LEDs) and Photodetectors (PDs) in VLC support reliable uplink and downlink for Device-to-Device communication indoors. There is emergence of the energy-efficient variant of the VLC due to the shortage of energy budget in the upcoming era. The VLC works well in low illuminance. Energy conservation is supportedby consuming much lower energy through the usage of LEDs in VLC.This can be achieved through the hybrid of single and multicarrier modulation. The work is about to discuss dimming techniques that support VLC in low illuminance and multicarrier modulation, which supports high data rate transmission.
... Some more sophisticated OOK schemes vary the duration of presence and absence [78]- [81]. • Pulse modulation: Pulse modulation is a simple modulation scheme where the transmitted signal is presented in form of pulses [82]- [85]. It is classified into three major types: --Pulse-width modulation/Pulse-duration modulation --Pulse-amplitude modulation --Pulse-position modulation • Orthogonal frequency division multiplexing: OFDM is a multi-carrier technique, where the available frequency band is divided into many small bands by the using of orthogonal sub-carriers [86]- [91]. ...
Wireless communications refer to data transmissions in unguided propagation media through the use of wireless carriers such as radio frequency (RF) and visible light (VL) waves. The rising demand for high data rates, especially, in indoor scenarios, overloads conventional RF technologies. Therefore, technologies such as millimeter waves (mmWave) and cognitive radios have been adopted as possible solutions to overcome the spectrum scarcity and capacity limitations of the conventional RF systems. In parallel, visible light communication (VLC) has been proposed as an alternative solution, where a light source is used for both illumination and data transmission. In comparison to RF links, VLC links present a very high bandwidth that allows much higher data rates. VLC exhibits also immunity to interference from electromagnetic sources, has unlicensed channels, is a very low power consumption system, and has no health hazard. VLC is appealing for a wide range of applications including reliable communications with low latency such as vehicle safety communication. Despite the major advantages of VLC technology and a variety of its applications, its use has been hampered by its cons such as its dependence on a line of sight connectivity. Recently, hybrid RF/VLC systems were proposed to take advantage of the high capacity of VLC links and better connectivity of RF links. Thus, hybrid RF/VLC systems are envisioned as a key enabler to improve the user rates and mobility on the one hand and to optimize the capacity, interference and power consumption of the overall network on the other hand. This paper seeks to provide a detailed survey of hybrid RF/VLC systems. This paper represents an overview of the current developments in the hybrid RF/VLC systems, their benefits and limitations for both newcomers and expert researchers.
In this paper, we demonstrate a hybrid Laser-LED transmitter module for indoor optical wireless communication with closed-loop, non-mechanical beam steering capability. The hybrid transmitter module consists of a near infrared laser diode for data communication and white LED array for illumination, combined on a diffuser surface. Dual-axis non-mechanical beam steering of the laser beam is implemented using two off-centered liquid lenses. The diffused laser beam directed towards the receiver is steered over an angular range of −7.6
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to 7.6
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(−1.7
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to 2.6
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) along the horizontal (vertical) axes spanning −200 to 200 mm (−44 to 67 mm) at the receiver placed 1.5-meter from the transmitter. M-QAM/OFDM in combination with adaptive bit-and power-loading is utilized to achieve a total data throughput of 5.15 Gbps for the diffused laser beam with steering. Laser intensity levels as measured at the receiver plane are kept below the maximum permissible exposure limit for indoor usage across the entire beam steering range. Closed-loop beam steering is also demonstrated by scanning the transmitted laser beam horizontally, measuring the signal strength using a low bandwidth photodetector and locking the laser beam to the receiver position for data-communication. Such hybrid transmitters offer the benefit of decoupling the data communication and illumination requirements of the indoor optical link, thereby tailoring the individual light emitter's performance to specific use-case.
Modern solid-state lighting that uses light emitting diodes is increasingly used in a wide range of lighting applications. These sources are more efficient than incandescent lamps and can have very long lifetimes. As the efficiency of these sources increases and their cost decreases, they may become the predominant source in most lighting applications. Due to their high modulation bandwidth (when compared with other lighting sources), which is in the megahertz range, using these sources for both illumination and communications is attractive. Such Visible-light communications is a growing area of research. In addition the use of visible sources for short-range data links is under consideration. This paper introduces the components used in a typical visible-light communications link and their typical performance. The challenges faced in improving the performance of these links are outlined, together with potential solutions. Efforts to develop standards in this area and possible applications are also summarised.
Zusammenfassung: Durch doppelte Nutzung ermöglichen Weißlicht-LEDs Synergie von Raumbeleuchtung und drahtloser optischer Kommunikation/ Nachrichtenverteilung. Für einen mit LEDs gut ausgeleuchteten mittelgroßen Büroraum wird die erreichbare Datenrate bei Basisband-und DMT-Übertragung ermittelt, wobei der Einsatz handelsüblicher LEDs und Photodioden angenommen wird. Die Resultate zeigen, dass trotz relativ geringer Systembandbreite Bitraten von mehr als 100 Mbit/s zu erwarten sind. Summary: Emergence of white-light LEDs allows synergy of lighting and broadcast/communication function in one optical source. We investigate possible data transmission rates in a moderate-size office room where we assume illumination conforming to standards and the use of commercially available LEDs and photodiodes. The performances of systems relying on base-band and DMT transmission show that data rates of more than 100 Mbit/s can be expected despite the rather low bandwidth of the system.
Emergence of white-light LEDs allows the combination of lighting and information broadcast functionality in one optical source. We investigate analytically and by Monte Carlo simulations feasible data transmission rates in a moderate-size office room, where we assume illumination conforming to standards and the use of commercially available LEDs and photodiodes. The performances of systems relying on baseband [i.e., pulse-amplitude modulation (PAM)] and discrete multitone (DMT) transmission show that data rates of more than 100 Mbit/s can be expected despite the rather low bandwidth of the system.
Light emitting diodes (LEDs) are devices that are used in a myriad of
applications, such as indicator lights in instruments, signage,
illuminations, and communication. This graduate textbook covers all
aspects of the technology and physics of infrared, visible-spectrum, and
white light-emitting diodes (LEDs) made from III-V semiconductors. It
reviews elementary properties of LEDs such as the electrical and optical
characteristics. Exercises and illustrative examples reinforce the
topics discussed.
High-power LEDs of different color have generated much enthusiasm because of the potential energy savings and reduced maintenance cost due to long lifetimes compared with traditional light source. Two schemes are widely used for LED dimming: continuous current dimming, or pulse-width modulation (PWM) dimming. The visual felling to the LEDs is the most intuitive judgment in the LED illumination and display. But the apparent brightness of the LEDs under these dimming ways has never been studied. In this paper, the research of the apparent brightness is approached through experiments. The results show that when the average intensities are the same, the apparent brightness of the PWM dimming LED is higher than that of the continuous dimming LED. In addition, to the PWM dimming LEDs, the contrast apparent brightness of various color LEDs is obviously discrepant as the duty cycle is less than 40%, but when it is above 40%, the gap between the contrast values becomes much smaller. Thus, in the LED applications, the LEDs using PWM driving method has higher brightness efficacy, and the duty cycle of the PWM should be above 40% to achieve the consistent apparent brightness between LEDs. The results have great availability to optimize the driver for the LEDs.
We have developed two brightness control methods for illumination and visible-light communication systems. One method is Pulse Width Modulation (PWM), the other is changing modulation depth. Using these proposed methods, we can achieve both dimmer i.e. brightness control and wireless communication at the same time. We discussed the relationship between PWM frequency, LED brightness, and communication performance. The results show that we can control brightness from 0% to 87.5% when we use PWM and data transmission possible when PWM frequency is high enough. Brightness can be controlled from 0% to 100% and communication performance is better than that of PWM when we change modulation depth.
The performance of advanced modulation schemes for spectrally efficient data transmission is reviewed, targeting short-range intensity-modulated optical channels with direct detection. Hereby, the focus lies on the performance of multilevel pulse-amplitude modulation combined with electronic equalization and, as an alternative modulation scheme, discrete multitone. A comprehensive statistical analysis of clipping noise is presented and exact expressions for the performance of symmetrically clipped discrete multitone are derived. It is shown that the clipping noise is impulsive and obeys a generalized Laplace distribution. The bit-error probability due to clipping is studied in detail, and it is found that the impact of clipping noise is reduced for an increasing number of subchannels. Finally, the optical link margins of multilevel pulse-amplitude modulation in combination with electronic equalization and that of discrete multitone in combination with margin-adaptive bit loading are compared. It is found that even symmetrically clipped discrete multitone suffers from its large crest factor in the peak-power-limited channel and that, in many instances, pulse-amplitude modulation provides higher link margins for the same target bit-error probability.
Spectrally efficient data transmission with white light-emitting diodes (LEDs) is a topic of increasing interest. In this letter, we report a visible light communication link operating at 200+ Mb/s net transmission rate (230 Mb/s gross) with a bit-error ratio for uncoded data below 10(-3). The link is based on a thin-film high-power phosphorescent white LED and offline signal processing of discrete multitone signals. Transmission at the brightness levels of about 1100 and 550 lx was investigated. Our results indicate that the achievable data rates are limited by detector noise.