Dimming Scheme Research Articles

Space-domain dimming control scheme based on SCFDM for visible light communications

Abstract In this paper, a space-domain dimming control scheme based on single-carrier frequency-division multiplexing (SD-SCFDM) is proposed for visible light communications (VLC). The SD-SCFDM scheme not only has the advantage of additional spatial dimming domain but inherits the strengths of SCFDM in resisting the clipping distortion and high-frequency attenuation, which can support the efficient communication under different illumination requirements. Considering the limited dynamic range of light emitting diode (LED) and bandwidth limitation in VLC system comprehensively, SD-SCFDM can achieve the communication with spectral efficiency of at least 1 bit/s/Hz higher than SD scheme based on orthogonal frequency-division multiplexing (SD-OFDM) in the whole dimming range. Additionally, the proposed SD-SCFDM has the low computational complexity of encoding. Meanwhile, for the proposed scheme with spectral efficiency of 2.5, 3 and 3.5 bit/s/Hz, the required number of LED chips in one lamp can be reduced by about 55.9%, 50% and 59% compared with its OFDM-based counterparts, respectively. In conclusion, the SD-SCFDM scheme shows the great potential and feasibility for future practical implementations of VLC.

The Spatial Dimming Scheme for the MU-MIMO-OFDM VLC System

Multiuser visible light communication (MU-VLC) systems utilizing multiple-input multiple-output (MIMO) and orthogonal frequency-division multiplexing (OFDM) are gaining increased attentions recently. Visible light communication (VLC) links are expected to work under different illumination conditions and, thus, the need for dimming control mechanisms. However, the traditional analog- and digital-based dimming schemes have adverse effects on the data communications performance, such as clipping distortion and the variation of the duty cycle. In this paper, spatial dimming schemes based on the zero-forcing and the minimum mean-squared error precoding schemes are proposed for direct-current biased optical OFDM based indoor MU-MIMO VLC system, and the bipolar optical OFDM signal is biased by a fixed dc level. Transmit antenna selection algorithms are designed for the optimum working light emitting diodes (LEDs) subset at each dimming level. Owing to the simultaneously exploration of the selection diversity of LEDs-based lights and the channel state information, the proposed spatial dimming schemes outperform the traditional dimming schemes, which is also verified by simulation results. Thus, the proposed schemes are shown to have a great potential to be applied in practical MU-MIMO-OFDM VLC systems.

A spectral-efficient dimming control scheme with multi-level incremental constant weight codes in visible light communication systems

As an essential requirement for visible light communication (VLC) system, dimming control has attracted increasing attentions where arbitrary brightness levels can be achieved. Conventional dimming schemes based on binary modulation are spectral inefficient. In this paper, we propose multi-level incremental constant weight codes (ML-ICWC) scheme to achieve dimming control via controlling the number of LEDs on per lighting source simultaneously. Meanwhile, the construction algorithm of the codeword set is developed accordingly to guarantee reliable data transmission. Finally, simulation results show that the proposed scheme achieves significant improvement in terms of spectral efficiency compared with existing dimming schemes under various dimming levels.

Spectral-Efficient Generalized Spatial Modulation Based Hybrid Dimming Scheme With LACO-OFDM in VLC

Visible light communication (VLC) is regarded as one of the promising candidates to complement the conventional radio frequency communication as it can potentially perform communication and illumination simultaneously. Recently, VLC is combined with the generalized spatial modulation (GenSM) technology to improve spectral and energy efficiencies. In order to provide high-speed communication and flexible dimming control simultaneously, in this paper, a spectral-efficient GenSM-based hybrid dimming scheme with layered asymmetrically clipped optical OFDM is proposed for VLC, which combines the spatial-domain and time-domain dimming strategies. The channel capacities of the proposed scheme are analyzed and the closed-form expressions of the channel capacity are derived in both the rich scattering scenario and highly correlated scenario. According to the required illumination level, the spatial-domain and time-domain strategies are realized based on the maximization of the channel capacity. Simulation results substantiate the superior performance of the proposed dimming scheme over the state-of-art dimming schemes.

Unary-Coded Dimming Control Improves ON-OFF Keying Visible Light Communication

An ideal visible light communication (VLC) system should facilitate reliable data transmission at high throughputs, while also providing flicker-free illumination at the user-defined dimming level. In this spirit, we conceive a unary code aided dimming scheme for ON-OFF keying (OOK) modulated VLC systems. The proposed unary-coded scheme facilitates joint dimming and throughput control, while relying on iterative decoding. It is demonstrated that the proposed unary-coded dimming scheme provides attractive throughput gains over its contemporaries and it is also capable of approaching the theoretical throughput limit. Furthermore, we design novel joint dimming-forward error correction coding schemes, which significantly outperform their compensation time dimming-based counterparts in terms of the attainable bit error rate performance as well as the throughput. Finally, in the quest for approaching the capacity, we also optimize our system using EXTRINSIC information transfer charts and demonstrate an SNR-gain of upto 6 dB over the compensation time dimming-based classic benchmarker.

Implementation of dimming control scheme based on joint coding and modulation

Implementation of dimming control scheme based on joint coding and modulation

A Novel Hybrid Dimming Control Scheme for Visible Light Communications

A dimming control scheme that combines analog dimming and spatial dimming is proposed. The basic idea of the combined scheme is that both the direct current bias level of each individual light-emitting diode (LED) and the number of glared LEDs are simultaneously adjusted to achieve a required dimming level. Besides, we design a space constellation to transmit additional information in spatial domain without compromising uniform illumination constraint, and this essentially improves the performance of the system. A maximum-a-posteriori probability estimator is also designed to estimate the received time domain and spatial domain signals. Since two degree of freedoms are simultaneously exploited for dimming control, the proposed scheme outperforms conventional dimming schemes, which only focus on signal domain design, and this is verified by simulation results. To the best of authors’ knowledge, this is the first design that effectively utilizes multidomain resources to achieve dimming control for visible light communications.

An Off-line Single-Inductor Multiple-Output LED Driver With High Dimming Precision and Full Dimming Range

This paper presents a single-inductor multiple-output (SIMO) LED driver with precise dimming and full dimming range. Based on the coordination of a string-level scheme and a system-level dimming scheme, the proposed SIMO LED driver can overcome practical constraints of existing SIMO LED drivers such as limited dimming range and needs for high-current switches. The proposal can achieve dimming precision up to an accuracy of 0.8% and also full dimming range. It has the flexibility of using either phase-shift or synchronous pulsewidth-modulated (PWM) switching for dimming control. The proposed circuit and control operations have been practically verified with a 25-W off-line SIMO-driven LED system. Practical evaluations of its power quality and energy efficiency are also provided.

Spatial dimming scheme for optical OFDM based visible light communication

A new dimming control scheme termed spatial dimming orthogonal frequency division multiplexing (SD-OFDM) is proposed for multiple-input and multiple output OFDM based visible light communication. The basic idea of SD-OFDM is that the illumination can be represented by the number of glared light emitting diodes (LEDs) in an LED lamp. As the biasing level of LEDs does not adjust to represent the required illumination level, the proposed scheme can significantly mitigate the clipping noise compared to analogue dimming schemes. Furthermore, unlike digital dimming schemes that control illumination levels by setting different duty cycles of pulse width modulation, the proposed scheme is always in the "on-state" for varied illumination levels. Both analytical and simulation results indicate that the proposed scheme is an efficient and feasible dimmable scheme.

Group statistical channel coding dimming scheme in visible light communication system

In this paper, we propose a group statistical channel coding (GSCC) scheme, which achieves dimming by changing the ratio of the 0–1 symbol of the original data stream through probabilistic statistics method. The simulation under various brightness conditions displays that the GSCC maintains good performance comparing to PWM dimming with half satisfice of transmission rate and a larger dimming intensity. Simulation of GSCC after combining with other channel coding schemes reflects that GSCC has good compatibility to arbitrary access coded signal.

Smart Household Environment Illumination Dimming and Control

This paper presents the design of a smart household environment illumination dimming-control. The control can be operated using either an Android App or a computer using either Wi-Fi or Zigbee to connect to a Database Management System (DBMS). The DBMS can synchronize with a central controller in order to achieve simple and convenient dimming-control of the user's home illumination. In this paper, a linear dimming scheme was adopted to reduce the light gleaming. In order to achieve suitable variations in the illumination environment, a highly-efficient three-color LED was used as the light source. This paper covers the designs of six environment illumination controls for users who can deliver the control states to the central controller and mobile phone. A 24 V DC power supply was designed in this system and can collocate with the DC/DC converter to form a power module suitable for general home use. The interface of the proposed environment illumination control is clear and simple; one can verify that the design presented in this paper possesses very high practicability from the experimental results.

Dimming schemes for visible light communication: the state of research

As a new generation green lighting source, the light emitting diode (LED) is rapidly replacing traditional incandescent and fluorescent light sources. Apart from providing energy savings, the use of LED lighting technology creates scope for an innovative optical wireless communication technology known as visible light communication (VLC), which takes advantage of the superior modulation capability of LEDs to transmit data through a wireless channel. VLC is capable of concurrently providing communication as well as illumination. For making commercial implementation of VLC feasible, it is necessary to incorporate it with dimming schemes that will provide energy savings, moods, and increase the aesthetic value of the place using this technology. However, general dimming techniques have an adverse effect on communication since they limit the achievable data rate of a VLC link. This drives the necessity of formulating efficient dimming techniques, which will create a balance between the two most basic functions of VLC: illumination and communication. This paper focuses on dimming mechanisms that can be implemented in VLC systems to save energy and provide precise illumination control. The motivation behind this control mechanism, current challenges in practical implementation, driver circuitry, recent progress, and future prospects are also concisely presented.

LED Backlight Driver Circuit With Dual-Mode Dimming Control and Current-Balancing Design

A dimmable light emitting diode (LED) driver circuit with dual-mode dimming control and current-balancing design for backlight applications was examined and implemented in this study. Parallel current balancing can be achieved by a passive differential-mode (DM) transformer. The driver has the main power stage constructed by one boost converter. Owing to the high switching frequency, continuous-current-mode operation, and DM transformer magnetizing inductance, the output side only needs an ultralow capacitor. Through the constant-current and constant-voltage dimming scheme, the LED has smoothed temporary voltage transient and will extend the lifetime of a LED lamp. Furthermore, simplicity, low cost, less capacitor, and gradual voltage rising slope can be achieved. This study included the analyses and discussions for the operational principles and design considerations of the proposed LED driver. A 10-W laboratory prototype was built and tested to verify the feasibility of the studied driver.

Design of Solar Energy Based Intelligent LED Street Lighting Controller

This paper aims to design an intelligent street lighting controller based on solar energy and LED. The controller can work in daytime mode, dusk mode based on detection of light intensity and photovoltaic voltage, and head into night mode after a certain period of time when in dusk mode. While in night mode, a dimming scheme is applied by introducing motion detection with passive infrared (PIR) sensors. The controller also integrates a ZigBee based WSN to report street lights status periodically and get instructions from the remote control center. Moreover, it can enable more efficient management and lower maintenance costs.

마이크로웨이브센서와 디밍제어를 활용한 조명제어시스템 설계 및 구현

In this paper, we present a novel illumination system for parking lots constructed underground. We design and implement this system using microwave sensors and dimming control of LED fluorescent lamps so that we can obtain lighting efficiency of the illumination scheme. We construct an effective illumination system in the aspects of performance and cost, resulting in energy-saving and electricity reduction. Recently conventional energy-saving method applied to old underground parking lots mainly relies upon turning off the half of total number of lamps installed in the parking lot. Sometimes there are some lots that have infrared sensor to be used to turn on/off the fluorescent lamps to realize these operations smoothing. The other schemes utilize timer to control lighting time of the fluorescent lamps. These conventional schemes are forcing to turn off a part of lamps installed so that we cannot apply them in a systematic way. Moreover they will be most inefficient when we leave them alone to be continuous consumers. The lighting control system proposed in this paper can recognize objects through microwave sensors and inform the appropriate lighting time, furthermore we can adjust brightness of LED lamps following the surroundings using dimming control scheme so that we can epochally improve the illumination system for underground parking lots. According to our sophisticated test experiments, we can maximally obtain 81.9% of energy-saving effectiveness using the system proposed in this paper.

Weighted roll-off scheme to remove block artifacts for low power local dimming liquid crystal displays

A roll-off algorithm has been incorporated into adaptive dimming LCDs to enhance the details of high gray levels. However, because a roll-off algorithm generates block artifacts in local dimming LCDs with 1-D or 2-D local blocks, we introduced a new roll-off algorithm for block artifact reduction in 2011 based on an ideal backlight without any light spreads. Whereas, this paper demonstrates a weighted roll-off local dimming scheme for low power LCD applications which eliminates block artifacts at a real backlight with light spreads. Both simulation and experimental results represent that a proposed weighted algorithm alleviates color difference values as well as block artifacts without any increases in power consumption. The measured backlight power consumption in a weighted roll-off 1-D dimming LCD of 5 local blocks is 27.60 W over 24 test images, on the average, compared to 62.45 W of a constant backlight. • Novel roll-off algorithms are introduced for ideal and real local dimming backlights. • Block artifact reduction scheme is evaluated by simulation and measurement. • A new weighted roll-off algorithm achieves better image quality at the same power consumption.

An image-space energy-saving visualization scheme for OLED displays

Current energy-saving color design approaches can be classified into two categories, namely, context-aware dimming and color remapping. The former darkens individual regions with respect to the user interactions, and the latter replaces the color set with a new color set that yields lower energy consumption. Both schemes have drawbacks: color dimming tends to cause loss of perceptual quality, and color remapping is an offline color design process.This paper introduces a novel saliency-guided color dimming scheme for OLED displays in both the context of 3D visualization and 2D visualization. The key idea is to eliminate undesired details while enhancing the visually salient features of each frame on-the-fly by leveraging the color and spatial information. A parallelizable image-space salient region detection algorithm is introduced to make the entire process GPU-friendly and real-time. We apply our approach on several representative visualization scenarios and conduct a preliminary user study. Experimental results demonstrate the effectiveness, efficiency, and quality of our approach.

Low color distortion adaptive dimming scheme for power efficient LCDs

This paper demonstrates the color compensation algorithm to reduce the color distortion caused by mismatches between the reference gamma value of a dimming algorithm and the display gamma values of an LCD panel in a low power adaptive dimming scheme. In 2010, we presented the YrYgYb algorithm, which used the display gamma values extracted from the luminance data of red, green, and blue sub-pixels, Yr, Yg, and Yb, with the simulation results. It was based on the ideal panel model where the color coordinates were maintained at the fixed values over the gray levels. Whereas, this work introduces an XrYgZb color compensation algorithm which obtains the display gamma values of red, green, and blue from the different tri-stimulus data of Xr, Yg, and Zb, to obtain further reduction on the color distortion. Both simulation and measurement results ensure that a XrYgZb algorithm outperforms a previous YrYgYb algorithm. In simulation which has been conducted at the practical model derived from the measured data, the XrYgZb scheme achieves lower maximum and average color difference values of 3.7743 and 0.6230 over 24 test picture images, compared to 4.864 and 0.7156 in the YrYgYb one. In measurement of a 19-inch LCD panel, the XrYgZb method also accomplishes smaller color difference values of 1.444072 and 5.588195 over 49 combinations of red, green, and blue data, compared to 1.50578 and 6.00403 of the YrYgYb at the backlight dimming ratios of 0.85 and 0.4.

A High Efficiency Step-Up WLED Driver with Wide Range PWM Dimming

A high efficiency step-up White Light Emitting-diode (WLED) driver with PWM dimming is presented in this paper. An integrated current sensing technique is used to improve system efficiency. Meanwhile, a novel PWM(pulse width modulation) dimming scheme is proposed to achieve wide range dimming frequency, which can be adaptive to dimming frequency from 200Hz to 200 KHz. The proposed driver is designed with CSMC 0.5um 40V bipolar-CMOS-DMOS process. Simulation results verify the functionality of the design and high efficiency is realized, with a peak value of 94.12% at 5.5V-input and 200mA-load.

PWM Series Dimming for Slow-Dynamics HPF LED Drivers: the High-Frequency Approach

This paper deals with the capability of pulse width modulation (PWM) dimming operation added to the high-power factor-integrated buck-flyback converter (IBFC), which was developed in previous works for LED lighting applications. First, the two main dimming techniques will be introduced, namely, analog dimming and PWM dimming. Then, the three main PWM dimming schemes found in the literature, that is, enable dimming, series dimming, and parallel dimming, will be briefly discussed. Afterwards, the IBFC topology will be tested performing both analog and enable dimming. In addition, a new proposal is introduced: the high-frequency series PWM dimming technique, which overcomes all the challenges faced when developing PWM dimming capabilities in low slew-rate constant-current fixed-frequency-controlled converters and offers all the advantages of PWM dimming over analog dimming while maintaining good efficiency. The proposed dimming-technique control loop, as well as the laboratory tests, will be presented, discussed, and compared to analog dimming and PWM dimming, showing satisfactory results in terms of dimming ratio, input current total harmonic distortion (THDI), and power factor.