LED Driver VLC Modulation with Dynamic Current Profiles
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Solution Overview
Problem
LED-based lighting applications face challenges in maintaining flicker-free visual light communication (VLC) while adjusting illumination settings and in increasing the data transmission rate per unit of time.
Innovation Solution
An LED driver with a control unit that determines current profiles for LEDs or LED groups to modulate intensity and color variations, enabling the transmission of variable length VLC codes, which can maintain desired illumination characteristics and increase data transmission efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If LED current is modulated to transmit VLC data, then data transmission capability is improved, but illumination quality deteriorates due to flicker
Solution Approach 1:
The patent applies dynamics by making the LED driver adaptable to different operating modes (VLC mode, illumination mode, and combined mode) through dynamic adjustment of current profiles. The control unit dynamically switches between different current profile configurations depending on whether VLC data transmission or stable illumination is the primary objective, thereby resolving the contradiction between data transmission capability and flicker prevention
Solution Approach 2:
The patent changes parameters by adjusting the current profile characteristics (amplitude, duration, shape) to simultaneously achieve VLC modulation and maintain stable illumination. By modifying the current waveform parameters and using techniques like DC offset addition and pulse shaping, the system transmits data while keeping illumination variations imperceptible to humans
2Illumination intensity
If illumination set-point is adjusted during VLC transmission, then illumination quality is improved, but VLC transmission reliability deteriorates
Solution Approach 1:
The patent applies preliminary action by pre-planning and pre-synchronizing illumination adjustments with VLC frame boundaries. Before adjusting the illumination set-point, the control unit ensures that the adjustment occurs at appropriate timing points that do not interrupt ongoing VLC data transmission, thereby maintaining both illumination quality and transmission reliability
Solution Approach 2:
The patent uses periodic action by synchronizing illumination adjustments with the periodic VLC transmission framework. Illumination set-point changes are performed at regular intervals aligned with VLC frame structures, ensuring that adjustments do not occur during critical data transmission phases while still achieving desired illumination quality
3Loss of information
If standard VLC modulation is used, then data transmission is achieved, but data transmission rate per unit time is limited
Solution Approach 1:
The patent applies dimensionality change by transitioning from traditional time-based VLC modulation to a two-dimensional approach that combines time-domain pulse positioning with frequency-domain carrier modulation. This allows simultaneous transmission of multiple data bits through different modulation dimensions, significantly increasing the data transmission rate while maintaining signal integrity
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution allows for accurate operation in VLC mode during transients and increased data transmission rates by modulating current profiles to represent data through intensity and color variations, ensuring both flicker-free and efficient data broadcasting.
Implementation Method 1
LED driver for driving a plurality of LEDs or LED groups... determine a current profile for each LED or LED group... whereby an envelope of a combined current profile of the current profiles is modulated in order for a corresponding intensity variation as perceived by a sensor to represent a variable length VLC code
Data Source
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Figure 4b
AI summary
An LED driver for driving a plurality of LEDs or LED groups to transmit light in a VLC mode is described, wherein the LED driver comprises a control unit that is configured to: - receive, at an input terminal, a set-point representing a desired illumination characteristic and data that is to be transmitted using VLC; - determine a current profile for each of the plurality of LEDs or LED groups to generate the desired illumination characteristic, whereby an envelope of the combined current profile comprises a modulation in order for a corresponding intensity modulation as perceived by a sensor to represent a variable length VLC code representing the data, the VLC code comprising code words, a code word comprising a plurality of symbols; - generate one or more control signals to drive the plurality of LEDs in accordance with the current profiles in order for the plurality of LEDs or LED groups to transmit the VLC code; and - upon receipt of a further set-point representing a different illumination characteristic during the transmission of the VLC code, determine an adjusted current profile or profiles for one or more of the plurality of LEDs or LED groups based on the different illumination characteristic, whereby the current profile is only adjusted for some, not all, symbols of a next code word to be transmitted; - generate one or more control signals to drive the plurality of LEDs or LED groups in accordance with the adjusted current profile or profiles, and - output, via an output terminal of the control unit, one or more control signals to drive the plurality of LEDs or LED groups in accordance with the adjusted current profile or profiles.