DC-Free Coded Light Modulation for Flicker Reduction
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Solution Overview
Problem
Existing coded light systems face challenges in controlling multiple light sources due to complex parameter variations and interference from other light sources, leading to visible flicker and susceptibility to low-frequency interference, which complicates intuitive control and decoding of information sequences.
Innovation Solution
A light driver system that maps source symbols to composite channel symbols, ensuring zero power spectral density at frequency zero and using signed averages or weighted averages of past and future symbols to smooth transitions, resulting in better spectral confinement and reduced visible flicker, while maintaining comparable complexity to Manchester coding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If Manchester coding is used to modulate coded light, then data transmission is achieved, but visible flicker occurs due to low-frequency spectral content
Solution Approach 1:
The patent applies parameter changes by modifying the coding scheme from Manchester coding to a DC-free code with improved spectral properties. The new code ensures zero power spectral density at DC and reduced low-frequency content by using balanced transitions (equal number of rising and falling edges), thereby eliminating visible flicker while maintaining data transmission capability.
2Ease of operation
If conventional coding schemes are used, then data transmission is simple, but the system is susceptible to interference from other light sources at low frequencies
Solution Approach 1:
The patent changes the spectral parameters of the coding scheme by designing a DC-free code with zero power spectral density at DC and suppressed low-frequency components. This is achieved through balanced transitions and specific code structure, making the system reliable against interference from incandescent, fluorescent, and other low-frequency light sources while keeping the coding scheme simple to implement.
3Object-affected harmful factors
If high modulation frequencies are used to avoid flicker, then visible flicker is reduced, but LED driver circuit implementation becomes difficult
Solution Approach 1:
Instead of increasing modulation frequency, the patent changes the temporal-spectral parameters of the code by ensuring zero DC component and reduced low-frequency content through balanced transitions. This approach reduces visible flicker while maintaining compatibility with standard LED driver circuits, avoiding the need for complex high-frequency circuitry.
4Measurement precision
If multiple light sources are controlled with individual controllers, then each light source can be precisely controlled, but the control system becomes complex and difficult to operate
Solution Approach 1:
The patent applies universality by enabling a single controller to address and control multiple light sources through coded light transmission. Each light source embeds its identifier in its light output using the DC-free code, allowing one controller to identify and precisely control individual light sources or groups, thereby maintaining control precision while dramatically simplifying the control system architecture.
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 proposed solution enables efficient spectral confinement, particularly at low frequencies, reducing visible flicker and interference, allowing for accurate and intuitive control of coded light systems with improved decoding capabilities.
Implementation Method 1
For the transmission of CL, mostly, light emitting diodes (LEDs) are considered
Implementation Method 2
The embedding of identifiers in the light output of luminaires has been previously proposed. This embedding of identifiers can be based on unique modulation of the visible light (VL) of the luminaire
Implementation Method 3
an information decoder for decoding an information sequence from a signal received from a light detector
Data Source
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Figure 4a~4c
AI summary
Coded light has been proposed to enable advanced control of light sources and transmit information using light sources. Sequences of channel symbols to drive the light source are determined from sequences of source symbols such that no visible flicker is present in coded light emitted by the light sources. Each source symbol is mapped to a composite channel symbol comprising at least one first channel symbol which may be identical to the current source symbol and at least one second channel symbol which may be a function of the current source symbol and at least one future and/or past source symbol.