PWM Visible Light Communication Flickering Elimination
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Solution Overview
Problem
Existing visible light communication technologies face challenges in achieving signal communication synchronization and experience flickering phenomena, especially at lower communication frequencies, making them inconvenient and noticeable to humans.
Innovation Solution
A light emitting device with a dimming visible light communication function that uses pulse width modulation (PWM) signals to transmit data, adjusting the frequency based on the data to be transmitted, thereby eliminating flickering and improving synchronization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If Manchester encoding with PWM and PPM control is used for visible light communication, then data transmission is achieved, but signal synchronization becomes difficult and flickering occurs at lower communication frequencies
Solution Approach 1:
The patent changes the encoding parameter from Manchester encoding to a simplified pulse position modulation scheme where data is transmitted by varying the position of pulses within a fixed period. This parameter change eliminates the synchronization difficulties inherent in Manchester encoding while maintaining data transmission capability.
Solution Approach 2:
The patent implements periodic pulse transmission where each data symbol is represented by a pulse positioned within a fixed periodic frame. This periodic structure provides natural synchronization references, making signal synchronization straightforward compared to the continuous encoding of Manchester protocol.
2Loss of information
If Manchester encoding with PWM and PPM control is used for visible light communication, then data transmission is achieved, but noticeable flickering occurs especially at lower communication frequencies
Solution Approach 1:
The patent uses periodic pulse transmission within fixed frames, ensuring that the light emission follows a regular periodic pattern. This periodic action at standardized frequencies minimizes perceptible flickering while enabling reliable data transmission through pulse position variations.
Solution Approach 2:
The patent transmits data by creating temporal copies of pulse patterns at different positions within fixed periods rather than using continuous Manchester encoding. This discrete pulse copying approach regularizes the light output pattern, reducing flickering artifacts.
3Productivity
If pulse width modulation signal frequency is changed according to transmitted data, then data transmission efficiency is improved, but device complexity increases
Solution Approach 1:
The patent employs frequency variation of the PWM signal to encode data, where different frequencies represent different data symbols. This parameter-based encoding achieves high data transmission efficiency while the control circuit implementation remains relatively simple by utilizing standard frequency synthesis techniques.
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 enables convenient signal synchronization and eliminates noticeable flickering, allowing for effective data transmission while adjusting luminance, thereby enhancing the usability of visible light communication systems.
Implementation Method 1
The light emitting device outputs visible light, is coupled to the control circuit, and receives the PWM signal
Implementation Method 2
The light sensing element converts the received light communication signal into an electric signal
Data Source
AI summary
A light emitting device with a dimming visible light communication function and an interaction device applying for visible light are provided. The light emitting device with the dimming visible light communication function comprises a luminance adjusting unit, a control circuit and a light emitting device. The luminance adjusting unit outputs a luminance adjusting signal according to luminance adjusted by a user. The control circuit coupled to the luminance adjusting unit outputs a pulse width modulation (PWM) signal according to the luminance adjusting signal. The light emitting device outputs visible light, receives the PWM signal, and is turned on or off according to states of a logic high voltage and a logic low voltage of the PWM signal. In an idle mode, the PWM signal operates at a first frequency. In a light communication mode, an operating frequency of the PWM signal is changed according to transmitted data.