VLC Modulation System Using Adaptive Pre-Distortion
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The modulation speed of high-brightness LEDs, which rely on phosphor, is limited to 1 MHz and 1 Mb/s data rate, and their combination with blue LEDs is not suitable for indoor visible light signal transmissions due to phosphor's limited relaxation time.
Innovation Solution
A visible light communication (VLC) modulation system that includes a visible light signal generating device with an adaptive filter and an arbitrary waveform generator, capable of generating a 20 MHz ASK waveform with a bit-error-rate less than 10−10 bits, using a first and second finite impulse response filtering unit, pre-distortion amount control, and up-sampling to achieve a 20 Mb/s transmission rate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If phosphor-based high-brightness LEDs are used for visible light generation, then illumination efficiency is improved, but modulation speed is limited to 1 MHz and data rate to 1 Mb/s
Solution Approach 1:
The system performs pre-distortion of the modulation signal before transmission through the LED channel. The pre-distortion amount control unit adjusts the signal characteristics in advance to compensate for the phosphor's limited relaxation time, enabling higher modulation speeds without sacrificing illumination efficiency
Solution Approach 2:
The invention changes the signal parameters by implementing adaptive filtering with variable filter coefficients and adjusting the pre-distortion amount dynamically. This allows the system to optimize both illumination efficiency and modulation speed by adapting signal characteristics to match the LED's response characteristics
2Illumination intensity
If blue LEDs combined with phosphor are used to achieve high-brightness LEDs, then brightness is improved, but the combination is not suitable for indoor visible light signal transmissions
Solution Approach 1:
The system employs an adaptive filter that continuously adjusts its coefficients based on feedback from the transmitted signal quality. This feedback mechanism compensates for the signal degradation caused by phosphor relaxation, making the blue LED-phosphor combination suitable for reliable indoor visible light communication
Solution Approach 2:
The pre-distortion unit modifies the signal in advance to pre-compensate for the known limitations of phosphor-based LEDs. This preliminary adjustment ensures that the signal arrives at the receiver with adequate quality despite the phosphor's relaxation time constraints
3Device complexity
If conventional modulation methods are used with phosphor-based LEDs, then system simplicity is maintained, but data rate is limited to 1 Mb/s
Solution Approach 1:
The pre-distortion amount control unit prepares the modulation signal in advance by applying appropriate distortion compensation. This preliminary processing enables higher data rates (achieved 20 Mb/s) without requiring complex hardware modifications to the LED itself
Solution Approach 2:
The invention introduces signal processing intermediaries (adaptive filter, pre-distortion unit, up-sampling unit) between the data source and the LED. These intermediaries enhance the data rate capability while keeping the LED hardware simple, effectively mediating between simple hardware and high-performance requirements
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 system achieves a higher data transmission rate of 20 Mb/s with a low bit-error-rate, suitable for indoor applications, by utilizing a white LED with a 100 lm output and a Si-based PIN receiving unit, extending the transmission distance and improving signal quality.
Implementation Method 1
The visible light generated by LEDs has certain advantages compared to visible light generated from other sources
Implementation Method 2
a visible light signal receiving device configured to receive the visible light signal
Data Source
AI summary
A VLC (Visible Light Communication) modulation system and method thereof, which includes a visible light generating device and a visible light receiving device. The visible light generating device includes a visible light emitting module and an arbitrary waveform generator. The arbitrary waveform generator further includes a first finite impulse response filtering unit, a pre-distortion amount control unit, and a second finite impulse response filtering unit.