Visible Light Communication Pulse Positioning for Flicker Reduction
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Solution Overview
Problem
Existing communication systems using frequency shift key modulated signals for data transmission via visible light often result in unwanted visible flicker due to human sensitivity to intensity variations, particularly when using solid state light sources.
Innovation Solution
A communication system that generates frequency shift key modulated signals by positioning pulses within periods such that the center of gravity of each pulse is at the center of its respective period, reducing human-perceivable frequency components by maintaining a constant time period between pulses, which is half the sum of the first and second periods, thereby minimizing low-frequency content in the visible light spectrum.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If frequency shift key modulated signals are used for data transmission via visible light, then data transmission capability is improved, but visible flicker is generated due to human sensitivity to intensity variations
Solution Approach 1:
The patent applies preliminary action by pre-positioning pulses at specific locations within their periods (at the center) before modulation occurs. This preliminary positioning ensures that when frequency shifting is applied for data transmission, the pulses maintain consistent temporal relationships that prevent visible flicker, thus resolving the contradiction between data transmission capability and visible flicker reduction.
Solution Approach 2:
The patent changes the temporal parameter of pulse positioning within periods, specifically setting pulses at the center position rather than at arbitrary positions. This parameter change in pulse timing and positioning eliminates the low-frequency components that cause visible flicker while preserving the frequency shift key modulation capability for data transmission.
2Object-affected harmful factors
If high switching frequency is used to make modulation invisible, then human perception of flicker is reduced, but data transmission rate is limited
Solution Approach 1:
The patent applies dynamics by implementing variable frequency shift key modulation where the carrier frequency dynamically changes according to the data being transmitted. Instead of using a fixed high frequency that limits data rate, the system dynamically adjusts between different frequency states (first and second frequencies) to encode data, thereby achieving both invisibility to human perception and high data transmission rates.
Solution Approach 2:
The patent uses periodic action through structured pulse sequences with specific period relationships. By arranging pulses in periodic patterns where the time between consecutive pulses follows specific mathematical relationships (half the sum of first and second periods), the system creates modulation that is imperceptible to humans while encoding substantial data information through the periodic frequency variations.
3Productivity
If frequency jumps are implemented for data encoding, then data transmission efficiency is improved, but low-frequency components reappear causing visible flicker
Solution Approach 1:
The patent applies asymmetry in an innovative way by creating a symmetric pulse structure within an asymmetric frequency modulation scheme. The pulse is positioned at the center of its period, creating temporal symmetry that cancels out low-frequency components. Meanwhile, the frequency itself undergoes asymmetric jumps between two distinct values to encode data efficiently, thus achieving both high data transmission efficiency and elimination of visible flicker.
Solution Approach 2:
The patent converts the potentially harmful effect of frequency jumps (which normally create low-frequency components and visible flicker) into a beneficial data encoding mechanism. By carefully controlling the timing and positioning of pulses during frequency transitions, the system transforms what would be harmful low-frequency artifacts into useful data-carrying frequency variations that are imperceptible to humans.
Data Source
AI summary
The invention provides a communication system (500), a lighting system, a method of transmitting information and a computer program product. The communication system according to the invention is configured for transmitting data via visible light. The communication system comprises a signal generator (530) for generating a light driving signal (200) being a frequency shift key modulated signal comprising a sequence of signal parts (215, 225), each signal part being modulated at a first or second frequency in accordance with the data, the signal parts modulated at the first frequency having first pulses in first periods (T0) and the signal parts modulated at the second frequency having second pulses in second periods (T1). Energy of the visible light corresponding to a pulse in a respective period has center of gravity in time. The pulses in the periods are positioned so that the center of gravity is at the center of the period for reducing human-perceivable frequency components in the visible light driving signal.