Visible Light Communication Pixel Alignment for High Data Rate
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Solution Overview
Problem
Current visible light communication (VLC) systems face limitations in data transmission speed due to the rolling shutter effect in CMOS image sensors, which results in temporal aliasing and artifacts, especially when detecting moving objects or changes in lighting levels, limiting their ability to handle data-hungry applications effectively.
Innovation Solution
The system optimizes data transmission by aligning the one-dimensional light patterns from the LED array orthogonally to the rolling shutter direction of the CMOS image sensor, allowing for increased data encoding per line of the image frame and maximizing the resolving power of the sensor, while also using two-way communication to ensure proper alignment and adjust the pattern direction based on the receiver's orientation and performance characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the rolling shutter effect is used in CMOS image sensors for VLC data reception, then the system can achieve low cost and good image quality, but temporal aliasing and artifacts occur that limit data transmission speed
Solution Approach 1:
The patent converts the harmful rolling shutter effect into a beneficial synchronization mechanism. By aligning the LED modulation frequency with the rolling shutter row exposure timing, the system transforms the temporal aliasing problem into a structured data encoding opportunity where each row captures a specific time slice of the modulated LED signal, enabling reliable high-speed data transmission despite the rolling shutter artifact.
Solution Approach 2:
The system changes the temporal parameters of the LED modulation to match the rolling shutter characteristics. Specifically, the LED modulation frequency is adjusted to correspond with the row exposure duration and timing of the rolling shutter, creating a synchronized relationship that eliminates temporal aliasing while maximizing data encoding capacity across multiple rows.
2Productivity
If individual LEDs or groups of LEDs are modulated independently to provide parallel bit streams, then data transmission rate increases, but the system complexity increases
Solution Approach 1:
The patent segments the LED array into multiple independently controllable groups or individual LEDs, where each segment can be modulated at different frequencies or with different data streams. This segmentation enables parallel data transmission through multiple spatial channels, increasing overall data rate while maintaining manageable complexity through modular control architecture.
Solution Approach 2:
The system transitions from single-dimensional temporal modulation to two-dimensional spatial-temporal modulation by utilizing both the spatial arrangement of multiple LEDs and temporal modulation patterns. This dimensional expansion allows parallel data streams to be encoded across different spatial positions and time slots, significantly increasing data transmission rate without proportionally increasing system complexity.
3Productivity
If the LED source spans multiple pixel rows to utilize rolling shutter for increased data rate, then parallel bit streams are achieved, but alignment precision between LED pattern and pixel rows becomes critical
Solution Approach 1:
The patent implements feedback mechanisms where the receiver detects the actual alignment between the LED modulated pattern and the rolling shutter row timing, then communicates this information back to the transmitter. The transmitter uses this feedback to adjust its modulation timing and pattern alignment, ensuring optimal synchronization and maximizing data rate while compensating for any misalignment drift.
Solution Approach 2:
The system employs dynamic adjustment of the LED modulation timing and pattern based on real-time conditions. Rather than using fixed static alignment, the system continuously adapts the modulation parameters to maintain optimal synchronization with the rolling shutter, allowing the alignment to be dynamically optimized for varying operating conditions such as relative motion or timing drift.
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
This approach significantly enhances data transfer rates by enabling the encoding of multiple bits per line and achieving higher data transmission speeds, maintaining reliability and low costs, and supporting more demanding applications.
Implementation Method 1
Data transmission involves modulating (i.e., flashing) a light source such as a light emitting diode (LED) to encode data
Implementation Method 2
receiving the modulated light at a light sensor such as a photodiode or a camera to decode the data
Data Source
AI summary
A visible light communication system has a two-dimensional array of sources and an image sensor with a pixel grid defining a pixel direction (which in some embodiments is a rolling shutter direction). Modulation of the light flashes the sources to define a series of one-dimensional patterns encoding the data to be transmitted. The patterns extend in a direction that projects onto the imager orthogonal to the pixel direction. In the case of a rolling shutter, the pattern is orthogonal to the rolling shutter direction, which allows the encoding of multiple bits per line of the image frame. In other cases, the orthogonal direction obtains the maximum resolving power available from the image sensor.