Visible-Light Wireless Communication Using VPPM and OFDM
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Solution Overview
Problem
Conventional visible-light wireless communication using Variable Pulse Position Modulation (VPPM) fails to incorporate orthogonal frequency division multiplexing (OFDM), resulting in low data rates, and requires a separate dedicated receiver for data communication.
Innovation Solution
A visible-light wireless communication apparatus and method that combines VPPM for brightness control and OFDM for high-speed data transmission, using a brightness control unit, modulation units, and optical signal transmission and reception units, enabling data communication through existing devices like smartphones without a dedicated receiver.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If VPPM transmission is used for visible-light wireless communication, then illumination brightness control is achieved, but data rate remains low
Solution Approach 1:
The patent combines VPPM and OFDM modulation techniques into a unified visible-light communication system. The VPPM-modulated signal controls illumination brightness while the OFDM-modulated signal provides high-speed data transmission, allowing both functions to operate simultaneously through signal superposition and joint processing at the receiver.
Solution Approach 2:
The illumination source (LED) is designed to perform multiple functions: it provides visible light illumination for lighting purposes and simultaneously transmits data signals through modulated light intensity variations. The system accepts both VPPM and OFDM input signals and processes them through a single optical transmission channel, enabling the same hardware to serve dual purposes.
2Device complexity
If conventional VPPM transmission is used, then illumination control is simple, but separate dedicated receiver is required
Solution Approach 1:
The receiver is designed to process both VPPM and OFDM modulated signals through a unified demodulation architecture. By incorporating both VPPM demodulation circuits and OFDM demodulation circuits, the receiver can selectively process different signal types, enabling existing image sensor-equipped devices to communicate using either modulation scheme without requiring dedicated receiver hardware for each protocol.
Solution Approach 2:
The patent uses image sensors (such as camera sensors in smartphones) as intermediary devices to detect the modulated light signals. These sensors convert optical signals into electrical signals that can then be processed by standard digital signal processing circuits, bridging the gap between optical transmission and electronic data processing without requiring specialized optical receivers.
3Productivity
If OFDM is incorporated with VPPM, then data rate increases, but system complexity increases
Solution Approach 1:
The modulation system is divided into separate VPPM modulation processing path and OFDM modulation processing path. Each path handles its specific signal type independently, with VPPM processing the illumination control signal and OFDM processing the high-speed data signal. This segmentation allows complex OFDM processing to be isolated from simpler VPPM processing, making the overall system more manageable and implementable.
Solution Approach 2:
The patent performs preliminary signal processing and preparation before the main modulation and transmission stages. Digital signal processing operations such as inverse fast Fourier transform (IFFT) for OFDM and pulse generation for VPPM are prepared in advance, allowing the actual transmission to proceed efficiently without real-time computational complexity during the critical transmission phase.
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 allows for high-speed data transmission and reception while controlling illumination brightness, enabling data communication through existing image sensor-equipped devices without the need for a separate receiver, thereby enhancing data rates and flexibility.
Implementation Method 1
an optical signal transmission unit configured to receive the second modulation signal and to output a visible-light wireless communication signal as the received second modulation signal
Implementation Method 2
enable data communication by receiving a transmitted signal through an existing device including an image sensor, e.g., through a smartphone having a camera mounted thereon
Data Source
AI summary
Disclosed herein is a method of performing visible-light wireless communication using light-emitting diode (LED) illumination, in which Variable Pulse Position Modulation (VPPM) is used for low-speed data transmission and dimming of illumination, and orthogonal frequency division multiplexing (OFDM) modulation is used in a VPPM on period for high-speed data transmission.