Expurgated Pulse Position Modulation for Visible Light Communication
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing wireless communication technologies, such as Optical Frequency Division Multiplexing (OFDM) and simple Pulse Position Modulation (PPM), face challenges in indoor visible light communication systems due to non-linear intensity of light emitting diodes (LEDs), flicker issues, and inefficiencies in spectrum consumption, which can cause health concerns and interference.
Innovation Solution
The implementation of an expurgated pulse position modulation (EPPM) technique, combined with multi-level EPPM (MEPPM) and optically-orthogonal codes (OOC), which allows for dimming control and reduced flicker, enabling high-speed data transmission while accommodating multiple users and devices with improved spectral efficiency and error reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If simple pulse position modulation (PPM) is used, then device complexity is reduced, but spectral efficiency deteriorates and flicker is caused
Solution Approach 1:
The PPM symbol period is segmented into multiple time slots, with each slot capable of carrying a pulse. The expurgated PPM technique selectively places pulses in specific slots based on the data to be transmitted, creating a more efficient use of the time domain while maintaining simple receiver detection logic.
Solution Approach 2:
The modulation scheme uses periodic time slots within each symbol period, where pulses can be positioned at specific intervals. This periodic structure enables the receiver to use simple correlation detection while the systematic placement of pulses improves spectral efficiency compared to basic PPM.
2Productivity
If optical frequency division multiplexing (OFDM) is used, then data transmission speed is improved, but compatibility with non-linear LED intensity deteriorates
Solution Approach 1:
The patent replaces the complex multi-carrier OFDM modulation mechanism with a time-domain pulse positioning mechanism. Instead of using multiple frequency carriers that are sensitive to LED non-linearity, the scheme uses temporal positioning of pulses, which is inherently more compatible with the non-linear intensity characteristics of LEDs while achieving high data rates through efficient coding.
3Device complexity
If simple PPM is used, then device complexity is reduced, but flicker is caused which leads to health concerns
Solution Approach 1:
The expurgated PPM technique applies different pulse placement patterns to different time slots within a symbol period. By strategically positioning pulses in specific slots and leaving other slots empty, the scheme creates a more uniform temporal distribution of light emission, reducing the perceptible flicker effect while maintaining simple modulation architecture.
4Productivity
If multi-level EPPM (MEPPM) is used, then spectral efficiency is improved, but device complexity increases
Solution Approach 1:
The multi-level EPPM scheme extends the basic EPPM by introducing multiple amplitude levels in addition to time slot positioning. This adds a second dimension (amplitude level) to the pulse representation, enabling more bits to be encoded per symbol period and improving spectral efficiency, while the modular structure keeps implementation complexity manageable.
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
EPPM and MEPPM techniques provide high-speed data transmission with reduced bit-error probability, controlled peak-to-average power ratio, and immunity to interference, ensuring safe and efficient indoor wireless communication.
Implementation Method 1
an optical source such as including one or more light emitting diodes can provide visible light for illumination
Data Source
AI summary
An expurgated pulse position modulation (EPPM) technique can be used to encode information for wireless transmission. Such an EPPM technique can be compatible with a simple receiver architecture, such as including a shift register and pulse position modulation (PPM) decoder. A multi-level EPPM (MEPPM) approach can increase the available symbols in the modulation constellation and can be used to accommodate multiple users or devices concurrently. Interleaving techniques can be used such as to reduce inter-symbol interference. An optical transmitter and an optical receiver can be used, such as including using energy in a visible range of frequencies. In an example, an optical source such as including one or more light emitting diodes can provide visible light for illumination, and the EPPM technique can include using codewords specified to provide a desired dimming level when such codewords are used to intensity modulate the optical source, without perceptible flicker.