Mains-Synchronous Spread Spectrum PLC for Noise Immunity
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Solution Overview
Problem
Very low frequency (VLF) power line communications in automated meter reading and advanced metering infrastructure face challenges due to high noise levels, which degrade channel capacity and reduce data rates, making it impractical without signal boosters or repeaters, and noise increases with decreasing frequency, offsetting desirable propagative properties.
Innovation Solution
A two-way communications system that modulates signals to be orthogonal to power line interference using a phase-locked loop and spread spectrum technique, ensuring the signals are synchronized with the mains signal and minimizing the impact of periodic noise, allowing for effective data transmission over power distribution systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If VLF band is used for power line communications, then propagative properties are improved (signals can travel over very long distances), but noise levels increase (noise is more energetic at lower frequencies) which degrades channel capacity
Solution Approach 1:
The patent applies periodic action by synchronizing the communication signal to the mains frequency (e.g., 60 Hz). The phase-locked loop locks to the periodic mains signal, and the spread spectrum sequence is modulated at this periodic rate. This periodic synchronization allows the receiver to distinguish the communication signal from periodic noise sources like harmonics, effectively filtering out interference while maintaining long-distance propagation capability in the VLF band.
Solution Approach 2:
The patent converts the harmful periodic noise (mains harmonics) into a beneficial reference by using the same periodicity to synchronize the communication signal. The noise that would normally degrade channel capacity is actually exploited to establish timing and phase reference, allowing the receiver to filter out interference more effectively. The harmful periodic interference becomes the basis for the synchronization mechanism that enables clean signal extraction.
2Power
If VLF band is used for power line communications, then signal energy is improved (high signal energies can be achieved), but data rate decreases (reduced available bandwidth) which reduces productivity
Solution Approach 1:
The patent applies dimensionality change by transitioning from traditional narrowband VLF modulation to spread spectrum modulation. Instead of concentrating signal energy in a narrow frequency band (which limits data rate), the signal is spread across a wider frequency spectrum. This dimensional expansion in the frequency domain allows the system to maintain high signal energy while increasing the effective data rate through spectral diversity and processing gain.
Solution Approach 2:
The patent changes key parameters including the modulation index, spread spectrum sequence length, and frequency distribution characteristics. By adjusting these parameters, the system optimizes the balance between signal energy and data rate. The phase-locked loop adjusts the locking range and acquisition characteristics to match the changed parameters, enabling the system to maintain high productivity while preserving the high signal energy advantage of the VLF band.
3Measurement precision
If traditional noise estimation algorithms are used, then noise characterization is achieved, but system complexity increases (requiring complex algorithms and signal boosters)
Solution Approach 1:
The patent applies self-service by having the communication system itself provide the noise characterization through its inherent synchronization mechanism. The phase-locked loop and spread spectrum sequence automatically reveal the noise characteristics by their interaction with the periodic mains signal. The system uses its own operational parameters (mains frequency synchronization) to characterize and filter noise, eliminating the need for separate complex noise estimation algorithms and external signal boosters.
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 increases the signal-to-noise ratio, enhances receiver fidelity, and makes VLF PLC more attractive for smart grid communications by reducing the need for complex noise estimation algorithms and signal boosters, thereby improving data transmission efficiency and reliability.
Implementation Method 1
The transmitter includes a phase-locked loop linked to the outbound message signal for locking the phase of the respective outbound message signals to the mains signal
Implementation Method 2
The transmitter also includes a spreader for spreading the spectrum of the communications signal before transmitting the outbound message signal. The outbound message signal is orthogonal to a source of interference on the power distribution system
Data Source
AI summary
A transmitter transmits an outbound message signal via the power distribution system. The transmitter includes a spreader for spreading the spectrum of the communications signal before transmitting the outbound message signal. A receiver despreads the spectrum of the received digitized signal and digitally demodulates the received despread signal to generate the message. The transmitted signal is orthogonal to a source of interference on the power distribution system.