Passive RFID Symbol Synchronization via Edge Clock Averaging
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Solution Overview
Problem
Passive RFID readers face challenges in accurately synchronizing tag signals distorted by transmission energy leakage, leading to difficulties in symbol timing lock due to DC-offset noise and local peak signals in subcarrier-type tag signals.
Innovation Solution
A symbol synchronization apparatus and method for passive RFID readers that includes an edge clock detector, preamble detector, symbol decision time extractor, and symbol decider to accurately extract symbol decision time by analyzing phase inversion positions and averaging distances between edge clocks, even in the presence of distortion noise, and adaptively tracks symbol decision time changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If general symbol synchronization is performed in the receiver stage, then the system can operate with standard synchronization algorithms, but accurate synchronization of tag signals distorted by transmission leakage cannot be achieved
Solution Approach 1:
The invention extracts only the necessary edge information from the preamble signal to generate edge clocks, separating the synchronization function from the corrupted data portions. This extraction approach allows the system to ignore distorted sections while capturing timing-critical edge transitions, resolving the contradiction between using standard algorithms and achieving accurate synchronization.
Solution Approach 2:
The invention introduces edge clocks as an intermediary element that mediates between the corrupted received signal and the symbol synchronization process. These edge clocks serve as a clean timing reference that bridges the gap between the distorted input signal and the synchronization requirement, enabling accurate symbol timing extraction despite transmission leakage.
2Loss of information
If the start data of the tag signal is used for synchronization, then the preamble information is available, but the data may be partially distorted or lost by transmission leakage signal
Solution Approach 1:
The invention converts the harmful transmission leakage distortion into a beneficial selection criterion by using it to identify and isolate the intact '010111' data portion. The distortion pattern itself becomes a marker that helps locate the reliable edge information, transforming the problem of data corruption into a method for finding clean synchronization signals.
Solution Approach 2:
The invention performs preliminary analysis of the preamble signal structure to identify the specific '010111' pattern before extraction. By pre-identifying the reliable data portion based on its known structure, the system can selectively process only the intact sections, avoiding corrupted data while maintaining synchronization accuracy.
3Difficulty of detecting and measuring
If matched filtering is performed on subcarrier signal, then signal detection is enabled, but local peak signals are generated making symbol timing lock difficult
Solution Approach 1:
The invention extracts only the edge clock information from the matched filtering output, separating the timing-critical edge transitions from the problematic local peak signals. By focusing exclusively on edge positions rather than peak positions, the system achieves symbol timing lock without being affected by the spurious local peaks generated during matched filtering.
Data Source
AI summary
Provided is a symbol synchronization apparatus and method of a passive RFID reader. The symbol synchronization apparatus includes: an edge clock detector generating edge clocks by detecting phase inversion positions of a received signal; a preamble detector detecting a preamble section by analyzing the generation times of the edge clocks; a symbol decision time extractor extracting a symbol decision time by averaging distances between the edge clocks consecutively generated in the preamble section, when the preamble section is detected; and a symbol decider deciding a symbol by analyzing the magnitude of the received signal, when the time reaches the symbol decision time.