Receiver Resampling Control for Long-Sequence Clock Synchronization
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Solution Overview
Problem
Existing communication systems face challenges in maintaining stable synchronization between transmitting and receiving devices, especially when the clock frequencies are asynchronous, leading to difficulties in correcting symbol timing differences, especially for long sequences of symbols exceeding 100,000, as conventional fractionally spaced equalizers have limitations in correcting clock frequency differences.
Innovation Solution
A receiving device configuration that includes a resampler, equalizer, correlation calculator, and rate controller to adjust the sampling rate and correct clock frequency differences by calculating correlation functions between oversampled signals, allowing for stable synchronization without relying on known sequences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If fractionally spaced equalization is used to correct symbol timing differences, then synchronization is improved, but the correctable difference in symbol phase is limited and stable synchronization cannot be maintained for long sequences exceeding 100,000 symbols
Solution Approach 1:
The patent segments the clock frequency correction function into two parts: fractionally spaced equalization for short-term symbol timing correction and a resampler with correlation-based timing detection for long-term clock synchronization. This segmentation allows each component to operate within its optimal range, with the resampler handling accumulated phase differences that exceed the equalizer's correction capability.
Solution Approach 2:
The patent introduces a resampler as an intermediary component between the equalizer and the demodulator. The resampler uses correlation calculation between the received signal and a local replica to detect symbol timing and generate timing correction signals, acting as a mediator that bridges the gap between the equalizer's limited correction range and the requirement for long-term stable synchronization.
2Measurement precision
If known sequences are used for timing detection, then symbol timing can be detected, but the method cannot be applied when known sequences are not embedded in the communication signal
Solution Approach 1:
The patent implements self-service timing detection by using the received signal itself (or a processed version thereof) as the reference for correlation calculation, eliminating the need for external known sequences. The equalizer output or a filtered version of the received signal serves as its own reference, allowing timing detection to work with any signal format including those without embedded training sequences.
Solution Approach 2:
The patent changes the reference signal parameter from a fixed known sequence to a dynamically generated signal based on the received signal characteristics. By using the equalizer output or a locally generated replica that adapts to the transmitted signal format, the system maintains timing detection capability across different modulation schemes and signal formats without requiring predetermined known sequences.
3Adaptability or versatility
If the clock frequencies of transmitting and receiving devices are asynchronous, then device independence is improved, but symbol timing difference accumulates making stable synchronization impossible for long sequences
Solution Approach 1:
The patent implements a feedback mechanism where the resampler continuously calculates correlation between the received signal and local replica, detects timing errors, and adjusts the sampling rate accordingly. This closed-loop feedback system compensates for accumulated symbol timing differences caused by asynchronous clock frequencies, maintaining stable synchronization even when devices operate independently with different clock sources.
Solution Approach 2:
The patent introduces dynamic adjustment of the sampling rate through the resampler, which continuously adapts to timing variations caused by asynchronous clocks. Unlike fixed-rate sampling in conventional systems, the resampler dynamically modifies the sampling instant based on real-time correlation-based timing detection, allowing the system to track and compensate for clock frequency differences over long transmission sequences.
Data Source
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AI summary
A receiving device (100) according to the present invention includes: a resampler (5) to convert a sampling rate of a reception signal, and output a first signal that is a signal having been subjected to sampling rate conversion; an equalizer (6) to perform an adaptive equalization process using the first signal as an input, and output a second signal that is a signal having been subjected to the adaptive equalization process and having a sampling rate that is an integer fraction of an input signal; a correlation calculator (10) to calculate a correlation function between the first signal and the second signal; and a rate controller (11) to control a rate conversion ratio for sampling rate conversion in the resampler on a basis of the correlation function.