Signal Synchronization Device CFO Compensation
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Solution Overview
Problem
In OFDM communication systems, the desirable autocorrelation characteristics of pseudo-random noise (PN) sequences are susceptible to carrier frequency offset (CFO), leading to attenuation of peak values in sliding correlators, which can result in lost symbol timing information, especially when the CFO reaches integer-folds of specific increments, complicating synchronization and increasing system complexity.
Innovation Solution
A method and device for signal synchronization that perform a first sliding correlation to obtain symbol timing, identify fractional CFO, calculate products to compensate for CFO effects, and perform multiple sliding correlations to identify integral CFO, allowing robust synchronization even with significant CFOs, implemented in a simple structure without requiring differential modulation at each base station.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If sliding correlation is performed with PN sequence for symbol timing synchronization, then symbol timing information can be obtained, but carrier frequency offset causes attenuation of peak values leading to loss of timing information
Solution Approach 1:
The patent segments the CFO compensation process into two distinct stages: fractional CFO compensation using phase rotation based on autocorrelation phase information, and integer CFO compensation using multiple sliding correlations with different phase shifts. This segmentation allows each stage to address specific aspects of CFO separately, preventing the peak attenuation problem that occurs when CFO is not compensated.
Solution Approach 2:
The patent performs preliminary fractional CFO compensation before integer CFO compensation by estimating the fractional CFO from the phase of autocorrelation values and applying phase rotation to the received signal. This preliminary action removes the dominant fractional CFO component, making subsequent integer CFO detection more reliable and preventing peak attenuation in the final timing detection.
2Reliability
If differential modulation is implemented at each base station to protect against CFO, then robustness to frequency offset is improved, but system complexity increases
Solution Approach 1:
The patent uses a copy of the PN sequence at the receiver side for sliding correlation, rather than requiring differential modulation of the transmitted signal. The local PN sequence copy enables the receiver to perform correlation-based timing detection while the patent simultaneously compensates for CFO effects through phase rotation and multiple hypothesis testing, achieving robustness without modifying the transmission scheme at base stations.
Solution Approach 2:
The patent replaces the mechanical/differential modulation approach at the transmitter with a signal processing approach at the receiver. Instead of modifying the transmitted signal through differential modulation, the patent uses digital signal processing techniques including phase rotation, autocorrelation-based fractional CFO estimation, and multiple sliding correlations with different phase shifts to achieve CFO robustness.
3Measurement precision
If multiple sliding correlations are performed to identify integer CFO, then accurate CFO identification is achieved, but processing time and computational complexity increase
Solution Approach 1:
The patent performs preliminary fractional CFO estimation and compensation using autocorrelation phase information before performing multiple sliding correlations for integer CFO detection. This preliminary action removes the fractional CFO component that would otherwise cause phase rotation and peak attenuation during the multiple sliding correlations, making the process more efficient and accurate.
Solution Approach 2:
The patent applies different compensation strategies to different components of CFO: fractional CFO is compensated using phase rotation based on local autocorrelation phase information, while integer CFO is handled through multiple sliding correlations with discrete phase shifts. This localized approach optimizes the processing for each CFO component type, balancing accuracy and computational efficiency.
Data Source
AI summary
A device for signal synchronization in a communication system is configured to perform a first sliding correlation for a received signal and a pseudo-random noise (PN) sequence to obtain information on symbol timing, identify a fractional carrier frequency offset (FCFO) using the information on symbol timing and the cyclic extension property of the PN guard interval (GI), and provide a first product by multiplying the received signal with the FCFO. The device is also configured to provide a set of second products by multiplying the first product with each of a set of phases related to integral carrier frequency offsets (ICFOs), perform a second sliding correlation for the PN sequence and each one of the set of the second products to thereby provide a set of peak values, and identify an ICFO by detecting an index number of a maximal value among the set of peak values.