Frequency Offset Estimation Using Segmented Reference Symbols
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Solution Overview
Problem
In wireless communication systems, existing methods for frequency offset estimation face challenges in balancing accuracy with reference signal overhead and are prone to errors due to phase ambiguity and aliasing, especially with oscillator imperfections and Doppler shifts.
Innovation Solution
A method involving a radio node that receives two sets of reference symbols using the same or different local oscillator frequencies, with the first set used to estimate a frequency offset, which is then applied to the second set to determine a more accurate frequency offset estimate, potentially reducing phase ambiguity and aliasing by varying the temporal pattern of reference signal reception.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a reference signal is used for frequency offset estimation, then frequency estimation accuracy is improved, but reference signal overhead increases
Solution Approach 1:
The frequency offset estimation process is segmented into two distinct stages: a first frequency offset estimate is determined from a first set of reference symbols, and a second frequency offset estimate is determined from a second set of reference symbols using the first estimate as a reference. This segmentation allows each estimation to focus on specific aspects of frequency offset, improving overall accuracy while maintaining efficient reference signal usage.
2Measurement precision
If frequency offset estimation is performed to compensate for oscillator imperfections and Doppler shift, then frequency tracking accuracy is improved, but phase ambiguity and aliasing errors occur
Solution Approach 1:
The first frequency offset estimate is determined as a preliminary step before determining the second frequency offset estimate. This preliminary estimation establishes a reference that enables more accurate phase unwrapping and reduces the likelihood of phase ambiguity and aliasing errors in the subsequent estimation process.
Solution Approach 2:
The first frequency offset estimate is used as feedback to improve the determination of the second frequency offset estimate. Specifically, the first estimate informs the phase unwrapping process for the second estimate, creating a feedback loop that enhances reliability and reduces estimation errors.
3Device complexity
If the same local oscillator frequency is used for receiving both sets of reference symbols, then device complexity is reduced, but frequency offset estimation range is limited
Solution Approach 1:
The invention changes the parameter of reference symbol processing by applying different phase unwrapping strategies based on the first frequency offset estimate. Instead of changing the local oscillator frequency, the method adapts the phase measurement range and unwrapping approach to accommodate different frequency offset scenarios, maintaining estimator versatility without increasing hardware complexity.
Data Source
AI summary
A radio node (14) is configured to perform frequency offset estimation. The radio node (14) in this regard receives a first set (22-1) of reference symbols of a reference signal during respective time resources, and determines a first frequency offset estimate (26-1) using the first set (22-1) of reference symbols. The radio node (14) also receives a second set (22-2) of 5 reference symbols of the reference signal during respective time resources, e.g., using the same local oscillator frequency for down conversion as with the first set (22-1). The radio node (14) further determines, based on the first frequency offset estimate (26-1), a second frequency offset estimate (26-2) using the second set (22-2) of reference symbols. In some embodiments, the radio node (14) determines a third frequency offset estimate as a sum of the first and 10 second frequency offset estimates, and tunes a local oscillator frequency, or performs frequency offset compensation, based on the third frequency offset estimate.