Receiver Node Frequency Offset Compensation
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Solution Overview
Problem
Current frequency offset compensation methods in radio communications networks are inadequate for high-speed scenarios, particularly at velocities exceeding 350 km/h, due to limitations in estimating and tracking frequency offsets, leading to ambiguity and errors in signal processing.
Innovation Solution
A method and apparatus in a receiver node that compensates frequency offsets by using two different frequency offset estimates, including a mirrored estimate, to accurately correlate and correct data symbols, enabling reliable communication even at high velocities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If reference symbols are received twice per subframe at 0.5 ms intervals for frequency offset estimation, then the estimation process is simple and based on available reference symbols, but the maximum estimable frequency offset is limited to ±1000 Hz which is insufficient for high-speed scenarios
Solution Approach 1:
The patent transitions from time-domain sampling (reference symbols at fixed intervals) to frequency-domain analysis by examining phase differences across multiple reference symbols. This dimensional shift allows estimation of larger frequency offsets by analyzing the cumulative phase rotation rather than being constrained by the sampling interval between individual reference symbols.
Solution Approach 2:
The patent changes the estimation parameter from direct frequency measurement (constrained by sampling rate) to phase difference measurement. By measuring the phase rotation between reference symbols and using the relationship between phase change and frequency offset, the system can estimate offsets beyond the Nyquist limit of the reference symbol sampling rate.
2Reliability
If frequency offset estimation is based on reference symbols sampled at fixed intervals, then the estimation method is straightforward, but frequency offsets above ±1000 Hz wrap around causing ambiguity and erroneous estimation
Solution Approach 1:
The patent performs preliminary phase difference calculation between reference symbols before final frequency offset determination. By pre-calculating the phase rotation and using it to guide the estimation process, the system可以避免 the wrap-around ambiguity problem and directly obtain the correct frequency offset value.
Solution Approach 2:
The patent introduces phase difference as an intermediary parameter between the raw reference symbol measurements and the final frequency offset estimate. This intermediary allows the system to resolve the ambiguity problem by using the continuous phase evolution information rather than discrete sampled values.
3Reliability
If the receiver node uses a single frequency offset estimate from reference symbols, then the processing is simple, but the estimate may be erroneous due to ambiguity at high velocities
Solution Approach 1:
The patent uses feedback by comparing the estimated frequency offset with expected values based on Doppler shift calculations from known transmission parameters. This feedback mechanism allows the system to verify the correctness of the estimate and correct any ambiguity errors by cross-checking with physically expected frequency offset ranges.
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 effectively resolves the ambiguity problem, allowing for accurate frequency offset compensation and reliable data transmission at high speeds, including in high-speed train scenarios, by using the receiver node's ability to select the most probable frequency offset estimate based on correlation with target reference symbols.
Implementation Method 1
One reason is that a downlink (DL) signal transmitted by the radio base station, to which the user equipment locks its local oscillator, may be affected by a Doppler shift due to the movement of the user equipment relative to the radio base station.
Data Source
AI summary
According to embodiments herein an ambiguity problem when compensating for frequency offset may be solved by compensating a received reference symbol according to two different frequency offset hypotheses; the estimated frequency offset and the a mirrored version of the same. Then by comparing the compensated reference symbol of the different frequency hypotheses with a target reference symbol, which is known at the receiver node 12, the frequency offset hypothesis which is most likely is used to compensate a received data symbol.