Automatic Frequency Control With Adaptive Loop Gain for HST Channels
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Solution Overview
Problem
In wireless communication systems, particularly in high-speed train environments, frequency offsets due to Doppler effects lead to degraded reception performance, as existing technologies fail to effectively adjust loop gains in response to rapid changes in Doppler shifts, affecting the accuracy of frequency correction.
Innovation Solution
An automatic frequency controller in terminals classifies downlink channels as High Speed Train (HST) or non-HST channels based on phase estimates, adjusting loop gains accordingly to correct frequency offsets by calculating phase errors and communicating with the base station to synchronize local oscillation frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed loop gain is used in the automatic frequency controller, then the device complexity is reduced, but the reception performance degrades in high-speed train environments due to inability to track rapid Doppler shifts
Solution Approach 1:
The patent implements dynamic loop gain adjustment by classifying the wireless channel into HST or non-HST types based on phase estimate characteristics. When HST channel is detected, a first loop gain (higher) is applied to track rapid Doppler shifts, while a second loop gain (lower) is used for non-HST channels to reduce jitter. This dynamic adaptation resolves the contradiction by making the loop gain variable rather than fixed, improving reception performance without requiring permanently complex hardware.
Solution Approach 2:
The patent changes the loop gain parameter based on channel classification. The processor determines whether to apply a first loop gain or second loop gain by comparing phase estimate statistics against thresholds, thereby adapting the frequency correction behavior to match the actual channel conditions. This parameter change enables the system to handle both high-speed and normal mobility scenarios effectively.
2Measurement precision
If a variable loop gain is applied to rapidly track Doppler shifts, then the frequency correction accuracy improves, but the device complexity increases due to channel classification requirements
Solution Approach 1:
The system performs self-classification of the wireless channel by analyzing its own phase estimate statistics without requiring external assistance or complex preprocessing. The processor calculates statistics of phase estimates from received reference signals and autonomously determines whether the channel exhibits HST characteristics, enabling the system to adapt its loop gain based on self-diagnosis of the propagation conditions.
Solution Approach 2:
The patent implements a feedback mechanism where the processor continuously monitors phase estimate statistics, compares them against predefined thresholds, and adjusts the loop gain accordingly. This closed-loop approach ensures that the frequency correction accuracy is optimized by using feedback from the actual channel behavior, allowing the system to respond dynamically to changing Doppler conditions.
3Adaptability or versatility
If loop gain is adjusted based on phase estimate statistics, then the adaptability to different channel conditions improves, but the processing time increases due to statistical calculation requirements
Solution Approach 1:
The patent applies partial action by using only the necessary statistical moments (mean and variance) of the phase estimates for channel classification, rather than performing full spectral analysis or more complex signal processing. This selective approach provides sufficient adaptability to distinguish HST from non-HST channels while minimizing the processing time and computational resources required.
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 solution improves reception performance by rapidly tracking and correcting frequency offsets in HST environments, ensuring stable communication even at high speeds by dynamically adjusting loop gains based on channel classification.
Implementation Method 1
The at least one processor is configured to obtain a phase estimate from a reference signal received from the base station
Implementation Method 2
when there is relative movement between the terminal and the base station, an additional frequency offset may occur due to the Doppler effect
Data Source
AI summary
Automatic frequency controllers, automatic frequency control methods, wireless communication devices, and/or wireless communication methods are provided. The automatic frequency controllers for correcting a frequency offset between a base station and a terminal includes at least one processor communicatively coupled to a memory and configured to execute computer-readable instructions stored in the memory to obtain a phase estimate from a reference signal received from the base station; classify a downlink channel as a High Speed Train (HST) channel or a non-HST channel based on the phase estimate; adjust a loop gain according to the classified downlink channel; calculate a phase error based on the phase estimate and the loop gain; correct the frequency offset using the phase error; and communicate with the base station after correcting the frequency offset.