AFC Doppler Compensation During Cell Handover
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Solution Overview
Problem
In 4G or 5G high-speed rail communication systems, Vehicle-to-Vehicle (V2V) systems, or Vehicle-to-Everything (V2X) systems, there is no effective solution to combat Doppler shift during cell handover, leading to interference and instability in signal reception.
Innovation Solution
A method and device that involve obtaining a Doppler shift estimation for user equipment at the moment of cell handover in the source cell, calculating its additive inverse, and using this inverse for Carrier Frequency Offset (CFO) compensation in the Automatic Frequency Control (AFC) system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional AFC methods are used during cell handover, then the system can maintain basic frequency control, but the Doppler shift mutation causes instability and high complexity in carrier frequency offset compensation
Solution Approach 1:
The patent applies preliminary action by obtaining and storing the Doppler shift estimation from the source cell before handover occurs. This pre-acquired information is then inverted and applied during handover to the target cell, allowing the system to proactively compensate for expected Doppler shift mutations rather than reacting to them after they occur. This reduces the computational burden and instability during the critical handover moment.
2Reliability
If antenna nodes are controlled to maintain radio cells in a single direction, then the Doppler shift reversal at handover can be solved, but the system complexity increases due to coordinated multi-node control
Solution Approach 1:
The patent applies copying by taking the Doppler shift estimation from the source cell and creating an inverted version of it for use in the target cell during handover. Instead of implementing complex multi-node coordination, the system copies the essential frequency compensation information and adapts it by inverting the sign, thereby solving the Doppler shift reversal problem through information replication rather than physical coordination complexity.
3Measurement precision
If GPS signals are used for Doppler shift compensation, then accurate frequency correction can be achieved, but the system cannot operate in GPS-denied environments such as indoor or urban canyons
Solution Approach 1:
The patent applies self-service by having the user equipment utilize its own previously acquired Doppler shift estimation from the source cell to compensate for frequency offset in the target cell. Instead of relying on external GPS signals, the system serves itself by reusing and inverting its own historical frequency information, thereby achieving environment-independent operation that works both in GPS-available and GPS-denied scenarios.
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 mitigates Doppler shift mutations during handovers, reducing computational complexity for uplink receivers and improving reception performance in various scenarios without relying on GPS signals.
Implementation Method 1
receiving the output signal of the frequency shift elimination module and performing automatic frequency control according to the output signal by a AFC circuit
Implementation Method 2
the Doppler shift will cause serious interferences to signals... a Doppler shift fd will occur... v is the relative speed between the transmitter and the receiver
Data Source
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AI summary
The embodiments of the present application disclose a method and device for combating Doppler shift. The method includes: obtaining, in a case where a user equipment performs cell handover, a Doppler shift estimation of the user equipment at a last moment in a source cell; and obtaining an inverse number of the Doppler shift estimation, and using the inverse number of the Doppler shift estimation for Carrier Frequency Offset (CFO) compensation in an Automatic Frequency Control (AFC).