Mobile Terminal Frequency Deviation Correction via SIR Scanning
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Solution Overview
Problem
Current automatic frequency deviation correction systems for WCDMA mobile terminals struggle to effectively manage large initial frequency deviations and Doppler frequency shifts, particularly at high speeds, requiring precise crystal oscillations and temperature compensation, which increases complexity and costs, and fails to maintain accurate frequency tracking during cell switching.
Innovation Solution
An automatic frequency deviation correction method and system that includes an initial frequency deviation scanning evaluation module to synchronize slots within a predetermined range, selecting the signal-to-interference ratio (SIR) for optimal frequency deviation, and a frequency deviation correction control module to maintain frequency within a predetermined range, using a temperature/frequency deviation control table to reduce crystal oscillation precision and track Doppler frequency shifts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the initial frequency deviation is large (greater than 1PPM), then the terminal cannot achieve synchronization and access to the network, but requiring the crystal oscillation precision to be less than 1PPM increases the requirement on crystal oscillation precision and temperature compensation
Solution Approach 1:
The patent performs preliminary frequency deviation scanning and evaluation before attempting network access. By scanning a predetermined frequency deviation scanning range and evaluating the signal-to-interference ratio at different frequency points, the system pre-determines the optimal initial frequency deviation value, ensuring synchronization can be achieved even when the crystal oscillation has larger initial deviations (greater than 1PPM).
Solution Approach 2:
The patent dynamically adjusts the frequency deviation parameter by scanning through a range of values and selecting the optimal one based on signal-to-interference ratio evaluation. This parameter optimization approach allows the system to compensate for crystal oscillation precision variations and temperature effects without requiring extremely high precision oscillators.
2Speed
If the mobile terminal moves at high speed (500km/h), then the Doppler frequency shift increases to about 0.5PPM requiring the terminal to track larger Doppler frequency deviations, but existing methods cannot effectively track such large Doppler shifts
Solution Approach 1:
The patent implements dynamic frequency deviation tracking by continuously monitoring and adjusting the frequency offset compensation value. The system evaluates the signal-to-interference ratio at different frequency deviation points and dynamically updates the compensation value to track Doppler frequency shifts, enabling reliable communication even at high speeds (500km/h) where Doppler shifts reach 0.5PPM.
3Temperature
If temperature compensation is implemented to maintain frequency accuracy across temperature ranges (-45°C to 80°C), then the frequency deviation can be tracked (±2.5PPM), but this increases device complexity and cost
Solution Approach 1:
The patent uses frequency deviation scanning and signal-to-interference ratio evaluation to dynamically determine the optimal frequency compensation value at different temperatures. Instead of using complex hardware temperature compensation mechanisms, the system adjusts the frequency parameter through software-based evaluation and compensation, achieving temperature adaptability (-45°C to 80°C) while reducing device complexity.
4Loss of time
If the frequency deviation scanning range is limited to a small range, then the initial access is faster, but the terminal cannot handle large initial frequency deviations or Doppler shifts
Solution Approach 1:
The patent segments the frequency deviation scanning process into two stages: first, a coarse scanning of a predetermined frequency deviation scanning range to quickly identify the approximate optimal frequency point; second, a fine-tuning evaluation around the identified point to achieve precise frequency locking. This segmented approach balances access speed with the ability to handle large frequency deviations and Doppler shifts.
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 enlarges the frequency deviation correction range, reduces the precision requirement for crystal oscillations, maintains accurate frequency tracking, and minimizes communication interruptions during cell switching, enabling efficient operation in adverse environments with reduced dropping-call rates and lower manufacturing complexity.
Implementation Method 1
A temperature detector is provided, and the frequency deviation value of the mobile terminal is ensured to always be able to track the effect of temperature on the frequency deviation (when the crystal oscillation is between -45°C to 80°C, the frequency deviation generally is ±2.5PPM) by maintaining a temperature/frequency deviation control table.
Implementation Method 2
when the mobile terminal initially accesses a cell, within a predetermined frequency deviation scanning range it synchronizes the slots at intervals of a predetermined frequency deviation, and obtains the signal-to-interference ratio (SIR) of the primary synchronization signals of the frequency deviation
Implementation Method 3
a voltage control oscillator whose oscillation frequency changes according to the change of control voltage; a feedback control loop... The frequency deviation correction control module calculates a new frequency deviation compensation value according to the current frequency deviation value, controls the voltage control oscillator and compensates the current frequency deviation value
Data Source
AI summary
The present invention provides an automatic frequency deviation correction method for a mobile terminal, comprising the step of configuring the mobile terminal with an initial frequency deviation value, which includes the following steps: when the mobile terminal initially accesses a cell, it synchronizes slots at intervals of a predetermined frequency deviation within a predetermined frequency deviation scanning range, and obtains the signal-to-interference ratio (SIR) of primary synchronization signal at the frequency deviation; after scanning the whole predetermined frequency deviation scanning range, the frequency deviation value corresponding to the maximum SIR of all the obtained SIRs as the initial frequency deviation value; and the mobile terminal is configured with the initial frequency deviation value to assure that the frequency deviation is controlled within the predetermined frequency deviation during the initial access. The present invention also provides an automatic frequency deviation correction system for a mobile terminal.