Polyphase Resampling for Base Station Frequency Synchronization
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Solution Overview
Problem
Base station test systems face challenges in synchronizing center and sampling frequencies, especially with multiple transceivers and wide bandwidth applications, leading to timing closure issues and inefficiencies in resource usage due to tunable clocks with poor jitter performance.
Innovation Solution
A base station test system utilizing a polyphase interpolator with finite impulse response (FIR) filters to calculate output sample values in parallel, reducing the need for extensive computing resources and employing a fixed frequency clock for improved jitter performance and resource efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a tunable clock is used to synchronize frequency, then frequency synchronization is achieved, but jitter performance deteriorates and circuit area increases
Solution Approach 1:
The patent replaces the mechanical/tunable clock system with a fixed frequency clock combined with a digital resampler. Instead of physically tuning the clock frequency to match the base station, the system uses a fixed clock and digitally resamples the received signal to achieve frequency synchronization. This substitution eliminates the jitter problems associated with tunable clocks while maintaining synchronization capability.
Solution Approach 2:
The patent introduces a resampler as an intermediary component between the fixed frequency clock and the base station signal. The resampler acts as a mediator that adjusts the sampling rate digitally to match the base station frequency without requiring the clock itself to be tunable. This intermediary approach allows frequency adaptation while keeping the clock fixed and stable.
2Measurement precision
If a tunable clock is used to synchronize frequency, then frequency synchronization is achieved, but device complexity increases
Solution Approach 1:
The patent replaces the complex tunable clock hardware with a simpler fixed frequency clock and a digital resampler implemented in software or FPGA. This substitution reduces circuit area by eliminating the voltage-controlled oscillators and tuning circuits required for frequency adjustment, while achieving the same synchronization function through digital signal processing.
Solution Approach 2:
The patent extracts the frequency adjustment function from the clock hardware itself and moves it to a separate digital resampling stage. By taking out the tuning capability from the clock circuit, the system reduces clock circuit complexity while maintaining frequency adaptability through the resampler that operates on the already-acquired signal.
3Measurement precision
If multiple frequency tuning iterations are performed, then frequency synchronization is achieved, but time consumption increases
Solution Approach 1:
The patent performs preliminary frequency estimation and offset calculation before the actual resampling operation. By pre-calculating the required resampling rate based on initial frequency analysis, the system avoids multiple iterative tuning cycles. The resampler is then configured with the pre-determined parameters, achieving synchronization in a single pass rather than through repeated adjustments.
Solution Approach 2:
The resampler serves as an intermediary that can be rapidly reconfigured with different sampling rates without requiring physical clock tuning. This allows the system to quickly adapt to frequency offsets by changing digital parameters rather than performing multiple analog tuning iterations, significantly reducing the time required to achieve synchronization.
Data Source
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AI summary
Method for variable arbitrary resampling that allows a base station test system to correct for sampling frequency errors relative to the base station. An output time calculation module obtains the required output sample times depending on the resampling rate, which can be tuned as needed. An input sample counter module counts the last input sample loaded into a polyphase interpolator, which can calculate any of M interpolated samples between two consecutive input samples. The polyphase interpolator uses the integer part of the required output sample times to decide what interpolated samples to calculate. A sequencer module compares the calculated output times against the input sample count to control all the blocks of the variable arbitrary resampler and determine if the output of the polyphase interpolator is a valid sample. Valid samples are transferred to other subsystems, such as a digital-to-analog data converter or another signal processing module.