DFT Coefficient Adjustment for Frequency Offset Compensation
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Solution Overview
Problem
Existing wireless communication systems face inaccuracies in distance measurements due to frequency offset between local oscillators in wireless nodes, leading to errors in fractional time determination and round trip time measurements, which affect the resolution and accuracy of distance calculations.
Innovation Solution
The implementation of discrete Fourier transform (DFT) blocks with complex multipliers and accumulators that adjust DFT coefficients based on estimated frequency offsets, allowing for phase value determination and compensation during the sounding sequence, thereby improving fractional timing and distance measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If standard DFT coefficients are used without frequency offset compensation, then the device complexity is reduced, but the measurement precision deteriorates due to frequency offset errors
Solution Approach 1:
The patent applies preliminary action by estimating the frequency offset before performing the DFT operation. The system calculates the frequency offset between transmitter and receiver oscillators in advance, then uses this estimate to pre-adjust the DFT coefficients. This preliminary frequency offset compensation ensures that the subsequent distance measurement uses corrected coefficients, thereby improving measurement precision without adding complex real-time adjustment mechanisms during the DFT computation itself.
2Measurement precision
If frequency offset compensation is implemented through DFT coefficient adjustment, then the measurement precision improves, but the device complexity increases due to additional processing blocks
Solution Approach 1:
The patent applies parameter changes by modifying the DFT coefficients based on the estimated frequency offset. Instead of adding complex hardware blocks, the system changes the parameters (coefficients) of the existing DFT operation. The frequency offset estimate is used to adjust the phase and frequency parameters of the DFT coefficients, allowing the system to compensate for oscillator mismatches by simply changing numerical values rather than adding substantial processing complexity.
3Reliability
If multiple DFT blocks with different coefficients are used for frequency offset compensation, then the reliability of distance measurement improves, but the device complexity increases
Solution Approach 1:
The patent applies universality by designing a single DFT processing path that handles both standard operation and frequency offset compensation through adaptive coefficient selection. The same DFT block structure is used, but the coefficients are dynamically adjusted based on the frequency offset estimate. This multi-functional approach allows the system to perform both uncorrected and corrected measurements using the same hardware resources, improving reliability without proportionally increasing device complexity.
Data Source
AI summary
A receiver includes a first discrete Fourier transform (DFT) block to perform a first single tone DFT on a positive tone associated with a sounding sequence. A second DFT block performs a second single tone DFT on a negative tone associated with the sounding sequence. A DFT coefficient generation block generates first DFT coefficients based on a nominal frequency of the positive tone and an estimated frequency offset between a transmitter frequency and a receiver frequency. The DFT coefficient generation block generates second DFT coefficients based on a nominal frequency of the negative tone and the estimated frequency offset. Multipliers in the DFT blocks multiply I and Q values of the sounding sequence with the coefficients. Accumulators in the DFT blocks accumulate multiplier outputs. An arctan function receives averaged accumulated values from the first and second DFT blocks and supplies first and second phase values used to calculate fractional timing.