UWB Ranging Clock Offset Compensation Using Two-Stage CIR Correction

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Solution Overview

Problem

The challenge of clock offset impairments, specifically sampling frequency offset (SFO) and carrier frequency offset (CFO), in UWB MMS ranging processes leads to CIR smearing and phase wrapping, hindering effective signal integration and extending the coverage range.

Innovation Solution

A low complexity two-stage timing frequency estimation method is employed to compensate for clock offsets by determining SFO and CFO, using interpolation and phase unwrapping to resample and phase rotate CIR fragments, thereby improving CIR combining performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Illumination intensity

If multi-millisecond ranging fragments are used to extend coverage range, then the signal-to-noise ratio is improved, but clock offset impairments cause CIR smearing and phase wrapping that degrade ranging precision

Engineering Contradiction:

Improvesignal-to-noise ratioVSAvoidranging precision

Core Design Contradiction:

Illumination intensityVSMeasurement precision

Solution Approach 1:

The patent applies preliminary action by estimating the sampling frequency offset (SFO) and carrier frequency offset (CFO) before combining the CIR fragments. The SFO is estimated from the peak locations of interpolated CIR fragments, and this estimate is then used to compensate the CFO and resample the fragments before coherent combination, preventing CIR smearing and phase wrapping from degrading ranging precision

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent implements feedback by using the estimated SFO to compensate the CFO and then using the compensated CIR to estimate a refined CFO. This feedback loop continues until convergence, allowing the system to adaptively adjust frequency offsets based on the actual measured CIR characteristics, thereby maintaining ranging precision despite clock offset impairments

Inventive Principle:

Principle #23Feedback

2Measurement precision

If conventional clock offset compensation methods are used, then ranging precision is maintained, but implementation complexity increases significantly

Engineering Contradiction:

Improveranging precisionVSAvoidimplementation complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent applies segmentation by dividing the clock offset compensation into two independent stages: first estimating the sampling frequency offset (SFO) from CIR peak locations, then using this SFO estimate to compensate the carrier frequency offset (CFO) and resample the fragments. This segmentation simplifies the overall complexity compared to simultaneous estimation of both offsets while maintaining ranging precision

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent uses parameter changes by transforming the CIR fragments through interpolation with a specific factor (e.g., 32) to upsample the frequency domain representation. This parameter change enables more accurate peak location detection and SFO estimation, which then guides the subsequent CFO compensation and resampling operations

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS20250358756A1Method of compensating a clock offset between devices in a UWB-MMS ranging process

Publication Date: 2025.11.20 NXP BV

AI summary

A low complexity clock drift estimation scheme for UWB-MMS ranging is proposed, assuming sampling frequency offset (SFO) and carrier frequency offset (CFO) are driven from the same clock source. SFO is first estimated with the multiple CIR fragments, and it is used to compensate the CFO for the CIR fragments. Then a fine CFO estimate is obtained from the compensated CIRs. Combining the coarse SFO and fine CFO estimate to resample and phase rotate the original CIRs can significantly improve the performance for CIR combining, thus, improve the performance for ranging.