BLE Phase Distance Measurement Using Frequency Slope Analysis
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Bluetooth Low Energy (BLE) distance measurement systems face errors due to noise and frequency offset or drift between local oscillators in initiator and reflector devices, leading to ambiguity in phase-based distance calculations, especially at higher frequency offsets.
Innovation Solution
A method involving phase unwrapping and averaging of multiple phase measurements to generate a final phase measurement, which reduces noise and frequency offset errors by accounting for phase wrapping and using a frequency compensation technique during a specific interval to align local oscillator frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If phase-based distance measurement is used in BLE systems, then distance measurement capability is enabled, but measurement precision deteriorates due to phase wrapping ambiguity at high frequencies
Solution Approach 1:
The patent segments the phase measurement process into multiple frequency points. Instead of measuring at a single high frequency where phase wrapping causes ambiguity, the system performs measurements at multiple distinct frequency points (e.g., f1, f2, f3). Each frequency provides a separate phase measurement, and the combination of these segmented measurements resolves the ambiguity through slope calculation, thereby maintaining measurement precision while avoiding the phase wrapping problem.
Solution Approach 2:
The patent transitions from a single-dimension phase measurement (at one frequency) to a multi-dimensional measurement approach by introducing frequency as an additional dimension. By measuring phase across multiple frequency dimensions and calculating the slope of phase versus frequency, the system extracts distance information while eliminating the phase wrapping ambiguity that plagues single-frequency measurements.
2Measurement precision
If multiple frequency points are used for phase measurement, then measurement precision improves, but device complexity increases due to additional measurement steps
Solution Approach 1:
The patent merges multiple phase measurements taken at different frequency points into a single distance calculation through slope computation. Instead of treating each frequency measurement as a separate operation, the system combines them by calculating the slope of the phase-vs-frequency line, which directly yields the distance. This merging approach maintains high precision while simplifying the overall measurement process.
Solution Approach 2:
The system uses the phase measurements themselves to automatically determine the correct unwrapped phase values through slope calculation. The mathematical relationship between phase and frequency inherently provides the distance information without requiring external calibration or complex unwrapping algorithms, allowing the measurement process to self-resolve the ambiguity.
3Measurement precision
If frequency offset compensation is performed, then measurement precision improves, but loss of time increases due to calibration interval requirements
Solution Approach 1:
The patent performs frequency offset compensation during an initial calibration phase before the actual distance measurements are taken. By completing the frequency synchronization and offset correction in advance (preliminary action), the system ensures that subsequent measurements are performed under optimal conditions without requiring additional time during the measurement process itself.
Solution Approach 2:
The system implements frequency offset compensation as a periodic calibration process that occurs at defined intervals. Rather than continuously adjusting frequencies, the system performs calibration at specific periods (e.g., when entering ranging mode), which maintains measurement precision while minimizing the time lost to calibration activities.
4Measurement precision
If local oscillator frequencies are aligned through compensation, then measurement precision improves, but device complexity increases due to compensation mechanisms
Solution Approach 1:
The patent implements a feedback mechanism where the system measures the actual frequency offset between local oscillators during the calibration phase and uses this measured offset to adjust and align the frequencies. This closed-loop feedback approach automatically compensates for frequency mismatches without requiring complex predictive models or manual calibration, thereby achieving high precision while keeping the compensation mechanism relatively simple.
Solution Approach 2:
The system achieves frequency alignment by dynamically adjusting the local oscillator frequency parameter based on measured offset values. Rather than using complex hardware synchronization mechanisms, the patent changes the operational frequency parameter of the oscillators to match, achieving precise alignment through simple parameter adjustment that minimizes additional system complexity.
Data Source
AI summary
In at least one embodiment, a method for measuring a distance between a first communications device including a first local oscillator and a second communications device including a second local oscillator includes unwrapping N phase values to generate N unwrapped phase values. N is an integer greater than one. Each of the N phase values indicate an instantaneous phase of a received signal. The method includes averaging the N unwrapped phase values to generate an average phase value. The method includes wrapping the average phase value to generate a final phase measurement of the first local oscillator with respect to the second local oscillator.