BLE Reflector Frequency Offset Compensation for Accurate Ranging
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Solution Overview
Problem
Phase-based distance measurement in Bluetooth Low Energy (BLE) systems is prone to errors due to frequency offset and noise, particularly in environments with significant frequency offsets between the initiator and reflector local oscillators, which can lead to inaccurate range calculations.
Innovation Solution
A method that involves detecting and compensating for frequency offsets by adjusting the local oscillators in both the initiator and reflector devices using sequential packet samples and continuous wave tones, ensuring accurate phase measurements and reducing phase wrapping errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If phase-based distance measurement is performed in BLE systems, then distance measurement capability is achieved, but measurement precision deteriorates due to frequency offset and noise
Solution Approach 1:
The patent applies preliminary action by performing frequency offset estimation and compensation before the actual phase-based distance measurement. The system estimates frequency offset using sequential packet samples and applies compensation adjustments to the local oscillator prior to ranging measurements, thereby eliminating frequency offset as a source of measurement error and improving both precision and reliability
Solution Approach 2:
The patent implements feedback by continuously monitoring frequency offset through sequential packet samples and applying real-time compensation adjustments. The system measures frequency offset, applies correction, and validates the correction through continuous wave tone measurements, creating a closed-loop feedback mechanism that maintains measurement reliability under varying frequency conditions
2Measurement precision
If frequency offset compensation is applied using sequential packet samples, then frequency offset accuracy is improved, but device complexity increases
Solution Approach 1:
The patent applies self-service by enabling each BLE device to autonomously estimate and compensate for its own frequency offset using its received packet samples. The device independently performs frequency offset estimation, calculates compensation adjustments, and applies corrections to its local oscillator without requiring external assistance, thereby improving precision while managing complexity through self-contained processing
Solution Approach 2:
The patent changes the parameter being measured from raw phase values to frequency offset estimates derived from sequential packet samples. By transforming the measurement parameter and using statistical methods on multiple samples, the system achieves higher frequency offset detection accuracy while the computational complexity is managed through efficient signal processing algorithms
3Reliability
If local oscillator adjustment is performed to reduce frequency offset, then measurement reliability is improved, but loss of time occurs during adjustment process
Solution Approach 1:
The patent performs frequency offset estimation and compensation as a preliminary action before the actual distance measurement phase. By completing the frequency compensation process in advance using packet samples, the system ensures measurement reliability is established beforehand, and the subsequent ranging measurements can proceed without additional time loss from frequency corrections
Solution Approach 2:
The patent maintains continuity of useful action by performing frequency offset estimation continuously during packet reception and applying compensation adjustments in real-time. This continuous process ensures that frequency compensation is always current when measurements are taken, maintaining reliability without requiring separate dedicated compensation time intervals
4Measurement precision
If phase measurements are performed to determine distance, then distance measurement capability is achieved, but measurement precision deteriorates due to phase wrapping errors
Solution Approach 1:
The patent converts the harmful effect of frequency offset into a beneficial measurement opportunity. By intentionally measuring frequency offset using the same phase measurement mechanism that causes wrapping errors, the system extracts useful frequency offset information from the phase measurements. This frequency offset measurement is then used to correct the original distance measurements, thereby converting the source of error into a tool for elimination
Data Source
AI summary
A method for communicating between a first radio frequency communications device including a first local oscillator and a second radio frequency communications device including a second local oscillator includes receiving a packet using a receiver of the first radio frequency communications device. The method includes detecting an average frequency offset based on sequential samples of the packet. The method includes applying a first adjustment to the first local oscillator to reduce a frequency offset between the first local oscillator and the second local oscillator. The first adjustment is based on the average frequency offset. The method includes, after adjusting the first local oscillator, transmitting a second packet to the second radio frequency communications device by the first radio frequency communications device using the first adjustment and the first local oscillator.