DS-TWR Carrier Offset Estimation for Phase-Based Distance Accuracy
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Solution Overview
Problem
Existing phase-based two-way ranging (TWR) systems suffer from carrier frequency offset (CFO) errors, leading to significant distance measurement inaccuracies, particularly in ultra-wideband technology, which are not adequately addressed by current methods that often require high computational complexity or insufficient accuracy.
Innovation Solution
A method for estimating carrier frequency offset (CFO) in double-sided two-way ranging (DS-TWR) systems, involving filtering and precise CFO estimation to improve distance measurement accuracy, allowing resolution of a half of the carrier period with high precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If phase-based two-way ranging is used to determine distance, then distance measurement capability is provided, but carrier frequency offset errors cause significant measurement inaccuracies
Solution Approach 1:
The patent applies preliminary action by performing CFO estimation and compensation before the final distance calculation. The system estimates CFO from packet exchanges, compensates the phase measurements using the estimated CFO, and then performs TOF calculation. This preliminary compensation step removes the harmful CFO effect before it degrades measurement accuracy.
Solution Approach 2:
The patent implements feedback by using the estimated CFO information to adjust and compensate subsequent phase measurements. The system continuously estimates CFO from exchanged packets and uses this feedback to correct phase-based distance measurements, creating a closed-loop system that actively counteracts CFO errors.
2Measurement precision
If existing CFO estimation methods are used, then some distance measurement capability is provided, but computational complexity increases or accuracy remains insufficient
Solution Approach 1:
The patent applies self-service by having each device estimate its own CFO using phase measurements from received packets. Instead of requiring one device to provide CFO information to the other, both devices independently perform CFO estimation and compensation using the same packet exchanges, eliminating the need for complex inter-device coordination.
Solution Approach 2:
The patent uses parameter changes by exploiting the phase parameter of received packets to estimate CFO. By measuring phase differences in exchanged packets and using these phase measurements to calculate CFO, the system transforms the problem into a parameter-based estimation that is computationally efficient compared to spectral methods.
3Device complexity
If phase-based single-sided TWR is used, then simpler protocol is achieved, but response delays introduce significant TOF estimation errors
Solution Approach 1:
The patent applies asymmetry by implementing different roles (master and slave) with different numbers of packets transmitted. The master device transmits three packets while the slave device transmits only one packet, creating an asymmetric protocol structure that enables more accurate TOF estimation by providing additional measurement opportunities for the master device.
4Measurement precision
If phase-based double-sided TWR with best-case methodology is used, then higher precision is achieved, but TOF resolution is limited to quarter of carrier period
Solution Approach 1:
The patent applies dimensionality change by combining phase-based measurements (providing precision within a carrier period) with packet timestamp information (providing absolute time reference). This multi-dimensional approach allows the system to achieve both high precision from phase measurements and extended resolution range from timestamp-based TOF calculation, overcoming the quarter-carrier-period limitation.
Data Source
AI summary
Disclosed is a method and wireless communication device for determining time-of-flight (TOF) in a two-way ranging system. The method involves performing a double-sided two-way ranging (DS-TWR) exchange between two devices, determining by way of processing circuitry of at least one of the devices a carrier frequency offset (CFO) of an initiator of one of the devices and a CFO of a responder of one of the devices, and response delay of the responder and a response delay of the initiator, thereby collecting exchange information. Other steps are filtering a CFO estimation by way of the processing circuitry; calculating by way of the processor a precise CFO estimation from the filtered CFO estimation and the exchange information; and calculating by way of the processor a TOF using the precise CFO estimation and the exchange information.