Two-Way Ranging Using Symmetric Channels to Mitigate Clock Drift
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Solution Overview
Problem
Existing two-way ranging technologies face challenges in achieving accurate distance measurements due to clock drift between nodes, particularly in ultra-low power and non-coherent wireless devices, where high clock drift accuracy is difficult to achieve.
Innovation Solution
The implementation of symmetric channels with low-complexity time-tracking algorithms allows for concurrent transmission and reception of pulses, reducing the relative clock drift and enabling accurate ranging measurements by minimizing the error associated with clock drift, even in ultra-low power devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional two-way ranging is used with ultra-low power devices, then energy consumption is reduced, but clock drift accuracy deteriorates
Solution Approach 1:
The system performs preliminary clock synchronization and drift compensation before the actual ranging measurement. By pre-adjusting clock offsets and establishing synchronized timing references in advance, the system eliminates the need for ultra-precise clocks during operation, enabling accurate ranging with low-power devices that would otherwise suffer from excessive clock drift.
Solution Approach 2:
The system implements a feedback mechanism where clock drift is continuously monitored and compensated during the ranging process. By measuring the actual drift between nodes and dynamically adjusting timing calculations, the system maintains measurement accuracy despite using low-power clocks that would normally exhibit significant drift.
2Device complexity
If traditional sequential transmission is used, then device complexity is reduced, but ranging accuracy deteriorates due to increased clock drift error
Solution Approach 1:
The system employs periodic pulse transmission with alternating transmit/receive intervals between nodes. Instead of sequential one-way communication, both nodes periodically exchange synchronized pulses, creating a rhythmic pattern that allows continuous timing reference updates and drift compensation without significantly increasing protocol complexity.
Solution Approach 2:
The system uses asymmetric timing roles where one node transmits while the other receives, then reverses roles in alternating periods. This asymmetric approach allows each node to have a dedicated transmit and receive window, simplifying the communication protocol while enabling continuous synchronization and drift measurement through the alternating pattern.
Data Source
AI summary
Relatively short turnaround times are provided in conjunction with two-way ranging to, for example, facilitate accurate ranging measurements when the relative clock drift between ranging nodes (e.g., devices) is relatively high. In some aspects, relatively short turnaround times are achieved through the use of a symmetric channel that is defined to enable concurrent transmission of ranging messages between nodes. For example, a symmetric channel may be established by configuring the nodes to receive one or more pulses associated with a received ranging message in between pulse transmissions associated with a transmitted ranging message. In this way, one node may send a ranging timestamp shortly after the other nodes sends its ranging timestamp, thereby mitigating the impact of the clock drift on the ranging measurements. In some aspects the pulses may comprise ultra-wideband pulses. The techniques described herein may be employed to provide two-way ranging in, for example, low power and/or non-coherent wireless devices.