WiFi Node Positioning via Time of Flight
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Solution Overview
Problem
Current methods for determining the physical location of mobile nodes in wireless mesh networks are costly and complex, often requiring GPS receivers or multiple message exchanges, which are not practical for all environments, especially in areas with metal obstructions or where asset tracking is necessary.
Innovation Solution
A method using WiFi radios capable of duplex operation on multiple bands to calculate distances between nodes with known locations by measuring the time of flight of signals, allowing for the determination of a mobile node's position without the need for GPS or complex synchronization, utilizing a repeater node to resend signals quickly and accurately.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If GPS receivers or multiple message exchanges are used to determine the physical location of mobile nodes, then positioning accuracy is improved, but system cost and complexity increase
Solution Approach 1:
The patent extracts the positioning function from complex external systems (GPS receivers, multiple message exchange protocols) and implements it using the existing WiFi radio infrastructure already present in mesh network nodes. By utilizing the duplex operation capability of standard WiFi radios to measure time of flight, the system achieves positioning accuracy without requiring additional GPS hardware or complex synchronization mechanisms.
Solution Approach 2:
The mesh network nodes use their own existing WiFi radios to perform positioning measurements. Each node with known location can independently measure the time of flight of signals from mobile nodes using its duplex operation capability, eliminating the need for external positioning infrastructure. The system serves its own positioning needs using resources already available within the network.
2Measurement precision
If GPS hardware is used for node location determination, then positioning capability is improved, but hardware cost increases
Solution Approach 1:
The patent makes the existing WiFi radio serve multiple functions: data communication and positioning measurement. By enabling duplex operation on the same radio frequency, the system allows the WiFi radio to both transmit/receive data and measure time of flight for positioning, eliminating the need for separate GPS receivers in each node and reducing overall hardware costs.
Solution Approach 2:
The system replaces expensive GPS hardware with the already-present, low-cost WiFi radio infrastructure. The existing WiFi radios in mesh network nodes are utilized for positioning measurements, avoiding the need to deploy additional expensive positioning hardware throughout the network.
3Measurement precision
If multiple message exchanges are used for positioning, then positioning accuracy is improved, but message transmission time increases
Solution Approach 1:
The patent implements a periodic ping-based measurement scheme where nodes exchange position measurement messages at regular intervals rather than continuously. This periodic action allows the system to maintain positioning accuracy through repeated measurements while minimizing the time loss associated with message exchanges by keeping the communication dormant between measurement cycles.
Solution Approach 2:
The system performs preliminary synchronization and setup of the duplex operation mode before actual positioning measurements begin. By pre-configuring the WiFi radios for simultaneous transmit and receive operation on the same frequency, the system eliminates the need for complex real-time synchronization during measurement, reducing message transmission time while maintaining positioning accuracy.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach simplifies and cost-reduces the process of locating wireless network nodes, enabling accurate positioning in various environments without the need for expensive GPS hardware or complex systems, while maintaining high accuracy by minimizing turnaround time and processing power requirements.
Implementation Method 1
A distance is derived between the unknown node and the first reference node from the time of flight of the first sent and first reply WiFi signals
Data Source
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AI summary
The physical position of an unknown node in a network is determined by sending a first sent WiFi signal from one of an unknown node and a first reference node having a known location, and repeating the sent WiFi signal in the other of the unknown node and first reference node with a first reply WiFi signal. A distance is derived between the unknown node and the first reference node from the time of flight of the first sent and first reply WiFi signals. A second WiFi signal is sent from one of the unknown node and a second fixed node having a known location, and repeating the sent second WiFi signal in the other of the unknown node and second reference node with a second reply WiFi signal, and a distance is derived between the unknown node and the second reference node from the time of flight of the second sent and second reply WiFi signals. A physical location of the unknown node is determined based on the derived distances between the unknown node and the first and second reference nodes.