Asynchronous Wireless Localization Using Time Difference of Arrival
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Solution Overview
Problem
Existing localization systems using time-of-flight information face challenges in accommodating a large number of mobile devices due to high power consumption and complexity, particularly in systems relying on two-way time-of-arrival (TOA) methods, and suffer performance degradation as the density of target devices increases, while time difference of arrival (TDOA) systems require complex synchronization of anchor nodes.
Innovation Solution
A wireless localization system where a mobile device broadcasts a request packet, and anchor nodes within range receive and respond with a second packet, allowing them to estimate the time difference of arrival, determining the mobile device's location without the need for synchronization among anchor nodes, and enabling efficient operation with low power consumption and reduced complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If two-way time-of-arrival (TW-TOA) method is used for location estimation, then location accuracy is improved, but the number of transmissions increases and power consumption increases
Solution Approach 1:
The patent combines the location estimation function with the existing data collection network infrastructure. Anchor nodes that already exist for other purposes are utilized for TDOA measurements, merging multiple functions into a unified system that reduces overall power consumption while maintaining location accuracy
Solution Approach 2:
The system employs periodic broadcasting by mobile nodes at controlled intervals rather than continuous transmission. This periodic action allows location updates while managing power consumption, as nodes can enter low-power states between broadcasts
2Use of energy by moving object
If time difference of arrival (TDOA) method is used to reduce transmissions, then power consumption is reduced, but anchor nodes require complex synchronization
Solution Approach 1:
The system implements self-service synchronization where anchor nodes automatically adjust their timing based on received broadcasts from mobile nodes. Each anchor node independently calculates arrival time differences and uses these measurements without requiring centralized synchronization control, eliminating complex synchronization infrastructure
Solution Approach 2:
The mobile node broadcast serves as an intermediary reference signal that all anchor nodes use for TDOA calculations. Instead of anchor nodes synchronizing to each other, they all reference the mobile node's transmission time, simplifying the synchronization mechanism
3Measurement precision
If anchor nodes are synchronized to a common reference timing source, then TDOA measurement accuracy is improved, but system complexity and installation cost increase
Solution Approach 1:
Anchor nodes perform self-calibration by comparing their received signal arrival times and automatically adjusting their internal clocks. This self-service approach maintains measurement accuracy without requiring external synchronization infrastructure or manual configuration
Solution Approach 2:
The system performs preliminary timing measurements during the initial connection phase to establish reference arrival times. These preliminary measurements are used to calculate offset corrections that are applied in subsequent TDOA measurements, maintaining accuracy without continuous synchronization
4Productivity
If the system accommodates a large number of mobile devices, then system capacity is improved, but transmission collisions increase and performance degrades
Solution Approach 1:
The system segments the communication space into multiple channels or time slots that can be dynamically allocated. Mobile nodes are assigned different transmission opportunities based on their location and priority, reducing collisions while maintaining high system capacity
Solution Approach 2:
The system dynamically adjusts transmission parameters such as power, timing, and channel assignment based on current network conditions and node density. This dynamic adaptation allows the system to maintain reliable performance as the number of mobile devices varies
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
The system effectively localizes mobile devices with reduced power consumption and complexity, supporting a larger number of devices without the need for synchronization among anchor nodes, resulting in improved robustness and efficiency.
Implementation Method 1
The anchor nodes receive both the first and second packets and estimate the time difference of arrival between the first and the response packets. The location of the device is estimated based on the time differences of arrival.
Data Source
AI summary
A system for locating a mobile device is disclosed. In one embodiment, the system includes a mobile device having a processor and a receiver, and at least three transceiver devices forming a network of transceiver devices. The mobile device and transceivers can transmit a request (REQ) packet by the mobile device; receive the REQ packet by the at least three transceiver devices; transmit, by a first one of the at least three transceiver devices receiving the REQ packet, a response (RSP) packet; and receive by at least some of the at least three transceiver devices the REQ and the RSP packet. The at least three transceiver devices that receive both the REQ and the RSP packet, the system determines a difference in arrival time between receiving the REQ packet and the RSP packet. The system can determine the location of the mobile device based on determined differences in arrival time.