WLAN Time-of-Flight Ranging via Null Data Packets
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Solution Overview
Problem
Current wireless communication systems, such as WLANs, face challenges in accurately determining the position of communication devices within buildings or tunnels due to the limitations of GPS technology and the need for improved ranging measurement techniques.
Innovation Solution
The method involves exchanging null data packets (NDPs) between communication devices to measure the time-of-flight, allowing for accurate distance calculations and location estimation using time and angle measurements, facilitated by integrated circuits in network interface devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If GPS technology is used for location determination, then outdoor positioning is achieved, but positioning accuracy deteriorates in indoor environments such as buildings and tunnels
Solution Approach 1:
The patent introduces WLAN infrastructure and communication devices as intermediary systems to enable positioning in environments where GPS is unavailable. Instead of relying directly on satellite signals, the system uses local WLAN-based time-of-flight measurements between communication devices to determine positions, effectively mediating the positioning function in GPS-denied indoor environments
Solution Approach 2:
The patent replaces the satellite-based electromagnetic signal system (GPS) with a localized wireless communication system (WLAN) for positioning. By substituting the GPS mechanical/satellite system with WLAN infrastructure and time-of-flight measurement protocols, the system achieves positioning capability in indoor environments where satellite signals cannot penetrate
2Reliability
If time-of-flight measurements are performed using WLAN transmissions, then indoor positioning capability is achieved, but measurement precision is affected by multipath propagation and signal reflections
Solution Approach 1:
The patent performs preliminary channel characterization and measurement in advance to establish baseline conditions for time-of-flight calculations. By pre-characterizing the wireless channel properties and performing calibration measurements before actual positioning operations, the system compensates for multipath effects and signal reflections that would otherwise degrade measurement precision
Solution Approach 2:
The patent implements feedback mechanisms where communication devices exchange measurement data and channel state information to refine time-of-flight calculations. Through iterative feedback loops, devices adjust their measurements and calculations based on observed signal characteristics, thereby compensating for multipath propagation and improving overall measurement accuracy in challenging indoor environments
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 enables precise ranging measurements and location determination in challenging environments by accurately calculating time-of-flight and using angle measurements, enhancing the accuracy of wireless communication systems.
Implementation Method 1
measuring a time of flight of WLAN transmissions between the first communication device and the second communication device
Data Source
AI summary
During a service period (SP) for a ranging measurement signal exchange between a first communication device and one or more second communication devices, the first communication device receives respective first null data packets (NDPs) from the one or more second communication devices, and transmits respective second NDPs to the one or more second communication devices. The first communication device transmits, during the SP, respective first ranging measurement feedback packets to the one or more second communication devices to allow each of the one or more second communication devices to determine a time-of-flight between the first communication device and the second communication device and/or receives, during the SP, respective second ranging measurement feedback packets from the one or more second communication devices to allow the first communication device to determine respective times-of-flight between the first communication device and the one or more second communication devices.