WiFi Access Point Antenna Array Calibration for Indoor Location
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Solution Overview
Problem
Existing indoor location systems using radio frequency transmissions face challenges such as multipath propagation and require expensive infrastructure, resulting in coarse accuracy and high maintenance efforts, which are inadequate for applications demanding centimeter-level precision and low response time.
Innovation Solution
The ArrayTrack system employs multiple wireless access points with multiple antennas to determine the angle-of-arrival of communication signals, using phase offsets to differentiate direct and multipath components, and combines angle-of-arrival information from multiple access points to estimate the location of mobile devices without prior calibration, leveraging existing WiFi infrastructure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If dedicated infrastructure with many receivers is deployed to achieve fine-grained indoor location service, then location accuracy is improved, but device complexity and maintenance effort increase
Solution Approach 1:
The patent enables existing WiFi access points to serve dual purposes: providing wireless network connectivity and enabling precise indoor location determination. By utilizing the phase information already captured during normal WiFi communication, the system eliminates the need for dedicated location infrastructure while achieving centimeter-level accuracy through angle-of-arrival calculations.
2Measurement precision
If calibration is performed to improve location accuracy, then measurement precision is improved, but loss of time increases
Solution Approach 1:
The system performs self-calibration by automatically determining phase offsets using signals from mobile devices during normal operation. The access points calculate angle-of-arrival information and adjust phase compensation values without requiring manual calibration procedures, external reference transmitters, or dedicated calibration time, thereby achieving both high accuracy and rapid deployment.
3Device complexity
If existing WiFi infrastructure is used without calibration to reduce complexity, then device complexity is reduced, but measurement precision deteriorates
Solution Approach 1:
The patent transforms the raw phase information from WiFi signals into accurate angle-of-arrival measurements by applying dynamic phase offset compensation. The system calculates and adjusts phase parameters for each antenna element based on the geometric relationship between access points and mobile devices, enabling precise location determination using existing uncalibrated WiFi infrastructure.
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 achieves centimeter-level accuracy and fast response times for indoor location determination using existing WiFi infrastructure, outperforming previous solutions in accuracy with fewer access points and without the need for extensive calibration, while being robust against multipath propagation and varying environmental conditions.
Implementation Method 1
Each antenna in the array having a respective internal phase offset phi(i), wherein phi(i) is determined by calibrating the wireless access point using a transmitter at a known location
Implementation Method 2
receiving a signal from at least one transmitter located at a substantially known bearing from the wireless access point
Data Source
AI summary
A method and apparatus are provided for calibrating a wireless access point comprising an array of multiple (m) antennas denoted Ai (i=1 . . . m), each antenna having a respective internal phase offset φi. The method comprises receiving a signal from at least one transmitter located at a substantially known bearing from the wireless access point. The method further comprises determining an estimated value for each internal phase offseti such that an angle of arrival (AoA) spectrum calculated for the received signal on the basis of said estimated values matches the known bearing, wherein said AoA spectrum is calculated by treating said multiple antennas as a phased array. A method and an apparatus are also provided for calibrating a wireless access point comprising first and second arrays of multiple antennas, each antenna array having a respective radio unit, and each antenna in an array having a respective internal phase offseti. The method comprises using an antenna in the first antenna array to act as a transmitter located at a known distance from each antenna in the second antenna array, such that a signal from said transmitter is received at each antenna in the second antenna array. A phase for the received signal at each antenna in the second antenna array is measured in the radio unit, while an expected phase for the received signal is calculated, for each antenna in the second antenna array, based on the known distance of that antenna from the transmitter. The internal phase offseti, for each antenna in the second antenna array can then be determined from the difference between the measured phase and the calculated phase for that antenna.