Interferometric WiFi Location Sensing Using Antenna Phase Difference
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Solution Overview
Problem
Existing wireless localization methods, such as GPS and cellular network triangulation, are inaccurate and unreliable in indoor and crowded urban environments, and existing WLAN-based methods are complex and unreliable.
Innovation Solution
Utilizing a method that involves detecting phase differences in signals received from multiple antennas of fixed transceivers to estimate angles of arrival or departure, allowing for accurate location determination of mobile transceivers without requiring association with the network, by computing temporal correlation functions and measuring phase differences between signals from different antennas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If GPS is used for location determination, then outdoor location accuracy is achieved, but indoor and urban environment reliability deteriorates
Solution Approach 1:
The patent introduces WiFi access points as intermediary devices to enable location determination in environments where GPS is unavailable. Instead of relying solely on satellite signals, the system uses locally deployed WiFi infrastructure as a mediator to provide location services indoors and in urban canyons.
Solution Approach 2:
The patent replaces the GPS satellite-based electromagnetic signal system with a terrestrial WiFi-based electromagnetic signal system for location determination. This substitution enables operation in environments where satellite signals are blocked or degraded.
2Ease of operation
If cellular network triangulation is used for location determination, then basic location capability is provided, but accuracy and reliability deteriorate
Solution Approach 1:
The patent changes the fundamental measurement parameter from signal strength-based triangulation to phase difference-based angle estimation. This parameter change enables more accurate location determination by exploiting the interferometric properties of wireless signals from multiple antennas.
3Adaptability or versatility
If existing WLAN-based localization methods are used, then indoor location capability is achieved, but system complexity and reliability deterioration occurs
Solution Approach 1:
The patent enables location determination using existing WiFi infrastructure without requiring special cooperation or configuration from access points. The mobile device autonomously performs phase difference measurements and angle calculations using standard WiFi signals already present in the environment.
Solution Approach 2:
The patent replaces complex signal processing methods with phase difference measurement between signals received at different antennas. This simpler approach leverages the natural interferometric pattern created by multiple transmit antennas, reducing computational complexity while improving accuracy.
4Measurement precision
If phase difference measurement between multiple antennas is used, then location accuracy is improved, but measurement complexity increases
Solution Approach 1:
The patent performs preliminary correlation processing to identify signal components from specific transmit antennas before measuring phase differences. This preliminary action simplifies the subsequent phase measurement by isolating the relevant signal components from the multipath environment.
Solution Approach 2:
The patent uses correlation copying to replicate the known transmit signal pattern at the receiver, enabling precise phase difference measurement. By correlating the received signal with expected signal patterns, the system can accurately extract phase information even in noisy 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
Enables accurate location determination of mobile transceivers relative to fixed transceivers, even in challenging environments, without dependence on GPS, by leveraging existing wireless infrastructure for precise indoor and urban navigation.
Implementation Method 1
detecting phase differences in signals received from multiple antennas of fixed transceivers to estimate angles of arrival or departure
Implementation Method 2
Interferometric location sensing
Data Source
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Figure 3A
AI summary
A method for signal processing includes receiving via first and second antennas (34) respective first and second input signals in response to an output signal that is transmitted from a wireless transmitter (27, 28, 30) and encodes a predefined sequence of symbols. A temporal correlation function is computed over the first and second input signals with respect to one or more of the symbols in the predefined sequence so as to identify respective first and second correlation peaks and extract respective first and second carrier phases of the first and second input signals at the first and second correlation peaks. A phase difference between the first and second signals is measured based on a difference between the first and second carrier phases extracted at the first and second correlation peaks. Based on the measured phase difference, an angle of arrival of the output signal from the wireless transmitter is estimated. There is additionally provided, in accordance with an embodiment of the invention, a method for location finding, which includes receiving radio signals transmitted between a plurality of fixed transceivers having multiple antennas at different, respective first locations and a mobile transceiver at a second location. A respective phase difference is detected between the received radio signals that are associated with each of the multiple antennas of each of the fixed transceivers. Multiple loci are computed, corresponding respectively to respective angles between each of the fixed transceivers and the mobile transceiver based on the respective phase differences. Location coordinates of the mobile transceiver are found based on the angles and the transmit locations of the transmitters by identifying an intersection of the loci as the second location of the mobile transceiver.