Passive Microwave Sensing Architecture Using Ambient Wi-Fi Signals
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Solution Overview
Problem
Existing microwave passive sensing technologies face challenges in detecting moving targets without additional RF devices and suffer from interference and high computational costs, limiting their flexibility and performance.
Innovation Solution
A microwave architecture that simultaneously retrieves transmitted and scattered signals using a non-cooperative microwave source, employing a low noise amplifier, mixer, and baseband amplifier to extract Doppler information without hardware modification or synchronization, leveraging ambient Wi-Fi, Bluetooth, and wireless power transfer infrastructure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If Wi-Fi access points are used for target detection without additional RF devices, then device complexity is reduced, but measurement precision deteriorates due to unpredictable fluctuations in communication links
Solution Approach 1:
The received signal is segmented into direct path components and reflected path components. By separately processing these segments and using channel state information to identify and remove direct path contributions, the system extracts pure target reflection signals, thereby improving measurement precision while maintaining low device complexity
Solution Approach 2:
Channel state information (CSI) acts as an intermediary that provides knowledge about the communication channel characteristics. This intermediary information enables the system to distinguish between direct path signals and target-reflected signals, allowing accurate target detection using existing Wi-Fi hardware without additional RF devices
2Ease of operation
If passive sensing is performed using existing Wi-Fi infrastructure, then ease of operation is improved, but reliability deteriorates due to interference from multiple reflections and scattering paths
Solution Approach 1:
The system extracts only the relevant target reflection information from the complex Wi-Fi signal by using CSI to identify and remove direct path components and unwanted reflections. This extraction process isolates the target signal from interfering multipath components, improving reliability while maintaining ease of operation
Solution Approach 2:
The system uses feedback from channel state information to continuously identify and compensate for direct path interference and multipath effects. This feedback mechanism allows the system to adapt to changing environmental conditions and maintain reliable target detection using existing Wi-Fi infrastructure
3Measurement precision
If CSI-based systems are used for fine-grained measurements, then measurement precision is improved, but device complexity increases due to specialized hardware requirements
Solution Approach 1:
The invention makes existing Wi-Fi access points and smartphones perform dual functions: both wireless communication and passive radar sensing. By utilizing the existing CSI capability of standard Wi-Fi hardware for both purposes, the system achieves fine-grained measurement precision without requiring specialized radar hardware, thus maintaining universality
4Measurement precision
If conventional radar methods are used for target detection, then measurement precision is improved, but use of energy increases due to active transmission requirements
Solution Approach 1:
The system uses ambient Wi-Fi signals from third-party transmitters (access points, smartphones) to perform passive sensing. The sensing device itself does not transmit signals but instead harvests and processes existing RF energy in the environment, thereby achieving accurate target detection with minimal power consumption through self-service from ambient energy sources
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 cost-effective and power-efficient detection of moving targets with improved spectrum efficiency, reducing interference and eliminating the need for dedicated RF transceivers and complex algorithms.
Implementation Method 1
a mixer coupled to the low noise amplifier
Implementation Method 2
a low noise amplifier coupled to the microwave receiver
Implementation Method 3
a baseband amplifier coupled to the mixer
Implementation Method 4
Microwave passive sensing makes use of electromagnetic waves emitted by a third-party transmitter to detect and localize targets
Implementation Method 5
the capability to simultaneously retrieve both the transmitted signal from a non-cooperative microwave source and the signals scattered by a target is the key to enable the identification of Doppler frequencies associated with the target of interest
Data Source
AI summary
A microwave passive sensor includes a microwave receiver, a low noise amplifier coupled to the microwave receiver, a mixer coupled to the low noise amplifier, and a baseband amplifier coupled to the mixer.