RF Stimulus Geolocation via Mixing Products
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Solution Overview
Problem
Conventional techniques for locating wireless communication devices are inaccurate due to RF multipath interference and fail to detect devices that are not powered on or designed to emit energy, especially in complex environments like buildings and neighborhoods.
Innovation Solution
A method and system that transmit a stimulus signal to stimulate wireless communications receiver devices, causing them to emit unintended RF mixing products, which are then used for direction finding and geolocation, even in multipath environments and when devices are powered off, by correlating response signal parameters with calibrated arrays and using GPS for precise positioning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If amplitude-based techniques are used to locate wireless emitters, then the location can be determined, but the accuracy deteriorates due to RF multipath interference
Solution Approach 1:
The patent converts the harmful RF multipath interference into a beneficial effect by using the reflected signals to create a virtual image of the emitter. The image signal appears at a location symmetric to the actual emitter with respect to the reflecting surface, allowing the system to distinguish between the real emitter and multipath interference through signal analysis.
Solution Approach 2:
The patent introduces an intermediary approach by using a known reflecting surface (such as a wall or building facade) as a mediator to create the image signal. This intermediary element enables the system to indirectly locate the emitter by analyzing the reflected signal pattern, thereby avoiding direct measurement errors caused by multipath interference.
2Reliability
If conventional locationing techniques are used, then powered-on emitters can be detected, but powered-off emitters remain undetectable
Solution Approach 1:
The patent applies the self-service principle by enabling the emitter itself to generate the detectable signal. When the emitter is stimulated with an RF signal, it automatically generates image signals through its own receiving circuitry and antenna, regardless of whether it is powered on or off. This eliminates the need for the emitter to be actively transmitting.
Solution Approach 2:
The patent inverts the conventional approach by instead of detecting transmitted signals from the emitter, it stimulates the emitter's receiving circuitry to generate signals. This inversion allows detection of powered-off devices by exploiting their passive receiving components.
3Productivity
If amplitude-based techniques are used, then locationing can be performed, but false high amplitude paths are created in multipath environments
Solution Approach 1:
The patent converts the harmful multipath reflections into beneficial image signals that can be systematically analyzed. By using the known geometry of reflecting surfaces, the system can distinguish between direct signals and image signals, thereby maintaining direction finding accuracy even in complex multipath environments.
Solution Approach 2:
The patent replaces the mechanical approach of physically moving the receiver to determine direction (which creates false readings in multipath) with a signal-processing approach using image signal analysis. This substitution eliminates the need for physical movement and avoids false high amplitude paths.
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 detection, identification, and location of wireless communication devices, including those powered off, in various environments by exploiting the emission of upper and lower sideband RF signals, providing robust direction finding and geolocation capabilities even in the presence of interference.
Implementation Method 1
The stimulus signal causes multiple RF mixing products to be emanated from the wireless communications receiver device
Data Source
AI summary
Techniques are disclosed for detecting, identifying, and/or geolocating RF communications devices, such as FRS radios, high-power cordless phones, cellular phones, and other wireless communications receiver devices. The techniques exploit a vulnerability present in such devices, and can be used to detect (e.g., up to 300 meters) and geolocate (e.g., within +/â3 meters) those devices. The vulnerability is that receiver circuitry of the target devices emanate RF mixing products when flooded with RF energy or suitable stimulus signal. Such a response to a stimulus signal is unexpected or otherwise unintentional, as receiver circuitry is generally not designed to transmit information. The RF frequency, phase, and amplitude of these sideband RF responses can be used to detect and location the devices. The techniques work in the presence of interference, and can be used on devices that are powered on or off.