RFID Direction Finding via Dynamic Power Adjustment
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Solution Overview
Problem
In environments with multipath, existing RFID tag locationing methods often inaccurately determine the direction of RFID tags due to strongest signal reflections, rather than direct paths.
Innovation Solution
The method involves transmitting RF signals in multiple directions, comparing receive signal strengths, and adjusting power levels to distinguish between direct and reflected signals, ensuring accurate direction estimation by prioritizing responses from direct paths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the RFID reader receives signals from multiple directions and selects the strongest signal, then the direction finding process is simple, but the accuracy deteriorates in multipath environments due to reflected signals
Solution Approach 1:
The patent applies dynamics by making the transmit power variable rather than fixed. The RFID reader dynamically adjusts transmit power levels based on received signal characteristics, switching between high power (to detect weak direct signals) and low power (to suppress strong reflected signals). This dynamic power adjustment resolves the contradiction by adapting the detection strategy to the specific signal environment, enabling accurate direction finding in multipath conditions without oversimplifying the process
Solution Approach 2:
The patent changes the power level parameter of transmitted signals to differentiate between direct and reflected paths. By transmitting at multiple power levels and observing which signals are received, the system can identify direct paths (which remain detectable at lower powers) versus reflected paths (which dominate at higher powers but disappear at lower powers). This parameter change enables accurate direction measurement while maintaining operational simplicity through automated power level selection
2Measurement precision
If transmit power is increased to detect weak direct path signals, then direct path detection improves, but reflected signals become stronger and cause false direction readings
Solution Approach 1:
The patent applies periodic action by transmitting signals at alternating power levels (high and low) and periodically switching between these states. This periodic transmission allows the system to observe signal behavior across different power conditions, identifying which receive directions consistently show signals at both power levels (indicating direct paths) versus those that only show signals at high power (indicating reflected paths). This periodic approach resolves the contradiction by using time-varying power to distinguish and eliminate harmful reflected signals
Solution Approach 2:
The system dynamically adjusts transmit power based on the detection needs. When seeking to detect weak direct path signals, the system temporarily increases power, then observes the effect on received signals. By dynamically switching power levels and analyzing the response, the system can identify and prioritize direct path signals while suppressing the influence of reflected signals, thus resolving the contradiction between detection sensitivity and interference
3Object-affected harmful factors
If transmit power is decreased to suppress reflected signals, then multipath interference reduces, but weak direct path signals may not be detected
Solution Approach 1:
The patent applies partial action by using low power transmissions only when and where needed to suppress multipath interference, rather than continuously using low power. The system performs high power transmissions initially to ensure detection of all potential signals, then uses targeted low power re-transmissions only in directions where reflected signals were detected. This partial application of low power achieves multipath suppression without sacrificing direct path detection capability
Solution Approach 2:
The system dynamically selects transmit power levels based on real-time signal conditions. After initial high power transmissions identify potential reflected signal directions, the system dynamically switches to low power transmissions specifically in those directions to suppress multipath interference. This dynamic, conditional power adjustment resolves the contradiction by applying low power only when necessary to suppress reflections while maintaining high power capability for detecting weak direct signals
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 enhances the accuracy of RFID tag direction finding by differentiating between direct and multipath signals, reducing false readings and improving locationing precision in complex environments.
Implementation Method 1
transmitting, by an RFID reader, a first transmit signal in a first transmit direction
Implementation Method 2
In environments where multipath may exist, the strongest signal received at an RFID reader may be a reflection that originated from an obstructed RFID tag
Data Source
AI summary
At least some embodiments of the present invention are directed to RFID reader systems configured to estimate a directional bearing of an RFID tag. In an embodiment, the present invention is an RFID system configured in a way that upon a detection of a variance in the direction of a maximum RSSI value for a given RFID tag in response to a plurality of interrogation signals transmitted by an RFID reader over a respective plurality of different directions, the RFID reader retransmits the plurality of interrogation signals over the respective plurality of different directions with successively lower power levels until the only response(s) being received no longer exhibit the previously detected variance.