Phased Array RFID Tag Location via Multi-Receiver Signal Correlation
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Solution Overview
Problem
Existing RFID systems with phased antenna arrays face challenges in accurately and rapidly locating RFID tags due to the practical limit on the number of antennas, resulting in imprecise location determination based on peak receive signal strength, and null steering techniques are not effective as they require minimum signal strength for tag detection and demodulation.
Innovation Solution
The system employs a phased antenna array with a primary RF receiver for conventional beam steering and multiple secondary RF receivers for null steering, allowing for accurate tag location by correlating reconstructed return RF signals across multiple steering angles, even when signal strength is below threshold, and enabling quick measurement of signal strength at different angles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the number of antennas in the phased antenna array is increased to narrow the beam width for more accurate tag location, then the location precision is improved, but the device complexity and cost increase beyond practical limits
Solution Approach 1:
The system segments the reception function by employing multiple secondary RF receivers that independently measure signal strength at different steering angles. Each receiver handles a specific angular sector, allowing the system to achieve fine angular resolution without proportionally increasing the total number of antennas in the phased array.
Solution Approach 2:
The system adds a temporal dimension to the measurement process by steering the beam through multiple angles and measuring signal strength at each angle sequentially. This multi-angle scanning approach transforms a single spatial measurement into a multi-dimensional measurement space, enabling precise location determination with fewer antennas.
2Measurement precision
If null steering techniques are used to improve location accuracy by creating sharper nulls, then the angular resolution is improved, but the tag becomes undetectable because the interrogating signal strength drops below the minimum required for tag operation
Solution Approach 1:
The system separates the transmission and reception functions: a single transmit antenna array creates the beam pattern, while multiple independent receive antennas measure signal strength. This segmentation allows the receive side to detect signals even when the transmit beam creates nulls, because each receive antenna can independently measure the residual signal strength without requiring the tag to operate at minimum signal levels.
Solution Approach 2:
Instead of using null steering to create regions of zero signal for location determination, the system inverts the approach by measuring the non-zero signal strength in the vicinity of nulls. The secondary RF receivers detect the small but non-zero signals that exist near null points, allowing location determination without creating complete signal blackouts that would make tags undetectable.
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 and speed of RFID tag location, overcoming the limitations of broad beam width and low signal strength at nulls, allowing for precise tracking of RFID-tagged items in controlled areas.
Implementation Method 1
steering an interrogating (transmit) beam over the controlled area to interrogate the tags and generate return modulated RF signals from the tags
Implementation Method 2
the RFID tag, which senses the interrogating RF signal, responds by transmitting a return RF signal. The RFID tag either generates the return RF signal originally, or reflects back a portion of the interrogating RF signal in a process known as backscatter.
Data Source
AI summary
A radio frequency identification (RFID) tag reading system having a phased antenna array accurately locates RFID tags in a controlled area, by steering an interrogating beam over the controlled area to interrogate the tags and generate return modulated RF signals. A primary receiver steers a primary receive beam at a primary steering angle that is fixed during each tag interrogation. A primary demodulator demodulates and reconstructs the received return modulated signals. A secondary receiver, independently of the primary receiver, steers a secondary receive beam at a plurality of secondary steering angles. A secondary correlator/demodulator demodulates the combined return modulated signals, and utilizes the reconstructed signal reconstructed by the primary demodulator at each of the secondary steering angles. Both the primary and the secondary receivers cooperate to accurately locate the same tag.