RFID Tag Interrogation via Spatial Diversity and Phase Dithering
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Solution Overview
Problem
Current passive UHF RFID systems face limitations in read range and reliability due to narrowband signals and fading effects, leading to incomplete tag reading, especially in environments with multiple tags in close proximity.
Innovation Solution
An RFID tag reading system employing spatial transmit/receive signal diversity with multiple antennas, combined RF signals, and dithering of frequency and phase during the tag inventory cycle to create constructive and destructive interference patterns, optimizing signal-to-noise ratio and reducing collisions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If passive UHF RFID tags are used to extend read range to ten metres, then the read range is improved, but the reliability of successful reading deteriorates due to fading effects and signal variations
Solution Approach 1:
The system divides the single antenna into multiple antenna elements that transmit signals simultaneously. By segmenting the transmit function across multiple antennas, the system achieves spatial diversity that mitigates fading effects at extended ranges while maintaining reliable tag reading probability
Solution Approach 2:
The patent introduces spatial dimension by arranging multiple antennas in specific geometric configurations (linear, planar, or three-dimensional arrangements). This dimensional expansion creates multiple signal paths to tags at extended ranges, overcoming the limitations of single-antenna systems through spatial diversity
2Quantity of substance
If multiple tags are present in a common region of space, then the quantity of tags to be read increases, but collisions between tags deteriorate reading performance
Solution Approach 1:
The system segments the tag population into different spatial zones using multiple antenna beams. Each antenna or antenna combination serves a specific spatial sector, dividing the dense tag population into manageable groups that can be read simultaneously without collisions
Solution Approach 2:
The patent adds spatial dimension to tag addressing by assigning different spatial locations to different antenna beams. This spatial multiplexing allows simultaneous reading of multiple tags in different locations without collisions, effectively handling dense tag environments
3Loss of energy
If narrowband signals are used for RFID communication, then the signal bandwidth is reduced, but fading effects generate large variations in free space loss that prevent successful reading
Solution Approach 1:
The system segments the narrowband signal transmission across multiple antennas with different spatial positions. Each antenna transmits the same narrowband signal but from a different location, creating multiple propagation paths that reduce the impact of fading effects on signal-to-noise ratio
Solution Approach 2:
The patent converts the harmful fading effect into a beneficial phenomenon by exploiting constructive interference. Through careful antenna phase and amplitude adjustment, the system creates constructive interference at tag locations, transforming the potentially harmful signal variations into enhanced signal strength
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 significantly enhances read/write performance, achieving nearly 100% tag reading success within a defined area while minimizing nulls and collisions, allowing for reliable operation over increased ranges.
Implementation Method 1
said system is configured to generate an interference between said simultaneously transmitted RF tag interrogation signals with defined relative phases from said plurality of antennas in said system
Implementation Method 2
a plurality of transmit/receive antennas coupled to said RF transmitter and to said RF receiver, to provide spatial transmit/receive signal diversity
Data Source
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AI summary
We describe an RFID tag reading system for reading one or more RFID Tags, the system comprising an RF transmitter and an RF receiver, a plurality of transmit/receive antennas coupled to said RF transmitter and to said RF receiver, to provide spatial transmit/receive signal diversity, and a tag signal decoder coupled to at least said RF receiver, wherein said system is configured to combine received RF signals from said antennas to provide a combined received RF signal, wherein said RF receiver has said combined received RF signal as an input; wherein said antennas are spaced apart from one another sufficiently for one said antenna not to be within the near field of another said antenna, wherein said system is configured to perform a tag inventory cycle comprising a plurality of tag read rounds to read said tags, a said tag read round comprising transmission of one or more RF tag interrogation signals simultaneously from said plurality of antennas and receiving a signal from one or more of said tags, a said tag read round having a set of time slots during which a said tag is able to transmit tag data including a tag ID for reception by said antenna, and wherein said system is configured to perform, during a said tag inventory cycle, one or both of: a change in a frequency of said tag interrogation signals transmitted simultaneously from said plurality of antennas, and a change in a relative phase of a said RF tag interrogation signals transmitted from one of said antennas with respect to another of said antennas.