RFID Transponder Localization via Frequency Offset
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Solution Overview
Problem
Existing transponder counting and localization technologies are unable to effectively handle unmodified transponders that transmit at a common carrier frequency and experience signal collisions, particularly in the absence of a media access control (MAC) protocol, limiting their application in toll collection and other smart city uses.
Innovation Solution
The method involves an RFID reader that processes concurrently triggered response signals from transceivers with distinct carrier frequencies, using spectral peak analysis and phase rotation properties of the Fourier transform to distinguish and count transponders, and determine their spatial locations, even in the presence of signal collisions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If highly directional antennas in isolated areas are used to prevent signal collisions, then signal collision is avoided, but device complexity and installation requirements increase
Solution Approach 1:
The patent changes the frequency parameter of the transponders by introducing intentional frequency offsets to each transponder. This allows multiple transponders to transmit simultaneously at different frequencies without collision, eliminating the need for highly directional antennas and isolated area requirements.
2Speed
If multiple transponders transmit simultaneously at the same carrier frequency, then response time is reduced, but signal collision occurs making detection difficult
Solution Approach 1:
The patent segments the single carrier frequency into multiple distinct frequency channels by assigning each transponder a unique frequency offset. This segmentation allows simultaneous transmission without collision, as each transponder occupies a different frequency segment of the spectrum.
Solution Approach 2:
The patent moves the differentiation from the time domain (sequential access) to the frequency domain (parallel access). By adding the frequency dimension as a new degree of freedom, multiple transponders can transmit simultaneously without interfering with each other.
3Reliability
If MAC protocols are implemented to manage transponder communication, then signal collision is avoided, but device complexity and protocol overhead increase
Solution Approach 1:
The patent extracts the collision avoidance function from the MAC protocol layer and implements it at the physical layer through frequency offset assignment. This eliminates the need for complex MAC protocols, timing coordination, and retry mechanisms, simplifying the overall system architecture.
4Ease of manufacture
If transponders operate at a common carrier frequency, then manufacturing simplicity is maintained, but counting and localization accuracy deteriorates due to signal overlap
Solution Approach 1:
The patent introduces frequency offset as an additional manufacturing parameter that is easily incorporated into the transponder design. This small parameter change enables accurate counting and localization through spectral analysis while maintaining manufacturing simplicity, as the frequency offset can be applied through standard frequency synthesis techniques.
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 enables accurate counting and localization of transponders without MAC protocols, allowing for broader applications such as traffic management and parking management, by leveraging manufacturing variations in transponder frequencies to differentiate between overlapping signals.
Implementation Method 1
determining characteristics of the number of transceivers based on the carrier frequencies of the transceiver response signals
Implementation Method 2
at least some of the transceivers have distinct transmit carrier frequencies offset from the channel carrier frequency
Data Source
AI summary
A method processes a concurrently triggered response signal at a number of transceivers configured to operate at a channel carrier frequency, where at least some of the transceivers have distinct transmit carrier frequencies offset from the channel carrier frequency. The method includes receiving, at a first receiver, a response signal in response to a trigger signal, the response signal including a combination of a number of transceiver response signals, each transceiver response signal of the number of transceiver response signals corresponding to a different transceiver of the number of transceivers and having a distinct transmit carrier frequency, wherein at least some of the transceiver response signals overlap in time, and determining characteristics of the number of transceivers based on the carrier frequencies of the transceiver response signals, including determining a number of transceivers in the number of transceivers.