Collaborative RFID Reader Using CDMA Orthogonal Codes
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Solution Overview
Problem
UHF RFID systems face high read failure rates in complex multi-path environments due to reader-to-reader collision and interference, which limits the read yield and coverage area, especially when multiple readers are used.
Innovation Solution
Implementing a collaborative reader CDMA protocol that allows simultaneous broadcasting and decoding of signals by multiple readers using orthogonal codes, enhancing data synchronization and read yield rates through harmonic backscattering and software-defined radio platforms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If multiple readers are deployed to enlarge coverage area and improve read yield, then the coverage area and read yield are improved, but reader-to-reader collision and interference occur causing severe system operation problems
Solution Approach 1:
The patent segments the shared communication channel into orthogonal code channels for each reader. Each reader is assigned a unique orthogonal code, allowing simultaneous transmission without interference. This code-based segmentation enables multiple readers to operate concurrently in the same physical space without causing reader-to-reader collision, thus enlarging coverage area while maintaining system reliability.
Solution Approach 2:
The patent introduces a new dimension for signal differentiation by using code division multiple access (CDMA) with orthogonal codes. Instead of separating readers in time (TDMA) or frequency (FDMA), the system separates them in the code domain. Each reader's signal is modulated with a unique orthogonal code, allowing receivers to distinguish and decode signals from different readers simultaneously, thereby enabling expanded coverage without interference.
2Reliability
If TDMA scheme is used for reader collision resolution, then reader-to-reader collision is resolved, but tag sampling rate is limited and real-time tracking of moving tags is restricted
Solution Approach 1:
The patent enables continuous and simultaneous communication between multiple readers and tags by using orthogonal codes. Unlike TDMA which requires time-division sequencing, the CDMA approach allows all readers to transmit and receive continuously at the same time. This eliminates the time delays inherent in TDMA schemes, thereby increasing tag sampling rate and enabling real-time tracking of moving tags while maintaining collision resolution through orthogonal code separation.
3Productivity
If readers broadcast commands simultaneously to improve efficiency, then communication efficiency is improved, but tags cannot decode commands correctly due to interference
Solution Approach 1:
The patent applies local quality by assigning different orthogonal code characteristics to different readers. Each reader's signal has a unique code signature that allows selective decoding. When tags receive simultaneous broadcasts from multiple readers, they can correlate the received signal with each reader's known orthogonal code to extract commands from the intended reader while filtering out interference from other readers, thus maintaining both communication efficiency and decoding accuracy.
Data Source
AI summary
The present disclosure provides collaborative radiofrequency identification (RFID) readers that employ code division multiple access (CDMA) encoding to simultaneously broadcast to and read responses from tags in an overlapping reading zone with improved data synchronization and read yield rates. In some embodiments, a harmonic backscattering scheme is used to enable the system to have a much higher signal-to-noise ratio (SNR) and sensitivity, while the reader CDMA protocol can be integrated with an initial TDMA polling process or alternative tag CDMA scheme.