Two-State Symmetric Protocol for RFID Tag Identification
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Solution Overview
Problem
Existing RFID tag interrogation systems face challenges in efficiently re-inventorying tags that were initially in a quiet state, as they may miss tags due to unfavorable multipath conditions, distance, or power fluctuations, leading to incomplete identification and potential interference issues.
Innovation Solution
The implementation of a two-state symmetric protocol allows tags to maintain persistent states (State A and State B) that persist for at least 20 seconds, enabling re-inventory without power, with commands like QuietA and QuietB ensuring tags are addressed and identified in subsequent rounds, even if initially missed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a ready-quiet protocol is used to inventory tags, then tags can be read one at a time, but tags in quiet state may be missed due to timeout or failed wake-up commands
Solution Approach 1:
The patent implements dynamic state management where tags transition between State A and State B based on persistent node values. The system dynamically adjusts which state is active based on the least recently used state, ensuring tags remain accessible without fixed timeouts. This dynamic approach resolves the contradiction by making the quiet state duration adaptive rather than static, preventing tags from being permanently missed while maintaining efficient inventory operations.
Solution Approach 2:
The patent changes the parameter of state persistence by implementing a persistent node that maintains state information across power cycles. Instead of using fixed timeout periods, the system uses the persistent node to track state A and state B, allowing tags to maintain their state indefinitely until explicitly changed by a command. This parameter change from time-based to state-based management ensures complete tag identification without time loss.
2Reliability
If a persistent quiet timeout is used, then tags remain in quiet state for a fixed duration, but manufacturing tight control of persistence time is difficult and time duration is insufficient for large inventories
Solution Approach 1:
The patent uses a persistent node that copies and stores state information (State A or State B) in non-volatile memory. Instead of relying on precise manufacturing of timeout circuits, the system copies the state value and preserves it indefinitely. This copying approach eliminates the need for tightly controlled persistence time in hardware, as the state is maintained through data storage rather than physical timing mechanisms, greatly simplifying manufacturing.
Solution Approach 2:
The patent replaces the mechanical/timing-based persistent quiet mechanism with a data-based persistent node system. Instead of using hardware timers or RC circuits that require precise manufacturing tolerances, the system uses memory storage to maintain state information. This substitution of mechanical timing with digital data storage eliminates manufacturing complexity while ensuring reliable state persistence.
3Productivity
If tags are placed in quiet state after inventory, then continuous monitoring can be performed, but tags may be missed if they remain in wrong state for extended periods
Solution Approach 1:
The patent implements periodic state reversal where the system alternates between inventoring tags in State A and tags in State B. By periodically switching which state is active for inventory, the system ensures that tags previously in quiet state become accessible in subsequent cycles. This periodic action maintains continuous monitoring capability while preventing tags from being permanently missed, as each state reversal brings previously quiet tags into an accessible state.
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 the performance of RFID tag identification by ensuring all tags can be inventoried timely and accurately, reducing missed tags and interference, and allowing continuous monitoring of tagged items.
Implementation Method 1
RFID tags which may be powered by the RF energy
Data Source
AI summary
An apparatus and method to identify devices including a first set of commands to identify devices in a first state and a second set of commands to identify devices in a second state, wherein devices identified in the first state are placed in the second state and devices identified in the second state are placed in the first state.