Introduction
In the modern business environment, efficiency and accuracy are key elements for business success. Radio Frequency Identification (RFID) technology, a contactless automatic identification technology, is increasingly becoming a powerful tool for improving the efficiency of supply chain management, inventory control and asset tracking. However, traditional RFID systems face significant challenges in specific application scenarios, such as the fast and accurate reading of large numbers of densely stacked RFID tags. These challenges, often referred to as the “stacked tag” problem, can lead to read errors, inefficiencies, and even data loss.
In this paper, we will delve into the nature of the “stacked tag” challenge in HF RFID applications and highlight how the ISO 18000-3M3 protocol is an advanced solution to effectively address the challenges of dense multi-tag reading. Comparative analysis, technical details, and a concrete test case will demonstrate the performance of the ISO 18000-3M3 protocol in real-world applications, providing valuable insights for organisations seeking efficient and reliable RFID solutions.
1. The “Stacked Tag” Challenge in HF RFID
Despite the convenience that RFID technology brings, a significant challenge arises when a large number of tags are tightly stacked together in a high-frequency (HF) RFID application, i.e., the “stacked tag” problem. This problem is mainly reflected in the following aspects:
Signal interference and attenuation: In high-frequency RFID systems, tags usually use inductive coupling principles for communication. When multiple tags are closely stacked, their electromagnetic fields will interfere with each other, resulting in signal attenuation and distortion. This interaction can make it difficult for the reader to accurately recognise and read the data from each tag.
“Blind Zone” effect: In the dense stack of tags, the tags located in the middle or bottom of the stack may be completely obscured by the upper layer of tags, resulting in the reader’s signal not effectively reaching these tags, thus forming a “blind zone”, resulting in missed reads.
Limitations of anti-collision algorithms: To solve the conflict problem when multiple tags enter the reader field at the same time, RFID systems usually use anti-collision algorithms. However, in the case of extremely dense stacking, even advanced anti-collision algorithms may be difficult to effectively distinguish and identify each tag, resulting in a significant reduction in reading efficiency, or may even be unable to complete the reading.
Environmental factors: In addition to the tag’s interference, the surrounding environment of metal objects (such as metal shelves) will reflect signals, liquids (such as containers filled with liquids) will absorb electromagnetic waves, which will further exacerbate the complexity of the problem of “stacked tags”, making it more difficult to read.
These challenges are particularly acute in high-value item management, archive management, libraries, chip management, and apparel retailing scenarios that require rapid inventory of large quantities of densely arranged or stacked items. Traditional high-frequency protocols, such as ISO 15693, are often overwhelmed when dealing with such extremely dense reads and are unable to meet the efficiency and accuracy requirements of real-world applications.
2. ISO 18000-3M3 protocol: the core of the solution
To address the serious challenge of “stacked tags” in HF RFID applications, the International Organisation for Standardisation (ISO) has developed the ISO/IEC 18000 3 Mode3 (ISO 18000-3M3) protocol. The protocol is specifically designed to address high-density, multi-tag reading scenarios and the high-frequency RFID standard, which provides key solutions in the following areas:
Advanced anti-collision mechanisms: The ISO 18000-3M3 protocol uses more efficient and robust anti-collision algorithms, such as those based on EPC Gen2 HF. This mechanism more effectively manages data conflicts when a large number of tags enter the reader field at the same time, ensuring that each tag can be recognised and read independently, even when they are tightly stacked together.
Optimised communication efficiency: The protocol improves data transfer rates and efficiency by optimising the air interface communication protocol. This means that the reader can communicate with more tags in less time, which significantly improves inventory speed in dense reading scenarios.
Robustness to tag-to-tag interference: The ISO 18000-3M3 protocol was designed with the problem of tag-to-tag interference in mind, and technical measures have been taken to enhance the system’s resistance to such interference. This makes it possible to maintain a high read success rate even in the case of closely stacked tags and complex electromagnetic environments.
High read rate: Thanks to its advanced anti-collision algorithms and optimised communication protocols, the ISO 18000-3M3 reader can achieve extremely high read rates, with typical tag processing speeds of more than 200 tags per second or even higher. This is critical for applications that require a fast, accurate inventory of large quantities of items.
Suitable for Specific Application Scenarios: The ISO 18000-3M3 protocol is particularly suited for applications with high requirements for densely stacked tags, such as archive management, libraries, ticket management, jewellery inventory, gaming chip management, and item-level management in apparel retail. In these scenarios, labels are typically in the form of cards, sheets or small objects that are large and often stacked.
In short, the ISO 18000-3M3 protocol, with its innovative collision avoidance technology and efficient communication mechanisms, provides strong technical support for HF RFID to handle the challenges of dense multi-tag reading, making it ideal for solving the “stacked tag” problem.
3. Comparison of ISO 18000-3M3 with other HF protocols
In order to better understand the benefits of the ISO 18000-3M3 protocol for dense multi-tag reading, it is necessary to compare it with two other common HF RFID protocols – ISO 15693 and ISO 14443. All three protocols operate at 13.56 MHz, but they are designed for different purposes and application scenarios, especially when dealing with multi-tag collision avoidance and dense reads.
ISO 14443 protocol: It is mainly used in proximity and high-security identification scenarios, such as contactless smart cards, public transportation cards and bank cards. Its reading distance is usually within 10 cm. The ISO 14443 protocol also has an anti-collision mechanism. Still, its design focuses more on a small number of tags for rapid identification, rather than a large number of dense stacked tags for batch reading. When multiple tags enter the field simultaneously, its anti-collision algorithm is relatively inefficient and is not suitable for handling large-scale, dense reading.
ISO 15693 protocol: suitable for medium distance (usually up to 1 meter) identification scenarios, widely used in library management, asset tracking, production line management, etc. ISO 15693 also has an anti-collision function, allowing simultaneous identification of multiple tags. However, its anti-collision algorithm is significantly less efficient when dealing with a large number of tags densely stacked, and is prone to missed reads or slow read speeds. This is because the anti-collision mechanism is mainly based on algorithms such as “time slot ALOHA” or “binary search tree”, and when the number of tags increases dramatically, the conflict resolution time will increase significantly.
ISO 18000-3M3 protocol: As mentioned earlier, this protocol is specifically optimised for solving high-density, multi-tag reading problems. It uses more advanced anti-collision algorithms (such as those based on EPC Gen2 HF) to more efficiently deal with large numbers of tags in conflict and achieve higher read speeds and accuracy. The design goal is to achieve fast, stable batch reads in environments where tags are densely stacked.
The table below summarises the comparison of these three protocols in terms of key features:
| Features | ISO 14443 | ISO 15693 | ISO 18000-3M3 |
| Typical applications | Payment, access control, public transportation cards | Library, asset tracking, production lines | File management, jewelry inventory, chip management, item level management |
| Read distance | Close range (<10 cm) | Medium range (<1 m) | Medium range (<1 m), but more focused on dense read performance |
| Collision Avoidance | For small number of tags, relatively low efficiency | For medium number of tags, efficiency decreases in dense batch | Designed for dense multi-tagging, high collision avoidance efficiency, fast speeds |
| Dense reading performance | Not suitable for dense batch reading | Easy to miss reading and slow speed in dense | Excellent, can realize fast and stable batch reading |
| Protocol complexity | High | Medium | High, but optimized for dense reads |
As you can see from the table above, while ISO 14443 and ISO 15693 excel in their respective areas, when faced with the specific challenge of “stacked tags”, the ISO 18000-3M3 protocol demonstrates unparalleled strengths with its collision avoidance mechanisms and communication optimisations tailored for dense read scenarios. The ISO 18000-3M3 Protocol
4. Practical application example: intensive multi-tag reading test
To visualise the performance of the ISO 18000-3M3 protocol in solving the challenge of “stacked tags,” let’s look at a specific test example. This test simulates an extremely dense reading scenario that may be encountered in real-world applications, and is designed to verify that the ISO 18000-3M3 system can achieve fast, accurate, and stable batch reads under demanding conditions.
Test Scenario:
Tag type: 112 RFID cards compliant with ISO 18000-3M3 protocol.
Tag Thickness: Each card is only 0.36 mm thick, simulating the case of an ultra-thin card or a dense stack of tags.
Stacking method: All 112 cards are tightly stacked together to form a highly concentrated tag pile.
Reader: A desktop reader that supports the ISO 18000-3M3 protocol.
Test Objective: To achieve 100% stable reading of all 112 stacked cards within 0.5 seconds.
Test process and results:
In the test, these 112 ultra-thin ISO 18000-3M3 cards were neatly stacked and placed in the sensing area of the desktop reader. After starting the reader, the system completed the identification and data reading of all 112 cards in a very short time (0.5 seconds). The test results showed that all cards were successfully recognised, none of them were missed, the reading accuracy reached 100%, and the whole reading process was very stable.
This test result fully proved the ISO 18000-3M3 protocol in dealing with high-density, densely stacked tags with a strong ability. Its built-in advanced anti-collision algorithm and optimised communication mechanism enable the reader to effectively penetrate the interference of multi-layer tags and accurately identify each tag. Even with a large number of tags and extremely close physical proximity, the system is still able to maintain efficient and reliable performance.
Test Implications:
This test example is significant for organisations that need to handle large quantities of densely packed items, for example:
Archives management: For situations where a large number of archive boxes or documents need to be inventoried quickly, ISO 18000-3M3 can realise efficient batch reading and significantly improve inventory efficiency.
Libraries: In the case of densely stacked bookshelves, the technology enables rapid book inventory and search, reducing the complexity of manual operations.
Jewellery/Chips Management: For high-value jewellery or gaming chips, their small size and dense storage make traditional RFID difficult to manage effectively, while ISO 18000-3M3 ensures accurate inventory management.
Apparel Retail: In apparel store inventory counts, dense stacking of large numbers of apparel tags is a common phenomenon. ISO 18000-3M3 enables retailers to achieve fast, accurate inventory management at the item level.
The test results show that the ISO 18000-3M3 protocol not only theoretically solves the challenge of “stacked tags” but also demonstrates its excellent performance and reliability in practical applications, providing an efficient dense multi-tag reading solution for various industries.
Conclusion
The problem of “stacked tags” has always been a pain point in HF RFID applications, especially in scenarios that require fast and accurate identification of a large number of densely arranged or stacked items. Traditional RFID protocols often struggle to provide a satisfactory solution to this challenge. However, the emergence of the ISO 18000-3M3 protocol has brought a breakthrough to this challenge.
Through the discussion in this paper, we can clearly see that the ISO 18000-3M3 protocol, with its advanced anti-collision algorithms, optimised communication efficiency, and strong robustness to inter-tag interference, can effectively solve the challenge of “stacked tags” in high-frequency RFID applications. Whether it’s for records management, libraries, jewellery inventory, or apparel retail, ISO 18000-3M3 provides efficient, stable and accurate dense multi-tag reading.
Our test example of 112 ultra-thin ISO 18000-3M3 cards achieving 100% stable reads in 0.5 seconds is a strong testament to the protocol’s superior performance in real-world applications. This not only means that enterprises can significantly improve inventory efficiency and reduce operating costs, but more importantly, it offers the possibility of achieving finer and more real-time item management.
For enterprises seeking to improve operational efficiency, optimise inventory management and asset tracking, choosing an RFID solution that complies with the ISO 18000-3M3 protocol is undoubtedly a key step toward intelligent and efficient management. RFIDlabel is committed to providing industry-leading RFID products and solutions that meet your needs in a variety of complex application scenarios, including responding to the most demanding “stacked label” challenge. Welcome to contact us to explore the infinite possibilities of RFID technology.
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