If you are familiar with RFID technology, you probably know that it uses radio waves to transmit data and facilitate communication between tags and readers. Since RF signals are radio waves, there is a great deal of interference and collision problems that we often face.
RFID readers can sometimes collide, causing interference and a whole host of troubles. Interference is also caused from metal and liquid environment.
To understand how RFID reader collisions occur, it's essential to grasp the basics. When multiple readers are nearby, they may transmit signals simultaneously. The immediate transmission can result in interference, making it challenging for the readers to receive accurate data from the tags, which results in corruption or lost data conditions and impacts the overall performance of the RFID system.
Let’s see how RFID reader collision problems occur and what solutions are available to ensure effective RFID application.
The RFID Reader Collision Problem
RFID reader collisions happen when multiple readers are located in a close location and attempt to transmit data simultaneously, leading to situations of data corruption and reduced accuracy and efficiency of an RFID system.
The reader collision mostly occurs in high volume tag reading environment where multiple handheld and fixed readers are deployed at various junctions. When multiple readers start detecting each other, it is called the RFID reader collision problem. The occurrence of ' reader collision’ is caused by the interference of one reader's signal with the search efforts of another reader trying to find a tag. It occurs in a dense reading environment, for example, in a warehouse where multiple readers are operating in the same space.
The impact of RFID reader collisions can be significant for businesses relying on RFID technology in industries like retail, logistics, and manufacturing. For example, in a retail store with multiple RFID readers, collisions can lead to inventory inaccuracies, resulting in misplaced items and frustrated customers.
Now, the main question arises: how to solve the RFID reader collision problem?
How do I solve the RFID reader collision problem?
Here I propose three main solutions that are often used in various industries to solve the RFID reader collision problem.
1. LBT (Listen Before You Talk)
Earlier in the EU region, the channels used were defined by EN 302 208 or EN 300 220. These channels were allocated to 10 high-power channels. There was a system called the Listen Before Talk (LBT) system in place. It involves a reader listening for other traffic on a channel and only transmitting a signal if the channel is free. The tag would then respond using the same channel. When there were only a limited number of readers, to be effective. To gain permission to use a certain channel, readers within a maximum radius of 1 km were not necessary because the threshold was set too low. Essentially, there could only be 10 readers operating within a 1-kilometer radius without any reduction in performance.
Let’s understand it with an example: When reader 1 is operating in a certain tag location, and at the same time, reader 2 is also operating nearer to reader 1, In that case, the reader 2 signal might interfere with the tag reading of reader 1 because a tag cannot select the operating channel by itself, and we all know that tags operate only on the power they are receiving. Stronger interrogation signals will always dominate weaker ones, leading to their failure. So, only one reader can read the specific tag population at a specific time.
2. DRM (Dense Reader Mode):
When the reader collision problem using LBT was acknowledged, the ETSI (European Telecommunications Standards Institute) introduced a new channel plan and method for multiple readers to operate in a dense reading environment known as DRM. The readers had access to only four (4) high-power channels.
Free channels are dedicated to replay tags and are kept in between high-power channels. The ETSI channel plan uses Miller sub-carrier encoding and link frequencies of 200–400 kHz to remove tags from reader channels, with the order of Miller encoding affecting spectral density to eliminate the collision issue of RFID readers.
3. EPC Gen2 standard for anti-collision mechanisms:
The EPC Gen2 (Electronic Product Code Generation 2) standard is a widely adopted protocol in RFID technology, featuring advanced anti-collision mechanisms. The anti-collision mechanism in EPC Gen2 is based on a slotted ALOHA protocol, which enables synchronized and organized communication between RFID readers and tags. It assigns a unique time slot to individual tags, and the standard minimizes the probability of signal collisions to ensure that each tag can be identified and read with precision even in crowded RFID environments.
Technology advancements have solved problems such as eliminating the LBT technique for new channel plans, DRM, and the EPC Gen2 standard for anti-collision mechanisms, increasing reading speed, preventing single readers from blocking channels, and allowing dedicated tag replay channels to block 40–120 dB lower signals.
To conclude, RFID technology is constantly evolving, with advancements aimed at overcoming the reader collision problem. LBT techniques for new channel plans and DRM are some of the ways to maintain seamless and efficient RFID operations. Various RFID manufacturing companies are aware of RFID reader collision problem and taking measures to prevent such issues in dense reading mode in high volume tag detection settings, such as retail inventory, supply chain and such.
Frequently Asked Questions
Q1) How does RFID reader collision affect tag identification?
RFID reader collisions can result in overlapping signals, making it difficult for readers to distinguish and identify individual tags. It hampers the reader's ability to effectively communicate with and retrieve data from RFID tags in a crowded RFID environment.
Q2) Can RFID reader collisions impact the overall performance of an RFID system?
RFID reader collisions can significantly impact the overall performance of an RFID system. Collisions may result in missed tag reads, leading to data inconsistencies and reduced system efficiency.
Q3) How does the number of RFID readers in an environment affect the collision probability?
The more RFID readers there are nearby, the higher the probability of collisions. As the number of readers increases, proper management strategies, such as anti-collision algorithms, become crucial to ensuring efficient and accurate communication with RFID tags.
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