While using an RFID system it is absolutely necessary to avoid interference from multiple tags when interrogated by an RFID Reader. An RFID Reader can read multiple RFID tags at once without a clear line of sight as RFID communication happens through electromagnetic fields and radio frequency signals. Radio waves travel freely from the reader to the tag and from the tag to the reader. In order to avoid interference and read the RFID tags on assets within a selected range of the reader, one must focus on RSSI Value.
RSSI value, which is short for Received Signal Strength Indicator, is a standard feature of every localization solution based on wireless communication. It is a crucial parameter for estimating target coordinates and helps with the accurate localization of tagged assets.
What is RSSI Value in an RFID System?
In simple terms, the RSSI value simply denotes the power of the signal received from the tag when interrogated by an RFID reader. If the RFID reader and tag are closer, the RSSI value is higher. For a typical RFID tag, the RSSI value range is approximately -30dBm to -80dBm. Which is basically a millionth part of the original power out being returned to the reader (typical signal strength is around 1 watt or 30 dBm). So, RSSI only gives an estimate of how close a certain RFID tag is to a reader. RSSI is measured in dBm (decibel milliwatt ) and a high value denotes a strong signal. So, the -30 dBm RSSI signal will be stronger than the -40 dBm one.
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RSSI Filters and How to Read or Write an RFID Tag within a Range?
While using an RFID system for a business solution if you want to read a specific RFID tag or RFID tagged assets within a certain read range of the reader. To overcome interference from other RFID tags nearby and from other materials in the environment, say metal, liquid, etc., you can adjust RSSI filters to have the reader respond to desired RFID-tagged assets within the range.
For writing on an RFID tag, the RSSI value needs to be higher, meaning the tag and the reader should be closer and maximum (signal) power should backscatter from the tag to the reader.
RSSI filters are also important in retail and warehousing operations where we need to only scan RFID tags and tagged assets in specific zones. RSSI filters and correct tag reading settings help optimize the overall RFID operations. It improves RFID tag detection and prevents collision issues.
You can use the min RSSI and max read range settings and the max RSSI and the min read range setting to find an appropriate level of RSSI and read range for optimal tag reading and writing.
In active RFID systems, the RFID tag continuously transmits the signals and RSSI becomes very crucial in localization applications and RTLS systems based on Active RFID tags. Here, RSSI value is directly proportional to the distance between the RFID tag and the antenna.
Factors that affect RSSI Value
To accurately find an RFID tag, the RSSI values should be higher. RSSI can vary due to many factors including the distance between the reader and the tag, environment, metals and liquids, tag orientation with respect to the reader, etc. Moreover, the type of material the tag is attached to, the height between the reader and the tag, walls, and other constructions that block signals also affect the RSSI value.
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Benefits of using RSSI Value and RSSI Filter Settings
Understanding how RSSI value works and how it affects tag detection is crucial. RFID systems optimized with correct RSSI value offer great tag detection and accurate reading of crucial information in businesses.
1.RSSI value helps with measuring the distance between the tag and the reader.
2. It also helps with detecting the correct direction of the movement of the tag and the reader.
3. It can help locate lost tagged assets, i.e. RFID item-finding mode.
4. RSSI can also help with setting up an optimal tag reading and writing environment.
To conclude, the RSSI value is a crucial indicator of how well the reader can detect the tag in the vicinity and by adjusting the RSSI value and settings, one can optimize RFID systems to detect the desired tags and tagged assets and offer accurate information to the end users.
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