Puck the Canucks!
Posted by P. Krishna on Thu, Jun 16, 2011
Well, that’s not a very sensitive blog title – eh! As a Bruin fan living in the heart of hockey Boston, that’s the best I can do! However, thankfully for the RFID industry, some of the RFID readers have been designed to be very sensitive.
A forward link limited system is limited by the receive sensitivity of the tag and hence beyond a certain distance there is not enough RF energy incident on the tag to energize it and then subsequently backscatter its response. On the other hand, a reverse-link limited is limited by the receive sensitivity of the reader, and hence beyond a certain distance between the tag and the reader, the reader is not able to decode the tag responses correctly. Passive UHF RFID systems are typically forward link limited. That is because the state-of-the-art reader manufacturers have done a very good job in designing in sufficiently high dynamic range such that a reader is never backscatter limited for passive UHF tags. The dynamic range of the state of the art UHF reader is about 120dB and improving. A 120dB dynamic range gives a RF link budget of 60dB each way – thus, starting at a transmit power 30dB with a 6dB gain (in FCC) and the forward link budget of 60dBm, the limiting receive signal strength at the tag is -24dBm, which is much lower than the receive sensitivity of the best tag available in the marketplace of -20dBm. For most of the implementations, the bottleneck with conventional UHF readers and passive tags, is the forward link to the tag as of now.
However, we have encountered a number of scenarios where better reader sensitivity was the recipe required for a robust and reliable RF layer. Couple of those scenarios includes:
- Reading set of densely packed tags moving through a chokepoint: Such situations occur quite often in many verticals including IT asset tracking and healthcare. Better reader sensitivities helped in taking the read success from 90% to 99.995%.
- When using BAP tags: The receive sensitivity of the state of the art BAP tag is -30dBm. This means that even at the limit (or the reader’s dynamic range) and beyond it, the BAP tag can be powered and respond to the reader’s signal. This means that the system becomes reverse-link limited when interrogating BAP tags. This places stress on the design and implementation of the reader’s receive path.
As tag designs continue to improve, the reader designs need to continue to improve their dynamic range performance. This will help the RFID industry as a whole by maximizing the performance in terms of read range, reliability and immunity to interference.
Go Bruins!