Overcoming Interference In Real-World UHF RFID Environments
By Larry Arnstein, Ann De Vries, and Casey Hagen, Impinj

Interference is an often misunderstood factor in the design of a successful RFID solution. While interference is a real concern and does affect system performance, there are many mitigation methods that enable robust system deployments, even in noisy RF environments. This article examines how ultra high frequency (UHF) Gen 2 RFID communication presents unique interference challenges, and how they are solved in practice.

The UHF Gen 2 RFID form of radio communication has three unique aspects when considering interference mitigation.

1. UHF Gen 2 tags have limited tuning capability. The integrated circuits (chips) embedded in RFID tags must be as small and as power-efficient as possible, and they must work with all readers in every region of the world (each region has different allowed frequency ranges). These tradeoffs leave the chips more susceptible to interference from radio signals than most communication circuits. Although RFID tag chips vary widely in their ability to filter out unwanted transmissions, none have the tuning capability that you might find in a normal radio system.
2. UHF Gen 2 readers transmit at a far greater power level than needed for communication alone. RFID tags do not have their own power source, so the reader must provide sufficient energy via the communication link to power the tag, and the energy needed to power a tag is much higher than the energy needed just to communicate. As a consequence, the physical space potentially affected by an operating reader is considerably larger than that which would be affected by two normal radios communicating over a similar distance.
3. UHF Gen 2 tags transmit their signal in such a way that it is centered in the same channel as the reader with which it is communicating (and possibly the same channel as other readers in the area as well). UHF Gen 2 tags do not generate their own signal on a separate channel — they simply reflect the reader signal, adding modulation to represent their data. The signal reflected by the tag is many orders of magnitude weaker than the signals transmitted by readers.

These factors create potential for interference that may not occur in other radio communications. Yet high-performance, dense-reader applications are practical with UHF Gen 2 systems, and this article will show you why, from both the tag and reader points of view.