RFID glossary for developers
This page explains the RFID terms used across this documentation set, written for software developers who have never worked with radio. Each entry tries to connect back to something you already know from the software world. Skim it once before the deployment guide; after that, return whenever a term looks unfamiliar.
Identity and tag data
EPC
Electronic Product Code: the identifier of an individual item, stored in the tag's memory and the field the reader returns most. It differs from a barcode in that a barcode identifies a product type, while an EPC identifies the individual: a hundred identical shirts carry a hundred different EPCs. For a developer, the EPC is the row's primary key, while the barcode is a foreign key pointing at the product table. How to generate them per the GS1 standard lives in EPC encoding.
TID
Tag Identifier: the chip manufacturer's serial number burned into the tag at the factory, unchangeable. The EPC is written by you and can be rewritten; the TID is like a phone's IMEI, welded to the hardware. It matters when you need anti-counterfeiting or to tell apart two tags that accidentally carry the same EPC.
PC word
Protocol Control word: a 16-bit block sitting next to the EPC in tag memory, stating how long the EPC is plus a few protocol flags. You almost never touch it directly: the SDK reads the PC word to know where the EPC ends, much like a response's Content-Length header.
RSSI
Received Signal Strength Indicator: the signal strength of a read, telling you how "loudly" the tag was heard. Higher usually means closer, but it is a rough estimate, bent by nearby metal and liquids, so never treat RSSI as a precise distance measure. A note specific to this SDK: the raw value ranges 0 to 255, not dBm; raw 128 is roughly -65 dBm.
Phase
The phase angle of the wave reflected from tag to antenna, in radians. Advanced locating systems use phase to estimate tag movement; a normal warehouse integration does not need the field and can ignore it.
Reading tags
Inventory
In SDK documentation, "inventory" is the reader's scan loop: continuously asking "which tags are in the zone right now" and pushing the answers back. Do not confuse it with the stock count operation in Easy Inventory, which is a business process with sessions and approvals. One run of the business stock count consumes a great many reader inventory rounds.
Read zone
The space where a tag receives enough energy to answer the reader. It is not a neat sphere around the antenna: the real shape depends on power, the antenna, the goods, and obstacles, and it changes per site. That is why this documentation keeps repeating: measure the zone with real goods at the installation spot instead of trusting datasheet figures.
Antennas and the antenna mask
One reader drives several antennas, each covering an area, say one dock door. The antenna mask is a bitmask parameter selecting which antenna ports join the read round, much like enabling individual consumers in a group. Keep the antenna_id on every tag event so you know which area a read came from.
Session and the inventoried flag
A Gen2 mechanism letting tags "briefly remember" they were counted. Each tag keeps an inventoried flag per session; once read, it flips the flag and stays quiet a while, so the reader is not re-counting the same tags in a dense population. For a developer, it resembles a message queue's visibility timeout: a received message temporarily disappears from the queue.
Q
A parameter of the Gen2 anti-collision algorithm, setting how many time slots tags draw from when answering. Low Q suits small populations, high Q suits dense ones: essentially the backoff parameter of a collision-avoidance protocol. Being off by a step or two usually still works, just slower; many reader firmwares tune it automatically.
Singulation
The process of the reader isolating exactly one tag in the zone to work with, mandatory before writing an EPC. Writing without singulation, with two tags present, means not knowing which tag you just overwrote.
Tag starvation
When one strong tag, usually right next to the antenna, hogs the air so weaker tags cannot get a word in. The symptom: total reads stay high while unique EPCs come in below the real item count. The cures are in the deployment guide: adjust the session, cycle antennas, lower power.
Radio and environment
Polarization
The orientation of the wave the antenna emits. A linear antenna concentrates energy in one orientation, reading farther but caring how tags are oriented; a circular antenna tolerates tags stuck sideways or upright, trading a little range. If tags go on goods every which way, pick circular.
Near field and far field
Two antenna styles for two distances. Near field reads close, within tens of centimeters, with a compact and predictable zone, suiting tagging stations and smart shelves. Far field reads out to several meters, suiting dock doors and conveyors. Pick the wrong style and you either fail to cover, or read into the neighboring area.
Duty cycle and LBT
Two kinds of legal transmission constraints that vary by country: duty cycle caps the fraction of time you may transmit, while LBT (listen before talk) requires the reader to hear a clear channel before transmitting. They are radio regulations, not performance options, so the first step of every deployment is pinning down the legal band and channel list for the site.
Dense Reader Mode
A reader transmission mode for environments where several readers operate near each other, trading some speed for the ability to coexist without cross-interference. From a handful of readers in one warehouse upward, plan for it, together with channel assignment and staggered scan timing.
Read next
- What to know before deploying RFID: how these concepts combine into a data model.
- RFID deployment guide: where the radio and environment terms drive installation decisions.