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# Glossary

This section of the ITK-C documentation explains common terms in RFID, RF systems, and embedded electronics. It also provides cross-references to relevant sections of the ITK-C documentation.

The glossary terms are grouped together by topic:

Glossary Sections:

- Glossary
  - RFID Terminology
  - RF Terminology
  - Impinj Terminology
  - Programming Terminology
  - Electrical Units

## RFID Terminology

The following terms are specific to RFID.

Access

  Access is the third operation performed by a reader on a population of tags, after they are configured by a select operation, and read by an inventory operation.

  The access operation allows the reader to read or write to arbitrary locations in tag memory, as well as perform other commands, such as lock, kill, etc.

  For more information about configuring the access operation in IRI, see the Access configuration example.

Active Tag

  A tag which has a power source independent of excitation by a reader, and is capable of actively transmitting data back to the reader instead of simply using backscatter. These tags have both a better forward link and reverse link than a passive tag.

  This is the most complex and least common type of tag in use in UHF RFID.

Backscatter
  The method by which UHF RFID tags modulate the reader transmitted carrier wave to implement a reverse link. Tags contain a switchable load that allows them to selectively absorb and reflect the CW using their antenna.
Backscatter Link Frequency
BLF
Link Frequency
LF

  The frequency at which the tag signals back to the reader by backscattering during Tag to Reader Modulation. Also known as Subcarrier Frequency. Usually specified in kHz.

  In FM0, where a single symbol represents a single bit, the Backscatter Link Frequency is equal to the Data Rate.

  In higher order Miller encoding schemes, where multiple symbols represent a single bit, the Backscatter Link Frequency is equal to the Data Rate times the Miller Number.

  BLF is a parameter of the Reverse Link portion of the Link Profile.

Battery Assisted Passive Tag
BAP Tag

  A tag which has a power source independent of excitation by a reader, but is still only capable communicating to the reader via backscatter. These tags have a better forward link than a passive tag, but the same reverse link.

  This is a moderately complex and uncommon type of tag in use in UHF RFID.

BlockPermalock

  A feature of RFID tags that allows specific blocks of their memory contents to be permanently locked using a BlockPermalock command so that they cannot be modified ever again.

  For more information on permalocking memory blocks with IRI, see the BlockPermalock configuration example.

BlockWrite

  A command that can be used as part of an access operation to write multiple values to tag memory.

  To write a single word to tag memory, the Write command may be used instead.

  For more details on writing tag memory with BlockWrite, see the Write configuration example.

Carrier Wave
CW

  Carrier wave describes a reader transmitted signal at the configured channel or frequency without any forward link modulation. CW allows tags to backscatter the reverse link, or simply stay energized and maintain their flag state, for example.

  For information on how to use test commands to transmit CW in IRI, see the CW configuration examples.

Channel

  A specific operating frequency within a given region‘s frequency band. Regions specify a list of channels within which readers must hop from one to the next at a set rate.

  For more details, see the regulatory regions documentation.

Command

  Each Gen2 UHF RFID operation is made up of one or more commands.

  For more detail about commands, see the Gen 2 UHF RFID EPC UHF Gen2 Air Interface Protocol specification.

Dense Reader Mode
DRM

  A category of RF Modes where RFID readers and tags are configured to minimize out-of-band interference with other readers and tags, enabling many readers to operate in the same physical location.

  For more information on the Indy Modules‘ RF Modes, see the key E_IPJ_KEY_RF_MODE and the configuration example RF Modes.

Divide Ratio
DR

  Specifies the Backscatter Link Frequency by instructing the tag how to interpret the TRcal symbol portion of the Query preamble.

  The tag sets its BLF by dividing the divide ratio by the TRcal symbol length. The DR is communicated by the reader as part of the Query command.

Double Sideband - Amplitude Shift Keying
DSB-ASK

  DSB-ASK is one of the two possible methods of Reader to Tag Modulation defined by the configurable Link Profile.

  DSB-ASK has more waveform transitions and thus increased bandwidth relative to PR-ASK.

Electronic Product Code
EPC

  One of the contents of the EPC memory bank on an RFID tag that is often used to store a unique identifier or other data. Different tags have different EPC sizes.

  For more information on how to read EPCs using IRI, see the Reading EPCs configuration example.

EPC Memory

  UHF RFID tag EPC memory, in bank `0b01`, contains a tag’s EPC, as well as the StoredPC, StoredCRC, and the optional extended protocol(XPC) words.

  For more information on reading tag EPCs using inventory operations in IRI, see the Reading EPCs configuration example.

  For more information on reading tag memory banks using the access operation in IRI, see the Access configuration example.

European Telecommunications Standards Institute
ETSI

  A European regulatory body that governs electronic emission of signals by radios.

  Also used as shorthand for the regulatory region ETSI EN 302 208-1, which occupies the frequency band of 865-868 MHz.

  For more details on the ETSI region, see the Region documentation.

Federal Communications Commission
FCC

  A US regulatory body that governs electronic emission of signals by radios.

  Also used as shorthand for the regulatory region FCC 15.247, which occupies the frequency band of 902-928 MHz. The FCC region operates within the ISM (Industrial, scientific, and medical) frequency band.

  For more details on the FCC region, see the Region documentation.

Flag

  UHF RFID tags have five flags, one selected flag and four session inventoried flags. The selected flag has an asserted and a non-asserted state. The session inventoried flags have an `A` and a `B` state. These flags are useful for tag population management using search modes.

  Tags have a certain specified flag persistence, which varies with each session. This persistence is specified broadly within the Gen2 spec, and more precisely in specific tag datasheets. Impinj’s Monza tag chip datasheets can be found on Impinj’s support portal here: https://support.impinj.com/hc/en-us/categories/200156298

FM0
M=1

  A Tag to Reader Modulation scheme where the Miller Number is equal to one, meaning each bit is communicated using a single symbol.

  This is the fastest but least reliable method of Tag to Reader Modulation.

  Miller Number is a parameter of the Link Profile.

Forward Link
R=>T Link
Reader to Tag Link

  The RF link by which UHF RFID readers power and communicate with tags.

  Readers transmit this signal at a configured transmit power using one or more antennas. An RFID system is said to be “forward link limited” if tags are not powered sufficiently by the electromagnetic signal transmitted by the reader.

  Forward link parameters include: R2T Modulation, TARI, and RTcal.

  The communication parameters of this link are specifed by the Forward Link portion of the Link Profile.

Gen2
EPC Gen2

  The protocol used by UHF RFID readers and tags to communicate with one another. Defined by GS1. Impinj’s readers and tags implement the Gen2 spec, and meet all of its mandatory requirements.

  For more details, see GS1’s EPC UHF Gen2 Air Interface Protocol spec.

Gen2v2
EPC Gen2v2

  An updated version of the Gen2 spec for UHF RFID. This version of the spec adds some new features, such as cryptography. Gen2v2 readers and tags are also Gen2 compliant. This means that Gen2 readers can read Gen2v2 tags, and Gen2v2 readers can read Gen2 tags.

  For more details, see the EPC UHF Gen2 Air Interface Protocol spec.

Handle
  A random 16-bit number generated by an individual tag in response to a Req_RN command, replacing the tag’s RN16 as a unique identifier for use by the reader.
Hop
  A transition from one channel to another by an RFID reader. Occurs automatically between inventory rounds and access operations, and will briefly cause the carrier wave to be interrupted, which may cause tag state to change. Region configuration will set the maximum time between hops.
Inventoried Flag

  Four of the flags implemented by UHF RFID tags. Tags maintain one inventoried flag for each of the four sessions. These flags are useful for population management using the select operation, and different search modes.

  Each session’s inventoried flag has two states: `A` and `B`. After reset, tags’ inventoried flags reset to the `A` state.

  For more information on flags and search modes, see this blog post on Impinj’s support portal: https://support.impinj.com/hc/en-us/articles/202756158

  To configure the search mode of an inventory operation in IRI, use the E_IPJ_KEY_INVENTORY_SEARCH_MODE key.

Inventory

  Inventory is the second operation performed by a reader on a population of tags after they are configured by a select operation, and before an access operation can be performed. During the inventory operation, selected tags respond to the reader with their EPC and other memory contents.

  For more information about configuring the inventory operation in IRI, see the Inventory configuration example.

Kill

  A feature of UHF RFID tags that allows them to be permanently disabled using a kill command as part of an access operation, along with the proper kill password.

  For more information on killing tags using the access operation in IRI, see the Kill configuration example.

Link Budget
  An RFID system’s link budget is a summation of the elements of the signal chain between the reader transmit and receive ports, including the forward link, tag backscatter, reverse link, etc. In a working RFID system, the sum of the gains and losses should be smaller than the difference between the transmit power and the receive sensitivity.
Lock

  A feature of UHF RFID tags that allows specific blocks of their memory contents to be temporarily locked using a lock command so that they cannot be modified until unlocked.

  For more information on locking memory blocks with IRI, see the Lock configuration example.

Memory Bank
Memory

  Information stored on RFID tags is broken up into memory banks which can be read and written to using the inventory and access operations, and used as select operation criteria.

  Tag memory is broken up into four blocks: Reserved Memory, EPC Memory, TID Memory, User Memory, in that order.

  For more information on accessing tag memory, see the Read and Write configuration examples.

Miller Number

  Miller Number is the number of symbols per bit transmitted in the Tag to Reader Modulation Miller sub-carrier coding scheme. In Gen2 UHF RFID, Miller Number can be as low as 1, and as high as 8, but is always a power of 2 (eg M=1, 2, 4, or 8).

  Higher Miller Numbers result in a lower symbol error rate, but slower tag to reader communication.

  Miller Number is a parameter of the Link Profile.

  The Tag to Reader Modulation Data Rate is equal to the the Backscatter Link Frequency divided by the Miller Number.

Operation

  A step performed by a reader to manage and interact with tag populations. Each operation is comprised of multiple commands. There are three operations: Select, Inventory, and Access, which are performed in that order.

  For more detail about operations, see the Gen 2 UHF RFID EPC UHF Gen2 Air Interface Protocol specification.

Passive Tag

  A tag which is only ever powered by the excitation of its antenna by a reader. Only communicates with the reader via energy backscatter.

  This is the least complex and most common type of tag in use in UHF RFID.

Password

  Tag memory values that allow some tags to selectively restrict their behavior.

  The access password allows preventing reads to or writes from tag memory.

  The kill password allows readers to kill tags so that they can no longer be read. Tags do not execute the kill command unless the password is correct and also non-zero.

  Not all tags implement the access and kill passwords.

  Both access and kill password values default to `0`. The access and kill passwords are stored in reserved memory. They can be written using the access command.

Phase Reversal - Amplitude Shift Keying
PR-ASK

  PR-ASK is one of the two possible methods of Reader to Tag Modulation defined by the configurable Link Profile.

  PR-ASK has fewer waveform transitions and thus reduced bandwidth relative to DSB-ASK.

Population Estimate

  Indy reader modules have a configurable population estimate which allows them to inventory a population of tags as quickly as possible by automatically setting an appropriate Q value.

  This population estimate should be set as close to the actual number of tags in the field as possible for optimal performance. A population estimate that is too high or too low will increase the amount of time it takes to inventory all of the tags in the field.

  Configure the population in IRI using the key E_IPJ_KEY_INVENTORY_TAG_POPULATION.

Pseudo-random Bitstream
PRBS

  A waveform that can be transmitted by a UHF RFID reader for testing purposes. This waveform starts as a string of random bits, and is then modulated onto the operating frequency according to the selected RF Mode.

  For information on how to use test commands to transmit PRBS in IRI, see the PRBS configuration examples.

Pulse Interval Encoding
PIE

  The method of data encoding used in the Reader to Tag Link, PIE involves using pulses of different lengths to signal 0s and 1s.

  PIE is used in all configurations of UHF Gen2 RFID because it guarantees power delivery above a certain minimum amount to tags in the field.

Q

  A parameter of the query command in the inventory operation. The Q value sets the number of response slots in the slotted aloha protocol, and tags assign themselves to slots randomly.

  In IRI, Q values are not set directly, but rather indirectly using the population estimate key E_IPJ_KEY_INVENTORY_TAG_POPULATION.

Query
Query Command
  The query command is the first command sent by readers during the inventory operation. This command instructs tags on how to respond to the reader, including RF Mode configuration, session and target, and Q value.
Radio Frequency Identification
RFID

  A family of technologies that use radio frequency wireless communication between a high powered reader and a passive tag to create a system for applications including authentication, access control, ticketing, and many others.

  RFID standards exist in three frequency bands: LF, HF, and UHF. Impinj makes UHF RFID tags and readers.

RAIN

  An industry alliance promoting UHF RFID standards and products.

  For more information about the RAIN alliance, see their website at http://rainrfid.org/.

Read

  A command that can be used as part of an access operation to read out values of tag memory.

  To read specific contents of memory out of a tag, use the access operation.

  For more details on reading tag memory, see the Read configuration example.

  The term “Read” is also sometimes used to describe inventory of tags.

Read Sensitivity

  A tag‘s read sensitivity is the lowest received power with which the tag can operate and backscatter in response to inventory and access commands.

  If a tag in a system cannot be powered at a level at or above its read sensitivity, the system is said to be forward link limited.

  Just because a tag’s read sensitivity requirement is met, and it is able to operate and backscatter a signal, does not mean that the reader will be able to receive that signal. In a system where the tag is backscattering a signal, but that signal does not meet the reader’s receive sensitivity requirement, the system is said to be reverse link limited.

  Tags’ read sensitivity can be found in tag datasheets. Impinj’s Monza tag chip datasheets can be found on Impinj’s support portal here: https://support.impinj.com/hc/en-us/categories/200156298

Reader
Interrogator

  In UHF RFID systems, the reader is the device that both powers the tags and also communicates with and configures them. A complete reader will include both the reader electronics and one or more antennas, as well as additional control or peripheral hardware, software, and logic.

  Impinj makes a variety of readers, including Indy embedded reader chips and modules, Speedway fixed readers, and xArray gateways.

  The terms reader and interrogator are used interchangeably.

Reader to Tag Calibration Symbol
RTcal

  A symbol that is communicated by the reader to the tag to specify the combined time to communicate both a `0` and `1` symbol using PIE. This symbol is used by the tag to calibrate the threshold between `0` and `1` symbols. Duration is measured in μs. The RTcal symbol is transmitted during the Query preamble, as well as during frame-syncs.

  RTcal is a parameter of the Forward Link portion of the Link Profile.

Reader to Tag Modulation
R2T Modulation
R=>T Modulation

  The method of forward link communication between the reader and tag. R2T Modulation is either PR-ASK or DSB-ASK, with data encoded using PIE, and occurs at a rate specifed using TARI and TRcal.

  R2T Modulation parameters are specifed by the Forward Link portion of the Link Profile.

Receive Sensitivity

  This is a measure of the lowest power of signal from a tag that can be received and understood by an RFID reader. Usually expressed with units of dBm. The receive sensitivity of the Indy Modules are listed in the Indy Module Datasheets.

  When describing tag sensitivity, the terms read sensitivity and write sensitivity are used.

Regulatory Region
Region

  A geographic area with a specific frequency band and channel list, along with other regulatory guidelines, such as out of band or spurious emissions standards.

  For more details, see the regulatory regions section of the ITK-C documentation.

Reserved Memory

  UHF RFID tag reserved memory, in bank `0b00`, contains a tag’s kill and access passwords, if they are implemented.

  For more information on reading and writing tag memory banks using the access operation in IRI, see the Access configuration example.

Reverse Link
T=>R Link
Tag to Reader Link

  The RF link by which UHF RFID tags communicate with readers.

  Tags backscatter this signal on top of the reader’s transmitted carrier wave. If this link is not strong enough to meet the receive sensitivity specifications of a reader, tags will not be read. An RFID system is said to be “reverse link limited” if tags are powered by the reader, but cannot be read by it due to sensitivity limitations.

  Reverse link parameters include: T2R Modulation, BLF, and TRcal.

  The communication parameters of this link are specifed by the Reverse Link portion of the Link Profile.

RF Mode
RF Profile
Link Profile

  The RF mode is made up of timing and RF parameters of the forward link and reverse link used by UHF RFID readers and tags. The reader configures its own forward link parameters, and communicates both the forward link and reverse link parameters to the tags in the field using both the preamble and fields in the query command.

  For more information on using RF modes with IRI, see the key E_IPJ_KEY_RF_MODE and the configuration example RF Modes.

RN16
  A random 16-bit number generated by each tag at the start of an inventory. Tags use the RN16 to uniquely identify themselves to the reader.
Search Mode

  Search modes allow UHF RFID readers to manage tag populations by using a specific session. Readers do this by setting the target inventoried flag for select and query commands.

  Multiple readers can independently manage tag populations by using their own sessions. This way the actions of one reader have no impact on the session inventoried flags being used by other readers.

  For more information on search modes, see this blog post on Impinj’s support portal: https://support.impinj.com/hc/en-us/articles/202756158

  To configure the search mode of an inventory operation in IRI, use the E_IPJ_KEY_INVENTORY_SEARCH_MODE key.

Select

  Select is the first operation performed by a reader on a population of tags to prepare them for the inventory and access operations. Select is also the name of a command that can be performed during the select operation. The select operation moves tags to the “ready” state, and may alter the values of their inventoried flag and selected flag based on certain criteria.

  For more information about configuring the select operation in IRI, see the Select configuration example.

Selected Flag

  One of the flags implemented by UHF RFID tags. Tags maintain a single “selected” flag that is useful for population management using the select operation.

  This flag has two states: asserted and non-asserted.

  For more information about using the selected flag by configuring the select operation in IRI, see the Select configuration example.

Session

  UHF RFID tags have four different sessions, numbered session 0 (S0) through session 3 (S3). Each session has its own inventoried flag. Having four unique session inventoried flags allows individual tags to maintain a different state for multiple readers, which is useful for population management. The sessions vary in their inventoried flag persistence, as described in the Gen2 spec, and more precisely in specific tag datasheets.

  For more details on population management, see the search mode.

Tag
Transponder

  In UHF RFID systems, the tag is the device that is powered by and communicates in response to the reader. Tags communicate with readers by backscattering the signal transmitted by the reader, rather than transmitting a signal themselves. Most tags are passive, and contain no internal power source, operating only when powered by a reader. Tags never initiate communication with a reader, only communicating when instructed to by reader operations.

  Tags are usually made up of a tag integrated circuit and an antenna. Impinj makes the Monza and Monza X tag integrated circuits, but does not build complete tags.

  There are three varieties of tags by power: Passive Tag, Battery Assisted Passive Tag, Active Tag.

Tag to Reader Calibration Symbol
TRcal

  A symbol that is communicated by the reader to the tag to specify the Backscatter Link Frequency, in conjunction with the Divide Ratio. Duration is measured in μs. The TRcal symbol is transmitted during the Query preamble.

  TRcal is a parameter of the Reverse Link portion of the Link Profile.

Tag to Reader Modulation
T2R Modulation
T=>R Modulation

  The method of reverse link communication between the tag and reader. T2R Modulation uses Miller sub-carrier coding by the tag, at the Backscatter Link Frequency. The number of symbols per bit is specified by the Miller Number. T2R Modulation data rate is set by BLF divided by the Miller Number.

  T2R Modulation parameters are specified by the Reverse Link portion of the Link Profile.

Target

  The target parameter of the select and query commands configure tag behavior with regards to session inventoried flags.

  The select command’s target value can be any of the 4 session inventoried flags, or the selected flag. This value determines which flag is set by the select command.

  The query command’s target value can be either of the potential flag states: `A` or `B`. This desired state, along with the session and selected parameters will determine which tags respond to the query and thus the entire inventory operation.

  For more information on configuring the select operation using IRI, see the Select Parameters configuration example.

  For more information on configuring the query command and thus the inventory in IRI, see the Inventory Parameters configuration example.

TID Memory

  UHF RFID tag TID memory, in bank `0b10`, contains a data that can be used to identify a tag’s model, as well as to uniquely identify the individual tag.

  For more details on tag TIDs, see the tag datasheet for the particular tag model in question. Impinj’s Monza tag chip documentation can be found on Impinj’s support portal here: https://support.impinj.com/hc/en-us/categories/200156298

  For more information on reading and writing tag memory banks using the access operation in IRI, see the Access configuration example.

  TID Memory on some Monza tags can also be read during inventory (without an access operation) using the FastID functionality.

Type A Reference Interval
TARI

  A symbol that is communicated by the reader to the tag to specify the forward link rate. Duration is measured in μs. The TARI symbol is transmitted during the Query preamble, as well as during frame-syncs.

  TARI is a parameter of the Forward Link portion of the Link Profile.

Ultra-high Frequency
UHF
  The type of RFID used by Impinj products, also known as RAIN RFID. The FCC region is within the ISM (Industrial, scientific, and medical) frequency band of 902-928 MHz.
User Memory

  UHF RFID tag user memory, in bank `0b11`, contains memory that can be used for arbitrary purposes in a given application.

  For more information on reading and writing tag memory banks using the access operation in IRI, see the Access configuration example.

Write

  A command that can be used as part of an access operation to write values to tag memory.

  To write a multiple words to tag memory, the BlockWrite command may be used instead.

  For more details on writing tag memory, see the Write configuration example.

Write Sensitivity

  A tag‘s write sensitivity is the lowest received power with which the tag can write to its own memory in response to reader access commands. Tag write sensitivity is always equal to or higher than its read sensitivity, as it takes more energy to write to memory than to simply read it.

  Tags’ write sensitivity can be found in tag datasheets. Impinj’s Monza tag chip datasheets can be found on Impinj’s support portal here: https://support.impinj.com/hc/en-us/categories/200156298

## RF Terminology

The following terms are general RF terms that are also used to describe RFID systems.

Antenna

  An antenna is an electrical component which acts as a transducer, translating an electromagnetic wave into a conducted electrical signal, and vice versa.

  Both RFID readers and tags use antennas to implement RF communications.

  In RFID readers, antennas can be configured for either monostatic or bistatic operation.

  For information on how to switch antennas with IRI, see the Antenna Switching configuration example.

Balun
  An electronic component that is used in RF circuits to transform differential signals to single-ended signals, and vice versa.
Bandwidth
BW
  The amount of frequency spectrum occupied by a signal. In UHF RFID systems, the bandwidth of the forward link and reverse link are set by the link profile.
Bistatic

  A bistatic antenna configuration is one in which each individual antenna only transmits or receives signals, not both. At minimum, two antennas are required to operate in a bistatic mode. This contrasts with a monostatic configuration, in which individual antennas both transmit and receive signals.

  A bistatic system is typically more sensitive than a monostatic system because the receive signal path does not contain interference from transmit signal reflections off of the antenna.

  The Indy Modules only operate in a monostatic mode.

Directional Coupler

  An electronic component that is used in RF circuits to combine the forward and reverse paths, isolating the transmit and receive signal chains from one another, limiting self-jamming.

  In some RF circuits, a circulator is used in place of a directional coupler. Circulators are generally larger and more expensive components, but provide better isolation performance.

Effective Isotropic Radiated Power
EIRP

  A measure of RF signal strength with units of Watts or dBm.

  Systems that operate under the FCC regulations are limited to transmitting 4 Watts EIRP (36 dBm EIRP). This means that a reader’s forward power, plus its antenna gain in dBi, minus any losses due to cabling or connectors, must be below 4 Watts.

  ETSI transmit power limits are specified as ERP.

  For more information about EIRP and ERP, see the Impinj support article here: https://support.impinj.com/hc/en-us/articles/202756628-EIRP-and-ERP

Effective Radiated Power
ERP

  A measure of RF signal strength with units of Watts or dBm.

  Systems that operate under the ETSI regulations are limited to transmitting 2 Watts ERP (33 dBm ERP). This means that a reader’s forward power, plus its antenna gain in dBd, minus any losses due to cabling or connectors, must be below 2 Watts.

  FCC transmit power limits are specified as EIRP.

  For more information about ERP and EIRP, see the Impinj support article here: https://support.impinj.com/hc/en-us/articles/202756628-EIRP-and-ERP

Forward Power
Transmit Power

  The magnitude of the forward link signal transmitted by an RFID reader. The actual forward power of the Indy Modules may differ from the configured transmit power, but should stay within the specifications listed in the device datasheets.

  Usually measured in dBm.

  To configure transmit power with IRI, write the E_IPJ_KEY_ANTENNA_TX_POWER key as shown in the Transmit Power configuration example.

  For information on how to read forward power with IRI, see the Measuring Reverse Power configuration example.

Frequency
  The rate at which a signal oscillates, or at which generic events occur. An LED which blinks once a second can be said to have a frequency of 1 Hz. A signal which has a peak every 1 microsecond can be said to have a frequency of 1 MHz.
Gain

  A measure of the change in signal amplitude when a signal passes through a specific component in a system. Components such as power amplifiers and antennas are said to have a specific gain, meaning signals that pass through them increase or decrease in amplitude by a certain amount.

  Antenna gain is usually measured in units of dBi or dBd, depending on the type of power measurement used.

  RF signal gain, such as the gain trough a power amplifier or loss through a filter, is usually measured in units of dB.

Insertion Loss

  A measurement of the signal power loss (negative gain) across a transition, usually between conducted power and an antenna, or across a connector in RF systems. This “lost” power is reflected back towards the signal source, in our case, an RF transmitter. It is equivalent to the scattering parameter S11, or the reflection coefficient. Insertion Loss usually varies across frequency, and can be improved by matching the load across the desired frequency using a passive component network.

  Insertion loss is usually measured in units of dB.

  For example, if an antenna has an insertion loss of 10 dB, and a 27 dBm signal is fed into it, a 17 dBm signal will be reflected back towards the feed line.

Monostatic

  A monostatic antenna configuration is one in which individual antennas both transmits and receives signals. This contrasts with a bistatic antenna configuration, in which multiple antennas are dedicated to either transmit or receive signals.

  A monostatic system is typically less sensitive than a bistatic system because the receive signal path contains interference from transmit signal reflections off of the single antenna.

  Indy reader chips and the RS2000 Module reduce the impact of signal reflections using Impinj’s self-jammer cancellation technology.

  A monostatic system may have more than one antenna, with the antennas multiplexed (switched) in time to provide more read zones.

  The Indy Modules only operate in a monostatic mode.

Multiplexer
Multiplex
Mux

  A multiplexer is an electronic component or circuit that allows signal interconnections to be reconfigured or “muxed” at run-time.

  In RFID circuits, multiplexing is frequently used to enable reconfiguration of transmit and receive paths at run-time. For example, a mux can be used to connect multiple antennas to a single antenna port, or to select between multiple SAW filters, enabling more regional support with a single hardware configuration. In RFID, multiplexing is usually performed using an RF Switch.

  For more information about multiplexing external antennas using the Indy reader modules, see the IRI_External_Antenna_Mux code example.

PA Case Temperature
  The temperature measured or estimated on the Power Amplifier Case in degrees Celcius [C].
PA Die Temperature
  The temperature measured or estimated for the Power Amplifier silicon die in degrees Celcius [C].
Phase
Phase Angle

  A measurement of the position in time of a periodic signal, or the difference in position between two periodic signals. Used in RF because as electrical or electromagnetic waveforms propogate through time and space, their phase changes, so phase and changes therein can indicate the spatial properties of an RF system.

  Usually expressed in units of degrees or radians.

  For information on how to measure phase with IRI, see the RSSI and Phase FAQ entry.

Power

  A measure of the amount of energy transmitted, received, generated, or consumed by a system. In RFID, typically used to describe the strength of a signal transmitted or received. Also used in electronic systems to describe energy consumption from a power source such as a power supply or battery.

  Usually measured in W, mW, or dBm.

  For information on how to set transmit power with IRI, see the Transmit Power configuration example.

  For information on the various Indy low power modes, see the Power Management configuration examples.

Power Amplifier
PA
  The electronic component that amplifies the transmitted RF signal to the desired transmit power level. This component typically generates a significant amount of heat during operation.
Radio Frequency
RF
  A generic term for electromagnetic wireless communication of electronics using high frequency signals. UHF RFID communication occurs in the UHF frequency band.
Receive
RX
  Relating to the signal input to an RF system from an antenna.
Receive Sensitivity
Rx Sensitivity
  The minimum signal power from an RFID tag that can be detected by a reader. If the RSSI from a tag is lower than this value, it will not be detected by a reader.
Received Signal Strength Indicator
RSSI

  In RFID, this is a measurement of the strength of the signal received by the reader from the tag. Can indicate properties of the reader, antenna, forward link, tag, or reverse link. Sometimes used to measure distance or orientation of a tag relative to a reader. Units are usually dBm.

  For information on how to read RSSI with IRI, see the Measuring RSSI configuration example.

Reverse Power

  The magnitude of the portion of the transmit signal reflected back into an RFID reader off of the antenna or other electrical hardware. Can be used to infer some information about the conditions of the RFID system, such as antenna connection, tuning, etc.

  Usually measured in dBm.

  For information on how to read reverse power with IRI, see the Measuring Reverse Power configuration example.

SAW Filter

  A SAW (Surface Acoustic Wave) filter is an electronic component that is commonly employed in RFID systems to improve regulatory performance, ensuring regional compliance and certification success. SAW filters are bandpass filters that pass the desired spectrum and block out-of-band energy.

  In RFID readers, a SAW filter is placed in the RF transmit path between the output port of the radio and the input of the power amplifier. Regional compliance in multiple regions can be accomplished by using additional components to multiplex the transmit signal through the different SAW filters.

  In the Indy reader modules, the internal SAW filters are configured automatically according to the regulatory region settings provided by the host.

Transmit
TX
  Relating to the signal output by an RF system onto an antenna.

## Impinj Terminology

The following are terms that are specific to Impinj’s UHF RFID products.

FastID

  A unique feature of Impinj’s Monza tags that allows readers to read both TID and EPC using just the inventory operation. Normally these two banks can only be read together using the access operation.

  The FastID functionality is configured in IRI using the key E_IPJ_KEY_FAST_ID_ENABLE.

Impinj Radio Interface
IRI

  The Impinj Radio Interface is a blanket term that describes both the interface by which hosts can communicate with the Indy reader modules, and also a host library that implements that interface.

  The host library is included in the IRI Toolkit.

Indy
  The trade name for Impinj’s UHF RFID reader chip and module products.
IRI Toolkit
ITK
  The IRI toolkit contains the IRI host libraries and many supporting elements, such as example programs, the latest Indy Module application image, and HTML and PDF documentation.
Key
Key Code

  In the Indy reader modules, keys are used to store configuration data and also information about operating conditions. They can be considered the Indy equivalent of microcontroller registers.

  For more information on Indy keys, see the key listing and Configuration Examples.

Module

  An electronic component in the form of a large package containing multiple components inside attached to a PCB, implementing an application-specific functionality.

  The Indy RS500, RS1000, and RS2000 are RAIN RFID reader modules.

Monza

  The trade name for Impinj’s mass market UHF RFID tags.

  For more information on Monza tags, see Impinj’s materials on the support portal here: http://www.impinj.com/products/tag-chips/

Monza X

  The trade name for Impinj’s specialized embedded UHF RFID tags.

  Monza X tags are differentiated from most passive RFID tags in that they have vastly larger user memory, include some additional digital peripherals, and are packaged in chips instead of bare die.

  For more information on Monza X tags, see Impinj’s materials on the support portal here: http://www.impinj.com/products/tag-chips/monza-x-8k/

QT

  A unique feature of Impinj’s Monza4QT tags aloowing them to have both a public and private profile, enabling enhanced confidentiality. These profiles can be controlled via a tag’s access password as well as using a sensitivity limitation on the tag.

  For more information on using the QT feature in IRI, see the QT configuration example.

Report

  The Indy reader modules communicate information back to the IRI host through reports. There are reports for tag operations, status, GPIO events, errors, etc.

  For information on how to read data out of reports, see the Reports configuration examples.

RS1000
  Impinj’s single antenna 27 dBm transmit power Indy reader Module. RS1000 is PCB footprint compatible with RS500.
RS2000
  Impinj’s four antenna 31.5 dBm transmit power Indy reader Module. RS2000 has a different PCB footprint than RS500 and RS1000.
RS500

  Impinj’s single antenna 23 dBm transmit power Indy reader Module. RS500 is PCB footprint compatible with RS1000.

  This version of the ITK release has limited support for the RS500. For more information, see the Backward Compatibility section of the release notes.

Self-Jammer Cancellation
SJC
  A technology that some Indy reader chip and module products use to improve sensitivity to tags. Reduces the impact of the reader’s transmit signal on its own receive sensitivity by measuring the transmit signal and removing it from the receive signal.
Speedway

  The trade name for Impinj’s fixed reader products.

  The Speedway fixed readers contrast with the Indy reader chips and modules in that they are completely enclosed, network enabled, and can be deployed in the field without additional electronics for control.

  For more information on Speedway readers, see Impinj’s materials on the support portal here: http://www.impinj.com/products/readers/

Stored Settings

  This term refers to the configuration that can be stored in non-volatile memory in the Indy reader modules so that the readers don’t require configuration every time they are reset.

  Also known as OEM(Original Equipment Manufacturer) configuration.

  For information on how to use stored settings with IRI, see the Stored Settings documentation.

System in Package
SiP

  A style of embedded circuitry packaging wherein multiple electrical components are soldered onto a PCB and sold as a whole system.

  Installed by soldering directly onto a carrier or motherboard.

  Sometimes used interchangeably with the term module.

TagFocus

  A unique feature of Impinj’s of Monza tags that allows a reader to increase the persistence of inventoried flags in session 1, which usually has a lower persistence than sessions 2 and 3.

  The TagFocus functionality is configured in IRI using the key E_IPJ_KEY_TAG_FOCUS_ENABLE.

xArray

  xArray is an overhead UHF RFID gateway from Impinj. It includes an RFID reader and phased antenna array, and is capable of inventorying, accessing, and locating tags.Impinj

  For more information on xArray, see Impinj’s materials on the support portal here: http://www.impinj.com/products/gateways/

## Programming Terminology

The following terms are used generally in embedded and PC programming, and are used frequently in the descriptions of the IRI host libraries and interfacing with the Indy Modules.

Application

  Generally speaking, the compiled code loaded into the non-volatile memory on a microcontroller.

  The Indy Modules contain an application image and a bootloader image. The application image in the Indy Modules can be updated using the bootloader, but the bootloader image cannot be updated. Updating the application image can add new features and improve performance.

Application Programming Interface
API

  A collection of code including functions, constant defines, structures, etc that help implement some functionality in a computer or microcontroller program.

  Impinj provides the IRI host libraries, which include an API for communicating with the Indy UHF RFID reader modules.

  For more details on the IRI host libraries and their API, see the API documentation.

Baud Rate

  The signaling rate of a digital communication interface such as UART. Indicates the number of bits of information per second, including overhead bits such as start, stop or parity bits.

  For more information on changing the baud rate in IRI, see the Change Baud Rate configuration examples.

Bit
  The smallest possible unit of binary data, a single digit of binary which can have a value of 0 or 1.
Bootloader
Bootstrap

  Generally speaking, elements of microcontroller firmware that allow updating of the contents of non-volatile memory to load new code.

  The Indy Modules contain a bootloader image that allows the application image to be updated, improving performance and adding new features.

  For more information on using the bootloader to update the application image in IRI, see the application update configuration examples.

Byte
  A commonly used data type in programming that consists of a specific number of individual bits. A byte is usually the smallest addressable block of memory in a system. In most systems, a byte is 8 bits, but 16 and 4 bit bytes are not unheard of.
Calibration

  A specific configuration that allows a device to perform as desired.

  The Indy Modules are calibrated during manufacturing such that they will meet the datasheet specifications.

Chip
  A semiconductor system packaged in a monolithic form factor with exposed leads for making electrical connections. For example, Indy is an embedded UHF RFID reader chip. Contrast with Module, which describes a different scale and style of packaging.
Data Type
Type

  Declarations in code that state the format for specific variables or memory locations. These types describe how data is arranged in memory and also what operations, such as APIs or macros, can be performed on them.

  For more information on the unique data types included in Impinj’s IRI host libraries, see the Defines section of the API Guide.

General Purpose Input/Output
GPIO

  Generally speaking, a pin or pad on a device that can be used for multiple input or output behaviors, usually digital.

  In Indy lingo, GPIOs are specifically a set of module pins that can be used as application controlled digital inputs or outputs. Indy Modules’ GPIOs can be controlled directly with host APIs, setting the values of outputs or reading the values of inputs. They can also be configured to automatically set outputs based on reader events, or automatically perform reader actions based on pin conditions.

  The GPIOs can be used to control an external antenna mux. For more information on this use case, see the IRI_External_Antenna_Mux code example.

  For more information on using the Indy GPIOs in IRI, see the GPIO configuration examples and the Indy Module Datasheets.

Image

  In embedded terminology, an image is a specific ordered set of data, usually containing code or some other kind of data to be placed in a specific location in memory.

  The Indy Modules have bootloader and application images, and can also be loaded with a stored settings image.

Microcontroller
MCU

  A highly integrated embedded component including a processor, both volatile(AKA RAM) and non-volatile memory(AKA flash), and analog and digital peripherals such as digital communication blocks, ADCs, DACs, etc.

  Microcontrollers are the most compact and economical option for IRI hosts, and the IRI host libraries are designed with them in mind.

struct
Structure

  A special data type in programming that contains additional data types within it, allowing “structured” logically grouped data to be arranged together in memory.

  For information on the structures used in IRI, see the Structures section.

Word
  A data type representing the most commonly used arrangement of bits in a computing or logical system. UHF RFID readers and tags use 16 bit words.

## Electrical Units

The following are electrical units that are often used to describe electrical and RF systems.

Ampere
Amp
A

  A unit of electrical current flow. Used in electronics to measure the rate at which units of charge (electrons) move from one location in a circuit to another.

  1 Ampere = 1 Volt / 1 Ohm

centi-decibel milliwatt
cdBm

  A unit of electrical power, equivalent to hundredths of dBm.

  3000 cdBm = 30 dBm = 1 Watt

decibel
dB

  A unit of gain between two signals. Frequently used in RF because of its logarithmic scaling, allowing large and small gains to be expressed using the same units.

  A difference of 3 dB indicates a ratio of 2.

  A difference of 10 dB indicates a ratio of 10.

decibel dipole
dBd

  A unit of gain between conducted and radiated power, for example as a rating of antenna performance, measured relative to standard half-wave dipole antenna power radiation.

  dBd is used as the antenna gain for calculation of reader system ERP.

  To convert a dBd measurement to dBi, add 2.15 dB.

decibel isotropic
dBi

  A unit of gain between conducted and radiated power, for example as a rating of antenna performance, measured relative to isotropic (omnidirectional) antenna power radiation.

  dBi is used as the antenna gain for calculation of reader system EIRP.

  To convert a dBi measurement to dBd, subtract 2.15 dB.

decibel milliwatt
dBm

  A unit of electrical power, interpreted as 1 milliwatt plus the specified gain in dB. Commonly used in RF because of its logarithmic scaling.

  0 dBm = 1 milliwatt

  30 dBm = 1 milliwatt + 30 dB of gain = 1000 milliwatts = 1 Watt

  An increase by 3 dBm corresponds to a multiplication of 2 in power.

  An increase by 10 dBm corresponds to a multiplication of 10 in power.

Kilohertz
kHz

  A unit of frequency. Used in RF to describe the rate at which a signal oscillates.

  1 kHz = 1,000 Hz = 1 / (1,000 seconds)

Megahertz
MHz

  A unit of frequency. Used in RF to describe the rate at which a signal oscillates.

  1 MHz = 1,000,000 Hz = 1 / (1,000,000 seconds)

microsecond
μs

  A unit of time. Frequently used in RFID to specify timing parameters of the Link Profile, which defines interactions between a reader and the tags it communicates with.

  1 second = 1,000,000 microseconds

milliwatt
mW

  A unit of electrical power.

  1 milliwatt = 0.001 Watts = 0 dBm

Ohm

  A unit of electrical resistance. Used in electronics to measure the difficulty of electrical flow between two points.

  1 Ohm = 1 Volt / 1 Amp

Volt
V

  A unit of electrical potential. Used in electronics to measure signal amplitudes and reference levels.

  1 Volt = 1 Amp * 1 Ohm

Watt
W

  A unit of electrical power. Commonly used to specify power consumption of embedded electronics. Less commonly used in RF because of its linear scaling.

  1 Watt = 1 Volt * 1 Amp.

  1 Watt = 1000 milliwatts = 30 dBm

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