User:GrahamAMM/ISO/IEC 18000-3 Mode 2

ISO/IEC 18000-3 MODE 2 is an ISO standard for passive RFID Item Level Identification and describes the Parameters for air interface communications at 13,56 MHz for the MODE 2 of ISO/IEC 18000-3. The target markets for MODE 2 are in tagging systems for manufacturing, logistics, retail, transport and airline baggage. MODE 2 is especially suitable for high speed bulk conveyor fed applications.

General Description
MODE 2 RFID tags are passive deriving their power from the interrogating signal generated by an RFID reader. Power is transferred from the reader to the tag by a high frequency magnetic field using coupled antennae coils in the reader and the tag. The powering field frequency is 13,56 MHz ± 7 kHz.

Dialogue between the reader and the tag is conducted on a Reader-Talks-First (RTF) basis. Following activation of the tag by the reader’s interrogating signal the tag waits silently for a valid command. After receiving a valid command the tag transmits a reply to the command. The air interface operates as a full duplex communication link. The reader operates with full duplex transmissions being able to transmit commands whilst simultaneously receiving multiple tag replies. Tags operate with half duplex transmissions.

Commands are transmitted from the reader to the tag by Phase Jitter Modulation (PJM) of the powering field. PJM transmits data as very small phase changes in the powering field. There is no reduction in the transfer of power to the tag during PJM and the bandwidth of PJM is no wider than the original double-sided spectrum of the data. The PJM sideband levels and data rates are decoupled allowing the sideband levels be set at any arbitrary level without affecting the data rate. The command data rate is 423,75 kbit/s encoded using Modified Frequency Modulation (MFM).

Tags reply to the reader by inductive coupling whereby the voltage across the tag antenna coil is modulated by a subcarrier. The subcarrier is derived from division of the powering field’s frequency. Tags can select from one of eight subcarrier frequencies between 969 kHz and 3013 kHz. The reply data rate is 105,9375 kbit/s encoded using MFM and modulated onto the subcarrier as Binary Phase Shift Keying (BPSK). To ensure that tags replying on different channels are simultaneously received tag replies are band limited to reduce data and subcarrier harmonic levels.

Multiple tag identification is performed using a combination of Frequency Division Multiple Access and Time Division Multiple Access (FTDMA). There are eight reply channels available for tags to use. In response to a valid command each tag randomly selects a channel on which to transmit its reply. The reply is transmitted once using the selected channel. Upon receiving the next valid command each tag randomly selects a new channel and transmits the reply using the new selected channel. This method of reply frequency hopping using random channel selection is repeated for each subsequent valid command. The reader can selectively mute identified tags to remove them from the identification process. When a tag is muted the tag will not transmit any replies. In addition to random channel selection the tags can randomly mute individual replies. When a reply is muted the tag will not transmit that reply. Random muting is necessary when identifying very large populations of tags. All FTDMA frequency and time parameters are defined by the command.

All commands are time stamped and tags store the first time stamp received after entering a reader. The stored time stamp defines precisely when the tag first entered the reader and provides a high resolution method of determining tag order which is decoupled from the speed of identification. Tag temporary settings, such as the time stamp, are stored in Temporary Random Access Memory (TRAM) that retains data contents during power outages caused by switching of the powering field in orientation insensitive readers.