Physical layer of Electronic Product Code (EPC) Gen 2 defines method of transmission of bits across the network. EPC is a universal identifier encoded on RFID (Radio Frequency Identification) tags to check identities of objects like inventory, assets and people, and track them. The second generation of this technology, as laid down by EPCglobal Tag Data Standard, is called EPC Gen 2.
EPC Gen 2 RFID network has two main components, tags and readers. Tags are affixed on objects that enables them to be identified or tracked. Readers are the intelligent part of the system that tracks the tags. The physical layer lays down how the bits are transmitted between the RFID reader and the RFID tags.
It defines the mechanism of transmitting the individual bits between the reader and the tags.
Bits are transmitted in the form of wireless signals in the 902 – 928 MHz, unlicensed ISM band (ISM: Industrial, Scientific and Medical).
The bandwidth is in ultra − high frequency (UHF) range. So, the tags are often referred as UHF RFID tags.
Frequency hopping is done by the reader at 400 msec intervals for spreading the signal in the network and also for reducing interference from other wireless networks operating in the same frequency band.
Reader and tags use half − duplex mode of communication.
In most cases, passive tag active reader is used where the tags use the radio wave energy of the reader to transmit its ID to the reader.
The tags send their EPC code to the reader through a mechanism called backtracking.
Different forms of Amplitude Shift Keying (ASK) modulation techniques are used to encode the bits.
The modulation techniques used are very simple so that the tags can runs on very low power.
Each bit (0 or 1) is encoded using anywhere from 1 – 8 pulse periods.