utilizing physical layer information to improve rfid tag

eply immediately. Tags that pick a nonzero value shall transition to the arbitrate
state and await a QueryAdjust or a QueryRep command. Assuming that a single
Tag replies, the query-response algorithm proceeds as follows:
1. The Tag backscatters an RN16 as it enters reply.
2. The Interrogator acknowledges the Tag with an ACK containing this same
RN16.
3. The acknowledged Tag transitions to the acknowledged state, backscattering its
PC, EPC, and CRC-16 [1].
In the ISO 18000-6C protocol, readers communicate with tags using DSB-ASK
or PR-ASK with Pulse Interval Encoding(PIE). The tag to reader communication uses
ASK modulation and FM0(bi-phase space) or Miller encoding for the data. Figure 3.3
shows the waveforms for FM0 encoding. FM0 inverts the baseband phase at every
symbol boundary; a data-0 has an additional mid-symbol phase inversion. The duty
cycle of a 00 or 11 sequence, measured at the modulator output, is a minimum of 45%
and a maximum of 55%, with a nominal value of 50%. FM0 encoding has memory;
consequently, the choice of FM0 sequences in Fig. 3.3 depends on prior transmissions.
FM0 signaling always ends with a dummy data-1 bit at the end of a transmission. [1]
Figure 3.3. Tag to reader data encoding [1].
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