Pulse-Interval Encoding
(PIE) [25] is used to encode data transmitted from readers to tags, and either FM0 [26] or
Miller encoding [27] is used to encode the backscattered data from tags back to readers
[25]. Additionally, many other possible physical layer encodings can be considered for
RFID communications.
This section describes how the physical layer decoder and encoder blocks can be
automatically generated from a high-level speci?¬?cation of the protocol. This design ?¬‚ow
38 RFID Handbook: Applications, Technology, Security, and Privacy
is described in Figure 3.3. The user describes the waveform features of the encoding
scheme such as edge transitions, level detection, pulse width detection, etc., from a
physical layer speci?¬?cation. The user can then combine one or more wave features to
represent bits or groups of bits. The physical layer synthesis tool then automatically
generates hardware blocks for encoding and decoding the signal in VHDL. These VHDL
descriptions are created from the combination of prede?¬?ned parameterized hardware
libraries and automatically generated hardware blocks for detecting and generating the
waveform features in the encoding.
3.3.1 Speci?¬?cation of Waveform
The user describes the features of the encoding scheme using a textual representation. This
representation is created from a physical layer speci?¬?cation such as an RFID standard.
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