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RFID Essentials
book

RFID Essentials

by Bill Glover, Himanshu Bhatt
January 2006
Intermediate to advanced content levelIntermediate to advanced
278 pages
12h 2m
English
O'Reilly Media, Inc.
Content preview from RFID Essentials
TAGS 61
Types of Keying
The term “keying” comes from the days of telegraphy, when an operator pressed a manual
key to make long and short tones. Keying describes which attributes of an analog carrier—
the analog carrier can be a wave or a field—may be modulated to represent the ones and
zeros of a digital message. There are three main types of keying:
Amplitude-shift keying (ASK)
A type of keying that sends digital data over analog carriers by changing the amplitude
of a wave in time with the data stream
Frequency-shift keying (FSK)
A type of keying that sends changes through the frequency of the wave (or how often a
wave crest comes along)
Phase-shift keying (PSK)
A type of keying that sends changes through the distance by which the waves lead or
follow a reference point in time
Encoding
Encoding determines the way the tag and reader will interpret changes in the analog car-
rier to represent digital data. Thus, an encoding is an agreement between sender and
receiver regarding what the keyed changes mean. Morse Code, one example of an encod-
ing, uses long tones to represent “dashes” and short tones to represent “dots.” If we substi-
tuted “0” for “dash” and “1” for “dot,” Morse encoding would work for sending
information over a serial bus.
It might seem odd to think of RFID as devices communicating over a serial bus, but even
though the components are wireless rather than wired, most tags and readers ...
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Publisher Resources

ISBN: 0596009445Catalog PageErrata