Appendix A - Radio Frequency Identification Defined Wireless Communication and Air Interface
Page A-4 MDE-3664B TRIND® Start-up, Service, and Parts Manual · June 2013
Wireless Communication and Air Interface
Communication of data between tags and readers is accomplished using wireless
communication. Two methods distinguish and categorize RFID systems, one based upon close
proximity electromagnetic or inductive coupling and one based upon propagating
electromagnetic waves. Coupling is via “antenna” structures forming an integral feature in
both tags and readers. While the term antenna is generally considered more appropriate for
propagating systems, it is also loosely applied to inductive systems.
Transmitting data is subject to the vagaries and
influences of the media or channels through
which the data has to pass, including the air interface. Noise, interference and distortion are the
sources of data corruption that arise in practical communication channels that must be guarded
against in seeking to achieve error free data recovery. Moreover, the nature of the data
communication processes, being asynchronous or unsynchronized in nature, requires attention
to the form in which the data is communicated. Structuring the bit stream to accommodate
these needs is often referred to as channel encoding and although transparent to the user of an
RFID system the coding scheme applied appears in system specifications. Various encoding
schemes can be distinguished, each exhibiting different performance features.
To transfer data efficiently via the air interface or space that separates the two communicating
components requires the data to be superimposed upon a rhythmically varying (sinusoidal)
field or carrier wave. This process of superimposition is referred to as modulation, and various
schemes are available for this purposes, each having particular attributes that favor their use.
They are essentially based upon changing the value of one of the primary features of an
alternating sinusoidal source, its amplitude, frequency or phase in accordance with the data
carrying bit stream. On this basis one can distinguish Amplitude Shift Keying (ASK), FSK,
and Phase Shift Keying (PSK).
In addition to non-contact data transfer, wireless communication can also allow
non-line-of-sight communication. However, with very HF systems more directionality is
evident and can be tailored to needs through appropriate antenna design.
Three frequency ranges are generally distinguished for RFID systems: low, intermediate
(medium), and high. The following table summarizes these three frequency ranges, along with
the typical system characteristics and examples of major areas of application.
Frequency Band Characteristics Typical Applications
Low 100-500 kHz • Short to Medium Read Range
• Inexpensive
• Low Reading Speed
• Access Control
• Animal Identification
• Inventory Control
• Car Immobilizer
Intermediate
10 - 15 MHz
• Short to Medium Read Range
• Potentially Inexpensive
• Medium Reading Speed
• Access Control
• Smart Cards
High
850-950 MHz
2.4-5.8 GHz
• Long Read Range
• High Reading Speed
• Line of Sight Required
• Expensive
• Railroad Car Monitoring
• Toll Collection Systems
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