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Conclusions 201
impact modulation and transmission schemes as well as coding trade-offs at the
MAC layer of the RF communications medium. A layered approach to RFID
reader protocol testing (following the ISO protocol stack) is proposed by Marlin
Mickle, who calls for revising RFID protocol specifications accordingly (Ch. 4).
The HF/UHF and near-field/far-field simulation environment; RFID Center of
Excellence, University of Pittsburgh
In the absence of a layered RF protocol specification that monitors connectivity at
the PHY layer prior to engaging MAC-layer communications, Marlin Mickle
cautions, we cannot accurately describe ‘‘RFID read rate’’ and ‘‘write time’’
performance. As a result project managers must identify ways to consistently
define reader performance according to specific operating characteristics in order
to successfully measure outcomes. For example, it has been shown that generic
UHF readers that have been modified to support HF frequencies using a UHF
protocol do not generally perform as well as native HF readers. In describing the
evaluation process for what frequencies to use for case- and/or item-level tagging,
Bill Hardgrave and Robert Miller cite concerns at large RFID installations where
HF read rates can be up to five times slower than UHF (Ch. 9). Similar concerns
are expressed in the evaluation by Duncan McFarlane and co-authors in the
Aero ID Initiative at Cambridge University (Ch. 10). Bernd Scholz-Reiter, Dieter
Ucklemann, and co-authors (Ch. 14) express the same concerns as per tests at the
LogDynamics Lab in Bremen, Germany, in which a hand-held UHF device exhibited
write times of about 3 seconds for 128 bytes using an EPC Gen II-compliant tag.
Strategies for using a single transponder, one reader with multiple antennas, or
perhaps a cluster of readers or even a sequence of readers installed throughout a
facility, as described in Sanjay Sarma’s introduction to RFID applications (Ch. 2),
constitute a further area requiring analysis.
To isolate each layer of RFID read/write performance the University of
Pittsburgh has produced a development suite that enables rapid design and
implementation of readers and tags compliant with ISO 18000 Part 7 and is close
to completion with a similar system that would do the same for readers and tags
compliant with ISO 18000 Part 6C. Marlin Mickle asserts the value of this
analytical approach in his concluding remarks for Ch. 4: ‘‘Rather than using an
RFID reader as the basis for drawing conclusions as to systems performance, you
really need to analyze the RF exchanges to see what is actually happening.
Transmitter power, receiver sensitivity, and noise are the primary variables to
measure, along with processor and memory size on the tags.’’ Furthermore,
Marlin Mickle proposes a layered approach to RFID protocols that could provide
the basis for frequency-independent protocol testers that would analyze RFID
performance in specific environments, beginning with whether or not interrogators
have established physical-layer wireless connectivity. Such a project will
likely require sponsored research collaboration with multiple RFID suppliers as
well as academic partners.