User's Manual

Lane Tuning Guidelines
4-5
Figure 4-1 Field Size, Shape, and Antenna Polarization Define the Reading
Range
One concern for lane tuning is how large the footprint needs to be for acceptable sys-
tem reliability. A rule of thumb frequently applied to this problem is that there should
be time for a minimum of four complete transactions
as the vehicle passes through the
capture zone. Thus, the system that has the more complex transaction requires the
larger footprint.
For example, if a toll agency requires an IT2200 tag read followed by a string of five
GENACKs, this constitutes a complete transaction, and the total time wo
uld be four
milliseconds for the IT2200 tag read plus four milliseconds for the five GENACKs for
a total of eight milliseconds for the entire handshake. Four complete handshakes
require 32 milliseconds. If the same agency has a maximum speed requirement of 60
mph through the lane, this translates to 88 feet per second, or 11.36 milliseconds/foot.
The agency could use the system with a footprint that is 32 milliseconds in duration,
which at 60 mph, translates to 11.36 milliseconds per foot or 2.82 feet. Any additional
footprint increases the reliability of the system because the system provides more
chances for the tag to interact with the reader.
1 read @ 4 milliseconds per read = 4 milliseconds
5 GENACK @ 0.8 milliseconds per GENACK=
4 milliseconds
= 8 milliseconds total, each full
handshake
For another example, if the toll agency requires three pages to be read from
the tag,
followed by three pages of data to be written to the tag, followed by five GENACKS,
the total transaction time is
To Be Provided.
PRELIMINARY