Among these three values, the number of candidate antenna locations N is
subject to design issues such as available portal space, the physical size of the antennas, etc.
However, the number of discretized points in the portal L and the number of discretized
orientations M can be freely selected. In general, larger values lead to better and more
reliable ?¬?nal solutions to the placement problem, but at the same time, also lead to
increased computational effort. Thus the choice of values for L and M is important because
it determines the quality of the solution as well as the amount of computation effort
required.
The tag space resolution, which determines the value of L, is a critical parameter because
it determines the number of evaluations for each set of reader??™s antennas. Moreover, a
decrease in search resolution (meaning searching more precisely) by a factor of 10 leads to
an increase in L by a factor of 1000.
Discretizing the tag orientation and location space is an approximation to what is truly a
continuous space and simply looking at the percentage of all points in the tag space that
receive coverage (as a measure of performance) can give rise to misleading results as a
result of this approximation. This can be illustrated in Figure 10.7, which shows a portal
equipped with a single reader antenna. Consider ?¬?ve consecutive grid points in the
discretization as shown, and suppose the vertical line represents the actual 90% read
accuracy boundary.
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