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time is proportional to the number of index and data pages to be retrieved, and
this number is a function of the query and independent of the number of air
channels.
In general, the hierarchical method requires less active time than the single-class
method. The hierarchical method searches only one large index tree, whereas
the single-class method searches through multiple smaller index trees and the
number of pages to be retrieved per index tree is proportional to the height of
the tree.
In both the single-class and the hierarchical methods, the indexing based on an
aggregation relationship requires lower active time than the inheritance method.
This is simply due to the fact that the inheritance relationship resulted in larger
objects, thus requiring the retrieval of more pages.
The simulator also measured the total energy consumption. It was concluded that
the total energy consumption of broadcasting without any indexing schemes is much
higher than that of broadcasting supported by indexing, and the energy consump-
tion of the single class method is lower than that of the hierarchical method. This
is very similar to the results obtained for the response time. When indexing was
supported, energy consumption, on the average, decreased about 15 to 17 times
in the case of the aggregation relationship and the inheritance relationship, respec-
tively. In addition, broadcasting over parallel air channels also reduced the power
consumption in comparison to the power consumption of the single air channel. Fi-
nally, the mobile unit's power consumption decreased as the number of channels
increased.
6 . 3 S e c t i o n C o n c l u s i o n
This section investigated an energy-efficient solution by the means of apply-
ing indexing schemes to object-oriented data broadcast over single and parallel air
channel(s). Two methods, namely the hierarchical and single-class methods were ex-
plored. Timing analysis and simulation were conducted to compare and contrast the
performance of different indexing schemes against each other. It was shown that in-
cluding an index moderately degrades the response time; however, such degradation
is greatly offset by the improvement in energy consumption. For a single air channel,
broadcasting with supported indexing schemes increased the response time when
compared with broadcasting without indexing support. However, the response time
is reduced by broadcasting data with an index along the parallel air channels. More-
over, the response time decreased as the number of air channels is increased. Relative
to non-indexed broadcasting, the mobile unit's energy consumption decreased rather
sharply when indexing is supported. For a set of queries retrieving objects along the
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