Broadcasting a Means to Disseminate Public Data in a Wireless Environment—Issues and Solutions - Advances in Computers - page 43

(load balancing), and (iii) cluster related objects close to one another (improving the
response time). Applying the largest object first heuristic showed an improvement
in load balancing. However, it was proved short in solving the third aforemen-
tioned requirement. The CCP algorithm was presented in order to compensate this
shortcoming. Relying on the critical path paradigm, the algorithm assumed several
heuristics and showed better performance.
As noted before, introducing methods that can reduce the overall response
time at the MH was the main objective of this chapter. Naturally, such reduc-
tion could also minimize the amount of power consumption at the MH. In spite
of such minimization, the MH has to scan the air channel(s) to locate its desired
data. In an effort to reduce such scanning time, providing an index for the ob-
jects on the broadcast channel(s) could be proved to be beneficial in minimizing
power consumption. In addition, application of parallel air channels could result
in conflicts and consequently, would effect both response time and power con-
sumption. These two issues are the subjects of discussion in the next two sec-
tions.

6. Energy Efficient Indexing

Due to the power limitation of the mobile host, in retrieving objects from the air
channel, one has to minimize the amount of power consumption. In general, in the
presence of an indexing mechanism one could use the following protocol to retrieve
data objects from the air channel(s):

(1) Initial probe : The client tunes into the broadcast channel to determine when
the next index tree is broadcast.
(2) Search : The client accesses the index and determines the offset for the re-
quested objects.
(3) Retrieve : The client tunes into the channel and downloads all the required data
objects.

In the initial probe, the mobile unit must be in active operational mode. As soon
as the mobile unit retrieves the offset of the next index, its operational mode could
change to doze mode. To perform the Search step, the mobile unit must be in active
mode, and when the unit gets the offset of the required data items, it could switch
to doze mode. Finally, when the requested data items are being broadcast ( Retrieve
step), the mobile unit changes its operational mode to active mode and tunes into the
channel to download the requested data. When the data is retrieved, the unit changes
to doze mode again.