The obtained
result reveals how the optimal protocol parameter setting depends upon
environmental and network conditions.
In the following sections, we shall present models for three specific problems
pertaining to data gathering in wireless sensor networks. In the first case
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Chapter 16 Modeling Data Gathering in Wireless Sensor Networks
study, we optimize the look-ahead parameter for an active querying mechanism
that provides a tunable tradeo?® between trajectory-based and floodingbased
querying. In the second case study, we optimize the cluster size for joint
routing and compression that minimizes the total transmitted information for
a prescribed level of correlation between the sources. Finally, in the third case
study, we look at a problem of querying for replicated information and identify
the optimal number of replicas that minimizes the total energy cost involved.
2 Active Querying with Look-Ahead
The ACQUIRE mechanism [2] is an active querying technique designed for
sensor networks. In essence, it consists of the following repeated sequence of
steps: (i) An active node which receives the query checks its local cache to
see if it contains the information requested. (ii) If the information in the local
cache is not fresh, the active node sends a controlled flood of the query to all
nodes within d hops of it to obtain a fresh update of the information. (iii) If the
query is still not resolved, the query is forwarded to a succeeding active node
that is 2d hops away along a trajectory (which could be random or guided in
some way).
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