None of the above works takes into account the possibility that the forwarding
nodes could aggregate the data that they forward towards the sink.
In [5], the authors use a network flow framework identical to the one used in
[8, 59], and formulate a network flow optimization problem by taking into account
the possibility of data aggregation along intermediate hops. Using this
framework, the authors determine upper bounds on the lifetime of a sensor
network. No distributed scheme is proposed in [5] to implement this optimal
routing and data aggregation policy, but the results could be used as a
guideline to determine the upper bound on the network lifetime.
Load Balancing
We saw in the previous sub-section that routing can be designed to exploit
load-balancing to ensure a more uniform energy drainage pattern across the
entire network. This in turn improves the network lifetime.
The principle of load-balancing can also be used for sharing the energy
burden in clustered sensor networks. In [23], the authors propose a protocol,
LEACH, that can be used in data gathering scenarios in homogeneous clustered
sensor networks. A homogeneous sensor network is a network in which all
the nodes have identical hardware capabilities. The clusterheads are responsible
for collecting data from the other nodes in the cluster, performing data
aggregation computations, and sending the aggregated data to the remotely
located sink.
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