However,
as noted in [35, 33], the many-to-one data flow also results in a non-uniform
energy drainage pattern in the network causing the nodes in certain regions
of the network may exhaust their battery energy earlier than other nodes due
to excessive relaying burden. Hence the routing algorithm has to be designed
to mitigate this problem.
4.3 Power-saving Algorithms for the Radio
Since a sensor network consists of a large number of nodes, each having a
limited communication range, the nodes may have to use multi-hop communication
to reach the sink. This requires using the neighboring nodes as relays.
However, if the relay nodes do not know the exact time instant at which they
are going to receive a packet for forwarding, they have to keep the receiver
circuitry of their radios on. This is referred to as idle listening. Keeping the
receiver circuitry on has battery energy overheads [44], and hence if the node
stays in idle mode for too long, the node battery drains out rapidly. In order
to reduce idle mode energy expenditure, the nodes can turn o?® their receiver
circuitry periodically. This is referred to as duty-cycling. Nodes going to sleep
causes changes in the network topology, and this may impact the routing algorithm.
Also, the fraction of the time for which a node is in the sleep mode
will have an impact on end-to-end latency of packet forwarding. Thus designing
power-saving algorithms to meet the delay and energy requirements of a
given application is an important design problem, and this problem has been
addressed in [26, 57].
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