03-09-2012, 02:21 PM
Energy and Rate based MAC Protocol for Wireless Sensor Networks
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Abstract
Sensor networks are typically unattended because
of their deployment in hazardous, hostile or remote
environments. This makes the problem of conserving energy
at individual sensor nodes challenging. S-MAC and
PAMAS are two MAC protocols which periodically put
nodes (selected at random) to sleep in order to achieve
energy savings. Unlike these protocols, we propose an
approach in which node duty cycles (i.e sleep and wake
schedules) are based on their criticality. A distributed
algorithm is used to find sets of winners and losers, who are
then assigned appropriate slots in our TDMA based MAC
protocol. We introduce the concept of of energy-criticality
of a sensor node as a function of energies and traffic
rates. Our protocol makes more critical nodes sleep longer,
thereby balancing the energy consumption. Simulation
results show that the performance of the protocol with
increase in traffic load is better than existing protocols,
thereby illustrating the energy balancing nature of the
approach.
INTRODUCTION
Wireless sensor networks (WSN) have become increasing
popular due to their wide range of applications
in both military and civilian environments, ranging
from battlefield surveillance to natural habitat monitoring.
A typical WSN consists of a large number of
autonomous sensor nodes that self-organize to form a
multi-hop network [1]. Sensor nodes are battery operated,
equipped with integrated sensors, and have embedded
processing and short-range radio communication
ability. Unlike standard wireless/ad-hoc networks, WSNs
are severely resource constrained and energy conservation/
efficiency is of paramount importance. The wireless
radio-communication interface consumes a significant
fraction of node energy. While substantial research has
been done on the design of low-power electronics to
reduce energy consumption at sensor nodes, due to fundamental
hardware limitations further energy efficiency
can only be achieved through the design of energy-aware
communication protocols.
RELATED WORK
Current MAC design for wireless sensor networks can
be broadly classified into two categories: contentionbased
protocols and TDMA protocols. IEEE 802.11
[2], although widely used because of its simplicity and
robustness against the hidden terminal problem, is not
an energy-efficient protocol since it does not address
the issue of avoiding overhearing and idle listening.
PAMAS [3] tries to avoid overhearing but does not
avoid collisions, which is a significant wastage of energy.
Collisions can occur between probe messages or
RTS/CTS messages. S-MAC [4], an improvement over
PAMAS, reduces further wastage from idle listening by
making idle nodes shut off their radios. It does not avoid
collisions between two RTS or CTS messages, which
is a significant wastage of energy. Also, the duration
of sleep is the same for each node, which is unfair
for the nodes with less energy. Making weaker nodes
sleep more can increase efficiency. S-MAC assigns sleep
schedules without taking into account the criticality of a
node. This also has the same problem as PAMAS: two
nodes simultaneously sending RTS packets can cause
collisions. Another protocol proposed by Woo and Culler
[6] uses an adaptive rate control mechanism based on
carrier sense multiple access (CSMA). This protocol
tries to achieve a fair bandwidth allocation to all nodes
rather than saving energy at each node in a multihop
network.
CONCLUSIONS
We have proposed a novel approach for energy management
at the MAC layer in a wireless sensor network.
The protocol uses TDMA along with periodic listen
and sleep to avoid energy wastage. The key feature of
our protocol is the leader election method by which
the most critical node is chosen to evade idle listening.
Our simulation results show that ER-MAC achieves a
significant gain in energy savings compared to other
existing MAC layer protocols.