Energy e?±ciency. The most important requirement of a MAC protocol
is to be energy-e?±cient. Power consumption is a critical issue in WSNs,
since sensor nodes are battery operated and replacing or recharging the
battery is usually infeasible.
2. Scalability. A MAC protocol should adapt and run properly in a dynamic
and scalable topology. The WSN is expected to contain a large number of
sensor nodes. Additionally, nodes may be added, die or move to di?®erent
locations.
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3. Latency. Depending on the application served, some latency delay can be
tolerated in general. The latency and energy conservation are two conflicting
attributes in the MAC layer design for WSN. Choosing the shortest
path without considering the current energy level of intermediate nodes
might prematurely deplete power resources of some nodes and trigger network
partition.
4. Fairness. Usually, fairness is not considered to be a critical parameter
since all the nodes in a WSN serve the same application. For example,
when nodes in the same vicinity have similar data to transmit to the
upper stream, unfairness among nodes in the same vicinity is acceptable.
5. Bandwidth utilization. Designing a MAC protocol that e?±ciently uses
the bandwidth is a desirable factor to enhance the WSN performance.
2.2 Classification of MAC protocols in WSNs
MAC protocols can be divided into two main categories [16, 17]: scheduledbased
protocols and contention-based protocols.
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