Categories for The MAC Protocols for Wireless Sensor Networks

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The MAC Protocols for wireless sensor networks are divided into two categories:
1. Contention-based: The Contention based protocols are used to avoid the hidden terminal problem. But the problems with these are idle listening, collision avoidance, and overhearing. IEEE 802.11, S-MAC are examples of this category
2. Reservation–based: TDMA protocols are based on reservation and scheduling. They have less energy-consumption compared to Contention based Protocols. Bluetooth is an example of TDMA based protocol
A. IEEE 802.11 Distributed Coordination Function
IEEE 802.11(DCF) is widely used contention-based protocol in wireless sensor networks. The DCF is a random channel-access scheme where every station begins its transmission based on
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Besides there is possibility of re-transmission of collided packets
The above three reasons are major sources for energy-wastage in conventional protocols They are avoided in Sensor MAC using two techniques: Periodic Sleeping and Adaptive Listening
Periodic Sleeping:-
Node must first listen to their neighboring nodes before starting their own listen and sleep schedules .There are two options for the Sensor Node
1. If the sensor node listens the schedule of any of the neighboring node ,then it becomes follower
2. If the sensor node doesn’t listen to any schedule from the neighboring nodes then it frames its own schedule and becomes Synchronizer. It broadcasts its own schedule
If the nodes don’t aware of each other, Periodic Neighboring node discovery solves the problem Advantages
Due to Periodic Sleeping there is Reduction in Energy Consumption
Due to periodic sleeping increase in latency occurs
Adaptive Listening:-
Adaptive Listening reduces the delay caused by Periodic Sleeping. In this technique, if the node overhears its neighbor’s transmission, it wakes up at the end of transmission for a short period of time. if
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