MAC and physical layer energy efficiency for ad hoc wireless sensor networks

Abstract

The research work undertaken involves the design of a new, energy efficient Medium Access Control (MAC) layer for Ad Hoc Wireless Sensor Networks (AHWSN). MAC solutions are either contention based or non-contention based. Energy inefficiencies in contention based MAC protocols suffered from collisions, overhearing, control overhead and idle listening. Non-contention based MAC protocols introduced TDMA I CDMA I FDMA that did not suffer from those problematic issues. However, they suffered from other problems, such as energy inefficient hierarchies. The hierarchy uses cluster-heads to co-ordinate neighbours which is a continual requires that is energy inefficient. The proposal named Colour TDMA MAC is introduced, which does not have a hierarchy or cluster-head problems. It uses a single channel and simple transmitters. It also uses a distributed algorithm from colouring graph mathematics to ensure that the hidden terminal and exposed terminal problems of wireless data communication do not occur. Colour TDMA MAC also introduces the two concepts that allow nodes to sleep longer. The two are: * The Timed PicoRadio * The Mailbox. A node may sleep when it is not using the channel. Yet it may use one of the above concepts to receive a message destined for it. In the case of the timed PicoRadio, the node is awakened if it is sleeping. In the case of the mailbox, the radio signal is stored in memory and when the microprocessor awakens, it can deal with the message. A comparison of the central idea (Colour TDMA MAC) to a mainstream contention based MAC protocol (S-MAC) for AHWSN reveals that S-MAC suffers from collisions and idle listening (to a great extent) which is energy wasted. Its other energy inefficiencies are overhearing and control overhead. The two scheduling algorithms are compared via timing diagrams to see which delivers a message successfully in the shortest time. They are also placed head to head in some random tests to evaluate which is more energy efficient. Research work shows that the Colour TDMA MAC greatly improves energy savings. On the downside, it trades off energy for channel usage, thus messages take longer to reach their destination. Results also show that the Colour TDMA MAC is exceptionally good for unicast messaging where both the sender and the destination are known.