Research On Traffic Adaptive Cross-layer MAC Protocol In Wireless Sensor Networks

In wireless sensor networks, MAC（Media Access Control）protocol, which isnear the underlying parts of network protocols and responsible for channel resourceallocation, is quite important for network performance. For the special feature ofwireless sensor networks, the designed MAC protocol should reduce the energyconsumption as much as possible. Meanwhile, delay and throughput should also betaken into consideration. On the other hand, traditional layered protocol can’t satisfythe demands of wireless communication, since it couldn’t fully utilize networkresource to achieve the best performance. Recently, the cross-layer optimizationdesign of WSN is becoming a hot research topic. Some researchers have proposed todesign network communication protocols through sharing interlayer information. Theresearch in this thesis is processed from the perspective of wireless sensor networksMAC protocol and cross-layer optimization.Firstly, existing wireless sensor network routing protocol and MAC protocol arepresented, the related technology in MAC protocol is analyzed and the cross-layerdesign approaches are summarized. EA-MAC protocol is proposed on the basis ofSMAC protocol to remedy the shortcomings of SMAC, in which nodes correlationanalysis algorithm and traffic adaptive duty cycle mechanism are added. The residualenergy is also introduced into the existing traffic adaptive bakeoff mechanism. In thenodes correlation algorithm, all network nodes are divided into several zones bycomputing nodes correlation of collected information and using “clustering”mechanism, and every zone chooses a node as a representative node to transmit data.This method can effectively reduce redundant nodes transmitting duplicate data. Intraffic adaptive duty cycle mechanism, duty cycle is regulated dynamically todecrease idle listening by comparing the threshold set before with the flow valueobtained from predict flow model. In backoff mechanisms, by adjusting the value ofcontention window and backoff time, the non-uniform distribution and long backofftime of nodes can avoid data collisions when network traffic is heavy. In addition,nodes with more remaining energy have priority to access the channel and shorterbackoff time, which can keep balance of the whole network energy consumption andlengthen network lifetime. Simulation results show that the EA-MAC protocol hasbetter throughput and shorter delay than SMAC protocol in network with dynamictraffic. Combined with cross-layer design, EACL protocol, which is based onenergy-aware, is proposed on the basis of EA-MAC protocol. When path isestablished, routing tables are built according to the expectation value ofcommunication cost between nodes and sink node and nodes residual energy. Whennodes start transmitting data, network layer calculates optimum transmit power valueby using interface function and calling the parameters of physical layer. With sharingthe routing information from network layer, MAC layer adds next-hop node field inCTS frame, therefore, insignificant nodes would go to sleep early to avoid idlelistening consumption and reduce data conclusion. Simulation results certify thatEACL has better delay performance when network traffic change dynamically, andhas less network consumption with the same numbers of received data packets whennetwork traffic keep fixed.