Research On IEEE802.15.4 MAC Protocols

In the last few years,wireless sensor networks have penetrated a wide variety of application domains.IEEE802.15.4 is a new standard uniquely designed for low rate wireless personal area networks.It targets low data rate,low power consumption and low cost wireless networking.The energy-efficiency and robustness of this new standard makes it a strong candidate to be a federating communication protocol for wireless sensor networks.This thesis is based on the National Development and Reform Commission project-"IPv6 wireless sensor networks nodes",focusing on MAC protocols of the IEEE802.15.4 standard.The first part of this article gives an overview of the research on wireless sensor networks, including the development,system configuration,node configuration and etc.Furthermore,we present the development of MAC protocols and the requirement for designing it.Then we give a brief description of IEEE802.15.4,and the relationship between IEEE802.15.4 and ZigBee is also presented.In the second part,MAC protocols of IEEE802.15.4 are researched deeply.Based on introducing categories of nodes,the configuration and the types of networks of IEEE802.15.4, the idea and the mechanisms of IEEE802.15.4 MAC are introduced in detail.And the analysis and conclusions of it are also presented later.After that,with the NS-2 simulator developed by Zheng and Lee,several efforts were made to study the performance of IEEE 802.15.4 with respect to the three different networking topologies.The result of the simulation indicates that IEEE802.15.4 is fitter for static environment.With low traffic loads,it can reach up to a high packet delivery ratio.By adoptting the indirect transaction mode,the nodes can save more energy, but the end-to-end delay may be sacrificed.Furthermore,the ACK mechanisms can also meet the reliability of system requirement well.In the third part,we implement most parts of IEEE802.15.4 MAC protocol,such as CSMA/CA mechanism,association process,and etc.Through the interfaces designed for MAC module in TinyOS,the module which we implentment can exchange information with the application module and hardware abstract module well.The debugging of MAC module on PC and DZ1611/DZ1612 board has already been completed,and it can provide basic services for the next layer on it and works well.The last part of this article emphasizes on the cluster-tree topology which is mentioned in IEEE802.15.4.Through the analysis of its traffic distribution and delay characteristic,an improved scheme is described.The proposed 802.15.4 MAC protocol can change the superframe active period adaptively,the results of the simulation and the analysis based on Markov module both show that this new scheme will have better delay performance,meanwhile,have nearly the same energy cost as the 802.15.4 MAC protocol.