Modeling And Analysis Of Access Mechanism Of IEEE802.15.4with Heterogeneous M2M Services

With the increasing business demands of people, communication system is facingunprecedented challenges for development. So IoT(Internet of Things) has been proposed,which has brought people enormous convenience and drawn worldwide attention.As the mainmanifestation of the Internet of things at current stage, M2M(Machine to Machine) has beenthe public focus due to its huge development potential. While the application of massiveheterogeneous M2M services in the future are going to launch challenges against the QoSguarantee of network, it is necessary to analyze and optimize the network performance withheterogeneous M2M services.IEEE802.15.4standard is aimed at LR-WPAN(Low-Rate Wireless Personal AreaNetwork) which has almost touch upon all aspects in our surrounding circumstances due to itssimple structure and low power consumption. The MAC of IEEE802.15.4network combinesthe virtues of a random access mechanism with contention and a GTS(Guaranteed Time Slot)allocation mechanism without contention, which can exactly offer QoS guarantee forheterogeneous M2M services. IEEE802.15.4network is considered to be the most importantbearing network of M2M services. Therefore, it is important to model and analyze the accessmechanism of IEEE802.15.4with heterogeneous M2M services. The analytical results canprovide a theoretical reference for performance evaluation and optimization in actual network.First of all, we study the application fields and typical examples of M2M communication.Considering the different characteristics of M2M services, MMBP(Markov ModulatedBernoulli Process) and IBP(Interrupted Bernoulli Process) are mathematically chosen todescribe the arrival process of real-time M2M services and non-real-time M2M servicesrespectively. The traffic models can lay a foundation for the access mechanism modeling andperformance analysis below.Secondly, we choose non-real-time M2M services as our research object and establish a3-D Markov chain model to investigate the contention access scheme of IEEE802.15.4. Thestochastic behavior of random access and the uncertainty of CCA(Clear Channel Assessment)make it difficult to obtain the probability distribution of service time. To solve this puzzle,based on the theory of signals and systems, a transfer function block diagram is applied toanalyze the service process of IEEE802.15.4MAC layer. Then the probability distribution of service time is derived, which can facilitate the analysis and calculation of service delay. Theworking mechanism of each station in IEEE802.15.4network is modeled as an IBP/G/1/Kqueuing system. We solve the model by embedding Markov chain method to obtain QoSparameters of M2M services in the IEEE802.15.4network, e.g. throughput, delay and others.By using these performance indicators, we study the transmission performances ofnon-real-time M2M services and summarize the changing trend of influences on systemperformance made by different factors.On this basis, we study the analytical model of access mechanism with heterogeneousM2M services. In view of different QoS requirements between real-time and non-real-timeM2M services, a system model is established to analyze the hybrid access mechanism withcoexistence of the contention access and deterministic GTS allocation. The analytical modelconsists of two components: the CAP(Contention Access Period) model of contention accessmechanism and the CFP(Contention Free Period) model of GTS allocation mechanism. In theCAP model, considering the interaction among different M2M services, a Markov chain isused to model the exponential back-off process of contention access mechanism. ThenMMBP/G1/1/K1and IBP/G2/1/K2are established to model the working mechanisms of M2Mreal-time and non-real-time services respectively. By solving the queuing models, we studythe service performances and explore the interaction between these two kinds of services. Inthe CFP model, a one-dimensional Markov chain is developed to model the stochastic processrepresenting the number of waiting requests in the coordinator, which can be used to analyzethe GTS allocation mechanism. The PDF of the number of successfully received GTSrequests by the coordinator during the CAP not only depends on the CSMA/CA mechanism ofCAP, but also can be the input to analyze the GTS allocation mechanism of CFP. Thus we usethe PDF of the number of successfully received GTS requests to build up the couplingbetween the CAP and CFP model and obtain a complete model of hybrid access mechanism.Finally, through simulation we analyze the influences made by different factors on accessperformance and put forward effective methods to improve system performance fromdifferent perspectives.