WSNs’ Performance Analysis Based On Network Calculus>S Mechanism

IEEE802.15.4/ZigBee standard supports collision-free and predictable access to thewireless medium through the Guaranteed Time Slot (GTS) Mechanism, thus Wireless SensorNetworks (WSNs) based on GTS mechanism could provide guaranteed service with highquality if they were configured well. Reasonable configuration parameters can be judgedthrough WSNs’ quantitative or qualitative performance analysis. When WSNs’ quantitativeperformance analysis is conducted by network calculus, the explicit mathematical relationbetween configuration parameters and performance bounds can be established, withoutrelying on complicated experimental simulation testbed. Based on deterministic networkcalculus and GTS mechanism, WSNs’ batch service models and network calculus models areproposed in the dissertation, which result in much tighter performance bounds. If these tighterperformance bounds were used in WSNs’ configuration, more network resourses might besaved. In detail, the main achievements of the dissertation are as follows:(1) The definitions of the three different service curves provided by the existing researchare too abstract to understand. Therefore, a detailed analysis is conducted to differentiate thethree curves’, with the applicable conditions of the left-over service curve are pointed out.(2) When WSNs’ performance analysis is being conducted, Active-Period (AP)sequences are proposed to be laid to the end of a Time-Division-Cluster-Schedule (TDCS),and all nodes’ burst tolerances arrive simultaneously as soon as WSNs have finished theirinitialization. The hypothesis avoids the low probability of burst tolerances’arriving just at theend of each node’s GTS, and makes the input data of the last node in the TDCS having themaximum scheduling time, meanwhile avoiding such cases as all service curves havingmaximum scheduling time.(3) Benefited from the analysis of a WSN node’s detailed service process for dataframes under the GTS mechanism, the size and distribution of data transmission efficient timeand ilde&wasted time in a GTS become explicit, with the fact that data can be transmittedcontinuously through neighbour time slots being pointed out. The equivalent bandwidth andservice curve which are based on TS method and much more factual are derived, whichresults in a node’s TS-based backlog upper bound and TS-based single-hop delay upper bound. Numerical analysis is conducted to compare the equilavent bandwidth and WSNs’ nodes’performance bounds both in the TS method and BI method. The numerical results illustratethat equivalent bandwidth is determined by many factors such as data frame length,inter-frame spacing, duty cycle ratio, maximum retries, and so on, and it is much less thannominal bandwidth. It is also shown that TS-based performance bounds are more factual.(4) In order to conduct multi-hop WSNs’ performance analysis, the expression of dataflow output upper bounds are analyzed at first. It’s found that the TS-Based and BI-basedoutput bounds are the same, and the output bound curve is the same as the arrival curve. Twoimportant properties, namely, the translational property of data flow arrival curve and theindeformable property of single flow arrival curve, are also discovered. Such concepts asinitial latency of service, modified latency of service, scheduling time of service, aggragatingtime of data flow and the segmental convergence flow are proposed. Then Chain WSNs aretaken as the object of study. The solution to the number of the segmental convergence flow isproposed, and batch service models and network calculus models of chain WSNs’performance analysis are established. Numerical analysis illustrated that, compared with theexisting research work, the method in the dissertation can result in greatly reduced upperbounds of nodes’ backlog and end-to-end delay. Meanwhile it’s discovered that the worst casein current research is not the worst one in the dissertation, on the contrast, it is surprisingly thebest one.(5) A network model of cluster-tree WSNs is defined, and the impact of linking typesbetween mobile sink nodes and cluster-tree WSNs is analyzed. Through analyzing the law ofdata flow’s transmission and aggregation in a simple single-level cluster-tree WSN, it’s foundthat multi-level cluster-tree WSNs’ batch service models and calculus models can beestablished, in the way of building “virtual chain WSNs”. Numerical analysis illustrated that,compared with the existing research work, the derived performance bounds derived in thedissertation are greatly reduced, and proper SD sequences can be chosen to derive goodWSNs’performance.