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Tham khảo tài liệu 'emerging communications for wireless sensor networks part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Throughput Analysis of Wireless Sensor Networks via Evaluation of Connectivity and MAC performance 133 n 1 more sensors are trying to do the same. We refer to Buratti Verdone 2008 2009 and Buratti 2009 Buratti 2010 for derivation and expression of PMAc n in Non Beacon- and Beacon-Enabled cases respectively. A finite state transition diagram has been used to model sensor nodes states in both cases Beacon- and Non Beacon-Enabled mode. Here we do not report equations for the sake of brevity. In these papers details on formulae are given and also a validation of the model against simulation is provided for n 50 and different values of D. 6.1 Numerical results Some examples of results obtained through the mathematical model developed are shown with the aim of comparing those achieved with the two operation modes i.e. Beacon- and Non Beacon-Enabled . In Figures 8 a PMAc n as functions of n for the Beacon-Enabled case for different values of SO with D 2 is shown. The cases of no GTSs allocated and Ngts equal to the maximum number of GTSs allocable are considered. As explained above this maximum number depends on the values of D and SO. As we can see Pmac decreases monotonically for n 1 when Ngts 0 and for n Ngts when Ngts 0 by increasing n since the number of sensors competing for the channel increases. Once we fix SO by increasing Ngts Pmac also increases since less nodes have to compete for the channel. Moreover once Ngts is fixed by increasing SO Pmac also grows since the CAP size is greater and nodes have a larger amount of time to try to access the channel. In Figure 8 b PMAc n for different values of D and Tq considering a Non Beacon-Enabled network is shown. As we can see a decrease of Tq results in a decrement of Pmac since nodes have a smaller amount of time to access the channel. Non BE mode Query Query Query CSMA CA CSMA CA Tq Tq BE mode SD Tq Fig. 7. Above part The IEEE 802.15.4 Non Beacon-Enabled mode. Below part The IEEE 802.15.4 Beacon-Enabled mode. 134 .
