Optimizing Performance of Slotted IEEE 802.15.4 Mac For Cap And GTS Allocation Using Stochastic Petri Nets

Wireless Sensor Networks (WSNs) have been attracting increasing interest for supporting a new generation of ubiquitous computing systems with great potential for many applications such as surveillance, environmental monitoring, health care monitoring or home automation. The IEEE 802.15.4 protocol proposes a flexible communication solution for Low-Rate Wireless Local Area Networks including sensor networks. It presents the advantage to fit different requirements of potential applications by adequately setting its parameters. When enabling its beacon mode, the protocol makes possible real-time guarantees by using its Guaranteed Time Slot (GTS) mechanism. In this work, the performance of both the modes of data transfer- the CAP and the GTS allocation mechanism in IEEE 802.15.4 is analyzed using stochastic model. The analysis gives a full understanding of the behavior of the CAP and GTS mechanism with regards to delay and throughput metrics. Accurate modeling of the delay constraints using GTS, considering acknowledgement signal by physical and network layer is provided. When addressing applications with soft or hard real timing requirements some inherent paradoxes emerge, such as power-efficiency versus timeliness. Consequently, there is the need of engineering solutions for an efficient deployment of IEEE 802.15.4 in such scenarios. This work also provides the optimum energy consumptions as a function of duty cycle is evaluated using various system parameters considering the number of nodes in the system and the probability distribution of number of GTS requests. Analytical modeling is done using Stochastic Petri Nets (SPN) and simulation is carried out in MATLAB and results are compared with those analytically computed.