“Inaccessibility in Wireless Sensor Networks”
Master’s thesis, Faculty of Sciences, University of Lisbon, Oct. 2013
Abstract: Wireless networks are seen as the communication networks of the future,providing communication capabilities where cables are not able to be used. Wireless technologies enable network flexibility and mobility, and reduce size, weight, and power consumption(SWaP) of communication devices. The IEEE 802.15.4 standard was designed to support the specification of wireless sensor networks (WSNs) and wireless sensor and actuator networks (WSANs), where is emerging their utilization within environments with realtime requirements, such as industrial and aerospace. The medium access control (MAC) layer is the control foundation of the network communication services. Disturbances in the MAC layer operation may lead to a network inaccessibility scenario, which consists in a temporary absence of network communication although the network is not considered failed. Examples of such disturbances are electromagnetic noise interference, glitches in the wireless device circuitry, or even obstacles in the communication path. A previous theoretical study indicates the occurrence of periods of network inaccessibility as a source of MAC transmission protocol delays which may induce application deadline misses which that compromise the dependability and timeliness properties of the whole networked system. Thus, this work aims to validate that previous study using the network simulator NS-2. The NS-2 simulator is a widely used tool supporting the simulation of IEEE 802.15.4 wireless networks. However, we discovered that its compliance to the IEEE 802.15.4 standard is imperfect. In order to perform the validation of the theoretical characterisation of network inaccessibility new mechanisms need to be introduced in the IEEE 802.15.4 simulation model. These improvements comprises: the support for real-time transmissions, through the incorporation of the contention free period (CFP) and of guaranteed time slot(GTS) ; IEEE 802.15.4 standard management operations not implemented in the official NS-2 release; A flexible tool capable of re-create the inaccessibility events and simulate different error conditions on the network, which include the Fault Injector and temporal and energetic analysis tool.
Research line(s): Timeliness and Adaptation in Dependable Systems (TADS)