On determining bandwidth usage threshold to support real-time multimedia applications in wireless multimedia sensor networks

Real-time multimedia applications require Quality of Service (QoS) provisioning in terms of bounds on delay and packet loss along with soft bandwidth guarantees. The shared nature of the available bandwidth in Wireless Multimedia Sensor Networks (WMSNs) causes interference. Interference combined with the overheads associated with a Medium Access Control (MAC) protocol limit the available bandwidth in WMSNs. These overheads can result in congestion, even if transmission rates of nodes are well below the maximum bandwidth supported by an underlying communication technology. Congestion degrades the performance of admitted real-time multimedia flow(s). Therefore, in this paper, we experimentally derive the IEEE 802.15.4 channel capacity using an unslotted Carrier Sense Multiple Access Collision Avoidance (CSMA-CA) MAC protocol. Considering the experimental channel capacity estimation results, and the characteristics of real-time multimedia flows, we determine the threshold on bandwidth usage, so that the QoS requirements of real-time multimedia flows in terms of delay, bandwidth, and packet loss rate can be met. We performed several simulations, and results show that QoS requirements of applications are met operating within the bandwidth usage threshold determined in this paper. Simulation-based results further show that marginally exceeding the determined threshold value results in the performance degradation of at least one real-time multimedia flow

Self-organising smart grid architectures for cyber-security

PhD ThesisCurrent conventional power systems consist of large-scale centralised generation and unidirectional power flow from generation to demand. This vision for power system design is being challenged by the need to satisfy the energy trilemma, as the system is required to be sustainable, available and secure. Emerging technologies are restructuring the power system; the addition of distributed generation, energy storage and active participation of customers are changing the roles and requirements of the distribution network. Increased controllability and monitoring requirements combined with an increase in controllable technologies has played a pivotal role in the transition towards smart grids. The smart grid concept features a large amount of sensing and monitoring equipment sharing large volumes of information. This increased reliance on the ICT infrastructure, raises the importance of cyber-security due to the number of vulnerabilities which can be exploited by an adversary. The aim of this research was to address the issue of cyber-security within a smart grid context through the application of self-organising communication architectures. The work examined the relevance and potential for self-organisation when performing voltage control in the presence of a denial of service attack event. The devised self-organising architecture used techniques adapted from a range of research domains including underwater sensor networks, wireless communications and smart-vehicle tracking applications. These components were redesigned for a smart grid application and supported by the development of a fuzzy based decision making engine. A multi-agent system was selected as the source platform for delivering the self-organising architecture The application of self-organisation for cyber-security within a smart grid context is a novel research area and one which presents a wide range of potential benefits for a future power system. The results indicated that the developed self-organising architecture was able to avoid control deterioration during an attack event involving up to 24% of the customer population. Furthermore, the system also reduces the communication load on the agents involved in the architecture and demonstrated wider reaching benefits beyond performing voltage control