A Study On Congestion Control For Wireless Multimedia Sensor Networks

Wireless Multimedia Sensor Networks(WMSNs)have emerged and shifted the focus from the typical scalar Wireless Sensor Networks(WSNs)to networks with multimedia devices that are capable to retrieve video,audio,images,as well as scalar sensor data.Congestion occurrence is a key factor that can negatively affect the performance of WMSNs.A robust solution is therefore required to mitigate this critical issue,yet to cope with challenging dynamic WSN?s nature.This dissertation "A Study on Congestion control for Wireless Multimedia Sensor Networks” studies the implementation and development of a secure system of WMSNs that is capable of delivering real time multimedia data at an acceptable level of QoS requirements with efficiently using the network scarce resources.For developing this system,firstly,outline of design challenges of WMSNs is presented,and a comprehensive discussion of the congestion control algorithms is presented in literature.Secondly,a potential solution to alleviate congestion has been alleviated by optimizing end-to-end delay with various channel conditions.In order to improve the end-to-end delay performance,the system has to drop few packets during network congestion.Our proposal is based on optimization of end-to end delay for WMSNs.Moreover,end-to-end delay constraint is optimized by assuming that each packet is allowed fixed number of retransmissions.To optimize the end-to-end delay,first,performance measures of the system,such as end-to-end delay and reliability for different network topologies(e.g.,linear topology,tree topology)and against different choices of system parameters(e.g.,data rate,number of nodes,number of retransmissions)are computed.Second,the impact of the end-to-end delay and packet delivery ratio on indoor and outdoor environments in WMSNs is studied.Thirdly,a traffic congestion control algorithm(TCCA)is proposed for WMSNs with linear topology.It is a joint rate control and error control of video over resource-constrained embedded devices.First,a combination of two different congestion indicators is introduced to differentiate between congestion levels and handle them accordingly.Second,a feedback based rate controller is developed to maximize received video quality,in which sensor nodes can adaptively adjust their sending rates.Finally,different retransmission mechanisms for different packets are proposed.Fourthly,to further improve the performance of TCCA,traffic congestion control algorithm is tested with tree topology.In a tree topology,sensor nodes receive video packets from their children nodes and forward these packets to their parent node to reach the sink node.All sensor nodes can generate and relay traffic.Fifthly,the algorithm proposed in the thesis is verified and evaluated on the Raspberry Pi board.