Research On Energy Saving In Wireless Multimedia Sensor Networks

The demand for completely monitoring the target environment with multimedia information and the availability of low-cost, small-scale hardware such as imaging sensors, CMOS cameras, and microphones, all of which can ubiquitously capture multimedia content form the field, have fostered the emergence and rapid development of Wireless Multimedia Sensor Networks (WMSNs). As a new and emerging type of sensor networks, WMSNs have received the immediate and significant attention of the research community and industry. WMSNs consist of sensor nodes equipped with imaging sensors, cameras, microphones producing multimedia content. These multimedia sensor nodes with the abilities of computing, storage and communication self-organize into distributed sensing networks that are able to collaboratively capture, retrieve, process and transmit the multimedia information such as audio and video streams, still images, and scalar sensor data from the environment covered by WMSNs. Most deployed traditional Wireless Sensor Networks (WSNs) mesure scalar physical phenomena like temperature, humidity, light intensity, or location of objects. However, WMSNs focus on the capture and processing of large multimedia information like audio and video stream, still images, which is the main difference from traditional WSNs. Therefore, novel technologies and methods are needed to solve crucial issues in each functional layer.Similar to traditional wireless sensor networks, Energy consumption is a fundamental concern in wireless multimedia sensor networks, even more than that in traditional wireless sensor networks. In fact, sensors are battery-constrained devices, while multimedia applications, which require higher transmission rates and more extensive processing capacity, produce large quantities of data. With the help of analysising the causes of energy consumption and taking into account of multimedia information sensing, processing and transmission, a type of layer collaboration energy saving system for wireless multimedia sensor networks is proposed in this thesis. On this basis, we design an energy saving localization method, a type of coverage and control algorithm for multimedia nodes, a kind of sleeping scheduling mechanism as well as an information processing and data transmission technology. Finally, a multi-network integration and network access system is built up to further reduce the energy consumption of WMSNs. The main works and contributions of this thesis are as follows:(1) An energy-saving localization algorithm based on difference of link quality is proposed in this thesis. Path loss factor could be obtained with the help of neighbor beacon node’s interaction and the high-accuracy localization information could be acquired on the basis of maximum likelihood estimation as well as the difference values of the link quality between beacon nodes and unknown nodes. Meanwhile, a type of spiral-like beacon motion model is created to reduce the cost of energy consumption. With the help of the mobile nodes, sensing direction of multimedia node could also be obtained.(2) Coverage and optimization schemes about WMSNs are also studied on the basis of their directional sensing model. A greedy algorithm as well as a type of voronoi diagram based method on sensing direction adjustment is proposed. Moreover, to effectively reduce energy consumption of wireless multimedia sensor networks, an energy-saving coverage scheme is proposed based on multi-objective genetic algorithms. Genomes are established according to the different opening sequences of nodes and the outstanding individuals are preserved due to the double cross operation as well as the best genome mutations which could open nodes as little as possible when meeting certain network coverage requirement.(3) We put forward a kind of prediction model on energy consumption and propose an energy-saving data transmission scheme based on life period division. Multi-layer cluster was constructed on the basis of energy consuming prediction and the life periods of sensor nodes were divided to ensure the balance of energy consumption. By changing node’s working mode, network lifetime was further extended. In addition, an information fusion method based on relative entropy for multimedia nodes is proposed. Moreover, areas of the overlapping sensing region between adjacent nodes could be calculated and a sleeping scheduling scheme in WMSNs is carried out.(4) An energy-efficient data sampling and transmission method in wireless multimedia sensor networks is proposed in this thesis as well. Energy consumption on sampling is reduced on the basis of periodical sleeping as well as different sampling granularities. Moreover, the transmission overhead is further brought down by means of color block matching. A compression cost estimation method is also described to minimize the node’s power cost on transmission and the network lifetime is optimized according to the regularity of multimedia event stream. Finally, a multi-path transmission method for multimedia sensor networks is proposed se well. By considering the transmission time, residual energy as well as transmission rate of the wireless links, three classes of paths are established with the help of metadata packets. Network congestion rate is reduced as well by adjusting time intervals of sampling.(5) A type of multi-network integration system based on WMSNs is created at the end of this thesis. The wireless image, audio and video sensor nodes with low power consumption as well as the gateway for WMSNs are developed as well. We also build up a wireless multimedia sensor network access system for types of infrastructure networks to realize energy management on WMSNs.