Research And Implementation Of Multimedia Sensor Network For Image Acquisition

With the increasing complexity of environmental monitoring, the simple information obtained by traditional sensor networks, such as temperature and light intensity, can not meet the needs of some special applications. As a novel information acquiring and processing technology, wireless multimedia sensor network(WMSN) introduces audio, images and video into traditional sensor networks, which can achieve more accurate and comprehensive environmental monitoring. Because of these, WMSN is of great practical value in economic development and military defense.After discussing the design requirements of hardware platform, software system and network protocol, a multimedia sensor network system for image acquisition is designed and implemented. The node with camera can capture an image, which would be preprocessed and then relayed through a multi-hop path to the sink node. Finally the image data is uploaded to the control center for display and analysis. The main contributions of the thesis are as follows:1. The sensor nodes are implemented with modular design according to three basic tasks-perception, processing and communication. Owing to the communication differences between sensor networks and the Internet, the sink node is extended with GPRS module to realize remote transmission. As the node would run many tasks concurrently with limited resource, the node software builds on TinyOS, a popular operating system developed specially for sensor networks.2. According to the particular requirements of image acquisition application, the tree-like network structure is adopted. Based on the existing Collection Tree Protocol(CTP), the energy factor is taken into account while selecting father node, and the timing of routing update is also improved. The implementation of the Energy-Aware CTP(EACTP) builds on IEEE802.15.4layer. EACTP can provide the next hop for data transmission. The simulation results show that EACTP can effectively balance the energy consumption of the whole network, and greatly extend the network lifetime.3. To transmit a large amount of image data, a high-speed data forwarding method based on one-way channel is designed. All packets of a single image are continuously forwarded to the next hop in a short time. At the same time, The statistics on packet reception is made for the retransmission of the lost packets. The experimental results demonstrate that the forwarding method is feasible, and the quality of transmission service achieves the desired effect4. As time synchronization is needed in the actual application, A low-complexity DMTS-based time synchronization method is implemented by combining with the tree-like structure. This method is suitable for some occasions in which the accuracy requirement of the time is not critical.