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Research On Some Algorithms In Multimedia Wireless Sensor Networks

Posted on:2011-10-02Degree:DoctorType:Dissertation
Country:ChinaCandidate:Z T LiFull Text:PDF
GTID:1118360308468946Subject:Computer application technology
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With the increasingly advancement of manufacturing industry, the further extensive application of sensor network and the pressing requirements for sensor network's function of multimedia from users, multimedia wireless sensor networks (MWSN) have attracted unprecedented attention. It has some unique characteristics, such as containing rich information, enormous data communication, and equal energy-consumption of each unit and so on. Because of these special characteristics of MWSN, it was very difficult to transplant research results of traditional scalar wireless sensor networks (SWSN) to MWSN directly. In various branch research hotspots of multimedia wireless sensor networks, time synchronization, routing protocols and image compression are parts of its key technologies. Among these, clock synchronization is an important service in any distributed system, including SWSN and MWSN. Most application of sensor network requires accurate clock synchronization among sensor nodes which includes coordinated work between nodes, location and moving target tracking. In all routing protocols, geographic routing has been regarded as one of the promising routing methods for sensor networks due to its simplicity and scalability. Multimedia node has a powerful ability to capture information, which leads to a surge in the amount of data and brings a challenge to store and transmit it for nodes and network. Image compression is an important way to save storage space, reduce data traffic and save bandwidth. It indirectly affects the scope of network application, the lifecycle and efficiency of network. This thesis focuses on the research of time synchronization, geographic routing, and image compression.Compared to SWSN, MWSN require high efficient in energy consumption and high synchronization precision. Existing researches on time synchronization and ranging are independent. Even if there was joint research, it was synchronization-based ranging and location. However, all time synchronization methods rely on some sorts of message exchange between nodes, the same to range estimation. Based on the common characteristic of time synchronization and range estimation, this thesis proposes a novel hybrid scheme:range-based time synchronization protocol, which has higher efficiency of energy consumption and smaller synchronization error. It can reach time synchronization and range estimation at the same time. The first step is to analyze the internal relationship between time and distance conversely. Secondly, range-based time synchronization protocol and its steps are introduced. As for time synchronization, it can achieve network-wide synchronization and external synchronization. As for range estimation, it can achieve relative ranging and absolute ranging. Finally, we do some simulations on the platform of NS2. The results show it outperforms timing-sync protocol for sensor networks (TPSN) and reference broadcast synchronization (RBS) in terms of the number of message exchanges and synchronization error.Existing geographic routing algorithms mainly focus on how to optimize the routing performance of transmitting single packet. In multimedia wireless sensor networks, data communication transmission is huge. It is a new way to combine source data characteristics for designing routing protocol. By analyzing the data flow characteristics of multimedia wireless sensor networks, this thesis presents asymptotically optimal geographical routing (AOGR) for MWSN. Its design goal is to optimize the average routing performance per packet. In AOGR, the reference of delivered packets to subsequent packets in routing will be exploited. By selecting some nodes as waypoints, the route will be controlled by the source node and the destination node plus these waypoints. It possesses desired properties:routing gradually converges to the optimal path; it can be embedded in existing geographical routing protocols. We have embedded AOGR to GPSR (greedy perimeter stateless routing) in this thesis. The average performance of AOGR is compared to GPSR and the benchmark shortest path algorithm. Simulation results show that on average the proposed algorithm can reduce as much as 50% of hops on the routes obtained by GPSR.As for image compression, the thesis summarized existing wavelet-based embedded coding algorithms and analyzed their advantages and disadvantages. In the advanced process of analyzing SPIHT (set partitioning in hierarchical trees), the author found that it did not follow the rules that "set first, element second" in D-set partitioning, which leading to prematurely split O-set. In addition, there is some state redundancy between different kinds of sets. This thesis presents an improved SPIHT embedded image compression algorithm and some advice of how to optimize SPIHT is also introduced. Main tasks are:(1) in coding procedure, the idea which set coding is prior to element coding is realized by estimating the importance of O set. (2) The redundancy of states between set and subset, node and its leaves are eliminated by predicting code. The experimental results indicate that the improved algorithm enhances the ratio of important coefficient in output bit stream and consequently obtains the PSNR which is superior to the SPIHT algorithm.
Keywords/Search Tags:Wireless sensor networks, Multimedia, Time synchronization, Geographic routing, Image compression
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