Coverage Control And Secure Transmission In Wireless Sensor Networks

Wireless sensor network (WSN) is predicted as an important technology to change the future world. Since its appearance, it has attracted a lot of interests among military circles, academia circles and industrial circles. The applying prospects of WSN include military, environment, medical treatment, building, agriculture and so on. However, some basic problems that support this network haven't solved very well yet. For example, the topology control, routing problem, coverage control, network security and so on. Although a lot of research works about WSN have been done, there are still a great many shortcomings and problems need to resolve.Coverage problem is the core problem in the surveillance application of WSN. However, researches of this problem still stay in the primary stage until now. Most of the existing literatures are based on simplistic disc sensing models that don't capture the disturbance caused by complex environments and noises. So it can't guarantee the performance of the coverage. A few works which based on probabilistic sensing models don't give full consideration to the collaboration among sensors. So the performances of their works are bad. How to get a network deployment at a high speed, such that the life cycle of the network is maximized under the high requirement of coverage performance, still deserves to study. Targets detection is the key technique of coverage control problem. Data fusion has shown as an efficient technique for improving system detection performance. However, for sensor networks employ data fusion, huge numbers of data need to transmit among sensors. Thus each sensor consumes a lot of energy. It is needed to study how to reduce the amount of transmitted data. In many applications of WSN (e.g. battlefield monitoring and target localization in military), when WSN has covered the whole region, sensor nodes have to transmit their messages to the base station or process center, then the secure transmission of the detection information should be considered. Due to the wireless channel, limited node resource, distributed network structure and outdoor node deployment, WSN is more vulnerable to attack. Furthermore, traditional security mechanisms can't work efficiently in WSN. So it is necessary to find secure transmission scheme without encryption algorithms.This work is about the targets coverage and the secure transmission of the information in WSN, the main contributions are as follows:1. For the WSN that deployed randomly, in order to prolong the network's life cycle, it often actives a subset of the sensor nodes. For the large scale WSN, it is important to choose the actived sensor nodes rapidly. This thesis studies the coverage problem based on probabilistic sensing model. The data fusion technique is used to improve the performance of coverage. And the saddle point approximation method is used to reduce the compution complexity. This thesis put forward the Central Coverage Algorithm and the Cooperate Grid Algorithm. The Cooperate Grid Algorithm divides the whole surveillance area to several overlapped grids. Each grid is looked as a fusion group. The adjacent grids cooperate with each other through the overlapped region. This algorithm can significantly reduce the number of sensors and improve the efficiency of the network configuration. Simulation experiments evaluated the superiority of the proposed scheme. We also compared the Cooperate Grid Algorithm with two existed coverage schemes.2. For some applications which require high coverage performance, it needs to deploy sensors accurately. Due to the high cost of network deployment, it is desirable to place sensors at optimal locations to achieve maximum detection performance with the least sensors. This thesis analyzed the computational complexity of finding the optimal location of sensors. Put forward the divide and conquer algorithm which can find the sub-optimal locations fast and ensure the high coverage performance. Moreover, this thesis put forward the divide and conquer algorithm based on clusters, which improve on the performance of the algorithm. It also analyzed the influence of the radius of impate region to the algorithm. The simulation experiment uses the real data in the DAPPA SensIT vehicle detection experiment. The results show that 49 sensors deployed by divide and conquer algorithm have the same coverage performance with 80 sensors deployed randomly. Moreover, we test and verified the performance of divide and conquer through numerical simulations and analyzed the influence by the parameters in the algorithm to the algorithm's performance.3. Compressed sensing is a new compression technique burgeoning in recent years. It can compress information in a distributed manner which improves the efficiency and reduces the computational complexity. In this thesis, we studied how to apply the compress sensing technique to target detection and gave the target detection scheme based on Bayes test. The system can make a detection decision without recover the compressed data. Simulations show that when we use the compressed sensing detection and if we give up a small amount of detection performance, then much larger communication traffic can be reduced.4. Secure network coding has proved to be a secure transmission scheme without any encryption algorithms. So it is very suitable to apply in WSN. However, existing researches on secure network coding are all based on an original network coding scheme. We found that the choice of original network coding scheme has serious impact on the network throughput. This thesis integrates consideration of the design of secure network coding scheme and the choice of the transmission topology such that the network throughput is maximized under the requirement of security. This thesis analyzed the relationship between the transmission topology and the weakly secure as well as the maximum transmission rate. Thus found the character of the optimal transmission topology. Then, we proved the problem of finding the optimal transmission topology to be a NP-hard problem. A determinant algorithm and a random algorithm for design source network coding are put forward. And the relationship between the transmission topology and the size of finite field used by coding is analyzed. This thesis put forward one optimal algorithm and three heuristic algorithms for finding the optimal transmission topology. The optimal algorithm can use when the capacity of the source and the destination is small. Heuristic algorithms can use for the general case. The previous two heuristic algorithms are designed for finding the optimal transmission topology such that the secure transmission is maximized. The last algorithm is designed for minimizing the size of the base field of coding and maximizing the probability of a random source network coding be weakly secure. We give simulation experiments for all heuristic algorithms. The results show that all algorithms in this thesis have a good performance for various scenarios.