Concerning the deficiency in scalability of the traditional hierarchical clustering algorithm when dealing with large-scale text, a parallel hierarchical clustering algorithm based on the MapReduce programming model was proposed. The vertical data partitioning algorithm based on the statistical characteristic of the components group of text vector was developed for data partitioning in MapReduce. Additionally, the sorting characteristics of the MapReduce were applied to select the merge points, making the algorithm be more efficient and conducive to improve clustering accuracy. The experimental results show that the proposed algorithm is effective and has good scalability.

The current applications of network coding in single-hop wireless network retransmission are based Single Sender Multiple Receiver (SSMR) scenes. Therefore, this paper proposed a retransmission mechanism named NCWRM (Network Coding Wireless Retransmission Mechanism) which can be used in multiple sender multiple receiver networks. Each node in the network can be either a sender or a receiver. The node can broadcast a coded packet which is combined by multiple lost packets in the second retransmission after packet failed in transmission and the first retransmission. Multiple recipients can simultaneously get their lost packets by decoding the coded packet, which can effectively improve the efficiency of retransmission. Theoretical analysis and simulation results show that NCWRM algorithm can significantly improve system saturation throughput, while reducing overhead and packet loss rate.

Group key agreement is one of the important stages to carry out secure multicast communication. A group controller node switch method was given pointing to the problem of satellite network topology changed dynamically. It could adjust controlling nodes in a dynamic way. Then, both authentication and integrality mechanism were used to attest agreement messages and group keys, a group key generation and renewing method was proposed, which could improve security of agreement messages. The results of simulation and analysis show that this group key agreement protocol leads to high efficiency and security.

In the current research and design of spectrogram based on Field Programmable Gate Array (FPGA), the direct indication of the spectrogram is not able to reflect the detail variation of spectrum. To solve this problem, a method for the display and enhancement of spectrogram based on FPGA was proposed in this paper. With nonlinear transformation, the high-resolution gray image was compressed to low gray-resolution image, so the detail variation of spectrum would be better reflected. Meanwhile，human vision is less sensitive to the difference between gray-scale pixels than that of colors, so with pseudo-color processing of the gray images, the results are displayed through Video Graphics Array (VGA). The experimental results show that more detail variation of spectrum can be obtained by the method.

Security routing protocol is a key element to guarantee satellite network security. To solve the problem that most of routing protocols lack security scheme, the Elliptic Curve Pintsov-Vanstone Signature Scheme (ECPVSS) was used to attain confidentiality and authentication of packets, and trust evaluation scheme could exclude internal malicious node from the route path. Then a security routing protocol oriented to High Altitude Platform (HAP)/Low Earth Orbit (LEO) architecture was formed. The analysis results show that the proposed protocol can prevent network from some common routing attacks.

A new search angine ranking algorithm named CategoryRank based on categorization was proposed, in order to yield more accurate search results. With this new algorithm, the notion of importance can be captured more accurately with respect to a particular category. For this, the link graph was first analyzed and computed based on the category difference between two web pages of this link to better reflect user behavior in surfing. Secondly, the category information was applied into each web page to distinguish the importance of this page for different kind of users. Finally, the offline model and online model of this algorithm were combined to detail the application in ranking of search engine.