Search

Mobile satellite network with Inter Satellite Links (ISLs), which consists of non-geostationary satellites, has the characteristic of network topology's variability. This is a great challenge to the design and management of mobile satellite network. This paper analyzes the characteristics of mobile satellite network, takes multimedia Quality of Service (QoS) as the chief object and presents a reference model based on Geostationary Earth Orbit (GEO)/ Low Earth Orbit (LEO) satellite constellation which adapts to the design and management of mobile satellite network. In the reference model, LEO satellites constitute service subnet with responsibility for the access, transmission and switch of the multimedia services for mobile users, while GEO satellites constitute management subnet taking on the centralized management to service subnet. Additionally ground control centre realizes the whole monitoring and control via management subnet. Comparing with terrestrial network, the above reference model physically separates management subnet from service subnet, which not only enhances the advantage of centralized management but also overcomes the shortcoming of low reliability in terrestrial network. Routing of mobile satellite network based on GEO/LEO satellite constellation is also discussed in this paper.

Terrain Height Error is one of the most important factors which influences the accuracy of direct system correction and has an obvious effect along the scanning direction. In this paper, taking Moderate-resolution Imaging Spectroradiometer (MODIS) data received from Earth Observing System (EOS) satellites as an example, and focusing on the high precision geolocation techniques of the moderate resolution optical satellite data, a high precision algorithm based on Digital Elevation Model (DEM) data and Ground Control Point (GCP) outlier detection is proposed to correct this kind of influences of Terrain Height Error. For more efficient and intelligent processing in practical applications, a group of GCPs should be used in the further geometric correction. But the correction result using GCPs is not so stabile, because it is often influenced by the data conditions. In this paper, a new idea based on local distortion similarity is proposed for the GCP outlier detection too. In this method, the distortion is described by a 2-D Gaussian distribution in the local area, and a decision rule is made to find out the abnormal GCPs according to the variance of the Gaussian distribution. Some experiment results using MODIS data show that the proposed algorithm based on DEM data and GCP outlier detection is feasible and valid. The final average location error of the new algorithm is about 0.13 pixels which is sufficient for many application requirements.

Stitching of images is the task of fusing a collection of images with smaller field of view (FOV) to obtain an image with a larger FOV. The need for this procedure is motivated by a variety of applications, especially including the application in the aviation remote sensing field. The paper puts emphasis on studying how to stitch the image set taken by the aviation swaying camera. In order to accomplish this task, we should know how the aviation camera sways. So the camera swaying model is presented firstly. The possible geometrical distortion of the image set can be known from the camera swaying model, and it includes two parts: the rotation and the perspective distortion. Aiming at the rotation distortion, we propose a novel image rotation method that can save the computation time. In this method, we rotate the four edge lines of the image utilizing the traditional rotation method. According to the relative position rotation invariability of any pair of points in an image, the other points except that on the four edge lines then can be rotated. The last step of the algorithm is the stitching which needs not only to search the optimal matching area between neighboring images but also to stitch the image set smoothly. The paper presents an extremum matching method based on the difference image, by which we can find the optimal matching areas between neighboring images in the image set. Through linearly changing the stitching weight of overlap areas, the image set can be stitched smoothly. The theoretical analysis and the experimental results have demonstrated the feasibility and validity of this stitching algorithm for the remote sensing images from the aviation swaying camera.

This paper proposes a new discrete transform called AP-Contourlet (All Phase Contourlet). Contourlet is a flexible and fixed transform for image representations of geometrical regularity. Because it has been concluded that APDCT (All Phase DCT) filter and APIDCT (All Phase IDCT) are excellent respectively in subband decomposition and image interpolation, this paper develops a novel mutliscale decomposition method based on the APDCT filter and APIDCT interpolators to replace Laplacian Pyramid at the fist step of contoulet. Experiments in denoising typical images have shown the performance of the proposed AP-contourlet is obviously superior to original contourlet both in vision and in signal to noise ratio (SNR).

Future space scientific missions are envisioned to incorporate a large number of satellites and spacecrafts deployed in different orbits to network together into Space Networks. These networks have some unique characteristics such as limited resource of nodes, large latency and intermittent connectivity, which pose challenges to routing. In this paper, we propose a Relay-based Routing Protocol for Space Networks (RRPSN), which exploits the predictability of nodes motion to help deliver packets. Nodes use the link state and trajectory information received from other nodes to construct the routing tables where the next hop node is selected from the current as well as the future neighbors. Three key components of the protocol, including dissemination link information, modified Dijkstra's algorithm and packet processing are described in this paper. The computation complexity and overhead of the protocol is analyzed.

The need for remote sensing image feature selection methods is discussed in this paper. A central problem in image classification and recognition is the redundancy of image features. To cope with many unnecessary and irrelevant features, we propose a mixture method based on principle component analysis (PCA) and rough set theory to alleviate this situation. The main contribution of this paper is to provide the method for remote sensing image classification with higher accuracy comparing to the single rough set theory and PCA method. Finally, some experimental results demonstrate that our proposed method is effective in feature selection for remote sensing image.

In satellite, Data transferring is very important and must be reliable. This paper first introduced an on-board network based on Control Area Network (CAN). As a kind of field bus, CAN is simple and reliable, and has been tested by previous flights. In this paper, the CAN frame is redefined, including the identifier and message data, the addresses for source and destination as well as the frame types. On-board network provides datagram transmission and buffer transmission. Data gram transmission is used to carry out TTC functions, and buffer transmission is used to transfer mass data such as images. Inter-satellite network for satellite formation flying is not designed individually. It takes the advantage of TCP/IP model and inherits and extends on-board network protocols. The inter-satellite network includes a linkage layer, a network layer and a transport layer. There are 8 virtual channels for various space missions or requirements and 4 kinds of services to be selected. The network layer is designed to manage the whole net, calculate and select the route table and gather the network information, while the transport layer mainly routes data, which correspondingly makes it possible for communication between each two nodes. Structures of the linkage frame and transport layer data segment are similar, thus there is no complex packing and unpacking. At last, this paper gives the methods for data conversion between the on-board network and the inter-satellite network.

For natural landscape, area-based matching can be successfully applied because the elevation is undulating rather gently. On the other hands, urban areas with the mixture of artificial structures such as buildings and natural landscape, where the elevation tends to have steeper changes, conventional area-based matching may not be successful. Many computer vision papers demonstrated matching methods based on features such as edge and regions extracted from images have much better performance for artificial structures. 2.5 m ground resolution of PRISM, however, may not be enough to extract detailed features enough to represent artificial structures. This may suggest the combination of area-based and feature-based matching approach can be more appropriate for ALOS PRISM data. This paper presents the results of experiments on the combination of the two approaches using simulated PRISM image generated from air-borne image sensor, TLS (Three Line Scanner).

The purpose of image fusion is to merge information from multi-sensor and to improve abilities of information analysis and feature extraction. In this paper, a new image fusion algorithm based on discrete multiwavelet transform to fuse multi-sensor images is presented. The detailed discussions in the paper are focused on CL (Chui-Lian) multiwavelet, a two-wavelet and two-scaling function multiwavelet, and use it to accomplish image fusion processing. The CL multiwavelets have several advantages in comparison with scalar wavelets, so that it is employed to decompose and reconstruct images in this algorithm. When images are merged in multiwavelet space, different frequency ranges are processed differently. It can merge information from original images adequately and improve abilities of information analysis and feature extraction in remote sensing area. The experiments, including the fusion of registered Visible (VIS) \Infrared (IR) images are presented in this paper. Comparing with other image fusion methods, satisfactory result has been obtained by applying this method on both objective and subjective performance measure.

This paper presents the formal definition of distributed cryptography based on the notion of distributed characteristics of space and time, and also defines algorithm group and correlation of algorithm that describes the relationship of algorithms of space and algorithm of time. Then, based on the idea of distributed characteristics of space and time, this paper establishes a model of distributed transmission. The model gives a new method to solve security transmission of space information.

The orbit determination (OD) accuracy of kinematic and reduced-dynamic method based on the spaceborne GPS data is strongly dependent on the quality and continuity of GPS observations, and the screening of the Low-Earth-Orbiter (LEO) GPS observations is substantially important. In this paper, an elaborate pre-screening procedure of zero-differenced spaceborne GPS observations was developed. This new efficient data-screening algorithm consists of two steps: in the first step, the "majority voting" method is used to locate the gross errors in zero-differenced GPS data; in the second step, the observation marked as gross error is corrected using the "Quasi-Accurate Detection of gross errors (QUAD)" method. In this step, an iterative least-square adjustment procedure is used to obtain residuals which are screened to detect bad observations thoroughly. For illustration of the feasibility and efficiency of the new algorithm, the processing of a numerical example of CHAMP satellite is presented in this paper.

How to deal with the relationship between GIS and normal management system is one of the most frequent problems that the developers meet when they are developing application system by using GIS. The reason is: the users have already had their own database or management information system before GIS, and the GIS developers always put all of the exiting data into the management of GIS but they always concentrated on GIS without concerning the different levels of the users. But, because the database function of many GIS softwares is very weak, it is difficult to achieve the task of managing normal database, which created some difficulties for developing the system. In addition, only a few functions of GIS have been used, even if all the exiting data have been put into GIS management. As a result, the cost of developing increased. Focusing on this problem, the authors proposed three developing models which combined management system with the advantages of GIS and based on analyzing users' demand in this paper. The authors also introduced the key techniques during developing this kind of application system in this paper.

The rapid development of web services technology ushers Geographical Information Systems (GISs) into the era of geographic information web services (GIWS), which requires a scalable and extensible GISs model to deliver distributed geographic information and GISs functions integrated as independently-provided, interoperable services in a distributed computing environment. Several distributed services can be dynamically chained as a new service to accomplish a specific task. Such a model of service chaining is one of the most important research topics of next generation GISs. The paper highlights the issues of service chaining, the process of combining several distributed, interoperable GIWS dynamically to construct customized applications, and analyses characters of each pattern. Then, based on pattern of client-coordinated chaining, we design a service chaining which is developed in a J2EE development environment using web services technology, and construct a web services-oriented Geo-spatial data integration and visualization platform in order to integrate multi-sources and heterogeneous Geo-spatial data using Geography Markup Language (GML) and Geo-spatial data integration technology, and to visualize geographic information using Scalable Vector Graphics (SVG) and JavaScript technology. During the process of design, several GIWS are defined, and functions, interfaces and related methods of these services are discussed in detail. The paper focuses on the method for chaining distributed GIWS, the mechanism for geographic information dissemination and error handling. Finally, forest Geo-spatial Data which have two typical types of data E00 and Shapefile (SHP) was used to test the platform. The result indicates that using service chaining for multi-sources and heterogeneous Geo-spatial data integration and visualization can efficiently meet customized needs, but further research is needed for better application.

Network intrusion detection systems (NIDS) are important parts of network security architecture. Although many NIDS have been proposed, there is little effort to expand the current set of NIDS to support IPv6 protocol. This paper presents the design and implementation of a Network-based Intrusion Detection System that supports both IPv6 protocol and IPv4 protocol. It characters rules based logging to perform content pattern matching and detect a variety of attacks and probes from IPv4 and IPv6.There are four primary subsystems to make it up: packet capture, packet decoder, detection engine, and logging and alerting subsystem. A new approach to packet capture that combined NAPI with MMAP is proposed in this paper. The test results show that the efficiency of packet capture can be improved significantly by this method. Several new attack tools for IPv6 have been developed for intrusion detection evaluation. Test shows that more than 20 kinds of IPv6 attacks can be detected by this system and it also has a good performance under heavy traffic load.

The compensation method of high resolution range profile of radar targets was talked over in this paper. Based on the need of the wide band high resolution signal processing, this paper discussed the one dimensional high resolution range profile (HRRP) obtained by the linear frequency modulated (LFM) wave. Because of the effect of velocity of the target, the one dimensional range profile will be displaced and defocused. We suggested some new methods to alleviate the effect of velocity, and simulated with the point scattering source model and the measured data of target model.

Images of astronauts must be transmitted to the earth in a low bit rate so as to lessen the tension of channel in spacecraft. In this paper, an approach to 384kbps Image Encoder for spacecraft is presented. With FPGA and special chips, a prototype which has a feature of lower time delays, better performance of motion estimation and higher resolution has been designed and implemented. This paper explores the motion compensation and texture coding as the basic coding structure, the MPEG-4 Image Encoder is coded in a content-based and object-based modern method, according to the thought of contour-texture. The coding module is the kernel component of the system that performs the DCT, quantification, motion texture coding, motion estimation and motion compensation, etc. Meanwhile, the digital video signals are compressed by this one. Pursuant to MPEG-4 standard, inter-frame coding and intra-frame DCT are adopted to reduce temporal and spatial redundancy. Variable length coding is also used to match the bit length and the signal frequency, in order to lower the bit rate further more. The bit rate ultimately reaches 384kbps. In special chips, data processing, transforming, coding, estimating and compensating are controlled by DSP which cooperates with FPGA. Error correction coding is also implemented by special chips under the control of DSP.

Urban large-scale digital mapping demanded a greatly efficient and speedy surveying method. The traditional surveying process lagged behind because it had many shortcomings in mapping cost, mapping period, data storage and further usage. It is an effective way to use high spatial resolution remote sensing image to make large-scale urban maps. Firstly this paper discussed the relationship between mapping scale and image spatial resolution, analyzed the way of processing image about large-scale mapping, explained the data-abstracted method based on customized rules, intelligent symbols and automated topology. Secondly this paper expatiated on the core technology of geo-database based on large-scale digital maps and high spatial resolution image, argued how to establish and maintain a spatial database and how to serve the other different applications by the public interface. The remote sensing image, large-scale digital maps, intelligent symbols, map elements, map-framing indexes and social statistics data were stored into the same spatial database which further provided comprehensive data and the thematic maps for urban administration, urban plan, land management, digital city and Urban GIS. And then the spatio-temporal geo-database was established by the "versioning" which could manage different spatial and temporal data. So it was feasible to produce large-scale digital maps using high spatial resolution remote sensing image and construct spatio-temporal database using "versioning." Furthermore it is a necessary way to urban informational and intelligent administration.

Navigation signals are the basis of satellite navigation systems, which determine the navigation systems' performance (such as tracking accuracy, anti-interference capability etc.), and are determined by some constraints (such as radio frequency resources, construction cost, technology level etc.). The aim of signal design is to select "proper" signals considering these above factors and make tradeoffs between performance and constraints. This paper will summarize the signal structure evolution of present satellite navigation and conclude some principles and issues which will be greatly valuable to our 2nd satellite navigation system. There's four main satellite positioning systems presently, the U.S. Global Positioning System (GPS), the Russian Global Navigation Satellite System (GLONASS), the Europe Galileo satellite navigation system and the Chinese BD-1 satellite positioning system. Among these systems, the signal characteristics of GPS and Galileo are good reference to our 2nd satellite navigation system. The improvement of GPS signals is a main aspect of GPS modernization. The aim of GPS modernization is mainly to modernize its signal structure so as to improve the whole systems' performance. The signal structure of Galileo has been revised for several times, and its present signal is the results of long time signal design. From GPS modernization and Galileo signals status, we can summarize some key specifications of navigation signals and some technologies to support these specifications. Based on this, we'll discuss some problems which should be attentive in our country's 2nd satellite navigation system and give some suggestions. This paper is organized into five sections. The first section will give a brief introduction of present satellite navigation system and their main features. Section two will review the GPS and Galileo signals structure evolution, including GPS modernization, Galileo signals status and the comparison of two systems' signals. In the third section, the relationship between signal parameters and system performance will be analyzed, including RF signal characteristics, modulation type, ranging code (such as code type, length and rate) and navigation data. In section four we will discuss some inspiration and technologies concerning our 2nd satellite navigation system, such as the use of multiple frequency signals (ionospheric delay estimation and carrier ambiguity resolution), pilot tones & dataless channel, binary offset carrier (BOC) modulation, and so on. The last section is conclusion, in which the whole paper will be retrospected and some useful conclusion will be given.

An on-orbit inspection satellite is a kind of small multi-purpose servicing spacecraft, which can periodically flying around a target spacecraft. It is very useful in on-orbit remote observation, malfunctions detection and maintenance. Observation trajectory design and control is one of the key applied techniques of on-orbit inspection satellite. The on-orbit observation trajectory is formed by the close range visual relative motion between the target satellite and the inspection or chaser satellite. And, it can be divided into natural inspection motion and fast controlled inspection motion. In this paper, the velocity impulse control model for observation trajectory control was established at first; Then, how the typical observation trajectories, which include stationary observation trajectory, straight line oscillation observation trajectory, flyaround football observation trajectory and fast controlled flyaround observation trajectory, formed and their characteristics were analyzed; Finally, the major factors affecting the on-orbit observation trajectory were discussed and some useful conclusions were given. The results indicate that the natural flyaround football motion and the fast controlled flyaround motion are the two effective on-orbit inspection modes and the initial state error and impulse control error are the two dominant factors affecting the on-orbit observation trajectory.

This paper addresses on our practices on the recent development in geo-spatial information technology. Specifically, these include a) spatial data capture technologies based on high resolution satellite imageries and laser scanning technology; b) modern GIS data modeling techniques - towards three-dimensional and dynamic data modeling solutions in GIS; c) spatial information distribution technology based on mobile computing and Internet technologies, and finally d) from certainty-based to uncertainty-based geo-spatial information science.

Frequency agile radar synthesis detection unit works in frequency hopping state in radio frequency (RF) band. For the limitation of the accuracy of instantaneous frequency measurement (IFM) technology, the frequency tracking accuracy can't be examined directly. The system design method proposed by the paper examines the frequency tracking accuracy of the frequency agile radar synthesis detection unit (FARSDU) at intermediate frequency. The method is realized in engineering and good performance has been got.

In this paper, a routing algorithm used in On-Board-Switch units is proposed in satellite Asynchronous Transfer Mode (ATM) networks. The routing algorithm named Ant Algorithm based Switching Routing Algorithm (AASRA) is based on globally optimizing ant algorithm to solve congestion problems in satellite ATM networks. Compared with Link State routing algorithm mostly used in ATM switch units, better performances of AASRA are achieved.

Firstly, this paper describes and illustrates briefly the functions and structure of the Flight Management and Command Guidance System for Flight Test. Through space information technology, system can make use of GPS and data of every intelligence source well. Considering characteristic that the many kinds, many data and strong real time of intelligence processing, this thesis take twice swerve volley guide method for example, and introduces vector theory analyzing volley guide method and mathematical model of system Which will improve command guide capability. In Flight management, Using SIT to integrating flight information, according to aviation statute and requirement of flight task, systems organize planes in air management area to ensure flight safety, advance time using efficiency. The whole system has the important application value for all kinds of command guide and air management of aero craft.

Speckle noise in synthetic aperture radar (SAR) images is characterized as multiplicative random noise. To address SAR image speckle denoising, this paper proposes a new method which is based on the combination of statistical model of wavelet coefficients and modification to the coefficients according to module-maximum-based (significant coefficient) rule. In our method, wavelet coefficients of image are firstly modeled as mixture density of two Gaussian (MG) distributions with zero mean. In order to incorporate the spatial dependencies into the denoising procedure, hidden markov tree (HMT) model is explored and expectation maximization (EM) algorithm is proposed to estimate model parameters. Bayes minimum mean square error (Bayes MMSE) method is used to estimate the wavelet coefficients free of noise. The wavelet coefficients are updated according to a rule whether the coefficient is a significant one or not. 2D inverse DWT is performed on the updated coefficients to get denoised SAR image. Experimental Results using real SAR image demonstrate that the method can not only reduce the speckle but also preserve edges and radiometric scatter points. Equivalent Number of Look Enl shows that the proposed method yields very satisfactory results compared with other methods.

The ambiguities must be resolved to their correct integer values in order to exploit the high accuracy of the carrier phase double-difference observables. The criterion used by ambiguity resolution technique is the selection of the integer combination that satisfies to the least squares adjustment. Integer ambiguity resolution could be regarded as a kind of global optimization search process. Genetic algorithm (GA) has the advantage to search the global optimum results in the robust and parallel way. Individual encoding is important to improve the efficiency of GA. This paper analyzed two encoding methods, which are binary code and real code, for GPS carrier phase double-difference short baseline ambiguity searching. Then the resolutions of the integer ambiguity using GA with binary and real code were compared. GA with binary code was used to determine the optimum integer estimation after float ambiguity solution resolved. However, due to non-integer nature of baseline vectors values, GA with real code was used to solve baseline vectors and double-difference ambiguity. Real encoding method made up for some deficiencies such as longer code lengthiness, larger solution space and longer time consumed in GA with binary code to non-integer solution. Numerical results showed that GA can be realized to resolve ambiguity resolution of DGPS with whether binary code or real code. The accuracy of both results was basically identical. On the premise of accurate float ambiguity solution, the convergence speed of GA with binary code was faster than that of GA with real code. The resolution of GA with real code was more robust and reliable because it did not depend on the accuracy of initial values.

With the rapid growth of wireless access to the Internet, there has been an increasing demand in providing high data rate real time traffic such as audio and video over wideband wireless channels. However, the transmitted multimedia traffic experience frequency-selective fading in wideband wireless channels. By dividing the wideband channel into several smaller sub-channels and sending multimedia traffic in parallel orthogonal sub-channels, which is widely known as orthogonal frequency division multiplexing (OFDM), the frequency-selective channel can be transformed into a set of frequency-flat channels. In this paper, we analyze the effect of sub-carrier assignment on the transmitted multimedia traffic. By increasing the number of sub-carriers, each sub-channel behaves practically as a quasic-static one, such that frequency-selective fading and intersymbol interference (ISI) can be alleviated. Sub-carrier assignment is thus important for multimedia applications. The multiplexing of sub-carriers is introduced to combat the variability of wireless channel, but the performance of wireless channel would also be degraded. We present a quality assessment of audio and video traffic over OFDM wireless channel based on sub-carrier assignment. Simulation results show that proper sub-carrier assignment could significantly reduce errors during high rate multimedia transmission.

Spatial data usually show as vector maps or raster images. The vector maps are composed of points, lines and polygons, while raster images are composed of grids. Spatial data have different character from common data, which makes it difficult to find knowledge from spatial database than from common database. Spatial Data Mining and Knowledge discovery (SDMKD) is considered as an advanced process to extract novel and interesting models from spatial database. However, visualization is a technique which can deal with substantive data and show this process as figures, images and charts by computers. But, SDMKD and visualization always keep separate and develop independently. A basic and important problem about visualization supporting SDMKD is seldom concerned. To make the process of SDMKD efficient and intuitional, this paper has a preliminary study on visualization of SDMKD through a mutual operation between the human and the computer. It realizes the visualization of data rebuilding and the process of data mining. Some techniques of visualization are used such as charts, maps, figures and images.

GPS-based positioning for AUV is a field of active researches, which integrates DGPS, radio sonobuoy, DSP, high speed data transmission technology with underwater telecommunication technogy. Many problems remain to be solved for GPS application to AUV because of the peculiarity of underwater environment. Some subjects in a GPS-based positioning system for AUV are reviewed in the paper. The development of underwater positioning and underwater GPS technology is introduced first. Secondly, the methods of underwater positioning are analyzed, followed with GPS-based AUV positioning algorithms. Thirdly, the origin of GPS error and its countermeasures are tudied. Finally, a conclusion is drawn that the GPS-based positioning system can provide high precesion positioning for 3D AUV in real time. It is promising in underwater applications. Some key technologies in underwater positioning are presented for future work.

This paper proposes a new data structure for GIS image data (wavelet pyramid structure) based on integer wavelet transform. With this structure, an original image is divided into an image of the lowest resolution and two groups of image detail coefficients. These coefficients are organized by a pyramid structure-wavelet pyramid structure. In comparison with R-trees, this structure can reduce data redundance and the original image can be restored perfectly and losslessly with this method.

Space information interaction process is so complex, distributed and intelligent that we have great difficulties in carrying through the advanced concept technology demonstration for it. To solve the problem, multi-agent-based modeling and simulation technology is applied to space warfare domain. By setting up the mapping from space warfare system's members to respective agents, the architecture of a distributed multi-agent system is designed and its control functions framework is discussed in this paper. As the farther analysis for the system's application, agent model is studied, and the inter-agent problems of task decomposition and task allocation are furthermore discussed. The established distributed simulation system model can be used to understand the external, complicated and intelligent space information interaction resources application activities and can afford advantage for realizing the dynamic space warfare action simulation.

This paper proposes a new clipping method that is capable of using arbitrary geometries in volume rendering. With the assistance of pre-computed outer contour mesh, the method adopts Constructive Solid Geometry (CSG) for clipping, and uses 3D texture for the rendering of clipping surface. The outer contour mesh defines the boundary of the volume data, and improves the efficiency of clipping and rendering. Furthermore, CSG-based clipping method protects the topology of geometries. This method computes the texture coordinate in vertex shader to implement the 3D texture mapping, and achieves high frame rates based on the powerful programming graphics hardware.

Autonomous on-orbit servicing provides flexibility to space systems and has great value both in civil and in military. When a satellite performs on-orbit servicing tasks, flying around is the basic type of motion. This paper is concerned with the design and control problems of a chaser satellite flying around a target spacecraft in non-coplanar elliptical orbit for a long time. At first, a mathematical model used to design a long-term flying around trajectory is presented, which is applicable to the situation that the target spacecraft flies in an elliptical orbit. The conditions of the target at the centre of the flying around path are deduced. Considering the safety and task requirements, a long-term flying around trajectory is designed. Taking into account perturbations and navigation errors which can cause the trajectory unstable and mission impossible, a two-impulse control method is put forward. Genetic algorithm is used to minimize the cost function which considers fuel consumption and bias simultaneously. Some simulation works are carried out and the results indicate the flying around mathematical model and the trajectory control method can be used in the design and control of a long-term flying around trajectory.

Dempster's rule of combination is a poor solution for the management of the conflict between the various information sources. It is proved that, if the false evidence can be correctly selected, Dempster's rule can deal with highly conflicting evidence combination efficiently. However, how to determine the false evidence is an open issue. In this paper, a novel method to identify the false evidence is proposed. First, the distance function between bodies of evidence is introduced to express the degree of conflict degree. Then, the confidence lever of each piece of evidence is obtained to reflect the reliability of each information source to some degree. By setting a threshold, the false evidence can be determined. The numerical example is shown to illustrate the efficiency of the presented approach.

Due to the complexity and non-regularity of tree shapes, traditional digital photogrammetry using stereo matching method is difficult to obtain the accurate tree height, This fact therefore limits the application of the aerial digital photogrammetry technology in the power line survey. This paper presents a method of tree height extraction from large viewing aerial image using the knowledge of segmented tree crown. This method is based on a rough digital surface model (DSM) of tree crowns and the exterior orientation of the image. The basic steps of this method is that the DSM is first used to find the region of interest in the image based on the exterior orientation, and then the edges of the distinct trees or branches are extracted using image segmentation technology. An algorithm that uses both the rough DSM height information and exterior orientation data to calculate the accurate heights of the segmented trees or branches is presented. The algorithm assumes that most of the trees are upright, and the projection in the large viewing angle images of the crown and branches can therefore be used to calculate their heights relative to the averaged DSM height. Hence, the accurate height of the trees around the rough DSM can be refined. Some experimental results are given with the image captured from multi-angular imaging system mounted on a helicopter in which a Position and Orientation System (POS) is onboard to record the exterior element of the cameras. The experimental results demonstrated that this algorithm can largely improve the accuracy of tree height extraction. The application in power line monitoring system is promising.

In this paper, a zero-tree wavelet video coding algorithm with extremely high compression is presented. The algorithm is for the purpose of solving the compression problem of stereo star field video. It uses the perspective correlation, temporal correlation and spatial correlation between star-field images as cues for compression. With the algorithm we have realized the real-time compression of stereo video streams with high fidelity.

This paper researches on the method of situation assessment for the air combat based on the Bayesian networks technology. It analyzes the events occur in the process of air combat, and presents a hybrid method of fuzzy sets and Bayesian networks to detect these events. Then, it presents a method to construct Bayesian networks using the events and then uses the networks to reason the purpose of enemy fighter pilots. Finally, it shows the method by an illustrative example.

This paper mainly discusses how to determine the optimized strategy for retrieval of Precipitable Water Vapor (PWV) with high accuracy from tropospheric zenith wet delay using ground-based GPS receivers. GPS analytical network are constructed on the base of two observation sites in Antarctica in 1999 and several IGS sites. Tests are conducted to study the performance of different network sizes and different schemes parameters. A high-accuracy GPS processing software package GAMIT/GLOBK is utilized; multiple schemes are adopted for searching the optimized parameters for accurate PWV. After having running GAMIT/GLOBK of all test combination, the results are analyzed by Baseline Repeatability Rate(BRR) and bias between calculated GPS water vapor and actual water vapor. The primary achievements and conclusion are reached including the optimal IGS sites involved, network configurations, elevation cut-off angles, processing periods, knots position.

Previous research employed natural background fractal features to detect man-made target for imaging infrared terminal guidance missile. The method is some effective but the optical turbulence is overlooked, which will disturb natural background intrinsic fractal. When the missile flies in atmosphere, there exits turbulent flow over the IR windows which will degrade the optical wave-fronts. In this paper, a new method considering degraded wave-fronts features is proposed for man-made moving target detection in natural background. To pre-process the infrared image and obtain the area in which target may exit, the image is divided into blocks and each block fractal dimension is calculated and compared. Then optical flow of the block is calculated from successive images to determine the moving target. The method is more applicable to actual missile fly environment, simulation results show that it reduces the optical flow calculation complexity and can detect the target availably.

This paper presents the conception and the main task of the precision 4-D guidance technology. The 4-D control technology and the formatting control technology based on the precision 4-D guidance are introduced. The structure of the 4-D control system, the data structure of the 4-D guidance data, the schemes of the velocity control and the formatting control principle are discussed. A simulation of the penetration probability demonstrates the important meanings of developing the 4-D precision-guided weapons to improve the operation effectiveness of the long-range weapons.

This paper describes a novel method of applying linear matrix inequalities (LMIs) to eigenstructure assignment (EA) approach for design of multivariable control system. Since the degree of freedom is available in EA using state or output feedback, respectively, numerous researchers have exercised this degree of freedom to make the system have good insensitively to perturbations in the system parameter matrices. We derive a series of equations to enhance system performance such as robust stability and parameter sensitivity according to left-over freedom in eigenvector and the solution of the lateral aircraft control system design is also derived using the proposed method, meanwhile, we find that this kind of design method can be classified into an optimization question and can be solved by inner point method using LMI. The implementation and verification of the control system is also presented. Simulation results on the aircraft demonstrate the good performance of the proposed control approach.

The satellite network consumption is related to the amount of the hops of the selected path. The smaller the amount of the hops is, the lower the expense of the network resources is; otherwise, the expense of the network resources is higher. So a new dynamic QoS routing protocol (QRP) which can select path according to the current flow of the network and provide certain QoS (limitation of hops) is presented in this paper. It divides Low Earth Orbit (LEO) satellites into groups according to the footprint areas of the Medium Earth Orbit (MEO) satellites in each snapshot period. Based on the information sent by LEO satellites, MEO satellite managers form two topology views separately for each layer, and then send them to their LEO members. The LEO or MEO satellites select path for arrived requests based on the view they own .The snapshot and group decision method is detailed, and the performance of QRP is evaluated through simulations and compared with that of HSRP protocol. Keywords: satellite network, routing protocol, two-tier satellite networks

A new method of initialization about the real-time GPS attitude determination system is presented. The combination solutions of the dualistic, non-linear equations and the ambiguity function method promote the computation efficiency of the initialization. The paper discusses the ambiguity function method and describes the observation equation in terms of geometry. The analytical solution of the dual non-linear coupled equation is given, and the real-time data are processed. As a result, compared with the normal method, the new method is more effective and economical.

Scarcity of the spectrum resource and mobility of users make quality of service (QoS) provision a critical issue in mobile cellular networks. This paper presents a fuzzy call admission control scheme to meet the requirement of the QoS. A performance measure is formed as a weighted linear function of new call and handoff call blocking probabilities of each service class. Simulation compares the proposed fuzzy scheme with complete sharing and guard channel policies. Simulation results show that fuzzy scheme has a better robust performance in terms of average blocking criterion.

Modernized GPS and Galileo will be available to civil users at the end of this decade, thus there is a need for unified platform that can receive multi-frequency signal of GPS/Galileo to develop and test for growing variety of diverse applications. The unified platform for various applications will speed the design process and reduce its cost. Such a platform need an open architecture and design flexibility so that modifications and testing can be done conveniently and efficiently. The flexible, reconfigurable, combined and software based Global Navigation Satellite Systems (GNSS) receiver will allow development, test and measurement of a variety of receiver architectures. This paper proposes a structure of combined multi-frequency software GPS/Galileo receiver for future GNSS receiver, which can utilize the planned GPS and Galileo publicly available signals. The receiver consists of a hardware multi-frequency front end responsible for both capturing all planned civil satellite-based radio-navigation signals. A followed programmable processor performs signal correlation. The correlator output then goes on signal processing totally using software. The correlator can be implemented either completely in software or using Field Programmable Gate Array (FPGA) for real time processing. The software modules for signal processing are easily updated. Improvements in accuracy and integrity are also achieved by GPS/Galileo Receiver Autonomous Integrity Monitoring (RAIM). The combined software implementation of processing modules makes this system a truly versatile GNSS receiver suitable for various applications.

This paper presents the performance analysis and optimization of LDPC coded OFDM system which provides high signal quality in LEO satellite communications. A three-state statistical channel model of LEO satellite channel is adopted including Rayleigh, Rician and shadowed Rician distributed submodels. The Irregular LDPC codes without loops of length 4 are optimized by the differential evolution algorithm under this LEO satellite channel. Simulations of BPSK, QPSK, 16QAM modulated systems are also conducted to analyze performances of theses systems.

The object-layering technology of Video Sequence is very important in many fields. Commonly, video image can be decomposed into background and moving objects. In this paper, based on features of different objects of the scene video sequence, aimed at the background object, we study the object-layering technology with background restoration based on neural network. This technology adopts two-stage pattern recognition and estimation with weighted multiple frames, increasing the reliability of the object-layering and extremely suppressing the noise. The experiments show the technology discussed is effective.

The rapid development of onboard processing (OBP) pushes broadband satellite networks to carry on multimedia traffic. However, the function of onboard routing cannot be provided in existing satellite networks with inter-satellite links (ISLs), and Quality of Service (QoS) of the satellite networks cannot be reliably guaranteed because of great difficulties in processing of QoS service. In this paper, a two-layered LEO and MEO satellite network (LMSN) is presented. Based on the idea of time-slot division, a novel dynamic hierarchical and distributed QoS routing protocol (HDRP) is investigated, and an adaptive Bandwidth-constrained Minimum-Delay Path (BMDP) algorithm is developed to calculate routing tables efficiently by using the QoS metric information which is composed of delays and bandwidth. The performances of the LMSN and HDRP are also evaluated through simulations and theoretical analysis.

The satellite network is suitable to provide multicast services with broadcast capability, especially for the low earth orbit (LEO) satellite network due to its short round-trip delays. A new multicast routing algorithm called dynamic approximate center tree (DACT) is proposed specifically for LEO satellite networks in this paper. And a simple core placement method is presented to find the root for every multicast tree. Since processing packets in intermediate satellites consumes much time, paths from the core to other member nodes of a group are built using multicast routing algorithm (MRA) to reduce the number of branches, which tries to merge the links wherever possible. The DACT algorithm can be applied to many-to-many communications in LEO satellite networks. Also it supports dynamic group membership. Delay and tree cost performances of DACT algorithm are compared with those of other two schemes, whose core placement methods are named random core and diameter core (DC) respectively. Simulation results show that DACT produces the lowest mean delay and tree cost among the three methods.

Based on the analysis of Mallat algorithm formulas, an improved wavelet transform implementation of high efficiency is proposed in this paper. Long sequence is partitioned into short ones by utilizing overlap-saving method. Cyclic convolution is proposed to be used in place of linear convolution in each section. Computer simulation shows that high accuracy and efficiency can be achieved by using this method. The speed of computation is greatly improved compared with Mallat algorithm involving linear convolution. This method is of good parallel property and is easy to be carried out in real-time by digital signal processor (DSP).

The sensitivity of channel bit error rate (BER) to the turbo coding parameters (i.e., code rate, iterative number and interleave length, etc) and the wireless channel statistic enlightens us to model a BER for turbo coding over Rayleigh channel. The model presented in this paper synthetically considers and quantificationally analyzes the impacts of all the coding parameters and the wireless channel statistic on the BER, and then emphasizes a simple equation that relates the BER at the encoder to the relevant coding parameters. Based on this model, the BER performance can be estimated even before channel coding given certain coding parameters set and channel statistic. The simulation results show that the model can handle the actual values with high accuracy. The maximal average predictive error is around 0.07%. Moreover, the proposed model is very regular and simple, and can be extended to other cases. These characteristics will make it more useful in nractice.