导航发射信道对双频复用信号质量的影响

在新一代全球导航卫星系统建设中,双频联合恒包络复用技术得到了广泛的应用。由于信号在星上传输过程中会产生失真,所以需要分析不同双频复用信号通过发射信道后的信号质量。首先建立了一个基于实际发射信道的模型,然后主要分析了AltBOC(Alternate Binary Offset Carrier)、TD-AltBOC(Time Division Alternate Binary Offset Carrier)、ACE-BOC(Asymmetric Constant Envelope Binary Offset Carrier)等不同双频复用方案通过发射信道后的功率谱、星座图、鉴相曲线过零点偏差、相关损失。对三种调制方式进行对比,结果表明在考虑捕获灵敏度的情况下,应优先考虑ACEBOC调制方式。

GNSS spoofing detection based on uncultivated wolf pack algorithm

In order to solve the problem that the global navigation satellite system（GNSS） receivers can hardly detect the GNSS spoofing when they are deceived by a spoofer,a model-based approach for the identification of the GNSS spoofing is proposed.First,a Hammerstein model is applied to model the spoofer/GNSS transmitter and the wireless channel.Then,a novel method based on the uncultivated wolf pack algorithm（UWPA） is proposed to estimate the model parameters.Taking the estimated model parameters as a feature vector,the identification of the spoofing is realized by comparing the Euclidean distance between the feature vectors.Simulations verify the effectiveness and the robustness of the proposed method.The results show that,compared with the other identification algorithms,such as least square（LS）,the iterative method and the bat-inspired algorithm（BA）,although the UWPA has a little more time-eomplexity than the LS and the BA algorithm,it has better estimation precision of the model parameters and higher identification rate of the GNSS spoofing,even for relative low signal-to-noise ratios.

DESIGN AND REALIZATION OF SINS/TWO-ANTENNA GPS INTEGRATED NAVIGATION SYSTEM

The strapdown inertial navigation system （SINS）/two-antenna GPS integrated navigation system is discussed. Corresponding error and the measurement models are built, especially the double differenced GPS carrier phase model. The extended Kalman filtering is proposed. And the hardware composition and connection are designed to simulate the SINS/two-antenna GPS integrated navigation system. Results show that the performances of the system, the precision of the navigation and the positioning, the reliability and the practicability are im proved.

APPLICATION OF INTERVAL KALMAN FILTER TO AN INTEGRATED GPS/INS SYSTEM

An interval Kalman filter (IKF) algorithm based on the interval conditional expectation is applied to an integrated global positioning system/inertial navigation system (GPS/INS). Because the IKF algorithm is applicable only to linear interval systems, the extended interval Kalman filter (EIKF) algorithm for non linear integrated systems is developed. A high dynamic aircraft trajectory is designed to test the algorithm developed. The results of computer simulation indicate that the EIKF algorithm is consistent with the traditional SKF scheme, and is also effective for uncertain non linear integrated system.

DESIGN & REALIZATION ON GPS/INS INTEGRATED NAVIGATION SYSTEM

This paper deals with the research of the GPS/INS integrated navigation system applying Extended Kalman Filter, which involves integrated principles, scheme and technology of combining with real INS and GPS receiver data. Emphases are placed on the modeling of system errors and implementation of the integrated system. Both loose and tightly coupled GPS/INS integrated in schemes are analyzed. On the basis of our experience accumulated in the research of GPS/INS for many years, the GPS/INS integrated navigation developing system is developed. It can be put into efficient and economic use in the study and design of integrated navigation system. It plays an important role in the aeronautical and astronautical fields in China. This system is not only a computer aided design software but also a semi physical simulation system by obtaining real INS and GPS receiver data. So the key software unit of the developing system could be conveniently transferred into practical engineering software in actual hardware integrated system. The application of this system shows that the design ideas and integrated scheme of this development system are successful, and can achieve good navigation result.

Revealing Storage-area Relationship of Open Water in Ungauged Subalpine Wetland-Napahai in Northwest Yunnan, China

Mountains and plateaus in Southwest China contain many subalpine and alpine wetlands, with signifieant hydroecological functions. But ungauged or poorly gauged eonditions limit the study and understanding of hydrological regimes of these wetland types. This study selects an ungauged subalpine wetland - Napahai in Northwest Yunnan, China - as a case for developing a practical approach to revealing its storage-area relationship of open water. A Trimble R8 GNSS （Global Navigation Satellites Systems） RTK （Real-time Kinematic system） and sonar fathometer were used to survey fine- resolution elevation data and generate a digital elevation model of the Napahai Wetland. Forty-four Landsat images from 1987 to 2Oll were collected, and the Normalized Difference Water Index was used to classify open water features in the area. The area of open water in Napahai was ealculated for each phase. With these data and a developed conceptual model, the storage of open water for each phase was estimated using ArcGIS tools. Both storage and area of open water showed significant intra-annual and inter-annual variations. In the rainy season, the monthly change of average storage of open water in Napahai showed about 1-2 months lag behind mean monthly rainfall. The storage-area relationship of open water was well fit by a power function equation （R2=0.91, n=44）. This study indicates that if detailedelevations are available for similarly ungauged subalpine wetlands in Southwest China, researchers can use this practical approach to estimate multi- temporal areas and storages and reveal the storage- area relationship of open water in the wetlands. The study provided valuable information of this ease wetland for optimizing its hydro-ecological managements and a new method to wetland researchers and managers for the hydrological study of similarly ungauged wetland complex.

Correlation Combination Ambiguity Removing Technology for Acquisition of Sine-Phased BOC(kn,n) Signals

Binary Offset Carrier(BOC) has been chosen as one of modulation methods in the future Global Navigation Satellite Systems(GNSS). Even though BOC signals can bring several advantages such as better track performance and higher positioning accuracy, there is a drawback that the autocorrelation functions have multiple side-peaks if BOC modulation is adopted. This characteristic will lead to false acquisition and the tracking loop will be locked in false phase point. The proposed Correlation Combination Ambiguity Removing Technology(CCART) cancelled all the side-peaks of the sine-phased BOC(kn,n) signals completely by making use of two kinds of correlation functions. Two kinds of sub-correlation functions were combined separately and then final correlation function without side-peaks was acquired. The simulation results are given and compared with other techniques. It is shown that acquisition will not be degraded with the increase of k.

Study on Design of Interplex Method for GNSS Signal

In order to satisfy sending multi-channel navigation signals in one frequency for modern GNSS（Global Navigation Satellite System）, the principle of Interplex multiplexing were introduced. And the three-way multiplexing structure and the four-way multiplexing method were also optimized. The Galileo E1 signal, as the example of Interplex reuse, was analyzed in detail. The power configuration of the multiplexing efficiency and the minimum of the multiplexing efficiency were obtained.

Volume Estimation of Small Scale Debris Flows Based on Observations of Topographic Changes Using Airborne LiDAR DEMs

This paper describes a geographic information system(GIS)-based method for observing changes in topography caused by the initiation, transport, and deposition of debris flows using highresolution light detection and ranging(LiDAR) digital elevation models(DEMs) obtained before and after the debris flow events. The paper also describes a method for estimating the volume of debris flows using the differences between the LiDAR DEMs. The relative and absolute positioning accuracies of the LiDAR DEMs were evaluated using a real-time precise global navigation satellite system(GNSS) positioning method. In addition, longitudinal and cross-sectional profiles of the study area were constructed to determine the topographic changes caused by the debris flows. The volume of the debris flows was estimated based on the difference between the LiDAR DEMs. The accuracies of the relative and absolute positioning of the two LiDAR DEMs were determined to be ±10 cm and ±11 cm RMSE, respectively, which demonstrates the efficiency of the method for determining topographic changes at an scale equivalent to that of field investigations. Based on the topographic changes, the volume of the debris flows in the study area was estimated to be 3747 m3, which is comparable with the volume estimated based on the data from field investigations.

Combined filter method for weakening GNSS multipath error

A filter method that combines ensemble empirical modal decomposition(EEMD)and wavelet analysis methods was proposed to separate and correct the global navigation satellite system(GNSS)multipath error more effectively.In this method,the GNSS signal is first decomposed into several intrinsic mode functions(IMFs)and a residual through EEMD.Then,the IMFs and residual are classified into noise terms,mixed terms,and useful terms according to a combined classification criterion.Finally,the mixed term denoised by wavelet and the useful term are reconstructed to obtain the multipath error and thus enable an error correction model to be built.The measurement data provided by the Curtin GNSS Research Center were used for processing and analysis.Results show that the proposed method can separate multipath error from GNSS data to a great extent,thereby effectively addressing the defects of EEMD and wavelet methods on multipath error weakening.The error correction model established with the separated multipath error has a higher accuracy and provides a certain reference value for research on related signal processing.

Calibration of GNSS positioning receivers

Nowadays global navigation satellite system(GNSS)receivers are the primary tool not only for precision surveying but also for geodesy,geophysics and many other industrial applications worldwide.The only way to assure the accuracy,universality and longevity of GNSS measurements is by calibration of its receivers.The parameters affecting the calibration accuracy of a single GNSS receiver are discussed in this paper.And a geodetic basepoint is established according to previous empirical studies to serve as a reference for calibration.Additionally,the traceability to the systeme international(SI)unit of such kind of calibrations is discussed.Stability of the base point is also verified through long-term measurements over three years.Eventually,a calibration of a sample single GNSS receiver is performed and the uncertainty budget is derived.

Landslide Monitoring Using Low Cost GNSS Equipment - Experiences from Two Alpine Testing Sites

Simple GNSS navigation receivers, developed for the mass market, can be used for positioning with sub centimeter accuracy in a wireless sensor network if the read-out of the carrier phase data is possible and all data is permanently broadcast to a central computer for near real time processing of the respective base lines. Experiences gained in two research projects related to landslide monitoring are depicted in terms of quality and reliability of the results by the developed approach. As far as possible a modular system set up with commercial off-the-shelf components, e.g., standard WLAN fur commtmication, solar batteries with solar panels for autarkic power supply and in cooperation of existing proofed program tools is chosen. The challenge of the still ongoing development is to have a flexible and robust GNSS based sensor network available - concerned not only for landslide monitoring in future.

Effect of Solving Models on Euler Vectors

In the process of solving Euler vectors based on GNSS horizontal movement field,the number of estimated parameters can affect Euler vector results. This issue is analyzed through theoretical deduction and practical example in this paper. Firstly,the difference between the results of Euler vectors in different solving models is deduced. Meanwhile, based on GNSS horizontal movement field in the Chinese mainland from 2004 to 2007,two common models( RRM and REHSM) are used to discuss the impact of solving models on Euler vectors and the follow-up study. The result shows that the maximum value of the difference in a block's entire rotation can reach 2. 6mm /a,and should not be ignored. Therefore,the results of horizontal movement are different using different kinematic block models,and this should be paid more attention in the analysis of crustal horizontal movement.

Simulator of GNSS signals for testing of space objects receivers in the earth conditions

A technique for testing space object receivers using global navigation satellite system （GNSS） signal simulator of the navigation field is proposed. Its structure consists of two blocks which allow synthesizing the scenario of reciprocal displacement of the receiver relative to navigation satellites and their signals. In the first block, according to the known coordinates of the receiver which are specified in tabular form or analytically, the distances between the receiver and the navigation satellites are calculated as well as their relative velocities. According to these data, the second block synthesizes the signals of navigational travelers with the specified characteristics which are transmitted via the air or cable with a given attenuation to the receiver. This allows testing on the earth receivers for airplanes and space objects under different scenarios of their movement, which not only reduces the risk of problems during the flight, but also avoids significant economic costs. Based on real data obtained by approaching two spacecraft using a simulator, the receiver was tested, which shows the promise of the proposed technology.

China Galileo Test Range and Its Critical Technologies

With the rapid development of global navigation satellite system (GNSS) and its applications, GNSS test range is becoming the focus of research. This paper, with the cooperation on Galileo Program between Europe and China as background, gives an overview of the development of test ranges for satellite navigation, proposes an implementation plan for China Galileo Test Range (CGTR), presents an analysis of CGTR and describes its overall objective, architecture, function and services, as well as operating modes. Particular analysis and study are given to the critical technologies related to CGTR implementation, including test range simulation and evaluation, time syn-chronizing and keeping, and pseudolite time division multiple access (TDMA) signal design. Research results of this paper can be helpful to GNSS testing and related applications.

Detection of solar radio burst intensity based on a mod ified multifactor SVM algorithm

To realize the automatic detection of solar radio burst(SRB)intensity,detection based on a modified multifactor support vector machine(SVM)algorithm is proposed.First,the influence of SRB on global navigation satellite system(GNSS)signals is analyzed.Feature vectors,which can reflect the SRB intensity of stations,are also extracted.SRB intensity is classified according to the solar radio flux,and different class labels correspond to different SRB intensity types.The training samples are composed of feature vectors and their corresponding class labels.Second,training samples are input into SVM classifiers to one-against-one training to obtain the optimal classification models.Finally,the optimal classification model is synthesized into a modified multifactor SVM classifier,which is used to automatically detect the SRB intensity of new data.Experimental results indicate that for historical SRB events,the average accuracy of SRB intensity detection is greater than 90%when the solar incident angle is higher than 20°.Compared with other methods,the proposed method considers many factors with higher accuracy and does not rely on radio telescopes,thereby saving cost.

Empirical model of correction for zenith tropospheric delay

The paper considers the possibility of correction of zenith tropospheric delays, and calculates it with the standard model, which takes into account the values of the refractive index of the troposphere at the time of measurement. Based on the experimental research, this empirical model of correction for zenith tropospheric delays can reduce the measurement er- ror of coordinates to about 30 % and altitude to about 40 %.

The Performance Evaluation of the Integration of Inertial Navigation System and Global Navigation Satellite System with Analytic Constraints

The integration of GNSS （Global Navigation Satellite System） and INS （Inertial Navigation System） using IMU （Inertial Measurement Unit） is now widely used for MMS （Mobile Mapping System） and navigation applications to seamlessly determine position, velocity and attitude of the mobile platform. With low cost, small size, ligh weight and low power consumtion, the MEMS （Micro-Electro-Mechanical System） IMU and low cost GPS （Global Positioning System） receivers are now the trend in research and using for many applications. However, researchs in the literature indicated that the the performance of the low cost INS/GPS systems is still poor, particularly, in case of GNSS-noise environment. To overcome this problem, this research applies analytic contrains including non-holonomic constraint and zero velocity update in the data fusion engine such as Extended Kalman Filter to improve the performance of the system. The benefit of the proposed method will be demonstrated through experiments and data analysis.

Methodology for Definition of the Three-Dimensional Geodesic Structures in the Olinda＇s Historical Site

It is shown to be a relevant study involving terrestrial methods of measurement, such as： forward and backward intersections, geometric leveling, trigonometric leveling with short distance targeted and spatial positioning GNSS methods, for the definition of field reference points and field-object points located in rough terrain. The geodesic structures were implemented in the Historic Site of Olinda employing GNSS （global navigation satellite system） receivers, total stations and digital level. The historical site of Olinda was recorded by UNESCO as Historical and Cultural Heritage of Humanity. The study area is located in the center of the busiest site with a quite roughly relief. This area has been studied since 2007 involving Research of Scientific Initiation and Pos-Graduation Course. This paper aims to present the realized experiments for the implementation and definition of geodesic structures in environments with very rough relief, including large old houses and historic monuments.

Towards a New Geoid Model of Tanzania Using Precise Gravity Data

The new geoid model of Tanzania is a major breakthrough in the determination of vertical heights for the past 60 years. A new geoid model has been computed using precise gravity data supplemented with marine gravity data from Gravity Recovery and Climate Experiment （GRACE） satellite and new high-resolution satellite gravity data from Gravity field and steady-state Ocean Circulation Explorer （GOCE）. A digital terrain model was also used based on 15＂ Shuttle and Rader Terrain Model （SRTM） data. The use of gravity data makes an orthometric height easily computed using Global Navigation Satellite System （GNSS）. The GNSS is being used in many African countries including Tanzania and soon it will replace conventional leveling technique and avoid frequent maintenance of benchmarks. This paper presents preliminary result of a new geoid model which shows that by using precious gravity data and Remove-Compute-Restore technique, an accuracy of 10 cm can be reached.