Overview of Jamming Technology for Satellite Navigation

As an important space infrastructure, Global Navigation Satellite System (GNSS) plays a significant role both in military applications and in economic development. Controlling and managing the GNSS constellation depends on few stations even only one station by dint of inter-satellite links is a international important research field. The ephemeris uploading, which refers to uploading ephemeris from ground station to satellite, is one of the core tasks of GNSS, and it has a significant impact both on the update rate and the age of the ephemeris, therefore influences the precision of the system service. This paper analyzes and compares the process of the ephemeris uploading with and without inter-satellite links of GNSS, and classifies the normal process modes of the ephemeris uploading of GNSS into multi-station-multi-satellite mode and single-station-single-satellite mode. Afterwards, this paper compares the characteristics of the two modes and discusses the advantages and disadvantages of the two modes. Then this paper establishes the process model of the two modes, analyzes the factors of influencing uploading satellites scheduling, and proposes the uploading satellite scheduling rules and algorithms. At last, this paper devises benchmarks for the problem according to the input of the proposed model, obtains uploading satellites and uploading links for the two modes via different selection rules and algorithms, and compares the link details. The research will be instructive to process optimization for the ephemeris uploading of GNSS.

A Global Navigation Satellite System (GNSS) concept based on an open system architecture (OSA) has been developed by the authors. As described in this paper, this GNSS OSA concept utilizes the Global Positioning System (GPS) signal-in-space interface as the foundation for its interoperability standards. So long as each GNSS component adheres to these interoperability standards, synergy is enabled at the individual satellite level and the overall whole becomes much more than the simple sum of its components. The biggest beneficiaries of this GNSS OSA concept are those military and civil/commercial users of satellite navigation services who already have equipment compatible with the GPS signal-in-space interface (i.e., dual use). With the recent decisions in Europe to proceed with the civil Galileo system, on-going international development of space-based augmentation systems, and several industry announcements of plans to build commercial regional positioning systems, the dual-use GNSS OSA concept described in this paper provides a technical roadmap for the future global evolution of satellite navigation.

At present, data security has become a key area of attention from all aspects. The proliferation of data leakage incidents, the acceleration of the introduction of data security laws and regulations, and the rising cost of enterprise compliance punishment jointly urge all enterprises to step up to improve their own data security system. In the construction of data security, data desensitization is always a core technical ability. In view of the current situation and future development trend of data desensitization technology and products, this paper introduces the development of data desensitization technology in detail from desensitization algorithm, anonymization, static data desensitization and dynamic data desensitization. At the same time, from the core function, product form, supply side status and other aspects of the data desensitization technology are described. On this basis, the standardization direction of data desensitization products in terms of core functions, concept definition, performance and stability is proposed. Finally, the development trend of data desensitization technology and products in four aspects of regularization, anonymization, intellectualization and contextualization are put forward.

During the course of studying how to improve and optimize the anti-jamming ability of the satellite navigation and positioning system, the satellite channel was faced with many types of jamming signals. It is difficult to adopt one kind of jamming suppression technology to effectively suppress all kinds of jamming. In order to solve these problems, a new anti-jamming architecture for satellite navigation and positioning system is proposed. That is adopting the jamming cognitive method combined with the time-frequency domain jamming type recognition, power analysis and jamming DOA estimation. Also, the anti-jamming architecture design of the satellite navigation and positioning system is given based on the jamming cognition. Theoretical analysis and simulation results show that the anti-jamming architecture can detect the different jamming signals according to different jamming types, simplify the jamming suppression algorithm, grade and classify to suppress jamming signals.

In the signal structure design of new global navigation satellite system (GNSS), the ideas of secondary/tiered code was introduced. However, due to the inherent vulnerability of satellite navigation signal, frequency interference (RFI) has become a potential threat. The continuous wave interference (CWI) has become one of the most serious interference types for the characteristics of power concentration, multiple types and wide distribution of the interference source. The impact assessment of CWI on the performance of navigation signals has become a hot spot of research. However, the existing assessment method lacks the quantitative evaluation for the effect of the secondary code on signal performance in the presence of CWI. To solve the above problems, the impact of tiered codes with different length on signal power spectrum was analyzed firstly, and then influence of tiered codes on tracking performance by discrete spectrum carrier-to-noise ratio was analyzed. The experimental results show that the traditional analysis model based on continuous spectrum is no longer suitable for navigation signal performance analysis under the condition of CWI; the smaller the line distance is, the two times the code period is doubled and the line spacing is 0.1 times that of the original; and when coherent integration time doubles and the tracking performance deteriorates 2–3 dB; and when length of tiered code increase, the tracking performance can improve 2–3 dB; and short coherent integration time and long tiered code should be used in receiver design. A compromise needs to be made between these two parameters to ensure the tracking performance under CWI and the robustness of receivers. The proposed method can provide effective theoretical guidance for the development of the new GNSS signal receiver.

The Global Navigation Satellite Systems (GNSS) applications are growing and more pervasive in the modern society. The presence of multi-constellation GNSS receivers able to use signals coming from different systems like the american Global Positioning System (GPS), the european Galileo, the Chinese Beidou and the russian GLONASS, permits to have more accuracy in position solution. All the receivers provide always more reliable solution but it is important to monitor the possible presence of problems in the position computation. These problems could be caused by the presence of impairments given by unintentional sources like multipath generated by the environment or intentional sources like spoofing attacks. In this thesis we focus on design algorithms at signal processing level used to assist Integrity operations in terms of Fault Detection and Exclusion (FDE). These are standalone algorithms all implemented in a software receiver without using external information. The first step was the creation of a detector for correlation distortion due to the multipath with his limitations. Once the detection is performed a quality index for the signal is computed and a decision about the exclusion of a specific Satellite Vehicle (SV) is taken. The exclusion could be not feasible so an alternative approach could be the inflation of the variance of the error models used in the position computation. The quality signal can be even used for spoofinng applications and a novel mitigation technique is developed and presented. In addition, the mitigation of the multipath can be reached at pseudoranges level by using new method to compute the position solution. The main contributions of this thesis are: the development of a multipath, or more in general, impairments detector at signal processing level; the creation of an index to measure the quality of a signal based on the detector's output; the description of a novel signal processing method for detection and mitigation of spoofing effects, based on the use of linear regression algorithms; An alternative method to compute the Position Velocity and Time (PVT) solution by using different well known algorithms in order to mitigate the effects of the multipath on the position domain.

Two dams on the Elwha River, Washington State, USA trapped over 20 million cubic meters of sediment, reducing downstream sediment fluxes and contributing to erosion of the river's coastal delta. The removal of the Elwha and Glines Canyon dams between 2011 and 2014 induced massive increases in river sediment supply and provided an unprecedented opportunity to examine the response of a delta system to changes in sediment supply. The U.S. Geological Survey (USGS) developed an integrated research program aimed at understanding the ecosystem responses following dam removal. The research program included repeated surveys of beach topography, nearshore bathymetry, and surface sediment grain size to quantify changes in delta morphology and texture following the dam removals. For more information on the USGS role in the Elwha River Restoration Project, please visit http://walrus.wr.usgs.gov/elwha/. This USGS data release presents data collected during surveys of nearshore bathymetry and beach topography of the Elwha River delta, Washington. Survey operations were conducted between September 5 and September 7, 2010 (USGS Field Activity Number W-03-10-PS) by a team of scientists from the U.S. Geological Survey Pacific Coastal and Marine Science Center (PCMSC), Washington State Department of Ecology (WA DOE), and Washington Sea Grant. Nearshore bathymetry data were collected using a personal watercraft (PWC) and a small boat, each equipped with single-beam echosounders and survey-grade global navigation satellite system (GNSS) receivers. Topography data were collected on foot with GNSS receivers mounted on backpacks. Positions of the survey platforms were referenced to a GNSS base station placed on a nearby benchmark with known horizontal and vertical coordinates. A total of 118 km of nearshore bathymetric survey lines and 49 km of topographic survey lines were collected during the 3 days of survey operations. Environmental conditions were favorable, resulting in good coverage of the beach and nearshore region. A continuous DEM surface of the primary survey area was produced from all available bathymetry and topography data using linear interpolation and a grid-spacing of 5 m. An additional DEM with 1-m resolution grid-spacing was produced using linear interpolation for areas adjacent to the river mouth. Digital files containing the nearshore bathymetry data, beach topography data and derived DEMs from this survey are available for download from the child item pages.

The number and scope of Global Navigation Satellite System (GNSS)-based space applications has grown significantly since the first GNSS space receiver was flown in the early 1980's. The vast majority of GNSS space users operate in Low-Earth Orbit (LEO), where the use of GNSS receivers has become routine. However, the use of GNSS has expanded to other orbit regimes like Geostationary Orbits (GEO) and High Eccentric Orbits (HEO) but has been very limited due to the challenges involved. The major challenges for such types of orbits including much weaker signals, reduced geometric diversity, and limited signal availability. In any case, considering the recent development of multiple GNSS constellations and ongoing upgrades to existing constellations, GNSS signal availability will improve significantly. As a result, this expanded multi-GNSS signal capability will enable improved on-orbit navigation performance and will also allow the development of new mission concepts. High altitude space users will especially benefit from this evolution, which will provide GNSS signals to challenging regimes well beyond Low Earth Orbit. These benefits will only be realised, however, if additional signals are designed to be interoperable, are clearly documented and supported. In order to enhance the overall GNSS performance for spacecraft's in regimes from LEO, GEO to HEO and beyond, all Satellite Navigation constellation providers and regional augmentation system providers are working together through the United Nations International Committee on GNSS (ICG) forum to establish an interoperable GNSS Space Service Volume (SSV) for the benefit of all GNSS space users. This paper provides an overview of the technical work and in particular the simulations, performance analysis and discussions of the outcomes and results obtained by the UN ICG Working Group-B in the context of the GNSS Space Service Volume activities, which were supported by all GNSS service providers.

A Global Navigation Satellite System (GNSS) enables continuous positioning anywhere on or near the Earth surface by means of radio signals transmitted from orbiting satellites. The system comprises a constellation of about 20 or more satellites, a network of ground stations for monitoring and control of the satellites, and an unlimited number of users who passively receive the signals and employ them for positioning and other applications. GNSS satellites transmit carrier signals in the range of 1.1–1.8 GHz, which are modulated by digital codes, termed pseudo‐random noise (PRN) codes. The codes are selected so as to enable all satellites in the constellation to transmit at the same frequency with minimal interference, and to permit range measurements to be made. Given information on the satellite locations and measurements of range to at least four satellites, a receiver on or near the surface of the Earth can solve for its three dimensional position and time. GNSS is widely used for navigation and positioning of aircraft and satellites. Aviation users in particular, have very stringent requirements that are driving current augmentation and modernization efforts.

The global navigation satellite system (GNSS) has become an important space infrastructure. Following GPS and GLONASS, Europe and China have been building their own global navigation satellite system, respectively, GALILEO and Compass. In order to consolidate the leadership of GPS in the globe, United States is gradually upgrading the traditional GPS. Simultaneously, Russia is also intensively restoring full performance of GLONASS. With the advancement of international satellite navigation system, satellite navigation frequency resources are already in short supply, and the design and use of the navigation signals are more sophisticated and complex due to commercial, disaster relief and other reasons. Since there may be many navigation signals in the same basic bandwidth, the coexistence of multiple systems and the combined application make intersystem mutual interference become the focus research. Under this background, the satellite navigation system mutual interference evaluation system needs to be established urgently to meet and support the compatibility and interoperability of the GNSS system. In the paper, through the performance analysis of the GNSS signal acquisition, carrier tracking, data demodulation and code tracking, the equivalent carrier to noise ratio model based on spectrum isolation coefficient is established, and the theoretical system of the GNSS signal mutual interference is proposed according to the mechanism, and the mutual interference of GPS, GALILEO and Compass system is analyzed and assessed.

Recurrence plot analysis of GPS ionospheric delay time series in extreme ionospheric conditions

With the continuous promotion of smart campus construction, the rapid development of big data era greatly promotes the process of University Library Intelligence. Under the background of Smart Library, the construction of book micro service is going to a higher level. In the era of big data and micro data, the application of artificial intelligence technology can be improved, and the convenience of big data service platform can be improved. This paper analyzes and summarizes the research status of micro service in university library, and summarizes the research direction, hot spots and difficult issues of Library micro service. Domestic and foreign related literature database access to relevant documents, guidance, analysis and summary. This paper puts forward the definition of micro service in University Smart Library, and summarizes the research direction of micro service in university library. This paper takes MVs intelligent technology as the research topic, analyzes the development status of MVS intelligent technology, and the future development trend of MVS technology in the era of big data. The experimental results show that this study is of great significance for the establishment of micro service in University Library under the background of smart campus in the era of big data.

As the Global Satellite Navigation Systems (GNSS) signals are received and processed by the GNSS receivers with an extremely low power, they are vulnerable to non-intentional and intentional interference. In particular, the intentional transmission of Radio Frequency interference, known as jamming, can completely prevent the operation of GNSS receivers. The integration of measurements from multiple sensors with complementary error characteristics offers a possible countermeasure against jamming and, therefore, it can provide a position solution that has sufficient accuracy for the applications. This paper shows how a Deeply Coupled (DC) integration of GNSS with Inertial Navigation Systems (INS) and visual sensors enhances the robustness of the navigation system in presence of jamming. In particular, the effect of DC integration for jamming mitigation is investigated for a dynamic scenario where jamming signals have been added to a pre-recorded GNSS scenario by using the record and replay approach, emulating different interference levels. The results presented in this paper show that the deep coupling of GNSS with INS and visual sensors can sustain the navigation in presence of high power jamming, although such a strong interference completely masks the GNSS signal denying the navigation of a GNSS stand-alone system. Moreover, the test procedures suitability of the record and replay approach for the jamming scenario generation and combination with real datasets are discussed and analyzed.

With the continuous advancement of communication technology, vehicles are becoming electrified, autonomous, and connected. Compared to conventional vehicles, connected automated vehicles contain many wireless technologies, including cellular (2G, 3G, LTE), Bluetooth, Wi-Fi, Global Navigation Satellite System (GNSS), collision avoidance radar, and more. Therefore, characterizing wireless onboard systems such as automobile-mounted antennas in-vehicle environments is important. Currently, over-the-air (OTA) measurement systems and techniques are widely used to evaluate the performance of automobile-mounted antennas. This article elaborates on the development trends of automotive OTA antenna testing technology, covering aspects such as standards development, testing principles, testing solutions, and engineering experience.

This paper systematically reviews the research status and future development trends of time synchronization technology in drone swarms. The paper first elaborates on the basic theory of time synchronization and defines the evaluation indicators for synchronization performance. Then, it deeply analyzes the characteristics and development status of time synchronization technologies such as centralized and distributed synchronization protocols, covering GPS time transfer, RBS, TPSN, FTSP, PTP, ATS, FF, and other synchronization protocols, as well as advanced directions such as time compensation technology under motion, communication technology, and hardware optimization technology. Finally, the paper summarizes the four major development trends of time synchronization technology: further improvement in accuracy, enhanced network robustness, faster clock servoing speed, and optimized communication resource allocation. This study provides an overview of the development of time synchronization technology in drone swarms under dynamic complex environments and analyzes possible future research directions.