Navigation Signals Research Articles

Novel pedestrian navigation system based on zero velocity update procedure technology and improved Sage‐Husa adaptive Kalman filter with index fading memory factor

AbstractTo acquire an accurate location on the occasions, such as in an indoor, tunnel, and valley, where satellite navigation signals fail. The paper designs a pedestrian navigation system by using the zero velocity update procedure technology (ZUPT) and Kalman filter to reduce the location error. The measurement noise characteristic (mean and variance) of the micro electro mechanical systems gyros is unknown and time variant, but in traditional studies, it is usually thought and calculated as a constant. So the optimality of the error estimation of the Kalman filter cannot be reached. To address this question, this paper proposes the improved Sage–Husa Adaptive Kalman Filter (SHAKF) based on the index fading memory factor to realise the state estimation of the Kalman filter and navigation error correction. The advantage of improved SHAKF is it can accurately estimate the state vector when the measurement noise is unknown and time variant. To verify the validity of novel navigation methods, walking experiments under outdoor environments and indoor environments are carried out. The results of actual walking experiments demonstrate that the proposed method can effectively reduce the pedestrian location error compared with the traditional ZUPT method. The mean location error is reduced by more than 10%, and the variance of the location error is reduced by more than 5%.

Four-dimensional indoor visible light positioning: A deep-learning-based perspective

Accurate indoor positioning has been a difficult problem as the last meter dilemma of localization and navigation due to lack of satellite navigation signals and complex characteristics of multipath and dynamic indoor channels. Indoor visible light positioning (VLP) provides a new possible paradigm for accurate and low-complexity indoor positioning using widely deployed light-emitting diodes (LED). In this paper, the received signal strength of the photodetector at a mobile terminal is utilized to extract the geometric features in order to infer the accurate position coordinate via deep learning. Specifically, a hybrid model, i.e., a convolutional-recurrent neural network (CRNN), is devised to learn the nonlinear mapping from the received signal strength to the position coordinates in the complex indoor visible light propagation environment. A four-dimensional (4D) VLP architecture based on CRNN is formulated to deal with the non-line-of-sight propagation of indoor visible light and different receiver orientation. Simulation results show that the proposed CRNN-based 4D VLP (CR4D-VLP) method can achieve centimeter-level positioning accuracy, and significantly outperforms other state-of-the-art deep-learning-based schemes in both line-of-sight and non-line-of-sight scenarios with various spatial patterns of LEDs and different room sizes.

Carrier Characteristic Bias Estimation between GNSS Signals and Its Calibration in High-Precision Joint Positioning

A distinctive feature of modern Global Navigation Satellite System (GNSS) signals is that they transmit multiple signal components at the same carrier frequencies. The idea of joints across the signal channels from the same carrier frequency and even across different frequencies has been presented in many studies for tracking purposes. Carrier joint tracking is required on the premise that the frequency and phase relationship between signals are nominal values, and the bias of carrier characteristics between signals is drowned in noise as the signal reaches the ground, which requires high-gain receiving equipment to restore the original signal. The space signal-quality monitoring and evaluation system built by the National Timing Center of the Chinese Academy of Sciences is based on a 40 m dish antenna, which can automatically track a single satellite and achieve a high-fidelity reception of navigation signals to a certain extent, realizing fine signal quality monitoring (SQM) of GNSS satellites. Based on this platform, we discuss four types of time distributions of the combined signals among different signal components and provide a method to estimate the carrier characteristic bias between GNSS signals. We derived the correction method of carrier characteristic bias in the joint reception by the joint tracking mathematical model. Under the conditions of narrow correlation and unobstructed case, the carrier characteristic deviation does not vary significantly with the correlator interval and the satellite elevation angle. Based on the results of stability analysis, it is recommended that the receivers should update the carrier frequency bias correction number of the intra-frequency signal and carrier phase bias correction number of the intra-frequency signal monthly. The carrier phase deviation correction number of the inter-frequency signal is performed daily. The measured data from satellites show that the phase accumulation error of the joint tracking carrier loop can be eliminated to achieve long-term stable tracking after frequency bias correction. After the carrier phase bias correction, the joint positioning accuracy of the B2a and B2b signals was improved by 0.81%, and those of the B1C, L1C, E1C, and B2a signals were improved by 0.35%, 0.04%, 0.20%, and 0.11%, respectively. The positioning accuracy improvement effect of inter-frequency signals was greater than that of intra-frequency signals after carrier phase correction.

Weak Signal Processing Method for Moving Target of GNSS-S Radar Based on Amplitude and Phase Self-Correction

Navigation satellite signals have the advantages of all-day, all-weather, and global coverage, and the use of navigation signals for the detection of moving targets has significant application prospects. However, the GNSS signal is very weak, and the signal power is greatly attenuated after being scattered by the target. In order to detect the echo signal, a long integration time is required. However, the movement of the target will cause the echo signal to produce unpredictable range migration and a Doppler frequency shift, which will weaken the cumulative effect of long-term integration. This paper proposes a weak signal processing method with amplitude and phase self-correction for moving target detection in the GNSS-S radar. First, the phase consistency of the echoes of a single GNSS satellite is realized by the block expansion compression and phase differential correction method to improve the coherent accumulation gain; then, multi-star joint accumulation is carried out after the signal amplitudes of multiple satellites are corrected by the improved keystone method, so as to obtain a stable echo signal track. This method can effectively improve the integral gain of the scattering signal of the moving target and realize target detection. The simulation results and field tests show that this method can effectively improve the SNR of the GNSS-S signal and can realize the detection of small moving targets such as cars with GNSS-S radar.

Satellite Navigation Spoofing Interference Detection and Direction Finding Based on Array Antenna.

Satellite navigation signals are feeble when they reach the ground, so they are vulnerable to attacks from outside interference signals. By emitting spoofing interference signals similar to real satellite signals, spoofing interference can make receivers give wrong navigation, position, and time information, and it is challenging to detect. This seriously affects the safe use of GNSS; therefore, it is essential to identify spoofing interference signals quickly and accurately. In our study, we proposed a novel six-array spoofing-interference-monitoring array antenna, which achieved the detection and identification of spoofing interference sources by monitoring the relevant peaks and combining an airspace-trapping algorithm. Moreover, we quickly accomplished our search for the whole circumferential ambiguity by using long- and short-baseline algorithms, which can realize the high-precision detection of spoofing interference sources. To verify this method's accuracy, we conducted outdoor real experiments using a special spoofing interference source, and our experimental results show that our proposed array antenna's directional accuracy for spoofing interference signals is kept within 2°, showing high spoofing interference direction-finding capability.

Influence of sweep interference on satellite navigation time-domain anti-jamming

The global navigation satellite system (GNSS), represented by global positioning systems (GPS), is widely used in various civil and military fields and represents an essential basis for space-time information services. However, the radar signals partially overlap with the frequency band of satellite navigation signals, seriously affecting the normal reception of weak satellite navigation signal power. To further improve anti-jamming with sweep interference in the time domain, this paper focuses on the sweep interference scenario, studies the influence of the sweep interference on time-domain-adaptive anti-jamming, and proposes a timing reset based on the adaptive filter. The proposed method can effectively deal with the influence of sweep interference on time-domain-adaptive anti-jamming and can suppress interference and protect signals at the same time. Simulation experiments verify the effectiveness of the anti-jamming method proposed in this paper. Under the typical simulation scenarios, the influence time of the frequency sweep interference on the navigation signal is less than 1 m when the timing reset period is 1 m, which is significantly reduced compared to traditional methods. The proposed anti-jamming method is of great significance for improving the survivability of satellite navigation receivers in sweep interference scenarios.

Spoofing’s Selection and Compensation in the Global Navigation Satellite System Consumer Navigation Equipment with Multi-Channel Antenna System

A method for selecting spoofing signals in consumer equipment with a multichannel antenna system is proposed. The method provides for consistent filtering of the received signals at the outputs of all antenna system elements and by ranging codes of all navigation satellites, detection and measurement of the time delay of the true and false navigation signals in each code channel by the output signal of one of the antenna system elements, measurement of the phase difference of the signals at the outputs of the antenna system elements and the selected reference element for the estimated time delay in each channel by code. Compensation of spoofing signals is carried out in the spatial domain by estimating the correlation matrix of processes at the outputs of the antenna system channels by the corresponding countdown of code channel signals after matched filtering and forming of a weight vector while minimizing the output power of spoofing signals by directly inverting the estimate of the correlation matrix and carrying out weight processing of the adopted implementation. The simulation results are presented, confirming the efficiency of the method.

Navigator-based slice tracking for prospective motion correction in kidney vessel architecture imaging

ObjectivesTo apply a navigator-based slice tracking method to prospectively compensate the respiratory motion for kidney vessel architecture imaging (VAI). Materials and methodsA dual gradient echo spin echo 2D EPI sequence was developed for kidney VAI. A single gradient-echo slice selection and projection readout at the location of the diaphragm along the inferior-superior direction was applied as a navigator. Navigator acquisition and fat suppression were inserted before each transverse imaging slice. Motion information was calculated after exclusion of the signal saturation in the navigator signal caused by imaging slices. The motion information was then directly sent back to the sequence and slice positioning was adjusted in real-time. The whole sequence was applied during a contrast agent pass-through. ResultsVAI parametric maps show the structural heterogeneity of the renal vasculature. The respiratory motion from the navigator signal was precisely calculated and slice positioning was changed in real-time based on the motion information. The vibration amplitude of the signal intensity of the liver tissue at the liver-lung interface in the case of prospective motion correction (PMC) on is about 28% of the PMC off case. Compared to the case of PMC off, the coefficient of variation was reduced 30% of the case of PMC on. ConclusionsThis study demonstrates the feasibility of the motion-compensating technique in kidney VAI. The sequence may improve the evaluation of microvasculature in kidney diseases.

Radio-Frequency Interference Considerations for Utility of the Galileo E6 Signal Based on Long-Term Monitoring by ARFIDAAS

<h3>Abstract</h3> The extent to which navigation signals in the E6 band may be impacted by shared spectrum allocations might be underappreciated. This paper presents top-level observations from a multi-year international radio frequency interference (RFI) monitoring project covering all L-band global navigation satellite system (GNSS) signals with specific focus on the challenges facing the E6 band. The context of this paper is the assumption that most users will be non-authorized and have access to only the open data-bearing signal component and not the encrypted pilot of the E6 Galileo signal. In virtually all locations where the Advanced RFI Detection, Analysis, and Alerting System (ARFIDAAS) monitoring stations were deployed, frequent disruption of the E6 band from systems such as radar installations or other authorized users of the spectrum was observed. In the presented paper, an effort is made to put the observations in the context of the expected use cases of the E6 signal.

Exploiting On-Demand 5G Downlink Signals for Opportunistic Navigation

This letter presents the first user equipment (UE)-based 5G navigation framework that exploits the “on-demand” 5G downlink signals. In this framework, the entire system bandwidth of incoming 5G signals is utilized in an opportunistic fashion. The proposed framework involves a cognitive approach to acquire the so-called ultimate reference signal (URS), which includes the “on-demand” as well as “always-on” reference signals (RSs). Experimental results are presented showing that the acquired URS: (i) spans the entire 5G downlink bandwidth, (ii) increases the carrier-to-noise ratio by 10 dB compared to state-of-the-art 5G user equipment (UE)-based opportunistic navigation receiver, and (iii) reduces significantly the carrier and code phase errors. A ranging error standard deviation of 2.75 m was achieved with proposed framework with a stationary receiver placed 290 m away from a 5G gNB in a clear line-of-sight environment, which is lower than the 5.05 m achieved when using the “always-on” 5G downlink signals.

A Flexible Ephemeris Representation for Global Navigation Satellite Systems and Alternative Positioning, Navigation, and Timing Signal Sources Using B-Splines

A Flexible Ephemeris Representation for Global Navigation Satellite Systems and Alternative Positioning, Navigation, and Timing Signal Sources Using B-Splines

Impact of Navigation and/or Communication Signal Unavailability on Unmanned Aircraft Systems

The vast majority of unmanned aircraft systems nowadays rely on satellite navigation to determine their position and altitude. These systems already achieve sufficient accuracy to be used for navigation during flights beyond the visual line of sight of a remote pilot. However, it is necessary to note that these systems are susceptible to reduced signal quality, which can pose a challenge, especially when operating within urban areas. This paper presents the results of experiments that aimed to simulate reduced GNSS signal quality through jamming and spoofing. Both static and dynamic tests were conducted using three specific categories of UAS. Successful jamming of GNSS signals was achieved across all selected UAS categories. The spoofing was successful with only one UAS category.

Analyses for the Mechanism of Solar Radio Burst Interfering Satellite Navigation Signal and Influence Presentation

太阳射电爆发是一种潜在的导航系统干扰因素。本文通过导航信号模型推导，分析了其干扰导航信号的机理，提出太阳射电爆发干扰导航通信的影响方程与太阳射电爆发流量、接收机性能以及太阳-天线高度角有关，其中太阳射电流量总功率与信号的信噪比下降呈正相关；同时，受到太阳-天线高度角和有效面积的制约，又与接收机环路滤波器响应函数呈卷积关系。通过对2003年10月28日、2006年12月6日和2015年11月4日事件中GPS失锁情况分析，发现同一次事件中同一站点不同接收机的失锁率不同；同一次事件中不同纬度的接收机失锁率不同，以及在同一次事件中L波段（1~2 GHz）太阳射电爆发频谱不均匀的条件下，L1和L2频段信号的信噪比下降情况也不同。 从上述三个事件的观测表征验证了上述影响方程的分析正确性。

Decision support for autonomous drone flight based on satellite navigation signal

Artificial intelligence algorithms, particularly machine learning, are used to effectively support autonomous flight decisions based on satellite navigation signals. These algorithms can learn to recognize various patterns in navigation data and use them to make decisions on flight direction, speed, and other parameters. In any case, a combination of various technologies such as artificial intelligence algorithms, navigation systems, sensors, and other tools is necessary to effectively support autonomous flight decisions based on satellite navigation signals. The article presents the results of research on GPS signal jamming for UAVs and proposes a method to protect against such attacks using an ELECTRE-based algorithm that analyzes jamming signals.

ПРИМЕНЕНИЕ ПРОГРАММИРУЕМЫХ ЛОГИЧЕСКИХ ИНТЕГРАЛЬНЫХ СХЕМ В СИСТЕМАХ МНОГОКАНАЛЬНОЙ ЦИФРОВОЙ ОБРАБОТКИ СИГНАЛОВ СПУТНИКОВОЙ НАВИГАЦИИ

The study analyzes multichannel digital satellite navigation signal processing systems for unmanned aerial vehicles. To advance interference insusceptibility of navigation equipment on the basis of adaptive change in settings, it is advisable to apply a field programmable gate arrays in order to implement variations of algorithms of signal processing without reconfiguring the equipment’s structure in changes in radioelectronic settings. A navigation complex with the function of interference insusceptibility is developed based on the field programmable gate arrays. It may simultaneously receive signals from such satellite navigation systems as GLONASS, GPS, QZSS, BeiDou, Galileo, and NavIC via four independently tuned channels and their digital processing using adaptive filtering algorithms. Patterns in spatial selectivity of signals are studied, as are the possibilities for navigation equipment adaptability in interference settings using programs for electrodynamic modeling of adaptive antenna arrays ‒ SolidWorks, Altium Designer, and Quartus.

Разработка имитационной модели определения координат воздушных объектов по отраженному от воздушного объекта и принятому на антенну навигационного приемника навигационному сигналу ГНСС

This article is devoted to the development of a simulation model for determining the coordinates of air objects based on the GNSS navigation signal reflected from the air object and received on the antenna of the navigation receiver. To solve the problem of radar of aerial objects using bistatic location based on the use of GNSS satellites, it was necessary to pre-evaluate the energy or energy potential of the satellite navigation signal reflected from the aerial object, which then comes to the receiving antenna of the navigation equipment of consumers. The results obtained in the form of the developed computational schemes will form the basis of the algorithmic and software of the passive radar system and will allow determining the requirements for its technical support carried out within the framework of the grant project of the Ministry of Education and Science of the Republic of Kazakhstan No. AP09260581. In this paper, simulation modeling is understood as such an approach to modeling complex systems, which allows us to develop a single meta-model that combines into an integral set of models of objects and processes of their interaction based on a single information and event space in a single discrete time scale, and implement the resulting meta-model in an electronically equivalent form on an electronic computer. One of the main tasks of the study of complex radio engineering systems by modeling is the choice of modeling principles that should allow the construction of the simulated system in accordance with the goals and objectives of the study in such a way that the model adequately reflects the processes and patterns of behavior of the system under study with the necessary degree of reliability and detail. One of the most productive methods of developing a software and hardware complex of simulation modeling is object-oriented modeling.

Integrated Navigation and Communication Service for LEO Satellites Based on BDS-3 Global Short Message Communication

Massive global Low Earth Orbit (LEO) constellations have been developed rapidly with the characteristics of larger number and shorter orbital periods of LEO satellites in recent years. The increasing requirements of real-time orbit determination and emergency data transfer in full arc can hardly meet the traditional strategies based on regional ground stations. An integrated communication and navigation service architecture based on the third phase of the BeiDou system (BDS-3) Global Short Message Communication (GSMC) is proposed, which enables global coverage and random access. The GSMC downlink single-frequency signal is used for real-time orbit determination, and is further combined with B1C navigation signal for real-time dual-frequency high-precision orbit determination. Considering fast moving of LEO satellites and short burst of uplink messages, the uplink BDS-3 satellite selection strategy based on carrier-to-noise ratio, and uplink high-precision compensation of frequency shift are adopted to increase the communication success rate. The service architecture proposed can improve the precision of the autonomous orbit determination and enhance the capability of real-time command transmission of LEO satellites even without the traditional ground stations involved. Integrated communication and navigation service has been validated by simulation and on-board BDS-3 GSMC test data. The precision of single-frequency real-time orbit determination can reach 2.86m, and the precision of dual-frequency can reach 0.26m. The average time delay of communication is about 11.45s, and the success rate is about 99.8%. The method may provide alternative means of real-time high-precision orbit determination and emergency data transfer of LEO satellites.

Improving GNSS Spoofing Awareness in Smartphones via Statistical Processing of Raw Measurements

Due to the low received power of Global Navigation Satellite Signals (GNSS), the performance of GNSS receivers can be disrupted by anthropogenic radio frequency interferences, with intentional jamming and spoofing activities being among the most critical threats. It is reported in the literature that modern, GNSS-equipped Android smartphones are generally resistant to simplistic spoofing, and many recent contributions support such a biased belief. In this paper, we present the results of a test campaign designed to further stress the resilience of such devices to simplistic spoofing attacks and highlight their actual vulnerability. We then propose an effective spoofing detection technique, that exploits the spatial and temporal correlation of the counterfeit signals by leveraging the statistical analysis of raw GNSS measurements. By not requiring access to the low signal processing level of the GNSS id=Greceiverprocessor, the proposed solution applies to id=Gany id=Gdevicedevices embedding a GNSS id=Greceiver that providesunit and providing output raw GNSS measurements, such as current Android smartphones. Vulnerability analysis and validation of the proposed technique were conducted in a controlled environment by transmitting realistic, id=Gcounterfeitfake Global Positioning System id=R1(GPS) L1/CA navigation signals to a variety of Android smartphones id=Gembedding also differentand embedded GNSS chipsets. id=GIn the process, id=GWWe show that, under proper conditions, the devices were vulnerable to the attacks and that the effects were visible through their raw measurements, i.e., Carrier-to-noise ratio (C/N0), pseudo-range measurements, and position estimates. In particular, the study demonstrates that cross-correlation between id=Gthe C/N0 time series provided by each device id=Gforabout different GNSS satellites id=Gincreasesincrease under spoofing conditions, thus constituting id=Gan effectivea proper metric to detect the attack within a few seconds.

GNSS-R monitoring of soil moisture dynamics in areas of severe drought: example of Dahra in the Sahelian climatic zone (Senegal)

ABSTRACT With population growth, water will increase in the following decades tremendously. The optimization of water allocation for agriculture requires accurate soil moisture (SM) monitoring. Recent Global Navigation Satellite System Reflectometry (GNSS-R) studies take advantage of continuously emitted navigation signals by the Global Navigation Satellite System (GNSS) constellations to retrieve spatiotemporal soil moisture changes for soil with high clay content. It presents the advantage of sensing a whole surface around a reference GNSS antenna. This article focuses on sandy SM monitoring in the driest condition observed in the study field of Dahra, (Senegal). The area consists of 95% sand and in situ volumetric soil moisture (VSM) range from ~3% to ~5% durinf the dry to the rainy season. Unfortunately, the GNSS signals’ waves penetrated deep into the soil during the dry period and strongly reduced the accuracy of GNSS reflectometry (GNSS-R) surface moisture measurements. However, we obtain VSM estimate at low/medium penetration depth. The correlation reaches 0.9 with VSM error lower than 0.16% for the 5–10-cm-depth probes and achieves excellent temporal monitoring to benefit from the antenna heights directly correlated to spatial resolution. The SM measurement models in our research are potentially valuable tools that contribute to the planning of sustainable agriculture, especially in countries often affected by drought.

IMPROVEMENT OF THE GPS SIGNAL RECEIVING RESISTANCE AGAINST ELECTROMAGNETIC INTERFERENCE, JAMMING, AND SPOOFING IS BASED ON THE USE OF THE ANTENNA ARRAY SYSTEM WITH DIGITAL BEAMFORMING AND NORAD TLE INFORMATION

Background. Currently, in radio navigation systems of the various purposes, the urgent issue is stability increase of the GPS signal reception under such a jamming and spoofing types of the interference influence. In this article, the authors propose a new solution to the stability increase problem of the GPS signal reception against the jamming and spoofing interference based on the spatial selectivity of the receiver antenna. Spatial selectivity is provided through the integrated application of phased array digital beamforming technology and the use of the TLE NORAD information.&#x0D; Objective. The research goal is to develop a methodology for the integrated identification of interference sources to the radio navigation system and to increase the noise immunity for receiving radio navigation signals via spatial selection through the digital beamforming technologies utilization.&#x0D; Methods. For the research process, theoretical methods for the digital beamforming of receiving phased antenna system were used as well as the description of a two-line NORAD information element content, and calculation algorithms for the spacecraft current position.&#x0D; Results. As a result of the research, the GPS signal reception model was formed using spatial selection of GPS signal sources and interference sources, the technique to increase the stability of GPS signal reception under the jamming and spoofing types of interference influence was developed, the block diagram was suggested for the receiving device that implements the developed technique through the integrated application of the digital beamforming technology of the phased array antenna and the TLE NORAD information utilization.&#x0D; Conclusion. A conceptual idea of the method and a technical solution for the proposed method implementation were submitted. The method implementation will improve the stability of GPS signal reception under the influence of jamming and spoofing types of interference.