Navigation Signals Research Articles

In-flight performance analysis of the navigation augmentation payload on LEO communication satellite: a preliminary study on WT01 mission

ABSTRACT With the development of the Low Earth Orbit (LEO) communication constellations, it has become a hot area of research to provide additional navigation augmentation services. Limited by volume, weight, power consumption, and running time, the in-flight performance of navigation augmentation payload remains to be investigated. In this paper, we analyze the data quality of on-board GNSS observation and evaluate the precision of short-arc dynamic Precise Orbit Determination (POD) performance based on the WangTong-01 (WT01) mission. Furthermore, the downlink navigation measurement data of WT01 satellites are analyzed and compared with the GNSS observations. The results show that the average multipath errors of the WT01 on-board GPS L1, L2 and BeiDou Satellite Navigation System (BDS) B1, B2 code observation are 0.54, 0.74, 0.65, and 0.58 m, respectively. The short-arc dynamic POD three-dimensional (3D) overlapping accuracy is 7.1 cm. The average multipath errors of downlink navigation signal Z1 and Z2 are 0.81 and 0.80 m, respectively, which at the same order of magnitude as GNSS signals. The maximum Carrier-to-Noise Ratio (C/N0) value of WT01 downlink measurement data can reach 60 dB Hz, which is much stronger than GNSS and indicates the navigation signals of LEO satellites can meet the basic requirement of navigation augmentation.

Research on Correlation Peak Distortion Detection Method of Satellite Navigation Signal

Correlation peak distortion is an important part of signal quality monitoring (SQM) correlation domain research, in which correlation peak distortion detection plays an important role in the traceability of abnormal satellite navigation signals. In this paper, the GPS navigation signal data is processed, and the actual correlation peak distortion range is obtained by using the idea of multi-correlator accumulation and averaging, and the detection of the navigation signal correlation peak distortion is realized by comparing the ideal correlation peak. The correlation peak distortion detection method proposed in this paper can realize the rapid detection of correlation peak distortion, and provide a new idea for the research of correlation peak distortion detection.

Research of the Receiving Module of Phase Measurements Based on a Navigation Signal with a Step-By-Step Frequency Change

The article deals with the formation of a navigation signal with a stepwise change in the frequency of a phase radio navigation system, a description of the method of signal formation is given, which ensures high performance of models and low resource requirements for hardware implementation. Structural diagrams of the models used in the study are presented, as well as the results obtained on assessing the accuracy of ranging with the use of such a signal at various signal-to-noise ratios.

Reckoning ionospheric scintillation S4 from ROTI over Indian region

• Study of Ionospheric scintillations indices S4 and ROTI in Indian region. • Relation between ROTI & S4 is useful for standard GNSS receivers to estimate S4. • Correlation of ROTI & S4 is better than 0.6, yet an estimate of S4 is unreliable. • Using obtained relation, a range of S4 values can be estimated from ROTI value. Ionospheric irregularities cause fluctuations (scintillations) in received satellite signal strength, degrading communication and navigation signals. The scintillation strength depends on the scale sizes of the irregularities and the frequency of the radio signal. The parameter S4 index describes the scintillation strength derived from the amplitude of high rate received signal sampled at 50 Hz, usually from special GNSS receivers. Most GNSS receivers have a lower data sampling rate, so an alternate parameter, Rate of Change of TEC Index (ROTI), is derived from the total electron content (TEC) sampled at 30 s. Here, the correlation between ROTI and S4 is performed for the Indian ionospheric region, with different elevation mask angles and ROTI calculated over different averaging intervals. An estimate of the S4 value from ROTI is unreliable even though the correlation between them is better than 0.6. Different elevation mask angles and ROTI with varying averaging intervals do not significantly affect the correlation between S4 and ROTI. Further, the correlation and occurrence percentages of S4 corresponding to ROTI are analyzed. An 80% confidence range is obtained to correlate the observed ROTI with the corresponding S4 index. These probability estimates of S4 values derived from ROTI values also vary with latitude. This relation between ROTI and S4 will be beneficial in using standard GNSS receivers for the studies of ionospheric scintillations.

Advanced methodology for multi-way transmission of ship data treatment from mechanical-navigational technical state sensors with using computational neural network computer systems

The paper presents a methodology for multi-track transmission processing of signals from mechanical-navigation sensors describing the state of the ship's motion vector by using a neural network computer system. The integration of mechanical systems with navigation systems on a sea vessel is aimed at creating a uniform decision-making module for the crew steering the ship and supervising propulsion systems in order to minimize the level of risk in controlling a sea vessel in hazardous situations. The concept of integrating radio devices with navigation and engineering systems will enable effective ship management based on sources coming from external and internal sensors of the ship. The processing of navigational and mechanical signals proposed in the article will allow to build an effective prediction of the developing situation in case of danger according to the proposed algorithm for the officer of the watch in charge of the ship. The paper presents a model of mathematical processing of signals from navigational-mechanical systems and illustrates its operation in an exemplary situation of a threat of collision of a sea vessel

Emvlight: A Multi-Agent Reinforcement Learning Framework for an Emergency Vehicle Decentralized Routing and Traffic Signal Control System

Emergency vehicles (EMVs) play a crucial role in responding to time-critical calls such as medical emergencies and fire outbreaks in urban areas. Existing methods for EMV dispatch typically optimize routes based on historical traffic-flow data and design traffic signal pre-emption accordingly; however, we still lack a systematic methodology to address the coupling between EMV routing and traffic signal control. In this paper, we propose EMVLight, a decentralized reinforcement learning (RL) framework for joint dynamic EMV routing and traffic signal pre-emption. We adopt the multi-agent advantage actor-critic method with policy sharing and spatial discounted factor. This framework addresses the coupling between EMV navigation and traffic signal control via an innovative design of multi-class RL agents and a novel pressure-based reward function. The proposed methodology enables EMVLight to learn network-level cooperative traffic signal phasing strategies that not only reduce EMV travel time but also shortens the travel time of non-EMVs. Simulation-based experiments indicate that EMVLight enables up to a $42.6\%$ reduction in EMV travel time as well as an $23.5\%$ shorter average travel time compared with existing approaches.

Effect of total lunar eclipse of 27th July 2018 on the D-region ionosphere by using VLF observations

• Total Lunar Eclipse of 27 July 2018 is investigated for its impact on lower ionosphere. • Change in D-region electron density is inferred from VLF observations and modeling. • Nighttime lower ionospheric density during the Total Lunar Eclipse was found to decrease. In this report, an effort for the first time has been made to investigate the effect of the total Lunar Eclipse that occurred on 27th July 2018 (the longest lunar eclipse in the 21st century) on the D-region ionosphere. Very Low Frequency (VLF) navigational transmitter signals recorded at Prayagraj (formally Allahabad) station in India is the primary dataset used. The signals from two VLF transmitters: NWC (19.8 kHz) from Australia, and JJI (22.2 kHz) from Japan, have been utilized. When compared to unperturbed night, NWC signal amplitude showed an anomalous decrease of ∼0.86 dB, while JJI amplitude showed an anomalous increase ∼0.26 dB during the lunar eclipse. The Wait’s lower ionospheric parameters: reflection height ( H’ ) and sharpness factor ( β ) are estimated by using a rather coarse method of modeling of VLF signals anomalies on eclipse day, which comes out to be H’ = 85.25 km & β = 0.689 km −1 and H’ = 84.59 km & β = 0.683 km −1 respectively for NWC and JJI path. Using wait parameters, the electron density ( N e ) profile is estimated and this showed a decrease in N e during eclipse time with reference to the nighttime ambient values. The N e values for the NWC path, showed relatively higher decrease compared to the JJI path. The plausible reasons for observed N e decrease on lunar eclipse night could be due to the reflected lunar Lyman‐α and X-ray’s radiation which may contribute to the nighttime ionization is blocked during the lunar eclipse, thereby decreasing the nighttime lower ionospheric N e .

Formation of a navigation signal with double meander modulation

Formation of a navigation signal with double meander modulation

Metamaterial absorber and antenna ground plane

Metamaterial absorber located near solid metal surface was investigated and antenna design was developed for receiving satellite navigation signals using absorptive ground plane comprises proposed material. The metamaterial structure has been developed, frequency characteristics have been analyzed by finite element method in frequency domain, operating dimensions of elements have been established. Modeling and analysis of radiation pattern for antenna with absorptive ground plane versus the antenna with the classic high impedance ground plane were carried out. Conclusions were drawn on the applicability of the proposed metamaterial structure. Keywords: GNSS Antenna, metamaterial absorber, high impedance ground plane.

Algorithm for distinguishing and estimating the parameters of radio navigation signals from a set of spaced correlators

Algorithm for distinguishing and estimating the parameters of radio navigation signals from a set of spaced correlators

Assessing Repeatable Accuracy Potential of LoRa: A Navigation Approach

Two main classes of radio navigation systems are satellite and ground-based systems. Examples of such systems are eLoran deployed as a terrestrial system, and BeiDou, Galileo, GPS and Quasi-Zenith Satellite System (QZSS) deployed as satellite Navigation Systems. These systems have been investigated in different navigation use-cases using a hybrid receiver capable of receiving any navigation signal. The goal of this paper is to demonstrate LoRa’s capability as a signal of opportunity (SoOP) to be used with other navigation technologies in order to improve repeatable accuracy. While researchers have investigated LoRa’s potential for navigation purposes, there is limited literature regarding the repeatable accuracy estimation using LoRa. Our work proposes using a weighted horizontal dilution of precision (HDOP) while incorporating SNR, spreading factors (SF) and the Ericsson 9999 path loss model. The gateway separation distances: 1500 m, 1000 m and 400 m respectively are employed at a bandwidth of 125kHz to determine repeatable accuracy within a 95% confidence limit. Our simulation results show that for 1500 m, 1000 m, and 400 m, gateway separation distances have a best repeatable accuracy of 1249 m, 284.2 m and 4.314 m, respectively, when the spreading factor (SF) is equal to 12. The initial repeatable accuracy results are promising and comparable to those obtained by other researchers. Our model’s limitation is that the best SNR was not used to determine position. A climatic model and stochastic channel interference observed in the 900MHz frequency band were also assumed to be negligible to provide a working model that can be modified as data becomes available.

Detection of Red Tide Over Sea Surface Using GNSS-R Spaceborne Observations

Due to the continuous intensification of human activities in the ocean, the frequent outbreaks of red tide have caused great harm to the marine environment and ecology. Thus, the rapid detection and monitoring of red tide become particularly important. At present, the main monitoring methods depend on artificial and buoy data, as well as optical satellite remote sensing. However, these methods may not be able to effectively deal with the characteristics of red tide bloom, such as suddenness and unpredictability. The global navigation satellite system-reflectometry (GNSS-R) is an emerging technology that makes use of navigation signals as a remote sensing opportunity to obtain Earth surface information. GNSS-R has already been proved to be capable of retrieving sea surface parameters (e.g., dielectric constant and sea surface roughness) closely related to the outbreak of a red tide. In this article, we proposed a new method to estimate red tide density, which utilizes an all-new model associating GNSS-R observations with sea surface red tide density. This method can remove the weather influence and greatly decrease the revisit period, which is much longer for optical red tide remote sensing methods. The Landsat-8 near-infrared data and TechDemoSat-1 (TDS-1) GNSS-R data of a red tide outbreak in the sea off the Tsingtao coast in China are used to build and test the proposed method. The results demonstrate that the correlation coefficient is 0.73, and the root mean square error of retrieved red tide density is 2.84%, which shows that the GNSS-R technology shows great potential to perform the rapid and preliminary red tide monitoring and judgment.

In-Vehicle Human Machine Interface: Investigating the Effects of Tactile Displays on Information Presentation in Automated Vehicles

<bold xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Background:</b> Semi-autonomous vehicles still require human drivers to take over when the automated systems can no longer perform the driving task. <bold xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Objective:</b> The goal of this study was to design and test the effects of six meaningful tactile signal types, representing six driving scenarios (i.e., navigation, speed, surrounding vehicles, over the speed limit, headway reductions, and pedestrian status) respectively, and two pattern durations (lower and higher urgencies), on drivers’ perception and performance during automated driving. <bold xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Methods:</b> Sixteen volunteers participated in an experiment utilizing a medium-fidelity driving simulator presenting vibrotactile signals via 20 tactors embedded in the seat back, pan, and belt. Participants completed four separate driving sessions with 30 tactile signals presented randomly throughout each drive. Reaction times (RT), interpretation accuracy, and subjective ratings were measured. <bold xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Results:</b> Results illustrated shorter RTs and higher intuitive ratings for higher urgency patterns than lower urgency patterns. Pedestrian status and headway reduction signals were associated with shorter RTs and increased confidence ratings, compared to other tactile signal types. Lastly, among six tactile signals, surrounding vehicle and navigation signal types had the highest interpretation accuracy. <bold xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Conclusion:</b> These results will be used as preliminary data for future studies that aim to investigate the effects of meaningful tactile displays on automated vehicle takeover performance in complex situations (e.g., urban areas) where actual takeovers are required. The findings of this study will inform the design of next-generation in-vehicle human-machine interfaces.

The impact of simple navigation signals multipath propagation on the effectiveness of eliminating the phase measurements ambiguity

The impact of simple navigation signals multipath propagation on the effectiveness of eliminating the phase measurements ambiguity

Mathematical models of navigation signals with the required form of spectral power density

Mathematical models of navigation signals with the required form of spectral power density

Autocorrelation functions of navigation signals with meander modulation at two subcarrier frequencies

Autocorrelation functions of navigation signals with meander modulation at two subcarrier frequencies

Electrostatic treatment of agricultural crops with an unmanned electric device

One of the options for improving the efficiency of the machine and tractor unit in the field is the use of course indicators, thrusters, hydraulic autopilots and other equipment. However, these devices do not exclude environmental pollution by exhaust gases and the presence of significant operating costs for fuel and lubricants. In this regard, the paper proposes an electric-powered unmanned device (EPUD), which can perform the tasks with high accuracy (deviations from the set course average 16 cm) due to autonomous movement on GPS/GLONASS satellite radio navigation signals on agricultural lands. For the effective application of liquid agents to agricultural crops, a device is proposed that provides an electric charge of the introduced fine aerosol, which is installed on the EPUD and reduces the electrical energy consumed by 23.5% compared to existing analogues. All this, combined, will reduce operating costs up to 10%, as well as improve the environmental performance of crop spraying. Based on the conducted studies of the EPUD, its design was developed and a prototype with a software and hardware part was created. A device for the electric charge of the introduced aerosol, which makes it possible to increase the uniformity of the aerosol application on the plant, has been developed and investigated. The effectiveness of the developed technical solution had been proved by laboratory and field tests.

Performance Analysis of Navigation Signal Based on FH-BOC Modulation System

Based on the traditional BOC modulation system, a new navigation signal system based on FH-BOC is proposed in this paper. The simulation and verification of FH-BOC signal are carried out, and the modulation characteristics, code tracking performance and anti-interference performance of FH-BOC signal are analyzed, and the advantages and disadvantages of the modified system are verified. The results show that FH-BOC signal has good ranging and anti-interference ability, which is suitable for navigation system and can reduce the ambiguity of BOC signal’s secondary peak to a certain extent. At the same time, the T has important scientific significance and application value to improve the countermeasure capability of other satellite navigation systems.

Multi‐Instrument Investigation of the Impact of the Space Weather Events of 6–10 September 2017

AbstractWe analyzed the space weather events of 6–10 September 2017 using the multi‐instrument approach. We focused on the four X‐class flares which emanated from the Active Region AR 12673 and the Ground Induced Currents hazard associated with the geomagnetic storm of 7–8 September 2017. The flare effect on the equatorial electrojet (EEJ) recorded on board the SWARM satellite and on the horizontal component of the geomagnetic field (H) records of ground‐based magnetometers was further examined. During the X2.2/X1.3 flares of 6/7 September, the maximum percentage Global Navigation Satellite System (GNSS) vertical Total Electron Content (VTEC) increase was 6.9%/5.0% in Dakar/Porto Velho. During the X9.3/X8.2 flare of 6/10 September it was 7.9%/18.8% in Ascension Island/Kourou. The strongest Solar Flare Effect occurred in Mbour and Kourou during the respective flare. However, the highest EEJ increase was observed during the X2.2 and X9.3 flares. Interestingly, the X.9.3 flare resulted in a stronger ionospheric response than the X8.2 flare. Furthermore, global TEC map showed a higher response in the African and South American longitude during the respective event. The total radio fade‐out lasted from 30 to 90 min at the Hermanus and Sao Luis ionosondes during the flares, while the risk level to critical ground infrastructures based on the geomagnetically induced currents hazard was very low risk. Our results highlight the potential GPS positioning errors induced by sudden increase in TEC and the loss of high‐frequency communication and GNSS navigation signals associated with these solar events.

A signal optimization strategy for next generation navigation and communication integration applications

For 6G and future communication technologies, integration of navigation and communication has become a hot research topic, which can greatly improve the transmission data rate and can be applied to self-driving vehicles. In former research, a novel integrated navigation and communication signal has been designed by combining traditional global navigation satellite system (GNSS) and cyclic code shift keying (CCSK) signals. In this paper, we design an enhancement strategy for this signal, optimizing the number of cyclic shifts of the CCSK signal, which can make larger values of cross-correlation function align with the peak value of self-correlation function to overcome the cross-correlation interference and improve communication performance. Simulation results validate that the proposal not only can avoid interference between navigation and communication signals, but also can improve the signal detection probability and reduce the transmit error rate. Taking Beidou B1I signal as an example, when the signal to noise ratio (SNR) is set to -27 dB, the detection probabilities for the navigation and communication signals increase about 11.4% and 13.5%, respectively, while the symbol error rate (SER) for the navigation and communication signals decrease about 16.3% and 17.8%, respectively.