Satellite Navigation Signals Research Articles

Receiver-channel based adaptive blind equalization approach for GPS dynamic multipath mitigation

Aiming at mitigating multipath effect in dynamic global positioning system (GPS) satellite navigation applications, an approach based on channel blind equalization and real-time recursive least square (RLS) algorithm is proposed, which is an application of the wireless communication channel equalization theory to GPS receiver tracking loops. The blind equalization mechanism builds upon the detection of the correlation distortion due to multipath channels; therefore an increase in the number of correlator channels is required compared with conventional GPS receivers. An adaptive estimator based on the real-time RLS algorithm is designed for dynamic estimation of multipath channel response. Then, the code and carrier phase receiver tracking errors are compensated by removing the estimated multipath components from the correlators’ outputs. To demonstrate the capabilities of the proposed approach, this technique is integrated into a GPS software receiver connected to a navigation satellite signal simulator, thus simulations under controlled dynamic multipath scenarios can be carried out. Simulation results show that in a dynamic and fairly severe multipath environment, the proposed approach achieves simultaneously instantaneous accurate multipath channel estimation and significant multipath tracking errors reduction in both code delay and carrier phase.

Radio Interferometric Research of Ionosphere by Signals of Space Satellites

AbstractSince 2012, the Radiophysical Research Institute and the Lobachevsky State University at Nizhny Novgorod, Russia and the Ventspils International Radio Astronomy Centre at Irbene, Latvia are making radio interferometric experiments on study of ionosphere parameters in a quiet (natural) state of medium and research of artificial turbulence of the ionosphere, heated by the emission from the SURA facility. Remote diagnostics of the ionosphere is implemented using a method of radio sounding by signals of navigation satellites in combination with the Very Long Baseline Interferometry (VLBI) method. As a result of spectral and correlation analysis, interferometric responses of the two-element (RRI–UNN) and three-element (RRI–UNN–Irbene) interferometers were received by observations of 12 satellites of the navigation systems GLONASS and GPS. Here the first results are reported.

Remote Sensing and Geospatial Science at Purdue University: 1960s into the 21st Century [Education

Purdue's research and education in the field of remote sensing was built upon a strong foundation of expertise in engineering, science, and agriculture. The Laboratory for Agricultural Remote Sensing (LARS) was formed in 1966 with the objective of using an interdisciplinary, teamwork approach to creating and using space-based technology for observing and managing agricultural resources. Since the 1980s, LARS has focused primarily on research and education in development of algorithms for analysis of remotely sensed data and agricultural applications. In the past decade, research has also expanded to include processing and application of LIDAR data, atmospheric remote sensing, Global Navigation Satellite System (GNSS) and signals of opportunity (SoOP). Examples of today's research, education, and outreach at Purdue are presented in this paper.

Differential coherent algorithm based on fast navigation-bit correction for airborne GNSS-R software receivers

Signals from the Global Navigation Satellite System (GNSS) scatter over the sea surface resulting in relatively low Signal-to-Noise Ratios (SNR). A differential coherent algorithm is given here to improve the SNR and reduce the performance degradation due to the Squaring-Loss and the navigation-bit effect. The algorithm uses fast navigation-bit correction for Delay-Doppler Maps (DDM) in airborne Global Navigation Satellite Signal Reflectometry (GNSS-R) software receivers. The system model is introduced with an analysis of the statistical properties with simulations to support the theoretical analysis. Field experiments with real airborne receivers then demonstrate the effectiveness of this algorithm. Comparisons with test results show that this algorithm offers a significant SNR gain over conventional algorithms.

Doppler utilised Kalman estimation (DUKE) of ionospheric delay for satellite navigation

The ionospheric delay experienced by the satellite navigation signals depends upon the Total Electron Content (TEC) and needs to be corrected. While the single frequency receivers always use parametric models to correct this delay, dual frequency receivers, when suffers a loss of lock of one of its signal, also has to resort to these models. Here, an alternative method, based on Doppler, surrogated by range rate variation, has been attempted to estimate the ionospheric delay using a Kalman filter. GPS data have been used for all visible satellites over four days selected around the equinox and solstice with nominal geomagnetic conditions and estimations done in continuous and calibrated modes. Results of continuous estimation, obtained for a mid latitude station, showed moderate accuracy while it was significantly better for the calibrated mode with no seasonal dependence. Estimations done for station within the extent of equatorial anomaly, has not only resulted in relative deterioration in performance, but also shown seasonal dependence. Compared with estimates of Klobuchar model, the Calibrated estimation showed superior performance, conspicuously in the mid latitude station. However, for the continuous mode, performance was at par with the model at higher latitudes but inferior to it in regions within the extent of the equatorial anomaly.

Частотные характеристики вариаций параметров тропосферы и ионосферы в периоды прохождения солнечного терминатора

T he paper presents an analysis of the spectra of atmosphere aerosol variations and variations Total Electron Content in the ionosphere (TEC). Monitoring of atmospheric aerosol performed with using of the two-wavelength (532, 1064 nm) atmospheric lidar (LSA-2S). Ionospheric TEC parameter determined from the observation of the navigation satellites signals GLONASS (Leica1200). The observations in the lower atmosphere and ionosphere were executed simultaneously in the period February — March 2012. Analysis of the observations showed that during the period of solar terminator passing in the lower and upper atmosphere, there are variations of parameters with periods close to the period Vaisala — Brunt in the lower atmosphere. It is assumed that such disturbances are excited in the lower atmosphere and propagate into the upper atmosphere. It is assumed that the disturbances with periods close to the period of the Vaisala — Brunt can take an important part in the implementation of dynamic relationships of lower and upper atmospheric layers.

Technology and Application of Integrated Satellite Navigation and Communication Signal

The integration of navigation and communication technologies can be divided into three levels: system level, terminal level and the signal level. The integration technology of satellite communication and navigation is introduced briefly at first. Then the combination of communication and navigation functions at the signal level is analyzed and researched in depth. A novel idea is proposed that pseudo-range measurement and positioning can be achieved while keeping the existing communication functions, only by adding positioning related information. Finally, application of communication and navigation signal integration is prospected.

A substitute for BOC modulation based on SS-CPM

CPM (continuous phase modulation) has been widely used in the field of satellite communication, which has high spectrum efficiency and constant envelope. This paper explores the applicability of CPM to satellite navigation. A SS-CPM (Spread-Spectrum CPM) modulation is investigated. The SS-CPM with tuned parameters can resemble the spectrum of Binary Offset Carrier (BOC) modulation and yields comparable performance in terms of tracking accuracy, multipath mitigation, anti-jamming, and compatibility. The BOC-like SS-CPM signal maintains the constant envelope at transmission and less out-band emission in radio determination satellite service (RDSS) band, which provides a reference modulation for COMPASS satellite navigation signal.

Multi-Stage Satellite Phase and Code Bias Estimation

Precise point positioning with satellite navigation signals requires knowledge of satellite code and phase biases. In this paper, a new multi-stage method is proposed for estimating of these biases using measurements from a geodetic network. The method first subtracts all available a priori knowledge on orbits, satellite clocks and multipath from the measurements to reduce their dynamics. Secondly, satellite phase biases, ionospheric delays, carrier phase integer ambiguities and the geometry combining all non-dispersive parameters are jointly estimated in a Kalman filter. Finally, the a posteriori geometry estimates are refined in a second Kalman filter for the computation of orbital errors, code biases and tropospheric delays. As the first Kalman filter introduces time correlation, a generalized Kalman filter for colored measurement noise is applied in the second stage. The proposed algorithm is applied to dual frequency GPS measurements from a local geodetic network in Germany. A remarkable bias stability with variations of less than 3 cm over 4 hours is observed.

Design of a Baseband Signal Generator in Navigation Satellite Signal Simulators

To improve simulation precision, the signal model of navigation satellite signal simulators is illustrated, and the generation mechanism and evaluation criteria of an important error source-phase jitter in baseband signal generation, are studied subsequently. An improved baseband signal generator based on dual-ROM look-up table structure is designed with the application of a newly-established concept-virtual sampling rate. Pre-storage of typical baseband signal data and sampling rate conversion adaptive to Doppler frequency shifts are adopted to achieve the high-precision simulation of baseband signals. Performance analysis of the proposed baseband signal generator demonstrates that it can successfully suppress phase jitter and has better spectral performance, generating high-precision baseband signals, which paves the way to improving the overall precision of navigation satellite signal simulators.

Key technology of mine underground mobile positioning based on LiDAR and coded sequence pattern

Technologies of underground mobile positioning were proposed based on LiDAR data and coded sequence pattern landmarks for mine shafts and tunnels environment to meet the needs of fast and accurate positioning and navigation of equipments in the mine underground without satellite navigation signals. A coded sequence pattern was employed for automatic matching of 3D scans. The methods of SIFT feature, Otsu segmentation and fast hough transformation were described for the identification, positioning and interpretation of the coded sequence patterns, respectively. The POSIT model was presented for speeding up computation of the translation and rotation parameters of LiDAR point data, so as to achieve automatic 3D mapping of mine shafts and tunnels. The moving positioning experiment was applied to evaluating the accuracy of proposed pose estimation method from LiDAR scans and coded sequence pattern landmarks acquired in an indoor environment. The performance was evaluated using ground truth data of the indoor setting so as to measure derivations with six degrees of freedom.

Application of quasi-cycle low-density parity check codes with high performance to satellite navigation signals

Application of quasi-cycle low-density parity check codes with high performance to satellite navigation signals

Navigation Using Images, A Survey of Techniques

The accuracy and availability of Global Navigation Satellite Systems (GNSS) has revolutionized navigation. As a result, world-wide, meter-level positioning is required for many applications. Unfortunately, satellite navigation signals are not available in all environments. To address this issue, researchers have devoted much effort into investigating the use of image sequences for navigation. Many different image-aided navigation techniques have been demonstrated, each with varying assumptions, and most using ad-hoc techniques. This results in little information on how to apply image-aided techniques to problems with differing assumptions. The goal of this article is to characterize the properties of various forms of image-aided navigation. Once the observability is established, additional measurements that can augment weak areas are presented and discussed. The limitations of current image-aided navigation techniques are shown to require additional measurements from a non-homogeneous sensor for reliable, long-term navigation.

Study of SAR imaging with COMPASS signal

A concept of space-surface bistatic synthetic aperture radar (SS-BSAR) passive imaging system is proposed, which is parasitic on the signal of COMPASS Navigation Satellite System (CNSS). The feasibility is demonstrated by analyzing the signal ambiguity function and the range resolution as well as the system topology. Due to the multiple peaks of signal in the auto-correlation function, a new correlation is used to remove the side-peaks. A double-channel receiver is employed to receive the direct satellite signal and the ground reflected signal. The direct signal is a reference signal in range compression, and may also be used for transmitter-receiver signal synchronization. The reflected signal is raw data collected for imaging. Then, a modified range-Doppler imaging algorithm is derived based on the system geometric models and BSAR imaging principle. The proposed algorithm is verified via signal simulation. The work in this paper is of great value to the further use of COMPASS signal, as well as other global navigation satellite signals in passive imaging.

Optimizing the Gabor Bandwidth of satellite navigation signals by MCS signal expression

Satellite navigation is playing an important role in social life. The performances of the services a navigation system provides are the concern of the builders and users. The signal structure determines the inherent ability of a satellite navigation system to provide these services. Therefore, it is necessary and reasonable to optimize the signal in the initial design. The waveforms of signals in satellite navigation chips are an important aspect of the signal’s structure, which impact the characteristics of the autocorrelation function and power spectrum in the time domain and frequency domain. The range accuracy of a navigation system is usually described by its Gabor Bandwidth. The Gabor Bandwidth of the Binary Offset Carrier (BOC) modulation in next-generation GNSS signal systems is not optimal. This paper presents a signal expression based on Multilevel Coded Symbol (MCS) signals, which can describe the fine structure of navigation signals. With this expression, we can optimize the Gabor Bandwidth of the signal, and find out the corresponding MCS vector and chip waveform, so as to get higher range accuracy. The method in this paper, in theory, is of great value in the design of next-generation navigation signals.

Urban environment solutions to GPS signal near-far effect

Our aim at improving GPS receivers' availability in an urban environment, weak GPS signal acquisition becomes one key issue in satellite navigation signal processing. In special signal propagation environments, such as indoors, urban crayons, and woods, various factors such as signal propagation power loss, amplitude attenuation, and phase, time, and frequency delay distortions produce at the signal receiving end, what is now known in the literature as, the GPS signal near-far effect, which results in severe degradation of the GPS signal acquisition performance. To mitigate the near-far effect, we focus on four main factors, which are the signal strength attenuation; the Doppler frequency distortion; carrier phase uncertainty; and multi-path distribution because a proper optimization of these factors appears to improve the acquisition performance effectively.

Experimental Determination of the Sea Correlation Time Using GNSS-R Coherent Data

The feasibility of the Global Navigation Satellite Signal Reflectometry (GNSS-R) techniques has been proven for remote determination of sea state. When using GNSS-R techniques, coherent integration time is limited by the correlation time of the surface under observation which, in the case of the ocean, depends on sea state. In this letter, a new technique to retrieve the sea correlation time at L-band using GNSS-R coherent data is presented along with experimental results.

Parameters of traveling ionospheric disturbances estimated from satellite beacon observations in low-earth orbit

Based on beacon sounding the ionosphere using coherent signals of low-orbiting navigation satellites, the following parameters of medium-scale traveling ionospheric disturbances have been determined: the effective thickness of the atmospheric waveguide and the altitude of its longitudinal axis, the horizontal spatial period, the velocity, the maximum amplitudes of disturbances, and the inclination of the disturbance phase front. It has been found that the horizontal spatial period of studied disturbances increases with increasing distance to an initiating impact location and its delay. In this case the minimum value of the horizontal spatial period always exceeds ∼150 km, and the disturbance amplitude increases with increasing horizontal period and distance from the initiating disturbance location and with decreasing altitude of the main ionization maximum. All disturbance parameters are independent of the initiating impact nature. It has been found that disturbances with relative amplitudes of 0.1–0.7 are often observed. Disturbances that are registered more often travel southward, and their absolute velocities are 7–60 m/s.

Using fuzzy logic controller with adaptive detection scheme for fast acquisition of satellite navigation signals

The paper presents a fuzzy logic controller (FLC) with adaptive threshold control scheme to regulate frequency search step size so as to enhance performance in global navigation satellite system (GNSS) signal acquisition. Conventional frequency search can be achieved utilizing step‐by‐step frequency bin search or through fast Fourier transform (FFT). Nevertheless, too large a frequency search step size and short length of FFT result in large loss of correlation, whereas too small frequency search step size and long length of FFT increase signal acquisition time. To shorten signal acquisition time without influencing the accuracy of signal parameters, the FLC is employed to regulate the frequency search step size in the frequency domain on the basis of an input variable: code correlation value and its rate of change. To enhance the robustness of signal acquisition performance, the signal detection threshold is adaptively adjusted and combined with FLC. Besides, the basis value of membership function in FLC is adjustable. Hence, the input and output parameters of membership functions (MFs) vary with the adjustment of the detection threshold. Simulations and experimental results demonstrate that the proposed method enhances acquisition performance with regards to execution time and precision of parameters in GNSS signals.

Acquisition of satellite navigation signals using dynamically chosen measurements

A new approach to sequential acquisition of satellite navigation signals is presented where the collection of measurement statistics is steered dynamically during the acquisition process. The process consists of a fixed number of operation cycles during which the state of the receiver is maintained as a vector of conditional probabilities of acquisition hypotheses, each hypothesis being associated with a code delay and a Doppler frequency. During each operation cycle, one hypothesis is singled out by applying a suitable policy on the state vector. The down-converted satellite signal is then despread and frequency shifted according to the hypothesis. The resulting signal is integrated and squared to form a statistic that is used to update the state vector according to Bayes' theorem. After completing the cycles, a decision is made in favour of the hypothesis corresponding to the highest posterior probability. Two policies are investigated, one based on the maximisation of one-step posterior probability and the other based on the maximisation of information gain. Simulation results are presented indicating that the proposed approach provides a significant performance advantage over standard techniques for a wide range of signal-to-noise ratios.