Multipath Rejection Research Articles

High precision 3-D coordinates for JSATS tagged fish in an acoustically noisy environment

BackgroundAcoustic tagging methods have been used to track fish for some time. Multiple systems have been developed, including those that give researchers the ability to position fish in three dimensions and time. However, proprietary positioning methods have suffered from a lack of transparency. The U.S. Department of Energy and the U.S. Army Corps of Engineers developed the Juvenile Salmon Acoustic Telemetry System (JSATS) to monitor the survivability of juvenile salmonids as they migrate downstream. With much smaller tags and high ping rates, JSATS positioning studies should be more prevalent, but implementation is difficult and often out of reach for small budget-minded studies. This study implemented a small scale JSATS positioning study using relatively inexpensive, autonomous, independent receivers. We will show that proper synchronization of the transmissions and elimination of multipath allows the positions of a smolt to be determined in three spatial dimensions over time with high precision.ResultsTracking of 172 tagged smolts produced a total of nearly 2,00,000 positions. We compared the performance of four different supervised machine learning classifiers (Support Vector Classifier (SVC), Gaussian Naïve Bayes (NB), Classification Tree (CART), and K-Nearest Neighbor (KNN). All algorithms performed well with high accuracy and precision, but recall rates decreased with distance from the source. The SVC and KNN were least restrictive in practice. Overall, the SVC had the longest time to solve.ConclusionPositions determined from fish outside of the convex hull of the hydrophones were effectively being extrapolated, while positions determined from within the convex hull nearly always met or exceeded 1-m precision. Having stationary submerged hydrophones was necessary to produce three-dimensional positions. The main technical advances presented are the hydrophone-clock synchronization scheme and the multipath rejection scheme, which found the best multipath classifier to be the K-Nearest Neighbor. Neither algorithm was capable of alleviating close proximity detection interference (CPDI), suggesting the need to reposition receivers from reflective surfaces or install baffling.

Surface Impedance Engineered Low-Profile Dual-Band Grooved-Dielectric Choke Ring for GNSS Applications

A novel low-profile grooved-dielectric choke ring with dual-band surface impedance resonance is proposed and experimentally demonstrated. The proposed structure is designed by engineering the surface impedance of a dielectric-based choke ring to introduce two resonant frequencies around the global navigation satellite system (GNSS) bands of L2 (1227.60 MHz) and L1 (1575.42 MHz). This provides capacitive surface impedances around both bands simultaneously, which is required for efficient surface wave suppression for higher multipath rejection performance. To demonstrate the proposed principle of surface impedance engineering, an in-house choke ring prototype of the proposed design is tested with the widely used Dorne and Margolin antenna. A high multipath rejection in both GNSS bands is experimentally confirmed with comparable performances to an otherwise bulky, heavy, and expensive conventional metallic choke ring.

GNSS Spoofing Detection and Mitigation Based on Maximum Likelihood Estimation.

Spoofing attacks are threatening the global navigation satellite system (GNSS). The maximum likelihood estimation (MLE)-based positioning technique is a direct positioning method originally developed for multipath rejection and weak signal processing. We find this method also has a potential ability for GNSS anti-spoofing since a spoofing attack that misleads the positioning and timing result will cause distortion to the MLE cost function. Based on the method, an estimation-cancellation approach is presented to detect spoofing attacks and recover the navigation solution. A statistic is derived for spoofing detection with the principle of the generalized likelihood ratio test (GLRT). Then, the MLE cost function is decomposed to further validate whether the navigation solution obtained by MLE-based positioning is formed by consistent signals. Both formulae and simulations are provided to evaluate the anti-spoofing performance. Experiments with recordings in real GNSS spoofing scenarios are also performed to validate the practicability of the approach. Results show that the method works even when the code phase differences between the spoofing and authentic signals are much less than one code chip, which can improve the availability of GNSS service greatly under spoofing attacks.

A Main Peak Extraction Method for High-Order BOC Signals

Binary Offset Carrier (BOC) modulation signals have been applied in Global Navigation Satellite Systems (GNSS) because they offer a higher positioning accuracy and higher multipath rejection. However, there is a drawback in that the autocorrelation functions have multiple side peaks, meaning that this technique also leads to the large main peak estimation error problem and a low correlation decision efficiency problem. In this paper, we propose a new Main Peak Extraction (MPE) method for high-order BOC signals to solve these problems. In the new method, the synthesis cross-correlation function is established, and the geometry graph is formatted to calculate the estimation main peak. We eliminate all side peaks and improve the main peak phase estimation precision under the condition that the sub-carrier phase is offset. The results of the simulation demonstrate that the new method can achieve better main peak decision efficiency, side peak cancellation ability and phase estimation performance than traditional methods.

GNSS Multipath Mitigation using Antenna Motion

A method is developed for characterizing and compensating specular GNSS multipath by considering signal amplitude and phase variations in response to antenna motion. This method seeks to improve multipath rejection capabilities. A known antenna motion profile is combined with a batch filter to estimate the code phase, carrier phase, and amplitude of the direct signal, the relative code phase, carrier phase, carrier Doppler shift, and amplitude of each significant multipath component, and the directions of arrival of the direct and multipath components. Hardware signal simulator results indicate accurate estimation of all multipath features, and experimental test results demonstrate measurable improvements in estimates of carrier amplitude in all cases, of direct-path carrier-phase in many cases, and of direct-path code phase in some cases. Anomalous results have also been obtained, including specular multipath component estimates that occur in doublets and that may represent attempts by the batch filter to approximate diffuse multipath. Copyright © 2015 Institute of Navigation.

On the General Mathematical Framework, Calibration/Compensation Method, and Applications of Non-Ideal Software Defined Harmonics Rejection Transceivers

Recently harmonic interference rejection has been recognized as a crucial bottleneck of truly wide-band software defined radio transceivers. Phase and gain mismatches among mixing paths, typical for nanoscale technology nodes, severely impact the achievable rejection ratio in classical harmonic rejection transceivers. This paper proposes an alternative digital intensive architecture, which enables increased harmonic interference rejection for wide-band SDR transceivers impacted by severe gain and phase mismatches. A generic mathematical framework of the target architecture is introduced to support a systematic design space exploration for multi-path harmonic interference rejection transceivers. With the framework, an iterative on-die estimation and compensation of mismatch for both the transmitter and receiver are presented. Case study with four mixing paths shows that ideal rejection can be achieved when targeting a single dominating harmonic interferer, and joint suppression of the 3rd and 5th order harmonic interferers of at least 70 dB can be obtained under realistic radio input scenarios.

Quantitative evaluation of multipath rejection capabilities of GNSS antennas

Multipath error remains the largest error source in many high precision GPS applications. To counteract this problem, solutions at both software and hardware level have been studied. Software processing by means of measurement redundancy or error predictability can be used in order to mitigate the multipath effects. In general, these techniques work properly only when the length of a reflection path exceeds that of the direct path by more than 10---20 m. Unfortunately, in most cases, reflections are generated in the area near the receiving antenna. For this reason, multipath rejection actuated at the antenna level is one of the most valid means to improve the accuracy of GPS systems. The scope of this work is twofold. First, a review of low-multipath reception requirements will be proposed for comparing different classes of high precision GNSS antennas. Based on this discussion, we introduce a quantitative evaluation of multipath rejection capabilities of a GNSS antenna. The proposed assessment technique is focused on the antenna pattern, but, in contrast to other parameters evaluating the antenna radiation characteristics, it is specifically conceived to capture the effects of multipath signals.

A Novel Design for the Ultra-Tightly Coupled GPS/INS Navigation System

This paper presents a sensor fusion method for the Ultra-Tightly Coupled (UTC) Global Positioning System (GPS)/Inertial Navigation System (INS) integrated navigation. The UTC structure, also known as the deep integration, exhibits many advantages, e.g., disturbance and multipath rejection capability, improved tracking capability for dynamic scenarios and weak signals, and reduction of acquisition time. This architecture involves the integration of I (in-phase) and Q (quadrature) components from the correlator of a GPS receiver with the INS data. The Particle Filter (PF) exhibits superior performance as compared to an Extended Kalman Filter (EKF) and Unscented Kalman Filter (UKF) in state estimation for the nonlinear, non-Gaussian system. To handle the problem of heavy-tailed probability distribution, one of the strategies is to incorporate the UKF into the PF as the proposal distribution, leading to the Unscented Particle Filter (UPF). The combination of an adaptive UPF and Fuzzy Logic Adaptive System (FLAS) is adopted for reducing the number of particles with sufficiently good results. The GPS tracking loops may lose lock due to the signals being weak, subjected to excessive dynamics or completely blocked. One of the principal advantages of the UTC structure is that a Doppler frequency derived from the INS is integrated with the tracking loops to improve the receiver tracking capability. The Doppler frequency shift is calculated and fed to the GPS tracking loops for elimination of the effect of stochastic errors caused by the Doppler frequency. In this paper, several nonlinear filtering approaches, including EKF, UKF, UPF and ‘FLAS assisted UPF’ (FUPF), are adopted for performance comparison for ultra-tight integration of GPS and INS. It is assumed that no outage occurs such that the inertial sensor errors can be properly corrected and accordingly the aiding information is working well. Two examples are provided for performance assessment for the various data fusion methods. The FUPF algorithm with Doppler velocity aiding demonstrates remarkable improvement, especially in the high dynamic environments, in navigation estimation accuracy with reduction of number of particles.

A Range Measurement Scheme for Chinese Terrestrial Television Broadcasting Signals Included Positioning Systems

This paper proposed a simple scheme for range measurement between the receiver and CTTB (Chinese Terrestrial Television Broadcasting) TV tower not depending on other aids. CTTB signals are used for range measurement and they are transmitted from CTTB TV tower. The scheme suits for any CTTB included positioning system. Simulated CTTB signals transmitted from CTTB TV tower are used to evaluate the performances of the proposed scheme. Simulations are done under both AWGN (additive white Gaussian noise) channels and real measured urban channels. And as a multipath fading exists in urban environment, we use a multipath rejection method to improve the range measurement accuracy. Our simulation results show that this range measurement scheme is effective in AWGN channels, and also in urban channels with the multipath rejection method. From the simulation results, we also know that the clock accuracy of the receiver affects the precision of this range measurement scheme.

Separation of sperm whale click-trains for multipath rejection

In this paper an algorithm is described for grouping sperm whale clicks received at a single hydrophone into click-trains associated with a given whale and propagation path. To accomplish this, features are extracted from pairs of clicks in order to derive a statistical measure of click similarity. Then, the algorithm maximizes a global measure of similarity between the associated clicks. In addition to grouping clicks according to click-trains, it classifies click-trains into a propagation path (direct, surface, bottom reverberation). The propagation path is identified using a combination of (1) a statistical classifier operating on features extracted from individual clicks and (2) the cross-correlation of click-trains to identify the relative time delays. The algorithm is demonstrated on at-sea recorded data, showing the elimination of time-delay ambiguities associated with the reverberation paths observed at sensor pairs.

1A1-D20 3次元地図を用いたマルチパス除去を含むGPSによる移動体の位置推定 : 衛星の影を用いたGPS測位の高精度化

1A1-D20 3次元地図を用いたマルチパス除去を含むGPSによる移動体の位置推定 : 衛星の影を用いたGPS測位の高精度化

Wideband multipath rejection for shallow water synthetic aperture sonar imaging

Synthetic aperture sonar (SAS) is an emerging technology for seafloor imaging, which has an appealing property of range- and frequency-independent spatial processing resolution. However, for a low-frequency SAS system operated in shallow water environments, there are often strong sea surface and bottom reflected multipath components that interfere with the desired echo signals. Based upon a small vertically displaced hydrophone array, several spatial processing algorithms have been proposed for multipath reduction. Most of these algorithms, however, are only applicable to narrowband signals, whereas wideband signals are usually used in low-to-medium-frequency SAS systems in order to achieve a high range resolution. This paper presents a steered robust Capon beamforming (SRCB) approach, and applies the approach, together with the data-independent delay-and-sum beamforming and the conventional wideband robust Capon beamforming, to wideband multipath rejection for shallow water SAS imaging. Numerical simulations of the proposed SAS processing have verified the performance improvements on output image quality over conventional processing in terms of both ghost target strength reduction and contrast enhancement.

English

The Office of Surface Mining Reclamation and Enforcement (OSM) and the West Virginia Department of Environmental Protection (WVDEP) have reviewed the costs and benefits of two very different types of data gathering to accomplish a specific mission. The agencies generated cross sections of large land disturbances using Trimble Geo Explorer series GPS receiver units ranging from the submeter GeoXT with EVERESTTM multipath rejection technology to the GeoXH with Trimble H-StarTM and optional ZephyrTM external antenna capable of approximately 25 cm. vertical accuracy post processed. Next, they tested the suitability of Lidar data for the same purposes and generated projected cost using that method on the same sites. The potential use of photogrammetry was also considered. By maintaining an accounting of all the time associated with both methods, the agencies gained a better perspective on the costs and benefits of these technologies for future decisions. In this project, the mission involved comparing pre, proposed and final graded slopes on eight large surface mines in steep slopes in West Virginia as part of the review of “Approximate Original Contour “ requirements under the coal mining regulatory program. The agencies found that use of remote sensing technologies, such as aerial based Lidar, can be a cost savings over obtaining digital information using GPS field devices on the ground. Additional

A Low-Multipath Wideband GPS Antenna With Cutoff or Non-Cutoff Corrugated Ground Plane

We compare the performance of the classic global positioning system (GPS) choke ring ground plane with a new shallower design. Both the choke ring and the new ground plane are here designed to operate uniformly between 1.15 GHz and 1.60 GHz while maintaining the required low-multipath performance in the whole bandwidth. To achieve reception in this wide range of frequencies, the radiating element chosen is a droopy bowtie turnstile. A classic choke ring is composed of deep concentric rings on a flat circular metal ground plane. We have modeled the choke ring as a metal corrugated surface of depth d such that lambda/4lesdleslambda/2 , operating at cutoff: the multipath suppression (i.e., the proper RHCP/LHCP pattern shaping) is obtained by eliminating the surface wave on the ground plane in a certain frequency band. When shallower concentric rings of depth dleslambda/4 are used, the corrugated surface operates at non-cutoff: the required multipath rejection can be achieved by cancellation (destructive interference) rather than suppression of surface waves. The comparisons performed in this study include theory, numerical simulations, and hardware tests. Our results show that both configurations, when properly optimized, are good candidates for reception of modernized GPS, GLONASS, and GALILEO satellite signals from GPS permanent stations.

Low Profile GALILEO Antenna Using EBG Technology

A dedicated low profile antenna for geodesic applications is presented. This type of antenna requires mitigation of multipath signals to achieve sub-centimeter level of precision. Typically, bulky and heavy choke ring structures have been used to reduce the effects of multipath interference. The antenna presented here consists of a low temperature co-fired ceramic (LTCC) patch antenna immersed in an electromagnetic bandgap (EBG) substrate. The EBG substrate reduces the effects of multipath by blocking the propagation of surface waves. The result is an antenna showing good multipath rejection and a stable phase center. The advantage of printed EBG substrates is that they can be realized in a low-weight, low-price, and low-profile fashion. First prototypes have been manufactured and tested, and its performance has been compared to that of a more classical choke ring antenna.

Comparison between Galileo CBOC Candidates and BOC(1,1) in Terms of Detection Performance

Many scientific activities within the navigation field have been focused on the analysis of innovative modulations for both GPS L1C and Galileo E1 OS, after the 2004 agreement between United States and European Commission on the development of GPS and Galileo. The joint effort by scientists of both parties has been focused on the multiplexed binary offset carrier (MBOC) which is defined on the basis of its spectrum, and in this sense different time waveforms can be selected as possible modulation candidates. The goal of this paper is to present the detection performance of the composite BOC implementation of an MBOC signal in terms of detection and false alarm probabilities. A comparison among the CBOC and BOC(1,1) modulations is also presented to show how the CBOC solution, designed to have excellent tracking performance and multipath rejection capabilities, does not limit the acquisition process.

Performance evaluation of shorted annular patch antennas for high-precision GPS systems

Even with the advances in signal processing, multipath error remains the major error source of high-precision global positioning system (GPS) applications. One of the most valid means to improve the accuracy of these systems is an appropriate design of the receiving antenna. Unfortunately, in many cases, the low-multipath-radiation requirements are very difficult to satisfy especially when physical constraints have also to be considered. As a possible solution, a study on the multipath rejection performances of shorted annular patch (SAP) antennas is presented here. In the first part, the SAP radiation characteristics will be deeply analysed by designing and testing three different antennas. Then, the results of a comparative test conducted on a GPS facility will be used to assess the on-field performances of the three prototypes. This experimental validation will show that a significant improvement of the SAP performances can be achieved when the reduced surface wave criterion, which has been widely adopted as a design rule in previous works, is relaxed and a trade-off between all the low-multipath-radiation requirements is considered. Moreover, comparison with two commercial GPS antennas will reveal that SAPs can be a very attractive and useful solution in high-precision GPS systems where severe physical constraints are imposed.

Multipath Reduction of GPS Measures through Heuristic Techniques of Compensation

The Global Positioning System, also known with the acronym GPS, is today widely used in civil and military applications, as for correct object positioning, as in other fields (ionospheric inferences, soil mapping and characterization, and so on). A limitation in the accuracy retrievable by differential GPS measures is due to multipath error which arises when GPS signal is reflected by surfaces around the antenna. In particular, many GPS receivers are projected with firmware implemented by means of classical mathematic algorithms, which can minimize multipath errors. This paper describes project criteria and experimental results obtained by a multipath rejection system based on Radial Basis Function Neural Networks, compared with measures retrieved by a commercial Differential GPS receiver.

Effects of polyline simplification of dynamic GPS data under forest canopy on area and perimeter estimations

The objectives of this study were to determine Global Positioning System (GPS) positional errors while moving under the forest canopy and to clarify the effects of polyline simplification on area and perimeter estimations. We used the Pathfinder Pro XR and GPSMAP 76S, which are categorized as “high-end mapping” and “general navigation” GPS receivers, respectively. The field tests were conducted in both natural and plantation forests. The results showed that the Pathfinder Pro XR, which has better multipath rejection technology, worked well, especially in the plantation forest under unfavorable conditions of higher stand density. We used analysis of variance to clarify the effects of the receiver type, positioning mode, stand type, and polyline simplification method on area and perimeter estimations. The receiver type and positioning mode were found to be significant factors that affected area estimation. The Pathfinder Pro XR estimated the area more accurately than the GPSMAP 76S, and differential GPS estimated the area more accurately than autonomous GPS. With respect to the perimeter, the receiver type, positioning mode, and polyline simplification method were found to be significant factors. The results showed that perimeter estimation was improved by using the velocity filter, and further improved by using the velocity filter and Douglas-Peucker algorithm, especially when the Pathfinder Pro XR was used. The GPSMAP 76S estimated the perimeter accurately without any filtering because its default speed filter worked well, even though the GPSMAP 76S is a general navigation GPS receiver.

LAAS Integrated Multipath-Limiting Antenna

ABSTRACT: A significant portion of the reduction of multipath in the Local Area Augmentation System (LAAS) ground system is accomplished by means of an integrated multipath-limiting antenna (IMLA). Many years of analysis, design, and development have been applied to the creation of a dual-beam IMLA that provides the performance necessary to meet the demanding requirements of accuracy, availability, and integrity for the LAAS Ground Facility (LGF). Ground multipath rejection on the order of 35 to 40 dB is achieved with the IMLA throughout the entire satellite hemispherical coverage volume. Flight testing of the LAAS utilizing the IMLA at both the Federal Aviation Administration's (FAA) William J. Hughes Technical Center and Ohio University has shown that the IMLA rejects multipath to levels demonstrated to allow full compliance with the LGF specifications.