Multipath Error Envelope Research Articles

A Novel Single Differencing Measurement for Multipath Detection

Increased global dependence on Global Navigation Satellite Systems (GNSSs) has resulted in a high demand for greater precision and reliable measurements from GNSS receivers. The multipath problem is the single largest source of errors in modernised GNSSs. Double differencing techniques, such as Code Minus Carrier (CMC) have been shown to accurately detect and measure multipath, allowing for corrections to be made via Ground Base Augmentation Systems (GBAS), for example. However, these techniques require at least two receivers and the protection provided is not extended to stand-alone receivers. This paper introduces a new single differencing technique for the accurate detection of multipath in standalone GNSS receivers receiving modernised Binary Offset Carrier (BOC)-modulated signals. Similarities to CMC are drawn before the novel measurement, Code minus Subcarrier, (CMS) is characterised statistically and a threshold for multipath detection is determined. The effectiveness and sensitivity of this novel measurement as a multipath detection technique are analysed through simulation and multipath error envelope analysis. It will be shown that multipath echos capable of inducing a psuedorange error larger than the threshold are detectable at any amplitude. The method is finally verified using simulated fixed offset multipath, confirming that when code and subcarrier early–late spacings are optimal, all ranges of multipath delays, even as small as 21 meters, are detectable. This novel method of multipath detection requires no additional complex correlators than already exist in the chosen tracking algorithm, thus, providing excellent detection with minimum complexity added to the receiver structure.

Binary Offset Carrier (BOC) and Binary Phase Shift Keying (BPSK) Modulation in Indoor Drones GNSS Recievers using Multipath Error Envelope MEE Technique

The applications of unmanned aerial vehicles (UAVs) have greatly eased the lives of human being. Due to the mass commerial production of UAVs (or Drones) and the support of the ongoing scientific research, it can now be used in disaster monitoring, surviellance, fire conrolling and many outdoor usages. However, the indoor applications have stricter requirements for the autonomous positioning capability of UAVs, requiring its positioning accuracy to be within the narrower areas and aisles. The Global Navigation Satellite System (GNSS) is currently the only guidance and autorecovery method that can be applied directly and consistently to UAV positioning. The current GPS L1C and/or Galileo E1 open services signals are being widely used for this purpose. Moreover, the Binary Offset Carrier (BOC) techniques have been recently adopted in Galileo and GPS BIII as one of the efficient mitigation methods to decrease the interference/multipath delays and to increase both the Position Accuracy and the immunity of GNSS interferences. This research aims to present a software method of assessing the improvements of the Accuracy, and yet the Availability, by producing the MEE for BOC technique. The used methodology is analyzing the theoretical equations behind the interfernece multipath error envelopes in both BPSK and the new BOC signals. The Results show a higher performance of BOC GNSS Recievers over BPSK ones, and less delay.

FH-BOC 신호를 위한 부분 상관을 이용한 비모호 상관함수

Binary offset carrier (BOC) modulation is a method of adding sub-carrier modulation to a signal with binary phase shift keying (BPSK) modulation. Compared to the correlation function of the BPSK-modulated spread signal, the main peak of the BOC signal is sharper. Sharper main peaks, are less affected by the multipath. However, the correlation function of the BOC-modulated spread signal has several side-peaks along with a sharp main peak, which easily causes false-locking during code tracking; this is reffered to as the ambiguity of BOC modulation. A frequency hopping (FH)-BOC modulation scheme is hence proposed to reduce the ambiguity of the BOC signal. However, many false-lock points still appear in the correlation function of the FH-BOC-modulated spread signal. In this study, to reduce the ambiguity of the FH-BOC-modulated spread signal, we propose an unambiguous correlation function using partial correlation. Compared to the FH-BOC-modulated signal, the proposed scheme has almost no false-lock points and is less affected by the multipath. From the simulation results, the highest value of the running average of the multipath error envelope (MEE) of the FH-BOC-modulated signal was about 0.822 m, while the highest value obtained with the proposed scheme under same conditions was about 0.524 m, about 36.2 % lower.

Multipath Mitigation Methods of BOC-Family Signals Based on Dual BPSK Tracking Techniques

It is well known that for binary offset carrier (BOC) signals the notorious ambiguity problem due to the multipeaked autocorrelation function must be tackled first in order to obtain the potential of improving ranging performance promised by its broader Gabor bandwidth. The existence of multipath makes it more difficult to solve. Dual binary phase-shift keying (BPSK) tracking (DBT) is a kind of low complexity, unambiguous tracking method for BOC-family signals, which makes full use of the coherence between the upper and lower sidebands and employs subcarrier phase locked loop (SLL) and delay locked loop (DLL) to track subcarrier and code components, respectively. Considering that the thermal noise performance of DBT has been fully studied, this article focuses on the analysis of multipath performance and the design of antimultipath methods under DBT framework. The influence of multipath on SLL and DLL of DBT is analyzed first and the corresponding subcarrier and code multipath error envelopes are obtained. Then according to different requirements of subcarrier and code multipath errors, a multipath mitigation scheme specially designed for DBT is proposed, in which SLL and DLL adopt offset correlator and narrow correlation, respectively. Theoretical analysis and simulation are given to verify the effectiveness of the proposed methods.

Effect of the polarization of satellite navigation antennas on multipath error envelopes

The paper estimates the envelope of error introduced by the effect of multipath propagation in global navigation satellite systems. Based on the mathematical model of the radio path of the direct and reflected signals, the results of the multipath error envelopes for various types of navigation antennas are obtained. Keywords: antenna, GNSS, multipath interference, interference, radiation pattern, multipath error envelope.

Developing a Spoofer Error Envelope for Tracking GNSS Signals

<h3>Abstract</h3> Global navigation satellite systems (GNSSs) are the most significant service for global positioning and timing. The high relevance and wide spread of these systems contrast with the risk for interference or even manipulations of GNSS signals. One specific threat is GNSS spoofing. A spoofer counterfeits satellite signals to mislead the receiver to an erring position/time estimation. The technological progress enabling affordable and easy-to-use spoofer hardware further increases the relevance of this threat. To maintain the integrity of the position/time information, it is mandatory to be able to assess the errors induced by spoofing. The paper at hand derives a bound of the code tracking bias in relevant spoofing scenarios extending the well-known Multipath Error Envelope. These new bounds can be used as a tool to estimate the position/time error, especially but not exclusively for receivers that are collateral damage of a spoofing attack.

Оценка пространственно-поляризационной селекции антенн спутниковой навигации на основе анализа ошибки огибающей многолучевой интерференции

The paper estimates error envelopes introduced by the effect of multipath propagation in global navigation satellile systems. Based on the mathematical model of the radio path of the direct and reflected signals, the results of the multipath error envelopes for various types of navigation antennas are obtained.

Extended Double-delta Correlator Technique for GNSS Multipath Mitigation

Multipath is one of the main error sources in global navigation satellite system (GNSS). Many multipath mitigation methods have been proposed, such as the narrow correlator technique and the double-delta (DD) correlator technique. In light of the BPSK modulated signals used in many GNSS, an extended DD (EDD) correlator technique expanding from the DD correlator, which uses multiple pairs of correlators with more general spacing and weight, is proposed in this paper. Furthermore, the paper provides the discriminator structure, the closed-form expressions for multipath error envelope under infinite bandwidth and the closed-form expressions for the relationship between multipath error, thermal noise performance and design parameters of the discriminator. Based on the explicit performance expressions, the appropriate selection principles of parameters are given and verified by theoretical analysis and simulation. The results show that the proposed method can improve the performance optimization freedom of the DD technique without significantly increasing the design complexity. Moreover, the multipath performance is better than DD under infinite bandwidth and has great adaptability to limited bandwidth and the next generation GNSS signals, such as BOC and MBOC. The EDD technique can also be utilized as a noncoherent discriminator and has better anti-multipath performance. Furthermore, the EDD technique can achieve balance between multipath mitigation performance and thermal noise performance by adjusting correlator spacing and weight and can be self-adaptive to multipath relative amplitude in the environment.

Improved MBOC modulations based on periodic offset subcarrier

With the development of global navigation satellite systems, the modernization of global navigation satellite systems has arrived, which takes the binary offset carrier modulation and related evolution as the typical feature. Moreover, the performance of multiplexed binary offset carrier modulation is related to global navigation satellite systems service. In the paper, an improved multiplexed binary offset carrier modulation based on period offset subcarrier was proposed, called MBOC-POS, where the subcarrier periodic shifting binary offset carrier modulation is used as the lower-order component instead of sine-binary offset carrier modulations. Meanwhile, the different implementations of MBOC-POS modulations are analysed and compared with traditional multiplexed binary offset carrier multiplexed binary offset carrier signals in multipath mitigation, tracking accuracy, anti-interference and compatibility. By simulation and analysis, the performance of reconstructed MBOC-POS modulation has been improved. Especially, for the mismatch reception, the Gabor bandwidth increases by 29.5% and the multipath error envelope is reduced by 35% with the filter bandwidth of 10 MHz. Therefore, the multiplexed binary offset carrier MBOC-POS modulation proposed in the paper can be used as a new option for MBOC modulations and next-generation signal design.

MBOC(6,1,4/33) 신호의 다중경로 영향 완화를 위한 새로운 Strobe 펄스 설계

In this paper, we propose a novel strobe pulse to mitigate the multipath effect of MBOC (6,1,4/33) signal and analyze its performance. By additionally modulating a passband Direct Sequence/Spread Spectrum (DS/SS) signal with a Binary Offset Carrier (BOC) sub-carrier, the signal band can be moved to a desired band, thereby increasing frequency efficiency. In addition, the correlation characteristics of the correct code synchronization point are improved, so that the multipath effect can be reduced to compare with the existing Binary Phase Shift Keying (BPSK) modulated signal. However, the multipath effect is still one of the major performance limitations of the Global Navigation Satellite Systems (GNSSs). A conventional scheme to mitigate multipath effects of GNSS is the Strobe pulse technique. In this paper, we design a new strobe pulse that can effectively mitigate the multipath effects of MBOC (6,1,4/33) signals, and multipath mitigation in the 2-Ray model, a representative channel environment to assess the multipath mitigation performance by computer-based simulation. In order to compare the performance of the proposed new strobe pulse, the W2 pulse scheme with similar implementation complexity is considered. The W2 pulse technique is the one of the Strobe pulse technique for BOC signal. Based on the output of the discriminator in multipath free environment, the pull-in range of the W2 pulse technique is about 0.2 chips, whereas the proposed scheme is about 0.6 chips, which is about 3 times wider. And the false-lock point of the proposed scheme is less than about 20% to compare the W2 scheme. In the same environment, the multipath error envelope of the W2 and the proposed schemes is shown, and both techniques are affected only by the closed-in multipath signal. Among them, the proposed scheme has significantly lower multipath errors due to the closed-in multipath signal compared to the W2 technique, and the maximum value of the proposed scheme based on the running average of the multipath errors is about 32% compared to the W2 scheme.

Performance comparison of time‐of‐arrival estimation techniques for LTE signals in realistic multipath propagation channels

<h3>Abstract</h3> Long term evolution (LTE) signals have the potential for use in positioning, especially in challenging environments. The time-of-arrival (TOA)-based technique supported by LTE is attractive due to its high positioning accuracy. However, it is vulnerable to multipath propagation effects in typical LTE channels. This paper will summarize several existing advanced TOA estimators for LTE signals, i.e., first peak detection, information theoretic criteria, super-resolution algorithm, and delay-lock loop (DLL). Later, the paper will evaluate the TOA estimation performances of these techniques with multipath propagation effects and varying signal conditions using simulations. For the DLL, the multipath error envelope metric is assessed for different signal bandwidths. The root mean square errors of the TOA estimations are compared to evaluate suitable TOA estimators under various conditions. Finally, some other performance characteristics of these techniques are also discussed.

Unambiguous Acquisition/Tracking Technique Based on Sub-Correlation Functions for GNSS Sine-BOC Signals.

The autocorrelation function (ACF) of the Binary Offset Carrier modulation (BOC) signal for Global Navigation Satellite System (GNSS) has multiple peaks, ambiguity is easily generated during the synchronization of the baseband signal. Some methods have been proposed to remove the ambiguity, but the performance is not suitable for high-order BOC signals or does not maintain narrow correlation characteristics. This paper proposes a sub-function reconstruction synchronization algorithm to solve this problem, of which the key is to design a new local auxiliary code: the local Pseudo-Random Noise (PRN) code is divided into several new codes with different delays. The auxiliary code performs a coherent integration operation with the received signal. Then, a correlation function without any positive side peaks is obtained by multiplying the two correlation results to make the acquisition/tracking completely unambiguous. The paper gives a design scheme of navigation signal acquisition/tracking and deduces the theoretical analysis of detection performance. The phase discrimination function is provided. The performance of the method is analyzed from both theoretical and simulation aspects. Compared with the Binary phase shift keying-like (BPSK-LIKE) method, Subcarrier Phase Cancellation (SCPC) method and the Autocorrelation Side-Peak Cancellation Technique (ASPeCT) method, the proposed method has the best detection probability for the acquisition, which is 0.5 dB-Hz better than ASPeCT. For tracking, the proposed method performs best in terms of phase-detection curve, anti-multipath performance, and anti-noise performance. For high-order BOC signals, the SRSA technique successfully removes the false lock points, and there is only one multipath error envelope, and the code tracking error is almost the same as the ASPeCT method.

Unambiguous Tracking Technique Based on Shape Code for BOC Signals

The multiple peaks characteristic of binary offset carrier (BOC) autocorrelation function (ACF) makes ambiguity easy to be generated. There are some methods to eliminate ambiguity, but for higher-order BOC Signal, it will sacrifice signal energy or cannot maintain narrow correlation. This paper studies these problems. According to the idea of GRASS algorithm shape code, this paper proposes an unambiguous tracking algorithm, Sub Cross-correlation Shift Technique (SCST), which is suitable for BOC(m,n) signals. The key to this algorithm is to generate a new cross-correlation function between the BOC signal and the PRN code based on the shape code. The new cross-correlation function is linearly combined with the autocorrelation function of the BOC signal to remove sub-peak interference and achieve high-accuracy tracking. The phase discrimination function is given, and the effectiveness of the tracking algorithm is analyzed theoretically. The disadvantage of this method is that it needs multilevel storage, which will bring extra resource consumption to the receiver. For comparison, Unit Correlation, ASPeCT, GRASS, and the algorithm proposed by Yan are proposed. Experiments show that SCST can completely remove the side peak, and the phase discriminator output has only two main peaks, which successfully eliminates the false lock point. The multipath error envelope has only one and the smallest area. In terms of code tracking accuracy, for a BOC(10,5) signal with a received signal-to-noise ratio (SNR) of −28 dB, SCST is less than 45.8%, 67.5%, and 12.2% of the Unit Correlation, GRASS, and Yan proposed algorithms.

Characterization of Signal Quality Monitoring Techniques for Multipath Detection in GNSS Applications.

The performance of Signal Quality Monitoring (SQM) techniques under different multipath scenarios is analyzed. First, SQM variation profiles are investigated as critical requirements in evaluating the theoretical performance of SQM metrics. The sensitivity and effectiveness of SQM approaches for multipath detection and mitigation are then defined and analyzed by comparing SQM profiles and multipath error envelopes for different discriminators. Analytical discussions includes two discriminator strategies, namely narrow and high resolution correlator techniques for BPSK(1), and BOC(1,1) signaling schemes. Data analysis is also carried out for static and kinematic scenarios to validate the SQM profiles and examine SQM performance in actual multipath environments. Results show that although SQM is sensitive to medium and long-delay multipath, its effectiveness in mitigating these ranges of multipath errors varies based on tracking strategy and signaling scheme. For short-delay multipath scenarios, the multipath effect on pseudorange measurements remains mostly undetected due to the low sensitivity of SQM metrics.

A Design Method of Code Correlation Reference Waveform in GNSS Based on Least-Squares Fitting.

The multipath effect is one of the main error sources in the Global Satellite Navigation Systems (GNSSs). The code correlation reference waveform (CCRW) technique is an effective multipath mitigation algorithm for the binary phase shift keying (BPSK) signal. However, it encounters the false lock problem in code tracking, when applied to the binary offset carrier (BOC) signals. A least-squares approximation method of the CCRW design scheme is proposed, utilizing the truncated singular value decomposition method. This algorithm was performed for the BPSK signal, BOC(1,1) signal, BOC(2,1) signal, BOC(6,1) and BOC(7,1) signal. The approximation results of CCRWs were presented. Furthermore, the performances of the approximation results are analyzed in terms of the multipath error envelope and the tracking jitter. The results show that the proposed method can realize coherent and non-coherent CCRW discriminators without false lock points. Generally, there is performance degradation in the tracking jitter, if compared to the CCRW discriminator. However, the performance promotions in the multipath error envelope for the BOC(1,1) and BPSK signals makes the discriminator attractive, and it can be applied to high-order BOC signals.

Strobe double phase estimator: a multipath mitigating technique for BOC signal in GNSS based on double phase estimator

Summary Double phase estimator (DPE) is an unambiguous binary offset carrier (BOC) tracking algorithm for band-limited receivers in Global Navigation Satellite Systems. Based on the strobe pulse method, the DPE was modified by introducing a strobe waveform in the prompt signal correlation process of the subcarrier phase lock loop in this paper.. This strobe DPE (SDPE) employs no additional correlators. Two different reference strobe waveforms and their receiving structures are provided. The performance of the SDPE is characterized according to the subcarrier multipath error envelope (SMEE) and the tracking jitter. Simulation results show that, relative to conventional DPE, the first waveform employed in this study provides a reduction in the SMEE area of 81.1% and 75.1% for BOC(1,1) and BOC(14,2) signal, respectively. The second waveform employed in this study provides a reduction in the SMEE area of 82.5% and 76.8% for BOC(1,1) and BOC(14,2) signal, respectively. They also both outperform the double estimator about 64.4% and 53.2% for BOC(1,1) and BOC(14,2) signal in the SMEE area. However, the SDPE experiences a loss of −6 and −7.25 dB, respectively, for two reference waveforms in terms of the post-coherent signal-to-noise ratio, which impacts its tracking precision. Copyright © 2016 John Wiley & Sons, Ltd.

A novel unambiguous composite binary offset carrier(6,1,1/11) tracking based on partial correlations

This paper proposes a novel unambiguous correlation function for composite binary offset carrier (CBOC) signal tracking based on partial correlations. In the proposed scheme, first, we partition sub-carriers of the CBOC signal into partial sub-carriers, and subsequently, we obtain partial correlations by correlating the partial sub-carriers with the received CBOC signal. Finally, a novel unambiguous correlation function with no side-peak is constructed by combining the partial correlations in a specially designed way. Unlike the conventional schemes, the proposed scheme does not require any auxiliary signal and from numerical results, it is found to offer a better tracking performance than those of the conventional schemes in terms of the tracking error standard deviation (TESD) and multipath error envelope (MEE).

General analytical models characterizing MBOC modulated signal

The modernized Global Positioning System (GPS) and Galileo satellite navigation systems have recommended the interoperable Multiplexed-Binary Offset Carrier (MBOC) modulation on L1C/E1 frequency band for their open service signals. MBOC signal multiplexes BOC(6,1) and BOC(1,1) according to a certain proportion, and can be implemented in a number of ways, including Composite BOC (CBOC) and Time-Multiplexed BOC (TMBOC). The complexity and the accuracy of the theoretical signal modeling pose a growing concern to scrutinize and to optimize signal characteristics and receiver performances. In this paper, the analytical expressions of the optimal correlation function (CF) for the new modernized MBOC signal are proposed. Also derived are the analytical models of the discriminator functions (DFs) and the multipath error envelopes (MEEs) in both coherent and non-coherent code tracking configurations. The validation of the proposed models is performed and the simulation results show that the proposed analytical models coincide with the numerical ones.

CSC Code Discriminator: Theoretical Analysis of Performance

This paper presents the theoretical development and analysis of a novel DLL discriminator robust to multipath errors, called the Combination of Squared Correlators (CSC). The CSC discriminator features a simple implementation based on four (complex) static correlators per channel, without falling into the wide family of patented architectures.In this paper, the theoretical analysis of the properties of the CSC architecture is developed in a well structured context: (i) definition of the discrimination rule; (ii) theoretical analysis in the absence of noise; (iii) theoretical noise tracking jitter analysis; and, (iv) multipath error envelope analysis. In all cases, the CSC results are compared to those of the Strobe discriminator, which is the natural benchmark.The promising performance of the CSC discriminator inserted in a complete software receiver is also proved in a heavy multipath scenario, expressly simulated to stress the code tracking loop robustness. Copyright © 2015 John Wiley & Sons, Ltd.

Analytical Models of Correlation Functions, DLL Discriminator Outputs and Multipath Envelope Errors for CosBOC(m, n) Modulated Signals in Coherent and Non-coherent Configurations

This paper focuses on analytically modeling the multipath error effects in the code tracking Delay-Locked-Loop (DLL) with standard and narrow early---late correlators of Global Navigation Satellite System (GNSS) for Cosine Binary Offset Carrier (CosBOC) modulated signal. The latter one will be part of the modernized American Global Positioning System (GPS), the Russian GLONASS (GLObal NAvigation Satellite System in English), the new European Galileo and the Chinese Compass/BeiDou systems, signal plan. The mathematical formalism of the analytical model of the Correlation Function is proposed for any CosBOC modulated signal. Also derived, are the models of the DLL Discriminator Functions and the Multipath Error Envelopes for both coherent and non-coherent configurations. The computer implementations have shown that all the proposed models match closely the numerical ones.