A Cumulant-Based Method for Acquiring GNSS Signals

The long spreading code and the binary offset carrier (BOC) modulation technique are used in the next-generation Global Navigation Satellite System (GNSS) to improve positioning performance and to reduce inter-GNSS interference; however, the signal acquisition process of a GNSS receiver can take more time and requires additional hardware resources than legacy Global Positioning System (GPS) receivers. This paper presents the BOC 2-D compressed correlator (TDCC) technique for the fast acquisition of the next-generation GNSS signals. In the proposed BOC-TDCC, signal power in neighboring code-phase hypotheses and Doppler frequency hypotheses can be coherently combined and tested by a single compressed correlator in the first stage, and the conventional correlator-based serial search technique is employed in the second stage to test each hypothesis combined in the first stage. The performance of the BOC-TDCC is demonstrated with numerous Monte Carlo simulations and tested with real data. The BOC-TDCC has much lower mean acquisition time (MAT) than other conventional search schemes, which demonstrates that the BOC-TDCC is an effective search scheme for next-generation GNSS signals.

It is well known that code and carrier-phase multipath, which has been under study for over two decades, is the limiting error sources in high-precision differential GPS applications. In virtually every study, however, the effects of autocorrelation function are considered little. This article focuses on the bounds of code and carrier-phase multipath error in terms of GNSS (Global Navigation Satellite Systems) signals autocorrelation functions, which result from a fundamental theoretical description and mathematical modeling of GNSS receiver. Firstly, an overview of the characteristics of the BOC (Binary Offset Carrier) signal ACF (autocorrelation function) is given in the paper. The impact on the DLL (delay-lock loop) and PLL (phase lock loop) discriminator functions are derived in the followed section and consequently a general description of multipath errors are obtained for the BOC signals. This quantifies the influence of limited bandwidth on receiver tracking error due to multipath. Finally, the simulation results show a distinct change in the error envelope for BOC signals from which has been got using current GPS C/A code signal.

The long PN code in a Binary Offset Carrier (BOC) modulated signal has a higher rate than the GPS C/A code, which makes the acquisition process in the new global navigation satellite system (GNSS) much more complex.To achieve a fast acquisition of the GNSS signal with a reduced number of correlators and low computational complexity, a two-stage deterministic compressed (DS) GNSS acquisition technique has been proposed.Nevertheless, the ambiguous threat of BOC signal isn't taken into account in the DS technique.To eliminate the ambiguity threat in the acquisition process of BOC (m, n) signal, an unambiguous deterministic compressed acquisition is proposed in this paper.The main idea of the proposed technique is to introduce a simplified GRASS algorithm in the second stage measurement.Theoretical analysis and simulation results show that, at the expense of some performance degradation the proposed technique can completely remove the undesired positive side peaks of BOC (m, n) signal, and reduce the chance of false peak acquisition compared with the DS technique.

The landscape of Global Navigation Satellite Systems (GNSS) signals is undergoing significant change. The parallel development of new, more robust and versatile signals along with two new GNSS systems with global reach is having a dramatic impact on the development of GNSS receivers. Receiver manufacturers are continually developing and implementing unique signal acquisition and tracking algorithms, advanced integrity monitoring algorithms, advanced multipath mitigation algorithms and a host of other enhancements in an effort to improve the performance of GNSS receivers and make their products stand out in a crowded field. The objective of this research is to develop a methodology for comparing the pseudorandom noise (PRN) code tracking performance of various receivers. While the overall performance of a receiver depends on many more factors, effective PRN code tracking is fundamental to the operation of a GNSS receiver. The methodology developed in this research requires three fundamental measurements from the receiver under test – code pseudorange, carrier pseudorange and carrier-to-noise-density ratio (C/No). These measurements are generated by all GNSS receivers but may not always be available to the user. Therefore, this methodology can only be performed on receivers that output these values. This methodology might be useful as a tool to evaluate the suitability of various receivers in certain environments or applications (e.g., weak signal environments, high dynamic environments, unfriendly radio frequency (RF) interference environments, etc.) and also as a means of comparing the relative performance of receivers in those environments or applications. Expectations for the research were that the data collection and analysis techniques would generate code loop tracking jitter plots that closely tracked with theoretical curves. In addition, it was expected that different receivers would yield slightly different jitter plots giving them a unique “signature.” Finally, it was expected that some receivers might incorporate scalar code tracking loops and others might incorporate vector tracking loops. The methodology was developed and refined using three receivers from three popular manufacturers, each with a unique set of capabilities. Raw data was collected from each receiver and processed using purpose built algorithms to estimate the code loop tracking jitter for each signal for each receiver. The code loop tracking observations for each of the three receivers tested were compared with theoretical curves generated using closed form equations published in previous papers. In most cases, the data compared favorably. However, there were some significant outliers that are worthy of additional research and analysis. In addition, the jitter plots for one receiver tested indicated that it used scalar code tracking loops and the jitter plots for the other two receivers indicated that they use vector tracking loops. It appears to be possible to determine if a receiver uses scalar tracking loops or vector tracking loops based on the jitter estimates generated in this research. This research indicated that the methodology might be a useful tool for 2 characterizing GNSS receivers and, eventually evaluating their performance in various environments. However, more data collection and analysis is required to further validate and refine the methodology. Also, more analysis of the signals that yielded “non-conforming” jitter plots should be examined in more detail.

To reduce the processing time in Global Navigation Satellite System (GNSS) signal acquisition and tracking, we first propose a parallel method of signal acquisition and tracking as well as the associated software implementation in this paper. This paper applies the Message Passing Interface (MPI) and Open Multi-Processing (OpenMP) techniques for parallel computation implementation. This parallel method could put the multi-cores microprocessors to be efficiently used in GNSS signal acquisition and tracking processes. To further enhance the performance, this paper then proposes a new GNSS acquisition and tracking method, and it includes the multi-PRN code acquisition method we proposed in [Y. C. Lin and C. C. Sun, ION GNSS 2007] to reduce the acquisition processing time and a new FFT (Fast Fourier Transform)-based tracking method. This FFT-based tracking method combines the conventional tracking method and the FFT technique to track the incoming signal. Consequently, the tracking process is divided into two phases: detection and FFT-based phases. This proposed FFT-based tracking method can reduce the computational load as well. This new acquisition and tracking method will be combined with the above parallel method to gain the maximum improvement in GNSS signal acquisition and tracking. Finally, we use the real data collected by a software GNSS receiver to validate the proposed method. This paper will also conduct the comparison between the proposed method and the conventional GNSS acquisition and tracking method, and the comparison criterions are the computational load and the processing time. The experiment results of this paper show the effectiveness of this proposed approach for GNSS signal acquisition and tracking.

With the rapid development of Global Navigation Satellite Systems (GNSS). The binary offset carrier (BOC) signal was proposed to separate new navigation signal from traditional BPSK in frequency and it has better accuracy and anti-multipath performance compared with the BPSK of the same code rate. But the ambiguity caused by the multi-peaks of auto-correlation function makes traditional acquisition technique not applicable to BOC.A novel unambiguous acquisition algorithm for sine BOC signals is proposed in this paper. There are two types of local reference signals: the BOC signal and a designed binary auxiliary signal. They are both correlated with the received signals. Then, a correlation function unambiguous for acquisition of BOC signal is obtained by multiplying the two correlation results. In the acquisition stage of BOC(10,5), the detection probability of the proposed method is approximately 1.5 dB better than that of GRASS and 2 dB better than that of SPAR. For BOC(14,2), the detection probability advantages of the proposed method increase to 6 dB and 7.5 dB . In conclusion, the proposed method can eliminate ambiguity and has significant performance advantages compared with the above methods.

The global navigation satellite system (GNSS) signal modulation type plays a crucial role in determining the performances of positioning, navigation and timing (PNT) services. Currently, the binary offset carrier (BOC) modulation signal and binary coded symbol (BCS) modulation signal are both bipolar signals, which greatly restrict the room of improving the GNSS signal performance. Therefore, multi-level coded symbol (MCS) modulation has received great attention in the field of GNSS signal design. The MCS modulation is the most extensive step-coded symbol modulation mode, where BOC modulation and BCS modulation are its special cases. Since the waveform symbol of the MCS modulation signal can be arbitrarily valued, the optimal GNSS signal can be designed. However, like the BOC modulation signal, the MCS modulation signal also has the problem of ambiguous tracking, and then results in a large pseudo range measurement error, which is unacceptable for the new generation GNSS with high accuracy. In recent years, the unambiguous tracking of GNSS signals has become a hot research subject in the navigation signal processing domain and many methods are presented, and those methods can be divided into three categories:BPSK-like method, bump jump (BJ) method, and side-peak cancellation (SC) method. However, these methods are designed for BOC signal, and they are not suitable for MCS signal. Therefore, in this paper we propose a general unambiguous tracking algorithm based on the pseudo correlation function (PCF), which is suitable for MCS modulated signals. Firstly, the unitary expression of MCS modulated signal based on waveform value vector is given, then the unitary formula of cross-correlation function for MCS signal is derived and the definition of PCF is given. Then the constraint condition which should be satisfied to realize unambiguous tracking is analyzed in depth, and the universal constructing method of two reference signals and the relationship between each other are derived according to this constraint condition, which brings great convenience for solving the specific MCS signal. The code tracking loop model of GNSS receiver based on the proposed method is illustrated. It is observed that the proposed method can receive different MCS signals under the same receiver loop framework, and can simplify the design of the receiver while eliminating the tracking ambiguous problem. Finally, as a special case of MCS signal, the applications of the proposed method in four kinds of BOC signals are discussed respectively, and then the waveform value vector of the reference signal and the unitary expression of code discriminator are derived. Simulation results show that the proposed method can effectively solve the ambiguous tracking problem of MCS signal, which has good performance and broad application prospect.

Binary offset carrier (BOC) modulation signals have been widely adopted in global navigation satellite systems (GNSSs) such as Galileo and modernized global positioning system [1] [2]. Although this kind of modulation offers excellent performances, a main drawback of BOC modulation is that ambiguous acquisition and biased tracking for its multi-peak autocorrelation function (ACF). This article presents herein a novel acquisition technique allows removal of side peaks thoroughly and acquire better acquisition performance. This scheme is applicable to BOC (n, n) modulation signals. Theoretical analysis and system simulation demonstrate the algorithm proposed has better performance in acquisition aspect compared with other typical algorithms under the influence of additive white Gaussian noise.

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.

Due to the low signal power, the Global Navigation Satellite System (GNSS) signal is vulnerable to interference and even cannot be captured or tracked in harsh environments. As an alternative, the Low Earth Orbit (LEO) satellite has been widely used in the navigation field due to the advantages of low cost and strong signals. It is becoming a significant component of the new combined navigation system with GNSS. The combination of an LEO Doppler signal and GNSS observables can improve the positioning accuracy and high-precision positioning convergence time of the GNSS receiver. However, the GNSS signal receiving capability cannot be improved from this data fusion level. We propose a novel assisted structure where GNSS signal acquisition and Doppler tracking are assisted by LEO Doppler positioning. The receiver uses the LEO signal to achieve Doppler positioning firstly. Then, the coarse position with the GNSS navigation messages received from LEO, as well as the estimated clock information, is used to assist in the acquisition and tracking of GNSS. In this way, the GNSS receiver’s sensitivity can get the benefit from this integrated system. The paper presents the structure of the assisted receiver and analyzes the assisted GNSS signal acquisition and carrier tracking performance in detail. Simulation experiments of this assisted structure are carried out to verify its superiority of acquisition and tracking sensitivity in comparison with standalone GNSS receivers. Theoretical analysis and experimental results show that the proposed acquisition method can achieve 90% detection probability at a carrier-to-noise ratio (C/N0) of 15 dB-Hz, which is about 8 dB higher than the conventional acquisition method without assistance; the proposed tracking method can track weak signals of 5 dB-Hz, which is about 4 dB higher than the conventional method. Therefore, this novel LEO-assisted receiver has significantly improved weak signal acquisition and tracking sensitivity.

Binary offset carrier (BOC) modulated signals have been introduced in global navigation satellite systems such as Galileo and modernized Global Positioning System. This type of modulation creates multiple side peaks in autocorrelation function. Thus, it causes challenges in the stages of signal acquisition and tracking. In this paper, we present a new method of side-peak cancellation for BOC-modulated signals in order to remove or diminish the side peaks while keeping the sharp and narrow main peak. This proposed method could be applied to cosine-BOC(n, n) modulated signals, which are adopted to Galileo signals. Moreover, this method has better performance in reducing the error caused by multipath propagation than traditional method.

A sparse global navigation satellite system (GLONASS) signal acquisition method based on compressive sensing and multiple measurement vectors is proposed. The nonsparse GLONASS signal can be represented sparsely on our proposed dictionary which is designed based on the signal feature. Then, the GLONASS signal is sensed by a normalized orthogonal random matrix and acquired by the improved multiple measurement vectors acquisition algorithm. There are 10 cycles of pseudorandom codes in a navigation message, and these 10 pseudorandom codes have the same row sparse structure. So, the acquisition probability can be raised by row sparse features theoretically. A large number of simulated GLONASS signal experiments show that the acquisition probability increases with the increase in the measurement vector column dimension. Finally, the practical availability of the new method is verified by acquisition experiments with the real record GLONASS signal. The new method can reduce the storage space and energy loss of data transmission. We hope that the new method can be applied to field receivers that need to record and transmit navigation data for a long time.

Improving tracking accuracy with subcarrier assistance and code monitoring for BOC modulated signal

Navigation receivers of global positioning systems that are operated in complex electromagnetic environment must have an increased noise immunity characteristic. One way of such noise immunity rising is to use incoherent operating mode of navigation receiver. There are known processing algorithms for navigation signals with Binary Phase Shift Keying (BPSK) modulation. But in the near-term outlook Global Navigation Satellite Systems (GLONASS), Global Positioning Systems (GPS) and Galileo known navigation signals with Binary Offset Carrier (BOC) modulation will be radiated. Processing algorithms for such signals are not described in scientific literature. So it is interesting to work out processing algorithms for BOC modulated signals in incoherent operating mode of navigation receiver. The article is devoted to synthesis and analysis of incoherent subcarrier tracking system under receiving BOC (1,1) navigation signals. To synthesize an optimal tracking system, optimal estimation theory and dual estimation method are used that allow taking into account multi-peak a posteriori distribution of delay that caused by the periodic process (digital sinusoid) in the radio signal modulation function. When analyzing the synthesized estimation algorithm, the procedure for describing delay discriminators and dual variable discriminators were used in the form of a statistical equivalent, including discrimination and fluctuation characteristics. New equations have been obtained that describe optimal tracking system for incoherent mode of a navigation receiver. New expressions for delay and dual variable discriminators are derived. The article gives a scheme for these discriminators and formulas for their statistical characteristics. Simulated results are provided that illustrate accuracy characteristics enhancement. The obtained tracking algorithms may be used in the navigation consumer equipment of GLONASS, GPS, Galileo and other radio-navigation satellite systems operating with BOC(1.1) modulated signals.

This paper presents a concept, “Cookie,” for a satellite particularly suited for dense spatial sampling by future Global Navigation Satellite Systems (GNSS) remote sensing constellations. Solely based on the reception of the direct and reflected signals transmitted by the GNSS, the satellite can provide observations of the Earth useful for a wide range of scientific and operational applications. The Cookie is capable of receiving direct and reflected signals, in both right- and left-hand circular polarizations, from any of the GNSS systems, and from virtually any arrival direction in both the upper and lower field-of-view hemispheres, i.e., providing nearly full 4π spherical coverage toward any navigation satellite not eclipsed by the Earth. The on-board remote sensing payload produces interferometric observables, e.g., the auto- and cross-correlation of several adequate combinations of the received signals. The interferometric processing is general, the same, and transparent, with respect to any of the signals transmitted by the current or planned GNSS systems. The instrument can implement any other suitable processing schemes too. Such payload can provide, in parallel, accurate GNSS Radio-Occultation (GNSS-RO) observations of the atmosphere and forward and backward GNSS Reflectometry (GNSS-R) measurements from the Earth surface. Several Cookies can be piled up inside the fairing of a rocket minimizing the launch cost of a constellation. A constellation of three Cookies has been simulated and its sampling performance characterized. The key concepts of the Cookie payload could be demonstrated through ESA's GNSS Reflectometry, Radio-Occultation, and Scatterometry experiment on board the International Space Station (GEROS-ISS).