Standalone Direct Acquisition of Weak Multi-Band Split-Spectrum Signals

The binary offset carrier (BOC) modulation was initially developed for easy sharing of spectrum between GPS modernization signals and legacy binary phase shift keying (BPSK)-modulated signals in the same band. It is now adopted by all GNSS constellations as a BOC signal has a larger Gabor bandwidth, producing better ranging (accuracy and multipath) performance. However, general BOC signal acquisition and tracking encounters the problem of multiple peaks (less an issue for MBOC, though), and many methods have been proposed to address this issue. A simple method to avoid such an ambiguity is to extract the upper and lower sidebands of the split spectrum of a BOC signal, treat them separately as a BPSK signal each, and then combine the results so as to recover the reduced sideband signal strength. Coherent combining is more gainful than the noncoherent counterpart particularly when the incoming signal is weak and/or when a strong interference signal is present. In this paper, a long coherent combining and integration (LCCI) scheme is presented, which enables standalone acquisition of a BOC signal without external aiding from a network or an inertial navigation system (INS) under combined narrowband and matched spectral interference signals. The LCCI scheme burns through the strong interference via building up the desired signal while averaging out noise and interference. To build up the desired signal, it makes use of all information resources available (e.g., L1 and L2, upper and lower sidebands, odd and even chips, and/or I and Q components) and applies coherent combining and long coherent integration, followed by non-coherent accumulation if necessary. Issues and enabling techniques are presented in this paper. The LCCI scheme is implemented on a software defined receiver (SDR) platform consisting of FPGA and ARM. Results of real-time demo with input RF signals generated by a Spirent GPS Simulator are described in the paper.

A multitude of GNSS signals are transmitted at the same frequency band, and even the same signal may have several components with different codes. For examples, different signals are modulated onto the in-phase and quadrature components (e.g., L1C-I and L1C-Q, I5 and Q5) and are time-division multiplexed (e.g., odd and even chips of M-code). Most of these signals adopt the binary offset carrier (BOC) modulation and thus have a split-spectrum as compared to the legacy signals that use binary phase shift keying (BPSK) and have a dominant lobe at the band center. BOC is used not only for the ease of spectrum sharing but also for its improved ranging performance due to a larger Gabor bandwidth. Both weak signals and in particular the presence of strong interference lead to an effective signal to noise ratio (SNR) that is very low. To pull such a signal out of noise and interference, it is necessary to combine multiple signal components available at the same time and then integrate them over time so as to add up the signal strength while averaging the noise and interference out in a burn-through process. However, it is not straightforward to apply the linear additive coherent operation due to the difference in phase and frequency between signal components as well as the presence of unknown data bits, which may become counterproductive if not treated properly. In this paper, we investigate several nonlinear multiplicative schemes including non-coherent, semi-coherent, and cross-conjugate-multiply for signal accumulation (combining and integration), and compare them to the coherent scheme. The study shows that according to the SNR definition at the output of nonlinear operations, some of the schemes may have the same SNR level per analysis of second-order statistics, yet they exhibit different Pd vs. Pfa characteristics, which can be attributed to different distribution tail behaviors (higher order statistics). Understanding of the detection performance is thus important in trading off combining and integration schemes for implementation. Extensive computer simulation results are presented to illustrate the functionality and performance of the schemes.

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.

Navigation and positioning in harsh environments is still a great challenge for many applications. Collective Detection (CD) is a powerful approach for acquiring highly attenuated satellite signals in challenging environments, because of its capacity to process all visible satellites collectively taking advantage of the spatial correlation between GNSS signals as a vector acquisition scheme. CD combines the correlator outputs of satellite channels and projects them onto the position/clock bias domain in order to enhance the overall GNSS signal detection probability. In CD, the code phase search for all satellites in view is mapped into a receiver position/clock bias grid and the satellite signals are not acquired individually but collectively. In this concept, a priori knowledge of satellite ephemeris and reference location are provided to the user. Furthermore, CD addresses some of the inherent drawbacks of the conventional acquisition at the expenses of an increased computational cost. CD techniques are computationally intensive because of the significant number of candidate points in the position-time domain. The aim of this paper is to describe the operation of the CD approach incorporating new methods and architectures to address both the complexity and sensitivity problems. The first method consists of hybridizing the collective detection approach with some correlation techniques and coupling it with a better technique for Doppler frequency estimate. For that, a new scheme with less calculation load is proposed in order to accelerate the detection and location process. Then, high sensitivity acquisition techniques using long coherent integration and non-coherent integration are used in order to improve the performance of the CD algorithm.

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 technology is gradually replacing the traditional BPSK modulation signal as the main modulation method of the new generation satellite navigation signal due to its superiority in multipath suppression performance and code tracking accuracy. However, the tracking and mis-locking problem of BOC signals has become a key point limiting the widespread application of BOC signals. In this paper, we use code reference waveform (CCRW) technology and optimized Bump-jump (BJ) algorithm to analyze the multipath performance of low-order BOC signals under five code reference waveforms. Aiming at the high peak BOC signal with many peaks and high peak-to-peak ratio, we propose a new code reference waveform ensures the high-order BOC signal has good anti-multipath performance and solves the problem of extremely easy mis-locking of its receiver.

Satellite navigation and positioning have become an indispensable component of smart devices and applications. In order to avoid signal interference in L1 frequency and provide novel services, Global Positioning System III (GPS III) updated a modern signal named L1C and tested in three Quasi-Zenith Satellite System (QZSS) satellites launched in 2017. In December 2018, the first GPS III satellite was launched, which implies the joint positioning using QZSS and GPS L1C signal is improved. L1C signal offers a series of advanced designs in signal modulation, message structure and coding, etc. In this regard, this paper presents complete methodologies for L1C signal joint receiving processing. For the on-air signals, this paper presents a methodology and results from collecting and assessing binary offset carrier (BOC) modulation and time-multiplexed BOC (TMBOC) modulation used in L1C signal. Using the same omnidirectional antenna and the test-equipment, the L1C signal was collected in Xi’an and Sanya, China, respectively. Experiments in Xi’an verified the joint positioning method to complement the GPS III and QZSS satellite constellations. The methodology in this paper evaluates the positioning error of BOC(1,1) and TMBOC(6,1,4/33) under the same environment and satellite constellation in Sanya. It is also verified that the joint positioning error is less than the QZSS-only positioning due to the optimization of the satellite constellation.

In this paper, a rotor rotation speed estimation method is studied. Firstly, the radar rotor micro motion echo model of the wideband frequency modulated continuous wave (FMCW) is established; then, the echo matrix is transformed into a vector, and the rough estimation of the speed is estimated by coherent integration. Secondly, the real-valued inverse Radon transform (RIRT) algorithm is used to estimate the precise rotor rotation speed based on the theory of minimum image entropy. The proposed method improves the estimation accuracy by coherent and non-coherent integration respectively. The simulation results and the measured data verify the feasibility and effectiveness of the proposed method.

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.

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.

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.

Frequency-hopping binary offset carrier modulation improves the anti-interference performance and mitigates the autocorrelation function (ACF) ambiguity problem of binary offset carrier modulation. To save payload resources and make high-power amplifiers on satellites operate at the nonlinear saturation region, there is further demand for finding an efficient constant-envelope frequency-hopping binary offset carrier multiplexing technique to combine several signal components. Thus, we propose a dual-sideband constant-envelope multiplexing modulation, named asymmetric constant-envelope frequency-hopping binary offset carrier multiplexing (ACE-FHBOC), which is also a multicarrier constant-envelope multiplexing modulation. ACE-FHBOC provides higher design flexibility in the number of subcarrier frequencies than ACE-BOC while maintaining the same flexibility of signal design as ACE-BOC in the number of signal components and power ratio among components. We first establish the theory and give implementation methods of ACE-FHBOC. Then, we develop a software-defined receiver to simulate and analyze the performance for several specific ACE-FHBOC and ACE-BOC signals. The results show that the recommended ACE-FHBOC signals have lower ACF ambiguity, better anti-narrowband interference, and multipath performance than ACE-BOC under the same conditions. With these advantages, ACE-FHBOC is a promising solution for the signal design of new generation global navigation satellite systems.

Navigation signals are the basis of satellite navigation systems, which determine the navigation systems' performance (such as tracking accuracy, anti-interference capability etc.), and are determined by some constraints (such as radio frequency resources, construction cost, technology level etc.). The aim of signal design is to select "proper" signals considering these above factors and make tradeoffs between performance and constraints. This paper will summarize the signal structure evolution of present satellite navigation and conclude some principles and issues which will be greatly valuable to our 2nd satellite navigation system. There's four main satellite positioning systems presently, the U.S. Global Positioning System (GPS), the Russian Global Navigation Satellite System (GLONASS), the Europe Galileo satellite navigation system and the Chinese BD-1 satellite positioning system. Among these systems, the signal characteristics of GPS and Galileo are good reference to our 2nd satellite navigation system. The improvement of GPS signals is a main aspect of GPS modernization. The aim of GPS modernization is mainly to modernize its signal structure so as to improve the whole systems' performance. The signal structure of Galileo has been revised for several times, and its present signal is the results of long time signal design. From GPS modernization and Galileo signals status, we can summarize some key specifications of navigation signals and some technologies to support these specifications. Based on this, we'll discuss some problems which should be attentive in our country's 2nd satellite navigation system and give some suggestions. This paper is organized into five sections. The first section will give a brief introduction of present satellite navigation system and their main features. Section two will review the GPS and Galileo signals structure evolution, including GPS modernization, Galileo signals status and the comparison of two systems' signals. In the third section, the relationship between signal parameters and system performance will be analyzed, including RF signal characteristics, modulation type, ranging code (such as code type, length and rate) and navigation data. In section four we will discuss some inspiration and technologies concerning our 2nd satellite navigation system, such as the use of multiple frequency signals (ionospheric delay estimation and carrier ambiguity resolution), pilot tones & dataless channel, binary offset carrier (BOC) modulation, and so on. The last section is conclusion, in which the whole paper will be retrospected and some useful conclusion will be given.

Modulation design has a significant effect on the accuracy of a navigation system. Two problems exist in current modulations for Global Navigation Satellite Systems (GNSS). One is the extremely low transmission rate of navigation messages. The other is the pseudorange error caused by multipath. To solve the restrictions, a novel GNSS signal system is proposed in this paper. In the new signal system, navigation messages are modulated by Orthogonal Frequency Division Multiplexing (OFDM) modulation for high transmission rate as well as excellent anti-multipath performance and conventional ranging code is still transmitted by Phase Shift Keying-Rectangular (PSK-R) or Binary Offset Carrier (BOC) modulation for precise ranging. Both the signal components supplement each other. Simulation results show that using the proposed GNSS signal system, stable and high transmission quality along with high transmission efficiency for navigation data are achieved. Also, the anti-multipath performance is significantly improved with less computational complexity.

New three‐level binary offset carrier (BOC) subcarriers are constructed, based on which the non‐orthogonal alternative BOC (AltBOC) modulation and its unequal power generalised form are achieved. The new constant envelope modulations have achieved a lower hardware complexity, which provide a solution to dual‐frequency multiplexing problem confronted by BeiDou B2 frequency band.