Binary Offset Carrier Modulated Signals Research Articles

A Multipath Cancellation Method Based on TK Operator for BOC Signals

The new generation of global navigation satellite systems will apply binary offset carrier (BOC) modulation technique, which can efficiently split the spectrums of navigation signals using the same frequency so as to reduce the interferences among different systems. But the autocorrelation function of BOC modulated signals has the drawback of multimodality, so it’s very hard to synchronize to the right peak when acquiring and tracking signals, especially under low SNR circumstances, which can decrease the positioning accuracy and even lead to wrong positioning results. Meanwhile, if there are multipath signals mixed in the receiving signal, the autocorrelation curve will be greatly distorted, and the number of side-peak will also increase exaggeratedly, which could deteriorate the situation mentioned above. A multipath cancellation method based on TK (Teager-Kaiser) operator is proposed in this article, which could not only detect the right peak in the autocorrelation curve, but also eliminate all the other multipath signals. As a result, this method could avoid the false lock of code phase and guarantee the high precision fix results.

Codeless processing of binary offset carrier modulated signals

Advanced and unexpected applications are recently raising new interest in Global Navigation Satellite System (GNSS) codeless techniques that can be used, for example, for signal authentication and spoofing detection. Moreover, the presence of a subcarrier in modern GNSS signals introduces new challenges and opportunities. To take advantage of modern signal structures, codeless processing needs to be modified to recover the subcarrier which can subsequently be used for signal quality monitoring. In this study, codeless tracking is modified for processing binary offset carrier (BOC) modulated signals where a subcarrier lock loop is used to remove the subcarrier component. The performance of the suggested architecture is thoroughly analysed and theoretical results are supported by Monte Carlo simulations. An open-loop, multi-correlator codeless architecture is also proposed to monitor the BOC subcarrier correlation function. The effectiveness of the proposed codeless framework is demonstrated using real data collected from the Galileo in-orbit validation satellites. The analysis supports the validity of the proposed architecture which enables quality monitoring of encrypted GNSS signals.

Mathematical Model of Non-Coherent-DLL Discriminator Output and Multipath Envelope Error for BOC (α, β) Modulated Signals

In this paper we propose the derivation of the expressions for the non-coherent Delay Locked Loop (DLL) Discriminator Curve (DC) in the absence and presence of Multipath (MP). Also derived, are the expressions of MP tracking errors in non-coherent configuration. The proposed models are valid for all Binary Offset Carrier (BOC) modulated signals in Global Navigation Satellite Systems (GNSS) such as Global Positioning System (GPS) and Future Galileo. The non-coherent configuration is used whenever the phase of the received signal cannot be estimated and thus cannot be demodulated. Therefore, the signal must be treated in a transposed band by the non-coherent DLL. The computer implementations show that the proposed models coincide with the numerical ones.

Unambiguous Tracking Method for Alternative Binary Offset Carrier Modulated Signals Based on Dual Estimate Loop

We propose an unambiguous tracking method for Alternative Binary Offset Carrier (AltBOC) modulated signals based on the Dual Estimate Tracking (DET) loops. The proposed method employs a combined PRN code and a pure cosine signal which can be easily implemented in the hardware to make DET loops available to the complicated AltBOC signal structure. The two dimensional correlation function for AltBOC is derived, and an unambiguous delay estimate is deduced according to the correlation function. Simulation results reveal that the proposed method performed better in tracking performance than the traditional unambiguous tracking methods.

Unambiguous S-Curve Shaping Technique for Multipath Mitigation in Cosine-BOC Signals

This letter proposes a new multipath mitigation technique based on the concept of S-curve shaping for the new cosine phased binary offset carrier (cosine-BOC) modulated signals, which will most likely be used in both European Galileo system and Chinese Compass system. The definition of an optimum S-curve is employed to reduce the false lock points and to improve the multipath mitigation capability via determining the weights of the local linear combined code. The structure of the code tracking loop for cosine-BOC signals is quite simple and only requires one correlator. Results demonstrate that the proposed technique provides superior multipath mitigation performance and removes the ambiguity completely.

The spectral characteristics of navigation alternative binary offset carrier modulated signals (AltBOC signals)

Analytical expressions are obtained for spectral densities and energy spectra of single elements and single periods of modulating functions of alternative binary offset carrier modulated signals (AltBOC signals) for new-generation satellite radio navigation systems (SRNSs) (in particular, the Galileo system). The spectral characteristics are presented and analyzed for an elementary (two-component) AltBOC signal, a complete AltBOC with a time-variable envelope (a four-component complete AltBOC signal), and a complete AltBOC with a constant envelope (an eight-component complete AltBOC signal) in the case when the multiplicity coefficient of meander pulses has an arbitrary value. Plots are depicted, and the properties of energy spectra of single elements of modulating functions of all groups of AltBOC signals are discussed in the cases of the following modulation types: AltBOC(10, 10), AltBOC(15, 10), AltBOC(20, 10), and AltBOC(25, 10).

Unambiguous BOC Modulated Signals Synchronization Technique

In this letter, a new unambiguous tracking technique is proposed for binary offset carrier (BOC) modulated signals, which will be utilized in global navigation satellite systems (GNSS). The proposed technique is a synthesized correlation function obtained by subtracting the cross-correlation between the received BOC signal and the local auxiliary signal from the cross-correlation of BOC signal between another local auxiliary BOC signals. The theoretical standard tracking error formulas are given. The results show that this technique can be a solution to remove the ambiguity completely with slightly degradation in acquisition and tracking for low modulation order BOC signals.

Complete alternative binary offset carrier modulated signals (AltBOC signals) with variable and constant envelopes for new-generation satellite radio navigation systems

The formation and structure of four- and eight-component complete alternative binary offset carrier modulated signals (AltBOC signals) for new-generation satellite radio navigation systems (SRNSs) (in particular, the Galileo and BeiDou-2 SRNSs) are considered. A four-component complete AltBOC signal has a time-variable envelope, while the envelope of an eight-component complete AltBOC signal is constant. The envelopes and phases of such AltBOC signals are analyzed for various values of the multiplicity coefficients of meander pulses. The combination components of an eight-component complete AltBOC signal are plotted, and the features of these components that ensure the time constancy of the envelope are revealed. A classification of AltBOC signals is proposed. Practical characteristics are analyzed on the basis of the AltBOC (15, 10) modulation, which is typical of the Galileo and Compass SRNSs.

Ambiguity Mitigating Technique for Cosine-Phased Binary Offset Carrier Signal

This letter focuses on mitigating ambiguity for cosine-phased binary offset carrier (BOC) modulated signals which are used in the global navigation satellite system (GNSS). The main idea is to use the cross-correlation function (CCF) of the received cosine-phased BOC signal with the specifically designed local auxiliary signal to counterbalance the undesired side peaks of the received BOC autocorrelation function (ACF), the final correlation function has only two small positive side peaks which can be rectified by combing with the classical bump jump (BJ) technique easily. The modulated symbol of the local auxiliary signal is derived and simulations show that at the cost of some degradation of detection probability in the acquisition phase the proposed method is better than the traditional BJ method in mitigating the ambiguity for cosine-phased BOC signals, especially when the subcarrier frequency is high and even under multipath interference.

IDENTIFYING NONSTATIONARY JAMMING SIGNAL VIA LAGRANGIAN COHERENT STRUCTURES

The anti-jamming scheme is an important issue in the modern communication system, where the spread-spectrum signals are usually adopted. In a complex electromagnetic environment where the jamming sources may be close to the communication devices, a large jamming-to-signal ratio is possible. How to achieve the desired accuracy for the communication system in the presence of strong jamming is a crucial and outstanding problem. To solve this problem, we propose a method to identify the desired signal and the nonstationary jamming signal via Lagrangian Coherent Structures (LCS), and a new algorithm for calculating the maximum Finite-Time Lyapunov Exponent (FTLE) is presented. As opposed to the current approach which requires a vector field in the state space at each instant time, the proposed algorithm is performed on the vector fields which are respectively built on the desired signal and the nonstationary jamming signal via Hilbert Transform. A simulation test is conducted on a binary offset carrier (BOC) modulated signal and a chirp signal. The results indicate that the proposed method can provide new features to efficiently identify the nonstationary jamming signal.

Joint code multipath mitigation for composite binary offset carrier modulated signals

A new multipath mitigation algorithm for composite binary offset carrier (CBOC) signals defined for the Galileo navigation system is presented. The pilot and data channels are jointly tracked by multipath mitigation windows (MMW). The proposed algorithm is demonstrated as an implementation of the optimum s-curve shaping for CBOC multipath mitigation applications.

Complex meander pseudorandom code sequences and alternative binary offset carrier modulation (AltBOC modulation) in new-generation satellite navigation systems

Complex meander pseudorandom sequences (MPRSs) that are the basis for formation of alternative binary offset carrier modulated signals (AltBOC signals) for new-generation satellite radio navigation systems (in particular, the Galileo and Compass systems) are considered. The properties and characteristics of MPRSs are analyzed. Analytical expressions for the spectral densities and power spectrum densities of complex and complex conjugate meander symbols (MSs) of the MPRS of a ranging code are found for various values of the multiplicity coefficient of meander pulses. The modulating function of an elementary AltBOC signal is considered. The power spectrum densities of complex and complex conjugate MSs are plotted and analyzed for typical values of the multiplicity coefficient.

The statistical characteristics of navigation cosine binary offset carrier modulated signals (CosBOC signals)

The features and statistical characteristics of cosine binary offset carrier modulated signals (BOC signals) of new-generation satellite radio navigation systems, in particular the Galileo system, are considered. Analytical expressions for the correlation functions (CFs) of the cosine meander symbols (MSs) of the pseudorandom sequence of a ranging code are found for various values of the multiplicity coefficient of meander pulses. The energy spectra of cosine MSs are obtained with the help of the Fourier transform of the CFs. Plots are depicted, and the CFs and energy spectra of cosine MSs are analyzed for the following types of meander modulation: CosBOC (1,1), CosBOC (15,10), CosBOC (10,5), and CosBOC (5,2).

Unambiguous sine-phased binary offset carrier modulated signal acquisition technique

In this letter, a side-peak cancellation unambiguous acquisition technique is proposed for sine-phased binary offset carrier (BOC) modulated signals. The test criterion used in this technique is based on a synthesized correlation function which has no major positive side peak. This synthesized correlation function is obtained by subtracting the cross-correlation between the received sin-BOC signal and an auxiliary signal from the autocorrelation of sin-BOC signal. For different types of BOC signal, the proposed technique employs corresponding modulated symbols of the auxiliary signal. The common solution of the symbol shape vector is derived, and the theoretical false alarm and detection performance formulas are given. Theoretical and simulation results show that at the expense of some performance degradation this technique completely removes the ambiguity threat in acquisition process.

Correlation functions of single symbols of meander signals in new-generation satellite radio navigation systems

Mathematical models of meander noise-like signals (binary offset carrier modulated signals (BOC signals)) of new-generation satellite radio navigation systems (SRNSs), in particular, the modernized GPS, the Galileo system, and the QZSS are presented. An analytic expression for the correlation function (CF) of single symbols of meander pulses is obtained for the arbitrary value of the multiplicity coefficient. The properties of CFs of various meander symbols are analyzed. The features of CFs are revealed for the even and odd values of the multiplicity coefficient. Examples of CFs are considered, and CFs of single symbols of BOC signals applied in new-generation SRNSs are plotted.

A General Model of Multipath Error for Coherently Tracked BOC Modulated Signals

A new class of signals, modulated using a binary offset carrier (BOC), is being implemented and tested in multiple Global Navigation Satellite Systems (GNSSs). A receivers that tracks a BOC signal is considered more resistant to interference than tracking a signal modulated with a binary phase shift key (BPSK). In this study, that resistance is evaluated by analytically modeling the impact of multipath interference on signal tracking. Signal tracking error is then mapped to errors in the measurements produced by GNSS receivers, pseudorange and carrier phase. The model is general so that it can apply to measurements derived from any BOC modulated signal, including those from Galileo or modernized GLONASS systems. The model incorporates a single reflector and signal tracking that is coherent with signal phase. The timing between early and late correlation processes is left as a free parameter in order to emulate the design known as narrow correlation. The error models are applied to predict errors inserted into the GPS control segment ephemeris generation process, when control segment begins tracking the BOC modulated M-Code. First, conditions by which it is possible for M-Code receivers to exhibit more multipath error than P/Y-Code receivers are solved. Second, the mean multipath error is examined. For carrier phase, the condition for zero mean is proven to be uniformly true. In contrast, pseudorange exhibits zero mean only in certain tracking conditions.

Unambiguous Technique for Multiplexed Binary Offset Carrier Modulated Signals Tracking

In this letter, we propose an unambiguous tracking technique for the new multiplexed binary offset carrier (MBOC) modulated signals, which will most likely be employed in both European Galileo system and modernized global positioning system (GPS). The discriminator used in this technique is based on a pseudo correlation function. It uses two kinds of gating correlators and a novel combination function, which completely removes side peaks from the correlation function while keeping the sharp main peak. Results demonstrate that this technique is totally unambiguous while maintaining the same level of tracking performance with respect to thermal noise as the traditional MBOC tracking method.

Code discriminator for multiplexed binary offset carrier modulated signals

A new discriminator design is shown to work efficiently for the new multiplexed binary offset carrier (MBOC) signals defined for the GPS and Galileo satellite navigation systems. A modified version is shown to be unambiguous for BOC(6,1).

Dual estimate receiver of binary offset carrier modulated signals for global navigation satellite systems

A dual estimate receiver of binary offset carrier (BOC) signals for GNSS applications is described. A unique estimate is derived solely from the code modulation. A more accurate but ambiguous estimate is derived solely from the subcarrier modulation. Any time difference between the two is rounded to the nearest subchip in order to correct the latter estimate. Implementation in the receiver is by a triple digital loop. The full potential accuracy of BOC is then reliably and unambiguously realised.

Erratum for ‘Dual estimate receiver of binary offset carrier modulated signals for global navigation satellite systems’

Erratum for ‘Dual estimate receiver of binary offset carrier modulated signals for global navigation satellite systems’