Multiplexed Binary Offset Carrier Research Articles

A Multi-Correlation Peak Phase Deblurring Algorithm for BeiDou B1C Signals in Urban Environments

With the widespread global application of BeiDou navigation, BeiDou B1C signaling based on Quadrature Multiplexed Binary Offset Carrier (QMBOC) modulation is expected to be extensively used in urban environments due to its wider signal bandwidth, smaller code pseudorange measurement errors, and stronger multipath capabilities. Despite offering higher positioning accuracy and secondary modulation characteristics of the BeiDou, B1C signals introduce the challenge of multiple peaks in the autocorrelation function. This leads to phase ambiguity during signal acquisition and tracking, resulting in positioning deviations of tens or even hundreds of meters. In urban environments, such deviations give rise to significant practical application issues. To address this problem, we have designed a multi-loop structure for the synchronous tracking of B1C signals and proposed a multi-peak phase-deblurring algorithm specifically tailored for the BeiDou B1C signal in urban environments. This algorithm considers the coupling relationship between the code and the carrier loops, and by matching the structural design of multiple loops, it achieves a precise and unambiguous phase estimation of the pseudocode, enabling the stable tracking of the entire loop for the BeiDou B1C signal. Simulation and actual testing demonstrate that the algorithm exhibits an error less than 0.03 for chip intervals when the signal-to-noise ratio is greater than −20 dB. Additionally, the accuracy can be improved by adjusting the set conditions, making it suitable for urban environments.

Theoretical assessment and application of modern GNSS signals acquisition performance

The application of the Global Navigation Satellite System (GNSS) is extensive and has widely infiltrated the national economy and social development in various fields. As critical part of the satellite navigation system design process, GNSS signals performance assessment has received tremendous attention for a long period of time. The mathematical model of GNSS signal detection is built based on single point detection test. An improved acquisition performance assessment method that considers the modulation type, code search step-size, and acquisition algorithms is proposed herein. This study investigates the performance of the overall detection and main/side peak detection for Binary Offset Carrier (BOC), Multiplexed Binary Offset Carrier (MBOC), and Alternative BOC (AltBOC) signals using matched and unambiguous acquisition methods, and obtains quantitative results. With a fixed code search step-size, the multi-peaks of the autocorrelation functions of BOC, MBOC, and AltBOC signals will degrade the acquisition performance. The higher the sub-carrier rate, the more serious is the degradation. Although signal-power loss occurs to some extent, Binary Phase-Shift Keying-like (BPSK-like) and Sub Carrier Phase Cancelation (SCPC) methods significantly improve the acquisition performance.

BDS-3 B1 signal modulation and multiplexing techniques with receiving performance

The navigation signal structure is one of the primary technologies of the satellite navigation system and also a symbol of the BeiDou global navigation satellite system (BDS-3). In this study, the design requirement and challenges of the BDS-3 B1 band signals are first analyzed. After that, the principle and development of an innovative modulation technique, namely Quadrature Multiplexed Binary Offset Carrier (QMBOC) modulation technique, and a generalized multi-frequency multi-component navigation signal constant envelope multiplexing technique, i.e., Constant Envelope Multiplexing via Intermodulation Construction (CEMIC), are introduced in detail. Also, the advanced performance of the new-generation B1 signal is verified through the reception and analysis of the signal transmitted by the BDS-3 satellites. The results from the performance analysis of the signal show that the QMBOC modulation can satisfy the requirements needed for the performance improvement of the next-generation navigation signal, diversified reception modes, as well as the compatibility and interoperability with other navigation systems. Also, the results reveal that the CEMIC multiplexing technique can solve the B1 multiplexing issue caused by the coexistence of new and legacy signals, as well as open and authorized signals. The QMBOC modulation and CEMIC multiplexing technique form the core of the BDS B1 signal scheme and, to a great extent, determine the time-frequency domain characteristics, reception performance, and the transmission efficiency of the signals, which embodies both the innovation of these techniques and their value in engineering application. Presently, these techniques have been applied to all BDS-3 satellites and provide services to the world, which becomes a major hallmark of BDS-3 surpassing the advanced level of the world.

Expressions for the Autocorrelation Function and Power Spectral Density of BOC Modulation Based on Convolution Operation

We present universal expressions for the autocorrelation functions (ACFs) of the Binary Offset Carrier (BOC), Multiplexed BOC (MBOC), and Alternative BOC (AltBOC) modulations based on convolution operations. We also derive the expressions for the power spectrum densities (PSDs) of these modulations using the Fourier transform of their ACFs. The results obtained in this contribution are useful for Global Navigation Satellite System (GNSS) signal simulation, performance evaluation, and high-performance acquisition and tracking algorithm design. The derivation methods of the expressions for the ACFs are common and can be used to derive expressions for the ACFs of other BOC-based modulations.

Design and implementation of a real‐time software receiver for BDS‐3 signals

The BeiDou Navigation Satellite System (BDS) is currently building its third phase (BDS-3), which will provide services to users around the world. In addition to backward compatibility with BDS-2, BDS-3 satellites are equipped with the B1C and B2 interoperable signals for compatibility with GPS and Galileo systems. To evaluate performance and optimize processing methods, we designed and implemented a real-time software receiver with the ability to process all BDS-3 signals in parallel. A complete description of all signal processing aspects is given. To reduce the reliance on high-performance hardware while maintaining the independent analysis capabilities of acquisition performance in real-time software receivers, a B1I-aided acquisition method for reducing the search space of other signals from the same satellite is applied. An unambiguous tracking method is proposed to solve the ambiguity problem of the Quadrature Multiplexed Binary Offset Carrier (QMBOC) signal that can be used for matching reception of the pilot component of the B1C signal.

Code phase discrimination function shaping method for Compass B1C QMBOC (6,1,4/33) signal

SummaryThe discrimination function shaping method has been proposed to improve the anti‐multipath performance for a global navigation satellite system receiver. However, the existing methods fail to fully exploit the potential anti‐multipath performance of multiplexed binary offset carrier (MBOC)–modulated signals. In this paper, a code phase discrimination function shaping method is proposed for a Compass B1C quadrature MBOC‐modulated signal. The in‐phase binary offset carrier (BOC) (1,1) signal and quadrature‐phase BOC (6,1) signal replicas are designed according to the least squares estimation. Then a shifted cross‐correlation function (CCF) between the in‐phase BOC (1,1) signal and its pseudorandom noise code is multiplied with the obtained CCFs to ensure an unambiguous tracking. Finally, a discrimination function with a small pull‐in range can be obtained by a weighed combination of the in‐phase and quadrature‐phase CCFs. A computer simulation is conducted to assess the performances under multipath and thermal noise conditions.

A Theoretical Survey of the Spreading Modulation of the New GPS Signals (L1C, L2C, and L5)

In this paper a survey of the spreading modulation of the new GPS signals (L1C, L2C, and L5) is considered. The new signals seem to offer several improvements which range from higher power, better code selection, and improved modulation schemes which offer receiver designers the opportunity to obtain unmatched performance in many ways such as in the case of a maximum likelihood GPS receiver. For example the Multiplexed Binary Offset Carrier (MBOC) spreading modulation has been recommended by the GPS-GALILEO Working Group on interoperability and compatibility because the MBOC(6,1,1/11) power spectral density is a mixture of BOC(1,1) spectrum and BOC(6,1) spectrum, that would be used by GALILEO for its Open Service (OS) signal at L1 frequency, and also by GPS for its modernized L1 Civil (L1C) signal. It is suggested that a number of different time waveforms can produce the MBOC(6,1,1/11) spectrum, allowing flexibility in implementation and maintaining interoperable waveforms for GALILEO and GPS. On the other hand, the timemultiplexed BOC (TMBOC) implementation interlaces BOC(6,1) and BOC(1,1) spreading symbols in a regular pattern, whereas composite BOC (CBOC) uses multilevel spreading symbols formed from the weighted sum of BOC(1,1) and BOC(6,1) spreading symbols, interplexed to form a constant modulus composite signal. New L1C provides a number of advanced features, which includes 75% of the power in a pilot component for enhanced signal tracking, advanced Weil-based spreading codes, an overlay code on the pilot that provides data message synchronization, support for improved reading of clock and ephemeris by combining message symbols across messages, advanced forward error control coding, and data symbol interleaving to combat fading. The resulting design offers receiver designers the opportunity to obtain a greatly improved performance in many ways. In this paper we perform a theoretical survey of the new signals and suggest a new code spreading modulation scheme which could provide even further improvements to the new GPS III signals.

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.

Unambiguous Sine-phased BOC(kn,n) Signal Acquisition Based on Combined Correlation Functions

Galileo and GPS have been developing their new signals in recent years. Multiplexed Binary Offset Carrier (MBOC) is the final implementation of Galileo E1 and GPS L1C, which is the multiplexing of BOC(1,1) and BOC(6,1). Therefore, it is helpful to satisfy the demand that the new signals must be compatible with GPS BPSK signal. BOC(kn,n) modulation will provide better track performance and higher positioning accuracy. However, the main drawback of the BOC modulated signal is that its autocorrelation has multiple side peaks around the main peak. This paper will focus on a family of signals: sine-phased BOC(kn,n). We are trying to explore a new method to cancel the side peaks of BOC(kn,n) autocorrelation, making use of two kinds of correlation functions. One is the correlation of the incoming signal and the sine-phased BOC(kn,n) modulated spreading code(PRN code multiplied by subcarrier), and the other is the correlation of the incoming signal and the PRN code only. Two kinds of correlation function are separated into several sub-correlations. Sub-correlations have less side peaks which are in different code delays. Corresponding parts of two sub-correlations will be combined to cancel the side peaks separately, and finally the new function without side peaks will be acquired after several correlations added together. Simulation results will be given. It is shown that the proposed method is contributed to the side peaks cancellation for unambiguous sine-phased BOC (kn, n) signal acquisition.

Ambiguity Mitigating Technique for Multiplexed Binary Carrier Signal Tracking

In this letter, a new unambiguous technique based on the pseudo correlation function (PCF) is proposed for multiplexed binary offset carrier (MBOC) signal, which will be utilized in European Galileo system and Chinese BeiDou II system. The proposed technique firstly designs two local auxiliary signals based on the shape of the received MBOC signal. The synthesized correlation function is obtained by subtracting the squared cross-correlation function between the received MBOC signal and the local auxiliary signal from the squared cross-correlation function between the received MBOC signal and another local auxiliary signal. The simulation results demonstrate that the proposed technique can remove the ambiguity completely with slightly degradation in tracking accuracy.

Codes cross-correlation analysis and data/pilot code pairs optimization for Galileo E1 OS and GPS L1C

The Galileo E1 open service (OS) and the global positioning system (GPS) L1C are intending to use the multiplexed binary offset carrier (MBOC) modulation in E1/L1 band, including both pilot and data components. The impact of data and pilot codes cross-correlation on the distortion of the discriminator function (i.e., the S-curve) is investigated, when only the pilot (or data) components of MBOC signals are tracked. It is shown that the modulation schemes and the receiver configuration (e.g., the correlator spacing) strongly affect the S-curve bias. In this paper, two methods are proposed to optimize the data/pilot code pairs of Galileo E1 OS and GPS L1C. The optimization goal is to obtain the minimum average S-curve bias when tracking only the pilot components a the specific correlator spacing. Figures of merit, such as S-curve bias, correlation loss and code tracking variance have been adopted for analyzing and comparing the un-optimized and optimized code pairs. Simulation results show that the optimized data/pilot code pairs could significantly mitigate the intra-channel codes cross-correlation, and then improve the code tracking performance of MBOC signals.

Unbalanced AltBOC: a Compass B1 candidate with generalized MPOCET technique

With the proposed new GNSS signals, enhanced navigation performance is expected in both civil and military applications. However, these new signals introduce the difficulty of combining multiple signal components into a constant-envelope signal. For the Compass B1 band, the problem is to multiplex a QPSK(2) signal and a new multiplexed binary offset carrier (MBOC) signal with a center frequency difference of 14.322 MHz. One approach for multiplexing spreading codes is the phase-optimized constant-envelope transmission (POCET) method proposed for the GPS L1 band. However, only binary spreading codes are considered in POCET. We first generalize the POCET method as a multilevel POCET (MPOCET) algorithm for multilevel coded signals. A new implementation of the alternative binary offset carrier (AltBOC) generator is derived from MPOCET. Secondly, the multiplexing problem for Compass is modeled by MPOCET. Multilevel subcarriers of AltBOC are adopted in the model. As a result, an 8-PSK unbalanced AltBOC (UAltBOC) modulation, which has a QPSK(2) signal at the lower sideband and a TMBOC signal at the upper sideband, is obtained. Simulations for signal model validation and power spectrum analysis are conducted. Numerical results indicate that UAltBOC successfully combines the QPSK and TMBOC signals with only 0.16-dB additional combining loss compared to AltBOC. The proposed MPOCET technique is demonstrated as a unified multiplexing method for navigation signals.

Weighted discriminators for GNSS BOC signal tracking

Modern Global Navigation Satellite System including Galileo and GPS III will employ multiplexed binary offset carrier (MBOC) modulation to achieve spectrum separation and enhanced tracking performance. A challenge of the MBOC or BOC signal tracking is the presence of ambiguities due to multiple sidepeaks of the autocorrelation functions. Several different techniques including multi-correlator and double estimator schemes have been proposed to address the ambiguity issue. We propose a class of ambiguity-free code tracking techniques by exploiting the unique features of the BOC modulation. In the proposed architecture, the incoming BOC-modulated signals are correlated with BOC-modulated replica and the spreading codes, respectively. Through a multiplicative combination strategy of the two correlator outputs, a noncoherent weighted discriminator is formed and shown to possess the ambiguity-free property. The multipath effect is assessed and compared with existing early-minus-late power and autocorrelation sidepeak cancellation technique discriminators. The noise effects of the theory and simulation are also discussed. In order to further verify the proposed scheme, a set of field data of a Galileo in-orbit validation satellite is collected and processed. It is demonstrated that the proposed method is simple to implement, free from ambiguities, and yields acceptable performance in the presence of multipath and noise.

Method for Assessing the Interference Impact on GNSS Receivers

The definition of new families of curves named interference error envelope (IEE) and interference running average (IRA) is presented. Such tools are able to assess the impact of RF interference on different GNSS receivers, taking into account the features of the in-band interference source. In fact the actual impact on the final performance is strictly related to the specific receiver architectures. Continuous wave (CW) and wide band (WB) interference signals are considered in order to assess by means of IEE and IRA the robustness of new modulations based on the multiplexed binary offset carrier (MBOC) scheme for several receiver configurations, by varying the discriminator spacing, type, and the front-end filter bandwidth. Interference robustness is evaluated and compared with those of the well-known binary phase shift keying (BPSK) and binary offset carrier BOC(1,1) modulations. Simulation and theoretical results are validated by means of laboratory tests, proving the reliability of IEE curves for interference impact assessment.

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.

MBOC and BOC(1,1) Performance Comparison

In recent months the US and the EU have agreed to change the modulation scheme for the new civil GPS and Galileo signals in the L1 band from Binary Offset Carrier (1,1) (BOC(1,1)) to a scheme having the so-called Multiplexed Binary Offset Carrier (MBOC) spectrum, although each system will implement this differently. This paper compares the performance of the new system in a number of areas against the original baseline. It is shown that the MBOC signal offers significant advantages in multipath and tracking performance, while retaining compatibility with BOC(1,1) receivers at the cost of a small correlation loss.

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).

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 of the Proposed Galileo CBOC Modulation in Heavy Multipath Environment

In the framework of the modernization plans of Global Navigation Satellite Systems (GNSS) a new Multiplexed Binary Offset Carrier (MBOC) modulation has been proposed as a possible Signal-In-Space (SIS) with improved performance with respect to the robustness against external sources of degradation. Discussion around such signal format are still on-going at the time of writing, anyway it is the most probable candidate signal that will be adopted by both GPS L1C and the Galileo E1 Open Service (OS) signals [( http://ec.europa.eu/dgs/energy_transport/galileo/documents/doc/2004_06_21_summit_2004_en.pdf , 2004)] as modernization of the present BOC(1,1). In the context of the integration between wireless communication and satellite navigation, one of the major problems is that usually the GNSS receiver has to work in a critical environment characterized by a heavy presence of multipath or interference sources. Some examples are urban canyons or light indoor spaces. These are also typical situations for the usage of personal communications systems. The new MBOC modulation have been studied with the specific goal to create a signal more robust with respect to multipath, bringing the high performance of Galileo in situations in which the present BOC(1,1) shows limitations. In this sense, future Location Based Services (LBS) provided on the basis of the GNSS OS will benefits from this intrinsic robustness of the signal. Throughout the paper a review of the MBOC structure will be presented, specifying that in the Galileo framework such a structure has been proposed in a version named Composite BOC (CBOC). In particular, the paper presents the simulation of the CBOC behavior in presence of multipath showing the extreme improvement with respect to other BOC solutions.