Binary Offset Carrier Modulation Research Articles

Meta-Signal Processing with Data/Pilot Combining for Beidou B2 Signals

Beidou Navigation Satellite System (BDS) third generation satellites currently broadcast Open Service (OS) signals into two closely spaced Radio Frequencies (RFs) in the B2 band. These are the B2a and B2b signal components, which form the current implementation of the Asymmetric Constant-Envelope Binary Offset Carrier (ACE-BOC) modulation. The B2a signal features both a data and a pilot channel, whereas the B2b component is data only with data symbols of 1 ms duration. The absence of a pilot channel and the fast data rate make the processing of the B2b component challenging. Tracking performance can, however, be improved by jointly processing the B2a and B2b components. In this respect, meta-signal approaches are investigated for jointly processing the B2a and B2b signals. Two meta-signal tracking architectures are proposed: the first considers the pilot channel of the B2a component and the data channel of the B2b signal. The second exploits all the power available and also implements data/pilot combining on the B2a channel. Both architectures allow the extension of the integration time beyond the data symbol duration using non-coherent approaches. Theoretical results are supported by simulations and real data analysis performed using a custom Software Defined Radio (SDR) receiver. Simulation and experimental results clearly show the benefits of the meta-signal approach, which can be effectively adopted for the processing of asymmetric modulations such as the current implementation of the ACE-BOC, which lacks a pilot channel on the B2b component.

GLONASS-K2 signal analysis

K2 is a new generation of GLONASS satellites that provides code division multiple access (CDMA) signals in the L1, L2 and L3 frequency bands in addition to legacy L1 and L2 signals based on frequency division multiple access (FDMA) modulation. The first GLONASS-K2 satellite was launched in August 2023 and started signal transmission in early September 2023. Based on measurements with a 30-m high-gain antenna, spectral characteristics of the various signal components are described and relative power levels are identified. A 3 dB (L1) to 4 dB (L2) higher total power is determined for the CDMA signal compared to the legacy FDMA signal and an equal power of the open service and secured CDMA signal components is found. The ranging code of the L2 channel for service information, which has not been publicly disclosed so far, is identified as a Gold code sequence consistent with the data channel of the L1 open service CDMA signal. The high-gain antenna measurements are complemented by tracking data from terrestrial receivers that enable a first assessment of user performance. An up to 50% improvement in terms of noise and multipath performance is demonstrated for the new L1 and L2 CDMA signals in comparison with their legacy counterpart, but no obvious differences between the different binary phase-shift keying and binary offset carrier modulations of the data and pilot components of these signals could be identified for the test stations. Triple-frequency carrier phase observations from L1, L2, and L3 CDMA signals exhibit good consistency at the noise and multipath level, except for small variations that can be attributed to slightly different antenna phase patterns on the individual frequencies. Overall, the new CDMA signals are expected to notably improve and facilitate precise point positioning applications once fully deployed across the GLONASS constellation.

Synthesized Binary Offset Carrier Modulation for Interoperable GNSS L1 Band Signals

Synthesized Binary Offset Carrier Modulation for Interoperable GNSS L1 Band Signals

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.

Enhanced Synchronization Algorithms for BOC Signals Based on Reconstructed Sub-Correlation Functions

Aiming at the ambiguous synchronization of binary offset carrier (BOC) and composite binary offset carrier (CBOC) modulation signals due to secondary peaks for Global Navigation Satellite System (GNSS), a reconstructed sub-correlation function synchronization algorithm (RSSA) for BOC and CBOC is proposed. The general autocorrelation subfunctions of BOC and CBOC are obtained by deriving the subfunctions of the cross-correlation function between BOC signals with different modulation orders. According to the characteristics of the subfunctions, the corresponding reconstruction rules are set to obtain the unambiguous correlation functions. To further reduce the complexity of the local auxiliary signal, a local auxiliary signal optimization algorithm (LASOA) is proposed based on RSSA, which only needs to generate a local two-level signal compared to the conventional CBOC local four-level signal. The simulations show that the two algorithms proposed in this paper reduce the amplitude of the side peaks of the normalized correlation peaks of BOC by at least 0.09 compared with the autocorrelation side-peak cancellation technique (ASPeCT), maintain a high detection probability, and the multipath error is smaller than that of the autocorrelation side-peak cancellation technique (ASPeCT) and other traditional algorithms. The phase discrimination curves show that the linear region slope gains of the two algorithms in this paper are above 2 dB compared with the ASPeCT and other conventional algorithms.

Stepped-Frequency Binary Offset Carrier Modulation for Global Navigation Satellite Systems

In this paper, we propose Stepped-Frequency Binary Offset Carrier (SFBOC) modulation for Global Navigation Satellite Systems (GNSS) that use spread spectrum signals. SFBOC modulation generates a Binary Offset Carrier (BOC) signal of which the subcarrier frequency varies stepwise within each period of the pseudorandom-noise (PRN) code. The generated SFBOC signal can have a sharp autocorrelation function (ACF) output and an almost flat spectrum over a wide frequency band. These characteristics result in correlation properties, multipath mitigation, and anti-interference that are superior to those of conventional GNSS modulations. To testify, we compare the performance of SFBOC in various aspects to conventional GNSS modulations and other time-varying subcarrier frequency (TVSF) modulations. From numerical simulations, we show that the proposed SFBOC has higher ranging accuracy, lower tracking ambiguity, and more robustness to noise, interference, and multipath than the conventional GNSS modulations. In addition, we demonstrate that the proposed SFBOC moulation has two advantages while other modulations with TVSF cannot have both; that SFBOC is robust to code-Doppler and that, when filterbank is employed, SFBOC improves the signal-to-noise ratio (SNR) significantly without any loss of weak early arrival path in the Non-line of sight (NLOS) multipath environments.

A Novel Unambiguous Acquisition Algorithm Based on Segmentation Reconstruction for BOC(n,n) Signal

In order to improve the frequency band utilization and avoid mutual interference between signals, the BD3 satellite signals adopt Binary Offset Carrier (BOC) modulation. On one hand, BOC modulation has a narrow main peak width and strong anti-interference ability; on the other hand, the phenomenon of false acquisition locking caused by the multi-peak characteristic of BOC modulation itself needs to be resolved. In this context, this paper proposes a new BOC(n,n) unambiguous acquisition algorithm based on segmentation reconstruction. The algorithm is based on splitting the local BOC signal into four parts in each subcarrier period. The branch signal and the received signal are correlated with the received signal to generate four branch correlation signals. After a series of combined reconstructions, the final signal detection function completely eliminates secondary peaks. A simulation shows that the algorithm can completely eliminate the sub-peak interference for the BOC signals modulated by subcarriers with different phase. The characteristics of narrow correlation peak are retained. Experiments show that the proposed algorithm has superior performance in detection probability and peak-to-average ratio.

Integrated Communication and Measurement System with BOC-Assisted OFDM

For unmanned aerial vehicles (UAVs), high-precision measurement and high-speed communication are necessary to realize flight and operational missions. In this paper, we propose an integrated communication and measurement system in a Doppler frequency offset environment. The system combines orthogonal frequency division multiplexing (OFDM) modulation with binary offset carrier (BOC) modulation to formulate an OFDM+BOC composite signal through power control. High-precision measurement is achieved through BOC modulation, and high data transmission is achieved through OFDM modulation. Furthermore, the high-precision Doppler frequency offset tracked by the BOC signal is adopted to assist in the demodulation of the OFDM signal. This substantially decreases the impact of the Doppler frequency offset on the OFDM signal. Moreover, the ranging error is within 10−2, and the maximum Doppler frequency error is within 2 Hz.

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.

차세대 GNSS를 위한 GIG 부호 기반 시간다중 이진부호심볼 변조기법

In this paper, we propose a time multiplexed binary coded symbol (TMBCS) modulation scheme based on Gray and inverse Gray (GIG) codes for the next generation global navigation satellite system (GNSS). A representative binary coded symbol (BCS) is a binary offset carrier (BOC). Compared to the existing binary phase shift keying (BPSK) modulation, which is a representative GNSS modulation scheme, BOC modulation has a high degree of freedom in terms of frequency band shape design and is less affected by multipaths because the correlation function is sharper at the correct code phase. However, since several sub-peaks occur in the correlation function of the BOC-modulated pseudo-noise signal, false locks can easily occur during code tracking. This disadvantage is called the ambiguity of the BOC modulated signal. Time multiplexed binary Walsh spreading (TMBWS) modulation, which is a TMBCS scheme that uses a Walsh code, is one method for reducing ambiguity and is a perfectly orthogonal code with a very good correlation among BCSs. However, Walsh codes can only be generated with a power of two length. In this paper, we propose a novel TMBCS modulation scheme using quasi-orthogonal GIG codes that can be generated with lengths that are multiples of 2. The proposed scheme maintains the same bandwidth and spectral separation coefficient compared to TMBWS when a symbol of length 8 is used. In addition, the proposed scheme has a higher degree of freedom in terms of band shape design compared to TMBWS modulation, because the length can be designed in multiples of 2 (such as 6, 10, or 12) and has high multipath immunity with unambiguity.

Dual-Sideband Constant-Envelope Frequency-Hopping Binary Offset Carrier Multiplexing Modulation for Satellite Navigation

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.

Assessing Availability of GNSS-GBAS Landing Systems in GAST-D/F Performance

The Ground-Based Augmentation System (GBAS) has been recently approved as CAT II performance (GBAS Approach Type D (GAST-D)) for the precision approach operations, and by using the GPS signals only. But the requirements of CAT III performance (GAST-F) are tended to be approved using dual Constellation by adding the European Galileo system. In this research, the availability of CAT III was assessed using Galileo system. A simulation tool was used to estimate which level of integrity and accuracy is needed for CAT II and CAT III performances, considering the new innovated Binary Offset Carrier (BOC) modulation and the increased power of +6 dB in Galileo signals. The results showed a promising performance of Galileo over Europe space.

Multifunctional Signal Design for Measurement, Navigation and Communication Based on BOC and BPSK Modulation

In a multi-node spacecraft or unmanned aerial vehicle (UAV) group, a multifunctional signal containing measurement, navigation, and communication functions is required to simplify the receiver structure, and to increase spectrum utilization. The paper proposes a multifunctional signal based on a binary offset carrier (BOC) and binary phase shift keying (BPSK) modulation. The signals which carry different functions are orthogonal in the frequency domain, which causes the data transmission signal to not be affected by BOC signal. In addition, in the high carrier to noise ratio (C/N0), the spreading gain of the BOC signal ensures that the communication signal has a slight influence on navigation signals. Moreover, the multifunctional signal can achieve communication and measurement functions at the same frequency point and fast switching in multinodes. These advantages can simplify the receiver design and improve the frequency band utilization. Finally, in this study we completed the design and verification of the hardware system.

Galileo E5 AltBOC Signals: Application for Single-Frequency Total Electron Content Estimations

Global navigation satellite system signals are known to be an efficient tool to monitor the Earth ionosphere. We suggest Galileo E5 AltBOC phase and pseudorange observables—a single-frequency combination—to estimate the ionospheric total electron content (TEC). We performed a one-month campaign in September 2020 to compare the noise level for different TEC estimations based on single-frequency and dual-frequency data. Unlike GPS, GLONASS, or Galileo E5a and E5b single-frequency TEC estimations (involving signals with binary and quadrature phase-shift keying, such as BPSK and QPSK, or binary offset carrier (BOC) modulation), an extra wideband Galileo E5 AltBOC signal provided the smallest noise level, comparable to that of dual-frequency GPS. For elevation higher than 60 degrees, the 100 s root-mean-square (RMS) of TEC, an estimated TEC noise proxy, was as follows for different signals: ~0.05 TECU for Galileo E5 AltBOC, 0.09 TECU for GPS L5, ~0.1TECU for Galileo E5a/E5b BPSK, and 0.85 TECU for Galileo E1 CBOC. Dual-frequency phase combinations provided RMS values of 0.03 TECU for Galileo E1/E5, 0.03 and 0.07 TECU for GPS L1/L2 and L1/L5. At low elevations, E5 AltBOC provided at least twice less single-frequency TEC noise as compared with data obtained from E5a or E5b. The short dataset of our study could limit the obtained estimates; however, we expect that the AltBOC single-frequency TEC will still surpass the BPSK analogue in noise parameters when the solar cycle evolves and geomagnetic activity increases. Therefore, AltBOC signals could advance geoscience.

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.

An Unambiguous Synchronization Scheme for GNSS BOC Signals Based on Reconstructed Correlation Function.

Binary offset carrier (BOC) modulation is a new modulation method that has been gradually applied to the Global Satellite Navigation System (GNSS) in recent years. However, due to the multi-peaks in its auto-correlation function (ACF), it will incur a false lock and generate synchronization ambiguous potentially. In this paper, an unambiguous synchronization method based on a reconstructed correlation function is proposed to solve the ambiguity problem. First, through the shape code vector constructed in this paper, the general cross-correlation function (CCF) expression of the BOC modulated signal will be obtained. Based on the features of the signal correlation function, it is decomposed into a matrix form of trigonometric functions. Then, it generates two local signal waves using a specific method, then the proposed method is implemented to obtain a no-side-peak correlation function by reconstructing the cross-correlation between the received signal and the two local signals. Simulations showed that it fully eliminates the side-peak threat and significantly removes the ambiguity during the synchronization of the BOC signals. This paper also gives the improved structure of acquisition and tracking. The detailed theoretical deduction of detection probability and code tracking error is demonstrated, and the corresponding phase discrimination function is given. In terms of de-blurring ability and detection probability performance, the proposed method outperformed other conventional approaches. The tracking performance was superior to the comparison methods and the phase discrimination curve only had a zero-crossing, which successfully removed the false lock points. In addition, in multipath mitigation, it outperformed the ACF of the BOC signal, and performs as well as the autocorrelation side-peak cancellation technique (ASPeCT) for BOC(kn,n) signals.

Generalized Modulation Scheme of GBOC for Global Navigation Satellite System

The Generalized Binary Offset Carrier (GBOC) modulations can offer additional degrees of freedom for shaping the spectrum of navigation signal and provide superior performance in code tracking, multipath and compatibility than traditional Binary Phase Shift Keying (BPSK) and Binary Offset Carrier (BOC) modulations. This paper proposes a generalized modulation scheme for GBOC modulation design. Firstly, the generalized waveform of GBOC modulations is proposed. Then, the proposed construction method of GBOC modulations is presented, and the consistency with traditional GBOC modulations is investigated. Finally, the generalized autocorrelation functions of GBOC modulations are derived based on the inverse Fourier transform method. The results show the new modulation scheme has good consistency with traditional method and can provide the opportunity for flexible satellite payload design.

Optimal Parameter Design of Continuous Phase Modulation for Future GNSS Signals

Continuous phase modulation (CPM) is a power and spectrum efficient modulation that intrinsically possesses constant envelope, phase continuity as well as less out of band (OOB) radiation, especially appropriate for stringently bandwidth-constrained systems employing non-linear power amplifiers. Such advantages render CPM as a promising modulation candidate with application to satellite navigation. CPM comprising of a few parameters has large amounts of modulation subclasses. This paper is devoted to optimal parameter design of CPM for future GNSS signals. Parameter design approaches endowing CPM with similar spectrum profiles as legacy binary offset carrier (BOC) and binary phase shift keying (BPSK) modulations are also proposed. Several optimal subclasses of CPM family are suggested as unimodal or bimodal GNSS signal solutions. The simulation results indicate that the designed CPM signals behave same or similar main lobes with BPSK and BOC signals, and proposed optimal subclasses of CPM family with high spectral efficiency are comparable or superior than legacy modulations, typical GMSK, and filtered multitone (FMT) signal using the squared root raised-cosine (SRRC) basic pulse in terms of tracking accuracy, multipath mitigation and compatibility. In addition, some constructive comments on CPM design are presented, which provides a reference for CPM applications in GNSS.

BOCC: A new modulation based on chirp subcarriers for future BeiDou LEO navigation‐augmented signal

For improving the anti-interference performance and compatibility of a navigation-augmented signal in future BeiDou Global Navigation Satellite Systems, a new modulation based on chirp subcarriers is proposed, named binary offset chirp carrier modulation, which is formed by multiplying a periodic binary chirp subcarrier with a spreading code signal. And it can make use of the time-varying frequency for shaping the spectrum and have superior performance in anti-interference, similar advantage in tracking accuracy, anti-multipath capability and compatibility compared with binary offset carrier modulations. The binary offset chirp carrier modulations proposed in this paper provide a potential signal design for the future low earth orbit (LEO) navigation-augmented Global Navigation Satellite Systems.

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.