Search Results (25)

Space-based gravitational wave detection relies on laser interferometry to measure picometer-level displacements over ${10}^5$–${10}^6$ km baselines. To integrate ranging and communication within the same optical link without degrading the primary scientific measurement, a low modulation index of 0.1 rad is required, resulting in extremely weak signals and challenging acquisition conditions. This study developed mathematical models for signal acquisition, identifying and analyzing key performance-limiting factors for both Binary Phase Shift Keying (BPSK) and Binary Offset Carrier (BOC) schemes. These factors include spreading factor, acquisition step, modulation index, and carrier-to-noise ratio (CNR). Particularly, the acquisition threshold can be directly calculated from these parameters and applied to the acquisition process of communication and ranging signals. Numerical simulations and evaluations, conducted with TianQin mission parameters, demonstrate that, for a data rate of 62.5 kbps and modulation indices of 0.081 rad (BPSK) or 0.036 rad (BOC), respectively, acquisition (probability ≈ 1) is achieved when the CNR is ≥104 dB·Hz under a false alarm rate of ${10}^{-6}$. These results provide critical theoretical support and practical guidance for optimizing the inter-satellite communication and ranging system design for the space-based gravitational wave detection missions. Full article

The rapid development of Low Earth Orbit (LEO) satellite navigation systems requires modulation schemes with strong anti-jamming capabilities, high spectral efficiency, and the ability to achieve precise tracking in high-dynamic environments. Traditional Binary Offset Carrier (BOC) modulation suffers from multi-peak ambiguity, leading to false lock issues. To address this, FH-BOC modulation, which integrates BOC modulationand frequency hopping, significantly improves both anti-jamming performance and spectral efficiency. Against this background, this paper proposes a comprehensive high-dynamic tracking algorithm for FH-BOC signals. (1) Based on the adaptive Kalman filter algorithm, high-precision carrier tracking was achieved in high-dynamic environments. (2) By leveraging the correlation between the ranging code and frequency-hopping offset carrier, a composite pseudo-code is generated through the XOR operation, and a corresponding composite code-tracking loop is introduced. (3) Based on code loop tracking results, the frequency-hopping moments of the subcarrier are detected, and a phase-locked loop for the frequency-hopping subcarrier is established. Simulation results indicate that the algorithm achieves centimeter-level pseudorange measurement accuracy for FH-BOC navigation signals under the JPL high-dynamic model. Full article

To enhance the anti-interference capabilities and increase flexibility in frequency allocation between the lower and upper sidebands of the navigation signal, we introduce frequency-hopping binary offset carrier modulation with independent frequency-hopping patterns in lower and upper sidebands (IFH-BOC). This novel modulation is classified as a constant-envelope multiplexing (CEM) method, with independent frequency-hopping patterns for the lower and upper sidebands, in contrast with frequency-hopping binary offset carrier (FH-BOC) and binary offset carrier (BOC) modulations, which share the same patterns. IFH-BOC represents a generalized modulation that incorporates FH-BOC and BOC, thus retaining their advantages while introducing new characteristics, such as independent frequency-hopping pattern design and flexible spectral splitting. The results indicate that IFH-BOC maintains the same time–frequency characteristics and measurement accuracy as FH-BOC when using identical modulation parameters, yet it demonstrates superior anti-interference performance due to its varied frequency-hopping patterns. Furthermore, IFH-BOC provides enhanced flexibility in spectral splitting compared with BOC modulation, potentially allowing for increased availability of L-band frequencies for satellite navigation. With these benefits, IFH-BOC is poised to be a promising modulation for the signal design of next-generation global navigation satellite systems. Full article

As unmanned aerial vehicles (UAVs) are widely used in various fields, there is an increasing demand for UAV anti-jamming, multipath mitigation, and covert secrecy. Frequency-hopping binary offset carrier (FH-BOC) signals possess higher anti-jamming and multipath mitigation capabilities than direct-sequence spread spectrum (DSSS) and binary offset carrier (BOC) signals. A prerequisite for constructing communication links between UAVs using FH-BOC signals is the design of efficient acquisition algorithms to capture the signals successfully. In this paper, the modulation and characteristics of the FH-BOC signal are introduced. The maximum relative velocity between UAVs is 5.5 km/s, the maximum acceleration is 50 g, and the maximum plus acceleration is 20 g/s. In this high dynamic environment, the parameters for the parallel code phase and Partial Matched Filter–Fast Fourier Transform (PMF-FFT) acquisition algorithms targeting FH-BOC(10,1) signals are designed, and the acquisition performance of these algorithms is comparatively analyzed. The acquisition time for the first and second algorithms is 4.3317 s and 6.137 s. The number of real additions required by the first and second algorithms is approximately $10.9\times {10}^9$ and $8.9\times {10}^9$, and the number of real multiplications is approximately $7.6\times {10}^9$ and $6.7\times {10}^9$. This helps in selecting the acquisition algorithm when FH-BOC signals are used to build inter-UAV communication links. Full article

Global Navigation Satellite Systems (GNSS) provide positioning, velocity, and time services for civilian applications. A critical step in the positioning process is the acquisition of visible satellites in the sky. Modern GNSS systems, such as Galileo—developed and maintained by the European Union—utilize a new modulation technique known as Binary Offset Carrier (BOC). However, BOC signals introduce multiple side-peaks in their autocorrelation function, which can lead to significant errors during the acquisition process. In this paper, we propose a novel acquisition method based on higher-order cumulants that effectively eliminates these side-peaks. This method is capable of simultaneously acquiring both conventional ranging signals, such as GPS C/A code, and BOC-modulated signals. The effectiveness of the proposed method is demonstrated through the acquisition of simulated signals, with a comparison to traditional methods. Additionally, we apply the proposed method to real satellite signals to further validate its performance. Our results show that the proposed method successfully suppresses side-peaks, improves acquisition accuracy in weak signal environments, and demonstrates potential for indoor GNSS applications. The study concludes that while the method may increase computational load, its performance in challenging conditions makes it a promising approach for future GNSS receiver designs. Full article

In order to address the ambiguous synchronization problem caused by the multi-peak nature of the autocorrelation function of the modulated signal of the Multiplexed Binary Offset Carrier (MBOC) in the Global Navigation Satellite System (GNSS), a new synchronization algorithm for MBOC signals is presented in this paper, which uses a reconstruction correlation function to effectively handle synchronization ambiguities associated with multi-peak signals. The paper proposes an algorithm for reconstructing the correlation function of the MBOC signal by analyzing its characteristics. The algorithm generates three local auxiliary signals, namely, pseudo-random codes (PRN), BOC(1,1) signals, and MBOC signals, which are correlated with the received signal. By combining the three correlation functions, the algorithm produces a reconstructed correlation function based on reconstruction rules, eliminating side peaks and achieving unambiguous synchronization. Simulation results show that the proposed algorithm in this paper eliminates all side peaks while maintaining a high detection probability, and its deblurring capability is optimal compared to other algorithms. In addition, the discriminant curve shows that the algorithm in this paper successfully eliminates all the mis-locked points, and the slope gain is improved by more than 2.5 dB compared with other algorithms, and the anti-multipath performance of the algorithm in this paper is better than that of other traditional algorithms, such as ASPeCT (Autocorrelation Side-Peak Cancellation Technique). Full article

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. Full article

Increased global dependence on Global Navigation Satellite Systems (GNSSs) has resulted in a high demand for greater precision and reliable measurements from GNSS receivers. The multipath problem is the single largest source of errors in modernised GNSSs. Double differencing techniques, such as Code Minus Carrier (CMC) have been shown to accurately detect and measure multipath, allowing for corrections to be made via Ground Base Augmentation Systems (GBAS), for example. However, these techniques require at least two receivers and the protection provided is not extended to stand-alone receivers. This paper introduces a new single differencing technique for the accurate detection of multipath in standalone GNSS receivers receiving modernised Binary Offset Carrier (BOC)-modulated signals. Similarities to CMC are drawn before the novel measurement, Code minus Subcarrier, (CMS) is characterised statistically and a threshold for multipath detection is determined. The effectiveness and sensitivity of this novel measurement as a multipath detection technique are analysed through simulation and multipath error envelope analysis. It will be shown that multipath echos capable of inducing a psuedorange error larger than the threshold are detectable at any amplitude. The method is finally verified using simulated fixed offset multipath, confirming that when code and subcarrier early–late spacings are optimal, all ranges of multipath delays, even as small as 21 meters, are detectable. This novel method of multipath detection requires no additional complex correlators than already exist in the chosen tracking algorithm, thus, providing excellent detection with minimum complexity added to the receiver structure. Full article

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. Full article

Space-Air-GroundIntegrated Network (SAGIN) has been becoming a promising future network construction to enable the integration of terrestrial communications, aerial networks and satellite systems, for achieving high data rate wireless access and seamless coverage. Focusing on the space-to-air propagation, which is requiring transmitted signal of large Doppler shift resilience in dynamic circumstances, the proposed signal as employing I/Q modulation to accommodate frequency-hopping binary offset carrier (FH-BOC) signal and orthogonal frequency division multiplexing (OFDM) signal, and to exploit respective benefits. Finally, numeric results are provided to demonstrate performance superiority on Bit Error Rate (BER) and signal tracking stability. In conclusion, our designed signal requires about 8 dB less energy per bit at the desired BER level than normally compensated OFDM signal. Full article

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. Full article

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. Full article

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. Full article

Recently, the Korean government has announced a plan to develop a satellite-based navigation system called the Korean Positioning System (KPS). When designing a new Radio Navigation Satellite Service (RNSS) signal, the use of the S-band has emerged as an alternative to avoiding signal congestion in the L-bands, and South Korea is considering using the S-band with the L-bands. Therefore, this study proposed possible S-band signal candidates and evaluated their performance, such as the radio frequency (RF) compatibility, spectral efficiency, ranging performance, and receiver complexity. Several figures-of-merit (FoMs) were introduced for quantitative performance evaluation for each candidate. Each FoM was calculated using an analytical equation by considering the signal design parameters, such as the center frequency, modulation scheme, and chip rate. The results showed that the outstanding candidate signal was different depending on the signal performance of interest and the reception environments. Therefore, we discuss and summarize the signal performance analysis results considering the whole FoMs together. Under the assumptions given in this paper, the binary phase shift keying (BPSK)(1), sine-phased binary offset carrier (BOC_s)(5,2), and BPSK signals were superior for the spectral efficiency, ranging performance, and receiver complexity, respectively. Full article

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. Full article