Adaptive carrier-tracking algorithm for Global Navigation Satellite System signals in high dynamic scenarios

While Global Navigation Satellite Systems (GNSS) have been the primary Positioning, Navigation, and Timing (PNT) solution since their advent, new technologies are being sought to address the limitations of GNSS. For the past few years, the strongest contender to offer global PNT solutions has been the use of Low Earth Orbit (LEO) satellites, not only to overcome the GNSS limitations but also to improve the positioning accuracy and coverage given the proliferation of new, more-demanding applications. The present work aims at shedding light on the LEO theoretically achievable positioning accuracy and interference robustness with respect to GNSS, depending on the choice of the carrier frequency, constellation design, hybridization with GNSS, and available satellite transmission power. The analysis uses a semi-analytical approach with 192,000 Monte Carlo runs, employing an in-house satellite constellation simulator to model 400 users across Europe operating in five representative outdoor scenarios, and for 480 different instances of satellite positions in time. This semi-analytical study provides the necessary insights to derive clear design takeaways depending on the choice of the aforementioned parameters. A moderate Effective Isotropic Radiated Power (EIRP) of 50 dBm is shown to be sufficient for achieving high accuracy outdoors, operating at the C-band in the urban scenarios where GNSS typically struggles. The most cost-effective hybrid LEO plus GNSS solutions come from the combination of 1) ‘CentiSpace-like’ plus BeiDou, and 2) ‘Çelikbilek 1’ plus GPS and Galileo, where LEO satellites drive performance in difficult environments while GNSS provides stability in nominal conditions. The findings suggest using the ‘Çelikbilek 1’ constellation with a 50 dBm EIRP at a 5 GHz carrier frequency or higher as the most effective system design.

Genetic fuzzy system for damage detection in beams and helicopter rotor blades

This paper includes the design and implementation of a fuzzy logic controller for level control system to overcome the limitations of the conventional controllers. Mostly preferred controller is a Proportional Integral Derivative (PID) controller which has fixed control parameters. Selection of wrong parameters in a PID design results into uncontrollable process. But fuzzy logic controller is a rule based. These rules are designed on the basis of heuristic information provided by an operator. Process model is identified and used for the design of Proportional Integral (PI) and fuzzy controllers by using MATLAB. To evaluate the performance of both the controllers, it is tested on a real time system with the help of Real Time Workspace (RTW) module of a MATLAB. From real time results it is understood that, fuzzy controller provides more stable and improved output for level control. Even fuzzy controller has ability to remove overshoot which is present in PI controller. Also it requires less settling time than PI controller. Hence fuzzy control system is more relevant control strategy to control the level.

Global Navigation Satellite System (GNSS) based positioning, navigation, and time synchronization services have a profound influence on human society. However, the fundamental system is vulnerable due to the low power and the public structure of GNSS signals. The traditional menace for GNSS is jamming which disables the positioning function of receivers. Unlike jamming, spoofing attacks could deviate a victim receiver’s reported position away from the authentic one. It is more precarious since the victim is unware of this threat. To detect such spoofing, a consistency check approach of measured and calculated carrier Dopplers is proposed. The measured Dopplers are extracted from carrier tracking loops; the calculated Dopplers are formulated by motion information of the receiver and satellites. The feasibility of the proposed method lies in the fact that the calculated Dopplers would be abnormal compared with the measured Dopplers when a position fix is spoofed away from the authentic one. To put the proposed method into practice and illustrate its performance, a generalized likelihood ratio test (GLRT) based statistical detection model is established in this paper. The simulation results demonstrate the theoretical performance. Moreover, the effectiveness of the developed detection method is validated by a replay spoofing test on a GNSS software-defined receiver. Besides, the spoofing detection performance is improved by a smoothing technique.

The paper presents a rule-based fuzzy logic controller to control the output power of a pulse width modulated (PWM) inverter used in a stand-alone wind energy conversion scheme (SAWECS). The self-excited induction generator used in SAWECS has the inherent problem of fluctuations in the magnitude and frequency of its terminal voltage with changes in wind velocity and load. To overcome this drawback the variable magnitude, variable frequency voltage at the generator terminals is rectified and the DC power is transferred to the load through a PWM inverter. The objective is to track and extract maximum power from the wind energy system and transfer this power to the local isolated load, This is achieved by using the fuzzy logic controller which regulates the modulation index of the PWM inverter based on the input signals: the power error; and its rate of change. These input signals are fuzzified, that is defined by a set of linguistic labels characterized by their membership functions predefined for each class. Using a set of 49 rules which relate the fuzzified input signals to the fuzzy controller output, fuzzy set theory and associated fuzzy logic operations, the fuzzy controller's output is obtained. The fuzzy set describing the controller's output (in terms of linguistic labels) is defuzzified to obtain the actual analog (numerical) output signal which is then used to control the PWM inverter and ensure complete utilization of the available wind energy. The proposed rule-based fuzzy logic controller is simulated and the results are experimentally verified on a scaled down laboratory prototype of the SAWECS.

Frequency-agile(FA) radars allow flexible changes in carrier frequency between adjacent pulses, offering significant advantages in anti-jamming performance. However, the discontinuity in echo phase renders the Fast Fourier Transform (FFT) unsuitable, resulting in a high computational burden for coherent integration.To address this challenge, this paper proposes a Frequency-Pulse Repetition Time(PRT) Coupled Agile (FPCA) waveform design scheme, wherein the velocity-induced phase within a coherent processing interval (CPI) is constrained to be an integer multiple of a constant, thereby facilitating subsequent coherent integration. We first derive the analytical relationship between carrier frequency and PRT in FPCA, and then propose two FPCA design approaches: one with a constrained lower PRT bound, and another with both upper and lower PRT bounds.Furthermore, a fast signal processing method tailored for the proposed waveform in multi-target scenarios is developed.After phase cancellation of the echoes, the Velocity Spectrum Profile (VSP) is obtained via FFT, and multiple VSPs are non-coherently accumulated to suppress cross-terms arising from phase compensation, enabling robust estimation of strong target velocities.Velocity compensation and IFFT are then applied to obtain range estimates for strong targets, followed by weak target imaging based on the CLEAN algorithm.Simulation results are provided to validate the effectiveness of the proposed scheme. Compared with existing coherent processing methods for frequency-agile radars, the proposed approach significantly reduces computational complexity, requiring only several to a dozen FFTs to obtain target parameter estimates, thus offering a practical frequency-agile solution for radar platforms with limited computational resources and stringent real-time requirements.

The traditional probe–pass integration system embeds communication information into a radar waveform, which leads to a high level of waveform autocorrelation sidelobes and a poor false symbol rate at low signal-to-noise ratios. This article proposes a three-dimensional indexed modulation-based design method for probe–pass integration waveforms. This method realises communication information modulation and demodulation by simultaneously indexing orthogonal waveform selection, transmitting pulse PRI changes and carrier frequency changes in three dimensions, and applying compressed perception technology to solve the problems of PRI shortcuts and carrier frequency, resulting in a velocity term in the received waveform that cannot be accumulated by phase reference to realise velocity super-resolution. Finally, the radar detection performance and communication performance are simulated and analysed, and the simulation results reveal that the method proposed in this paper can not only satisfy the radar detection performance requirements but also achieve a lower unsigned rate on the basis of an improved communication rate.

It is hypothesized that proportional changes in echo amplitude and carrier frequency might aid obstacle avoidance in cf bats by means of acoustic flow perception. This approach appears to be feasible in principle for single targets, however, obstacle avoidance, unlike prey capture in midair, is invariably prone to constitute a multiple target problem, which has to be addressed in assessing the hypothesis’ validity. In order to map a compound excitation pattern formed by superposition of responses to multiple echoes back into target space by means of an acoustic flow approach, instantaneous (carrier) frequency and amplitude together with their first-order derivatives must be recovered individually for each echo to be perceived as a separate entity. The primal sketch serving as a substrate for this operation is impoverished in that it is only preserving response envelopes. At the same time, the system design might capitalize on knowledge about the transfer functions of the filter bank’s channels as well as at least a rough guess about the echo spectrum. Consequently, it is attempted to explain compound excitation patterns as a sum of superimposed responses to individual echoes, which are known for any given frequency location to a scaling constant.

A fuzzy control improvement method is proposed with an integral line-of-sight (ILOS) guidance principle to meet the needs of autonomous navigation and high-precision control of ship trajectories. Firstly, a three-degree-of-freedom ship motion model was established with the battery-powered container ship ZYHY LVSHUI 01 built by the COSCO Shipping Group. Secondly, a ship path-following controller based on the ILOS algorithm was designed. To satisfy the time-varying demand of the look-ahead distance parameters during the following process, especially under different navigation conditions, fuzzy logic controllers were designed for different navigation conditions to automatically adjust the look-ahead distance parameters. Thirdly, a controller was applied that uses a five-state extended Kalman filter (EKF) to estimate the heading, speed, and heading rate based on the ship’s motion model with the assistance of Global Navigation Satellite System (GNSS) position measurements. This provides the necessary navigational information, reduces the algorithm’s dependence on sensors, and improves its generalizability. Finally, path-following experiments were carried out in the MATLAB experimental platform, and the results were compared with different following algorithms. The simulation results showed that the new algorithm has a better following performance, and it can maintain a smooth rudder angle output. The research results provide a reference for the path-following control of ships.

Measurements of carrier frequency phase differences of global navigation satellite system signals between multiple antennas are used in many coordinate and navigation applications. Global navigation satellite systems signal simulators are used for controlling global navigation satellite systems receiver’s instrumental errors. Therefore, it is necessary to determine the systematic error of the carrier frequency phase of generated signals for signal simulators. For this purpose a new calibration method of global navigation satellite systems simulators was developed. Method is based on refined errors model of generated phase differences of two radio frequency channels of the simulator. The proposed method was implemented using a wideband oscilloscope as an analog-to-digital converter. Approbation of the calibration method was carried out by comparison with the measurement results obtained using the State secondary standard of units of complex transmission coefficients in the range of 0...–60 dB and complex reflection coefficients in the range of 0.002–1 in the frequency range of 0.05–65 GHz (registration No. 2.1.ZZT.0210.2015). The calibration method allows one to determine carrier frequencies phase offsets of navigation signals for global navigation satellite systems simulators with expanded uncertainty (with a coverage factor of 3) of 1°. The proposed method provides the required accuracy of generating phase differences of the carrier frequencies of global navigation satellite systems signals is ensured for modern types of global navigation satellite systems simulators.

The effects of electrical vestibular stimulation upon movement and perception suggest two evoked sensations: head roll and inter-aural linear acceleration. The head roll vector causes walking subjects to turn in a direction dependent on head pitch, requiring generation of torque around a vertical axis. Here the effect of vestibular stimulation upon vertical torque (T(z)) was investigated during quiet stance. With the head tilted forward, square-wave stimuli applied to the mastoid processes evoked a polarity-specific T(z) response accompanied by trunk yaw. Stochastic vestibular stimulation (SVS) was used to investigate the effect of head pitch with greater precision; the SVS–T(z) cross-correlation displayed a modulation pattern consistent with the head roll vector and this was also reflected by changes in coherence at 2–3 Hz. However, a separate response at 7–8 Hz was unaffected by head pitch. Head translation (rather than rotation) had no effect upon this high frequency response either, suggesting it is not caused by a sense of body rotation induced by an inter-aural acceleration vector offset from the body. Instead, high coherence between medio-lateral shear force and T(z) at the same frequency range suggests it is caused by mechanical coupling to evoked medio-lateral sway. Consistent with this explanation, the 7–8 Hz response was attenuated by 90 deg head roll or yaw, both of which uncouple the inter-aural axis from the medio-lateral sway axis. These results demonstrate two vertical torque responses to electrical vestibular stimulation in standing subjects. The high frequency response can be attributed to mechanical coupling to evoked medio-lateral sway. The low frequency response is consistent with a reaction to a sensation of head roll, and provides a novel method for investigating proprioceptive-vestibular interactions during stance.

A new design method of PID self-tuning immune fuzzy control was proposed to control the steam temperature system in fossil-fired power plant. Two fuzzy controllers, fuzzy self-tuning controller and immune P fuzzy controller, are designed to strengthen the normal PID cascade control. The outputs of self-tuning fuzzy controller are applied to tune the parameters of PID; the output of immune P fuzzy controller is transformed to regulate the proportion gain by the law of immunity feedback response in biology. Simulation results show that the control performance of this strategy is superior to that of normal PID cascade control. It is featured by strong robustness and self-adaptability, and can readily accommodate itself to the parameters variation.

A particular threat to global navigation satellite systems (GNSS) are small scale ionospheric disturbances. These can lead to fluctuations of the received satellite signal, so called signal scintillations. Strong scintillations can lead to a loss of lock between satellite and receiver. All GNSS signals are affected by this phenomenon. The influence of the short scale disturbances on the different GNSS signals is expected to be different for each signal, since the signals are transmitted by different carrier frequencies and are constructed in different ways.

Global navigation satellite system (GNSS) multipath reflectometry (MR) has emerged as a new technique that uses signals of opportunity broadcast by GNSS satellites and tracked by ground-based receivers to retrieve environmental variables such as snow depth. The technique is based on the simultaneous reception of direct or line-of-sight (LOS) transmissions and corresponding coherent surface reflections (non-LOS). Until recently, snow depth retrieval algorithms only used legacy and modernized GPS signals. Using multiple GNSS constellations for reflectometry would improve GNSS-MR applications by providing more observations from more satellites and independent signals (carrier frequencies and code modulations). We assess GPS and GLONASS for combined multi-GNSS-MR using simulations as well as field measurements. Synthetic observations for different signals indicated a lack of detectable interfrequency and intercode biases in GNSS-MR snow depth retrievals. Received signals from a GNSS station continuously operating in France for a two-winter period are used for experimental snow depth retrieval. We perform an internal validation of various GNSS signals against the proven GPS-L2-C signal, which was validated externally against in situ snow depth in previous studies. GLONASS observations required a more complex handling to account for topography because of its particular ground track repeatability. Signal intercomparison show an average correlation of 0.922 between different GPS snow depths and GPS-L2-CL, while GLONASS snow depth retrievals have an average correlation that exceeds 0.981. In terms of precision and accuracy, legacy GPS signals are worse, while GLONASS signals and modernized GPS signals are of comparable quality. Finally, we show how an optimal multi-GNSS combined daily snow depth time series can be formed employing variance factors with a ~59%-90% precision improvement compared to individual signal snow depth retrievals, resulting in snow depth retrieval with uncertainty of 1.3 cm. The developed combination strategy can also be applied for the European Galileo and the Chines BeiDou navigation systems.

The paper proposes a modified particle swarm optimization algorithm (MPSO) for online tuning to the fuzzy controller of power system stabilizer (PSS). The hybrid fuzzy controller combines concepts from fuzzy systems and particle swarm optimization to produce powerful system controllers that are used for adaptive control. Two synchronous generators fitted with a PSS and are connected via double transmission lines will be the system under study. Three types of PSS controllers such as Conventional lead-lag PSS (CPSS), Static Fuzzy Logic Controller (SFLC) and online tuning Fuzzy Logic Controller based on PSO algorithm will be considered. The modified PSO algorithm used to adjust the fuzzy set parameters of each Fuzzy Logic Controller (FLC-PSO) online. The speed error and the change of error are the input vector, and the stabilizing signal is the output of both fuzzy logic controller (FLC). The FLC controllers will be tested under different disturbances for a wide-range of operating points. The computation time and the complexity of the fuzzy controller are reduced. The simulation results ensure the effectiveness of the proposed FLC-PSO controller for achieving the good dynamic response of the system under study.