Performance Evaluation of Adaptive Tracking Techniques with Direct-State Kalman Filter

This paper evaluates the performance of robust adaptive tracking techniques with the direct-state Kalman filter (DSKF) used in modern digital global navigation satellite system (GNSS) receivers. Under the assumption of a well-known Gaussian distributed model of the states and the measurements, the DSKF adapts its coefficients optimally to achieve the minimum mean square error (MMSE). In time-varying scenarios, the measurements’ distribution changes over time due to noise, signal dynamics, multipath, and non-line-of-sight effects. These kinds of scenarios make difficult the search for a suitable measurement and process noise model, leading to a sub-optimal solution of the DSKF. The loop-bandwidth control algorithm (LBCA) can adapt the DSKF according to the time-varying scenario and improve its performance significantly. This study introduces two methods to adapt the DSKF using the LBCA: The LBCA-based DSKF and the LBCA-based lookup table (LUT)-DSKF. The former method adapts the steady-state process noise variance based on the LBCA’s loop bandwidth update. In contrast, the latter directly relates the loop bandwidth with the steady-state Kalman gains. The presented techniques are compared with the well-known state-of-the-art carrier-to-noise density ratio (C/N0)-based DSKF. These adaptive tracking techniques are implemented in an open software interface GNSS hardware receiver. For each implementation, the receiver’s tracking performance and the system performance are evaluated in simulated scenarios with different dynamics and noise cases. Results confirm that the LBCA can be successfully applied to adapt the DSKF. The LBCA-based LUT-DSKF exhibits superior static and dynamic system performance compared to other adaptive tracking techniques using the DSKF while achieving the lowest complexity.

A filter algorithm for receiver tracking loops assisted by inertial information

In traditional satellite navigation receivers, the parameters of tracking loop such as loop bandwidth and integration time are usually set in the design of the receivers according to different scenarios. The signal tracking performance is limited in traditional receivers. In addition, when the tracking ability of weak signals is improved by extending the integration time, negative effect of residual frequency error becomes more and more serious with extension of the integration time. To solve these problems, this paper presents out research on receiver tracking algorithms and proposes an optimised tracking algorithm with inertial information. The receiver loop filter is designed based on Kalman filter, reducing the phase jitter caused by thermal noise in the weak signal environment and improving the signal tracking sensitivity. To confirm the feasibility of the proposed algorithm, simulation tests are conducted.

On the Relation between Mains-Side Current THD and DC Link Voltage Loop Gain in Grid-Connected Unity Power Factor Operating Converters

<p>It is well-known that attainable DC link voltage loop bandwidth in grid-connected converters operating with unity power factor is limited due to trade-off with AC-side current total harmonic distortion (THD). The letter reveals that THD requirement directly imposes the value of voltage loop gain magnitude at double-grid frequency; therefore the dynamic performance may be improved without deteriorating the grid-side current quality by modifying the controller structure such that the loop gain magnitude at double-grid frequency and the crossover frequency are decoupled. Experimental results validate the revealed findings.</p>

On the Relation between Mains-Side Current THD and DC Link Voltage Loop Gain in Grid-Connected Unity Power Factor Operating Converters

<p>It is well-known that attainable DC link voltage loop bandwidth in grid-connected converters operating with unity power factor is limited due to trade-off with AC-side current total harmonic distortion (THD). The letter reveals that THD requirement directly imposes the value of voltage loop gain magnitude at double-grid frequency; therefore the dynamic performance may be improved without deteriorating the grid-side current quality by modifying the controller structure such that the loop gain magnitude at double-grid frequency and the crossover frequency are decoupled. Experimental results validate the revealed findings.</p>

Adaptive Notch Filter for Piezo-Actuated Nanopositioning System via Position and Online Estimate Dual-Mode

Due to the excellent advantages of high speed, high precision, and driving force, piezoelectric actuators nanopositioning systems have been widely used in various micro/nanomachining fields. However, the inherent resonance dynamic of the nanopositioning system generated by the flexure-hinge greatly deteriorates the positioning performance and limits the closed-loop bandwidth. Even worse, the notch filter for eliminating the effect of resonance does not work due to the varying resonant frequency resulting from the external disturbance or mass load. To this end, an adaptive notch filter for piezo-actuated nanopositioning system via position and online estimate dual-mode (POEDM) has been proposed in this paper, which can estimate the varying resonant frequency in real-time and suppress the resonance to improve the closed-loop bandwidth. First, a novel variable forgetting factor recursive least squares (VFF-RLS) algorithm for estimating resonant frequency online is presented, which is robust to the noise and provides the performances of both fast tracking and stability. Then, a POEDM method is proposed to achieve the online identification of the resonant frequency in the presence of noise and disturbance. Finally, a series of validation simulations are carried out, and the results indicate that, the frequency of input signal and the bandwidth have been achieved up to 12.5% and 87.5% of the first resonant frequency, respectively.

Investigation of Doppler Collision Effects in Kinematic Conditions and its Mitigation for NavIC System

NavIC (Navigation with Indian Constellation) constellation consists of four geosynchronous and three geostationary satellites and it is developed by ISRO, India. It provides position, velocity and timing services. Doppler Collision (DC) is a phenomenon where tracking errors are introduced in the measurements due to cross-correlation between the satellites. If relative doppler between satellites is less than the code loop bandwidth, then DC occurs. In this paper, to analyze DC impact on NavIC, the Doppler shift of each GEO satellite is calculated, the most effected GEO satellite pair is identified. In high dynamic applications like missile launches the effect of DC is very significant. In order to investigate DC in high dynamic conditions a simulation of trajectory path of the receiver is considered. For the precise position estimation, the contribution of DC error will be high, so it needs to be minimized. An efficient algorithm is developed to mitigate the DC using narrow correlator design of the receiver. Using the proposed algorithm, the DC duration for 1C-1G satellite pair has been reduced from 50min 21sec to 2sec in static conditions. Whereas in dynamic conditions from 4h20min 28sec to 5sec with DLL bandwidth of 4Hz and 0.1 chip spacing of receiver design.

A Boost Converter Employing Quadratic Sawtooth Waveform Generator for SiPM-Based Radiation Sensors

This paper proposes an optimized step-up power converter using a quadratic sawtooth waveform generator for a silicon photomultiplier (SiPM) used as a radiation sensor for mobile radiation dosimeters. Although our step-up converter uses the topology of a switched inductor boost converter in voltage mode, it achieves a fast transient performance thanks to the proposed quadratic sawtooth waveform generator, which can increase the loop bandwidth. As a result, the proposed boost converter can stably regulate the bias voltage of an SiPM, even in a situation where the radiation particles are injected. In addition, since the proposed quadratic sawtooth waveform generator can be designed with low power, it was able to achieve 86% peak efficiency even under the light load conditions.

Considerate Regulation of Output Disturbances

Recently, I have considered a multi-variable feedforward control practice in a novel way being called “considerate control”. It was shown how the considerate control is related to Bristol gains, which indicate accurately either the required increase in input scope or the reduced output scope as compared to inconsiderate control. Here, considerate control is expanded to regulating control, necessitating some feedback design. Clearly, high-gain feedback leads to considerate control results in low frequency. Considerate pre-compensation decouples loops also at higher frequencies. However, as an analysis of the included examples demonstrates, such considerate design may insert non-minimum phase-lag into loops that did not have it, thus, reducing the loop bandwidth relative to that achievable in a skillful inconsiderate design, sometimes very significantly. As is often the case, there is a trade-off between consideration and performance.