High-sensitivity GNSS Receivers Research Articles

Fuzzy logic applied to GNSS

Limiting the weight of bad signals can recover the accuracy of the GNSS solution in signal-degraded scenarios, where multipath reflections and obstructions can easily generate multiple blunders. The fuzzy integration of the available information related to the quality of the received signals is exploited in this paper to derive an effective weighting schema in a Weighted Least Square estimation process. To validate the proposed schema, its performance in the position domain is compared to the most common weighting strategies proposed in the literature, based on GPS data collected through two different High Sensitivity GNSS receivers placed in urban canyons and processed in Single Point Positioning using pseudorange measurements.

C/N0 estimators for high-sensitivity snapshot GNSS receivers

We address the problem of estimating the carrier-to-noise ratio (C/N0) in weak signal conditions. There are several environments, such as forested areas, indoor buildings and urban canyons, where high-sensitivity global navigation satellite system (HS-GNSS) receivers are expected to work under these reception conditions. The acquisition of weak signals from the satellites requires the use of post-detection integration (PDI) techniques to accumulate enough energy to detect them. However, due to the attenuation suffered by these signals, estimating their C/N0 becomes a challenge. Measurements of C/N0 are important in many applications of HS-GNSS receivers such as the determination of a detection threshold or the mitigation of near-far problems. For this reason, different techniques have been proposed in the literature to estimate the C/N0, but they only work properly in the high C/N0 region where the coherent integration is enough to acquire the satellites. We derive four C/N0 estimators that are specially designed for HS-GNSS snapshot receivers and only use the output of a PDI technique to perform the estimation. We consider four PDI techniques, namely non-coherent PDI, non-quadratic non-coherent PDI, differential PDI and truncated generalized PDI and we obtain the corresponding C/N0 estimator for each of them. Our performance analysis shows a significant advantage of the proposed estimators with respect to other C/N0 estimators available in the literature in terms of estimation accuracy and computational resources.

A framework for risk reduction for indoor parking facilities under constraints using positioning technologies

Traffic simulation is a mature field, with several decades of development. While many mainstream aspects can be assumed to be at a level where most challenges have been overcome, there are still edge cases that are not adequately covered. For example, traffic simulation of mixed networks in conditions close to exceeding capacity or in emergency cases is still a challenge. This research aims at developing a risk-reduction framework for large-scale parking facilities and depots (for either passenger vehicles or commercial fleets) under constraints. An integrated methodological framework is therefore analyzed and then the emphasis is placed on the localization of vehicles under these conditions using a combination of state-of-the-art technologies. A case study is implemented to test the feasibility of the proposed technologies including smart-phone accelerometers, radio frequency identification technology, high-sensitivity GNSS receivers and Ultra-wideband technology. Then, an experiment was conducted in a large-scale parking facility, including vehicle positioning in indoor, outdoor and hybrid environments. This information is used as input for a simulation-based evacuation analysis of a large parking facility in Athens, Greece. The evaluation of four evacuation scenarios suggests that considerable risk reduction benefits can be obtained by suitable emergency response strategies.

Design and test of HiSGR: a novel GNSS/INS ultra tight coupled receiver

With the support of the national nature science foundation, the Academy of Space Electronic Information Technology is developing a novel compact spaceborne GNSS receiver, referred to as the HiSGR (High Sensitivity GNSS Receiver). This receiver can operate effectively in the full range of Earth orbiting missions, from LEO (Low Earth Orbit) to geostationary and beyond. Improved signal detection algorithms are used in the signal process section of the HiSGR and an inertial sensor is used for GNSS/INS ultra tight coupled design, which makes the acquisition process fast and provides improved tracking performance for weaker GPS signals in the presence of high dynamics. Extensive tests are performed using the HiSGR to demonstrate the good performance of some crucial specifications, by employing a real GNSS signal received in an open field and through hardware- in-the-loop simulation. Receiver performance is demonstrated for LEO and GEO scenarios. A ground vehicle running test is performed for demonstration of fast acquisition and reacquisition capabilities under conditions of signal loss. The HiSGR showed good performance and it was stable during the simulations and tests, which proved its capability for future space applications.

Design of a High Sensitivity GNSS receiver for Lunar missions

This paper presents the design of a satellite navigation receiver architecture tailored for future Lunar exploration missions, demonstrating the feasibility of using Global Navigation Satellite Systems signals integrated with an orbital filter to achieve such a scope. It analyzes the performance of a navigation solution based on pseudorange and pseudorange rate measurements, generated through the processing of very weak signals of the Global Positioning System (GPS) L1/L5 and Galileo E1/E5 frequency bands. In critical scenarios (e.g. during manoeuvres) acceleration and attitude measurements from additional sensors complementing the GNSS measurements are integrated with the GNSS measurement to match the positioning requirement. A review of environment characteristics (dynamics, geometry and signal power) for the different phases of a reference Lunar mission is provided, focusing on the stringent requirements of the Descent, Approach and Hazard Detection and Avoidance phase. The design of High Sensitivity acquisition and tracking schemes is supported by an extensive simulation test campaign using a software receiver implementation and navigation results are validated by means of an end-to-end software simulator.Acquisition and tracking of GPS and Galileo signals of the L1/E1 and L5/E5a bands was successfully demonstrated for Carrier-to-Noise density ratios as low as 5–8dB-Hz. The proposed navigation architecture provides acceptable performances during the considered critical phases, granting position and velocity errors below 61.4m and 3.2m/s, respectively, for the 99.7% of the mission time.

Indoor doppler error characterization for high sensitivity GNSS receivers

Indoor Doppler measurements in high sensitivity receivers are often biased due to the indoor multipath and user dynamics. The work presented here investigates the relationship between Doppler errors and some key channel parameters. A directional multipath channel model is introduced and some essential channel parameters are defined. In nonsymmetric scattering environments, the Doppler biases are shown to be explicitly related with these parameters. Theoretical simulation and experimental data are analyzed and demonstrated to be consistent.

Demonstration of a high sensitivity GNSS software receiver for indoor positioning

Advances in signal processing techniques contributed to the significant improvements of GNSS receiver performance in dense multipath environments and created the opportunities for a new category of high-sensitivity GNSS (HS-GNSS) receivers that can provide GNSS location services in indoor environments. The difficulties in improving the availability, reliability, and accuracy of these indoor capable GNSS receivers exceed those of the receivers designed for the most hostile urban canyon environments. The authors of this paper identified the vector tracking schemes, signal propagation statistics, and parallel processing techniques that are critical to a robust HS-GNSS receiver for indoor environments and successfully incorporated them into a fully functional high-sensitivity software receiver. A flexible vector-based receiver architecture is introduced to combine these key indoor signal processing technologies into GSNRx-hs™ – the high sensitivity software navigation receiver developed at the University of Calgary. The resulting receiver can perform multi-mode vector tracking in indoor environment at various levels of location and timing uncertainties. In addition to the obvious improvements in time-to-first-fix (TTFF) and signal sensitivity, the field test results in indoor environments surrounded by wood, glass, and concrete showed that the new techniques effectively improved the performance of indoor GNSS positioning. With fine GNSS timing, the proposed receiver can consistently deliver indoor navigation solution with the horizontal accuracy of 2–15m depending on the satellite geometry and the indoor environments. If only the coarse GNSS timing is available, the horizontal accuracy of the indoor navigation solution from the proposed receiver is around 30m depending on the coarse timing accuracy, the satellite geometry, and the indoor environments. From the preliminary field test results, it has been observed that the signal processing sensitivity is the dominant factor on the availability of the indoor navigation solution, while the GNSS timing accuracy is the dominant factor on the accuracy of the indoor navigation solution.

A low-phase-noise LC-VCO with an enhanced-Q varactor for use in a high-sensitivity GNSS receiver

An LC-VCO with an enhanced quality factor (Q) varactor for use in a high-sensitivity GNSS receiver is presented. An enhanced A-MOS varactor is composed of two accumulation-mode MOS (A-MOS) varactors and two bias voltages, which show the improved Q and linearization capacitance-voltage (C−V) curve. The VCO gain (KVCO) is compensated by a digital switched varactors array (DSVA) over entire sub-bands. Based on the characteristics of an A-MOS, the varactor in a DSVA is a high Q fixed capacitor as it is switched off, and a moderate Q tuning varactor when it is switched on, which keeps the maximal Q for the LC-tank. The proposed circuit is fabricated in a 0.18 μm 1P6M CMOS process. The measured phase noise is better than −122 dBc/Hz at a 1 MHz offset while the measured tuning range is 58.2% and the variation of KVCO is close to ±21% over the whole of the sub-bands and the effective range of the control voltage. The proposed VCO dissipates less than 5.4 mW over the whole operating range from a 1.8 V supply.