Cyril Botteron

Multipath mitigation techniques for CBOC, TMBOC and AltBOC signals using advanced correlators architectures

Multipath mitigation in urban canyons and indoor environments is an open issue for the reception of GNSS signals for high precision applications, as the presence of multipath components can lead to signal fading and ranging errors. New families of navigation signals, such as AltBOC, CBOC and TMBOC bring potential improvements, such as more signal power, better multipath mitigation capabilities and more robust navigation. Therefore the goal of this paper is to investigate multipath mitigation capabilities of CBOC, TMBOC and AltBOC with different discriminator architectures through theoretical analysis and realistic set-up with measurements in order to provide an overview of their performance in different environments.

Acquisition of modern GNSS signals using a modified parallel code-phase search architecture

The acquisition of global navigation satellite system signals can be performed using a fast Fourier transform (FFT). The FFT-based acquisition performs a circular correlation, and is thus sensitive to potential transitions between consecutive periods of the code. Such transitions are not occurring often for the GPS L1 C/A signal because of the low data rate, but very likely for the new GNSS signals having a secondary code. The straightforward solution consists in using two periods of the incoming primary code and using zero-padding for the local code to perform the correlation. However, this solution increases the complexity, and is moreover not efficient since half of the points calculated are discarded. This has led us to research for a more efficient algorithm, which discards less points by calculating several sub-correlations. It is applied to the GPS L5, Galileo E5a, E5b and E1 signals. Considering the radix-2 FFT, the proposed algorithm is more efficient for the L5, E5a and E5b signals, and possibly for the E1 signal. The theoretical number of operations can be reduced by 21%, the processing time measured on a software implementation is reduced by 39%, and the memory resources are almost halved for an FPGA implementation.

Implementation and performance of a GPS/INS tightly coupled assisted PLL architecture using MEMS inertial sensors.

The use of global navigation satellite system receivers for navigation still presents many challenges in urban canyon and indoor environments, where satellite availability is typically reduced and received signals are attenuated. To improve the navigation performance in such environments, several enhancement methods can be implemented. For instance, external aid provided through coupling with other sensors has proven to contribute substantially to enhancing navigation performance and robustness. Within this context, coupling a very simple GPS receiver with an Inertial Navigation System (INS) based on low-cost micro-electro-mechanical systems (MEMS) inertial sensors is considered in this paper. In particular, we propose a GPS/INS Tightly Coupled Assisted PLL (TCAPLL) architecture, and present most of the associated challenges that need to be addressed when dealing with very-low-performance MEMS inertial sensors. In addition, we propose a data monitoring system in charge of checking the quality of the measurement flow in the architecture. The implementation of the TCAPLL is discussed in detail, and its performance under different scenarios is assessed. Finally, the architecture is evaluated through a test campaign using a vehicle that is driven in urban environments, with the purpose of highlighting the pros and cons of combining MEMS inertial sensors with GPS over GPS alone.

Analysis of Galileo E5 and E5ab code tracking

The world of global navigation satellite systems has been enhanced with several new or improved signals in space aiming to optimize accuracy, reliability, navigation solution, and interoperability between different constellations. However, such developments bring various challenges to the receivers’ designers. For example, acquisition and tracking stages turn into more complex processes while handling the increasing bandwidth requires additional processing power. In this context, we study the code tracking of Galileo E5ab in a full band or of only one of its components, i.e., either E5a or E5b. More specifically, an architecture for tracking the E5 pilot channel as an AltBOC(15,10) or BPSK(10) modulation is introduced, and the performance of well-known discriminator types is analyzed using analytical derivations and simulations of linearity and stability regions, thermal noise tracking errors, multipath error envelopes and tracking thresholds. Different parameters, such as the front-end filter bandwidth, the early/late chip spacing, un-normalized and normalized discriminators, are taken into consideration. The results obtained are used to illustrate the main advantages and drawbacks of tracking the E5 signal as well as to help defining the main tracking loop parameters for an enhanced performance.

Soil Moisture & Snow Properties Determination with GNSS in Alpine Environments: Challenges, Status, and Perspectives

Moisture content in the soil and snow in the alpine environment is an important factor, not only for environmentally oriented research, but also for decision making in agriculture and hazard management. Current observation techniques quantifying soil moisture or characterizing a snow pack often require dedicated instrumentation that measures either at point scale or at very large (satellite pixel) scale. Given the heterogeneity of both snow cover and soil moisture in alpine terrain, observations of the spatial distribution of moisture and snow-cover are lacking at spatial scales relevant for alpine hydrometeorology. This paper provides an overview of the challenges and status of the determination of soil moisture and snow properties in alpine environments. Current measurement techniques and newly proposed ones, based on the reception of reflected Global Navigation Satellite Signals (i.e., GNSS Reflectometry or GNSS-R), or the use of laser scanning are reviewed, and the perspectives offered by these new techniques to fill the current gap in the instrumentation level are discussed. Some key enabling technologies including the availability of modernized GNSS signals and GNSS array beamforming techniques are also considered and discussed.

UWB-based Local Positioning System: From a small-scale experimental platform to a large-scale deployable system

A few years ago an experimental platform was designed and built in order to demonstrate the feasibility of Ultra-Wideband (UWB) technology applied to indoor positioning. This small-scale demonstrator proved to be a valuable research tool with the flexibility to study, test and assess the performance of various system architectures and signal processing algorithms.

Two-Step Galileo E1 CBOC Tracking Algorithm:When Reliability and Robustness Are Keys!

The majority of 3G mobile phones have an integrated GPS chip enabling them to calculate a navigation solution. But to deliver continuous and accurate location information, the satellite tracking process has to be stable and reliable. This is still challenging, for example, in heavy multipath and non-line of sight (NLOS) environments. New families of Galileo and GPS navigation signals, such as Alternate Binary Offset Carrier (AltBOC), Composite Binary Offset Carrier (CBOC), and Time-Multiplex Binary Offset Carrier (TMBOC), will bring potential improvements in the pseudorange calculation, including more signal power, better multipath mitigation capabilities, and overall more robust navigation. However, GNSS signal tracking strategies have to be more advanced in order to profit from the enhanced properties of the new signals.In this paper, a tracking algorithm designed for Galileo E1 CBOC signal that consists of two steps, coarse and fine, with different tracking parameters in each step, is presented and analyzed with respect to tracking accuracy, sensitivity and robustness. The aim of this paper is therefore to provide a full theoretical analysis of the proposed two-step tracking algorithm for Galileo E1 CBOC signals, as well as to confirm the results through simulations as well as using real Galileo satellite data.

A 120mV startup circuit based on charge pump for energy harvesting circuits

In this paper, a 120mV input startup circuit based on novel charge pump architecture is proposed. The startup circuit can boost input voltages ranging from 120mV to 300mV while supplying voltages 280mV to 1.6V at the output with approximately 23% efficiency. To verify the circuit behavior, the test circuit has been implemented using 0.18µm CMOS process. The low voltage, low area startup circuit is suitable for ultra low voltage applications such as energy harvesters and allows for single chip integration.

Design of a GPS and Galileo Multi-Frequency Front-End

GNSS platforms such as the American Global Positioning System (GPS) or the Russian GLONASS system are being continuously updated with new satellites offering new signals, new frequencies and new functionalities. Moreover, new GNSS systems such as the European Union’s Galileo system or the Japan’s Quasi-Zenith Satellite System (QZSS) are currently being developed and planned to be in function within a couple of years. Taking advantage of these new signals requires the use of a multi-frequency Radio-Frequency (RF) Front-End (FE). In this paper, we highlight the design of such a FE based on a sub-sampling architecture. Indeed, with the technology advances in the Integrated Circuits (IC) industry, and more particularly the availability of GHz bandwidth analog-to-digital converters (ADC), this is one of the most attractive ways to achieve a multi-frequency FE. While a sub-sampling architecture has already been presented in some other publications [1], [2], we present a methodology that takes into account the effects of the filters characteristics and out-of-band noise. As a practical example, we apply our methodology to the design of a multi-frequency RF FE for the simultaneous acquisition of the GPS L1C; L2C; L5, and Galileo E1b;c; E5a;b signals.

Standalone GPS L1 C/A Receiver for Lunar Missions

Global Navigation Satellite Systems (GNSSs) were originally introduced to provide positioning and timing services for terrestrial Earth users. However, space users increasingly rely on GNSS for spacecraft navigation and other science applications at several different altitudes from the Earth surface, in Low Earth Orbit (LEO), Medium Earth Orbit (MEO), Geostationary Earth Orbit (GEO), and feasibility studies have proved that GNSS signals can even be tracked at Moon altitude. Despite this, space remains a challenging operational environment, particularly on the way from the Earth to the Moon, characterized by weaker signals with wider gain variability, larger dynamic ranges resulting in higher Doppler and Doppler rates and critically low satellite signal availability. Following our previous studies, this paper describes the proof of concept “WeakHEO” receiver; a GPS L1 C/A receiver we developed in our laboratory specifically for lunar missions. The paper also assesses the performance of the receiver in two representative portions of an Earth Moon Transfer Orbit (MTO). The receiver was connected to our GNSS Spirent simulator in order to collect real-time hardware-in-the-loop observations, and then processed by the navigation module. This demonstrates the feasibility, using current technology, of effectively exploiting GNSS signals for navigation in a MTO.