Lionel Ries

Development and validation of an OFDM/DVB-T sensor for positioning

The use of Global Navigation Satellite System (GNSS) for positioning has grown significantly in recent years thanks in particular to the development of several mass-market applications, such as car navigation or mobile positioning. Unfortunately, in difficult environments such as dense urban or indoor areas, GNSS exhibits degraded performances in terms of precision and availability. The use of signals of opportunity is one of the solutions to replace or assist GNSS in those environments. These signals are communication signals that are usually designed to provide a service in dense environment and can thus be used in location where GNSS is unavailable. Several commercial positioning services based on signals of opportunity already exist such as ROSUM with ATSC digital TV signals, or Skyhook with Wi-Fi signals

Positioning principles with a mobile TV system using DVB-SH signals and a Single Frequency Network

Mobile receiver positioning has received a lot of attention, both in research and standardization bodies, due to regulatory (E-911) or commercial (Location-Based Services) incentives. This paper investigates the possibility of self-positioning a mobile receiver using a mobile TV broadcasting system based on the European DVB-SH standard. This OFDM-based standard offers the interesting possibility of using a Single Frequency Network (SFN) of emitters, meaning that the transmitters are synchronized, which is extremely precious for navigation applications based on Time of Arrival measurements. This paper proposes to base our positioning service on the use of the estimation of the channel done by the receiver, in order to use Time Differences of Arrival techniques. In order to detect several emitters in a SFN, it is proposed to introduce artificial delays between adjacent emitters. The impact of this modification is investigated and some particular DVB-SH signal parameters are found to be well-suited to this solution.

A New Multipath Mitigation Method for GNSS Receivers Based on an Antenna Array

the potential of small antenna array for multipath mitigation in GNSS systems is considered in this paper. To discriminate the different incoming signals (Line of sight and multipaths), a new implementation of the well known SAGE algorithm is proposed. This allows a significant complexity reduction and it is fully compatible with conventional GNSS receivers. Theoretical study thanks to the Cramer Rao Bound derivation and tracking simulation results (in static and dynamic scenarios) show that the proposed method is a very promising approach for the multipath mitigation problem in GNSS receivers.

Use of OFDM-based digital TV for ranging: Tests and validation on real signals

This article presents results of tests on real signal of a method of positioning using a digital TV DVB-T signal-of-opportunity which is based on an OFDM modulation. OFDM and DVB-T standard are presented and the positioning method using the DVB-T signal is detailed. The result on real signal are analyzed qualitatively and quantitatively in static and dynamic scenarios and indoor and outdoor environments. In static scenarios, the standard deviation of pseudorange error is about 8 cm outdoor and 0.7 m indoor. In dynamic scenarios the pseudorange estimation is considerably disturbed and additional experiments are necessary to quantify the performance in this case.

A new GNSS multi constellation simulator: NAVYS

With the multiplication of navigation systems (GPS, GALILEO, GLONASS, QZSS, …) and the large variety of signals to be received, GNSS constellation simulators need to be more and more flexible. In the scope of its navigation activities, the CNES has expressed the need for a simulator that, in addition to allow the test of a large variety of receivers, satisfies a twofold objective: the emulation of a propagation channel representative of degraded environments, typically indoor or urban and high level of flexibility to generated new type of signals in order to assess the performances of future GNSS systems. For that purpose, Thales Alenia Space and Elta are currently developing a highly flexible and modular GNSS constellation simulator under CNES contract. In this development, they take benefit of their experience inherited from the realization of a flexible NSGU modulator that can handle a large diversity of modulations and can cope with most of the current and future GNSS systems. These modulations comprise BOC, BPSK, ALTBOC, CBOC, TMBOC, on selectable frequency bands. This paper describes the GNSS multi constellation simulator (NAVYS) design and architecture, includes validation test results and presents the status of the development of this equipment.

An Enhanced Correlation Processing Multipath Mitigation Technique for BOC Signals

Multipath is an issue of paramount importance in the GNSS context. The presence of reflected signals gives place to a worrying bias when estimating the propagation delay of the direct signal. This paper presents the design and the evaluation of a correlation processing technique that computes an estimation of the tracking error induced by the presence of multipath. This technique is especially designed for BOC signals and attempt to exploit the particular shape of its autocorrelation function.

Development of a flexible real time GNSS software receiver

With the multiplication of navigation systems (GPS, GALILEO, GLONASS, QZSS, …) the variety of radio navigation signals to be received increases greatly and involves 8 frequency bands and about 20 different signals. The paper presents an innovative receiver architecture resting on a full flexibility concept, allowing any tracking channel to be allocated to any kind of signal. The resulting software defined receiver stands for a high sensitivity and high accuracy receiver coping with very large dynamic, making the concept adapted to any kind of mission.

A new operational low cost GNSS software receiver for microsatellites

This paper presents a new low cost GNSS Software (SW) receiver for Microsatellites. Syrlinks (Bruz, FRANCE) has been chosen by CNES for developing and manufacturing this equipment which should be tested on board the scientific microsatellite named MICROSCOPE that will be launched in 2015. The GNSS receiver under development is a highperformance equipment specially designed and optimized for the needs and constraints of small platforms for which small volume, low mass and low power consumption are important parameters. This equipment is based on COTS (Commercials Off The Shelf) in order to exploit the performance of the advanced technology developed for terrestrial applications and to reduce significantly the global cost of the equipment. The structure of this GNSS receiver is organized around a reconfigurable architecture with the use of one FPGA (Field Programmable Gate Array) associated with one DSP (Digital Signal Processor). The GNSS function is then split in two main parts according to the real time requirements of the processing and navigation operations. The hardware (HW) architecture has been optimized to be able to support a low power mode through a fractioned activity that has been implemented by introducing standby time frames during the mission. An orbital extrapolator is also implemented for propagating position and velocity without pseudo range measurements. This receiver is able to process GPS (L1) and GALILEO (E1) signals simultaneously in the first version of the software and will be able to evolve in a second step to a dual frequency mode, compatible with E5a/E1, or with E5b/E1. This GNSS receiver dedicated to low earth orbit (LEO) satellites will withstand the radiation environment therefore the hardware and software architecture has been defined to reduce the single event effects (SEE) and to maximize the service availability.

Implementation of Code Shift Keying signalling technique in GALILEO E1 signal

One of limitations of the current GNSS signals is their low data information rate. This low data information rate does not allow, for example, the transmission of additional commercial services or the transmission of redundant ephemeris data. The Code Shift Keying (CSK) is a signaling technique specifically designed to increase the transmission bit rate of a spreading spectrum signal. Therefore, one solution to increase the data information rate of the GNSS signals is to introduce the CSK technique in them. In this paper, the implementation of the CSK technique into GNSS signals is inspected through the development and analysis of the likelihood ratio expression of the bits transmitted inside a CSK symbol, and through the identification of the best mapping between bits belonging to a word and bits transmitted inside a CSK symbol. Finally, the impact of the CSK technique on the GALILEO E1 signal is analyzed by calculating the CSK demodulation performance for a given scenario and the drawbacks of the technique on the signal acquisition and tracking processes.

Field test performance assessment of GNSS/INS ultra-tight coupling scheme targeted to mass-market applications

This article describes field test results of hybridization between MEMS inertial measurement unit (IMU) and GPS L1 C/A signal using an ultra-tight coupling (UTC) architecture. A software receiver is used to post-process raw GPS signal and IMU measurement recorded during the field tests. Both indoor and outdoor environments are explored and UTC with MEMS is compared to UTC with high-grade IMU and vectorized GNSS standalone positioning.