Youssef Tawk

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.

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.

A New FFT-Based Algorithm for Secondary Code Acquisition for Galileo Signals

The innovative spreading codes used to modulate the new Galileo signals creates new challenges for receiver designers. It is well known in GNSS systems that longer integration times are needed to obtain a better sensitivity. However, the existence of the new tiered code concept that consists of the presence of a secondary code on top of the primary code to modulate the RF signal puts a limitation on the coherent integration time for pilot channels similarly to the effect of data bit ambiguity in data channels. Within this context, this paper tackles this issue by introducing a new algorithm for wiping off the secondary code and increase the coherent integration time. The algorithm is based on the combination of serial and parallel searches. The search for the primary code phase is performed serially within one primary code length, and the secondary code phase is searched in parallel over the entire length of the secondary code. Furthermore, the proposed algorithm improves the Doppler offset estimation and reduces the overall acquisition time.

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.

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.

U-SBAS: A universal multi-SBAS standard to ensure compatibility, interoperability and interchangeability

Several regional augmentation GNSS systems (like SBAS) are already fully operational and other are under development with new frequencies and signals on the way. Therefore, it becomes imperative to guarantee for all GNSS users the compatibility, interoperability and interchangeability between all these systems. The goal is to ensure that the users multi-mode receiver can choose and mix signals from different GNSS and SBAS systems to achieve more availability, accuracy and robustness. Attaining that objective will require agreements on frequency plans and signal designs, as well as other details including means to ensure interoperability of system times and geodetic reference systems. This paper suggests a Universal-SBAS (U-SBAS) standard, compatible with all the existing and planned regional GNSS systems (and their evolutions) in the world, like IRNSS, QZSS, PCW, BEIDOU-1, WAAS, EGNOS, SDCM, GAGAN, MSAS. The proposed worldwide multimodal U-SBAS standard carries additional channels (signals and messages) to cover the non-aeronautical specific Safety-of-Life (SoL) services, and also High Precision Positioning Services (HPPS), Position Velocity Time (PVT), authentication services, safety services, scientific application services, High Precision Timing Services (HPTS), etc. U-SBAS is designed to be fully interoperable with the current SBAS standards and to allow significant performance and service improvements in operational, scientific and/or security areas. Finally usage examples of the proposed standard are given for different types of applications such as science, aviation, precise point positioning, timing, security, robust positioning, maritime and reflectometry.

A New Movement Recognition Technique for Flight Mode Detection

Nowadays, in the aeronautical environments, the use of mobile communication and other wireless technologies is restricted. More specifically, the Federal Communications Commission (FCC) and the Federal Aviation Administration (FAA) prohibit the use of cellular phones and other wireless devices on airborne aircraft because of potential interference with wireless networks on the ground, and with the aircrafts navigation and communication systems. Within this context, we propose in this paper a movement recognition algorithm that will switch off a module including a GSM (Global System for Mobile Communications) device or any other mobile cellular technology as soon as it senses movement and thereby will prevent any forbidden transmissions that could occur in a moving airplane. The algorithm is based solely on measurements of a low-cost accelerometer and is easy to implement with a high degree of reliability.

Performance Comparison of Different Correlation Techniques for the AltBOC Modulation in Multipath Environments

In this paper, different correlation techniques (narrow correlator, double delta correlator and subcarrier processing) that can be applied to the new Galileo alternate binary offset carrier AltBOC(15,10) modulation are discussed with respect to their functionality, implementation, and multipath mitigation performance. Moreover, effects of the receiver parameters (precorrelation bandwidth, spacing between correlators) on the ranging errors are also presented. The performance of the multipath mitigation concepts is illustrated in 2D and 3D multipath error envelopes assuming multipath scenarios with one and two multipath components and constant signal attenuation factors. The main purpose of this paper is to provide a better understanding of the performance of the AltBOC modulation and the effect of multipath on code and carrier measurements for different multipath environments, and thus help the receiver designers to select the best correlation technique for their particular applications.

Dual Channel Optimization of Tracking Schemes for E1 CBOC Signal

New generation of satellite navigation signals, such as AltBOC (Alternative Binary Offset Keying), CBOC (Composite Binary Offset Keying) and TMBOC (Time Multiplex Binary Offset Keying) bring enhancements in the tracking process, such as more signal power, better multipath mitigation capabilities and more robust navigation. Moreover, one of the most important improvement they bring into the GNSS story is the presence of the two channels: data and pilot. The pilot channel, although dataless, carries the same information about the frequency, carrier and code phase as the data channel.Therefore, the information from both channels can be used to improve the tracking performance. In this context, the main point that is addressed in this paper is the optimization of the data/pilot combining tracking strategies in order to increase tracking stability, accuracy and robustness. Towards this end, non-coherent and coherent data/pilot combining strategies with different weights on each channel are presented, and the outputs from the DLL and PLL tracking loops using different discriminator types are analyzed and discussed. Moreover, an investigation for an optimal trade-off between the minimal tracking error and the best stability is reported with the corresponding results discussed.