Showing papers by "Mohamed Sahmoudi published in 2009"

Introduction to the Issue on Advanced Signal Processing for GNSS and Robust Navigation

Abstract: WE are pleased to have this opportunity to organize a special issue on advances in signal processing for Global Navigation Satellite Systems (GNSS) and robust navigation. This we consider as the first and a seminal issue on this important subject to appear in any IEEE journal or transaction. The goal of this interdisciplinary special issue is to bring together a diverse and complementary set of contributions in the area of signal processing for positioning and navigation, introduce the navigation problems to the larger signal processing community, promote further advances in the area, and help to establish a larger research community around this field.

A constrained maximum-likelihood approach for efficient multipath mitigation in GNSS receivers

Abstract: In this paper, we develop a new method for mitigating multipath effects in GNSS receivers, based on a constrained maximum-likelihood (CML) estimates of the multipath parameters. First, we apply a nonlinear transformation on the signal parameters to reduce the search space. Then, we define a new criterion for constraining the relative amplitude of the received secondary signal, and use the Lagrange multiplier method to solve the CML optimization problem. The resulting likelihood cost function has a unique minimum and yields to closed-form parameters estimates. The proposed method does not suffer from the correlation multi-peak problem, as for the standard discriminators, thus it can be used for any type of GNSS signal to mitigate both code and carrier phase multipath errors, including the new BOC signals. Numerical examples show that the CML approach gives a significant refinement to reach the optimal positioning solution.

Robust mitigation of multipath and ionospheric delays in multi-GNSS real-time kinematic (RTK) receivers

Abstract: In this paper, we develop a new scheme for RTK positioning using multi-constellation GNSS measurements in presence of multipath and ionospheric delays. The proposed procedure for multi-frequency ambiguity resolution is based on four steps: 1) at each epoch, a Gaussian sum particle filter is used to track the user position and the float ambiguity solution adaptively to the dynamic environment by minimizing the noise level and estimating the ionospheric errors ; 2) we utilize a new carrier phase multipath indicator to reject integers candidates that are affected by multipath errors, 3) we apply LAMBDA method to search the integer ambiguities; and finally 4) validate the fixed solution using a robust statistical test. Real-data test results show the effectiveness of the overall developed procedure for long-baseline RTK positioning.

Contribution to the Worldwide multimodal SBAS standard

Abstract: Several studies have been done or have been started in order to extend the current aeronautical Space Based Augmentation System (SBAS) DO-229D Minimum Operational Performance Specification (MOPS) SBAS standard mainly defined by the Radio Technical ComiteeCommittee for Aeronautical applications (RTCA), Sub-Committee 159, Working Group 2 (RTCA SC-159 WG-2). The SBAS message is transmitted by geostationary satellites using a modulation scheme similar to GPS wherein the same Gold code family, chipping rate, BPSK modulation of the same GPS carrier frequency of 1575.42 MHz with the difference being that the a 500 bps bit stream is also modulated instead of the 50 bps data stream as in GPS. The 500 bps data stream are symbol bits which encode the actual and already standardized through GPS-like C/A codes carrying navigation and integrity 250 bps SBAS message stream at 1575,42 MHz. The aeronautical SBAS is an ICAO standard and can be adopted by any state. The intent is to have aeronautical SBAS establish itself as a world-wide standard and service. Aeronautical SBAS main purpose was to provide near real-time GNSS integrity world-wide. That concept evolved to also providing differential corrections and optionally a ranging signal. In addition, every aeronautical SBAS service provider has the ability to certify and then designate his service for Safety-of-Life (SoL) service. Once certified as a SoL service, the respective aeronautical SBAS service provider would also transmit the appropriate messages and data indicating that the particular transmission (and data) can be used for SoL applications. Data within the aeronautical SBAS message stream indicates over which regions the differential messages can used. Today, aeronautical SBAS is capable of supporting LPV (Localaizer with Precision Vertical) approaches to 200 foot (about 66 meters) minimums. These are CAT-I ILS (Category 1 International Landing System) equivalent approaches. For further technical details, the reader is referred to the RTCA/DO-229D MOPS.