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Selected Topics in Signal Processing, IEEE Journal of

Issue 4 • Date Aug. 2009

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Displaying Results 1 - 25 of 28
  • Table of contents

    Page(s): C1 - C4
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  • IEEE Journal of Selected Topics in Signal Processing publication information

    Page(s): C2
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  • Introduction to the Issue on Advanced Signal Processing for GNSS and Robust Navigation

    Page(s): 537 - 540
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  • A GPS Receiver for High-Altitude Satellite Navigation

    Page(s): 541 - 556
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1608 KB) |  | HTML iconHTML  

    Although GPS has found wide application for precision spacecraft navigation and formation flying applications in low Earth orbit (LEO), its application to geosynchronous (GEO) and other high-altitude missions has been limited to an experimental role because of the sparsity and weakness of the GPS signals present there. To fill this gap, NASA Goddard Space Flight Center (GSFC) has developed a new space-borne GPS receiver called Navigator that can operate effectively in the full range of Earth orbiting missions from LEO to GEO and beyond. Navigator employs special signal processing algorithms in radiation-hardened hardware that enable very fast signal acquisition capabilities and, more importantly, greatly improved sensitivity (a 10-dB improvement over previous space-based GPS receivers). Because of these unique capabilities, Navigator has generated a large amount of interest in the spacecraft navigation community. The first flight version of the receiver has been integrated into a relative-navigation experiment on the Shuttle-based Hubble Space Telescope Servicing Mission 4, due to launch in 2009. Navigator will be also serving as a critical navigation sensor on NASA's Magnetospheric Multiscale mission, which is one of NASA's first high-altitude formation-flying missions, NASA's Global Precipitation Measurement mission, and the Air Force Research Lab's Plug-and-Play spacecraft. Finally, key aspects of the Navigator design are being integrated into a GPS receiver being developed for NASA's Orion Crew Exploration Vehicle. View full abstract»

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  • GNSS Signal Acquisition in the Presence of Sign Transition

    Page(s): 557 - 570
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1690 KB) |  | HTML iconHTML  

    In this paper, the problem of acquiring the pilot and data channel of the next-generation systems (as Galileo, and GPS modernization) is addressed and analyzed, focusing the majority of the attention to the problem of managing the higher sign reversal transition rate due to the navigation message in the data channel and to the secondary code in the pilot channel. It must be considered that in the case of the Galileo E1 signals, each period of the spreading sequence may suffer of a sign change which can reduce the correlation gain. Moreover, the sign transition occurred on the block of samples being processed produces a correlation peak splitting along the Doppler axis of the search space matrix constructed during the acquisition phase and this may lead to a wrong Doppler estimate. Here, we propose an acquisition detection methodology in order to cope with the aforementioned impairments. The main idea behind the proposed algorithm derives by the fact that even though a sign transition occurs, the total useful signal energy remains unchanged, so it is possible to process the search space in order to recover in a nonambiguous way not only the presence of a satellite but also the correct spreading code delay phase and its Doppler shift. The effectiveness of the proposed method will be deeply assessed with a simulation campaign in terms of detection and false detection rate, which will be presented by means of the so-called receiver operative characteristic curves and compared with the state-of-the-art acquisition methodologies. View full abstract»

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  • Closed-Loop Sequential Signal Processing and Open-Loop Batch Processing Approaches for GNSS Receiver Design

    Page(s): 571 - 586
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    Global navigation satellite system (GNSS) receiver design is considered in terms of closed-loop and open-loop receiver architectures that utilize sequential and batch processing techniques. The paper uses the Global Positioning System (GPS) as a case study to demonstrate that an open-loop approach that combines batch and sequential signal processing improves GNSS signal tracking characteristics as compared to the traditionally applied closed-loop sequential receiver design for a number of important application areas. Particularly, for flight test scenarios considered, it is demonstrated that open-loop batch/sequential processing improves the GPS tracking margin by 8 dB as compared to the closed-loop sequential tracking for the case of deep GPS/Inertial Navigation System (INS) integration mode that performs code and carrier phase tracking and data bit recovery. View full abstract»

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  • Positioning Accuracy Improvement With Differential Correlation

    Page(s): 587 - 598
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (475 KB) |  | HTML iconHTML  

    The success of satellite navigation in the mass consumer market will depend greatly on its performance in deep urban and moderate indoor environments. The signal obstructions in these environments lead to low signal-to-noise ratios, which substantially degrade the positioning accuracy of GPS and Galileo receivers. New ranging techniques are required to increase the positioning accuracy to an acceptable level for pedestrian navigation in urban and indoor environments. Differential correlation is such a new ranging technique. It can replace the state-of-the-art noncoherent integration with very little implementation overheads. It improves performance as it utilizes the statistical properties of GPS and Galileo signals. This paper analyzes the resulting positioning accuracy for GPS and Galileo receivers when differential correlation is utilized. The probability density functions for early-late code discrimination with differential correlation are algebraically derived in closed form. The resulting positioning accuracies are presented for signals with binary phase shift keying (BPSK) and binary offset carrier (BOC) modulation in a large variety of reception conditions. The results indicate that differential correlation can replace noncoherent integration for all relevant configurations of GPS and Galileo receivers. It increases the accuracy of the measured receiver-to-satellite distances by 40% to 77% when compared to noncoherent integration. View full abstract»

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  • Compass-M1 Broadcast Codes in E2, E5b, and E6 Frequency Bands

    Page(s): 599 - 612
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1932 KB) |  | HTML iconHTML  

    With the launch of the compass-M1 satellite on 14 April 2007, China is set to become the latest entrant into global navigation satellite systems (GNSS). Understanding the interoperability and integration of the Chinese Compass with the current GNSS, namely the U.S. Global Positioning System (GPS), the European Galileo, and the Russian GLONASS, requires knowing and understanding its signal structures-specifically its pseudorandom noise (PRN) codes and code structures. Moreover, the knowledge of the code is a prerequisite for designing receivers capable of acquiring and tracking the satellite. More important is determining if the signal may degrade performance of the current GNSS in the form of interference. Finally, we are eager to learn from the code and signal design of our Chinese colleagues. For this research, we set up a 1.8-m dish antenna to collect the broadcast Compass-M1 signals. Even with the dish antenna, the received signal is still weak and buried in thermal noise. We then apply signal processing and are able to extract the PRN code chips out of the noise in all three frequency bands. The PRN codes are thousands of bits long. In addition, we find that the Compass-M1 PRN codes in all frequency bands are Gold codes. We also derive the Gold code generators to represents thousands of code chips with fewer than a hundred bits. Finally, we implement these codes in our software receiver to verify and validate our analysis. View full abstract»

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  • Collaborative Code Tracking of Composite GNSS Signals

    Page(s): 613 - 626
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1659 KB) |  | HTML iconHTML  

    Modern and modernized global navigation satellite system (GNSS) signals exhibit significant structural innovations such as the use of two channels, namely the data and pilot components, which separately carry the navigation message and ranging information. These innovations have stimulated the development of new techniques that fully exploit the potential of these new signals. This paper analyses two different strategies, noncoherent and coherent channel combining, that enable collaborative tracking of the data and pilot components, thus circumventing the drawback of having the available power split between two channels. Traditional single channel discriminators are modified in order to accommodate the data/pilot structure and the different combining strategies. The performance of each algorithm is analyzed in terms of tracking jitter and a new characterization, based on the sign error rate (SER), is proposed for evaluating the coherent channel combining with sign recovery. This characterization, supported by simulations, is, to the best of the authors' knowledge, new and represents one of the main contributions of this paper. View full abstract»

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  • A Nonlinear Code Tracking Filter for GPS-Based Navigation

    Page(s): 627 - 638
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1305 KB) |  | HTML iconHTML  

    Current Global Positioning System (GPS)-based navigation systems are highly susceptible to unintentional and intentional jamming due to relatively low signal power at the receiver antenna and, in part, due to suboptimal code tracking loop designs that do not account for measurement nonlinearities near loss-of-lock. A nonlinear code tracking filter is developed whose architecture is based on a rigorous minimum-variance solution of the navigation problem, rather than using prespecified tracking loop architectures. The filter implementation can be viewed in terms of the classical notions of error detector functions, which depend on signal-to-noise ratio (SNR) and root mean square (rms) code tracking error. Detector functions are defined for both code tracking error and code tracking error variance. The filter responds more rapidly than current designs to rapidly varying jammer power due to a measurement-dependent term in the covariance calculations. Extended-range tracking is utilized, yielding linear state vector error detector functions (i.e., the filter is essentially optimum) out to the maximum allowed by the correlator range, and reducing the need for reacquisition. Significant antijam improvements relative to current designs are predicted from high-fidelity simulation and hardware demonstrations. Computational requirements are comparable to extended Kalman filter/vector tracking loop techniques. View full abstract»

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  • Nonlinear Filtering in GNSS Pseudorange Dynamics Estimation Combining Code Delay and Carrier Phase

    Page(s): 639 - 650
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (605 KB) |  | HTML iconHTML  

    In Global Navigation Satellite System (GNSS) receivers, code delay measurements yield unambiguous but noisy pseudorange estimates. On the other hand, the pseudorange obtained with carrier phase measurements is almost noiseless, but is affected by an ambiguity term multiple of the carrier wavelength. In this paper, we propose a structure for code and carrier phase estimation and a novel technique to merge those estimates. The overall architecture consists of 1) a bank of correlators, each one feeding an extended Kalman filter, 2) an interpolation algorithm to produce the best code delay and carrier phase estimates, and 3) a nonlinear filter that combines these estimates to reduce progressively the phase ambiguity, yielding precise pseudorange estimates in high dynamics scenarios and in the presence of weak signals. The proposed approach is able to accommodate the majority of the new GNSS signals (modernized GPS and Galileo), produces smaller mean square errors than the conventional code/phase merge technique (Hatch filter), is robust to transients that may affect the phase estimation during the reception of weak signals, and is free from false code-locks. View full abstract»

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  • Phase/Frequency Tracking in a GNSS Software Receiver

    Page(s): 651 - 660
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (845 KB) |  | HTML iconHTML  

    In the paper, a software-based technique for the tracking of frequency and phase of Global Navigation Satellite System (GNSS) signals is proposed. It is shown that a software-based receiver with precomputed, zero-phase carrier replicas for phase tracking is subject to phase jump in phase tracking and ambiguity problems in frequency estimation. A phase/frequency tracking architecture is proposed in which the frequency of the incoming signal is estimated based on a lead-lag structure which is similar to a traditional delay locked loop and the phase, after de-rotation, is estimated using a frequency-aiding phase locked loop. The effects of thermal noise and resolution-induced noise are analyzed and verified using simulation. The significance of frequency aiding in enhancing the phase tracking response is also described. View full abstract»

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  • Performance Analysis of Vector Tracking Algorithms for Weak GPS Signals in High Dynamics

    Page(s): 661 - 673
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1635 KB) |  | HTML iconHTML  

    This paper explores the ability of vector tracking algorithms to track weak Global Positioning System (GPS) signals in high dynamic environments. Traditional GPS receivers use tracking loops to track the GPS signals. The signals from each satellite are processed independently. In contrast, vector-based methods do not use tracking loops. Instead, all the satellite signals are tracked by a lone Kalman filter. The Kalman filter combines the tasks of signal tracking and navigation into a single algorithm. Vector-based methods can perform better than traditional methods in environments with high dynamics and low signal power. A performance analysis of the vector tracking algorithms is included. The ability of the algorithms to operate as a function of carrier to noise power density ratio, user dynamics, and number of satellites being used is explored. The vector tracking methods are demonstrated using data from a high fidelity GPS simulator. The simulation results show the vector tracking algorithms operating at a carrier to noise power density ratio of 19 dB-Hz through 2 G, 4 G, and 8 G coordinated turns. The vector tracking algorithms are also shown operating through 2 G and 4 G turns at a carrier to noise power density ratio of 16 dB-Hz. View full abstract»

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  • Multifrequency, Multisatellite Vector Phase-Locked Loop for Robust Carrier Tracking

    Page(s): 674 - 681
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    A new vector phase-locked loop (PLL) for joint tracking of carrier phase from all satellites on multiple frequencies is presented. It increases the robustness to ionospheric scintillations, carrier phase multipath and interference from jammer. The tracking error is split into a position error, a clock offset, ionospheric, and tropospheric errors which are filtered individually. The filter coefficients are optimized with orthogonal projections of the tracking error that eliminate the nuisance parameters. The tracking performance is determined recursively, and a significant reduction of the tracking error is observed during strong ionospheric scintillations with deep amplitude fades. View full abstract»

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  • A General Model of Multipath Error for Coherently Tracked BOC Modulated Signals

    Page(s): 682 - 694
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    A new class of signals, modulated using a binary offset carrier (BOC), is being implemented and tested in multiple Global Navigation Satellite Systems (GNSSs). A receivers that tracks a BOC signal is considered more resistant to interference than tracking a signal modulated with a binary phase shift key (BPSK). In this study, that resistance is evaluated by analytically modeling the impact of multipath interference on signal tracking. Signal tracking error is then mapped to errors in the measurements produced by GNSS receivers, pseudorange and carrier phase. The model is general so that it can apply to measurements derived from any BOC modulated signal, including those from Galileo or modernized GLONASS systems. The model incorporates a single reflector and signal tracking that is coherent with signal phase. The timing between early and late correlation processes is left as a free parameter in order to emulate the design known as narrow correlation. The error models are applied to predict errors inserted into the GPS control segment ephemeris generation process, when control segment begins tracking the BOC modulated M-Code. First, conditions by which it is possible for M-Code receivers to exhibit more multipath error than P/Y-Code receivers are solved. Second, the mean multipath error is examined. For carrier phase, the condition for zero mean is proven to be uniformly true. In contrast, pseudorange exhibits zero mean only in certain tracking conditions. View full abstract»

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  • A Bayesian Approach to Multipath Mitigation in GNSS Receivers

    Page(s): 695 - 706
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    Multipath is known to be one of the most dominant sources of accuracy degradation in satellite-based navigation systems. Multipath may cause biased position estimates that could jeopardize high-precision applications. This paper considers the problem of tracking the time-variant synchronization parameters of both the line-of-sight signal (LOSS) and its multipath replicas. In particular, the proposed algorithm tracks time-delays, amplitudes, phases and proposes a procedure to extract Doppler shifts from complex amplitudes. However, the interest is focused on LOSS time-delay estimates, since those provide the means to compute user's position. The undertaken Bayesian approach is implemented by a particle filter. The selection of the importance density function, from which particles are generated, is performed using a Gaussian approximation of the posterior function. This selection provides a particle generating function close to the optimal, which yields to an efficient usage of particles. The complex-linear part of the model, i.e., complex amplitudes, is tackled by a Rao-Blackwellization procedure that implements a complex Kalman filter for each generated particle, thus reducing the computational load. Computer simulation results are compared to other Bayesian filtering alternatives (namely, the extended Kalman filter, the unscented Kalman filter and the sequential importance resampling algorithms) and the posterior Cramer-Rao bound. View full abstract»

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  • Simulating Ionosphere-Induced Scintillation for Testing GPS Receiver Phase Tracking Loops

    Page(s): 707 - 715
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    A simple model is proposed for simulating equatorial transionospheric radio wave scintillation. The model can be used to test Global Positioning System phase tracking loops for scintillation robustness because it captures the scintillation properties that affect such loops. In the model, scintillation amplitude is assumed to follow a Rice distribution, and the spectrum of the rapidly-varying component of complex scintillation is assumed to follow that of a low-pass second-order Butterworth filter. These assumptions are justified, and the model validated, by comparison with phase-screen-generated and empirical scintillation data in realistic tracking loop tests. The model can be mechanized as a scintillation simulator that expects only two input parameters: the scintillation index S 4 and the decorrelation time tau0. Hardware-in-the-loop tests show how the model can be used to test the scintillation robustness of any compatible GPS receiver. View full abstract»

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  • Nonlinear Tracking-Differentiator for Velocity Determination Using Carrier Phase Measurements

    Page(s): 716 - 725
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3459 KB) |  | HTML iconHTML  

    Differential computation is necessary in velocity determination using carrier phase measurements from the global navigation satellite system (GNSS). A method of nonlinear tracking-differentiator is proposed to suppress both noise amplification and time delay introduced by differentiation. The carrier phase rate can be derived more precisely using the nonlinear tracking-differentiator and the time delay is compensated by second-order derivative estimation from the outputs of the differentiator. Simulation and experiments for the Gobal Positioning System (GPS) and Chinese Beidou system show that this approach can effectively improve the accuracy of velocity determination, especially under noisy or bad geometry situations. View full abstract»

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    Page(s): 726 - 727
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    Page(s): 728
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    Page(s): 729
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    Page(s): 730
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    Page(s): 731
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    Page(s): 732
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Aims & Scope

The Journal of Selected Topics in Signal Processing (J-STSP) solicits special issues on topics that cover the entire scope of the IEEE Signal Processing Society including the theory and application of filtering, coding, transmitting, estimating, detecting, analyzing, recognizing, synthesizing, recording, and reproducing signals by digital or analog devices or techniques.

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Meet Our Editors

Editor-in-Chief
Fernando Pereira
Instituto Superior Técnico