The Soviet Union's GLONASS Navigation Satellites

GLONASS (Global Orbiting Navigation Satellite System) is the most recent satellite navigation system developed by the Soviet Union and currently in the pre-operational stage. Obvious parallels exist between GLONASS and the NAVSTAR Global Positioning System (GPS) developed in the United States and also, at present, in a pre-operational phase. In the progress towards operational status, the launch capability for NAVSTAR satellites has been seriously affected by the recent failure of the Space Shuttle Challenger, clearly increasing the prospects of GLONASS reaching operational status first. It is therefore the main purpose of this paper to discuss certain aspects of the GLONASS satellite navigation system, in particular its orbital features and radio-frequency signal characteristics. Comparisons with NAVSTAR are inevitable and for this reason, the paper begins with a brief resume of relevant features of the NAVSTAR GPS system for later reference. The main section of the paper then deals with orbital behaviour, radio frequency signal structure and channelisation using NAVSTAR as a reference point for discussion.     

Characterization of NAVSTAR GPS and GLONASS on-board clocks

Investigation into navigation satellite on board clock frequency references and performance are reported. The focus is on the stability of the clocks aboard the NAVSTAR GPS (Global Positioning System) and GLONASS satellites as well as those used by their respective maser control stations and associated time scales. Allan-variance techniques have been applied to determine the long-term time-domain behavior of satellite clocks in an attempt to identify different regions of power spectral density. Coupled with analysis of relative-frequency drift over a period of many weeks, this behavior allows the type of satellite onboard standard to be tentatively identified. The known nature of the GPS clocks has shown that the different types of clocks aboard the satellites (crystal, rubidium, and cesium) are distinguishable given a sufficient sample time. The same approach has been applied to the GLONASS satellites, and a comparison of the results obtained from GPS has allowed conjecture on the type of clock used by the GLONASS satellites. It appears that GLONASS has used clocks of the quality of rubidium atomic oscillators since at least 1986, and that the quality and performance of onboard standards have increased steadily with time. Some current satellites perform well enough in terms of frequency drift, flicker FM noise floor, and long-term stability to compare favorably with the cesium beam standards carried on NAVSTAR GPS satellites launched in 1983-84     

New approach to a multistatic passive radar sensor for air/spacedefense

A method to apply the latest technology in Global Navigation Satellite Systems (GNSS), in particular the U.S. NAVSTAR GPS (NAVigation System for Timing And Ranging Global Positioning System) and the Russian GLONASS (GLObal'naya Nqvigatsionnaya Sputnikovaya Sistema), as a silent multistatic or parasitic radar for air defense is described. These satellite systems serving as navigational aids are well suited for low power radar applications due to the similarity and compatibility of the transmitted satellite signals with modern radar signals, such as spread spectrum modulation and Pseudo Random Noise (PRN) codes. Preliminary flight tests with airships, jet and propeller aircraft, helicopter, anti tank missiles and spaceborne targets (MIR) to study effects have been conducted     

A relative navigation system for formation flight

A relative navigation system based on both the Inertial Navigation System (INS) and the Global Positioning System (GPS) is developed to support situational awareness during formation flight. The architecture of the system requires an INS/GPS integration across two aircraft via a data link. A fault-tolerant federated filter is used to estimate the relative INS errors based on relative GPS measurements and a range measurement obtained from the data link. The filter is constructed based on a reduced-order model of the relative INS error process. A method for analyzing the filter performance is presented. A case involving two helicopters in formation flight is studied under three different night trajectories to account for the effect of vehicle motion on the INS state transition matrix. The results of the covariance analysis are compared with actual night results over an instrumented test range.     

Navigation sensors and systems in GNSS degraded and denied environments

Position, velocity, and timing(PVT) signals from the Global Positioning System(GPS)are used throughout the world but the availability and reliability of these signals in all environments has become a subject of concern for both civilian and military applications. This presentation summarizes recent advances in navigation sensor technology, including GPS, inertial, and other navigation aids that address these concerns. Also addressed are developments in sensor integration technology with several examples described, including the Bluefin-21 system mechanization.     

Effects of ionospheric scintillation on differential demodulation of GPS data

Global Positioning System (GPS) receivers that must operate under fading propagation conditions can use differential phase-shift keying (DPSK) and reference bits to reliably demodulate GPS data. The demodulation performance of such receivers is analyzed for nonfading and Rayleigh fading channels. Theoretical results derived here are compared with measured error rates taken during scintillation testing of a prototype GPS/DPSK receiver.     

差分GPS在飞行试验中的应用

ＧＰＳ是美国正在大力发展的高精度卫星导航系统。主要叙述差分ＧＰＳ在飞行试验中的应用，首先介绍ＧＰＳ的伪距测量定位原理和测速原理，ＤＧＰＳ提高定位精度的原理。     

Enhancing filter robustness in cascaded GPS-INS integrations

Filter robustness is defined herein as the ability of the Global Positioning System/Inertial Navigation System (GPS-INS) Kalman filter to cope with adverse environments and input conditions, to successfully identify such conditions and to take evasive action. The formulation of two such techniques for a cascaded GPS-INS Kalman filter integration is discussed This is an integration in which the navigation solution from a GPS receiver is used as a measurement in the filter to estimate inertial errors and instrument biases. The first technique presented discusses the handling of GPS position biases. These are due to errors in the GPS satellite segment, and are known to be unobservable. They change levels when a satellite constellation change occurs, at which point they introduce undesirable filter response transients. A method of suppressing these transients is presented. The second technique presented deals with the proper identification of the filter measurement noise. Successful formulation of the noise statistics is a factor vital to the healthy estimation of the filter gains and operation. Furthermore, confidence in the formulation of these statistics can lead to the proper screening and rejection of bad data in the filter. A method of formulating the filter noise statistics dynamically based on inputs from the GPS and the INS is discussed     

On precision of GPS C/A code

The accuracy of clear acquisition (C/A) code for civilian users of the Global Positioning System, in comparison with precise (P) code, is discussed. Different design techniques for GPS receivers are presented. The 1-ms range ambiguity of C/A code is discussed, and a solution is given. Intentional degradation of GPS signals and denial of accuracy is discussed, and some predictions are presented. The issue of government support and protection of domestic GPS industry against possible unfair international competition is briefly discussed     

Flight Test Evaluation of a New GPS Attitude Determination Algorithm

A new Global Positioning System (GPS) Attitude Determination Algorithm (GADA) is proposed, featuring the capability to keep its accuracy, even when the line-of-sight angle (LOS) of a given satellite vehicle (SV) is below the GPS horizontal antenna plane (HAP). The GADA model has been developed and evaluated through simulations and flight test campaigns, which comprised static and dynamic flight profiles, to best characterize the algorithm performance. As attitude reference a complete flight tests instrumentation (FTI) system was integrated into the testbed for the flight test campaign. The attitude measurements given by GADA and REQUEST algorithms are compared with those given by FTI (i.e., reference system). The results show that GADA accuracy is significantly better than that of REQUEST, for all flight conditions.     

Processing of filtered GPS data

General sufficiency conditions are developed for the stability of a discrete-time cascaded-filter architecture. An application of the result is in the filtering of prefiltered Global Positioning System (GPS) data during times in which the GPS receiver is tracking less than four satellites. Simulation results are presented for the case where the master filter processes the GPS filter estimate after the GPS filter attains uniform complete observability and controllability following its third filter cycle as well as the case where the observability condition is not met     

Development of GPS-based attitude determination algorithms

This paper describes two Global Positioning System (GPS) based attitude determination algorithms which contain steps of integer ambiguity resolution and attitude computation. The first algorithm extends the ambiguity function method to account for the unique requirement of attitude determination. The second algorithm explores the artificial neural network approach to find the attitude. A test platform is set up for verifying these algorithms.     

Position-fixing using the USSR's GLONASS C/A code

The possibility of the USSR's global satellite navigation system GLONASS and the NAVSTAR Global Positioning System using a common navigation system can only be determined following exhaustive testing of two systems in a variety of satellite and receiver modes and configurations. The authors describe their first attempts to carry out basic position-fixing and timing measurements with a single-channel, sequencing digital receiver in a C/A code phase-measurement mode using the GLONASS satellites. The receiver used to produce the fixes was a digital sequencing unit with a single stage of downconversion and followed by 1-bit quantization. Code acquisition was accomplished using 1-Q channels measuring code phase. The number of satellites available in the present preoperational phase heavily restricts the time and satellite configurations which can be tested. However, the results have encouraged the authors to propose a range of experiments aimed at evaluating the two systems and eventual integration     

Instantaneous GPS attitude determination

A procedure for instantaneous GPS (Global Positioning Satellite) attitude determination, i.e., a solution for the GPS integrated carrier Doppler wavelength ambiguities using only measurements at a single epoch, is described. Most previous techniques to solve the phase ambiguity problem have required some form of time history processing relying on GPS satellite and/or user motion to provide enough geometry change to eliminate false solutions. The algorithm described assumes three noncollinear antennas and integrated carrier Doppler measurements from four or more satellites. Double-difference processing provides at least three independent observables for the two antenna separation vectors to compute the three attitude Euler angles     

Field test results prove GPS performance and utility

Statistical and operational results of extensive government field-testing of the Rockwell-Collins Global Positioning System (GPS) units are summarized. The equipment has exhibited better than 16-m spherical-error probable-position accuracy in over 6300 hours of testing conducted during the past two years. One-channel, two-channel, and five-channel receivers were subjected to thorough evaluation. Their respective signal-processing and data-processing architectures are described. Data highlighting dynamic position accuracy, static position accuracy, acquisition times, and field reliability are presented. GPS equipment integration and operation with nine different host vehicles is described. The results of mission scenarios, such as area navigation, rendezvous, and weapon delivery, are presented     

Reduction of interference from DGPS transmissions in the MF bandusing a GMSK modulation scheme

The accuracy of the Global Positioning System (GPS) can be improved by differential techniques. For maritime applications a DGPS service with transmissions by maritime radiobeacons in the MF band is provided. It offers a position accuracy of approximately 5 m. For the data link a minimum shift keying (MSK) modulation scheme has been recommended. The adjacent channel interference at the maximum transmission rate might not be consistent with existing frequency plans     

Ensuring GPS navigation integrity using receiver autonomousintegrity monitoring

The many advantages of Global Positioning System (GPS) based navigation have created a tremendous amount of interest in using GPS as the primary navigation aid onboard commercial and civil aircraft. Even in the presence of Selective Availability, the accuracy of GPS is sufficient to guide aircraft point-to-point between airports without requiring other navigation aids such as VOR or DME. Unfortunately, there is a finite probability that a GPS satellite will fail, causing the transmission of potentially misleading navigation information. Thus, before GPS can be widely adopted as a navigation aid, techniques must be devised to detect any possible failures and notify the user prior to the degradation of navigation accuracy. This paper discusses the problem of detecting possible GPS satellite failures using a technique called Receiver Autonomous Integrity Monitoring (RAIM)     

Measuring Aircraft Carrier Flexure in Support of Autonomous Aircraft Landings

This paper quantifies the experimental measurements of aircraft carrier flexure (deformation) at sea in support of the United States Department of Defense sea-based Joint Precision Approach and Landing System (JPALS) that aims to deliver automatic landing capabilities to inbound aircraft aboard aircraft carriers. The methodology for measuring ship flexure using the Global Positioning System (GPS) and inertial sensors is described. Results indicate that flexure on the aircraft carrier used for testing has a standard deviation of approximately 1–2 cm. For the ship tested, the most significant flexure effects are in the port/starboard direction and correlate best with roll or lateral acceleration.     

Aiming at a 1-cm Orbit for Low Earth Orbiters: Reduced-Dynamic and Kinematic Precise Orbit Determination

The computation of high-accuracy orbits is a prerequisite for the success of Low Earth Orbiter (LEO) missions such as CHAMP, GRACE and GOCE. The mission objectives of these satellites cannot be reached without computing orbits with an accuracy at the few cm level. Such a level of accuracy might be achieved with the techniques of reduced-dynamic and kinematic precise orbit determination (POD) assuming continuous Satellite-to-Satellite Tracking (SST) by the Global Positioning System (GPS). Both techniques have reached a high level of maturity and have been successfully applied to missions in the past, for example to TOPEX/POSEIDON (T/P), leading to (sub-)decimeter orbit accuracy. New LEO gravity missions are (to be) equipped with advanced GPS receivers promising to provide very high quality SST observations thereby opening the possibility for computing cm-level accuracy orbits. The computation of orbits at this accuracy level does not only require high-quality GPS receivers, but also advanced and demanding observation preprocessing and correction algorithms. Moreover, sophisticated parameter estimation schemes need to be adapted and extended to allow the computation of such orbits. Finally, reliable methods need to be employed for assessing the orbit quality and providing feedback to the different processing steps in the orbit computation process. This revised version was published online in August 2006 with corrections to the Cover Date.