Introduction and Fundamentals of Satellite Navigation

Flashcards covering the definitions of key terms from the introduction to GNSS and the fundamentals of satellite navigation including coordinate systems, orbital mechanics, signal types, and time scales.

Navigation

The science of getting a craft or person from one place to another.

Radionavigation aids

Navigation aids that transmit electronic signals to enable a user to compute their position.

Global Navigation Satellite System (GNSS)

The collection of all SATNAV systems and their augmentations, providing three-dimensional position, velocity, and time information.

Core Constellations

Global constellations within the GNSS, nominally consisting of 24 or more medium Earth orbit (MEO) satellites.

Passive Ranging

A technique where users only receive signals, allowing the system to serve an unlimited number of users.

One-way Time of Arrival (TOA) ranging

A technique where satellite transmissions are referenced to atomic frequency standards to determine the transit time and range.

Direct-Sequence Spread Spectrum

A technique used by SATNAV systems to broadcast ranging codes and navigation data on two or more frequencies.

Standard Positioning Service (SPS)

A GPS service free of direct user fees, used by civil and commercial users worldwide.

Precise Positioning Service (PPS)

An encrypted GPS service intended for military and authorized government users.

GLONASS

The Russian Global Navigation Satellite System, which provides multifrequency L-band navigation services.

Galileo

The European Union's satellite navigation system designed specifically for civilian use worldwide.

BeiDou Navigation Satellite System (BDS)

The Chinese multifunctional satellite navigation system integrating RNSS, RDSS, and wide-area differential services.

Radiodetermination Service (RDSS)

A service unique to BDS that includes rapid positioning, short messaging, and precision timing via GEO satellites.

Quasi-Zenith Satellite System (QZSS)

A regional Japanese satellite system providing high-elevation coverage to complement and augment GPS over Japan.

Navigation with Indian Constellation (NavIC)

The Indian regional satellite system, formerly IRNSS, transmitting in both the L5-band and S-band.

Differential GNSS (DGNSS)

A method of improving positioning performance by using one or more reference stations at known locations to provide corrections.

Pseudorange ($\rho$)

The distance determined by multiplying the signal propagation velocity by the time difference between the satellite and receiver clocks.

Earth-Centered Inertial (ECI)

A coordinate system with its origin at the center of mass of the Earth and axes fixed with respect to the stars.

Earth-Centered Earth-Fixed (ECEF)

A Cartesian coordinate system that rotates with the Earth, commonly used to compute latitude, longitude, and height.

Sagnac effect

A correction needed in the ECEF system due to the Earth's rotation during the signal transit interval.

Geodetic Altitude ($h$)

The minimum distance between the user and the reference ellipsoid.

Geoid

The surface of constant geopotential, $\text{W} = \text{W}_0$, representing global mean sea level.

Keplerian Orbital Elements

A set of six parameters (semimajor axis, eccentricity, inclination, longitude of ascending node, argument of perigee, and mean anomaly) that define an orbit.

Inclination ($i$)

The dihedral angle between the Earth's equatorial plane and the satellite's orbital plane.

Stationkeeping

The requirement to maintain orbital parameters within a specified range through periodic maneuvers.

Walker Constellation

A constellation design using circular inclined orbits of equal altitude and inclination with specific notation $\text{T/P/F}$.

L-band

The radio frequency range of $1$ to $2\,GHz$, commonly used for GNSS signals.

Binary Phase Shift Keying (BPSK)

A digital signaling scheme where the RF carrier is shifted by $180^{\circ}$ to represent digital bits.

Pseudorandom Noise (PRN) code

A deterministic, periodic binary sequence used for spreading the spectrum in GNSS signals.

Binary Offset Carrier (BOC)

A modulation technique that employs portions of a square wave for spreading symbols to enhance performance.

Pilot Component

A signal component not modulated by navigation data, allowing for more robust tracking in challenging environments.

Allan Variance ($\sigma_y(\tau)$)

The standard method for describing the short-term stability of oscillators in the time domain.

Atomic Second

The duration of $9,192,631,770$ periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom.

Universal Time 1 (UT1)

A nonuniform time scale based on the Earth's rotation angle with respect to the Sun.

International Atomic Time (TAI)

A uniform time scale derived from over $400$ atomic standards located in laboratories worldwide.

Coordinated Universal Time (UTC)

A composite time scale comprised of TAI and leap seconds to maintain synchronization with the Earth's rotation.