Navigation Systems Lecture 2: Fundamentals of Satellite Navigation

A comprehensive set of vocabulary flashcards covering the fundamentals of satellite navigation, including system architecture, signal processing, and augmentation techniques based on the TTT4150 lecture.

PNT

Positioning, Navigation, and Timing; the three primary purposes for which satellite navigation receivers are used.

Control Segment

The ground segment of a GNSS architecture containing ground stations that communicate with, monitor, and correct errors in the satellites.

Space Segment

The portion of the GNSS architecture consisting of the satellites in orbit.

User Segment

The receivers that consume satellite navigation signals to calculate position, time, or velocity.

WGS84

World Geodetic System 1984; an ellipsoidal model for the earth with the origin at the earth's center of mass, defining specific Z and X axes based on the IERS Reference Pole and Meridian.

Ephemeris

Parameters containing accurate orbit and clock terms for individual satellites, typically valid for only 8 hours due to the use of model approximations.

Almanac

Approximate information about all satellites in a constellation that helps a user determine which satellites are over the horizon and their expected doppler shifts.

Autonav Mode

A satellite mode where vehicles use cross-link connections to maintain clock and orbital accuracy even if contact with ground stations is lost.

Sidereal Day

The time required for the Earth to turn so distant stars appear in the same position, approximately $23:56$ hours; GPS satellites orbit twice per sidereal day.

Nadir Pointing

A satellite orientation strategy where the spacecraft orients itself to point straight down toward the Earth.

Faraday Rotation

The rotation of a signal's polarization as it passes through the ionosphere; GPS uses circular polarization to remain insensitive to this effect.

Dispersive Medium

A medium, such as the ionosphere, where the amount of signal delay is related to the frequency of the signal.

TECU

Total Electron Content Unit; represents $10^{16}$ electrons encountered by a signal; one TECU causes a range bias of approximately $0.162\,m$ for the L1 frequency.

CDMA

Code Division Multiple Access; a multiple access scheme where each satellite signal has its own unique code sequence, allowing multiple satellites to be received simultaneously on the same frequency.

FDMA

Frequency Division Multiple Access; the multiple access scheme used by GLONASS where satellites transmit on different frequency channels.

DSSS

Direct Sequence Spread Spectrum; a technique where a narrowband data signal is multiplied by a high-rate signal to spread the energy over a much wider frequency spectrum.

Gold Codes

A family of codes used in GPS that provide low cross-correlation (lower than $-21\,dB$) and low off-peak autocorrelation.

Coherent Integration Time

The amount of time a receiver 'adds up' a signal without squaring it to boost the Signal-to-Noise Ratio (SNR).

DLL

Delay Locked Loop; a tracking architecture that uses a feedback loop to steer the local code to match the incoming spreading code.

TOW

Time of Week; a value derived from the Z-count in the Handover Word (HOW) that gives the number of seconds since the start of the week in 6-second increments.

Selective Availability (SA)

An intentional pseudorandom wander of the satellite range used by the U.S. military to degrade GPS accuracy for civil users; it was deactivated in 2000.

SBAS

Space Based Augmentation System; systems like WAAS or EGNOS that use geostationary satellites to provide atmospheric models and integrity data to improve accuracy to about $0.5\,m$.

RTK

Real Time Kinematic; a high-accuracy positioning technique that uses carrier phase measurements and double differencing to solve for ambiguous cycles and achieve cm-level accuracy.

PPP

Precise Point Positioning; a technique that provides sub-decimeter accuracy without a local base station by using dual-frequency measurements and external high-accuracy orbit/clock correction data.