Glossary and Acronyms

C/A code -The standard (Course/Acquisition) GPS code. A sequence of 1023 pseudo-random, binary, biphase modulations on the GPS carrier at a chip rate of 1.023 MHz. Also known as the "civilian code."

Control segment - A world-wide network of GPS monitor and control stations that ensure the accuracy of satellite positions and their clocks.

Differential positioning - Accurate measurement of the relative positions of two receivers tracking the same GPS signals.

DGPS - Differential GPS

Ephemeris - The predictions of current satellite position that are transmitted to the user in the data message. A table given for successive days the positions of heavenly bodies.

GLONASS - GLObal NAvigation Satellite System - Russian

GPS - Global Positioning System

Latitude - the location on the Earth measuring how far north or south of the equator one is.

Longitude - the location on the Earth measured east or west

LORAN - LOng RAnge Navigation

Nautical mile - length measurement used in navigation and is 1/60 of 1 degree of the equator. One nautical mile is 6,080.2 feet whereas one mile is 5,280 feet.

NAVSTAR GPS - the Navigation Satellite Timing and Ranging GPS

P-code - The Precise code. A very long sequence of pseudo random binary biphase modulations on the GPS carrier at a chip rate of 10.23 MHz which repeats about every 267 days. Each one week segment of this code is unique to one GPS satellite and is reset each week.

Precise Positioning Service (PPS) - The most accurate dynamic positioning possible with standard GPS, based on the dual frequency P-code and no SA.

Pseudolite - A ground-based differential GPS receiver which transmits a signal like that of an actual GPS satellite, and can be used for ranging.

RTK - Real Time Kinematic

Satellite constellation - The arrangement in space of a set of satellites.

Selective Availability (SA) - A policy adopted by the Department of Defense to introduce some intentional clock noise into the GPS satellite signals thereby degrading their accuracy for civilian users.

Space segment - The part of the whole GPS system that is in space, i.e. the satellites.

Standard Positioning Service (SPS) - The normal civilian positioning accuracy obtained by using the single frequency C/A code.

User segment - The part of the whole GPS system that includes the receivers of GPS signals.


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