Global Navigation Satellite System(GNSS)• Used to determine the location of a user’s receiver anywhere on earth

• GPSUS Department of Defense

• GlonassRussian Federation Department of Defense

• Beidou 2 / CompassChinese system

• GalileoEuropean initiative

• Augmentation systems WAAS, EGNOS, MSAS, GAGAN

The Global Positioning System (GPS)

• A satellite-based navigation system

• N/W of 24 satellites placed into orbit

• NAVSTAR, the official U.S. Department of Defense

name.

• Approximately 12,000 miles above the earth.

• Powered by solar energy

The Global Positioning System (2)• Originally intended for military applications • Later became available for civilian use.

• Works in any weather conditions

• Works anywhere in the world, 24 hours a day

• No subscription fees or setup charges to use GPS

Some facts about Navstar

• First GPS satellite launched in 1978

• A full constellation of 24 satellites was achieved in 1994

• Each satellite built to last about 10 years

• Replacements are constantly being built and launched into

orbit.

• A GPS satellite weighs approximately 2,000 pound

• Transmitter power is only 50 watts or less

GPS Structure• Space segment

composed of the orbiting GPS satellites

• Control segment

a master control station (MCS),

an alternate master control station,

four dedicated ground antennas and

six dedicated monitor stations

GPS Structure (2)

• User segment– hundreds of thousands of U.S. and allied military

users of the secure GPS Precise Positioning Service

– tens of millions of civil, commercial and scientific users of the Standard Positioning Service

– GPS receiver

How GPS works

• GPS satellites circle the earth twice a day in a very precise orbit

• Transmit signal information to earth

• GPS receivers take this information

• Time difference b/w sending and receiving tells the GPS receiver how far away the satellite is

GPS Signals

• Transmit two low power radio signals, designated L1 and L2

• Carrier L1 L2• Frequency 1575.42 MHz 1227.60 MHz• Wavelength 19cm 24cm

Good vs Poor Satellite Geometry

GPS Modernization(2)

• Safety of Life (L5)

A civilian-use signal, broadcast on the L5 frequency

(1176.45 MHz)

Improves signal structure

Higher transmission power than L1 or L2C

Wider bandwidth

GPS Modernization(3) • New Civilian L1 (L1C)

A civilian-use signal, to be broadcast on the same L1

frequency

New code on L1 frequency

Compatible with Legacy GPS, Interoperable with Galileo

First GPS III launch planned 2013

Full constellation planned 2020

Beidou

• Beidou-1 ( 4 sat )Geostationary over China, 2 operational and 2 backups

• Beidou-2 ( 35 sat )Independent satellite navigation system, similar GPS

• 5 Geostationary• 30 MEO satellites, global coverage

2 Levels of Service• Free in China, 10 m location-tracking accuracy• Military, more accurate and used for communication

Only 1 test satellite in orbit - launched 2007

Galileo• European Alternate to GPS

• 30 MEO satellites was originally scheduled to be operational in 2010

• First experimental satellite was launched on 28 December 2005

• The receivers will be able to combine the signals from both Galileo and GPS satellites to greatly increase the accuracy

• Expected to be in full service by 2020

GLONASS

• Russian Global Navigation System

• Based on a constellation of active satellites which continuously transmit coded signals in two frequency bands

• Consists of 21 satellites in 3 orbital planes, with 3 on-orbit spares

GLONASS(2)

• The system fell into disrepair with the collapse of the Russian economy.

• As of February 2011, the constellation consists of 22 operational satellites