Almanac

GPS data that contains the location of satellites at a specific time. GPS satellites continuously transmit this information to GPS receiver so that its distance can be computed.

Atomic Clock

GPS satellite has an atomic clock which is so precise that it shows just one second time error in every million years. GPS receiver synchronizes its less accurate clock with atomic clock and computes the time taken by GPS signal to reach it.

Bluetooth

A way of transmitting data without the need of wires. Both transmitting device and the receiver should have compatible Bluetooth devices to achieve this.

CDMA

Code Division Multi Access. A telecommunication method that GPS receiver uses to find out the unique code sent by satellite to find its location.

Cold start

When the GPS receiver is turned on for the first time, it starts to collect essential GPS information like almanac and this takes a few minutes to compute its initial location. This is called cold start.

Control segment/component

One of the three parts of GPS system that controls the satellites and updates the information received from them. Control segment consists of four unmanned, ground monitoring stations and one master control station. The unmanned ground stations receive the data from satellites and send it to the master control station which corrects and update the information and sends it back to satellites using antennas.

Differential GPS (DGPS)

A network of GPS receivers placed in fixed locations gets the satellite signals and corrects the errors and transmits the precise GPS information to other receivers. DGPS provides better accuracy than standard GPS system and computes its location with an accuracy of less than 5 meters.

Ephemeris

One of three bits of information that GPS signals transmit to GPS receivers. While almanac contains time & position information based on where the satellites are supposed to be at any given time, it has to be updated as the satellites may deviate from their orbital paths at periodical intervals. This updated information containing the exact location of satellites is called ephemeris. It is the master control segment that sends ephemeris data back to satellites.

GPS Receiver

Also known as user component/segment, GPS receiver has antenna to pick the signals from the satellites and the in-built processor computes the its location and other information and displays it on user-interface like touch-screen, LCD display.

GPS signal

There are two types of signals. Unencrypted, SPS signals transmitted at 1575.42 MHz for civilian GPS users. Another type is encrypted PPS signal that is used for military purpose. GPS signal contains three kinds of information - pseudorandom code, almanac and ephemeris.

GPS signals are low powered and travel on line of sight so they can be easily blocked by solid objects like rocks, thick foliage, tunnels and mountains.

Mapping software

Most GPS units come with base map that show regional information like major roads, important places, airports, rivers, lakes etc. Some GPS navigation receivers can download detailed maps that contain streets, restaurants, petrol stations, marine navigation details, topography etc. These maps can be purchased and need to be updated now and then. GPS sat nav system can store the mapping software in their memory cartridge or in their hard drives using DVD drive.

Multi-path signal error

One of the potential time errors that occur when GPS signals gets reflected off tall buildings or other solid structures before they reach GPS receiver. This means, the signals took more time than usual, resulting in time errors. GPS receivers rectify or minimize this error by calculating the average time taken by different multi-path signals and determine the location.

Mhz

Mega Hertz. Measure of unit used to find the frequency of radio signals. For example, GPS signals travel at a frequency of 1575.42 MHz.

NAVSTAR

A constellation of GPS satellites that orbit the earth and aid satellite based navigation for both military and civilian use. The US Department of Defense launched the first NAVSTAR satellite in 1978 and completed stationing the full constellation of 24 GPS satellites in 1994.

Orbit

The path of GPS satellites that round the earth. GPS satellite takes nearly 12 hours to make one orbit thus it completes two orbits every day.

Pseudorandom code

A kind of noise that contains coded information which is transmitted by GPS satellites to GPS receivers. Pseudorandom code helps the GPS unit to identify a specific satellite so it can find out its location and distance.

Points of Interest (POI)

POIs include airports, restaurants, petrol filling stations, hotels, tourists attractions and other places of importance. Most GPS units come with POIs

Precise Positioning Service (PPS)

A type of GPS signal which is encrypted and transmitted by satellites so that only military service can access it.

Satellite

Man-made object that orbits the earth and transmit various data to the ground stations. Digital TV, weather forecast and GPS navigation are some of the applications of satellite based technology.

Availability (SA)

One of the sources that affected GPS signals earlier. SA was the outdated method practiced by the US Department of Defense to deliberately degrade the GPS signals as a military maneuver. However, SA has been dropped now.

SPS

Standard Positioning Service. A type of GPS signals, which are unencrypted and transmitted at 1575.42 MHz.

Triangulation

Method by which GPS receiver deduces its location. For more information, read How does a GPS work?

TTFF

Also known as acquisition time, TTFF signifies the time that a GPS receiver to acquire GPS signals and compute its location when it is turned on for the first time.

User component/segment

See GPS Receiver

WAAS

Wide Area Augmentation System. Advanced GPS system that provides better accuracy and computes a location with a preciseness of less than 3 meters.