GPS – Global Positioning System is a satellite navigation system. First conceived as navigation aid by the military now number of GPS satellites broadcasts accurate timing signals by radio to GPS receivers.GPS provides a set of coordinates which represent the location of the GPS unit with respect to its latitude, longitude and elevation on planet Earth thus allowing them to accurately determine their location anywhere on the earth at anytime. It has become an important tool for map making and land surveying and is also used for very precise time reference needed for scientific research like the study of earthquakes. GPS receivers come in various formats, from devices integrated into cars, to phones to watches.

The GPS satellites broadcast accurate clock information in two forms:

Coarse Acquisition code/C/A-This is used mainly for civilian navigation which broadcast at 1,023 MHz repeating every millisecond. Each satellite sends a distinct C/A code, which allows them to be identified.

Precise code/ P-code- The P-code broadcast at 10.23 MHz, but it repeats only once per week. The P code is first encrypted into the Y-code, or P(Y), which can only be decrypted by units with a valid decryption key.

Applications of GPS:

There are number of fields where GPS has been used such as:

Military

It plays an important role in the military by helping to find precise targeting of military weapons such as missiles and precision guided munitions. It also provides good location awareness thus helping in controlling of forces and command.GPS satellites also carry nuclear detonation detectors.

Navigation

If you are someone who are likely to always get lost while driving then GPS is what you need in your car. It is used as navigation aid in cars, ships and planes. Hikers and trekkers use hand held GPS receivers to find their way. Even visually impaired people use this GPS equipment to guide their way.

Surveying

Construction workers also use GPS receivers for surveying the land to locate boundaries, structures, and survey markers, and for construction of roads.

Geocaching

GPS receivers are also used in recreational activities like geocaching where a hand held GPS receiver is used. Geocachers use this to travel to specific longitude and latitude walking or hiking to natural locations, searching for particular objects hidden by the other geocachers.
Aircraft passengers

Airline passengers can use GPS units in some airlines inside the aircraft except while landing and taking off as they have very little risk of interference. These airlines integrate aircraft tracking into the seat-back television entertainment system, available to all passengers even during takeoff and landing.

Precise time reference

For accurate time GPS is used. In time code generators GPS is used as a reference clock and also when sensors are deployed they are used to provide accurate time for each recording apparatus. Even atomic clocks are set to GPS time.GPS time is counted in days, hours, minutes, and seconds, in the manner that is conventional for most time standards.

Location-based services

Location based services also use GPS to locate all mobile phones. It provides a location solution is dependent more on mobile phones and less on telecommunications network topology. This also helps to provide specific location information to the mobile phone.

The biggest problem faced in GPS is that the atmospheric conditions can change the speed of the GPS signals while passing through the ionosphere. This effect gets minimized when the satellite is directly overhead and becomes greater toward the horizon.

By: Jeffrey Meier