Good effort, on a very technical topic. Well done on getting a hyperlink in as well. Subheadings and more savvy formatting would have helped, perhaps.

A- B+

GPS stands for Global Positioning System and is increasingly becoming more vital to our everyday lives. GPSs are used from SatNavs in our car to helping the RAF to find injured people that are stuck on the side of a mountain.

A GPS receiver calculates its position by precisely timing the signals sent by satellites in space. Each satellite has to transmit messages such as the time the message was transmitted and its position at time of message transmission.

Typically, a GPS will decipher its location by taking an average from four different satellite transmitters. The space segment is composed of at least 24 satellites, at any given time, which all orbit the Earth at roughly the same speed (1 orbit of the Earth = 12 hours) but in different places.

Each GPS satellite continuously broadcasts a navigation message at 50 bits per second on the microwave carrier frequency of approx 1600 MHz .FM radio, for comparison, is broadcast at between 87.5 and 108.0 MHz and Wi-Fi networks operate at around 5000 MHz and 2400 MHz. More precisely, all satellites broadcast at 1575.42 MHz (this is the L1 signal) and 1227.6 MHz (the L2 signal).
A visual example of how satellites orbit the Earth to give an accurate postion for the GPS at 45°N.
A visual example of how satellites orbit the Earth to give an accurate postion for the GPS at 45°N.
The U.S Air Force were the first to use GPS in practice and used it in their aircraft for the navigation of their pilots. Each transmission lasts 30 seconds and carries 1500 bits of encrypted data. This small amount of data is encoded with a high-rate pseudo-random (PRN) sequence that is different for each satellite. GPS receivers know the PRN codes for each satellite and so can not only decode the signal but distinguish between different satellites.

GPS was made fully available to the general public in 2007 when the U.S military agreed to the letting of their satellites to certain companies such as Garmin and TomTom who make Satellite Navigation Devices for our cars and sice that may different companies have latched on to the idea of using GPS in SatNavs.

The civillian transmitters and rcievers give an accuracy of about:
  • 100 metre horizontal accuracy
  • 156 metre vertical accuracy
  • 340 nanoseconds time accuracy

This is compared to the U.S.A's army transmitters and recievers which give an accuracy of around:
  • 22 metre Horizontal accuracy
  • 28 metre vertical accuracy
  • 200 nanosecond time (UTC) accuracy.

This effectively translates to be an accuracy of +/- 4 metres in the more modern GPS devices.

This has enabled the SatNavs in cars to give an incredibly acccurate representation of the area that a motorist requires to avoid or reach.

Unfortunately, it seems that violent crimes and abduction are going to be a horrible reality for this and future generations. Personal GPS tracking systems are already being used to enhance the safety of many children and adults, and as

GPS tracking systems continue to become more affordable, it's likely that they'll be used even more for this purpose.

With GPS tracking systems popping up in cell phones, watches, and shoes, there's no doubt that GPS tracking devices are making their way into all walks of daily life. Other advancements in technology such as the breakthrough invention of 3D televisions, could prove to be a help in the future of GPS devices, as we may see more real-looking images of the surrounding terrain and quicker/ more accurate imaging and timings.

Outdoor gamers can even use a GPS receiver to take part in treasure hunts for the digital age known as 'geocaching'. The organizers hide a cache of "treasure" at a secret location and then provide clues to its whereabouts that rely on the use of a GPS receiver to find the bounty.

From the outside a navigation device looks like nothing more than a sleek digital device, with a touch screen, however, within the shell is a host of modern electronics that allows it to pick up signals from the satellites that are in orbit.
Each component inside a navigation device has a specific purpose and each is essential to the functioning of the device. The rechargeable lithium-ion battery provides the power for the screen and the internal electronics. There are also circuits to control the display and to respond to user interaction via the touch-sensitive display and buttons. There are circuits too that control the information, map and route displayed as well as to produce spoken directions .
In order to carry out its main job of locking on to the global positioning system (GPS), a Navigation device has an aerial inside. This receives the microwave signals from the satellites in the GPS constellation. These signals are then amplified and fed to the integrated circuits that analyze the signals and calculate your position. The circuitry uses a system known as trilateration, which is the 3D equivalent of trilateration on a map. The trilateration process depends on the GPS device being able to determine the distance to the satellites by timing the signals using its inbuilt clock. The clock itself is an electronic circuit known as an oscillator.

Inside of a navigation device
Inside of a navigation device