Satellite Navigation or Sat Navs, as they are commonly known, is a system used to find your exact position at any point of time, using satellites and the positioning device, the GPS. The need to find the direction has been a quest from ancient times onwards. Our fore fathers, first used the sun to track the direction. Slowly the magnetic compass made finding the direction and positions more accurate. Then sextons were used, which by using the position of the sun was able to determine the position of the observer and the direction of travel. They were cumbersome and difficult to use accurately without training. For general directions those methods were fine, but to locate an address accurately, a more exacting method was needed and thus for this we can use the Sat Navs.

Initially the Sat Navs had only military applications and civilian systems were not in vogue. Slowly governments started allowing its use in civilian applications and this was a boon to the general public. All you had to do was enter the address you wanted to go to and using Sat Navs, the GPS would give audiovisual directions. Over time they became sophisticated and the accuracy was in a few meters. If you did not take the turning as directed, the GPS, using the Sat Navs would recalculate and reroute you to your destination. It was that simple. The user may find it simple, but behind its simplicity lay an advanced and complex technology.

How does this system work? It uses a system of satellites orbiting the earth to get a fix. Many countries have a global system of coverage such as US and Russia. China, India and Europe are developing their own systems. GPS, GLONASS, GALILEO are some of the Sat Navs in use today. The most commonly used is the US GPS. The US system uses a number of satellites, to broadcast a signal that contained orbital data, to enable calculation of the position of the satellite and also the time the signal was broadcast. The orbital data is transmitted as a data message with a superimposed code for time reference. All the satellites in the system use an atomic clock to be in sync with each other. The receiver, by comparing the encoded time of broadcast with time of reception, as measured by the internal clock, could determine the time of flight to the satellite. Multiple fixes simultaneously to different satellites allows for a continual fix to be generated in real time. By taking several such measurements a point where they intersect can be determined and this is the fix or position. This is the basic method, but a lot of other technology is used to overcome and reduce various errors.

It is now possible to buy a GPS at a low cost. Some are given away free in promotional campaigns. Even the more sophisticated ones are reasonably priced. You may have to pay for the maps, though free versions are available. The system has become so versatile that Sat Navs signals are available on almost all corners of the earth. The technology is advancing with each passing day and the GPS has become ubiquitous. Soon getting lost will be a thing of the past. Sat Navs have become a part and parcel of our daily lives.

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