Satellite Navigation Technology Basics

By: Paul Haughney

Introduction

Satellite navigation isn't rocket science once you know how. Satellite Navigation was originally designed for military applications. The first satellite navigation system was Transit, a system deployed by the US military in the 1960s. For these reasons, a satellite navigation system is an essential asset for any aspiring military power. However due to the growing use of satellite navigation e.g. marine use, engineering use and the ever growing in car sat use the growth of satellite navigation for everyday applications is set to continue.

Accuracy

In general, the more satellites used the greater the positioning accuracy. Numerous errors can degrade the accuracy of a positioning. Therefore, the accuracy of the navigation solution depends on how the receiver compensates for the different error sources. This is largely dependent on how the manufacturers of satellite navigation systems implement the relevant decoding on their receivers. Most publicly available receivers have an accuracy if about 5-10 metres. However in built up areas where the signals from the satellites can be corrupted the accuracy can be a little worse. Given the military put the system in place you can be their accuracy will be a lot better than that seen by the public.

Position

Satellite navigation receivers reduce errors by using combinations of signals from multiple satellites and multiple correlators, and then using techniques such as Kalman filtering to combine the noisy, partial, and constantly changing data into a single estimate for position, time, and velocity. Three and four satellites are the minimum needed to determine positions on the surface of the Earth and above it. This is done from a global network of reference stations on the ground, whose positions are known to within centimetres. The best known is called differential satellite navigation, which uses a fixed receiver in a known position as a reference. GPS receivers, which use differential GPS, can have an accuracy error of less than 1 metre and even down to a few centimetres. This type of receiver is now commonly used in many civil engineering works.

How the public benefit from satellite navigation (Sat nav)

The explosion of sat nav usage is due to the low sat nav costs and how practical they are, especially if you are driving alone and you have no one to help map read. With more and more motorists venturing abroad in their cars the sat nav is an indispensable device to help them navigate around foreign countries. The latest sat nav systems also incorporate Traffic Congestion warnings and then work out an alternative route, with voice instructions, to help avoid a lengthy delay in traffic.

Conclusion

Satellite navigation is increasingly becoming a vital component of aircraft, ships and cars and Europe is concerned about relying entirely on the US system. The clearest of these is the fact that satellite navigation will become a fully redundant service for civil aviation users in the event of a satellite or system failure.