Why Use Gps For Precise Time?

The GPS system is increasingly becoming the standard means of synchronising time on computers and computer networks

. This article introduces GPS time and its use in NTP time servers for computer network timing systems.

The Global Positioning System (GPS) is a US military system for global navigation and positioning. It is widely used in civilian applications for marine location and car navigation systems. The system itself consists of 24 orbiting satellites arranged in a uniform constellation orbiting the Earth. Each satellite broadcasts accurate time and positioning information that can be used to calculate precise positioning information anywhere on the face of the planet.

Very precise time is a fundamental element of the GPS system. Each orbiting satellite has a highly accurate atomic clock on board synchronised to a master clock at the US Naval Observatory (USNO). Very precise time is required to triangulate a position on earth. Positioning accuracy is directly related to the accuracy of the timing systems of the satellites in orbit. The timing component can be also be used to provide highly accurate time for the synchronisation of computers and computer networks.

GPS has a number of advantages over other hardware reference clocks, particularly radio time broadcasts. The GPS signal can be received anywhere on the face of the planet, providing a truly global solution. Radio systems have a finite transmission range and generally are not available too far beyond the national boundary from which the signal originates. GPS signals have an identical format, regardless of which part of the world they are being received. Whereas, there is no common format for radio time broadcasts, they all differ by frequency and transmission format. GPS also achieves a very high degree of accuracy unsurpassed by any radio time transmission.

Ideally, a GPS antenna needs to have a good view of the sky. For static timing applications this can often mean sitting an antenna on a rooftop with a full 360-degree view of the skyline. In turn, this can often require long cable runs from the computer room, where a time server may be located, to the rooftop. GPS can be quite sensitive to large signal losses over longer cable runs. However, high quality, low-loss coax often allows for extended cable distances. Typically, low-cost RG58 coax can be used up to 50m, while low-loss coax, such as LMR400, can be used up to 120m. For even greater distances an amplifier can be used to boost signal levels. Also, the introduction of GPS over fibre optics allows antennas to be sited many kilometres away from a receiver or time server.

Modern GPS receivers often have a high sensitivity mode. This mode often allows GPS signals to be received in very challenging areas, such as indoors without a direct view of the sky. Indoor reception often works well in normal brick or wooden buildings with a low number of floors above the receiver. However, metal structures can often cause reception problems, receivers located in metal clad buildings may well struggle.

New technology also allows timing receivers to operate from a single satellite in view. This means that timing information can be provided with an antenna located with a much-reduced view of the sky, such as on the side of a building or in a Window. This functionality provides a potentially large saving on installation costs when compared to roof-mounted antennas.

Future developments will see the introduction of Galileo, the EU funded global navigation system, which is an alternative and complementary system to the US system. Galileo is intended to provide even more precise timing and positioning than the current GPS system. EU nations see the system as providing a reliable system that cannot be withdrawn after political disagreements with other countries. Agreement has been reached between the EU member states, which should see the system operational by 2013.

To summarise, the GPS system is a fantastic means of providing time servers with very precise time for computer network synchronisation. It is a system that operates globally and can easily be received with relatively low-cost equipment.

by: Dave Evans

POST COMMENT

Gps Vehicle Tracking- Passive Or Real-time Devices Essential For Transportation FORD MONDEO Focus 2008 2009 s-max GPS GPS Fleet Tracking Software Leads to Increased Efficiency Multi-utility Gps Cell Phone How Are Your Cars Suspension And Steering Works? Garmin Forerunner 305 GPS Receiver With Heart Rate Monitor How To Check And Change Your Air Filter Is Very Important. GPS Jammer Jams the GPS Signals Effectively The Axion Geo-632-your Personal Navigation System How to Navigate in Australia with Your Car GPS Best Blackberry Deal: Phones Which Are Beyond The Comparison Sunno S880 WIFI GPS SmartPhone Running Windows Miobile / Android Dual System God's Gps