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Standards for GPS

written by: Piyush Jain•edited by: Tricia Goss•updated: 4/27/2011

If you rely heavily on GPS data for business or recreation purposes, you should know what the standards are so you an idea how accurate the data is that you are relying on. The accuracy of the data might be the difference between life and death for you.

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    GPS Since first being launched in 1978, positioning, navigation and timing services following GPS standards have been provided by Global Positioning System (GPS) satellites to civilian and military users. So long as a person has a civilian or military GPS receiver, they can pinpoint their location anywhere in the world through GPS satellite tracking, be it night or day and in any kind of weather. GPS technology has evolved since 1978 so that currently, not only can mobile phones be used as GPS receivers, but they can serve as personal tracking devices as well.

    When the system was implemented, certain standards were set in place to ensure that complete, consistent, and appropriate performance standards are uniform for all users – civilian and military. When additional advancements are seen in the technology we currently have, the standards for GPS will also be updated.

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    GPS Performance Characteristics

    To understand the standards set in place, we first have to understand the performance characteristics that are being measured against these standards. These performance characteristics are as follows:

    • Availability
    • Accuracy
    • Integrity
    • Continuity

    Availability is defined as the probability that all slots in the GPS constellation will be covered by transmitting satellites to ensure 100% coverage. Accuracy, from a statistical point of view means that the data must be at least 95 percent accurate over a given period. Integrity is defined as the trust which can be placed in the correctness of the provided information, while continuity is defined as the probability that a GPS satellite will continue to provide information without any unscheduled interruption on a given time interval.

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    GPS Standards in Relation to Performance Characteristics

    When talking about availability, the standard set is that there should be 100 percent coverage of the world. Simply put, with the proper GPS receiver, any person anywhere in the world should be able to determine their GPS coordinates because there is a GPS satellite tracking every inch of the Earth and providing information.

    Accuracy has set standards of less than or equal to 7.8 meters, 95 percent Global Average User Range Error over all data. This means that at any given time, the GPS coordinates displayed on your receiver should not be more than 7.8 meters away from your actual position and this should be the case 95 percent of the time. Accuracy is very important, especially when you use a receiver as a personal GPS tracking device.

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    The standard set for integrity is that an error occurrence in the provision of GPS information should be less than or equal to one times 10 to the negative five probability over any hour of normal operations. This means that a GPS satellite must continue beaming accurate information to receivers almost all the time and the room for error should be minuscule.

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    The standards for continuity states that probability of a satellite continuing to provide accurate information in the event of an unscheduled interruption should be greater than or equal to 0.9998.

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    GPS standards are set in place to ensure that the information being provided can be relied upon. With the growing dependence of users on GPS data, standards should consistently be reevaluated to ensure that they are still appropriate to the technology that they measure.