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GPS III – Delivering Impressive GPS Navigation Benefits

Since the removal of selective availability, the United States Global Positioning System (GPS) services have become progressively integrated into our everyday lives. Few would realize that as well as providing navigation services, the incredibly accurate time keeping provided by GPS satellite atomic clocks is used in time dependant activities such as stock trading, electricity grid control and credit card transactions. Yet, for all the progress there is still much to come.

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GPS III Satellite
GPS navigation devices will become more capable through improvements to the device itself such as the recently discussed miniaturization of atomic clocks. However, improvements in the technology of the GPS satellite fleet will also foster impressive improvements. The most recent upgrade to GPS satellite technology and capabilities underway is referred to as GPS III.

When GPS III is fully operational, improvements over the present satellite fleet will include three new signals designed for civilian use: L2C, L5, and L1C. For backwards compatibility for existing GPS devices the legacy civil signal (L1) will still be broadcast. GPS III satellite services which will provide more powerful signal strength and improved accuracy, reliability, integrity, and availability. The US Department of Commerce has assessed the economic benefits of the L2C signal alone are likely to be more than $5.8 billion in user productivity gains over 30 years.

New Civilian L2 (L2C) Signal
The new civilian L2C signal will provide improved accuracy of navigation to only 1 m compared to 5 m (at best) presently. This sort of improvement makes it possible to think about guiding a blind person along a path as well as a car along a road. With the higher signal power, signal acquisition will be faster and interference from surrounding buildings, terrain and foliage will be reduced.

One factor leading to improved navigation accuracy is the availability of two frequencies enabling the direct measurement of the ionospheric delay error for each satellite rather than using an estimate. This is an important advancement as ionospheric delay is currently the largest source of error for the current civilian GPS signal. Receivers which can calcualte the ionospheric delay error from two signals are called dual frequency receivers. Professionals already possessing dual-frequency devices will benefit from faster signal acquisition, enhanced reliability and greater operating range. The stronger signal will also support manufacturers in further miniaturization of GPS chipsets for mobile applications. Tracking devices will be a significant beneficiary of reduced size and power requirements.

Many professional grade GPS receivers currently achieve high accuracy today by using codeless or semi-codeless techniques that exploit the encrypted military GPS signals without actually decoding them. This technique will be obsolete when the new civil GPS signals are operational.

Third Civil Signal (L5)
The third civil signal (L5) is to be will be in a protected aeronautical radio navigation system (ARNS) band intended for aviation and other safety-of-life uses. There are the benefits of a protected spectrum, higher power signal transmission, greater bandwidth and other features.

Fourth Civil Signal (L1C)
The fourth civilian signal (L1C) is to enable interoperability between the United States GPS and other satellite navigation systems such as Galileo being deployed by Europe. This signal features a Multiplexed Binary Offset Carrier (MBOC) waveform designed to improve mobile reception in cities and other challenging environments.

Categories: GPS Technology

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