Patent recognises software GPS solution

CSI Wireless has been awarded a US patent for its e-Dif or "extended differential" software.

CSI Wireless has been awarded a US patent for its e-Dif or "extended differential" software that enables GPS receivers to achieve the much higher accuracy available from differential GPS (DGPS), but without any help from accuracy-enhancing differential signals.

e-Dif enables a standard GPS receiver, typically capable of only 10 or 15m accuracy, to internally generate differential corrections that improve its accuracy to 1m - without the expense or potential uncertainties of DGPS signals.

e-Dif computes corrections that last for as long as 40min, after which the receiver recomputes a fresh set of corrections that last for another 40min.

"e-Dif can save customers the cost of paying subscription fees for DGPS signals in regions - such as South America, Africa and Australia - where DGPS signals are not free", said Stephen Verhoeff, President and CEO of CSI Wireless.

"Even in North America, where DGPS signals are free, e-Dif is a valuable back-up against signal outages.

And in northern latitudes, including many parts of Canada, e-Dif can achieve better accuracy than what is possible using free DGPS signals from public satellite networks such as WAAS, or when a receiver is on the fringe of ground station networks such as beacon DGPS".

Standard GPS involves a ground-level receiver using pre-programmed data to know the orbital location of each of 24 GPS satellites - collectively known as the US Government's Global Positioning System (GPS) - that circle 22,000km above Earth.

The receiver, by comparing the location data with the time required to receive a satellite's signal, calculates its own position on Earth.

A standard GPS receiver cannot calculate its own position any more accurately than about 10 or 15m - mainly because the signals coming from satellites are distorted while travelling through the ionosphere (60 to 100km above the Earth) and troposphere (6 to 15km above the Earth).

Accuracy can be improved to one metre when differential corrections - which highlight the difference between the actual signal and the distorted signal - are broadcast to the GPS receiver from ground-based beacon networks, from public satellite networks such as the United States' Wide Area Augmentation System (WAAS) and Europe's EGNOS that is under development, or from private satellite networks such as OmniSTAR.

However, all of these correction systems require DGPS signals, and some involve yearly subscription fees that can total thousands of dollars.

In contrast, the e-Dif option, which may be installed at the factory or in the field, does not require DGPS signals, does not involve any risk of potential DGPS signal outages, and features a very affordable one-time price of about US $1200.

The software computes corrections at a specific moment and then, after making sophisticated adjustments for ionospheric and tropospheric conditions, continues to forecast accurate corrections for as long as 40 minutes - after which the receiver computes corrections at another specific moment and starts the forecasting again.

"e-Dif represents a very cost-effective method of achieving DGPS accuracy", Verhoeff said.

"It is significant that the US Patent Office has recognised the very unique and special nature of our revolutionary new software".

The software, developed by CSI Wireless' Satloc LLC subsidiary in Scottsdale, Arizona, has already been incorporated into several CSI and Satloc products including the DGPS MAX, SLXg3, SERES and AgIQ receivers, and the popular Outback S precision guidance agricultural product that is sold exclusively through RHS e-Dif is one of several patents and intellectual properties owned by CSI Wireless, the result of a concerted research and development programme that totalled $8.1 million in 2001.

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