how does the iphone's infineon chip compare with that in terms of accuracy and ability to detect weak signals? Do you know how many satellites the iphone's chip tracks at once to determine the signal?
The chip family that the iphone uses has published the ability to track 1t least 12 birds at once, but its not clear that the actual model in the iphone can do that, nor is it clear if it can track 12 in parallel or by time-slicing. See:
http://www.gpsinformation.org/dale/why12.htm The key takeaway is that even three physical channels can give you 12 channel tracking, and only 4 are needed for a fix.
As for comparison to other chip sets, bear in mind that this chip was selected based on cost, and the requirement to perform E-911 functions, and anything else is gravy.
What you get in a hunting GPS or a Garmin are typically much more accurate, down to 12 foot accuracy on my Garmin. Best I've seen on the iPhone is 56 feet.
(Accuracy estimates are reported by some apps like the Track Thing, or gpsCompass (both free in the app store). Both can tell you exactly where you are without any map data from the cellular network.
Accuracy is one thing, Sensitivity is another.
The Infineon chipsets great claim to fame is the low low power and high sensitivity. Some of this alleged sensitivity comes from the fact that it gets its catalog information from cell towers, which means it knows exactly when specific satellites are supposed to be over head and exactly which frequency to listen on.
With this information it can tune in to that precise frequency an pick up the satellite a lot quicker with a lot weaker signal (such as when inside a building).
