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GPS Performance Compared
Posté le 13 septembre 2009 à 19:02:21 par gpspassion.

4. May 2006 - TomTom AIOs - GO500/ONE/GO910

1. Introduction/ 2. Analyzing the Tracks/ 3. Analyzing the Numbers /
4. Conclusion/ 5. Forum Discussion

1. Introduction
After an interruption in April for some in depth "coated windshield" GPS testing (WIP), let's resume these comparisons with a family of GPS systems over time, the TOMTOM GO500, ONE (not released in the USA but same design as the RIDER) and 910. As a reminder the GO500 uses the SiRFXtracv2 chipset, the ONE uses the SiRFstarIII and the GO910 uses the SiRFstarIII v2 or "second generation" to use the term coined by Navman for its new 530/720/750 AIOs. Actually this might be a bit far-fetch as the only change is the switch from a dual chip (RF and Baseband) to a single chip design (RF+CPU, "single chip") mostly of interest to the manufacturers as it makes for easier integration on the boards and reduced costs. The risk with this type of integration is that it can increase RF interference and a GPS works best when it has the cleanest RF signal.

Make sure you don't let your browser resize the pictures as there is a lot to look at

2. Analyzing the Tracks
Each system has been given the same track color throughout these screen captures. It should be noted that prior to the test run, all the systems had been given a good view of the sky to have a valid set of ephemeris in their memory.

Starting out between high rise buildings in the budding town of Noisy-le-Grand outside Paris, for some "urban canyon" testing. The GO500 does not hold the fix and goes for the "straight line", the GO910 holds the fix but the position is not very accurate and will confuse the navigation software. The ONE does much better and will feed useful data to the software with the slight multipath induced error being easily handled by the "snap to road" feature.

Driving back through this narrow street between these buildings but starting out from a less obstructed environment. The GO500 is off to a bad start being up North and then loses the fix when I made a sharp turn into the narrow street. The ONE follows the turn pretty closely, but the GO910 overshoots more before coming back on course. Typically this will appear as a delayed map rotation when navigating and can become a problem if you're in doubt as to whether you've made the right turn or not.

A series of sharp turns, first in a "building busy" street and under a building and then around high rise buildings in construction. The 500 loses the fix first, followed by the 910, while the ONE just has a small "hiccup" before proceeding, not quite on course though, but the "snap" will take care of that.

3. Analyzing the Signal

The signal analysis confirms the observations made in the track analysis above, with the ONE holding on to the fix, the 910 losing it from time to time and the 500 quite a bit more often. One can see the correlation power of SiRFstarIII in action with the 910 tracking more satellites on average, in spite of the significantly lower signal level it must work with. So it seems that this is the weak point of the 910, a much lower signal lever, which has several consequences : more time to fix in the morning or after being turned off for 4 hours (TomTom's QuickFIX SIF will help when it becomes available), more lost fixes and less accurate tracking. What is it due to ? A less sensitive internal antenna ? Unlikely because it uses a patch antenna that is larger than on the ONE, an overall design more prone to interference ? The switch to the single chip SiRFstarIII v2 ? Unlikely because the similarly equipped Navman iCN750 performs well (upcoming comparison), so the design is probably the reason for this.

4. Conclusion
With this first "GPS Family" comparison, it appears that newer does not necessarily mean "better" when it comes to raw GPS performance. The ONE (and RIDER) certainly improved on the GO500, but the 910 disappoints compared with the ONE as users who have upgraded have already noticed. There are a couple of fixes though, the upcoming QuickFIX and using an external antenna as on the GOv1/GO500 that also performed worse than other Xtrac v2 GPS systems, only this time it uses a standard MCX connector.

There are two comparisons planned for June, "high end" AIOs (GO910, Navman iCN750 and Magellan RM3000T) and GPS PDAs (Mio P350, Mio A701, Yakumo DeltaX and Loox N560). If you want to suggest other systems feel free to use the thread below or drop me a line via email.

If you have questions, comments or suggestions, you can use this thread of the forums

<< 3. March 2006 - 11 Systems : AIO, Bluetooth, CF, Sports, TMC GPS Receivers 5. November 2006 - Manhattan Testing : MTK vs SiRFstarIII vs NemeriX >>

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