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

5. November 2006 - Manhattan Testing : MTK vs SiRFstarIII vs NemeriX

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

1. Introduction
Picking up where we left things in May and as you know a lot of testing has occurred since, but it has been sprinkled in articles throughout the site, so here's a more formatted comparison between three Bluetooth GPS receivers sporting three different chipsets, the popular Globalsat BT-338 with a SiRFstarIII chipset, the iTrek M5 with a NemeriX NJ-1039 chipset and the iBlue 737 with the brand new MTK chipset that we've covered in detail here. Paul drove into Manhattan with these three units on his dashboard and logged the raw data and sent over to me for analysis in the "GpsPasSion Lab" currently located in France. Now let's see what can me made of these recordings.

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

2. Analyzing the Tracks
The "interactive" testing premiered in the first part of GPS PDAPhone comparison article is back so this means you can scroll around the map, zoom in, zoom out, switch to aerial, street or topo maps, turn off a track or the other (click on the legend). When you're done, let's meet below for some comments.

So what do these tracks tell us? I think the first comment would be for the overall quality of the tracks, how far we've come since GPS receivers were barely usable in the urban canyons of Manhattan and particularly in the financial district. The BT-338/SS3 and iBlue 737/MTK clearly come out on top only losing the fix in the Holland tunnel as expected (for some reason the BT-338 maintains a lat/long reading in the NMEA data in the tunnel, hence the "straight line"). The iTrek M5/NemeriX takes a while to get a fix after exiting the tunnel and then loses it several times in the financial district. When you switch to the map view, you can see that the BT338 and iBlue 737 do fall prey to multipath but you can still make out the driving pattern and navigating software would likely not have been confused. The tracks are naturally "choppy" in the financial district, with the 338 showing a few more "jumps" then the 737. Driving up North, the tracks are much smoother for both and also for the M5 that got back on its feet.

Zooming in on the Financial District

3. Analyzing the Signal

The signal analysis confirms the observations made in the track analysis above, with the 338 and 737 showing a low 6%of lost fixes corresponding to the portion in the tunnel, while the M5 lost it 20% of the time. The better accuracy noted above for the 737 appears in the lower (better) HDOP and higher number of satellites in the fix on average.

4. Conclusion
Not a lot to add, the MTK based iBlue 737 continues to impress, which is all the more surprising since this is MTK's first attempt at a GPS chipset as far as I know. I've heard reports of problems in dense urban environments, but they did not appear in this test drive in Manhattan. Let's also keep in mind that the Globalsat BT-338 used here is running the 3.1 firmware, while SiRF are now releasing the v3.2 version with tweaked performance. A v3.2 vs v3.2 comparison will be the subject of another article in this series. NemeriX have a more powerful chipset in the works, the NJ-2020 that is to be used on the upcoming iBlue 727 originally slated for release in August, and it will likely be able to keep the fix like the SS3 and MTK chipsets.

Next up we'll have the Pharos/Microsoft family of receivers through the years, from 2003 to 2006. 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

<< 4. May 2006 - TomTom AIOs - GO500/ONE/GO910 6. March 2007 - GPS PDAPhones - SiRFstarIII vs Qualcomm gpsONE and the impact of A-GPS >>

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