Sunday, April 10, 2011

The benefit of Glonass?

Another study I am carrying out is how much benefit the availability of Glonass satellites really brings. Low-cost dual constellation GPS-Glonass standalone receiver are starting to show up in the market: Skytraq released the S4554GNS-LP and the S2525G2F, and NVS is soon coming out with their NV08C.

Well, I assembled a few S455GNS-LP on a carrier board:

Figure 1: Kopeke10 USB GPS-GLonass receiver
..and drove in the countryside doing some tests.

Figure 2: Test drive with two dual constellation antennas: a non-branded one (20EUR, left) and a Tallysman TW2400 (80EUR, right).
On the left antenna I had:
- a S1315F-RAW
- a S4554GNS-LP

on the right antenna I had:
- a uBlox LEA-5H evaluation kit
- a S1315F-RAW
- a S4554GNS-LP

So that I would make sure to test my receivers with both antennas and compare them against a good reference. Some preliminary results are shown below.

Figure 3. The roundabout is always good to test how much filtering the PVT solution has. Considering that Google Earth might not necessarily be super-accurate, all the receivers perform pretty well.
 
Figure 4. Driving under a big junction does not affect the receivers very much. Well done!

Figure 5. Uhm? What the heck is that? The Skytraq receiver obviously picked up quite a bit of multipath from the South-East building when I stopped. The good LEA-5H -on the same antenna- did not make a move, and neither the other S4554GNS-LP.



Figure 6. Approching a parking slot just after the road bends, running along a bunch of trees. Multipath has again an interesting different effect on the receivers. But I am more likely to have parked where the uBlox said :)

I will soon add some results in urban environment, where having twice as many satellites should make a real difference.


EDIT 26/08/2011:
Recently, I went out again to compare data from the Sytraq S455GNS-LP and a NVS NV08C-CSM which I soldered onto a carrier board called Denga10 (shown below). The antenna was a low-cost GPS/Glonass magnet-mount patch.

Figure 7. Denga10 carrier board for NV08C-CSM GPS/Glonass receiver.


NVS provides easy software to manage their receivers and translate what is a unconventional NMEA stream:

$GPGGA,203211.00,4340.7619,N,01020.8364,E,2,14,00.8,002.0,M,47.9,M,,*59
$GPRMC,203211.00,A,4340.7619,N,01020.8364,E,00.00,218.2,020811,,,D*5B
$GPGSV,4,1,13,03,65,155,48,06,53,140,47,11,32,282,44,14,24,117,41*7D
$GPGSV,4,2,13,16,19,193,46,18,22,048,41,19,77,307,49,22,58,066,48*7B
$GPGSV,4,3,13,24,21,268,41,32,14,210,40,33,33,214,43,37,38,164,41*7A
$GPGSV,4,4,13,39,37,159,00*48
$GLGSV,2,1,06,66,55,046,46,73,09,307,24,74,05,353,20,81,52,106,38*6C
$GLGSV,2,2,06,82,62,338,44,83,12,313,01*6D
$GNGSA,A,3,03,14,19,06,24,32,22,16,11,18,,,01.3,00.8,01.0*16
$GNGSA,A,3,66,73,82,81,,,,,,,,,01.3,00.8,01.0*10
$PORZD,A,002.8*36

Figure 8. Navis converter to generate a KML from the GPS/Glonass NMEA output of the NV08C-CSM
Also Skytraq is working hard and recently added a GNS Viewer to their software in order to allow customers to quickly evaluate what is again a non conventional NMEA stream:

$GNGNS,203211.170,4340.7630,N,01020.8350,E,AA,16,0.7,14.1,45.7,,0000*53
$GNGSA,A,3,03,06,22,14,18,19,24,32,11,16,,,1.1,0.7,0.9*23
$GNGSA,A,3,66,81,82,73,65,74,,,,,,,1.1,0.7,0.9*25
$GPGSV,3,1,12,19,77,308,49,03,65,155,49,22,58,067,48,06,54,141,46*7B
$GPGSV,3,2,12,11,32,283,44,14,24,118,40,18,23,049,41,24,21,268,40*71
$GPGSV,3,3,12,16,19,194,46,32,14,210,40,28,02,333,,08,00,299,*79
$GLGSV,3,1,09,82,62,338,44,66,56,047,47,81,52,106,37,83,12,314,15*6C
$GLGSV,3,2,09,73,10,307,24,74,06,354,32,65,05,030,32,88,03,125,*6D
$GLGSV,3,3,09,80,00,261,*51
$GNRMC,203211.170,A,4340.7630,N,01020.8350,E,000.0,221.9,020811,,,A*7B
$GNVTG,221.9,T,,M,000.0,N,000.0,K,A*1B

Figure 9. Skytraq GNS Viewer.
Some results are shown below. Seems that the NVS tends to filter a bit too much. Luckily it's possible to upgrade the firmware of these receivers and hopefully NVS has already worked on it to improve accuracy.






Figures 10. The NVS receiver tends to filter too much compared to the Skytraq.

EDIT 07/12/2011: NVS released recently a new firmware for their NVS08C-CSM. I will update Denga10 and have another test session very soon!

Questions?

To be continued (again),
Michele

4 comments:

Darius said...

I hear speculations that GLONASS might be better for indoors, because signals are on separate frequencies. Would love to see some studies about this.

Michele Bavaro said...

Hi Darius,

Certainly worth having a little walk around in the city centre. I will update this post accordingly :)

Cheers,
Michele

Darius said...

Did you had a chance to do the tests?

Michele Bavaro said...

Hi Darius,

Nope, I really don't have time now. There is Galileo Masters competion and I am giving it a go, sorry..

Michele