Sirfstar Iii Chipset

[+ICHTHYS]

What's with the SirfStar III chipset that is offered in the new x line of Garmin GPSr's.

 

Does this only effect processor speed or does it have anything to do with the units ability to get a signal, especially in dense tree cover?

[stevesisti]

What's with the SirfStar III chipset that is offered in the new x line of Garmin GPSr's.

 

Does this only effect processor speed or does it have anything to do with the units ability to get a signal, especially in dense tree cover?

It would be hard to surmise what the sirf lll chip will mean in actual performance in a handheld unit until the first units are out. My crude understanding is that the "advantage" is due to signal processing by the chip and not by improved antenna design. On a common sence level, for garmin to sign a "major" contract with them for chip supply, Sirf must have something of value in their technology.

 

I have only seen or read about "external" units incorporating the technology to date..the reviews seem good...my only question is if the increased sensitivity can be maintained in "handheld" units, using the same antennas as they exist now. Time and user reviews will tell.

[kerecsen]

Let me clarify: the Sirf III is a GPS receiver chipset, or in other words, the part of the handheld GPS responsible for receiving the GPS signals and figuring out the current coordinate. It's a very dumb piece of equipment otherwise, it doesn't know about maps or menus or keyboards. All it cares about is outputting a coordinate every second. (Well, actually it also tells you about the available satellites, their signal strengths and such, but that's just a minor detail.)

 

Typically a handheld will have a GPS chipset and a miniature computer (typically an ARM microcontroller nowadays). The chipset just keeps dumping position data to the microcontroller and the microcontroller is responsible for displaying all the screens, as well as storing the tracks or communicating with your PC. (Just to digress: sometimes the GPS chipset has a built-in microcontroller, which may perform double-duty.)

 

The currently available Sirf III-based GPS receivers (typically bluetooth, CF and SD card units) run circles around Garmin handhelds. They acquire much faster, hold the lock better and are more accurate under challenging circumstances. The difference is large enough to be easily noticable to any user, not just the pros.

 

See http://www.gpspassion.com/fr/articles.asp?id=143&page=3 for a comparison of chipset accuracy (the Garmin GPS10 is about the same or slightly better than most current handhelds).

 

The reason why SIII is so much better has to do with the architecture of the chip. While previous generations of chips (such as the Garmin chips or the Sirf II) were solving the position-equations more or less sequentially (iterating to more and more likely solutions), the SIII has a huge number of correlator units that try to find the solutions in a brute-force manner in parallel.

 

It basically means that the SIII doesn't have to approach the solution in a continuous "line", it can afford to go on wild goose chases and try to find a whole bunch of local optimums at the same time.

 

Since it can try a much larger spectrum of possibilities, it can actually make good use of reflected and very weak signals. It can say to itself: hmm, what if this was a reflected signal with x delay -- would that give a more consistent solution? (And do this for thousands and thousands of hypotheses all at once.) The traditional designs did their best to filter out reflected and unreliable data, because it would confuse the iterative algorithm -- the SIII uses them to improve accuracy instead.

 

Some people tried using an external antenna with their BT Sirf units and they reported that it didn't make too much of a difference. So it is safe to assume that the Garmin antennas will provide similar or better performance than the tiny patch antennae in common external units.

Edited December 10, 2005 by kerecsen

[+Insp Gadget]

Can we assume that GPS in general will be faster in operation? I find my 60C is slow updating map screens etc. Would this new chip speed that up?

[JDMC]

kerecsen: Excellent explanation of the SiRF III !

 

Insp Gadget: No.

[+ICHTHYS]

So it would be faster, better reception, but not faster map drawing, etc...?

[+jon & miki]

and from what I've read, much lower power consumption=>longer battery life

[+JohnnyVegas]

On a common sence level, for garmin to sign a "major" contract with them for chip supply, Sirf must have something of value in their technology

Or it could be that they offered Garmin a good price.

I like the Idea of the Sirf chipset, But not for what it will do for Garmin, becuase I have stock in Sirf

[+Alan2]

kerecsen: I wasn't aware the SirfIII is available is Cf and SD inserts type, only BT. Where can I find them?

 

I'm currently using a Fortuna non-SirfIII type. In it's high sensitive mode, it is always 2-3 seconds behind which makes it problematic when in my car when I'm autonavigating. You can speed by the intersection you have to turn at. Has this problem been overcome with the SIRFIII? Thanks.

[kerecsen]

kerecsen:  I wasn't aware the SirfIII is available is Cf and SD inserts type, only BT.  Where can I find them?

 

I'm currently using a Fortuna non-SirfIII type.  In it's high sensitive mode, it is always 2-3 seconds behind which makes it problematic when in my car when I'm autonavigating.  You can speed by the intersection you have to turn at.  Has this problem been overcome with the SIRFIII?  Thanks.

A good place to start for GPSes of all kinds is Semsons.

 

I've seen mention on some forum of a lag issue with early Sirf II units. I've never had this problem with my Sirf III.

 

However, depending on your hardware (PPC) and software, you may get lagging with pretty much any GPS (through no fault of the GPS itself).

[+Timpat]

kerecsen: Excellent explanation of the SiRF III !

 

Insp Gadget: No.

Here, here! Thank you for the Excellent! explanation of the SiRF III. Very informative!

[+Alan2]

kerecsen:  I wasn't aware the SirfIII is available is Cf and SD inserts type, only BT.  Where can I find them?

 

I'm currently using a Fortuna non-SirfIII type.  In it's high sensitive mode, it is always 2-3 seconds behind which makes it problematic when in my car when I'm autonavigating.  You can speed by the intersection you have to turn at.  Has this problem been overcome with the SIRFIII?  Thanks.

A good place to start for GPSes of all kinds is Semsons.

 

I've seen mention on some forum of a lag issue with early Sirf II units. I've never had this problem with my Sirf III.

 

However, depending on your hardware (PPC) and software, you may get lagging with pretty much any GPS (through no fault of the GPS itself).

Thatnks for the info I just order a GlobalSat BC-337 for $95 buck includes shipping. It's a SF insert GPS with the SIRF III. I'll let the forum know how it works out.

[+Hynr]

As we start getting reports from geocachers about using GPSr units with the SiRF chips I am surprised that the general position accuracy under normal circumstances is not improved. I don't know why I thought that overall accuracy would be better. In fact, in another thread at these forums someone indicates seeing an accuracy of no better than 25-30 ft under normal circumstances even with WAAS. That's a problem as far as I am concerned.

 

So I went to the Sirf tech page http://www.sirf.com/ to check out the technical stats and find this:

Position Accuracy

  Autonomous <10m

  SBAS <5m

I am not sure what SBAS means, but on the whole that does not seem particularly optimistic; 10m is slightly worse than the conventional equipment. So I wonder if we will be sacrificing accuracy in the majority of geocaching uses as a trade-off for improvements under weak conditions.

[+Timpat]

I am not sure what SBAS means, but on the whole that does not seem particularly optimistic; 10m is slightly worse than the conventional equipment. So I wonder if we will be sacrificing accuracy in the majority of geocaching uses as a trade-off for improvements under weak conditions.

SBAS means Space Based Augmentation Sytem. Check this SBAS explaination out for a start.

 

Briefly it says: "The WAAS system is the first of a number of planned regional Space Based Augmentation Systems (SBAS). Other regional systems are in development in Europe, Japan, Brazil, India and other regions of the world. "