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Regarding WAAS


Barkoff
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The user manual makes a rather confusing remark - that WAAS can both increase AND decrease accuracy. So I think the ability to turn it off simply allows you to ignore the WAAS system in case something strange is going on with it. To me, it indicates that Garmin isn't comfortable with WAAS as a core or required part of the system.

 

I doubt battery life would be affected. The receivers stay on trying to acquire GPS satellites constantly, and the WAAS signals are just mixed in with the bunch.

 

The backlight would have far greater impact on battery life than receiving a WAAS signal.

 

Dan

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When you turn off WAAS you turn off your GPS receiver reserving 2 channels for the WASS signals, therefore freeing up 2 more channels for standard GPS satellites. Not really a useful thing since it's hardly ever possible to receive all 12 GPS satellites at one time anyway. And they are all not well above the horizon anyway also.

 

If your GPS has 12 channels like most then this could possibly be of use.

If your GPS is newer and has 16 channels then this is totally useless.

If your GPS is really old and has 1 channel, with time division multiplexing then this is totally good in that processing time is not wasted on WAAS satellites which might not be in good position.

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When you turn off WAAS you turn off your GPS receiver reserving 2 channels for the WASS signals, therefore freeing up 2 more channels for standard GPS satellites. Not really a useful thing since it's hardly ever possible to receive all 12 GPS satellites at one time anyway. And they are all not well above the horizon anyway also.

 

If your GPS has 12 channels like most then this could possibly be of use.

If your GPS is newer and has 16 channels then this is totally useless.

If your GPS is really old and has 1 channel, with time division multiplexing then this is totally good in that processing time is not wasted on WAAS satellites which might not be in good position.

I think it uses only 1 channel (only 1 WAAS satellite is needed to correct all the others that are visible to you). Anyway, you'll get much better accuracy and precision (meaning more repeatable results) using that 1 channel to get WAAS corrections, if available, than you will using it to get 1 more satellite on the horizon. However, applying the WAAS corrections do chew up some CPU time, so it probably does have some quantifiable impact on battery life.

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I think you would want to turn it off in areas where the WAAS correction data is not relevant to your location. ie if you were near the equator you would still be able to lock onto the WAAS satellites but the correction data would be usueful if not degrading your accuracy as there are no WAAS base stations in that area. I think only lower 2/3 of North America and Alaska are serviced by these WAAS Base stations so if you are outside this area WAAS is of no use to you.

 

Rob

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A few reasons.

 

First, WAAS becomes screwed up and you don't want to futz up your normal GPS accuracy.

Second, Battery Life. Garmin's do save a little battery power when you turn off WAAs.

Third, GPS performance. On mine turning on WAAS creates a noticable lag in my GPS updating. Sometimes this gets frustraing so I turn it off. This may not be as much an issue for newer GPSs.

Fourth, you are in an area that doesn't have WAAS. Then you are just wasting your time for a non existant function that could impact your accuracy.

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On a related note, on my eTrex Vista HCx, the WAAS used to reset to OFF every time I turned the unit off and on, but since I recently updated the software and firmware, the WAAS now stays on between power cycles (if I had it set to on). I am happy that I don't have to keep remembering to turn on WAAS each time I turn on my GPSr.

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I think it is speculation that it uses extra battery life. My manual says nothing to that fact.

 

Dan

The WAAS signal has a higher data rate and more complicated encoding. So, all things being equal, WAAS channels use quite a bit more power than GPS channels.

 

But the newer high sensitivity chips sample the GPS range measurements faster now, and at least the SiRF chip doesn't range off the WAAS GEO's. So the difference in battery life may not be as significant as it used to be.

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A few reasons.

 

First, WAAS becomes screwed up and you don't want to futz up your normal GPS accuracy.

Second, Battery Life. Garmin's do save a little battery power when you turn off WAAs.

Third, GPS performance. On mine turning on WAAS creates a noticable lag in my GPS updating. Sometimes this gets frustraing so I turn it off. This may not be as much an issue for newer GPSs.

Fourth, you are in an area that doesn't have WAAS. Then you are just wasting your time for a non existant function that could impact your accuracy.

I've tried it both ways and have found that using waas doesn't seem to help any. I leave it disabled since i don't see any difference and figure it may serve to shorten battery life.

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A few reasons.

 

First, WAAS becomes screwed up and you don't want to futz up your normal GPS accuracy.

Second, Battery Life. Garmin's do save a little battery power when you turn off WAAs.

Third, GPS performance. On mine turning on WAAS creates a noticable lag in my GPS updating. Sometimes this gets frustraing so I turn it off. This may not be as much an issue for newer GPSs.

Fourth, you are in an area that doesn't have WAAS. Then you are just wasting your time for a non existant function that could impact your accuracy.

I've tried it both ways and have found that using waas doesn't seem to help any. I leave it disabled since i don't see any difference and figure it may serve to shorten battery life.

You may want to rethink that. One simple test might not show you the difference. There's another thread on here within the last 2 months or so where someone posted a picture of two tracklogs while the GPSr was stationary--with WAAS and without WAAS. The track points with WAAS were clustered much more tightly around the single point with fewer outliers than the track points recorded without WAAS. It may not be reflected in your reported accuracy (not sure about that point), but your real-world accuracy is going to be closer to the best-case (probably +/- 3 meters) a higher percentage of the time with WAAS enabled.

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...I've tried it both ways and have found that using waas doesn't seem to help any. I leave it disabled since i don't see any difference and figure it may serve to shorten battery life.

When I first turned on WAAS, nothing much changed. I turned it off. Every now and then I'd turn it on and see that nothing much changed. Once I forgot to turn it off. When I finally noticed that for the first time I had a single digit EPE...I noticed that WAAS was on and working. Apparently it takes some time for your GPS to "Bake" and work with WAAS as it should. I'm not 100% sure how and why. That was just my observation. After that time, enabling WAAS did result in a difference (at least for the EPE).

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I've had WAAS on for awhile now and not seen any reduction in battery life (with a Venture Cx). The accuracy here in the UK is much better with it on with accuracy down to 2ft rather than twelve or more. If I'm getting WAAS signals it shows up on the satellite display as little Ds on each satellite signal-strength bar (you have to have a reasonably clear view to the south).

 

For me I've found WAAS ON as a total benefit with no negative points. I guess older GPSr may have problems one way or another though.

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Here's a thread with power consumption measurements on a Vista HCx and a Venture Cx.

 

Neither saw any substantial difference in power consumption with WAAS on or off. As expected, the backlight is the massive power consumer, more than tripling power consumption when used on high compared to off.

 

Dan

Edited by oisact
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