Satellite-Based Augmentation System (SBAS) for NZ?

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Varkk

643 posts

Ultimate Geek

#2263292 24-Jun-2019 11:46

Technofreak:

The turbo props landing in fog is entirely possible with this technology as it can give equivalent accuracy to the ILS which is used in Auckland, BUT and it is a BIG BUT you also need all the ground infrastucture that goes with the CATIII approach which is installed in Auckland and providing the aircraft are properly equipped and the crew appropriately trained. But to say simply say SBAS will allow them to land in fog is a stretching it a bit when you consider the context in which this was said.

I think I read somewhere it gives equivalent of ILS CAT I. Would help smaller regional airports in low cloud conditions (I think it still requires something like 600M visibility at ground level)

Technofreak

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#2263307 24-Jun-2019 12:09

frankv:

One of the issues for general aviation is the expense of certified GPS systems... multiple thousands of dollars for a GPS receiver that is no more accurate than a cellphone, but does know when it is inaccurate. This is particularly significant given the imminent mandatory upgrade to Mode-S transponders, which need a GPS to feed location information.

An aviation certified GPS has a little bit more to it than your cellphone. You can buy a Mode S transponder compete with it's own GPS without the need to buy a separate GPS.

frankv:I'd hope that this new improved system would (a) work on "ordinary" GPS receivers, and (b) provide 100% availability. However, I can't see how it will provide either of these things. You'll need a way to receive the corrections from the new geostationary? satellite (why couldn't these also be received by some other comms path?), and there won't be any improvement in GPS satellite geometry and availability.

It seems to me that we could set up a bunch of "ground satellites" (GPS transmitters at fixed locations, high points like hilltops and mountain peaks for maximum accessibility) which would giveus those benefits.

SBAS works in a variety of GPS receivers used in the Aviation, Agriculture and Marine industries. Any GPS receiver that has the ability to receive and process the signal can use SBAS. What do you mean by ordinary GPS receivers? Any receivers compliant with RTCA/DO-229C MOPS will work with any SBAS system. The system provides 100% availability or that damn close to it.

Why not via another comms path? You want 100% availability, what other system will do that to the extent that a geostationary cannot?

Your proposed system would require more ground stations and the associated infrastructure to go with that. To get the accuracy required each of the ground stations need to be linked to the NAVSTAR control centre. Plus you still need a way for those "ground satellites" to communicate with the GPS receivers.

It starts getting complicated, each ground station would need a unique identifier and each GPS receiver would need to know about each of these ground stations. Each GPS receiver would need to be able to receive the signals from the "ground stations" meaning they would need a specially configured chip, one that is different to normal. Who is going to build special chips just for little old New Zealand?

Why reinvent the wheel? There's a perfectly good system already tested and proven, let's just use that.

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Technofreak

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#2263315 24-Jun-2019 12:17

Varkk:

I think I read somewhere it gives equivalent of ILS CAT I. Would help smaller regional airports in low cloud conditions (I think it still requires something like 600M visibility at ground level)

Correct similar accuracy to Cat I ILS. Using Auckland Cat 1 figures 200' cloud base and 800 metres visibility or with RVR, 550 metres. Still no good for fog but certainly a very useful IFR approach minima.

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Technofreak

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#2263383 24-Jun-2019 13:15

In my first post I said more on that later, well here it is.

In my opinion the authorities in both New Zealand and Australia have dragged their feet on SBAS.

Eleven years ago I was told it was

Too expensive
Better technology will be available

Here we are today embracing an SBAS system.

What follows in the next couple of paragraphs are are my thoughts alone and I have no evidence to back this up but since the rest of the western world has embraced SBAS why haven't we till now? There has to be a reason.

I think the delay is due in part to the Air Service providers in both countries not being keen on SBAS as it didn't suit their business model. Since they weren't providing the infrastructure they had no conduit to levy charges for instrument approaches using SBAS.

Air Services Australia spent a tidy sum developing a GBAS (Ground Based Augmentation System) at Kingsford Smith airport in Sydney in conjunction with Honeywell rather than adopt SBAS. They can charge for the GBAS approaches. GBAS may be technically slightly better than SBAS but the ability of SBAS to provide coverage over a significantly larger area than a GBAS system in my opinion makes SBAS a far better choice, however they would not be able to levy an approach charge especially at regional airports where they don't even provide a tower or approach control service.

That's my rant over.

Now to the cost. Cost has trotted out as an excuse. Apparently we needed to get our own satellite launched. I am aware of a turnkey proposal from Thales for the Australian/New Zealand area that was a fraction of the amount being touted by our authorities as to what SBAS would cost and it could have been done quite quickly. There was a suitable geostationary satellite already in orbit with a spare transponder, no need for a special satellite.

There is no need for a uniquely Australian/New Zealand version of SBAS. We can just replicate what has been done elsewhere.

SBAS has significant economic benefits as it has uses in many industries, forestry, agriculture, land transport, marine and aviation. Aviation is one of the high profile users but is in fact one of the smallest areas when it come to the economic gains. A study in Australia showed SBAS would give a 1 to 2 % increase in GDP Studies in other parts of the world back up these figures.

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linw

2849 posts

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#2263478 24-Jun-2019 15:22

Dingbatt: Feet not metres.

Ooops, sorry.

frankv

5680 posts

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#2263529 24-Jun-2019 16:11

Technofreak:

frankv:

One of the issues for general aviation is the expense of certified GPS systems... multiple thousands of dollars for a GPS receiver that is no more accurate than a cellphone, but does know when it is inaccurate. This is particularly significant given the imminent mandatory upgrade to Mode-S transponders, which need a GPS to feed location information.

An aviation certified GPS has a little bit more to it than your cellphone. You can buy a Mode S transponder compete with it's own GPS without the need to buy a separate GPS.

frankv:I'd hope that this new improved system would (a) work on "ordinary" GPS receivers, and (b) provide 100% availability. However, I can't see how it will provide either of these things. You'll need a way to receive the corrections from the new geostationary? satellite (why couldn't these also be received by some other comms path?), and there won't be any improvement in GPS satellite geometry and availability.

It seems to me that we could set up a bunch of "ground satellites" (GPS transmitters at fixed locations, high points like hilltops and mountain peaks for maximum accessibility) which would give us those benefits.

SBAS works in a variety of GPS receivers used in the Aviation, Agriculture and Marine industries. Any GPS receiver that has the ability to receive and process the signal can use SBAS. What do you mean by ordinary GPS receivers? Any receivers compliant with RTCA/DO-229C MOPS will work with any SBAS system. The system provides 100% availability or that damn close to it.

An "ordinary" GPS receiver is one like in any cellphone. No need for external antennas and suchlike... just software. I Googled and skimmed the RTCA docs, but couldn't find anything about antennas.

Why not via another comms path? You want 100% availability, what other system will do that to the extent that a geostationary cannot?

Yes, cellular has black spots. But SBAS technology will not be available to most people if it requires extra hardware. Geostationary isn't 100% available either, especially if you have a small antenna. Think rain-fade on Sky. With a 24-inch, fixed, dish antenna.

Your proposed system would require more ground stations and the associated infrastructure to go with that. To get the accuracy required each of the ground stations need to be linked to the NAVSTAR control centre. Plus you still need a way for those "ground satellites" to communicate with the GPS receivers.

I figure the ground sites function exactly like a satellite, except (obviously) they don't move. They transmit on the same frequency, just like a satellite. The software does the same calculations, except that it doesn't have to calculate the orbital location of the transmitter, because that's fixed.

Why reinvent the wheel? There's a perfectly good system already tested and proven, let's just use that.

It's not perfectly good, or they wouldn't be adding another layer to it. Or do you mean that SBAS is perfectly good?

Technofreak

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#2263616 24-Jun-2019 20:05

frankv:

An "ordinary" GPS receiver is one like in any cellphone. No need for external antennas and suchlike... just software. I Googled and skimmed the RTCA docs, but couldn't find anything about antennas.

I'd consider a cellphone GPS to be a useful toy rather than a full blown GPS. The GPS's that will make full use of SBAS will have functions like RAIM (Receiver Autonomous Integrity Monitoring) where by the GPS receiver can monitor the integrity of the GPS signals it is receiving and exclude erroneous signals to ensure accurate positioning. Cellphone GPS cannot do that. Unless a GPS unit has RAIM, being able to access SBAS is a waste of time.

frankv:

Yes, cellular has black spots. But SBAS technology will not be available to most people if it requires extra hardware. Geostationary isn't 100% available either, especially if you have a small antenna. Think rain-fade on Sky. With a 24-inch, fixed, dish antenna.

Yes, SBAS requires specific equipment but for those users that will benefit from SBAS the GPS units they are using will have that capability by default.

Rain fade isn't an issue for GPS, probably related to the bands being used. Remember GPS was originally built by the military and to be reliable.

frankv:

I figure the ground sites function exactly like a satellite, except (obviously) they don't move. They transmit on the same frequency, just like a satellite. The software does the same calculations, except that it doesn't have to calculate the orbital location of the transmitter, because that's fixed.

I doubt you would get access to the frequencies used by GPS

frankv:

It's not perfectly good, or they wouldn't be adding another layer to it. Or do you mean that SBAS is perfectly good?

Yes, I was talking about SBAS

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XJ9

6 posts

Wannabe Geek

#2300540 16-Aug-2019 18:23

Technofreak:

Do you know if smartphone receivers can leverage SBAS technology in the near future?

I know that Lenovo has had success getting an accuracy of +-1m in their Lenovo Z6 Youth model which has dual band support.

The Snapdragon 855+ webpage says that it supports SBAS but I'm not sure what that means in practise.

I know that there was a bottle neck with previous versions of Android not giving developers full access to the positioning hardware.

ref:

https://www.gpsworld.com/dual-frequency-gnss-smartphone-supports-bds-phase-iii-signal/

https://www.qualcomm.com/products/snapdragon-855-plus-mobile-platform

Technofreak

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#2301062 17-Aug-2019 23:29

XJ9:
Technofreak:
Do you know if smartphone receivers can leverage SBAS technology in the near future? I know that Lenovo has had success getting an accuracy of +-1m in their Lenovo Z6 Youth model which has dual band support. The Snapdragon 855+ webpage says that it supports SBAS but I'm not sure what that means in practise. I know that there was a bottle neck with previous versions of Android not giving developers full access to the positioning hardware. ref: https://www.gpsworld.com/dual-frequency-gnss-smartphone-supports-bds-phase-iii-signal/ https://www.qualcomm.com/products/snapdragon-855-plus-mobile-platform

What do you mean by near future?

SBAS is supposed to be becoming available in New Zealand, it my guess it could be still 3 to 5 years away. Once SBAS is available I'd say any chip that supports it will be able to use SBAS.

I struggle to see why it would any use on a device that cannot support RAIM. If you need that accuracy you also need to know you have sufficient coverage to guarantee that accuracy. I doubt a smartphone will have RAIM

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