Primarily for general aviation discussion, but other aviation topics are also welcome.
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By rjc101
#1803562
gaznav wrote:
ADSB is CAA and NATS preferred solution. They asked and paid QinetiQ for the report.
Any consultancy producing a report don't have to falsify anything, just don't report on issues the customer might not want to see.
The report is based on the data the customer supplied ;-)
Fox guarding the hen house or what :D


That’s a bit like saying that a house survey, that you pay for, that values a prospective property that you are buying, is written so that is doesn’t “report on issues the customer might not want to see“. We know that is bunkum or there would be a serious problem in the housing market - I’ve walked away from properties that I have invested in due to a survey that I have paid for. I have also walked away from the purchase of an AA-5, having paid £300 for an engineer to survey it for me.

Sorry, I’ll say again, QinetiQ is a world leading company that lives and dies on it’s reputation on research and scientific consultancy. This report probably cost a few thousand quid and QinetiQ is worth around £1.3Bn. It would be CRAZY for it to risk it’s reputation and worth for a few thousand quid.

Finally, the choice of 12 Jun 06. So the CAA and NATS chose a day in the summer, towards the start, when it is more likely for people to be flying after the slow improvements in weather from the winter. Why on earth would they choose a day when it is quiet in the middle of summer? Why would they risk challenge by stating the date of the data and also for something that will affect the safety of others that could later be challenged in Court? Again, that doesn’t make sense. You wouldn’t spend all this money and effort to do this by picking a ‘phoney day’ - especially when it involved the safety of people (pilots and passengers and those that live underneath on the ground)?

I’m sorry, this is another mad conspiracy theory developing here. I’ve said it before, I’m a fan of “Occam’s Razor” (look it up), and the most likely thing here is that a scientific report has proven that low power ADS-B is ok for the use that they intend.


The report and research is all fine, it answers the question asked of it. For all reports people will pick at all source data as not representative etc. it just happens.

What the report does state is a potential issue with 1090MHz loading, and that to mitigate that the use of lower power ADS-B transmitters would be the better choice to mitigate additional loading on 1090MHz.
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By gaznav
#1803568
@rjc101

The report was not commissioned to determine anything to do with congestion of the 1090MHz frequency as a whole.


The 2012 and 2014 studies were. The report that you appear to refer to appears to be the 2015 one that looked at the potential effects on ACAS/TCAS - again, they concluded that below 70W would be OK. The CAA eventually went for 20W just to be safe, which is probably the way to go considering what the low power ADS-B transceiver is expected to be used for (and is right now with no reported effects). :thumright:
By rjc101
#1803569
Cessna571 wrote:What I don’t understand about all the “congestion naysayers”

If Flarm transmits more often than ADSB and a large proportion of those 80 gliders use Flarm, how does it work at all?

How will ADSB become congested but p3i not when P3i transmits more frequently.

it’s just another clutching at straws thing to try and stop people fitting ADSB when it’s already been properly looked in to.

I’m actually concerned about not bumping into people rather than a daft SE2 vs PAW war, but I don’t have a commercial interest in either.


Non ADS-B EC transmissions are very low power, hence shorter range. So the number of transmitters in a given volume of airspace needs to be higher to cause a problem.

The issue isn't ADS-B as such, but the frequency 1090MHz. This is used by Transponders and ADS-B transmissions.

Every time a radar head 'paints' a transponder (Mode A, C, or S), it replies on 1090MHz.
If a TCAS transmitter sends a pulse on 1030MHz, the replies from transponders are all on 1090MHz.
A Mode-S ES enabled transponder will reply to being painted by a radar head, and also regularly transmit data on 1090MHz.
A portable ADS-B Out device will regularly transmit data on 1090MHz, though at a lower power.

For FLARM and PAW, the only things on those frequencies in range, is FLARM and PAW.

The 1090 MHz frequency band is 'busy', everything you see on Flightradar or similar has been picked up from it's transmissions on 1090MHz.

So what happens when one transmission overlaps another? That depends on the receiver. If it is receiving a packet and another starts to arrive, both may be considered corrupt and discarded. It may spot the new packet pre-amble and start to receive and decode that, only throwing away the previously partially received corrupted packet. For ADS-B you need two packets to make a valid message, so data will be missed. It happens, and is the nature of RF transmission.

The simple solution is to lower the transmission rate ADS-B Out devices, to reduce the potential of the packets colliding.
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By gaznav
#1803571
@rjc101

The simple solution is to lower the transmission rate ADS-B Out devices, to reduce the potential of the packets colliding.


I agree, but I also would point out that it may not be that “simple”. ADS-B emits to an ICAO agreed standard. Any stepping away from that standard, including reducing data packet transmission rate, will need international agreement again. So, it will take time if the world agrees that there is a need.

I posted this a year or so ago from a Eurocontrol report:

2.1.3.2 1030/1090 MHz Frequency Band

The high number of SSR Mode A/C radars configured with relatively high interrogation rates and interrogator power has, over recent years, lead to congested usage of the 1030/1090 MHz frequency band.

As ACAS and all the cooperative surveillance techniques are dependent upon this frequency band its use is considered to be fundamental to the future of surveillance. Deploying an alternative band would be expensive, time consuming and would introduce technical difficulties. It is preferable to manage, monitor and protect the current frequency assignments in recognition that the 1030/1090MHz as a valuable asset that is to be used with care. The protection of the 1030/1090 MHz frequencies is a key objective of this surveillance roadmap.

Various measures ranging from the removal of spectrally inefficient Mode A/C SSRs (such as promoted through the Implementing Regulation No 1206/2011 Ref Doc 6) through to improvements in ACAS technologies (hybrid surveillance) or the clustering of SSR Mode S ground-stations will lead to improvements in this band and obviate the need for deployment of an alternative frequency band. The deployment of WAM techniques has the potential to reduce excessive transmissions in the 1030/1090 MHz band when compared with conventional SSR systems. However it should be noted that Active Wide Area Multilateration systems configured with broad-beam or omni-directional transmit stations can also place a significant impact upon this frequency band and the surveillance sensors that depend upon it.


The number and density of expensive SSR heads interrogating on 1030Mhz to get replies on 1090Mhz are also reducing right now. So again, this is a part of the problem with 1090Mhz in the past - there were simply to many interrogators asking for a reply which also then increased the amount of replies. Don’t forget that Xaon MRX, PAW and PowerFLARM rely upon these interrogations happening to be able to do their Mode C proximity reporting (another draw back to this system) as if no-one is interrogating line-of-sight and in range of your Mode A/C or Mode S transponder then no 1090 Mhz transmission will be made. Finally, ACAS/TCAS are also a part of the problem - they are mini flying SSR heads that are constantly interrogating too - so if ADS-B was global (where it is heading) then using ADS-B for separation would also ease the 1090Mhz congestion issue as the number of unnecessary interrogation/replies would be drastically cut. So with ideas like yours and the evolution of SSR towards WAM then there is still plenty of room for manoeuvre on 1090Mhz; especially if 978Mhz comes in to play too in the future for small drones, etc...
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#1803575
gaznav wrote:
Finally, the choice of 12 Jun 06. So the CAA and NATS chose a day in the summer, towards the start, when it is more likely for people to be flying after the slow improvements in weather from the winter. Why on earth would they choose a day when it is quiet in the middle of summer? Why would they risk challenge by stating the date of the data and also for something that will affect the safety of others that could later be challenged in Court? Again, that doesn’t make sense. You wouldn’t spend all this money and effort to do this by picking a ‘phoney day’ - especially when it involved the safety of people (pilots and passengers and those that live underneath on the ground)?


If the choice of 12 Jun 06 is relevant to the discussion, I note it wasn't a good gliding day, at least in East Anglia. My club just launched its training fleet and didn't do any soaring. No cross country at all. So the GA model may not be particularly good.

More generally, having spent most of my career in a technical consultancy, I know that it is possible for such consultancies, including QinetiQ, to write things that are wrong, not well thought through, or address a different question from the one now being asked. I have no idea whether that happened here, but an appeal to authority ["It's QinetiQ, they are big, therefore they must be right"] isn't particularly compelling. (It's not necessary to assume nefarious practices, though consultancies delivering the answer a client wants are not unknown). Better I think to actually look at what they did, and what the basis of their conclusions are.

It's a fairly complicated problem. It's not as simple as less power = less range. At these frequencies, range can be up to line of sight (we know we can pick up Flarm signals from gliders > 100km away with a suitable antenna, and Flarm is the lowest power of the systems we're discussing). Often the driver of whether you can see a signal at a receiver in a congested network, is the signal to noise - and the noise is the contribution from everything that's emitting in line of sight).

And then what's the question? Is it "Is System X suitable for GA Air to Air traffic detection, at least most of the time" Or is it, "Is System X suitable for CAT separation all of the time?"

So I think we need to be quite specific about the question we're trying to answer, and look closely at the modelling which is used to answer it. Do we have these?

Paul
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#1803581
PaulisHome wrote:
If the choice of 12 Jun 06 is relevant to the discussion, I note it wasn't a good gliding day, at least in East Anglia. My club just launched its training fleet and didn't do any soaring. No cross country at all. So the GA model may not be particularly good.

More generally, having spent most of my career in a technical consultancy, I know that it is possible for such consultancies, including QinetiQ, to write things that are wrong, not well thought through, or address a different question from the one now being asked. I have no idea whether that happened here, but an appeal to authority ["It's QinetiQ, they are big, therefore they must be right"] isn't particularly compelling. (It's not necessary to assume nefarious practices, though consultancies delivering the answer a client wants are not unknown). Better I think to actually look at what they did, and what the basis of their conclusions are.

It's a fairly complicated problem. It's not as simple as less power = less range. At these frequencies, range can be up to line of sight (we know we can pick up Flarm signals from gliders > 100km away with a suitable antenna, and Flarm is the lowest power of the systems we're discussing). Often the driver of whether you can see a signal at a receiver in a congested network, is the signal to noise - and the noise is the contribution from everything that's emitting in line of sight).

And then what's the question? Is it "Is System X suitable for GA Air to Air traffic detection, at least most of the time" Or is it, "Is System X suitable for CAT separation all of the time?"

So I think we need to be quite specific about the question we're trying to answer, and look closely at the modelling which is used to answer it. Do we have these?

Paul


Before we get too wrapped up in this it may be worth thinking through what happens if the frequency does get congested in a couple of years. It does'nt seem likely to me that the CAA would revert to using the "open" frequencies that Flarm and P3i use, more likely they would adopt the UAT (978) datalink solution used in the US, which would have the advantage of making a lot of kit available to us.

I don't know whether a SkyEcho would need just a software change to work with this, or require replacement, certainly both PAW and Flarm would need changes/upgrades made. However I would bet it will take the CAA at least 5 years and probably more like 10 years to make such a change (given that it's taken 5 years to decide on the current strategy). So my guess is anything you buy now which fits the current approach is good for minimum 5 years, probably 10. Since the average life of a mobile phone, notepad or PC is anywhere from 3-7 years I don't think it is unreasonable to spend a couple of hundred pounds now for this sort of lifespan - whichever route you want to take.

So the debate about whether ADSB on 1090/ES is the "right" long term strategy is technically interesting, but I would hate for it to delay anyone from getting some form of EC now - you only have to look through the Airprox reports to see why it's a good idea.
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#1803586
Cub wrote:
Straight Level wrote:
I've been in industry long enough to realise if you ask a consultancy to determine if something will work they will give you a good reason as to why it will work especially if you give them the data to make that analysis in the first place.

Interesting !


If you have been in the industry that long you would appreciate that people do not look to falsify or manipulate the data to fit the picture when that would have a fundamental and potentially detrimental impact on your core business?

ANSPs certainly do not take likely any study or suggestion that may indicate an impact on their ability to deliver safe and robust surveillance services. It is what their whole business is based upon.

Suggesting that a highly respected research organisation’s study is somehow bias or weighted towards the answer the customer may want is disingenuous at the least. Regardless of independent studies, do you honestly not believe that the major ANSPs are not continuous evaluations and monitoring the present and future scenarios with an extremely critical eye?

You are correct to point out that the situation is changing constantly with the rapid uptake of ADS-B amongst the GA fleet and the allocation of a second ADS-B frequency to be exploited by growing sectors of the market and data services.


Cub, thank you for your answer.
I didn't say I have been in the industry ;-)
#1803592
gaznav wrote:
ADSB is CAA and NATS preferred solution. They asked and paid QinetiQ for the report.
Any consultancy producing a report don't have to falsify anything, just don't report on issues the customer might not want to see.
The report is based on the data the customer supplied ;-)
Fox guarding the hen house or what :D


That’s a bit like saying that a house survey, that you pay for, that values a prospective property that you are buying, is written so that is doesn’t “report on issues the customer might not want to see“. We know that is bunkum or there would be a serious problem in the housing market - I’ve walked away from properties that I have invested in due to a survey that I have paid for. I have also walked away from the purchase of an AA-5, having paid £300 for an engineer to survey it for me.

Sorry, I’ll say again, QinetiQ is a world leading company that lives and dies on it’s reputation on research and scientific consultancy. This report probably cost a few thousand quid and QinetiQ is worth around £1.3Bn. It would be CRAZY for it to risk it’s reputation and worth for a few thousand quid.

Finally, the choice of 12 Jun 06. So the CAA and NATS chose a day in the summer, towards the start, when it is more likely for people to be flying after the slow improvements in weather from the winter. Why on earth would they choose a day when it is quiet in the middle of summer? Why would they risk challenge by stating the date of the data and also for something that will affect the safety of others that could later be challenged in Court? Again, that doesn’t make sense. You wouldn’t spend all this money and effort to do this by picking a ‘phoney day’ - especially when it involved the safety of people (pilots and passengers and those that live underneath on the ground)?

I’m sorry, this is another mad conspiracy theory developing here. I’ve said it before, I’m a fan of “Occam’s Razor” (look it up), and the most likely thing here is that a scientific report has proven that low power ADS-B is ok for the use that they intend.


Gaz,

I think it is a reasonable question to ask, why the report only used a "typical" day and not a worst case scenario.
You answered with QinetiQ is big and worth £1.3B and you assume the cost of the report is minimal.
You have made an assumption about the amount of traffic on the 12th June 06.
Was it quiet, typical or busy?
Why use such old data?

When stress testing systems, it is normal practice to do exactly that.
Adding 25% traffic to a typical day may not approach the traffic we see on a busy day. It is not stress testing the system.
It is my opinion based on the above, the report which you quote so often, is flawed.

By all means answer with some facts, but don't bother if its on the lines of "QinetiQ is a world leading company" :roll:
Last edited by Straight Level on Sat Oct 17, 2020 5:34 pm, edited 1 time in total.
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By T67M
#1803614
Whilst I agree with most of what gavnav has just written:

gaznav wrote:Finally, ACAS/TCAS are also a part of the problem - they are mini flying SSR heads that are constantly interrogating too - so if ADS-B was global (where it is heading) then using ADS-B for separation would also ease the 1090Mhz congestion issue as the number of unnecessary interrogation/replies would be drastically cut.


I think we are violently agreeing with each other that the problem of 1090MHz congestion won't go away until all Mode A/C TCAS systems are replaced with ADS-B TCAS systems, as until then you are effectively "blinding" aircraft equipped with older TCAS. To re-equip all airliners will take a long time, and until they are, you cannot disable Mode A/C transponders to free up the spectrum.

gaznav wrote:So with ideas like yours and the evolution of SSR towards WAM then there is still plenty of room for manoeuvre on 1090Mhz; especially if 978Mhz comes in to play too in the future for small drones, etc...


My bold. This is correct, but misses out the critical piece that if some airspace users are ADS-B on 978MHz and some are ADS-B on 1090MHz, you either need TIS-B uplinks on both frequencies to enable the two classes of users to "see" each other, or you need all users to have both receivers. Since ADS-B on 978MHz is not (currently) a true standard and thus not fitted to airliners, this again isn't going to happen quickly as it will require all airliners to be re-equipped.

For what it's worth, I maintain that we (the UK as a country) should have adopted split-frequency ADS-B on 978MHz and 1090MHz around the same time the Americans adopted it (2013/14/15), then this entire debate would be over by now. As always, however, the problems aren't technical, they are an excess of political won't and a lack of treasury funding.
#1803619
I believe the SkyEcho 2 can already receive traffic on 978mhz (they will correct me if I’m wrong) so if some section of traffic (like drones) does end up emitting on that frequency, it’s future proof.
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By ls8pilot
#1803623
T67M wrote:....
For what it's worth, I maintain that we (the UK as a country) should have adopted split-frequency ADS-B on 978MHz and 1090MHz around the same time the Americans adopted it (2013/14/15), then this entire debate would be over by now. As always, however, the problems aren't technical, they are an excess of political won't and a lack of treasury funding.


I quite agree, taking the same route as the US would have resulted in a much bigger market, so a lot more options for available equipment and a lot more attractive to potential vendors. Can't see the current direction being reversed for some significant time (if ever) though....
#1803648
I've just read the 'NHS Drone delivery service ' thread. There are more reports of other danger areas being set up for drone experimenting. Could this be whats driving the government push for ADSB, once drones are let loose they will presumably use ADSB for avoidance, and rely on us all to have it so they can avoid us. if so this leaves PAW out on a limb, unless they modify to emit ADSB.
Flyin'Dutch', Crash one, Nick and 1 others liked this
#1803652
There is the inexorable march of the drones, such as published in this thread: viewtopic.php?f=1&t=116996&p=1803634#p1803634

Made me think do they see anything else than ADS-B such as PAW?
Last edited by Flyin'Dutch' on Sat Oct 17, 2020 8:05 pm, edited 1 time in total.
#1803657
Tim Dawson wrote:I believe the SkyEcho 2 can already receive traffic on 978mhz (they will correct me if I’m wrong) so if some section of traffic (like drones) does end up emitting on that frequency, it’s future proof.


SkyEcho 2 can already receive traffic on 978MHz but only instead of FLARM Traffic. The ‘second’ receiver (and presumably antenna) is ‘selectable’ in software in the configuration to receive either 978 or FLARM, but not both.

PilotAware can also receive 978MHz if required. All it needs is a couple of minor additions to hardware (easily added retrospectively) and ‘reactivation’ of a software option already tested during the previous weather trials.

Peter
(PilotAware Development Team)
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