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#11
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Low Cost ADS-B Transceivers
On 3/18/2010 2:32 AM, Andy wrote:
On Mar 17, 9:22 am, Darryl wrote: I worry about how well we will have ADS-B ground station coverage along busy low-level routs like major ridge soaring locations, the white mountains etc. Without that, gliders with UATs and 1090ES will not see each other. Darryl, Was I mistaken in taking from the survey that ADS-B supports aircraft- to-aircraft position reporting without a ground station repeater? I figured that would allow two gliders in any remote location to see each other if they both had ADS-B transceivers (like the Mitre unit). With ground stations you then should get position reporting between transponder and ADS-B. I figured any collision avoidance advice would be a function of on- board software capability, not constrained by the means of position reporting - as long as you know your position and track and a target's position and track, shouldn't you be able to figure out the collision avoidance part? It seems to me that you should be able to design ADS-B such that you no longer need transponders. What did I miss? 9B If both gliders have ADS-B UAT transceivers they will be able to see each other without a ground station, just like FLARM. The same is the case if both gliders use 1090ES transceivers. The problem is if one glider has ADS-B UAT and the other uses 1090ES, then they can't see each other unless they are within range of a ground station. In addition, the ground station will transmit the position of any Mode C/S transponder equipped aircraft to an ADS-B equipped aircraft. As a result, if you are within range of a ground station, an ADS-B equipped aircraft will see all other ADS-B or conventional transponder equipped aircraft in its vicinity. If you have a MITRE transceiver connected to a PDA or a device like an iPhone, there is nothing stopping someone from implementing a poor man's TCAS in addition to showing other aircraft on a moving map display. The new iPhone is a particularly intriguing device, as it has a built in sensor that permits you to display a compass bearing. As a result, you could implement a voice warning system that could actually tell you the bearing, distance, and relative altitude of a collision threat based on your current heading. This could be very useful in a glider that is in a thermal, where the heading is constantly changing. -- Mike Schumann |
#12
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Low Cost ADS-B Transceivers
Andy On Mar 17, 11:32 pm, Andy wrote: On Mar 17, 9:22 am, Darryl Ramm wrote: I worry about how well we will have ADS-B ground station coverage along busy low-level routs like major ridge soaring locations, the white mountains etc. Without that, gliders with UATs and 1090ES will not see each other. Darryl, Was I mistaken in taking from the survey that ADS-B supports aircraft- to-aircraft position reporting without a ground station repeater? I figured that would allow two gliders in any remote location to see each other if they both had ADS-B transceivers (like the Mitre unit). With ground stations you then should get position reporting between transponder and ADS-B. That is TIS-B and that only happens if the transponder equipped aircraft is within range of ATC radar. The ATC radar data is processed by back-end systems and then relayed through an ADS-B ground station. Just being within range of an ADS-B groudn station does *not* mean you see nearby transponder equipped aircraft. The ADS-B ground statiosn are going to provide coverage over vast areas where there is no ATC radar coverage. I think some people might be confused about this, thinking maybe the ADS-B ground stations have radar or multilateration etc. can can locate transponder equipped aircraft. They cannot. That data that is delivered as TIS-B (SSR radar/transponder derived data) comes from existing ATC radar systems. This is one reason it's nice to have say PCAS in the PowerFLARM so you can get some warning of nearby transponder equipped aircraft even outside radar coverage (in the case of PCAS outside of ATC radar coverage this assumes some other interrogator like TCAS in overflying aircraft). BTW one of the interesting problems with the whole alphabet soup of ADS-B/TIS-B/ADS-R/FLARM/PCAS/TCAD/TCAS etc. is threat deduplication. There are many problems that can cause a threat to appear duplicated if detected via different technologies or you can even see a ghost of yourself. I expect this to be an interesting problem with many of these systems, and we'll need to see how well they work in practice. ATC radar coverage is not I figured any collision avoidance advice would be a function of on- board software capability, not constrained by the means of position reporting - as long as you know your position and track and a target's position and track, shouldn't you be able to figure out the collision avoidance part? It seems to me that you should be able to design ADS-B such that you no longer need transponders. What did I miss? 9B TCAS uses transponders, that's how it works. We can't change that just becasue it seems antiquated (which it does). TCAS "sees" other aircraft based on Mode C or Mode S interrogations. TCAS-II is deeply integrated with Mode S and uses Mode S data links between different TCAS-II equipped aircraft to coordinate resolution advisories. If you even want to think about using ADS-B for collision avoidance you need everybody carrying ADS-B data-out. That won't happen in the USA for another 10 years. The only technology designed to be used in cockpits that issues an RA that pilots are supposed to follow is TCAS. Today in areas like around Reno/Minden (where Andy flys), TCAS is the last fallback for avoiding a collision between a glider and a fast jet or airliner. For other folks flying out in the boondocks, I don't care, but around dense airline and jet traffic we need to make sure we have compatibility with TCAS. Collision avoidance (vs. traffic awareness) is complex, TCAS is a RTCA standard, there is no equivalent standard developed for collision avoidance using ADS-B. Without that manufactures cannot make something, regulatory agencies cannot require it, etc. It just does not exist. As ADS-B technologies roll out we also need a back-up in the national airspace system, and ATC radar and transponders will be that backup so I just don't see them going away in our lifetimes. The FAA has been struggling to just get mandatory ADS-B data-out carriage by ~2020. The motivations for getting that adopted in GA has been muddled, which is a pitty I think this could have been marketed much better to owner/pilots. But without wide option of ADS-B data- out, let alone data-in doing TCAS style collision avoidance based on ADS-B makes no sense. But I don't really blame the FAA, they've been trying to work all this and Nextgen out, with a awful lack of overall funding. Long long terms (==decades) ADS-B based systems could offer more than TCAS or could work better with it. Today TCAS-II version 7 can use ADS-B to reduce the transponder pinging between aircraft but it never issues an RA based on ADS-B position data. It would be great to see a system that offers the capabilities of TCAS-III like horizontal RA maneuvers, and maybe better range than TCAS in crowded airspace environments. TCAS-III became so complex it never got to market. And again just be careful exactly what you are getting in any scenario. ADS-B data-out just sends your position, and you have to add a GPS source (which today if you wanted to fully comply with future carriage requirements (which don't apply to gliders) is expensive). You can have a box that does ADS-B data-in but how is traffic displayed? Just having an "ADS-B receiver" does not mean you will get traffic warnings. The box might well happily watch the treat aircraft as you both collide. That traffic display/warning happens at an application layer above ADS-B. There are standards for symbology etc. to display in aircraft for ADS-B data but much of that is not that relevant to us. Some new traffic awareness system from vendors like Garmin will mix active transponder interrogation (TCAS-I like) with ADS-B 1090ES data-in derived traffic. But those systems never issues RAs anyhow. --- Like Mike says. UAT will see UAT directly, 1090ES will see 1090ES directly. We are going to have both in the USA glider fleet and need to start realizing that. The FAA thought that UAT would be popular in the GA/low-end market etc. but they never really produced a convincing driver for adoption of ADS-B in general or of UATs over 1090ES. Way way back when this started transponders looked expensive and complex but market dynamics produce things like the Garmin GTX 330 in GA and the Trig TT21 well suited for gliders. If you are engineering a modern Mode S transponder it is not much to add the capability to do 1090ES data-out and add a small box to do 1090ES data-in. In the GA market that makes sense since most aircraft are required to have a transponder anyhow so you might as well do ADS-B over 1090ES. Europe has mandated Mode S transponder usage so we are seeing lots of Mode S innovation driven by that, that's why we have the Trig TT21. And that is why European glider related avionics companies like Butterfly/PowerFLARM and Garrecht have 1090ES based products. UAT should have benefits, like lower power consumption (but the TT-21 has pretty low power consumption), maybe FIS-B (needs a way to display the data), maybe lower cost - but we've got to see actual products in market to be sure about the cost. Current UAT transceivers are not really low cost/suitable for gliders, hopefully this will change. The marketing guy in me thinks the time to market will have a big impact on adoption of 1090ES vs UAT in gliders, and right now 1090ES based devices from Europe like the TT21 and PowerFLARM are becoming available. For several $k you will soon be able to set up a pretty impressive Trig TT21+1090ES data-out+PowerFLARM system, not bad for early adopter costs. For folks with only Mode C transponders or who fly in areas where there are no need for transponders I would hope low- cost/low-power UAT transceivers do become available. It is going to be interesting to see what happens. How is that for a rambling reply? Darryl |
#13
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Low Cost ADS-B Transceivers
The real mess is that 1090ES is basically another layer of bailing wire
added to a 1940s vintage technology platform that has EXTREMELY limited bandwidth. There is a lot of concern, that if everyone was 1090ES equipped in high density environments like NYC, Atlanta, and LA, the whole system would collapse. ADS-B UAT is new technology with none of these problems and LOTS of bandwidth, so it has the potential for a long future, permitting tons of future innovations, and no technical risks in high density environments. It is also very inexpensive to implement if you are allowed to use commercial grade components. The frustrating problem is that by focusing on IFR applications, and ignoring (until recently) low cost VFR options, the FAA has created a vacuum that is being filled by 1090ES equipment, that is going to muddle things for a long, long time to come. The world would have been a lot simpler, and cheaper in the long run, if the FAA would have picked ADS-B UAT as the single US standard and bitten the bullet on a quick conversion, whose end result would be a complete phase out of Mode C/S transponders. Instead we are going to add the ADS-B layer on top of the Mode C/S stuff, with no clear strategy on how any of this legacy technology will ever disappear. Mike Schumann On 3/18/2010 1:37 PM, Darryl Ramm wrote: Andy On Mar 17, 11:32 pm, wrote: On Mar 17, 9:22 am, Darryl wrote: I worry about how well we will have ADS-B ground station coverage along busy low-level routs like major ridge soaring locations, the white mountains etc. Without that, gliders with UATs and 1090ES will not see each other. Darryl, Was I mistaken in taking from the survey that ADS-B supports aircraft- to-aircraft position reporting without a ground station repeater? I figured that would allow two gliders in any remote location to see each other if they both had ADS-B transceivers (like the Mitre unit). With ground stations you then should get position reporting between transponder and ADS-B. That is TIS-B and that only happens if the transponder equipped aircraft is within range of ATC radar. The ATC radar data is processed by back-end systems and then relayed through an ADS-B ground station. Just being within range of an ADS-B groudn station does *not* mean you see nearby transponder equipped aircraft. The ADS-B ground statiosn are going to provide coverage over vast areas where there is no ATC radar coverage. I think some people might be confused about this, thinking maybe the ADS-B ground stations have radar or multilateration etc. can can locate transponder equipped aircraft. They cannot. That data that is delivered as TIS-B (SSR radar/transponder derived data) comes from existing ATC radar systems. This is one reason it's nice to have say PCAS in the PowerFLARM so you can get some warning of nearby transponder equipped aircraft even outside radar coverage (in the case of PCAS outside of ATC radar coverage this assumes some other interrogator like TCAS in overflying aircraft). BTW one of the interesting problems with the whole alphabet soup of ADS-B/TIS-B/ADS-R/FLARM/PCAS/TCAD/TCAS etc. is threat deduplication. There are many problems that can cause a threat to appear duplicated if detected via different technologies or you can even see a ghost of yourself. I expect this to be an interesting problem with many of these systems, and we'll need to see how well they work in practice. ATC radar coverage is not I figured any collision avoidance advice would be a function of on- board software capability, not constrained by the means of position reporting - as long as you know your position and track and a target's position and track, shouldn't you be able to figure out the collision avoidance part? It seems to me that you should be able to design ADS-B such that you no longer need transponders. What did I miss? 9B TCAS uses transponders, that's how it works. We can't change that just becasue it seems antiquated (which it does). TCAS "sees" other aircraft based on Mode C or Mode S interrogations. TCAS-II is deeply integrated with Mode S and uses Mode S data links between different TCAS-II equipped aircraft to coordinate resolution advisories. If you even want to think about using ADS-B for collision avoidance you need everybody carrying ADS-B data-out. That won't happen in the USA for another 10 years. The only technology designed to be used in cockpits that issues an RA that pilots are supposed to follow is TCAS. Today in areas like around Reno/Minden (where Andy flys), TCAS is the last fallback for avoiding a collision between a glider and a fast jet or airliner. For other folks flying out in the boondocks, I don't care, but around dense airline and jet traffic we need to make sure we have compatibility with TCAS. Collision avoidance (vs. traffic awareness) is complex, TCAS is a RTCA standard, there is no equivalent standard developed for collision avoidance using ADS-B. Without that manufactures cannot make something, regulatory agencies cannot require it, etc. It just does not exist. As ADS-B technologies roll out we also need a back-up in the national airspace system, and ATC radar and transponders will be that backup so I just don't see them going away in our lifetimes. The FAA has been struggling to just get mandatory ADS-B data-out carriage by ~2020. The motivations for getting that adopted in GA has been muddled, which is a pitty I think this could have been marketed much better to owner/pilots. But without wide option of ADS-B data- out, let alone data-in doing TCAS style collision avoidance based on ADS-B makes no sense. But I don't really blame the FAA, they've been trying to work all this and Nextgen out, with a awful lack of overall funding. Long long terms (==decades) ADS-B based systems could offer more than TCAS or could work better with it. Today TCAS-II version 7 can use ADS-B to reduce the transponder pinging between aircraft but it never issues an RA based on ADS-B position data. It would be great to see a system that offers the capabilities of TCAS-III like horizontal RA maneuvers, and maybe better range than TCAS in crowded airspace environments. TCAS-III became so complex it never got to market. And again just be careful exactly what you are getting in any scenario. ADS-B data-out just sends your position, and you have to add a GPS source (which today if you wanted to fully comply with future carriage requirements (which don't apply to gliders) is expensive). You can have a box that does ADS-B data-in but how is traffic displayed? Just having an "ADS-B receiver" does not mean you will get traffic warnings. The box might well happily watch the treat aircraft as you both collide. That traffic display/warning happens at an application layer above ADS-B. There are standards for symbology etc. to display in aircraft for ADS-B data but much of that is not that relevant to us. Some new traffic awareness system from vendors like Garmin will mix active transponder interrogation (TCAS-I like) with ADS-B 1090ES data-in derived traffic. But those systems never issues RAs anyhow. --- Like Mike says. UAT will see UAT directly, 1090ES will see 1090ES directly. We are going to have both in the USA glider fleet and need to start realizing that. The FAA thought that UAT would be popular in the GA/low-end market etc. but they never really produced a convincing driver for adoption of ADS-B in general or of UATs over 1090ES. Way way back when this started transponders looked expensive and complex but market dynamics produce things like the Garmin GTX 330 in GA and the Trig TT21 well suited for gliders. If you are engineering a modern Mode S transponder it is not much to add the capability to do 1090ES data-out and add a small box to do 1090ES data-in. In the GA market that makes sense since most aircraft are required to have a transponder anyhow so you might as well do ADS-B over 1090ES. Europe has mandated Mode S transponder usage so we are seeing lots of Mode S innovation driven by that, that's why we have the Trig TT21. And that is why European glider related avionics companies like Butterfly/PowerFLARM and Garrecht have 1090ES based products. UAT should have benefits, like lower power consumption (but the TT-21 has pretty low power consumption), maybe FIS-B (needs a way to display the data), maybe lower cost - but we've got to see actual products in market to be sure about the cost. Current UAT transceivers are not really low cost/suitable for gliders, hopefully this will change. The marketing guy in me thinks the time to market will have a big impact on adoption of 1090ES vs UAT in gliders, and right now 1090ES based devices from Europe like the TT21 and PowerFLARM are becoming available. For several $k you will soon be able to set up a pretty impressive Trig TT21+1090ES data-out+PowerFLARM system, not bad for early adopter costs. For folks with only Mode C transponders or who fly in areas where there are no need for transponders I would hope low- cost/low-power UAT transceivers do become available. It is going to be interesting to see what happens. How is that for a rambling reply? Darryl -- Mike Schumann |
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