Q&A for Link16

tiag

#anchor(Question & Answers about Link16 in BMS)

Hey you all,

U4 is here with many new toys to play with. Link16 is one of them. Link16 in BMS is a 10K+ LOC where most of our team has been working in the last months. It was a monster to dev since we had to touch almost every F-16 avionics and BMS code: all displays HSD/B-Scope/HUD/HMS, radar, implementation of the new MIDS/JTIDS, messages, MP code, Campaign, Agg/Deagg logic, UI, DED, ICP, cockpit and so on. But sometimes you gotta get the bulls-by-the-horn and simply do it.

Our Doc team lead by Micro on the Viper and Dusty on the Eagle did a great job on writing up all new avionics and symbology. This post is not a substitute to this awesome work, but a send-to-thread when someone has a quick question.
I will keep it updated and link to the docs later.

… and here we go…

1) Why the circles of Link16 on the HMS are not always perfectly overlapping with the aircraft?

BMS simulates drift of the HMS in a very accurate way. As in real life, the HMS needs to be re-aligned a couple of times during a mission.
We suggest to align at ramp start, end-of-runway (EOR) checks and fence-check in. This will mitigate the offset but will not eliminate completely, as in the real aircraft.

2) Why the circles on HMS and HUD keep jumping around and sometimes do not overlap with the aircraft?

Link16 is a network based on updates at given times. Update times can be fast within few seconds for FLIGHT PPLIs to very long values (3 minutes) like fuel updates for PPLIs.
So, depending on the track type (PPLI or SURVEILLANCE) and track quality, these updates times may change significantly and lead to these jumps.
Remember, Link16 is not an continuous signal. MIDS/JTIDS receive signals and do extrapolations.
If the aircraft makes abrupt changes in flight path between updates, circles etc will not overlap at all with aircraft anymore.
Moreover, BMS implementation in U4 simulates delays, precision and different types of updates.

3) Everything seems correct on UI, but I cant see any L16 symbology on my displays.

Check if MIDS is on, DTC loaded, Net sync.

4) I am trying to run an old TE/Campaign but I cant see any L16 symbology in cockpit.
(variation) I am trying to run an old TE/Campaign but in ATO all channels are displaying —

Link16 in BMS requires a configuration file for the network (extension

xxx.l16.txtpb

).
This file is already set for all campaigns and new TEs created in 4.37.4.
For old TEs and campaigns you need to follow these steps:

Simply make a copy of the Te_New.l16.txtpb
Rename it with the name of your TE/Campaign. For example, if the file is Operation_Puma.tac , then rename the copy of the Te_New.l16.txtpb to Operation_Puma.l16.txtpb

And you are good to go.

5) I can see the PPLI circles in green and blue, but I dont see any other white, yellow or red circles.

These other circles are Surveillance circles. In order to see them, there are a couple of things which are required:

The Link16 Network design must have a Surveillance NPG.
You need an AWACS on your team.
AWACS must be able to detect these tracks. It takes into account terrain/altitude, if in range and if jammed by SOJ platforms.
You need to be in range of the JTIDS of the AWACS to get the signal. The JTIDS of a E-3 is more powerful than than MIDS of the F-16 (about 400nm ish range)

6) Why some Link16 symbology keeps disappearing and reappearing in the MFDs?

BMS simulates the MIDS/JTIDS by implementing the so called System Track File(STF). This file is a container for a up to 40 tracks.
BMS simulates a priority system to display the most important tracks. So, the simulated logic may drop less important tracks in situations with many tracks.
For example, friendly surveillance tracks far away from own aircraft are less important than tracks identified as hostile at closer range.
Logic in the MIDS/JTIDS to store tracks on the STF follows this priority system as per real life:

PPLI of FLIGHT and TEAM are always stored.
Mission objectives track (N/I in U4)
FLIGHT and TEAM members TOI (N/I in U4)
FLIGHT and TEAM members shotlines (N/I in U4)
DONOR tracks (TOI and shots) (N/I in U4)
Surveillance Tracks (range, ID, closure rate)
DONOR PPLIs (range)
Other PPLIs (range)
additionally, the PDLT is ALWAYS stored

7) I cant distinguish surveillance friendlies from PPLI tracks.

The surveillance friendlies are green circles with dashed lines. Due to the low resolution of the MFDs in U4, it is indeed hard in some cases
distinguish them from PPLI tracks, specially when circles are overlapping.

8 ) If I shot down an enemy AWACS E-3, will the enemy loose its Link16 capability?

No, only the SURVEILLANCE NPG will be out. PPLI NPG will still be active as far the aircraft are in range of each other.
MIDS/JTIDS in fighters has a typical range of 150nm.

9) I dont understand this NPG thing.

This first round of development of Link16 in U4 enables two types of NPG (Network Participation Groups): Precise Participant Location and Identification (PPLI) and SURVEILLANCE INFORMATION (SURVINFO).
The PPLI is a type of NPG where aircraft (and later ground units, ships, patriots, etc) with a Link16 terminal (like the MIDS) share tons of data like ammo, position, speed, altitude, etc.
The SURV is a type of NPG where a C2 unit (in BMS = AWACS) shares tracks it has detected. As you can imagine much less information is available and in U4 it (try to) aligns with our AWACS Request Picture/Declare the best we can.

The way NPGs were implemented allows to implement Link16 in different ways. In U4, one can have a three different types of Link16 networks:

One with PPLI and SURVINFO
One with only PPLI
One with only SURVINFO

All that is configurable via the xxxxl16.txtpb files.

Structure of l16.txtpb files
Lets take an example of Save0.l16.txtpb in KTO for Team 2, the South Korea and USA alliance:

teams {
  team_number: TEAM_2
  nets {
    channel_number: 0
    npg_type: NPG_PPLIA
    npg_type: NPG_PPLIB
    npg_type: NPG_SURVINFO
  }
  nets {
    channel_number: 54
    npg_type: NPG_MISSION
  }
  nets {
    channel_number: 33
    npg_type: NPG_EW
    npg_type: NPG_F2F
  }
  nets {
    channel_number: 101
    npg_type: NPG_MISSION
    npg_type: NPG_F2F
  }
  nets {
    channel_number: 125
    npg_type: NPG_MISSION
  }
}

The first Net is on Channel 0 and has the NPGs PPLI (A and B, no difference in U4) and the SURVINFO. These enables Channel 0 for Team 2 with these NPGs.
If one wants to have only PPLI, then one only needs to remove the line with npg_type: NPG_SURVINFO from this net:

nets {
     channel_number: 0
     npg_type: NPG_PPLIA
     npg_type: NPG_PPLIB
   }

For a Link16 network without PPLI but only SURVINFO, then it is the other two lines:

nets {
     channel_number: 0
     npg_type: NPG_SURVINFO
   }

The other channels and NPGs are not active in U4 and are placeholders for other types of NPGs (->4.38).
Finally, this way of defining the different channels with NPGs will give lot of flexibility for many tactical situations like SURVINFO NPGs in different channels linked to different AWACS, separated F2F channels for different geographic regions mission types, etc.
Here is an example of how a Link16 Network is constructed source :

10) Why are tons of F16s flying in Korea without any PPLI?

Not all F-16s have Link16. The F-16s block 32 of ROKAF are one example.

11) Where are the shot-lines in the HSD?

N/I in U4. Check 4.38.

12) When I am deep into enemy territory, I only see the blue circles of my FLIGHT PPLI. Why is that?

You are too far away from the AWACS to receive SURV tracks (>400nm ish) and too far away from other PPLI (> 150nm ish).

13) How does EW interference or jamming impact Link16 data representation accuracy?

BMS models in U4 only the effect of stand-off jamming (SOJ) platforms like the EF-18Gs and EA-6A/Bs. An SOJ decreases the capability of the AWACS radar to detect and, thus, suppress the generation of a track.

14) I have edited my campaign or TE file in Mission Commander (MC) and now I dont have any Link16 tracks anymore?
Edits in MC are compatible with Link16, however, when you save the edited TE or campaign with a different name, MC does NOT save the Link16 network definition file with the new name.
You can simply avoid this issue by saving the new edited TE or campaign with the same name as the original one (virtually overwritting it) OR make a copy of the old of the original l16.txtpb definition file and rename it for your edited TE or campaign.
For example:

Old TE was called OPERATION_PUMA.tac with the link16 file called

OPERATION_PUMA.l16.txtpb

You edited your TE in MC and saved it as

OPERATION_PUMA_V2.tac

You need now to make a copy and rename the the original l16.txtpb to

OPERATION_PUMA_V2.l16.txtpb

15) Are you planning to further develop the Link16?
Yes. We have developed only about 30ish% of what is the public domain.

Known Bugs

If you go to P3 of the Datalink pages in the DED and move to OWN# field, and while there you RTN, the numerical pad on the ICP will be frozen.
To restore functionality you have to go back to the P3 page with LIST->ENTER->…P3 and move to another field (e.g. any STN position) before you leave the page again.
If during the click-dance in the UI you click on another flight, which is not yours, and directly after you save the data cartridge, the Link16 information of this flight will be saved -> will pork your track number since you will have the track number of another flight.

Scorpion82

Thanks for the detailed overview @tiag

I suppose there are a few keybinds introduced inline with it?

farazparsa

@tiag jesus Christ
you guys did an amazing job…
i have one question tiag
do you have any plans to implement CEC(Cooperative Engagement Capability) or HTC triangulation data capabilities for cooperative Sead in future?
Thank you

sasah320

@tiag The work you have done here is just unspeakably huge. Congratulations my friend!! You and your team have done a LOT!

tiag

@Scorpion82 yes all in the tech docs by
@Kolbe-49th

tiag

@farazparsa
CEC has been modeled in CMO so far very broadly because it is not in public domain. Unless some more detailed information appears in public domain, we are not modelling it.

Note that I put tons of videos about L16 on another thread and that is what we got in U4.

tiag

@sasah320 we did, we did, tchê!
Falcões da Noite did their part!!!

alfagolf

Can you explain the right start-up sequence?

Micro_440th

@alfagolf -34 (Page 246-248, also 256)

jayb

In the spirit of a Q&A how about a list of link-16 relevant abbreviations and their meaning

alfagolf

@jayb better I suggest a “Link16 for dummies” thread

Scorpion82

@tiag

Thanks, have found them already. Only thing missing are the switch & DOF list entries now.

madeiner

I can’t seem to get SURV tracks for bogeys in the campaign, while i can get them in the training mission and in other tests.
AWACS is 200nm away from the FLOT and calls all sorts of contacts on radio but nothing shows on HSD. I tried adding it as donor and team/flight member (the campaign doesn’t seem to do it automatically) but nothing changes. Once i get to around 150nm from the AWACS it correctly shows blue if he’s in flight list.

What am i doing wrong?

Master Yoda

Reading the dash 34 I am left a bit confused as to the following: Will you see the positions of all friendlies within 150nm regardless of whether they are part of your fc subnet? I understand the 40 track limit but it’s bit unclear whether you pick up positions from non team/donor aircraft.

pyhg

@Master-Yoda same question for me somehow. I created a topic about this 10 minutes ago. It looks like you get many positions whether or not you share the FC or MC or not.

I guess FC and Donnor might be useful instead for target sorting/sharing

tiag

Please read here:
https://forum.falcon-bms.com/topic/27468/q-a-for-link16

Master Yoda

@tiag couldn’t find a relevant answer to my question in that q&a

tiag

@Master-Yoda
yes, it is there.
It says 150nm and does not mention the FC channel.
So this is the answer. No effect.

And about the positions it is also there, question #6, which I copy for you:

6) Why some Link16 symbology keeps disappearing and reappearing in the MFDs?

BMS simulates the MIDS/JTIDS by implementing the so called System Track File(STF). This file is a container for a up to 40 tracks.
BMS simulates a priority system to display the most important tracks. So, the simulated logic may drop less important tracks in situations with many tracks.
For example, friendly surveillance tracks far away from own aircraft are less important than tracks identified as hostile at closer range.
Logic in the MIDS/JTIDS to store tracks on the STF follows this priority system as per real life:

PPLI of FLIGHT and TEAM are always stored.
Mission objectives track (N/I in U4)
FLIGHT and TEAM members TOI (N/I in U4)
FLIGHT and TEAM members shotlines (N/I in U4)
DONOR tracks (TOI and shots) (N/I in U4)
Surveillance Tracks (range, ID, closure rate)
DONOR PPLIs (range)
Other PPLIs (range)
additionally, the PDLT is ALWAYS stored

nekoworkshop

Regarding the “strength” number in A2A track expanded data

Strength data is received via the J3.2I message. When the received strength is unspecified, it defaults to “1.” The text color in this field corresponds to the sovereignty associated with the aircraft type.

If I’m understanding this correctly, since BMS currently does not simulate the J3.2I (or is it the same as J3.2? ) message, does this means currently all SURV tracks have a strength of 1?

I’ve played a bit during the weekend and so far I haven’t seen any strength number other than 1.

tiag

@nekoworkshop
yes, BMS simulates that.
Tracks close to each other are joined as a single track depending on ID, distance and other parameters.

In general: The more distance a track is from you and the less hostile it is (unknown->suspected->hostile) , the more aggregated it will be as a strength larger than 1.

Q&A for Link16

… and here we go…

Known Bugs

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