Looking for someone who can answer how DJI FPV communication works.
My devices:
1. Goggles
2. Drone
3. Remote Control
4. Motion Controller

what communicates with what in wich direction?
1 <--> 2 ?
3 --> 2 ?
3 --> 2 ?
3 --> 1, 2?
4 --> 1, 2?
2 --> 1

2 —> 1 is obvious, for telemetry and video receiving

Can 3 and 4 communicate at the same time to the drone 2, useful for a 2º person learning? Does it depend only on firmware?

Can 3 and 4 communicate at the same time to the drone 2, useful for a 2º person learning? Does it depend only on firmware?

2 <—>1,3/4

How I see the DJI FPV communication!
Please clarify if Goggles communicate in 5.8GHz to drone or only at 2.4GHz,
from documentation, goggles have 3 transmission antennas and one receiving antenna.
Drone has 2 transmission antennas and 2 receiving.
Remote and motion controller have no information about antennas, maybe with a single antenna each.

EiraSYS Posted at 5-3 11:20
How I see the DJI FPV communication!
Please clarify if Goggles communicate in 5.8GHz to drone or only at 2.4GHz,
from documentation, goggles have 3 transmission antennas and one receiving antenna.

This is a very helpful diagram! I'm new to the FPV (just got it last week), and there's a lot I'm still trying to figure out.

How do "Audience Goggles" fit into this data flow? My understanding is that the Audience Goggles get their signal from the Primary Goggles.

Is that right?

Thx!

TCS

Chaosrider Posted at 5-4 07:24
This is a very helpful diagram! I'm new to the FPV (just got it last week), and there's a lot I'm still trying to figure out.

How do "Audience Goggles" fit into this data flow? My understanding is that the Audience Goggles get their signal from the Primary Goggles.

Have no idea, DJI does not inform us about it. I would say that Audience mode is a setting sent to the drone to broadcast video without exclusive protection for our goggles. Maybe the goggles can work as a repeater for the video, but that wouldn't be necessary.

EiraSYS Posted at 5-4 07:58
Have no idea, DJI does not inform us about it. I would say that Audience mode is a setting sent to the drone to broadcast video without exclusive protection for our goggles. Maybe the goggles can work as a repeater for the video, but that wouldn't be necessary.

It's a bit surprising to me that there isn't a clear definitive answer to this question...

Chaosrider Posted at 5-8 07:40
It's a bit surprising to me that there isn't a clear definitive answer to this question...

Where can we get more information about DJI O3 (OcuSync 3.0) Transmission System?
Any patent or technical paper out there available to read?

EiraSYS Posted at 5-8 13:40
Where can we get more information about DJI O3 (OcuSync 3.0) Transmission System?
Any patent or technical paper out there available to read?

Probably.

I saw a good explanation from an OP in a private message. It seems that the video signal to the primary goggles requires 2-way communication between the primary goggles and the aircraft for the transfer of "data correction packets". The audience goggles don't transmit to the aircraft, so they can't get these "handshaking required" packets.

What's wrong with the "basic" video stream that it requires these "data correction packets"? What's in the DCPs? Why is active handshaking required to get the DCPs?

No clue, but I'm still poking at the issue!

Thx,

TCS

Chaosrider Posted at 5-9 06:35
Probably.

I saw a good explanation from an OP in a private message. It seems that the video signal to the primary goggles requires 2-way communication between the primary goggles and the aircraft for the transfer of "data correction packets". The audience goggles don't transmit to the aircraft, so they can't get these "handshaking required" packets.

Send me a copy of that private OP message!
Makes sense the data correction packets handshaking, the goggles may work just like a wifi router
that connects to several clients, one is the drone, the other is one of the controllers (standard one or
the motion controller) and the audience goggles are clientes that receive corrected video packets from
the goggles sent from the drone. Maybe there is no connection between the drone and the audience goggles.
What do you mean with "DCPs"?
There are several major flaws with those goggles, some I will reveal later, one of them is the fact that
we can't see all available information on a tablet, just like we see in the goggles.
The positive side is the motion controller, it can be further developed with complex behaviors
and works very fast!

The new diagram version!

EiraSYS Posted at 5-10 11:41
Send me a copy of that private OP message!
Makes sense the data correction packets handshaking, the goggles may work just like a wifi router
that connects to several clients, one is the drone, the other is one of the controllers (standard one or

DCP=Data Correction Packets

If, as I used to believe, the audience goggles got their signal from the primary goggles, there's no obvious reason why there would be any video quality degradation to the audience goggles, as long as the two were close together. And yet, most people report that their is.

On reflection, the audience goggles getting their signal from the drone produces an economy of transmission channels. The drone is transmitting anyway, so nothing new has to happen in that sense. If the audience goggles got their signal from the primary goggles, that would require an additional transmission path, since there would be no other requirement for the primary goggles to transmit.

But the question remains, what are these data correction packets, and why are they necessary?

That seems to be the root cause for the signal degradation in the audience goggles compared to the primary, the inability to get these DCPs, because the architecture requires handshaking to get the DCPs to the primary goggles, and the audience goggles can't do that.

I'll see if I can come up with a way to describe this more clearly.

Thx,

TCS

Chaosrider Posted at 5-11 13:55
DCP=Data Correction Packets

If, as I used to believe, the audience goggles got their signal from the primary goggles, there's no obvious reason why there would be any video quality degradation to the audience goggles, as long as the two were close together. And yet, most people report that their is.

The reason may be bandwidth, more image quality means more bandwidth, if there are errors in the transmission then those correction packets must be sent again to achieve high image quality. In the other hand, if you want higher frame rate you will loose image quality and those packets will not be retransmitted. This setting is available in primary goggles (high quality vs low latency) . I suppose that audience goggles will have low frame rate and low image quality to avoid bandwidth loose in the primary goggles. It may or should be a hidden software setting for audience broadcast.

EiraSYS Posted at 5-11 10:16
[view_image]The new diagram version!

Audience Goggles receive video from the drone not the pilot Goggles.
I am pretty sure there are other errors in the diagram. I will elaborate more tomorrow when I am at a computer.

Chaosrider Posted at 5-11 13:55
DCP=Data Correction Packets

If, as I used to believe, the audience goggles got their signal from the primary goggles, there's no obvious reason why there would be any video quality degradation to the audience goggles, as long as the two were close together. And yet, most people report that their is.

"the audience goggles getting their signal from the drone produces an economy of transmission channels. The drone is transmitting anyway, so nothing new has to happen in that sense."

Agreed.
Encoding and transmitting video is computationally expensive. The audience goggles receives whatever video it can. As you said, the pilot goggles are giving the drone feedback so the drone can optimize the video signal. The audience goggles don't benefit from this sort of optimization.

I'm not sure, but I don't think the goggles and the controller communicate directly.

One thing which puzzles me, is how much computing power appears to be in the controller. There's a sizeable heat sink in there. There's a lot more going on inside the controller than inside other RC transmitters.
The flight log in the drone records the quality of the link with the controller.

Duane Degn Posted at 5-12 22:05
"the audience goggles getting their signal from the drone produces an economy of transmission channels. The drone is transmitting anyway, so nothing new has to happen in that sense."

Agreed.

This is helpful, thanks! I'm starting to get at least a fuzzy image in my head about the need for the DCPs.

I haven't had many flights yet, but it's clear the the degradation/pixilation in the primary goggles (the only goggles I have so far!) is heavily dependent on speed and distance. Given that, and the need for the DCPs, it makes sense that the audience goggles would degrade/pixelate in proportion to the degradation in the pilot goggles, but higher in magnitude.  So if you fly close and slow, ther won't be a problem.

But if you want to do that...why buy an FPV...?

;-)

I'm still not tracking on the need for the DCPs. If the combination of the "basic" signal and the DCPs produces a better picture, then bandwidth is the same as if the data was all included in the basic signal. Right?  Part of what I'm lookin g for is what the limiting factor in the overall transmission architecture requires that the basic signal, and the DCPs, be separate?

You may be on to something with the question about processor capability in the controller itself. I can imagine an architecture where the DCPs get processed through the controller rather than the goggles.  But I can't (yet) imagine why it would be done that way. Perhaps the DCPs come on the control channel, rather than the video channel?

Thanks for your help in trying to unravel this mystery!

:-)

TCS

Makes sense, the Drone is the router, all other devices connect to it as clients, that's why we
must make the connection to each device using the defined sequence in the manual.
I don't have an audience goggles available, but someone can test if image quality is good when
pilot goggles are far away from the drone and the audience goggles is near it. In this situation
there shouldn't be signal degradation for the audience, so no need for DCPs, at the same time
pilot goggles should be receiving DCPs because pilot goggles may loose some data.

The controllers should also have data correction packets since they are critical for performance and control.
They may work in 2.4GHz for longer range.

Computing power of the controllers may be only for fast analog/digital data aquisition and wifi transmission.
I'm more curious about the power of each device, they have small batteries that last for at least 3 drone batteries
and are mainly used for communication with the drone, except the goggles that spend more energy with the screen.
Why the goggles have 3 transmitting antennas and only 1 for receiving data? Read it in documentation.

The new revision of the diagram:

EiraSYS Posted at 5-13 15:23
Makes sense, the Drone is the router, all other devices connect to it as clients, that's why we
must make the connection to each device using the defined sequence in the manual.
I don't have an audience goggles available, but someone can test if image quality is good when

I don't have an audience goggles available, but someone can test if image quality is good when
pilot goggles are far away from the drone and the audience goggles is near it. In this situation
there shouldn't be signal degradation for the audience,....

I've tested this several times.  There is one particular scenario where the primary goggles, audience goggles and controller are within 10 feet of each other. And the drone is about 1500 distant from the primary goggles, audience goggles and controller. In this scenario the primary goggles are never pixelated and the audience goggles are always pixelated.

This may be of some interest. The audience goggles are on the left and the primary goggles are on the right.


Notice at the end around 6:21 the FPV is about 100 feet from the primary and audience goggles yet there is some pixelation seen in the audience goggles.

BudWalker Posted at 5-13 20:10
This may be of some interest. The audience goggles are on the left and the primary goggles are on the right.

https://www.youtube.com/watch?v=549MufZoqnA

Quite interesting. So this means that even if the audience goggles are near the drone it won’t get the same image quality as the primary/pilot goggles! One more reason to test the scenario I described, put the audience goggles far away from the primary goggles then fly the drone from the primary to the audience and back again. You should see better image quality in the audience when the drone is near the audience goggles and it will fail with increasing distance. In my opinion the audience goggles get interference from the messages sent by the controller and the primary goggles, since it can not correct the information it will show degraded image quality. If the audience is far away from interference then you should get good image quality! ??? Try it!

EiraSYS Posted at 5-14 12:29
Quite interesting. So this means that even if the audience goggles are near the drone it won’t get the same image quality as the primary/pilot goggles! One more reason to test the scenario I described, put the audience goggles far away from the primary goggles then fly the drone from the primary to the audience and back again. You should see better image quality in the audience when the drone is near the audience goggles and it will fail with increasing distance. In my opinion the audience goggles get interference from the messages sent by the controller and the primary goggles, since it can not correct the information it will show degraded image quality. If the audience is far away from interference then you should get good image quality! ??? Try it!

I tried to do that experiment recently but I didn't get very far. Take a look at
https://fpvdronepilots.com/threads/dji-fpv-video-quality-problems-with-second-goggles.4904/page-3#post-39702

You might also be interested in this thread
https://fpvdronepilots.com/threads/audience-mode-quality.4477/#post-36769

BudWalker Posted at 5-14 20:17
I tried to do that experiment recently but I didn't get very far. Take a look at
https://fpvdronepilots.com/threads/dji-fpv-video-quality-problems-with-second-goggles.4904/page-3#post-39702

The tests described in the links did not get any conclusion. I keep what I said. Primary goggles and audience goggles set far away from each other, at least 2Km apart or up to 5Km! Audience Goggles should get good image quality in this situation.
Another test that can be done is to control battery current of each goggles. When there is interference battery will drain faster because goggles will transmit to drone more required correction packets as well as all the necessary processor power for it. If audience drain similar energy from the battery as the primary goggles this means it is also sending correction packets to the drone. Then the difference of audience or primary would be just software settings, giving bandwidth preference to primary goggles.

More important, the fan rotating faster means the current is also higher because of all  processing power consumption. I would like to know if anybody heard the fan and simultaneously had the message in the primary goggles of interference nearby!??? (No need for the audience goggles in this case)
This situation occurred to me in countryside in a empty area, no antennas, no houses, no electric network, no reason for any interference. Just the Drone alone! Anybody?

EiraSYS Posted at 5-15 05:00
The tests described in the links did not get any conclusion. I keep what I said. Primary goggles and audience goggles set far away from each other, at least 2Km apart or up to 5Km! Audience Goggles should get good image quality in this situation.
Another test that can be done is to control battery current of each goggles. When there is interference battery will drain faster because goggles will transmit to drone more required correction packets as well as all the necessary processor power for it. If audience drain similar energy from the battery as the primary goggles this means it is also sending correction packets to the drone. Then the difference of audience or primary would be just software settings, giving bandwidth preference to primary goggles.

You are correct. No conclusion from that test. That's an on going problem trying to determine the cause of the audience pixelation issue.

A 2 km to 5 km separation test will be logistically tough. In order for the audience goggles to connect  the primary goggles must first be connected. I don't know if that means the audience and primary need to be in range for the audience to connect. Or, a non-video link between audience and primary goes through the drone. After audience connect the audience goggles will have to be driven the 2 km away.

Just to be clear. I've not concluded that 1) the link is just between the audience goggles and the drone, or 2) the link is just between the audience and primary goggles. My current theory is that it's both.

Since there are no comments from DJI developers this will be my last assumption about the communication architecture! The DJI FPV communication may be a WiFi Mesh Network, with one or several Mesh Routers and several Mesh Clients. This will ensure safety and reliable communication even when one of the elements fail because all elements may communicate between them. Looking at the specs of each device, they all seam to share the same WiFi circuit and drivers, with the same power and frequency ranges. The Drone has more transmitting power compared to all other devices. The topology should certainly be a Mesh that can have firmware updates connecting to the internet with a mobile phone or iPad. Several competing Drones may even share data between them, optimizing the communication channels and ensuring stable video broadcast. Is there any additional information on the goggles when several drones are flying? Do they detect each others in Auto Channel mode? Have no way to test this, for now!
The new diagram:

EiraSYS Posted at 5-15 14:52
Since there are no comments from DJI developers this will be my last assumption about the communication architecture! The DJI FPV communication may be a WiFi Mesh Network, with one or several Mesh Routers and several Mesh Clients. This will ensure safety and reliable communication even when one of the elements fail because all elements may communicate between them. Looking at the specs of each device, they all seam to share the same WiFi circuit and drivers, with the same power and frequency ranges. The Drone has more transmitting power compared to all other devices. The topology should certainly be a Mesh that can have firmware updates connecting to the internet with a mobile phone or iPad. Several competing Drones may even share data between them, optimizing the communication channels and ensuring stable video broadcast. Is there any additional information on the goggles when several drones are flying? Do they detect each others in Auto Channel mode? Have no way to test this, for now!
The new diagram:[view_image]

I think you are on the right track. This would explain why the audience goggles sometimes seems to be linked to the primary goggles and other times connected to the drone. And, sometimes both.

I made another attempt yesterday. The primary and controller were at one location with the secondary location behind a hill and about 1500 feet distant. In addition, there was a third location with a larger hill between it and the secondary location. The drone was flown between these three locations. The observations made by the guy wearing the audience goggles support the claim that the drone-to-audience-goggles link has the most effect on the pixelation issue. Unfortunatley, the audience goggles stopped recording when the drone temporarily landed back at the launch site. We are going to give it another go.

Hi guys I’m new and have very limited experience with drones and anything computer
Please can you advise or explain the avata MC unit does this talk to the goggles that in turn talk to the drone? Or does the MC communicate with the drone directly the diagram posted on the fpv is helpful Imwas just wondering if yheee is any technical info on the avata ?

You are doing the same question I did! The diagram is not from DJI, I did it. They keep secret on that subject. I suppose it’s a mesh grid, having the drone as the main router. So all devices may talk to each other using DJI ocusync 3 proprietary protocol.