H Plus Team Mode and Live Streaming to a Base Station

[jbeav]

Now that people are getting more experience with the team mode on the plus, does anyone know the distance that two controllers can be separated while running team mode? I'm not fully sure how everything communicates. Is the camera control signal sent from the slave to the master and then on to the drone? Or, does the slave send its own signal directly to the drone? If it is the latter, it seems that the controller distance to the drone is the limiter, but if it's the former, it would likely be the controller-controller distance that is limiting.

Ultimately, I just want "follow me" capability with video streaming to a tv at a base station. To me, one way to do this would be to have the master controller on the moving object with the slave at the base station. Hopefully someone can provide some insight on this!

 

[Steve Carr]

If both controllers are connected to the camera then Team mode doesn't work. The two controllers have to bound together as master and slave and the master is connected to the camera. So it appears the master acts as a relay for the video and camera control from/to the slave. At least that is my understanding.

The distance and video lag are good questions. I don't know that anyone has experimented to test it. You may be the first.

 

[jbeav]

Thanks for the reply, Steve. Doing the stream through team mode probably isn't the most efficient way, even if it is possible. I'll let everyone know if anything develops further on my end... but maybe don't hold your breath!

 

[DCH]

Yes, like @Steve Carr said the Slave is linked to the Master and the camera control signal from the Slave is sent thru the Master.
Think of the Master ST16S as a WiFi router for the 2.7gHz control signal from the slave. This distance will depend on many factors, it could ultimately be the same limiting distance of the aircraft as long as line of sight is maintained between the two ST16Ss. However I have learned from testing the range of Team Mode that the Slave receives its 5.8gHz signal from the C23 directly, not thru the Master. If the Slave looses that 5.8gHz camera signal the Slave video will go black, Team Mode will cancel itself immediately, and all control is returned to the Master. Therefore the most limiting range factor is quite likely the 5.8gHz video link to the Slave, so LOS must be maintained to both the Master and the Aircraft at all times.

 

[Steve Carr]

the Slave receives its 5.8gHz signal from the C23 directly, not thru the Master.

Ah. I didn't realize both controllers link to the camera. That would seem to increase the lag and shorten the video distance.

 

[DCH]

That would seem to increase the lag and shorten the video distance.

Possibly, but I have a hard time understanding how that is possible. In the RF world (which is right up my alley), a transmitter transmits a given signal with a certain amount of power. That power determines the potential range, not the number of receivers that will/or can receive that signal, there is no limit to the number of receivers a signal can be received by.

That said, the sUAV world may have different laws of physics attributed to it that I don't fully understand. If this is the case I would like someone to explain to me how another video receiver can cause decreased range of the transmitter. As far as introducing lag into that signal, I am equally baffled, this would only be the case if a signal were being repeated by the Master, but it is a direct feed from the camera, so how can there be a lag?

Both video range and lag seem to be either accepted fact or tribal knowledge, either way it appears I need to understand this theory better. Is there a post or thread I can read on the subject?

 

[Steve Carr]

The video is sent using wifi. When connecting more that one device the camera wifi has to send the packets to each device. Each packet has an address for the intended receiver so.....2 receivers means the camera sends twice the number of packets. As distance increases more packets are lost. Every lost packet has to be resent by the camera. That results in a delay in sending the next packet which shows up as lag in the video. As more packets get lost the display becomes pixelated as distance is increased until the video freezes.

 

[DCH]

Thank you Steve! That I can understand. My mind was only thinking in terms of RF, not data transmissions.

 

[DoomMeister]

That is an advantage that most FPV pilots have. They do use RF radio and not data for the video. They can’t afford the lag!

I am going to hit the hay. I’ve been up since 5AM. If you want, copy that info to the thread so others can understand.

Thanks!

Steve

 

[Steve Carr]

That is an advantage that most FPV pilots have. They do use RF radio and not data for the video. They can’t afford the lag!

Truth there, but most of the videos I've seen suffer from very bad quality. So guess there is a trade-off.

 

[DoomMeister]

Truth there, but most of the videos I've seen suffer from very bad quality. So guess there is a trade-off.

Only the video recorded from the feed to the goggles. Those that have onboard SD card recording are quite good. 1080p is common and a lot are now going to 4K onboard recording.

 

[Steve Carr]

Only the video recorded from the feed to the goggles. Those that have onboard SD card recording are quite good. 1080p is common and a lot are now going to 4K onboard recording.

Yes. Understand. I suppose it depends on how good the image needs to be with the goggles.

 

[10-8]

The video is sent using wifi. When connecting more that one device the camera wifi has to send the packets to each device. Each packet has an address for the intended receiver so.....2 receivers means the camera sends twice the number of packets. As distance increases more packets are lost. Every lost packet has to be resent by the camera. That results in a delay in sending the next packet which shows up as lag in the video. As more packets get lost the display becomes pixelated as distance is increased until the video freezes.

Not sure that is exactly correct. The camera is blind transmitting to both receivers, given that they are equally bound to the camera (ie, authorized to Rx). There is no 're-sending' of video. Each Rx will either get the signal or not. Unlike analog video (as used by most FPVers) where the signal gets fuzzy, scrolling, etc., digital video is either there or it isn't (hence the freezing of frames when the signal is incomplete). In range testing team mode, the controller using the omni would generally lose video just before the patch. While watching the screens during range testing, there was no difference in the lag and both screens displayed the same images at the same time. This is similar to the way Digital TV works now. Stations broadcasting HD over the air are now digital. There is no degradation of signal with more people receiving. All antennas in range will either get the signal or not based on antenna and location.

That's my understanding anyway, and may or may not be.

 

[DoomMeister]

I believe free air transmission of digital HDTV is actually a digital signal imposed over an RF carrier and is not at all like streaming through optical fiber or cable that uses IP addresses to control services. It therefore does not rely on a two way data link and dropped frames are not recovered as there is no buffer.

 

[DoomMeister]

Yes. Understand. I suppose it depends on how good the image needs to be with the goggles.

If I recall correctly my son has the FatShark HDO system with 960X720 resolution, and using HDMI in does 1080p if used for gaming. It has OLED screens so they have super contrast and color depth.

 

[10-8]

I believe free air transmission of digital HDTV is actually a digital signal imposed over an RF carrier and is not at all like streaming through optical fiber or cable that uses IP addresses to control services. It therefore does not rely on a two way data link and dropped frames are not recovered as there is no buffer.

I believe that is correct and the way that the video is used on 5.8 to the controller. Video is one way transmission only and the Tx on the camera is not aware that the signal is being received or not.

 

[Steve Carr]

I believe that is correct and the way that the video is used on 5.8 to the controller. Video is one way transmission only and the Tx on the camera is not aware that the signal is being received or not.

That is an interesting concept. I'm trying to think of a method of testing it. Heretofore I have not seen one way communication with wifi.

 

[10-8]

That is an interesting concept. I'm trying to think of a method of testing it. Heretofore I have not seen one way communication with wifi.

I found this, and interestingly it is specific to video broadcast from drones. It's called 'WiFiBroadcast':
What wifibroadcast makes different
Wifibroadcast puts the wifi cards into monitor mode. This mode allows to send and receive arbitrary packets without association. Additionally, it is also possible to receive erroneous frames (where the checksum does not match). This way a true unidirectional connection is established which mimics the advantageous properties of an analog link. Those are:

• The transmitter sends its data regardless of any associated receivers. Thus there is no risk of sudden video stall due to the loss of association
• The receiver receives video as long as it is in range of the transmitter. If it gets slowly out of range the video quality degrades but does not stall. Even if frames are erroneous they will be displayed instead of being rejected.
• The traditional scheme “single broadcaster – multiple receivers” works out of the box. If bystanders want to watch the video stream with their devices they just have to “switch to the right channel”
• Wifibroadcast allows you to use several low cost receivers in parallel and combine their data to increase probability of correct data reception. This so-called software diversity allows you to use identical receivers to improve relieability as well as complementary receivers (think of one receiver with an omnidirectional antenna covering 360° and several directional antennas for high distance all working in parallel)
• Wifibroadcast uses Forward Error Correction to archive a high reliability at low bandwidth requirements. It is able to repair lost or corrupted packets at the receiver.

Not sure if this is exactly how Yuneec is working, but certainly something similar. Certainly it is what I experienced in testing when working with team mode.

EDIT: This may be what is used. Found something similar on the PX4 developer site:

Wifibroadcast Overview
The Wifibroadcast project aims to mimic the advantageous properties of using an analog link to transmit HD video (and other) data when using WiFi radios. For example, it attempts to provide a video feed that degrades gracefully with signal degradation/distance.
The high level benefits of Wifibroadcast include:

• Minimal latency by encoding every incoming RTP packet to a single WiFi (IEEE80211) packet and immediately sending (doesn't serialize to byte stream).
• Smart FEC support (immediately yield packet to video decoder if FEC pipeline without gaps).
• Stream encryption and authentication (libsodium)
• Distributed operation. It can gather data from cards on different hosts, so that bandwidth is not limited to that of a single USB bus.
• Aggregation of MAVLink packets. It doesn't send WiFi packet for every MAVLink packet.

 

[Steve Carr]

It makes perfect sense. That method would eliminate some of the drawbacks with a typical wifi system. It would also explain why I am unable to find the ST16 with a wifi analyzer.

 

[John Hennessy]

I believe that is correct and the way that the video is used on 5.8 to the controller. Video is one way transmission only and the Tx on the camera is not aware that the signal is being received or not.

Hi All,
I use a HDMI cable if it is within 100 feet of me with an amplifier in the cable or any bigger distance I use wireless HDMI dongle on the st16 to a receiver in my Ute where the tv is running of a 12 volt dc to 240 volt a.c. inverter for the power for both devices , being the hdmi receiver and the 26 inch flat screen tv, for my clients to view with out hanging over my shoulder during the job.
Johnno Hennessy.