LightBridge synchronization

[ptt]

Hi,
I am doing a research about spectral features of lightbridge and I have some questions. Using a Spectral Analyzer in 2.4GHz band with video transmission and control data, I could see that there are a temporal synchronization between the OFDM signal to transmit video and some frequency hopping control pulses. Anyone have any idea about this? Because I can understand it...
Thank you!

 

[UAVIZ]

Its voodoo magic or alien technology?... Seriously I have nothing good to add to this thread lol ... Hope someone drops some science though, interesting.

 

[Loz]

Perhaps try different forum, may get better chance of someone offering you opinion on this proprietary protocol

 

[oconnb]

Will there be a test on this?

 

[ptt]

Perhaps try different forum, may get better chance of someone offering you opinion on this proprietary protocol

Thank you, but I am non sure what would be the correct forum. Have you got any idea about other forums? Thank you so much

 

[higherperspective]

You might want to try hacking into an internal DJI engineers forum. Not sure anyone else could help you.

 

[kamleshverma]

Hi,
I am doing a research about spectral features of lightbridge and I have some questions. Using a Spectral Analyzer in 2.4GHz band with video transmission and control data, I could see that there are a temporal synchronization between the OFDM signal to transmit video and some frequency hopping control pulses. Anyone have any idea about this? Because I can understand it...
Thank you!

Hey! Did you get more information about this? like is telemetry and video data are encapsulated and then transmitted if so then how to decode the OFDM symbols to
get the telemetry data? How to estimate the channel ?

 

[quaddamage]

The thing is built on WiMAX hardware. Maybe just assume it's WiMAX and see how far you can get.

 

[kamleshverma]

Thanks, I'll proceed with the Wimax protocol for now and keep on posting updates here. After analyzing the spectrogram of the Phantom 4 pro signal, I got two spectra with bandwidths of 1.4MHz and 10MHz. I think the first is command and control and the second is video+telemetry signal.

 

[quaddamage]

Telemetry is unlikely to be a part of video feed.

All DJI drones use DUML packets to exchange info between modules, both internally (within AC and within RC) and through the radio link. These include a packet for stick positions, as well as exchange of status between components.

So the link does contain two parts: one is video feed, another is data exchange. And the data exchange contains DUML packets, most likely somewhat encrypted.

 

[kamleshverma]

Here I'm saying the first spectrum is control and command because almost the same spectrum signal they used in the Ocusyc protocol. And in Ocusyc I was able to see three signal spectrums such as video, telemetry, and control. In the case of lightbridge protocol, I'm only seeing two spectrums, so I doubted they might encapsulate video and telemetry in one signal.

I capture the signal when the drone and RC are just ON. Once I'll capture the signal in flying condition to check if a different signal is there for telemetry or not.

 

[kamleshverma]

Time domain Long preamble of WiMAX does not match with the video and RC signal preamble.

 

[quaddamage]

Oh. So the WiMAX compliance ends at physical layer. Pity.

Looking at functional diagam, the rx/tx data streams seem to be handled completely in an FPGA.
Figuring out the bitstream format and what the programmed circuit does would be a task for years..
Maybe we can simulate it, to relatively quickly verify what exactly are its outputs?
Getting the bitstream is easy with firmware tools, it's in module m1900.