Long Range Digital Video Link, 5 Km, 433Mhz- open source

dramida · Post by **dramida** » Fri Jan 04, 2013 11:18 am

One thing that could revolutionize drones is a reliable high quality video link. Now it is possible with cheap hardware under 100 $ to build a device that can transmit crystal clear PAL/NTSC video through buildings with a 5Km range estimated.

Here is the building block concept: An digital encoder to H264 (1-2 MBPS variable bitrate) and a bunch of 256Kbps modems. The system can be programmed as transmitter or receiver, or even both.

: Long Range digital video link- open source project

The radio link uses a friendly RFM23BP, a 256Kbps, 1W radio modem in ISM band (433/915 Mhz) http://www.hoperf.com/rf/fsk/RFM23BP.htm

The video processing could be made using Raspberri PI embeded PC:

: Embedded PC

ARM 700Mhz uC, 512MB RAM, VIDEO input and hdmi output. There are lots of docs and projects online about it.

The solution coud be made by hardware DSP like in this video:

http://www.engineeringtv.com/video/DL-M ... a-Link-and

Any idea about how this project should be done is welcome.

timecop · Post by **timecop** » Fri Jan 04, 2013 11:34 am

Realtime (what you'd expect from analog equivalents of fpv transmitters) H264 encoders are not small nor cheap.
256kbit isn't enough for any kind of useful video, either.

People flying fpv are bitching about microsecond delays on gopro live video out, imagine when you have lunix + software h264 encoder delaying the video by > 1 second?

dramida · Post by **dramida** » Fri Jan 04, 2013 11:41 am

I know this digital solution has some drawbacks but 1 s delay is huge. I expect some delays, but not so big. Moreover we need positive smart people who can tell us how could be done in a resonable manner. If you watch the movie above you will see that some folks already did it but the price is huge.

Latest edit:

I found Gumstix, a software on Ubuntu linux witch is concerned with real time video processing.
http://www.jumpnowtek.com

Here is a working H264 encoder example using Gumstix
http://www.oz9aec.net/index.php/gumstix ... is-working

copterrichie · Post by **copterrichie** » Fri Jan 04, 2013 12:30 pm

The aircraft has to be MORE autonomous, that is the solution to the Digital link. Personally, I am working on Wifi for both video and data links.

timecop · Post by **timecop** » Fri Jan 04, 2013 12:58 pm

dramida wrote:I found Gumstix, a software on Ubuntu linux witch is concerned with real time video processing.
http://www.jumpnowtek.com

Here is a working H264 encoder example using Gumstix
http://www.oz9aec.net/index.php/gumstix ... is-working

ubunto or any other lunix is not the solution when you want low latency realtime video encoding.
dedicated (expensive) hardware is the only solution.

And then you have the inherent problem of DIGITAL video - the quality depends on how much frame ahead you have.
Look at H264 or MPEG2 for example, when using b-frames and lookahead. Sure, you can encode everything as I-frames but then your bandwidth will be wasted. You will need to buffer x frames "ahead" to do predictive encoding so that your quality isn't total shit, and if you think about it, at 30fps, each frame is a "huge" 33ms. So if you're buffering say 4-5 frames (a common count for a predictive realtime encoder, you already have a latency of 132-165ms. There's no fucking way you're reaching ANYWHERE near that kinda latency with lunix, so without even clicking the link you provided above I'd guess their concept of "realtime" means "something less than 10 seconds".

copterrichie · Post by **copterrichie** » Fri Jan 04, 2013 1:12 pm

What is your solution? Inquiring minds would like to know. Hmmm.

dramida · Post by **dramida** » Fri Jan 04, 2013 1:17 pm

We need solutions, not educated excuses, in the first post you have the proof that concept works http://www.engineeringtv.com/video/DL-M ... a-Link-and

timecop · Post by **timecop** » Fri Jan 04, 2013 1:24 pm

What is stopping you from purchasing the said solution? It's not going to get any cheaper, no matter how much you ghetto it up.
According to OMM, AR.Drone 2.0 is 200ms latency for it's 720p link. I was pretty impressed by that, so maybe you can go ahead and buy ardrone and tear out its video transmitter and use it? Oh, wait, wifi only, right.

copterrichie · Post by **copterrichie** » Fri Jan 04, 2013 1:28 pm

dramida wrote:We need solutions, not educated excuses, in the first post you have the proof that concept works http://www.engineeringtv.com/video/DL-M ... a-Link-and

Impressive!

copterrichie · Post by **copterrichie** » Fri Jan 04, 2013 1:31 pm

Hmmmm: http://www.raspberrypi.org/archives/2555

Eric · Post by **Eric** » Fri Jan 04, 2013 2:51 pm

timecop wrote:What is stopping you from purchasing the said solution? It's not going to get any cheaper, no matter how much you ghetto it up.
According to OMM, AR.Drone 2.0 is 200ms latency for it's 720p link. I was pretty impressed by that, so maybe you can go ahead and buy ardrone and tear out its video transmitter and use it? Oh, wait, wifi only, right.

To get high quality and low latency, AR Drone equipped with 1G CPU and 1G DSP.

It is the DSP to encode the mpeg4 and do other video processing. Such as speed estimation with camera optical flow and corner tracking.

Without dedicate hardware such as video DSP, you can not encode mp4 in real time, even with a desktop computer.

Maybe you can buy some webcam support mpeg 4 output. Not mjpeg.

Mpeg 4 streaming does not require much bandwidth as it checks differences between frames, over differences are transmitted.

timecop · Post by **timecop** » Fri Jan 04, 2013 3:04 pm

H264 webcam + Arduino Due + ???? = Profit!

dramida · Post by **dramida** » Fri Jan 04, 2013 4:22 pm

timecop wrote:H264 webcam + Arduino Due + ???? = Profit!

That would be an interesting case to study. But we still need a DSP at receiver end. It would be nice to use the same device for transmitting and receiving.
Also we have the advantage that for PAL/NTSC standard, we need half computing power than 720p.

Other ideeas?

Eric · Post by **Eric** » Sat Jan 05, 2013 11:13 am

Normal smart phones has built-in h264 acceleration. Is it possible to use a phone to display the video?

Eric · Post by **Eric** » Sat Jan 05, 2013 11:22 am

timecop wrote:H264 webcam + Arduino Due + ???? = Profit!

Don't think Arduino has the power/io to forward the video traffic.

I can not find any cheap h264 webcam.

In my setup, a cheap usb mjpeg webcam is used.

I can stream the video at 640x480.

The webcam can not generate error free jpegs. If it could, I can use the hardware jpeg decode on the iPhone, then I can stream 720p video.

Eric · Post by **Eric** » Sat Jan 05, 2013 11:25 am

dramida wrote:
timecop wrote:H264 webcam + Arduino Due + ???? = Profit!

That would be an interesting case to study. But we still need a DSP at receiver end. It would be nice to use the same device for transmitting and receiving.
Also we have the advantage that for PAL/NTSC standard, we need half computing power than 720p.

Other ideeas?

Respberry PI is able to play HD video, will it be an option?

copterrichie · Post by **copterrichie** » Sat Jan 05, 2013 4:53 pm

Ubiquiti XR9 XtremeRange 900MHz Embedded Radio module

I came across this while researching wireless solutions and seems very possible to create a long range WiFi connection between the GCS and aircraft using an onboard micro computer.

http://diydrones.com/profiles/blogs/ubi ... dio-module

dramida · Post by **dramida** » Sat Jan 05, 2013 5:21 pm

Ubiquiti XR9 XtremeRange 900MHz Embedded Radio module together with Raspberry PI has the power to revolutionize video downlink among other avatar-like features. Let's hope some smart people will see the opportunity and actually do it.

MultiWii