After much chasing, and testing, I have found this to be an efficient way of getting low latency high quality HD video out of an Aircraft. The latency is around 0.4 seconds at worst which would be OK for an FPV with an APM doing the hard work.
I will continue to search for methods to drop the latency down further, but this is a lot better than the 6-12 seconds I was getting on my first attempts.
Any comment (with useful instructions) would be appreciated.
For the wireless link, I am using two UBIQUITY ROCKET M 900 with Australian ACMA approved firmware, at the base station, I am using a tracking (yet to built the tracker...) 1.5 meter long X and Y polarised Yagi, and on the plane, two RF Design flexible strip antennas, placed at right angles to each other.
but how you do that bit is up to you.....
the critical bit is getting the Raspberry Pi's to chat to each other.
I have tried to make this as user friendly as possible... good luck.
Setting up IP video for Raspberry Pi 1080p video (FPV)
You will need 2 B model Raspberry Pi's and 1 Pi Camera. (Element 14, or RS components)
Preparing your Raspberry Pi for first boot…
Follow the instructions at http://www.raspberrypi.org/wp-content/uploads/2012/04/quick-start-guide-v2_1.pdf
Install the prepared SD card in the Pi and boot.
Setting up your Pi
Connect the Pi to your router with a network cable.
On Start-up it will resize the FAT partition and present you with a menu.
Set your language, and keyboard layout.
Select Raspbian… then click install.
After this has extracted (will take a while….) it will reboot into the configuration screen (again will take a while for this first boot.)
The important things to change here are
- Enable the camera
- In advance options…..
- Set the host name (camera, for the camera end, receiver, for the viewing end)
- Memory split, set the memory for the GPU to 256
- Enable SSH ( will come in handy later, as you may need to talk to the Pi in the air.....
Then finish and reboot.
First login
Username: pi
Password: raspberry
Setting up the required programs for video streaming
Install the dependencies by running the following in a terminal:
sudo apt-get install mplayer netcat
cd /opt/vc/src/hello_pi
make –C libs/ilclient
make –C libs/vgfont
cd /opt/vc/src/hello_pi/hello_video
make
cd ~
Now repeat this for the other Pi….
Streaming…
First set up the receiver….
Ensure the receiver is connected to your network and run
ifconfig
after you press enter, you can find your ip Address. Note this down.
Then run the following.
mkfifo buffer
nc -p 5001 -l > buffer | /opt/vc/src/hello_pi/hello_video/hello_video.bin buffer
the Pi will now wait for the feed.
On the Camera Pi
Ensure camera is connected to the Pi
Ensure Pi is connected to the network (you can confirm this with ifconfig)
(see instructions at http://www.raspberrypi.org/camera for how to connect the camera)
In the following command, replace the ip address with the one you just noted down.
raspivid -t 0 -fps 15 -o - | nc 192.168.1.85 5001
if all goes well you should be streaming 1080P video at 15fps with less than 0.5seconds of delay..
now add your wireless bridge between the two, and away you go J
This information has come from the Raspberry Pi foundation website, and other sources, tested and proven by myself..
Comments
as far as I understand, Rocket M5 vs M900 is all about frequency... and I feel like with 900mghz you can reach a longer distance than with 5ghz
The choice between M5 and M900 will not change the latency. The experiments I have done with the PI show <100ms latency using the Raspberry PI -> Windows PC configuration, either with a direct Ethernet link, or using wireless. My results from PI - to -PI were not so good as the receiving PI has trouble keeping up when decoding the video stream, even when directly connected via a cat5 cable. The bit rate can be as low as 1Mbs and still get pretty good results using a Windows PC (or higher power linux box), so latency vs. bandwidth should not be an issue, with either the M5 or M900. For the M5 setup I am using, I have two small RHCP mushroom-stlye antennas that are very compact, and give good performance, and on the receiving end, a 16 dbi, spiral RHCP on an antenna tracker. I think it 'could' (under optimum conditions), go to 10km by upgrading to a parabolic on the receiver. I would need to beef up the antenna tracker to mount a dish, so if I were designing a longer range system, I would opt for the smaller antennas, and use a high-gain configuration with a tracker, rather than going to 900mhz, but I like to keep things small.
With Arduplane (APM:plane) flight controller sometimes you don't need low latency to observe the plane position/movement etc, as you can do automatic flights or 'point-and-click' flights with a mission planner. But HD Video link is still important, it just does not require low latency.
Andrew, If you don't need FPV, you can just record the flight using a go-pro or other camera. Otherwise, what is the purpose of the video link?
sounds good, I have no limitation for a ground base station antenna, but what about TX antenna? are there any compact options?
I was looking for 10+ km range with M900, is that possible?
btw, for me latency is not important at all, i'm not going to use HD camera as an FPV camera
I picked the M5 because it keeps the antenna size small. I am using an antenna tracker with my setup but I don't have a 'maximum' range tested yet, but I expect it will go 5Km+. What kind of range are you looking to get?
What range/distance you are considering when trying to set up a link with Rocket M5?
I feel like M900 might be a better choice for a long range video transmission... Has anyone ever done long range tests?
Update - using the Rocket M5 / Nano M5 with the Raspberry PI camera and gstreamer-1.0 on Windows and on the PI.
On the PI, gstreamer command is :
raspivid -t 0 -w 1280 -h 720 -fps 30 -b 2000000 -hf -vf -o - | gst-launch-1.0 -v fdsrc ! h264parse config-interval=1 ! rtph264pay ! udpsink host='your PC's host name' port=9000
On Windows:
gst-launch-1.0 udpsrc port=9000 ! application/x-rtp,encoding-name=H264, payload=96 ! rtph264depay ! avdec_h264 ! video_convert ! autovideosink
Using the Ubiquiti Rocket M2/Nano M5 as the transmitter / receiver combination, I experienced zero latency that was noticeable. Even works good using a tablet PC like the Dell Venue 8 with an Atom processor. Bit rate is around 2 to 3 mbs.
Next - will try in UAV and post a video.
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