sending video on a wireless modem

[Medve]

just a quick question. I'm considering using a wireless modem connected directly to my GPS on board the plane, to send real time telemetry down, since it would be a very simple matter to the run any moving map display GPS software on a laptop. However, I was wondering if there was an easy way to transmit video down this same signal. I'd hate to have to use both a video transmitter and a wireless modem. Especially in such close proximity. Thanks for any ideas.

[Steve McBride]

The bandwidth requirement for full motion video is too great for a typical modem operating at something like 9600 baud. Additionally, sending NMEA GPS along with video would require some custom hardware and software I would think.

Others have mentioned sending GPS data down the audio channel of a wireless video transmitter. Operates at around 1200 baud I think, but it does work and you get both video and GPS NMEA on one transmitter.

Good luck with it!

Steve

[Iraqigeek]

Sending telemetry data over a wireless digital modem shouldnt be hard, as many of those modems provide a transparent serial interface link. However, video is a totally different story. Even if you could have a real time encoder embedded on board without that encoder being too big or requiring a lot of power to run, you would require something like 300kbps to get that video feed to the ground (if you want a real time video stream). Even if operating at 1fps@CIF (352*288) you would require at least a 33kbps link.

As far as relaying NMEA information, I think this is overkill, as you only need to relay the GGA packets (fix data). Putting a microcontroller between the GPS and the modem would enable resetting and initialising the GPS in the event a fix was lost and to filter the unecessary information (such as number of satellites used to btain a fix, signal strength of each satellite, and the relative position of each satellite).

IMHO, relaying telemetry information through the audio channel is the most economic way to go. Though it wouldnt be easy, it would be possible to embedd the telemetry data several times, into several audio frequency bands (and possibly even ultrasonic frequencies) to get some sort of redundancy, as each frequency band may be differently affected by channel noise.

[typicalaimster]

A little know $200 device is something called the SlingBox. It's a set top TV encoder that inputs your TV signal and plays it back on a remote device. The unit itself weighs in at about 12oz with the case on. It consumes about 6v @2amps. It sends the data out a standard network cable. Depending on how you configure the player it can consume about 100k-1500k of bandwidth and have about a 3 second delay.

I'm very sure if you wanted to try you could remove the case from the Slingbox to lighten the load. You could then somehow devise a 802.11 bridge between the Slingbox in the air and the playing device on the ground. I haven't really toyed with the player much to see if I could remove the delay. I would imagine there is ways to configure it. The best part at that point your data is converted into IP traffic and you could route it where ever in the world you wanted to.

This doesn't really solve sending video data back over a 9600 baud link.. Hopefully it'll give you an idea of some of the devices out there..

[Iraqigeek]

If you want to go the wifi route, just use a wifi network camera instead, it will cost you about the same as the slingbox alone, and have considerably lower latency, and consume a lot less than the 12W required to run the slingbox. However, going the wifi route you will not be able to go that far as WiFi is not designed for long range links on its own. To get a long range WiFi link you will need amplifiers at both ends (even if you are transmitting on one side only, as WiFi relies on RTS-CTS signaling) and will need to have high gain antennae on both the plane and the ground station. In any case, dont even think of using WiFi for control signaling due to the latency of the standard.

[myulgong]

If you need digital transmission, then wireless LAN would be necessary. One point to consider is the maximum allowed putput power for such devices in your country.

[typicalaimster]

Wifi may not be the only solution. Cingular and Verizon both put out their versions of a HSDPA wireless card. It is fast enough for me to download 'digital videos' and mp3s. If HSDPA is unavailable it falls back to 3g. The card plugs into a PCMCIA slot on a laptop. At that point once again your at the mercy of the internet for route back.

[chrisgood]

Microhard in Canada makes several small modems that work at 115200 bps and above. They recently came out with a 230kbps modem with great range.

Several companies build small video hardware encoders that would fit in a small UAV. One in particular caught my eye at AUVSI last year. It had variable encoding rates and was the size of a PCMCIA card. It encoded to MPEG4. I will try to find the manufacturer.

I did some experiments with UAV recorded footage a few years ago, using TMPenc and different rates. I was able to knock down the frame rate and encoding quality to the point where it was below 115200 bps, but still usable. This was all done using MPEG4, ffdshow encoder:
320x240 @ 10fps, 12fps, 30 fps,
-> 108kbps, 115kbps, 2000kbps

Note: the bit rate is not explicitly tied to the framerate - that is just what I happened to set them at for each framerate.

I finally settled on 12fps, 115kbps as the best quality versus bandwidth. With the higher serial rates available now from modems, that quality could be significantly increased.

hris

[Frisk151]

I am currently working to connect the video downlink from my 30' Airship through my laptop, through an EVDO card and then to my server where it will be viewable on my website. The downlink is the easy part and already accomplished. I use a Pinnacle Systems USB device to record and display on the laptop but I have a network / web guy that co-owns the colo center I keep my servers in on getting it up and online in real time.

I do like the idea of using a wifi webcam to possibly be a cheaper alternative and even allow for multiple cams. I currently use Blackwidow AV downlinks.

[coafin]

I do like the idea of using a wifi webcam to possibly be a cheaper alternative and even allow for multiple cams. I currently use Blackwidow AV downlinks.

I tested and never again:

-power consumption is 10x bigger (2.5 amps, about 15 watts = very hot)
-weight is 10 bigger (over 400 grams)
-size is 10x bigger (size of McFeast)
-latency is 10x bigger (500 msec)
-expensive Dlink piece of crap (250$ or something)

I didn't test range, because I had better things to do (I watched The Bold and the Beautiful renewals).

[sodman12]

i heard of a search drone plane that was used in rescue efforts that had a range of about 10 miles and could stream video at an avg of 10mbps.
isnt there a data transfer on wirless modems that enable you to trasfer data up to 50 miles. i know there is something like this but i cant recall exactly what it was (maby computer to computer link?) it was made for to building that were across a street to link up at fast speeds without wires

[dalbert02]

It may have been mentioned, but instead of trying to put the video on the telemetry signal, how about putting the telemetry on the video signal? I take the GPS NEMA sentence and send it to a TinyTrak3 then connect this to the audio portion of the Black Widow video transmitter. On the ground, AGW packet engine takes audio and converts it back to NEMA where AGWtracker plots the path on the moving map.
-dave