Transmitting video over wireless serial

[bear24rw]

I'm thinking about using two xstream modems (www.maxstream.net) for a project but I want to stream video over my wireless link. I don't think that these modems will be fast enough (xstream only transfers data at 19.2Kbps) to stream video in near real time. What kind of wireless links do robot that stream video back, such as all the army robots, use?

[Cody Carey]

I'm not sure about what is used on army robots, but I was thinking about doing something very similar (a remote control trashcan with video feedback) and my conclusion was that A consumer wireless camera that operated on a different frequency from the radios used for main robot controller would be easies and cheapest. If you were planning on Analyzing the data that the camera sends out, you could just have it patched into a computer on the receiving end, and use a program like Proce55ing to interpret it. Sorry that I didn't really answer your post... I just had a different way of thinking about it.

[bear24rw]

Yeah, I was thinking about that but I really wanted to have it all go over one line. I want to be able to go at least a mile and the maxstream modems are perfect for that but i need a camera to see where im going lol but i'm stuck as to how to stream that back at a decient speed...

[Bongle]

Wikipedia confirmed my suspicions that the Predator UAV uses a satellite link. I imagine that most army robots will be similar, using very costly but high-bandwidth and high-reliability systems that you won't have access to.

Option 2: There's got to be a radio camera that broadcasts and receives via analog radio rather than digital. This will be much harder to integrate into an autonomous sensor suite (you'd need to convert it to a digital signal before processing), but if it is only for human usage (i.e. the driver looks at the screen, then decides what to do), an analog link should be good.

Option 3: Get something that broadcasts over a wireless standard (802.11b/g/n), and you'll have pretty ridiculous amounts of bandwidth, but may have to deal with interference from other consumer devices using that same frequency band.
Example: This is a webcam that works over wi-fi with a 640x480 resolution - http://www.amazon.com/D-Link-DCS-100.../dp/B000067JZF

Yeah, I was thinking about that but I really wanted to have it all go over one line. I want to be able to go at least a mile and the maxstream modems are perfect for that but i need a camera to see where im going lol but i'm stuck as to how to stream that back at a decient speed...

You can get wifi antennas that point in a certain direction to increase the power of the signal by concentrating it. One of my coworkers who was outside of the DSL region for his city got a friend to subscribe to the DSL for him, then bought some Wifi super-antennas to broadcast over about 3 miles from his friend's house to his barn. Problem is, the antennas need to be very carefully aimed, which will be a problem with a moving robot.

19.2kbps is a pretty low bandwidth but if, for instance, you only go for 5fps, it could be done. You'd need to write an image compressor on the robot side, because 19.2kbps of raw images at 5fps would be 5 20x20 grayscale images per second.

Continued:
This is a 5fps 320x240 resolution grayscale video that runs at 14.4kbps of 1281's 2006 robot pushing another robot at the waterloo regional last year. So it can be done, and I think the end video would be useful for a driver trying to drive. HOWEVER: This is encoded with the xvid codec, which means that each frame is dependant on the frame before it, and vastly increases the complexity of encoding. That is to say, I don't think a teeny embedded processor will be doing xvid encoding on the fly. The difference in size and quality between this and a 14.4kbps video encoded with a non-time-dependant compressor would probably be enormous. To get an idea of the kind of quality to expect, compress some .jpg files so that they are each 480 bytes, and that'll give you an idea of how much bandwidth you have to work with at 5fps@19.2kbps.

[Kevin Watson]

Originally Posted by bear24rw

I'm thinking about using two xstream modems (www.maxstream.net) for a project but I want to stream video over my wireless link. I don't think that these modems will be fast enough (xstream only transfers data at 19.2Kbps) to stream video in near real time. What kind of wireless links do robot that stream video back, such as all the army robots, use?

We use FreeWave radio modems on some of our experimental rovers for long distance communications (802.11g otherwise) and they work really well. Several years ago I used a pair on a high altitude balloon experiment and I was able to maintain a 115.2 Kb/s data link from 60 miles away using just low gain omnidirectional antennas.

-Kevin

[DonRotolo]

At both NJ and Buckeye, we had streaming video (30 fps) of the field from the stands down to the pits over 802.11a (although 802.11g would be equivalent). The issue is how far you need your wireless link to be. Line of sight and under a mile, 802.11a/g would be a good choice. Further, consider 802.16 gear.

Your serial modems would be poor at best, 19k2 just isn't fast enough* for video. 56k maybe, 128k no problem, 320k is what the Champion Webcasts were running. The encoding (which introduces loss and distortion) and the image size both affect bandwidth requirements, and wider bandwidth affects how far you can go wirelessly.

Note that Ham Radio can do all this, too, with far fewer pesky power and antenna limits...

Don

*Yes, it can be done, but not well.

[lynca]

I've used aerocomms and maxstream's at 19.2 Kb/s with success. I've stepped up aerocomm 900Mhz modems to higher baud rates 115.2 with moderate success due to a higher rate of bit errors.