best possible method for full duplex, high bitrate radio link?

Whelzorn

I need some kind of radio link capable of transmitting video one way, and signals the other. I would like to stay away from using two seperate transmitter/receiver pairs for size and power reasons. I mentioned full duplex in the title, and I know that this is not possible with same frequency radio, but as long as the bitrate remains high enough, half duplex is ok. I am aiming for a fairly high range (about 1000' to a mile). I noticed that the xbee pro modules (www.maxstream.net/products/xbee/xbee-pro-oem-rf-module-zigbee.php) are capable of a 1 mile range and the "interface data rate" is 115.2 kbps (I assume that means the data rate at half-duplex). Is that high enough for transmitting black&white video with no sound?

thank you,
Justin W

Kevin Wood

If this a non-commercial project, you might want to consider amateur television.

If you are in the US, you can can get started with a Technician-class license, which isn't very hard to get.

Whelzorn

well, the problem with using amateur television is that it would be harder to transmit serial data over, and I would like to keep everything at the same frequency (900 mhz - 2.4 ghz). The main purpose of this project is to have a radio controlled robot, in which the radio control is a serial or USB device connected to my PC, on which there is the control software. I would like the video to be in a format I can read from my computer without the need for a tuner card (usb or serial only would be best). So in short: I want a two way wireless link, with a range of approx. 1 mile, that can transmit video one way, and misc. control signals the other way.

John R.

I believe the "killer" here might be the 1 mile range. At this level of power, I believe you'll fall firmly into the land of FCC control (assuming your in the US of A). If you rule out Amateur TV, you might be able to get that range on the "family radio band". You can get "walkie talkies" cheap enough, and maybe you can find a way to modulate the signal on top of thier carrier. I don't know if you could get the bandwidth needed for video, or what the FCC would think about this whole concept.

The "wireless" stuff that doesn't require a license is typically limited in power so that it has a 1,000 foot range (under good conditions).

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John R.

8 + 8 = 10

Whelzorn

well, I can get quite a few wireless modules that have a 1 mile range (such as the one I linked in my first post). I suppose the only limitation there is the data rate. I am not sure if video bitrates can go as low as 115.2 kbps. In fact, if I wanted to pay quite a bit more, I could buy some modules from the same company with a 40 mile range that have a 230.4 kbps data rate.
Does anyone know what the bitrate of a small low res (320 lines of res. or so) camera would be? or even what the lowest bitrate of a logitech quickCam is? I suppose if I needed to, I could lower the framerate of the camera in order to lower the bitrate...

Robert Kubichek

Whelzorn said...
I need some kind of radio link capable of transmitting video one way, and signals the other. I would like to stay away from using two seperate transmitter/receiver pairs for size and power reasons. I mentioned full duplex in the title, and I know that this is not possible with same frequency radio, but as long as the bitrate remains high enough, half duplex is ok. I am aiming for a fairly high range (about 1000' to a mile). I noticed that the xbee pro modules (www.maxstream.net/products/xbee/xbee-pro-oem-rf-module-zigbee.php) are capable of a 1 mile range and the "interface data rate" is 115.2 kbps (I assume that means the data rate at half-duplex). Is that high enough for transmitting black&white video with no sound?

thank you,
Justin W

You're trying to do 2 things using the same type of data on the same data channel, which will not work....
Video which can include sound AND superimposed text data would be from ROBOT to reciever/controller.
Commands from controller to BOT would be on a seperate channel/frequency.
With the right equipment you can transmit audio/video for quite a long distance.
Some video surveylance transmitter/recievers would work nicely.
A VERY high-gain directional recieving antenna coupled to a good reciever will substantually increase the usable distance.
Sending control data would be even easier, using a high-gain antenna on the BOT with a good tranmitter and highly directional antenna on the controller.

Imagin a video screen with real-time video and a couple of lines of text across the bottom showing heading,
speed, GPS co-ordinates, enviromental data, and bot data (battery charge ect.) And mono sound???
Add in a control channel with audio to BOT's speaker...

Well you get the idea..

Bob N9LVU

Post Edited (Robert Kubichek) : 2/18/2006 10:49:48 PM GMT

gibbman

Justin said...
I noticed that the xbee pro modules (www.maxstream.net/products/xbee/xbee-pro-oem-rf-module-zigbee.php) are capable of a 1 mile range

Justin,

A few thoughts. The 100mw Maxstream Zigbee module is advertised up to a mile...but frankly, unless you have an absolutely clear line-of-sight (and a dry wind blowing in the right direction) you need to make adjustments. I will buy the 1000' under "normal" conditions where a branch of a tree might be in the way. I am trying to make a Maxstream unit work as a method of harvesting data from some sensors in a marsh. I don't expect more than that, and the transmission path is pretty clear. And I'm only trying to get a few hundred bytes to the data acquisition unit (as it goes by in a boat). Probably not the way to go for video of any kind, as you couldn't stand the retransmissions which will occur; that is good for keeping data straight, but not for a real-time link.
Not to be a wet towel,
Jim

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In the end, it seems that it's all about getting the LEDs to blink....

Whelzorn

well, I suppose then, I do not have to use the Xbee modules. I considered them for price and ease of use reasons, but I suppose any other wireless link would work. The main problem I have with all of these video transmission suggestions is that they are all using standard video transmitters, made to be picked up with a video reciever. The reason this is a problem is because I want all of the data to be read straight into my computer without any kind of tv tuner cards or anything. If I could find a wireless link that features multiple channels and a high enough bitrate, then I would be happy. If anyone knows of something like this, that would be great.

Whelzorn

Ok, I have found out that the CMUcam2 (and probably other CMUcam versions) will output raw serial video at many different bitrates (from 1200 up to 115200, which is the range of baud rates the xbee/xbee pro supports at half-duplex). So if I use a CMUcam, the xbee modules should work fine. The only problem is, I don't need all of the functionality that the CMUcam has (object tracking, servo control, etc.) So now I would like to know if there exists a camera that simply outputs serial video at a bitrate within that range, but does not do everything else. If anyone knows of something like this, I would love to hear about it.

Whelzorn

I just found this: www.surveyor.com/SRV_info.html and now I know that what I am trying to do is entirely possible with the xbee module, because this is the same exact thing I am trying to do. THe only thing I don't like is the fact that these people got there first [noparse];)[/noparse] Oh well, I guess the only question I have now is, does anyone know where to get the camera he has mounted on the front of his robot? I fount them for sale here, but they are out of stock. Does anyone know anywhere else I can find these?

edit: for some reason the second link doesn't work right, so the URL is: www.electronics123.com/s.nl;jsessionid=ac112b2a1f43d859fe07491e45ab9395f6527ba6bb59.e3eSbNyQc3mLe3iKax0KbxqSe6fznA5Pp7ftolbGmkTy?sc=8&category=241&it=A&id=2027

Post Edited (Whelzorn) : 2/19/2006 3:58:13 PM GMT

gibbman

Hi Justin,
Cool link and project! He does quote 1000m range with clear line of sight (and the Xbee Pro module) but just remember that line of sight thing...a bot radio 6" off the ground tends to encounter a lot of obstacles to a clear path between sender and receiver. But very cool!
Jim

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In the end, it seems that it's all about getting the LEDs to blink....

Whelzorn

I think I found a place to buy them, but the website looks awful, and i'm not quite sure what to think. Heres the link to the site: www.uoptions.info/, it's under the "PARTS" link. I would still like to find out if there are any alternatives, though.

hgordon

Some comments on the XBee Zigbee modules - they do work quite well, especially with the version of firmware that went to beta 2 months ago (v1090), but at least in my experience, they're half-duplex 115kbs, not full-duplex, and sometimes the data going one direction will clobber data in the other direction. This is manageable, but something to bear in mind. The bit error rate is quite low, but non-zero, so you need to take that into consideration in your communication protocol. We actually haven't run any distance tests to check line-of-sight range, so we just quote the Maxstream specs, but we're pretty happy with indoor results - we've easily run 50 meters with the XBee Pro modules at 50mW, around corners, into remote rooms, etc, before running out of places to go. The standard XBee modules at 1mW have quite a bit shorter range - maybe 1/2 or 1/3 what we get with the Pro version. Other than that, the price is great, they are available, and they allow us to do projects now that we couldn't do 2 years ago, so I'm happy.

Howard Gordon
Surveyor Corporation

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stuff I'm working on
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Post Edited (hgordon) : 3/24/2006 2:38:30 AM GMT