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mgamache

New To SDR Advice - Small Device?

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mgamache   

I am wondering if it's practical to have an SDR transmitter small enough to fit in a person't pocket? The range doesn't need to be great (4 meters). I just need to transmit data at a rate of 1mbs from an untethered person (WiFi is not allowed) back to a base station. Any advice?

 

 

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mgamache   

thanks, those look interesting. They certainly are small and low power. It looks like 1mbs is the max bandwidth? What's the easiest way to experiment with sending data between two of these?   I see they have a USB version. Again, totally new to SDR. 

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Have you considered using a Xbee and Arduino?  May not be the most cost effective method but would allow simple setup and development.  You can find several tutorials for setup and operation.  It would be possible to have one for mobile "in a pocket" and another as a ground station hooked up to a computer. 

Here is a basic setup tutorial: https://learn.sparkfun.com/tutorials/xbee-shield-hookup-guide

Link to one of the many zigbee boards: http://www.mouser.com/ProductDetail/Digi-International/XB24CAUIT-001/?qs=%2FPVulymFwT182AEOKkqEXw%3D%3D&gclid=EAIaIQobChMIiJKXg86p1QIVl4izCh3arg7REAYYASABEgKVefD_BwE

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mgamache   

Thanks for the Xbee reference, but my understanding is that Xbee bandwidth is limited to < 250kbit/sec. That's not quite fast enough for my use case. Also, price is not a driving factor. 

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I see.  When you say "no wifi" do you mean as in a connection to a wifi network to tx/rx data or no wifi rf band? The wifi xbee offers data rates up to 72 mbps and can be used as a direct connection between two modules.  Here is a basic setup guide: https://learn.sparkfun.com/tutorials/xbee-wifi-hookup-guide?_ga=2.159357427.839007374.1501162703-1446297197.1501162703     

You may want to directly refer to the "Communicating with Other XBees" part of the guide. This allows a direct point to point connection between two modules.

This will only work though if the wifi frequency band is an option. Xbee is probably not an option if no wifi band is required. 

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mgamache   

Thanks, the way I read that is you can communicate between two xbees, but they need to be connected to Wifi. Have you set these up without wifi? Note: 2.4 ghz is okay, but no Wifi allowed. 

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I forgot to attach the link to this PDF that describes how to setup an ad hoc connection:  http://ftp1.digi.com/support/documentation/90002124_K.pdf  refer to page 29 of the manual.

This would be a point to point connection between two xbee modules or you could also do an ad hoc connection with one xbee wifi module and a laptop with wifi card. Just have to configure your xbee and laptop card accordingly. 

 Another option would be have a router at your base station with a private hidden network.  This would allow you to have multiple portable units sending data back to the same base station. Im not sure if this would be out of your "no wifi" parameter but just another possible solution.

Im sure there are plenty of other solutions out there.  I just have been recommending the xbee due to the huge amount of documentation, tutorials, videos, etc that can help in setup and troubleshooting!

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mgamache   

Thanks again, I think this could be useful. If you've used these in ad-hoc mode, I have a couple of questions:

  • Is the SSID broadcast?
  • Can you filter who gets connected? 

I am working with a client that has disallowed WiFi for security reasons.  If it smells like WiFi and be attacked using the same vectors it will be a non-starter. 

 

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The way I understand RF is that any signal can be hacked.  It depends on the talent of the hacker and the quality of their equipment.   Security is going to rely more on encryption and less on a decision between WiFi and other RF methods.

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mgamache   

@PaPawGeek  I agree. FYI, I am not defending the exclusion of WiFi by my client (I think it's irrational), but that's the environment in which I need to work.  I'll have to add robust encryption and security at the app level. My main worry is that the Xbee unit will broadcast its SSID and look like a WiFi connection (thus running afoul of my requirements). I like the Xbee suggestion from @trapman16 as it's a clear path to implementation, just trying to lean on his experience. 

 

 

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@PaPawGeek has some valid points in my opinion.  @mgamache I am not completely sure on the xbee broadcasting ssid for I have not used them in the exact setup that we are talking about, but I do believe there is a to make it act as a hidden network.  Now depending on your requirements this might still be an issue if your attacker was using something like aircrack-ng suite that can find hidden ssid networks.  Like previously said, I think your best defense would be encryption.  The xbee itself can implement WPA-PSK, WPA2-PSK and WEP.  Also like you said app level encryption would be great if you know the rf will be possibly under attack. 

Like I said though, I have not used the modules in the exact configuration being discussed.  I would do some testing out of curiosity but I don't currently have any xbee wifi modules on hand.  Depending on your budget you could probably purchase all the hardware required between $100 - $150 for the xbee setup and do some actual testing.  Some websites offer dev kits that come with modules, breakout boards, etc for a good price. 

Edited by trapman16

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mgamache   

@trapman16 thanks. The dollar cost is not a big deal, it's more about wasted time on dead ends. It sound like it's worth a shot. What's the easiest way to test Xbee WiFi Ad-hoc?

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Just depends on your setup preference.  One way would be to buy two xbee wifi modules, one USB breakout for connection to a base station computer, and then whatever you mobile "pocket sized" hardware would be.  One mobile option being an arduino with xbee dev board.  This option probably has the most documentation.

Im not sure but I would think you could possibly use a raspberry pi as well.  Just have to do some research on that topic.  

One thing you never stated is what kind of data you are looking to transmitter back to a base station?  You said it would require 1 mbps but is it a particular app or data logged from a sensor?  The reason I ask is this could really alter what your mobile main board requirements are.  If it is sensor data then an arduino would probably fit the bill.  But if it is something along the lines of a software application then you will have to pick something based on that apps running requirements.  

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