USRP and Visible Light Communication

[sundevilkz]

Hello,

We are doing a small college project with USRP N210. We are trying to transmit a simple ascii code (Hello world) using usrp and visible light communications. Right now we are trying to figure out how to hook up LED transmitter to the USRP. I've seen some papers that suggest using daughterboards as an interface between LEDs and the radio. I was wondering if anyone else had any experience with this? Thanks

[M0535]

Hi sundevilkz,

I am not sure about how to go about communicating with visible light with the USRP N210, but I would check out Ettus' Support since the N210 is one of their products. We do not support different daughter boards, but Ettus does.

http://www.ettus.com/support

I do know that if you are trying to do this at a high frequency, you will probably run into switching issues with the LEDs not being able to switch fast enough.

[ErikL]

Howdy!

If you want to use LabVIEW with the USRP you're in the right place.  Harald Haas has been doing VLC with LabVIEW and NI software defined radio for some time.  Also some of the communinty memebers are modulating lasers with their USRP.

What daugherboard are you using?

Regards,

Erik

[sundevilkz]

We have LFTX and Basic TX daughterboards available to us. As of now we are researching which would suit us best. We have no experience using daughterboards, so we are wondering if you had any suggestions on how to replace the conventional antennas and build a transmitter using an array of LEDs

[ErikL]

Yes, your LF and Basic daughterboards are compatible with the NI USRP 292x or N210 as of the LabVIEW driver in NI-USRP version 1.2.  As for the daughterboards, the LF boards provide a direct connection to the ADC / DAC on the motherboard +/- 1 V. While the Basic boards go through a transformer (AC coupled) +/- 1 V.  Both provide very low current so you'll probably want to drive a transistor to switch the LED on and off.  Schematics can be found here:  http://files.ettus.com/schematics/

[cochenob]

I'm about a month late to the party on this one.....

Depending on your modulation rate, the LFTX/RX should work well if you want to drive LEDs.  As Erik mentions...it's basically just an A/D or D/A.  That said...if you're just doing OOK...then there actually might be other NI products (multifunction DAQ, etc) that allow you to generate an OOK signal and also do fast digitization.  In other words, you may find there's another hardware product that's easier to hook up to you LED driver, etc..  The AC coupling may/may not be problematic for your application.  Given the bandwidth limitations between the radio and PC, and your desired number of samples per bit, you may find that the actual useable sample BW is lower than the analog BW capability of the daughterboad.....All depends on your application.

I've also used the WBX extensively (and a bit with the B210) to modulate and demodulate laser diodes and fiber lasers at higher frequencies.  We've been quite pleased with how easy it is to do this.  Use the Tx end to synthesize modulation (possibly with some amplification or biasing afterwards depending on the laser driver requirements), and the Rx end to demodulate and capture IQ for RF processing in LabView.

Always fun to hear about SDR applications with optics and lasers! 

----
Brandon