BER issue using USRP

[mubashir1989]

Hi

I have an issue. I am trying to implement cooperative communication network using three USRPs. One for transmitter, other for receiver and third for relay. And I want to compare BER with direct communication with cooperative communication which is via relay.

I have the issue that when I place two USRPs even 40 feet apart i didn't get any BER. 

Can you guide me how to get BER in my problem?

I am measuring BER using builtin VI in labVIEW. I alaways get BER=0 even if reduce transmit and receive gain to 0.

Regards

[Ben_Co]

Hi Mubashir1989,

Which code are you using to do your BER measurements? I'd recommend starting with your USRP's connected directly over cables rather than antennas and taking a simple Modulation Toolkit example that does the modulation scheme you are looking for for both Rx and Tx. The QAM examples in "C:\Program Files\National Instruments\LabVIEW 2016\examples\instr\niUSRP\ModulationToolkitExamples" should be about what you need to verify that you're getting BER, and will give you a good reference to build on. 

Thanks,

Ben C

Applications Engineer

[mubashir1989]

Hi ben

I am using packet based link code. I am attaching the code here and in receiver you can see how im measuring BER. actually I am measuring BER by generating transmitted bits again in receiver.

I always get BER between 0 to 0.1 but never get BER between 0.1 to 1 even if I place USRPs at distance of 40 feet. I want to get different poor BER values for low transmit gains.

the type of graph I want to achieve for single relay cooperation is attached in figure.

[Ben_Co]

Hi mubashir1989,

Unfortunately I cannot run the code you sent, we're missing several subVI's. You can try posting your full project with all subVI's in a zip file, and we can see if there's any glaring issues. 

I still recommend starting with the QAM TX/RX examples and see if you get the desired BER out of those examples. From there, you can take that working implementation and add it to your exisiting code. 

Ben C.

Applications Engineer