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Bit Error Rate (BER) with PXIe5651 using OOK modulation

Hello,

 

I need to generate 433MHz pseudo random bit sequence signal with Manchester encoded OOK modulation and feed it into my DUT's antenna's input. Then read back the decoded signal (using PXIe 6341) and compare it with the original. Then calculate BER. I am using CVI and TestStand. Is there a tool that can simplify this process?

When I tell my PXIe6341 to generate this pseudo-random bit sequence, is there a way to read it back so it can be compared?

Thanks

J.

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Hi J,

 

There's certainly a lot going on here. So just to start with, the Modulation Toolkit includes examples on both the generation and acquisition side that might be helpful. There are amplitude shift keying examples you can set M-ary = 2 to do OOK, and mod toolkit will generate PN sequences as well. On the acquisition side, there's also a Calculate BER function in modulation toolkit. To start off, you could look at the MT niRFSA ASK Demod on the receive side and MT RFSG Generate ASK on the generation side. Note though that both of these examples use Mod Toolkit for the signal processing but use RFSA/RFSG for the hardware interaction. Since you mention using a 6341 multifunction DAQ card, obviously you'd have to change out the hardware VIs.

 

On that note, are you using a downconverter or something to get a low frequency signal to the 6341? Obviously that card isn't going to be able to do anything with a 433 MHz signal, since it tops out at 500 kS/s.

 

Cason

NI Applications Engr.

NI Product Support Engineer
FlexRIO & High Speed Serial
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Hi Cason,

 

Thank you for your response. To answer your question, my DUT will demodulate the data and I will use 6341 to digitize it.

When I read "readme" file for demodulation toolkit I do not see my generator (PXIe-5651) being listed. Is it possible to do this without using demodulation toolkit? If I can generate all my points in a file, can I read it, convert it to binary and use it for modulation?

 

Thanks

Jerry.

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Jerry,

 

I believe that's correct, the 5651 would not be explicitly supported by Mod Toolkit. Most of that toolkit is really about software signal analysis and construction, so it may be possible to work the code to be usable with the 5651, but for the PXIe 565x analog generators there's actually a dedicated example that just comes with the RFSG driver, RFSG 565x Digital Modulation.vi, that would be a great starting place. That example can do OOK with the 5651 out of the box. There's a companion Analog Modulation example VI as well that does FM and PM modulation for example.

 

Your last point on generating your own waveform is valid, that can certainly be done. The Digital modulation example allows you to put in a user-defined waveform. You'd need to read the file and parse it properly, but there's nothing stopping you writing that in. 

 

Regards,

 

Cason

NI Applications Engr.

NI Product Support Engineer
FlexRIO & High Speed Serial
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Hi Cason,

 

Thanks for your reply. Could you explain in more details or point me to where the information is about how the user defined waveform is used for modulation? I can see in the example that it's just a plain conversion to integer values. So 88 will be converted to 10001000b, sort of like BCD? What about 11? Will it become 11b or 00010001b?

Thanks

Jerry

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I'm actually not sure, I haven't personally used that function before. Since it's expected an array of 8 bit integers, I expect it'll parse each individual number into 8 bits of message data. So I'd expect a two element array of 8 and 11 to parse out as 00001000 and 00001011 actually. But I admit that's just a guess, I'd suggest trying it to be sure. I couldn't find it explicitly documented.

 

Cason

NI Applications Engr.

NI Product Support Engineer
FlexRIO & High Speed Serial
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Cason,

 

I need to generate 5 kHz squarewave using user-defined modulation. Where do I turn for information? How do I define these 1024 points to produce a squarewave? I am assuming these kind of details would not be included in any printed documentation.

 

Thanks

jerry

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That sounds like something you should be able to do with that Digital Modulation example. Set your Modulation Type to OOK, modulation wfm to User Defined, and just set your user waveform to alternate 0's and 1's. I don't have one of these generator, but I did simulate one in MAX and determined the user waveform is just supposed to be the message bits. If you enter anything other than 0 or 1 into those array elements it'll throw an error. So for a 5 kHz square wave with a 50% duty cycle you just need to alternate between 0 and 1 at a 10 kS/s symbol rate. If you needed a different duty cycle you could adjust the proportion and symbol rate, like three 0's and one 1 per period at 20 kS/s to get a 25% duty cycle. 

 

Cason

NI Applications Engr.

NI Product Support Engineer
FlexRIO & High Speed Serial
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