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How to use DSSS or FHSS sequencing methods in LabVIEW using modulation pallete

Hi

I would really appreciate it if you give me an example how to use DSSS or FHSS using modulation pallete. I searched for any example or tutorial for spread spectrum techniques but I couldn't find anything useful. even a very basic vi might be really helpful for m

Many thanks

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Message 1 of 17
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I would really apperciate any help about how to implement DSSS and FHSS using modulation toolbox

 

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Hello 

In which wireless standard, do you want to implement DSSS? Do you have the LabVIEW Modulation and WLAN toolkits? You can download these to evaluate the software from https://lumen.ni.com/nicif/us/evaltlktsigproc/content.xhtml  and   https://lumen.ni.com/nicif/us/evalwlan/content.xhtml

 

Regards

 

William A
National Instruments UK
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Hi William

I have the modulation toolkit and I want to use DSSS and FHSS with PSK and FSK modulation and demodulation blocks in a noisy channel. I don't use any special standard but I might try it in Wifi and Zegbee in future but the most important thing right now is how to use FHSS and DSSS in a chain with modulation and demodulation blocks 

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Hello,

I have not come across any prewritten examples for implementing DSSS. I would recommend you call into the NI office, speak to your sales representative who will be able to arrange for a field engineer to visit you to discuss your exact requirements and develop a P.O.C for you.

 

Regards

William A
National Instruments UK
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Actually, you may find the attached VIs which implements DSSS based on WLAN 802.11 b & g useful. BUt i would strongly recommend arranging a meeting with one of our rf specialists about your application

 

Regards

 

NOTE: you will need the WLAN toolkit to be able to open the VIs. Evaluation copy downloadable from here : https://lumen.ni.com/nicif/us/evalwlan/content.xhtml

William A
National Instruments UK
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Many thanks for the VIs William

I am still struggling and I don't know how to use it.Just one question there is one block in the modulation toolbox called MT Spread Symbols.Can I use this block for DSSS? 

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Message 7 of 17
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Hi en99,

 

Yes I believe you can use the MT Spread Symbols VI for DSSS.

 

The detailed help for this VI explains that it:

 

"Performs the DSSS spreading operation given a user-defined spreading code. The spreading code algorithm performs non-return-to-zero (NRZ) encoding of the input bit stream and the spreading code. However, the output is an array of zeros and ones."

 

Hope this helps!

 

Kind regards,

Tori
Student
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Message 8 of 17
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Hi en99,

  apologies for a very late reply and I'm sure you've figured this out by now anyway but just in case, here's a quick and dirty example of using dsss with a PN sequence and QPSK.

I'm not re-applying the matched filter here since the de-spread requires a tight alignment to the original timings (if you de-spread the wrong chips then you won't get your symbols out correctly so you do need some level of synchronisation).

Have a play with the Eb/No and the filtering from the front panel - you'll see the un dsss'ed spectrum narrow up as expected with some level of filtering, but the aim of dsss is to spread that out.

 

Hope this is useful.

Thanks

Sacha Emery

ATE Systems Engineer (NIUK)

 

example dsss snippet.png

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Message 9 of 17
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Hi SachaE,

 

I have tried your dsss comparison.vi and I wonder if the spread spectrum (red line) should not it be lower in the amplitude than the direct spectrum (white line)? 

 

dsss.png

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