M-PSK Modulation and demodulation Sync

[mcanbas]

Hello,
I have a problem with M-PSK modulation and demodulation. I think its because of sync... but i am not sure. My problem is; when i try to comare my modulators input bit stream and my demodulators output stream they are different . I mean they are so much different it has BER=1 . I export my modulators input bitstream and my demodulators output bitstream to exel, i compare them , they are very very different. How can i fix it? i want to calculate BER and draw its BER-EB/N0 graph. first i need to compare them but i cant. waiting for helps . have a nice day.

[kevins33]

Hi,

Thank you for posting to the NI forums! Can you attempt to run an example and see if you are able to setup the M-PSK modulation/demodulation? The Modulation Toolkit examples are located here: C:\Program Files (x86)\National Instruments\LabVIEW 2014\examples\Modulation

Of course that will change slightly based on the version of LabVIEW that you are using.

What hardware are you using? Please let us know!

[mcanbas]

i am just trying with the simulation, 
i might be try on usrp 2920 in laboratory if simulation succesfull. 
i tried examples but  lots of them has sync problem i think, i cant get  the input bit and output bits same .. they are always different and bit error rate like 1... I'am just a liscence student. that will be my graduation study to communication with two usrp and calculating ber. i need simulation for this term, i failed. 

[kevins33]

Hi,

After looking into this a little more, I would encourage you to run the example called MT PSK BER vs EbN0 graph [Reed-Solomon coding].vi found in this location: C:\Program Files (x86)\National Instruments\LabVIEW 2014\examples\Modulation\simulation examples\Programming

Thanks!

[mcanbas]

i have labview 2013

[mcanbas]

i found that example but there is no demodulation here? why ? just generator and output of awgn compared in that example . Can you help me why we dont use demodulator ? 

[ahmetemir]

In additon to these answers, I am interested in calculating BER of USRP using LabView. Is there any example VI available for BER Calculation. ? I couldn't see BER calculation for USRP. I  tried USRP  examples .I'm using  two USRP 2943R. Also I wonder that we must use extra synchronization blocks to implement modulation or demodulation , or  usrps could adjust automatically synchronization bits for correct BER calculation.

For Tx part , I changed Ni's Tx_PSK_vi because we didn't want to use continous BB PSK modulation. Instead of these I used  vi that I attached for Tx. I used  Rx example without changed. Which part of block(s) should I change for BER calculation?

[kevins33]

Hi mcanbas,

The demodulation is taking place in the MT Map Symbols to Bits.vi

Hi ahmetemir,

There is not a specific example that I was able to find showing how to take a BER measurement with the USRP, but you will need the USRP driver and the Modulation Toolkit in order to take both of these measurements. 

NI-USRP driver

http://www.ni.com/download/ni-usrp-15.0/5679/en/

NI Modulation Toolkit

http://sine.ni.com/nips/cds/view/p/lang/en/nid/210568

The VI that you will use is the MT Calculate BER.vi. 

Thanks!

[ahmetemir]

First of all thanks for your help Kevin S.,

We have Academic Suite for Labivew 2014. I set up USRP driver and Modulation Toolkit a couple of mounts ago. I have two important questions only. Could you give us advice about these questions please? Questions are present below

1) Should I do synchronization on TX part or Rx part in order to calculate correct BER  calculation?

2) Which options would I prefer choose for correct demodulation to calculate correct BER calculation? Should I take place  MT Map Symbols to Bits.vi from Rx part instead of MT_PSK_Demodulation block like simulation? 

[kevins33]

Hi ahmetemir,

I have found a good community example that shows how to program the USRP with the Modulation Toolkit. https://decibel.ni.com/content/docs/DOC-25758

For BER, you will need to compare the transmitted bit stream to what is received, but they don't need to be synchronized if you use the MT Calculate BER and specify a User Defined Pattern. If you do this, then you can simply supply the transmitted bit stream to the received bit stream. 

For your second question, this will depend on the type of modulation that you wish to perform. If you want to do PSK, then chose the PSK for the demodulation, if you are doing a custom modulation, then you can do the MT Map Symbols to Bits.vi

Thanks!