OFDM Transmitter using RFSG

[centrums.ni]

Hello all, I am a newbie in LabVIEW and I am trying to transmit this OFDM vi I got from document by ErikL (https://decibel.ni.com/content/docs/DOC-34781). But I got some error while trying to connect this vi to RFSG transmitter block (at the wire error out after rfsg Resample and Write block). The IQ rate set by default 5M with 1250 input bits. This is the error explanation: 

Error 1 occurred at rfsg_Determine Parameters for Resampling (Validate Inputs).vi

Possible reason(s):
The Waveform Sample Rate must be greater than 1.

I construct it using Labview 2015 and PXIe 5646R. 

Can anyone please help me with this problem? Any sample or answer would be very helpful.

[Bumblebee_Tuna]

Hi,

Would you be able to post the actual code here? The link you posted has been deleted it looks like. One thing you can do is place an indicator on the IQrate property that is being written to the Resample VI that is throwing the error to ensure that the value going to that VI is the IQrate you are requesting.

[centrums.ni]

Hi Bumblebee_Tuna,

Here I attach the modified version I made. I tried to combine OFDM transmitter code I got from here https://forums.ni.com/t5/Software-Defined-Radio/Streaming-OFDM-Transmitter-and-Receiver/ta-p/3491402 and the RFSG block from here https://forums.ni.com/t5/Example-Code/NI-RFSG-FM-Radio-Transmitter/ta-p/3525616 . I've tried to add the indicator, and it shows that it gives the same value as the value I added as input from the front panel. But I still can't figure out how it could cause an error afterwards.

Renita,

ITB

[Bumblebee_Tuna · Accepted solution]

Hi Renita,

A couple things that I noticed while looking through the OFDM TX.vi. First thing, the error you are seeing is because the dt is being used as the sample rate in the subvi that is returning that error. If you turn on highlight execution and follow the error code into the subvis you can see this for yourself. As I looked through the code I noticed a few locations where the dt and sample rate were being interchanged. The first place this mistake happens is in the top level VI(OFDM TX.vi). If you follow the IQ rate control that is at the top of the loop you will see that it is wired into the dt for the waveform without the reciprocal function to translate between the two. 

The second thing to take note of is how you are handling the embedded while loops in the lop level VI(OFDM TX.vi). There are two separate stop buttons, one for each loop. This makes it such that depending on the state of the execution and which stop button you press, the program may not shutdown properly, meaning you'll have to use the abort button, which should be avoided.

Another small architectural thing to notice is how the "Status" indicator is being written to as a variable and as the actual indicator in the inner while loop over to the right in the OFDM TX.vi. Both GenerThis creates a race condition. Here's a help page that details local variables and race conditions:

https://www.ni.com/docs/en-US/bundle/labview/page/using-local-and-global-variables-carefully.html

It looks like you have a great start at setting up OFDM with RFSG. Hopefully the above suggestions will point you in the right direction. 

Regards,

Jayk

[centrums.ni]

Hi BumbleBee_Tuna

Thank you so much for your help, it's finally working 🙂

Regards,

Renita

[LetMeLogIn]

Can you post final VI pls? 

[centrums.ni]

Hi LetMeLogin,

Over all it's just the same with the previous VI, I only added two reciprocal, one after IQ rate control and one after unbundle by name (dt). Then I also tried to connect both stop button using a blank case as portrayed in the link Jayk suggested. And another one is by dragging the stopped status to outer loop so that it doesn't cause race condition. 

Regards, 

Renita