# Issue with Results from GR-CDMA

**URL:** <https://www.ruby-forum.com/t/issue-with-results-from-gr-cdma/234048>\
**Category:** GNU Radio\
**Created:** [February 2, 2015, 7:29pm UTC](https://www.ruby-forum.com/t/issue-with-results-from-gr-cdma/234048 "2015-02-02T19:29:53Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![addis\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c4cdca/32.png) [@addis\_a](https://www.ruby-forum.com/u/addis_a)\
**Post date:** [February 2, 2015, 7:29pm UTC](https://www.ruby-forum.com/t/issue-with-results-from-gr-cdma/234048/1 "2015-02-02T19:29:53Z")

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Frank,

see some comments inline.

Achilleas

> Hello sorry for the last message thought i attached my screenshot results  
> at first. I am having some problems as to whether the information from  
> the  
> cdma transmission and reception are accurate. I have posted my  
> screenshots  
> for clarification hopefully.  
> [http://imageshack.com/a/img633/757/Yx8B7r.png](http://imageshack.com/a/img633/757/Yx8B7r.png)  
> The first screenshot is from executing the “cdma\_txrx.grc” which seems  
> to  
> test well I believe because moving the sliders around and threshold I am  
> able to notice when it performs tracking and acquisition of the signal  
> automatically.

A: I do not recall a “noise voltage” block in the cdma\_txrx application.  
The SNR is controlled by the slider aptly called “EsN0dB”.

[http://imageshack.com/a/img631/8451/CDqdTM.png](http://imageshack.com/a/img631/8451/CDqdTM.png)  
The second screenshot is me loading two USRP’s. This is the execution of  
the "cdma\_tx.grc file with the UHD:USRP Sink and its WX GUI FFT Plot. My  
issue here is the FFT plot doesn’t look right to. By the way the channel  
model for this is AWGN.

A: You are saying “FFT plot doesn’t look right”. What is it that you  
expect  
to see and you don’t ?  
Can you please elaborate on what does not look right about this?  
BTW, you don’t need the cdma\_tx to get this FFT plot: the cdma\_txrx  
should  
give you exactly the same at the output of the tx.

[http://imageshack.com/a/img538/7792/1xXqN4.png](http://imageshack.com/a/img538/7792/1xXqN4.png)  
After running the “cdma\_tx.grc” file, I proceed to go to my other laptop  
and run the “cdma\_rx.grc” file which is connected to that USRP(UHD USRP  
SOURCE. The image above is what I get. In the beginning it seems to be  
acquiring the packets then a few seconds later a lot of invalid packets  
get  
detected. Overall all are these images close to what I should be seeing.

A: you have not told us anything about your system, so we cannot help  
you.  
For instance, what is your hardware setup (daughtercards, carrier  
frequency, sample rate, etc),  
what is the expected frequency error,  
what are the RX parameters that you have set?  
are they compatible with you working environment?  
is your laptop handling well the acquisition load (have you checked the  
load on your CPU cores?)

Achilleas