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problem with pskmod in MATLAB

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eran135

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problem with pskmod

Hi,
i m trying to simulate DS-cdma BER performance using MATLAB for multiusers. My problem is that "pskmod" function only accepts positive values from 0-M and in
DS-CDMA when adding different spreaded codes i get some negative
values that cant be given to "pskmod" e.g. " -1 1 1 -1 1 -1 -1..."
So, how can i pass the spreaded codes using "pskmod"?
i am trying to modulate with qpsk.
its very urgent, i really need your help.
thanks very much!
 

Re: problem with pskmod

you need to convert -1 to 0. Do it by adding 1 with all the bits and then divide it by 2. You input this to pskmod. You can convert the zeros to -1 later when you need it.
 

Re: problem with pskmod

eran135 said:
Hi,
i m trying to simulate DS-cdma BER performance using MATLAB for multiusers. My problem is that "pskmod" function only accepts positive values from 0-M and in
DS-CDMA when adding different spreaded codes i get some negative
values that cant be given to "pskmod" e.g. " -1 1 1 -1 1 -1 -1..."
So, how can i pass the spreaded codes using "pskmod"?
i am trying to modulate with qpsk.
its very urgent, i really need your help.
thanks very much!
Click to expand...

I had this problem sometime ago. The solutions are:

(1) Do a reverse mapping i.e from -1 -> 0 and +1 -> 1

(2) Modulate the data first and then spread (go for this one)

Hope this helped....
.... I had to search a lot before this headache was gone
 

Re: problem with pskmod

Communications_Engineer,
thanks for your help but i did not understand something.
does not the modulation has to be after the spreading?
 

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