I was reading someone's thesis and now i am more confused about CDMA system. From what i understood is CDMA is multiplexing which allows multiple signals to transmit over single channel. so general structure of CDMA communication system should be like shown below:

Binary Data --> Multiply PN Code --> XOR(spreading) -->BPSK/QPSK Modulation --> RF End 
Restore Data <-- Despreading <-- Aquistion and lock <-- RF Demodulation <--    RF Reception 

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And Now I had come across block diagram in the thesis, Pg.27 which basically modulate and they do spreading. enter image description here

From my understanding it should be spreaded before doing modulation. This is my understanding, please correct me if i am wrong.

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But can someone please confirm which one is right ? It would be great if you explain a little bit.


1 Answer 1


Since spreading and symbol modulation are memoryless linear operations, the order makes absolutely no difference. Both methods of writing the same thing down are equally valid, and the one you choose mainly depends on what is convenient for the rest of your text.

  • $\begingroup$ It does not matter if i spread before modulation or after and also unrelated to modulation scheme, right ? $\endgroup$
    – Jay Patel
    Commented Jan 23, 2021 at 15:11
  • $\begingroup$ see my first sentence! $\endgroup$ Commented Jan 23, 2021 at 15:17

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