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I am a bit confused regarding the implementation of Pulse shaping filter in OFDM (Both CP-OFDM & SC-FDMA) system. I am explaining my concept in the following,

  1. The difference between CP-OFDM and SC-FDMA is the use of DFT block before subcarrier mapping.Reference.

  2. I am not sure if I need implement pulse shaping filter before or after the DAC block in the reference.

  3. The implementation of pulse shaping filter is the most confusing part for me. I am explaining my difficulty using an example. Assume, channel BW= 20MHz. Waveform SC-FDMA. SCS=15 KHz. The number of FFT points Nfft= 2048. Which makes sampling rate 30.72 MHz. While I try to implement the RRC filter using Matlab,

     Nsym = **?**;           % Filter span in symbol durations
     beta = 0.3;         % Roll-off factor
     sampsPerSym = **?**;    % Upsampling factor
    rctFilt = comm.RaisedCosineTransmitFilter(...
    'Shape','Normal', ...
    'RolloffFactor',beta, ...
    'FilterSpanInSymbols',Nsym, ...
    'OutputSamplesPerSymbol',sampsPerSym)
    

My question: Note: The time domain representation of the OFDM samples are the sum of all the subcarrier in time domain.

1.What should be the filter span (Nsym) for my example explained above?

  1. What should be sample per symbol? The reason is that DAC can be used to over-sample the signal. Does RRC filter also increase the sample rate while implement in discrete domain using MATLAB?

  2. Can anyone please clarify my concept regarding the design procedure of RRC transmit filter for OFDM system (CP-OFDM & SC-FDMA)?

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    $\begingroup$ There's rare exceptions, but you do not do pulse shaping on OFDM. Why would you do that? It makes everything worse. Which kind of system does that? Are you looking at some turn-of-the-millenium legacy system that needs to fulfill a RRC-defined spectral mask? This is interesting! But in that case, it wouldn't be an SC-FDM system. So, really confused now. $\endgroup$ Sep 4, 2022 at 7:05
  • $\begingroup$ @MarcusMüller Thank you for your explanation. So, I should not use any RRC filter. As your suggestion I am no more interested in RRC on OFDM. I got my answer. $\endgroup$ Sep 4, 2022 at 7:34
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    $\begingroup$ Oh, that came surprising! Md., just an external perspective: the dBc question, but also the DC cancellation question show you're trying to apply concepts to systems that do not apply. That's not bad! Because that's how innovation is done: you take things that exist separately and combine them, inventing the things necessary to combine them underway. But: the trick there is to understand why something is done before trying to apply it to something else. RRC pulse shaping is done for simple reasons, which you don't show any reflection of; otherwise you could have seen this! $\endgroup$ Sep 4, 2022 at 7:36

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