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    • #22639
      Dhananjay Patel
      Participant

      I am working on OFDM system whose design is attached here with. I have certain query to make:

      1. What is the significance of these global parameters:

      Sequence length
      Samples per bit
      Guard Bits
      Symbol rate
      Number of samples

      2. What is the use of position array in OFDM block.

      3. What is the relationship between the number of sub carrier, position array, number of FFT point

      4. How to decide the roll of rate of the LP cosine filter?

      5. Also in my input and output constellation, I am finding a huge difference, kindly let me know the reason behind it.

    • #22687
      Ashu verma
      Participant

      Hello Dhanjay

      I try to explain the points and question you raised about the parameters of OFDM

      First of all, sequence length is the no. of bits transmit and the sequence length is directly relates to the word length that you can set from PRBS. In the case of OFDM the sequence length is long.

      Samples per bit are the instants to sample the the one bit and total sampling freq. is your bit rate x sample per bits.Sample per bit in the case of OFDM are chosen to be less due to long sequence length which results into high no. of samples.

      Gaurd bits are used to reduce ISI in the OFDM system.

      Symbol rate quantifies the number of symbols transmitted per second.

      No. of sample=Seq. length x Sample per bit

    • #22688
      Ashu verma
      Participant

      In the addition to the above points,for the FFT points go to the link i have given below

      Optisystem OFDM Block


      For Understanding of Lp cosine filter and roll of factor visit the given link
      https://en.wikipedia.org/wiki/Raised-cosine_filter

      For the last one,can you attach the system setup screen shot along with constellation diagrams as i am not able to open the file you have attached.
      Hope you got your all answers
      Thankyou

    • #22690
      alistu
      Participant

      Hi Dhananjay,

      I believe I gave you the answer for some of the questions you have asked above in the forum below:

      Design error

      Your constellation on receiver side looks strange! After all, you have only sent 4 symbols but you are receiving more!

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