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increasing fiber data rate

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(joined April 2014)
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hello everyone
i did asimulation to 20MHz 16QAM-OFDM signal with 54Mbps , but the data rate on fiber also 54Mbps and i want to increase it without changing the signal bandwidth (20 MHz) , so how can i do that if anyone help me please .
i will attache my file here

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Responses (20):

    • #28119
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      feras
      Participant

      hello everyone
      i did asimulation to 20MHz 16QAM-OFDM signal with 54Mbps , but the data rate on fiber also 54Mbps and i want to increase it without changing the signal bandwidth (20 MHz) , so how can i do that if anyone help me please .
      i will attache my file here

      Attachments:
    • #28132
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      alistu
      Participant

      Hi Feras,

      Since we have discussed this in another topic and I remember you told me you did not want to use filters for this purpose, can you please say if you are trying to reproduce the results of another paper? In this case, I think it might really be helpful if you introduce that paper here.

      Regards

      • #28144
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        feras
        Participant

        hi alistu
        actually i am working on lte radio over fiber simulation as i said before but i don’t have any paper yet , i am trying to write it for my study.and i want to transmit the lte signal on the fiber using high data rate

        • #28153
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          alistu
          Participant

          In this case, I would have gone on with my project using filters if necessary to control the bandwidth. Nevertheless, using filters to control bandwidth may sometimes result in performance degradation based on the signal bandwidth. In other words, there may be a compromise between signal bandwidth and system performance if the reduction of signal bandwidth is necessary.

          Regards

        • #28154
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          feras
          Participant

          hi
          alistu

          so u said that we cannt put tow different data rate in one simulation first one for the transmitter and the other one for fiber Chanel?
          and we must use filters but where we have to use the filters ?

        • #28164
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          alistu
          Participant

          You never asked about two different data rates being used in one simulation. I merely suggested when you choose the data rate and the modulation scheme, the bandwidth produced depends on the data rate (the bandwidth shows frequencies that exist, which depend on how fast the data is being produced). If you elaborate more on two frequencies being used in one simulation, I will state my opinion about it.

          Regards

        • #28172
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          feras
          Participant

          hi alistu
          actually i want to increase the transmitting bit rate on the fiber only without changing my transmitter parameter to keep on 20MHz bandwidth signal

        • #28174
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          alistu
          Participant

          So if I am getting it right, by “bit rate on the fiber” you mean the symbol rate, whose symbols are created according to the adopted coding scheme in the M-ary coder in transmitter. If you use modulations of higher order, the “bits per symbol” will increase and the symbol rate will decrease.

        • #28175
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          feras
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          hello alistu
          i tried to increase the symbol rate to 200 Giga and the system still work and show a good result and , the BER didn’t change is that normal??

        • #28176
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          alistu
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          The symbol rate should be set according to the coding scheme and the number of bits per symbol in the coder/modulator. As far as I know, increasing it in layout parameters has no effect on system performance unless in some of the system components like filters, its value is being used in script mode.

        • #28177
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          feras
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          so how we can set the symbol rate on the optical fiber Chanel

        • #28178
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          alistu
          Participant

          The bit rate is set for all the system, including the fiber channel, and so is the symbol rate. So like I said, the symbol rate should be chosen according to the “bits per symbol” parameter in the coder or modulator. For example, if in a system with a bit rate of 7.5GHz this parameter is 3 (for a modulation scheme like 8-psk), then the symbol rate would be 2.5 GHz.

        • #28179
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          feras
          Participant

          hello alistu
          so as we said before we cannt Separate between fiber channel data rate and transmitter data rate

        • #28182
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          alistu
          Participant

          If by “data rate” you mean the system bit rate, then no. The bit rate is determined by pseudo random bit sequence generator (or BER test set) and its value can be set in layout parameters window. However, the symbol rate, which is dependent on the bit rate and coding scheme, can be different from bit rate.

          Regards

        • #28189
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          feras
          Participant

          for example i put the pseudo random bit sequence generator bit rate (120 Mbps ) and the bit rate in layout parameters ( 5 Gbps ) , but when i did that the system didn’t work correctly

        • #28190
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          alistu
          Participant

          Some parameters like time window and sample rate are created with regard to the value that you set for the bit rate in the layout parameters. So you’d better choose the same value for them (you can use script mode to set the bit rate value of PRBS generator easily from the layout parameters).

        • #28191
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          feras
          Participant

          ok alistu ,i was thinking to transmitt LTE radio signal on the fiber in a high bit rate but its ok with 120Mpbs , thank you very very much for your helping and your answers , it was very helpful for me

        • #28193
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          alistu
          Participant

          You’re welcome Feras. Good luck on your research work.

          Regards

    • #28135
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      Gokul Boro .
      Participant

      If the data rate is increased, should we increase the number of subcarriers? In some simulations I tried increasing the number of subcarriers and the constellation points were better and less error rate.

      • #28139
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        alistu
        Participant

        I have also experienced this, but I cannot say this always happens, as I have experienced some cases in which less subcarriers have resulted in better system performance. This may happen especially in the systems with less stationary behavior when short Fourier transform may be helpful.

      • #28145
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        feras
        Participant

        hi Gokul Boro .
        actually i want to increase the transmitting bit rate on the fiber only without changing my transmitter parameter to keep on 20MHz bandwidth signal .

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