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I have:

  • Bit rate $ R_b = 25.6 [Mbit/s]$
  • Sampling frequency at the input of the receiver: $ f_p = 8 [MHz]$
  • Protective spacing between successive OFDM symbols: $ τ = 16 [µs] $
  • The combined length of the OFDM symbol and the prefix: $ T_s = 80 [µs]$

Tasks:

1. The number of signal samples per cyclic prefix

So here is the problem because I don't know how can I calculate this number of samples. I can calculate the number of data bits by this formula:

$R_b = B/T $ where T is the total transmission time ($80 [µs]$).

But I want samples, so maybe I should use the time of the cyclic prefix that is $ 16 [µs] $, but what next?

2. The size of the constellation (number of points) on a given sub-channel (assumption: in each sub-channel the same constellation and all sub-channels transmit data)

So I know this equation:

$T_s = N*T_p$

$T_p = 0.000000125 $

But N here equals 640, so 640 = $2^k$, isn't there something wrong?

3. Size N of FFT / IFFT transformation

Isn't this that 640 I have counted above?

4. Provide the effective value of data transmission speed $R_b$ if 64 subchannels in each OFDM symbol are used for transmitting pilots

I don't know how to do this one

5. The number of information bits transmitted in each single OFDM symbol

Should I use this formula (thanks MarcusMuller!)?:

$\frac{\log_2{N} k}{\frac{l_\text{FFT}}{f_\text{sample}}}$

But there is another problem with k (because of 640 = $2^k$)...

Any suggestions? I will be grateful for any help!

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