Why lteOFDMinfo gives the same results for signals with 75 and 100 resource blocks?

Why the following commands gives the same result?

           enb = struct('NDLRB',75,'CyclicPrefix','Normal');
           lteOFDMInfo(enb)

answer

          SamplingRate: 30720000
                  Nfft: 2048
              Windowing: 8
    CyclicPrefixLengths: [160 144 144 144 144 144 144 160 144 144 144 144 144 144]

And the same command using 100 resource blocks:

enb = struct('NDLRB',100,'CyclicPrefix','Normal');
lteOFDMInfo(enb)

answer:

          SamplingRate: 30720000
                   Nfft: 2048
              Windowing: 8
    CyclicPrefixLengths: [160 144 144 144 144 144 144 160 144 144 144 144 144 144]

link about lteOFDMInfo is here

Answer 1

[Graham Freeland]

Both of these carrier bandwidths will use the same 2048 point IFF/FFT therefore the sampling rate and CP lengths in samples will be the same.

See the help of lteOFDMModulate for more info on how the FFT size is selected in LTE System Toolbox:

In general, Nfft is the smallest power of 2 greater than or equal to 12*NRB/0.85. It is the smallest FFT that spans all subcarriers and results in a bandwidth occupancy, 12*NRB/Nfft, of no more than 85%.

Cheers,

Graham