Why the IFFT length in LTE is not in the power of 2 for bandwidth of 3MHZ &15 MHz

Question

for 3MHZ it is 320 which is not the power of 2 and for 15 its 1536 again which is not the power of 2

Answer 1

>> IFFT size/length means number of sine waves the IFFT takes as input to construct the time domain signal. In case of 20 MHz the IFFT size is 2048 that means 2048 sub-carriers are used to construct the time domain signal. (Note: not all are occcupied).

the IFFT size is "IDFT(Tx)/DFT(Rx) size" in the table provided above.

So for 3 Mhz it is 256 not 320.

for 2nd Query -

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