Baseband spectrum in LTE

Many books has been published about LTE wireless communication, but I cannot find any information about baseband spectrum. Maybe it is obvious issue, but...

For maximum FFT-size, which is defined in LTE Rel.11 specification: 2048.

We have sampling frequency 2048*15kHz = 30.72 MHz;

Spectrum bandwidth: 20 MHz (by specification);

So, Sampling theorem says that we should use sampling frequency more 40 MHz.

Another way: to shift baseband spectrum so that middle subcarrier moves to zero point (see picture).

Baseband spectrum for LTE uplink

Well, we should always remember that the 1st subcarrier doesn't mean the lowest frequency in the spectrum, especially it is important, when you want to design IQ-imbalance algorithm...