Physical resource block (PRB) is the minimum unit for resource allocation in LTE. It consists of

• 12 consecutive subcarriers in frequency domain
• and the time duration of 0.5 ms.

During the 0.5 ms transmission time, 6 or 7 OFDM symbols, depending on the length of appended cyclic prefix, can be transmitted. The subcarrier spacing in LTE is set to 15 kHz. Thus, the bandwidth of one PRB amount to 180 kHz. User equipments (UEs) are assigned with multiple PRBs for transmission. Since the minimum required transmission time interval (TTI) is 1 ms in LTE, allocations are done in pairs of PRB. Shown in the figure, the two PRBs form a subframe with minimum bandwidth of 180 kHz and minimum TTI of 1 ms.

In the following demos, users are able to define assigned number of subcarriers for one PRB. The spectral density can be plotted for different number of PRBs (consecutively assigned in frequency domain, thus adjacent channel interference can be observed).