Regarding the technical characteristics of the NB-IoT air interface, which of the following descriptions are correct? (Multiple choice)
A . Uplink adopts SC-FDMA with a bandwidth of 3.75kHz or 15kHz
B . Downlink adopts OFDMA with a bandwidth of 15 kHz
C . Downlink adopts OFDMA with a bandwidth of 3.75kHz
D . Uplink adopts SC-FDMA with the bandwidth is fixed at 3.75kHz
Answer: AB