NB-loT sub-channel broadband includes ()? (Multiple choice).

NB-IoT (Narrowband IoT) operates within a total channel bandwidth of 180 kHz. For uplink transmissions, it supports two different subcarrier spacings to accommodate different use cases. Single-tone transmission uses a very narrow sub-channel of 3.75 kHz, which is ideal for maximizing coverage and power efficiency for devices in poor signal conditions. Multi-tone transmission uses a subcarrier spacing of 15 kHz, allowing for higher data rates when signal conditions are better.

C. 180 kHz is the total channel bandwidth of an NB-IoT carrier, equivalent to one LTE Physical Resource Block (PRB), not a sub-channel bandwidth.
D. 60 kHz is not a standard subcarrier spacing or channel bandwidth defined in the 3GPP specifications for NB-IoT.

1. 3GPP TS 36.211, "Evolved Universal Terrestrial Radio Access (E-UTRA); Physical channels and modulation," V15.2.0, Section 10.1.1 "Uplink physical channels," specifies the 3.75 kHz and 15 kHz subcarrier spacings for NPUSCH (Narrowband Physical Uplink Shared Channel).

2. Huawei. (2017). NB-IoT Technology Introduction White Paper. Section 2.2 "Key Technologies" explains the physical layer design, mentioning that "For the uplink, single-tone (3.75 kHz) and multi-tone (15 kHz) transmissions are supported."