F-OFDM over the NR air interface uses flexible subcarrier spacing to meet the requirements of...

F-OFDM (Filtered Orthogonal Frequency Division Multiplexing) over the NR air interface uses flexible subcarrier spacing to meet the requirements of different 5G service scenarios. F-OFDM is a 5G physical layer waveform that is designed to provide high spectral efficiency, low complexity and low latency. It uses a flexible subcarrier spacing, which can be adjusted to meet the requirements of different 5G services. The subcarrier spacing can be 15KHz, 30KHz, 60KHz, or 120KHz.

Sub-6GHz 5G networks are designed to provide wide-area coverage and support high data rate services such as mobile broadband, IoT, and critical communications. Sub-6GHz band is mainly used for 5G deployment in rural areas, and in-building coverage.

Therefore, the subcarrier spacing that is not supported by Sub-6GHz is 120KHz. So the correct answer is A. 120KHz. It's worth noting that each subcarrier spacing has its own advantages and disadvantages. 120KHz spacing is mainly used for low mobility services such as fixed wireless access, while 15KHz spacing is mainly used for high mobility services such as mobile broadband.