Not all radio spectrums are equal. Sub 1GHz offers the best coverage profile; however, the amount of low band spectrum available is limited.
Frequency range two (FR2), i.e. greater than 6GHz, offers a large amount of spectrum with a significantly wide bandwidth (up to 400MHz), but it offers limited coverage.
In fact, it is an excellent radio channel for gigabit throughput, but the coverage is limited to hundreds of feet. C-band spectrum, which is part of frequency range one (FR1), and also called mid-band spectrum, offers a good compromise between coverage and high throughput.
As part of 3GPP release 15, three bands n77, n78, and n79 were identified for 5G operation in the C-band, with a potential service bandwidth of up to 100 MHz.
With 100 MHz of bandwidth, C-Band can truly enable the enhanced mobile broadband (eMBB) use case for 5G. One thing to note is that C-band offers only Time Division Duplexing (TDD).
TDD delivers a full-duplex communication channel over a half-duplex communication link. This means both the transmitter and receiver use the same frequency but transmit and receive traffic at different times by using synchronized time intervals. Advances in digital signal processing and the computation speed of hardware allow for TDD operations, but it does offer some challenges. Let’s review the benefits of TDD and some of the timing and synchronization requirements to ensure it can deliver a similar quality of RF services as Frequency Division Duplexing (FDD).
TDD turns out to be a more attractive option from the spectral efficiency point of view because it requires only an unpaired spectrum for the operation which is beneficial considering the scarcity of frequency resources. Also, physical layer features such as massive MIMO, beamforming, and precoding, that rely on channel state information (CSI) measurement in the uplink are more robust due to channel reciprocity.
Reference: 5G Timing and Synchronization Handbook for TDD Deployment