ARFCN is an Absolute Radio Frequency channel number that is generally used for initial cell search where UE scans all frequencies and tries to latch on the legitimate frequency. It is a code that specifies a pair of reference frequencies used for the transmission and reception in a radio system. In 5G NR, duplex methods are divided as FDD(Frequency Division Duplex) and TDD (Time Division Duplex). In FDD systems, one ARFCN is required for uplink and one is for downlink as the frequencies for uplink and downlink are different while for TDD systems, one frequency is required for both uplink and downlink as in this only one frequency is required for uplink as well as downlink.
5G ARFCN is known as NR-ARFCN (New Radio – Absolute Radio Frequency Channel Number). NR band types are categorized as FDD (Frequency Division Duplex) band, TDD (Time division duplex) band, SDL (Supplementary Downlink band), and SUL (Supplementary uplink band). NR band frequency ranges are divided as FR1 (Frequency Range 1) and FR2 (Frequency RAnge 2).