5G NR supports both Frequency Division Duplexing and Time Division Duplexing, but the balance between them has shifted dramatically compared to LTE. FDD uses paired spectrum with separate frequencies for uplink and downlink transmitting simultaneously. TDD uses a single unpaired frequency band and alternates between uplink and downlink in time domain slots. In 5G the key mid-band allocations around 3.5 GHz and all millimeter-wave spectrum are unpaired, making TDD the dominant duplexing mode for new 5G deployments while FDD continues on refarmed low-band carriers.