Comparing TDD and FDD Two-way communications schemes need separate channels for each direction of communication  Frequency Division Duplex (FDD): directions separated in frequency  Time Division Duplex (TDD): directions separated in time TDD  requires single block of spectrum  especially efficient where communications may be asymmetric (e.g., data)  leverages maximum benefits from adaptive antennas FDD  requires paired spectrum  less efficient with unknown or varying data asymmetry  benefits for extreme long-range operation (10's of km)  adaptive antennas provide significant benefits
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