The difference lies in the LTE frame structure in both the FDD and TDD versions of the LTE.
In FDD there will be pair of frequencies assigned in the downlink and uplink directions and hence transmissions from multiple subscribes can happen at the same time but on different frequencies as mentioned. Interference between neighbouring base stations less as transmission and reception is done on seperate frequencies.
In TDD, one single frequency will be used at different time instants by multiple subscriber terminals (UEs). Both frame versions of LTE will have 1 ms sub-frame duration and 0.5 ms slot duration. Interference between neighboring base stations more, as transmission and reception is done on the same frequency
FDD deployments provide greater coverage than TDD
Mobile devices in a Frequency Division Duplexing (FDD) system transmit on a continuous basis,
which enables devices to achieve cell edge rates farther from the base station. Mobile devices in
a Time Division Duplexing (TDD) system transmit periodically (e.g., 1/2 or 1/3 of the time
compared to FDD); hence, required rates cannot be achieved at similar distances when
compared to FDD. The FDD advantage is consistent regardless of the radio technology being
used.
6
FDD needs fewer base stations than TDD
Since FDD devices achieve desired cell edge rates at farther distances, the number of base
stations required to achieve a given area of coverage is reduced.
In a coverage-limited system comparison using the same frequency band, the TDD system
required 31% more base stations than FDD when using a 1:1 TDD system and 65% more base
stations when using a 2:1 TDD system. Higher frequency bands required even more base
stations.
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