TDD ASPECTS : WHY HAS 3GPP STANDARDIZED BOTH FDD AND TDD FOR LTE?

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  • Most of the standardization work within LTE done initially was emphasizing the Frequency Division Duplex (FDD) mode. In FDD, a paired frequency band is used and uplink and downlink channels are selected from different frequency bands. To be able to use unpaired frequency bands, a time division duplex (TDD) mode is supported as well. In TDD, uplink and downlink in a cell use the same frequency but the transmissions do not happen simultaneously. A major difference as compared to half duplex FDD, is that not only the UEs, but also the eNodeBs cannot receive and transmit at the same time.
  • The objective is to make LTE a Global standard, so that it can be deployed world-wide. Therefore, unnecessary differences between TDD and FDD are avoided, unless motivated by significant performance benefits.
  • Due to this, it simplifies implementation of dual mode FDD/TDD equipment. Mainly UEs can be manufactured at a reasonable price which everyone can afford.
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