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Difference between FDD-LTE and TD-LTE

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The two versions of LTE are very similar. In fact, they differ only in the physical layer and, as a result, the version implemented is transparent to the higher layers. This means that UE will be able to support both TD-LTE and FDD-LTE with one chipset with only minor modifications required. UE based on those chipsets are (or will soon be) available from Sony Ericsson, Huawei, Samsung, Nokia, and others.

TDD-FDD-1
TDD-FDD-2
The following features are unique to TD-LTE:
1. Frame structure – 3GPP has specified a special subframe that allows switching between downlink and uplink transmission.

2. Random access – Several additional random access formats exist
in certain subframes. Also, several random access channels exist in
every subframe.

3. Scheduling – The scheduling for the uplink is multi-frame.

4. HARQ – The number of HARQ processes depends on the uplink/downlink resource allocation.

5. ACK/NACK – Multiple acknowledgements and negative acknowledgements are combined on the uplink control channels.This ultimately leads to increased control signaling and lower spectrum/resource utilization.

6. Guard periods – These are used in the center of special subframes. They allow for the advance of the uplink transmission timing.

Another difference between FDD-LTE and TD-LTE is that in FDD-LTE every downlink subframe can be associated with an uplink subframe. In TD-LTE the number of downlink and uplink subframes is different and such association is not possible.

In terms of spectrum efficiency, the performances of TD-LTE and FDD-LTE are similar for non-delay sensitive traffic. The lower performance of TD-LTE is due to the guard periods mentioned above.

Finally, TD-LTE and TD-SCDMA work together with minimum interference issues, even if both technologies are deployed in the same frequency band (assuming that the TD-LTE UL:DL configurations are chosen correctly and both systems are synchronized to the same time source).

posted Mar 5 by anonymous

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It's quite informative doct. Thanks for sharing the same.

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