TDD offers flexible deployments without requiring a pair of spectrum resources. For TDD deployments in general, interference between UL and DL including both basestation-to-basestation and UE-to-UE interference needs to be considered. One example includes layered heterogeneous network deployments, where it may be of interest to consider different uplink-downlink configurations in different cells. Also of interest are deployments involving different carriers deployed by different operators in the same band and employing either the same or different uplink-downlink configurations, where possible interference may include adjacent channel interference as well as co-channel interference such as remote basestation-to-basestation interference.
Currently, LTE TDD allows for asymmetric UL-DL allocations by providing seven different semi-statically configured uplink-downlink configurations. These allocations can provide between 40% and 90% DL subframes. The semi-static allocation may or may not match the instantaneous traffic situation. The current mechanism for adapting UL-DL allocation is based on the system information change procedure. Additional mechanisms could include e.g. dynamic allocation of subframes to UL or DL.
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