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MAC CE : TCI States Activation/Deactivation for UE-specific PDSCH MAC CE

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The concept you're referring to is quite specific to the 3GPP LTE (Long-Term Evolution) standard, where MAC CE (Medium Access Control Control Element) is used for control information exchange between the eNodeB (base station) and User Equipment (UE).

Let's break down the topic step by step:

1. MAC CE:

MAC CE stands for Medium Access Control Control Element. In LTE, the MAC layer is responsible for mapping logical channels onto transport channels, scheduling of resources, and multiplexing/demultiplexing of data for multiple UEs.

A MAC CE is a type of control element used to carry specific control information from the eNodeB to the UE or vice versa.

2. TCI States:

TCI (Transport Channel Identity) states are used to identify a specific PDSCH (Physical Downlink Shared Channel) on which the UE should receive its data. The TCI states help the UE to identify and decode the PDSCH carrying its specific data.

3. TCI States Activation/Deactivation:

When a UE is scheduled to receive data on a specific PDSCH, the eNodeB assigns a TCI state to the UE. This TCI state essentially tells the UE which PDSCH to monitor and decode for its incoming data.

  • Activation: When the eNodeB wants the UE to start monitoring a specific PDSCH, it sends a MAC CE to the UE with the necessary information, including the TCI state that should be activated.
  • Deactivation: Conversely, if the eNodeB wants the UE to stop monitoring a particular PDSCH (perhaps due to reconfiguration, handover, or other reasons), it will send a MAC CE to the UE instructing it to deactivate the particular TCI state associated with that PDSCH.

4. UE-specific PDSCH:

PDSCH (Physical Downlink Shared Channel) is a downlink channel used to transmit user data and control information. When we say "UE-specific PDSCH," it means that the PDSCH is specifically allocated for a particular UE. The UE needs to monitor this channel to receive its data.

When a UE-specific PDSCH is activated for a particular UE, the eNodeB uses the MAC CE to inform the UE about the TCI state that it should use to monitor and decode this PDSCH. Similarly, when deactivating, the MAC CE will instruct the UE to stop monitoring that specific TCI state/PDSCH.

Conclusion:

The TCI states activation/deactivation mechanism using MAC CE in LTE ensures that UEs know which specific PDSCH to monitor and decode for their data. By activating or deactivating TCI states using MAC CEs, the eNodeB can efficiently manage resources, ensuring that each UE receives its intended data on the correct PDSCH. This mechanism enhances the flexibility and efficiency of LTE resource management and data transmission.