Default Beam Selection When PDCCH DCI Omits TCI
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Solution Overview
Problem
In wireless communication, when Downlink Control Information (DCI) carried by a Physical Downlink Control Channel (PDCCH) does not include a Transmission Configuration Indication (TCI) state indication field, the terminal device faces challenges in determining a transmission beam, particularly for Physical Downlink Shared Channel (PDSCH), leading to potential communication failures.
Innovation Solution
The terminal device determines a default beam using one or more TCI states corresponding to a second PDCCH when the TCI state is absent in the first DCI, employing methods such as using the TCI state of a control resource set with a minimum CORESET ID, or selecting TCI states based on their IDs or pool indexes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If DCI carried by PDCCH does not include TCI state indication field, then the terminal device cannot determine transmission beam according to the first DCI, but the terminal device can determine default beam using TCI states corresponding to second PDCCH
Solution Approach 1:
The terminal device pre-acquires TCI states corresponding to the second PDCCH (e.g., through MAC CE signaling or previous DCI) and stores them as default beam information. When the first DCI lacks TCI state indication, the terminal device can immediately apply these pre-acquired TCI states to determine the default beam, ensuring continuous communication without interruption.
Solution Approach 2:
The TCI states corresponding to the second PDCCH serve as an intermediary mechanism to bridge the gap when beam indication information is missing in the first DCI. These intermediary TCI states provide the necessary beam configuration information to maintain communication link reliability.
2Reliability
If the terminal device uses TCI states corresponding to second PDCCH to determine default beam, then communication link can be established even without TCI state in first DCI, but additional processing steps are required
Solution Approach 1:
The terminal device performs preliminary acquisition of TCI states corresponding to the second PDCCH in advance (through MAC CE or previous DCI), so that when the first DCI lacks TCI state indication, the default beam can be determined using these pre-acquired states without requiring complex real-time processing.
Solution Approach 2:
The terminal device copies the TCI states from the second PDCCH configuration and applies them as default beam information when the first DCI does not provide TCI state indication, avoiding the need to create new beam configurations from scratch.
Data Source
AI summary
A method for determining a default beam is performed by a terminal, and includes: receiving first downlink control information (DCI) carried on a first physical downlink control channel (PDCCH); and determining that a transmission beam is unable to be determined according to the first DCI, and determining a default beam according to one or more transmission configuration indication (TCI) states corresponding to a second PDCCH.