NR-U 60 GHz Beam Management via Aperiodic CSI-RS
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Solution Overview
Problem
Legacy beam management procedures are inadequate for supporting New Radio (NR) beam management at the 60 GHz band, particularly due to limitations in channel occupancy time (COT) considerations, insufficient periodic reference signals, and challenges in beam failure recovery, leading to delayed recovery and reliability issues with narrow beamwidths.
Innovation Solution
The implementation of multi-slot aperiodic CSI-RS and SRS resources for beam management and beam failure recovery, along with cross-carrier CSI-RS validation and LBT-free CSI-RS transmissions, enhances the efficiency and reliability of beam management by allowing flexible scheduling and validation of reference signals across multiple slots and carriers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If periodic CSI-RS is used for beam management outside of COT, then beam evaluation can be performed continuously, but channel access conflicts and LBT failures occur in unlicensed spectrum
Solution Approach 1:
The gNB performs LBT and acquires COT in advance before transmitting beam management reference signals. The UE is configured with multiple candidate beams that can be used for beam failure recovery, preparing recovery resources before actual beam failure occurs. This preliminary preparation ensures that when beam failure detection occurs, recovery can proceed without waiting for additional LBT attempts.
Solution Approach 2:
The system transitions from periodic CSI-RS transmission to aperiodic CSI-RS transmission triggered within COT. The reference signal transmission mode changes from fixed periodic intervals to flexible triggering based on channel access success, adapting the transmission parameters to the unlicensed spectrum environment where channel availability is uncertain.
2Reliability
If beam width is narrowed to increase beamforming gain, then coverage and signal strength improve, but beam alignment becomes more difficult and susceptible to blockage
Solution Approach 1:
Multiple candidate beams are pre-configured and made available to the UE before beam failure occurs. When beam failure is detected, the UE can immediately select from pre-prepared candidate beams without needing to perform extensive new beam training, thus maintaining alignment while benefiting from narrow beam gains.
Solution Approach 2:
Different beams with different characteristics (widths, directions) are configured for different purposes. Some beams may be wider for initial access and others narrower for data transmission, allowing the system to optimize for both alignment ease and signal strength in different operational contexts.
3Loss of time
If beam failure detection threshold is set to detect failures quickly, then recovery time is reduced, but false detections increase causing unnecessary recovery procedures
Solution Approach 1:
The system uses multiple reference signals (CSI-RS and SSB) for beam failure detection, providing redundant measurement opportunities. The UE can cross-validate measurements across multiple signals and time instances, reducing false detections while maintaining quick detection of actual failures through aggregated feedback from multiple sources.
Solution Approach 2:
The system configures multiple candidate beams and multiple reference signals for detection, using more measurement opportunities than the minimum single instance. This excessive use of measurement resources increases detection reliability by providing statistical confidence, reducing false positives while maintaining fast recovery capability.
4Adaptability or versatility
If aperiodic CSI-RS is used for beam management, then flexibility in scheduling is improved, but overhead and complexity increase
Solution Approach 1:
The aperiodic CSI-RS resource configuration is designed to work with existing DCI formats and triggering mechanisms already present in NR. The same DCI structure used for other purposes is extended to trigger aperiodic CSI-RS for beam management, avoiding the need for entirely new signaling protocols and reducing overall system complexity despite the flexible scheduling capability.
Data Source
AI summary
Disclosed is an electronic device including at least one processor, and at least one memory operatively connected with the at least one processor, wherein the at least one memory stores instructions, which when executed, instruct the at least one processor to receive, on a control channel, a control channel message, receive a set of reference signals (RSs) in which each RS corresponds to a beam direction, decode the control channel message to obtain a list of transmission state indicator (TCI) state information for one or more slots, wherein each TCI state information comprises a channel occupancy time (COT) duration indicator for each of the slots, and determine, based on the TCI state information list, whether each RS of the set is valid.