Idle-Mode CSI-RS Signaling for UE Mobility Power Saving
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Solution Overview
Problem
In NR (New Radio) networks, user equipment (UE) in idle or inactive states relies on Synchronization Signal blocks (SSB) for measurements, which have long intervals, leading to inefficient energy usage due to extended wake-up times, while detailed methods for providing CSI-RS for mobility to idle UEs are lacking.
Innovation Solution
Network nodes provide idle UEs with indications of available CSI-RS for mobility occasions through higher layer signaling, such as system information or dedicated RRC signaling, allowing UEs to utilize these additional reference signals for power savings by reducing SSB measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If SSB signals are used for measurements in idle mode, then UEs can perform cell quality measurements and synchronization, but the long time intervals between SSB signals cause extended wake-up times and increased energy consumption
Solution Approach 1:
The network pre-configures UEs with CSI-RS resource information (time, frequency, scrambling ID) before the UE enters idle mode. This preliminary configuration enables the UE to know exactly when and where to find reference signals, allowing it to enter deeper sleep states without missing measurement opportunities, thus reducing energy consumption while maintaining measurement capability
Solution Approach 2:
CSI-RS signals are introduced as an intermediary between SSB signals and UE measurements. These CSI-RS signals are transmitted more frequently and can be configured to occur during periods when the UE would otherwise be sleeping, serving as a mediator that provides measurement opportunities without requiring the UE to wake up for every SSB transmission
2Stability of the object's composition
If SSB signals are used for measurements in idle mode, then UEs can maintain synchronization, but the long intervals require UEs to stay out of deep sleep for extended periods
Solution Approach 1:
CSI-RS resources are configured with flexible periodicities (including ms4, ms5, ms10, ms20, ms40 options) that can be optimized for the specific deployment scenario. This periodic structure provides regular measurement opportunities without requiring the long intervals inherent in SSB transmissions, allowing UEs to maintain synchronization with shorter, more efficient wake-up cycles
Solution Approach 2:
The network provides advance notification to UEs about upcoming CSI-RS occasions through higher-layer signaling. This preliminary information allows UEs to plan their wake-up schedules efficiently, entering deep sleep between known CSI-RS occasions without risking loss of synchronization, thereby reducing the time UEs must remain active
3Device complexity
If detailed methods for providing CSI-RS to idle UEs are not established, then network complexity is reduced, but UE power saving opportunities are limited
Solution Approach 1:
The patent extracts only the essential CSI-RS configuration parameters needed for idle mode measurements (time domain allocation, frequency domain allocation, scrambling ID) and provides them through streamlined higher-layer signaling. This selective extraction of necessary information enables effective CSI-RS-based power saving without requiring the full complexity of connected mode CSI-RS configuration management
Solution Approach 2:
The patent introduces new configuration parameters specifically for idle mode CSI-RS (such as slotConfig with ms4/ms5/ms10/ms20/ms40 periodicities, firstOFDMSymbolInTimeDomain, frequencyDomainAllocation) that differ from connected mode parameters. These parameter changes enable simplified, purpose-optimized configuration that balances network complexity with UE power saving benefits
Data Source
AI summary
A method by a network node to provide connected mode channel state information-reference signal, CSI-RS, for mobility to an user equipment, UE, while in idle mode includes providing the UE with an indication that CSI-RS for mobility occasions are available in idle mode based on determining that the UE is transitioning into idle or mode or is in idle mode. The method includes transmitting a CSI-RS for mobility occasion to the UE while the UE is in idle mode.