CSI Reference Slot Configuration for High Mobility NR Systems
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Solution Overview
Problem
In high or medium velocity scenarios, the throughput in 5G NR systems drops significantly due to outdated channel state information (CSI) caused by fast channel variations.
Innovation Solution
A method is proposed to extend the CSI framework in NR systems by defining two CSI reference slots: one for CSI measurement and another for CSI computation. Additionally, the UE can be configured with a CSI computation period consisting of one or multiple slots, divided into non-overlapping sub-periods, to compute and report wideband and subband CSI.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If CSI is calculated based on the located slot of CSI reference resource (past slot), then measurement simplicity is maintained, but CSI becomes outdated due to fast channel variation in high velocity scenarios
Solution Approach 1:
The patent introduces a future CSI reference slot that occurs after the uplink slot for CSI reporting. The UE is configured to compute CSI based on this future reference slot, allowing the gNB to obtain CSI that is valid for future channels rather than outdated past channels. This preliminary action of defining a future reference point resolves the timeliness issue in high velocity scenarios.
Solution Approach 2:
The patent makes the CSI reference slot dynamic by allowing it to be configured relative to the uplink slot (e.g., uplink slot + offset). This dynamic configuration enables the system to adapt to different velocity scenarios, where the reference slot can be positioned in the future to compensate for fast channel variations, transforming the static past-reference approach into a flexible dynamic system.
2Device complexity
If one-shot CSI measurement is used, then measurement complexity is reduced, but CSI cannot predict future channel variations
Solution Approach 1:
The patent configures the UE to perform CSI computation based on a future reference slot that occurs after the uplink reporting slot. This preliminary configuration allows the system to anticipate future channel conditions without requiring complex real-time tracking, maintaining measurement simplicity while improving future validity through proactive reference slot positioning.
3Reliability
If CSI computation period is extended to cover multiple slots, then CSI robustness to channel variation improves, but reporting overhead increases
Solution Approach 1:
The patent segments the CSI computation period into multiple non-overlapping sub-periods. The UE can be configured to compute and report wideband CSI and subband CSI for the whole computation period and/or for each sub-period. This segmentation allows flexible reporting strategies that balance robustness and overhead by selecting appropriate granularity for different scenarios.
Solution Approach 2:
The patent enables selective reporting where the UE can report CSI for the whole computation period or only for specific sub-periods based on configuration and channel conditions. This partial action approach allows the system to obtain sufficient CSI robustness without always incurring maximum reporting overhead, adapting the reporting quantity to actual needs.
Data Source
AI summary
A method of downlink channel state information (DL CSI) computation and reporting is proposed to support high velocity in new radio (NR) systems. In a first novel aspect, two CSI reference slots are defined. CSI reference slot for CSI measurement is defined for determining which CSI-RS/SSB occasion(s) is used for computing CSI. CSI reference slot for CSI computation is defined for determining the slot where UE assumes the CSI computation should be based upon the channel at that time onwards. In a second novel aspect, UE can be configured with a CSI computation period consisting of one or N slots and can be divided into multiple sub-periods without overlap. UE can be configured to compute and report wideband CSI and subband CSI for the whole CSI computation period and/or for each sub-period.