UE-Initiated Reference Signal Requests for Lower CSI Latency
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Solution Overview
Problem
Conventional reference signal scheduling techniques in wireless communication systems, such as 5G NR, face limitations in feedback delay and overhead, particularly with aperiodic CSI and SRS, as there is a delay between the UE detecting an issue and the base station scheduling a response.
Innovation Solution
User Equipment (UE) initiates requests for reference signals like CSI-RS and SRS, autonomously determining the need and transmitting an uplink request with a trigger state, allowing for reduced latency and flexibility in channel measurements, using RRC and MAC-CE configurations to activate specific trigger states and map them to physical uplink resources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the base station schedules reference signals in response to UE-detected issues, then the system maintains centralized control and proper resource allocation, but feedback delay increases due to the time required for the base station to detect and schedule the response
Solution Approach 1:
The base station pre-configures multiple trigger states and their corresponding reference signal resources before the UE needs to request reference signals. When the UE detects channel conditions matching a trigger state, it can immediately request the pre-configured reference signal without waiting for base station scheduling decisions, thereby reducing feedback delay while maintaining centralized control through the pre-established configuration framework
2Productivity
If the UE autonomously requests reference signals based on detected channel conditions, then latency is reduced and flexibility is improved, but system complexity increases due to the need for trigger state configurations
Solution Approach 1:
The reference signal request mechanism is segmented into distinct trigger states, where each trigger state corresponds to specific channel conditions and references a pre-configured reference signal resource. This segmentation allows the UE to autonomously select appropriate reference signals based on current channel conditions without complex real-time decision-making, reducing latency while managing configuration complexity through structured state definitions
3Adaptability or versatility
If multiple trigger states are configured for different reference signal requests, then the system gains flexibility in handling diverse channel conditions, but overhead increases due to the need for mapping and activation management
Solution Approach 1:
Multiple trigger states are configured to handle diverse channel conditions, with each trigger state mapping to specific reference signal resources. The base station activates only the necessary trigger states based on current network conditions and UE requirements, allowing the system to maintain flexibility for various scenarios while reducing overhead by not all states being simultaneously active or configured for every UE
Data Source
AI summary
A user equipment (UE) and a base station (BS) may transmit reference signals (RS) for the other device to estimate a channel and perform measurements. This disclosure provides for a UE to request a reference signal such as a channel state information (CSI) or a sounding reference signal (SRS). The BS transmits a radio resource control (RRC) message that configures the UE with one or more trigger states for CSI, SRS, or a combination thereof and a media access control (MAC) control element (CE) that activates a subset of the configured trigger states. In one aspect, the UE transmits an uplink request that indicates a trigger state for the UE. corresponding to at least one configured RS. The UE and the BS communicate the at least one RS corresponding to the trigger state for example, based on a grant from the BS or a time offset from the uplink request.