Aperiodic SRS Transmission via Uplink Grant in Carrier Aggregation
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Solution Overview
Problem
In carrier aggregation systems, there is a lack of defined methods for aperiodic sounding reference signal (SRS) transmission, specifically determining which uplink component carrier (UL CC) to use for aperiodic SRS transmission among multiple CCs, which affects channel estimation and scheduling reliability.
Innovation Solution
The method involves transmitting an aperiodic SRS through a specific UL CC that is identical to the one used for physical uplink shared channel (PUSCH) scheduling, with the uplink grant containing a message for triggering SRS transmission, and using downlink control information (DCI) formats to indicate the UL CC, potentially linking it to a downlink CC for resource allocation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If aperiodic SRS transmission method is not defined in carrier aggregation systems, then system flexibility is maintained, but channel estimation reliability deteriorates
Solution Approach 1:
The system uses existing uplink grant structures and DCI formats to self-indicate the UL CC for aperiodic SRS transmission without requiring new signaling mechanisms. The uplink grant itself carries the information needed to trigger and identify the carrier for SRS transmission, making the system self-sufficient.
Solution Approach 2:
The uplink grant and DCI formats serve multiple functions: they schedule PUSCH transmissions, trigger aperiodic SRS transmissions, and indicate which UL CC should be used for SRS. This multi-functionality resolves the contradiction by using existing structures for multiple purposes rather than creating dedicated new structures.
2Adaptability or versatility
If multiple UL CCs are available for SRS transmission, then transmission flexibility improves, but carrier selection complexity increases
Solution Approach 1:
The DCI format acts as an intermediary that carries the carrier indication information. Instead of requiring complex direct mapping between SRS transmission needs and carrier selection, the DCI format mediates this relationship by embedding the UL CC identifier within its structure, simplifying the selection process.
Solution Approach 2:
The indication of UL CC for SRS transmission is merged with the existing uplink grant signaling. Rather than creating separate signaling channels for carrier indication, the patent combines multiple functions (scheduling, triggering, and carrier indication) into a single unified DCI structure.
3Speed
If aperiodic SRS transmission is triggered without proper UL CC indication, then transmission speed improves, but scheduling reliability deteriorates
Solution Approach 1:
The UL CC indication is prepared and included in the uplink grant before the actual SRS transmission occurs. By pre-configuring the carrier information in the grant, the system enables immediate SRS transmission without delays for carrier determination, while ensuring scheduling reliability through advance indication.
Data Source
AI summary
A method for transmitting, by a user equipment (UE), an aperiodic sounding reference signal (SRS) in a wireless communication system; and the UE are discussed. The method includes receiving a downlink control information (DCI) format, which schedules a physical uplink shared channel (PUSCH) and includes an SRS request for triggering transmission of an aperiodic SRS, from a base station (BS); detecting the SRS request; and transmitting, when the UE is not configured with a carrier indicator field (CIF), the aperiodic SRS to the BS on a first uplink (UL) component carrier (CC) in which the PUSCH is scheduled, or, when the UE is configured with the CIF, the aperiodic SRS to the BS on a second UL CC in which the PUSCH is scheduled with a value of the CIF.