UE BWP Switching HARQ-ACK Retransmission
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Solution Overview
Problem
Current NR specifications result in performance loss due to Hybrid Automatic Repeat request-Acknowledgement (HARQ-ACK) dropping during Bandwidth Part (BWP) switching, leading to increased latency and throughput reduction, as UE is not expected to transmit HARQ-ACK if it changes its active UL BWP between the detection of DCI format 1_1 and the corresponding HARQ-ACK transmission time.
Innovation Solution
The user equipment determines the earliest available slot on a second or third BWP to transmit dropped UCI, reducing feedback latency and improving system performance by utilizing the earliest available slot for HARQ-ACK transmission, which is specified in standards or configured by RRC, and can be transmitted in PUCCH or PUSCH.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If UE drops UCI during BWP switching period as per current NR specification, then BWP switching can be completed, but feedback latency increases and throughput is reduced
Solution Approach 1:
The UE determines the earliest available slot for UCI transmission in advance by calculating the offset between the BWP switching slot and the first available uplink slot. This preliminary determination allows the UE to prepare the UCI transmission timing before actual transmission, minimizing feedback latency while ensuring BWP switching is completed.
Solution Approach 2:
The solution dynamically adjusts the UCI transmission timing based on the BWP switching configuration. By using the formula n'=n+k where k is the offset between BWP switching slot and first available uplink slot, the system adaptively determines the optimal transmission slot that balances BWP switching completion and feedback timing, rather than using a fixed dropping rule.
2Loss of time
If UE transmits UCI immediately after BWP switching, then feedback latency is reduced, but BWP switching may not be completed properly
Solution Approach 1:
The UE performs preliminary calculation to determine the earliest available slot for UCI transmission by considering the BWP switching timing and the offset to the first available uplink slot. This ensures that UCI transmission is scheduled only after BWP switching is completed, maintaining reliability while minimizing latency.
Solution Approach 2:
The system implements a feedback mechanism where the UE monitors BWP switching completion status and uses this information to determine the appropriate transmission slot. The offset-based calculation ensures that UCI is transmitted at the earliest opportunity after switching is confirmed, creating a feedback loop that balances timing and reliability.
3Device complexity
If UE uses fixed UCI transmission timing, then transmission scheduling is simple, but feedback latency increases during BWP switching
Solution Approach 1:
The solution changes the timing parameter dynamically by introducing an offset-based calculation (n'=n+k) instead of using a fixed transmission slot. This parameter adjustment allows the system to adapt to BWP switching conditions while maintaining a relatively simple scheduling mechanism based on slot offsets and availability checks.
Data Source
AI summary
Provided are a user equipment, base station and wireless communication methods related to resource determination for UCI in case of BWP switching in NR. A user equipment comprises: a receiver operative to receive, from a base station in a slot, a Downlink Control Information (DCI) for Bandwidth Part (BWP) switching from a first BWP to a second BWP; circuitry operative to drop a Uplink Control Information (UCI) to be transmitted in a BWP switching period of the first BWP, and to determine the earliest available slot of the second BWP or a third BWP, the BWP switching period being from the slot where the DCI for BWP switching is received until starting the second BWP to which the first BWP is switched according to the DCI; and a transmitter operative to transmit the dropped UCI in the determined earliest available slot of the second BWP or the third BWP to the base station.