Uplink Control Channel Codebook Design for Unlicensed Spectrum
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Solution Overview
Problem
In wireless communication systems operating in unlicensed radio frequency spectrum bands, conventional uplink control channel codebook designs are inadequate due to the uncertainty of listen-before-talk (LBT) procedures, leading to inconsistent feedback reports and disruptions in the hybrid automatic repeat request (HARQ) process between base stations and user equipment (UEs).
Innovation Solution
The solution involves adding one or more bits to downlink grants to indicate whether a downlink grant is the last for a reporting occasion, allowing UEs to determine the correct format for feedback reports based on received grants, thereby ensuring accurate ACK/NACK information transmission and maintaining HARQ process reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional uplink control channel codebook designs are used in unlicensed spectrum, then device complexity is reduced, but feedback report consistency and HARQ process reliability deteriorate due to LBT procedure uncertainty
Solution Approach 1:
The base station performs preliminary actions by determining in advance whether a downlink transmission is the last one before a reporting occasion and encoding this information in the DCI. This allows the UE to proactively prepare the appropriate codebook format without encountering LBT uncertainty at the reporting moment, thereby ensuring feedback report consistency while managing complexity through advance planning.
Solution Approach 2:
An intermediary indicator bit is introduced in the downlink control information to mediate between the base station's transmission decisions and the UE's feedback preparation. This indicator serves as a communication bridge that conveys the 'last transmission before reporting occasion' information, enabling the UE to select the correct codebook format without directly experiencing the LBT uncertainty that affects the base station's channel access.
2Adaptability or versatility
If the format for feedback reports changes based on the number of downlink data transmissions, then adaptability is improved, but reliability deteriorates due to LBT procedure disruptions in unlicensed spectrum
Solution Approach 1:
The base station performs preliminary action by determining in advance whether a downlink transmission is the last one before a reporting occasion and encoding this information in the DCI. This allows the UE to proactively prepare the appropriate codebook format without encountering LBT uncertainty at the reporting moment, thereby ensuring feedback report consistency while managing complexity through advance planning.
Solution Approach 2:
The codebook design is segmented into different formats (first format and second format) based on whether the last downlink grant is received. This segmentation allows the system to adapt to different transmission scenarios while maintaining reliability by clearly distinguishing between cases where LBT may have disrupted the last grant versus cases where it did not.
3Measurement precision
If downlink grants include indication of last transmission status, then feedback report accuracy is improved, but device complexity increases due to additional signaling bits
Solution Approach 1:
The indication of whether a downlink transmission is the last one before a reporting occasion is extracted as a separate indicator bit in the DCI. This extracted information is specifically designed to help the UE determine the correct codebook format, providing high measurement precision for last grant detection while minimizing the increase in device complexity by using a compact binary indicator rather than more complex signaling mechanisms.
Data Source
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AI summary
Methods, systems, and devices for wireless communications are described. A user equipment (UE) may receive a plurality of downlink grants for a corresponding plurality of data transmissions, wherein each downlink grant identifies resources for receiving the corresponding data transmission and indicates whether the corresponding data transmission comprises a last data transmission for a reporting occasion. The UE may determine, based at least in part on the received downlink grants, that a last downlink grant for the last data transmission associated with the reporting occasion was not received. The UE may transmit a feedback report during the reporting occasion, wherein a format of the feedback report is based at least in part on the last downlink grant for the last data transmission not being received.