Uplink Contention Window Adjustment via Downlink Position Feedback
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Solution Overview
Problem
In wireless communication systems supporting unlicensed bands, there is a need to adjust the contention window size (CWS) for uplink listen-before-talk (LBT) by user equipment (UE) when the base station (BS) does not provide hybrid automatic repeat request-acknowledgement (HARQ-ACK) information for each uplink subframe, to effectively manage uplink signal transmissions in unlicensed bands.
Innovation Solution
The method involves receiving a downlink control signal from the BS indicating the position of a successfully received uplink signal within a predetermined number of subframes, and adjusting the CWS based on this information and the latest uplink transmission burst by the UE, to perform uplink LBT and adjust the CWS accordingly for subsequent transmissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the BS provides HARQ-ACK information for each uplink subframe, then the UE can accurately adjust CWS based on transmission success, but the signaling overhead increases
Solution Approach 1:
The patent extracts only the essential information needed for CWS adjustment - specifically, the position of the first successfully received subframe - from the complete HARQ-ACK feedback that would otherwise be required. This selective extraction allows the UE to make accurate CWS decisions without receiving comprehensive acknowledgment information for every uplink subframe, thereby reducing signaling overhead while maintaining adjustment accuracy.
Solution Approach 2:
The UE autonomously determines CWS adjustment by itself based on the limited downlink control signal information it receives about successful uplink subframe positions. Rather than relying on the BS to provide detailed HARQ-ACK feedback, the UE uses its own transmission records combined with the minimal BS indication to self-determine whether to adjust CWS, reducing the need for extensive signaling.
2Loss of information
If the UE adjusts CWS autonomously without BS feedback, then the signaling overhead is reduced, but the CWS adjustment accuracy deteriorates
Solution Approach 1:
The downlink control signal acts as an intermediary that carries the critical position information of successfully received uplink subframes from the BS to the UE. This intermediate information bridge allows the UE to make informed CWS adjustment decisions autonomously without requiring complete HARQ-ACK feedback, maintaining accuracy while minimizing signaling overhead.
3Reliability
If the UE waits for HARQ-ACK information from BS, then the CWS adjustment reliability is improved, but the transmission delay increases
Solution Approach 1:
The BS provides position information of successfully received subframes in advance through downlink control signals, allowing the UE to perform CWS adjustment proactively before the next uplink transmission opportunity arises. This preliminary action enables the UE to prepare appropriate CWS values ahead of time, reducing waiting delays while maintaining reliability through accurate position-based decisions.
Solution Approach 2:
The system implements a simplified feedback mechanism where the BS provides essential position feedback about successful uplink receptions rather than complete HARQ-ACK information. This feedback approach gives the UE sufficient information to reliably adjust CWS without the time penalty of waiting for comprehensive acknowledgment feedback, achieving a balance between reliability and speed.
Data Source
AI summary
Disclosed in the present invention are: a method for controlling a contention window size (CWS) for uplink listen-before-talk (LBT) in a wireless communication system supporting an unlicensed band; and a device for supporting the same. More particularly, disclosed are a base station centric CWS controlling method, a terminal centric CWS controlling method, and devices for supporting the same.