Adaptive LBT Procedures for Uplink Channel Access
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Solution Overview
Problem
In wireless communication systems, especially in shared radio frequency spectrum bands, existing listen-before-talk (LBT) techniques face challenges in efficiently managing channel contention and scheduling for uplink transmissions, leading to inefficiencies and unreliable communications due to intermittent availability of carriers.
Innovation Solution
The implementation of a shortened and full LBT procedure selection mechanism, where the UE performs a shortened LBT if the base station has reserved the channel for uplink transmissions and a full LBT otherwise, with parameters like contention window size and timing thresholds adapted based on ACK/NACK feedback and channel reservation duration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a full LBT procedure is performed by the UE for every uplink transmission, then channel access reliability is improved, but transmission delay and loss of time increase
Solution Approach 1:
The patent applies dynamics by making the LBT procedure adaptive rather than static. The UE dynamically selects between full LBT and shortened LBT based on whether the base station has reserved the channel (indicated by downlink transmission detection) or not. This dynamic adaptation resolves the contradiction by performing full LBT only when necessary (when channel reservation is not detected, ensuring reliability) and using shortened LBT when channel reservation is detected (reducing delay).
Solution Approach 2:
The patent changes the parameter of LBT duration based on channel reservation status. When the base station has reserved the channel (detected via downlink transmission), the UE uses a shortened LBT procedure with reduced monitoring time. When no reservation is detected, the UE performs a full LBT procedure. This parameter change resolves the contradiction by adjusting the LBT duration to match the actual channel conditions.
2Productivity
If a shortened LBT procedure is used to reduce transmission delay, then productivity is improved, but channel access reliability deteriorates
Solution Approach 1:
The system dynamically adjusts the LBT procedure length based on channel reservation detection. When the UE detects downlink transmission from the base station (indicating channel reservation), it applies shortened LBT for improved productivity. When no reservation is detected, it uses full LBT to maintain reliability. This dynamic approach resolves the contradiction by applying shortened LBT only under safe conditions.
Solution Approach 2:
The base station performs preliminary channel reservation through downlink transmission before the UE attempts uplink transmission. The UE detects this preliminary action (downlink transmission) and uses it as a basis for selecting shortened LBT. This preliminary reservation action enables the shortened LBT procedure while maintaining reliability, resolving the contradiction between productivity and reliability.
3Reliability
If the base station reserves the channel for uplink transmissions, then uplink transmission reliability is improved, but channel utilization efficiency may deteriorate due to longer reservation duration
Solution Approach 1:
The patent applies partial action by having the UE perform only a shortened LBT procedure (partial monitoring) when the base station has already reserved the channel through downlink transmission. The UE doesn't need to perform the complete full LBT procedure because the base station's reservation provides sufficient guarantee. This partial action improves channel utilization efficiency while maintaining reliability under reservation conditions.
4Adaptability or versatility
If multiple LBT parameters are adjusted based on ACK/NACK feedback, then system adaptability is improved, but device complexity increases
Solution Approach 1:
The patent implements feedback mechanisms where the base station sends ACK/NACK signals in response to UE uplink transmissions. Based on this feedback, the base station adjusts LBT parameters such as contention window size and retry limits. This feedback loop improves system adaptability by allowing parameter optimization based on actual transmission outcomes, while the automated feedback mechanism manages the complexity burden.
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AI summary
Techniques for performing listen before talk (LBT) channel contention procedures in a shared radio frequency spectrum band are provided. The LBT techniques may include a shortened LBT procedure that may be selected if a base station has reserved a shared channel for a duration of expected user equipment (UE) uplink transmissions, and a full LBT procedure that may be selected if the base station has not reserved the channel for the duration of expected UE uplink transmissions. The shortened LBT procedure may include detecting energy levels of the channel for a relatively short time period relative to the full LBT procedure. The shortened LBT procedure may be selected if a time period between a UE receiving a grant of uplink resources and the beginning of the uplink resources is less than a threshold time value.