Sidelink Contention Window Control for Fair Unlicensed Access

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Solution Overview

Problem

In unlicensed bands, fair channel access is challenging due to the coexistence of multiple systems, necessitating improvements in Listen Before Talk (LBT) mechanisms for terminal apparatuses in 5G communication systems.

Innovation Solution

A terminal apparatus determines a contention window size based on the number of second sidelink transmissions with HARQ-ACK feedback disabled, applying this size to channel sensing and performing first sidelink transmission.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If Listen Before Talk (LBT) based on Clear Channel Assessment (CCA) is used for coexistence in unlicensed bands, then channel access fairness among multiple systems is improved, but channel access efficiency and productivity deteriorate due to increased sensing time and contention delays

Engineering Contradiction:

Improvecoexistence capabilityVSAvoidchannel access efficiency

Core Design Contradiction:

Adaptability or versatilityVSProductivity

Solution Approach 1:

The patent dynamically adjusts the contention window size parameter based on the number of detected sidelink transmissions. When multiple transmissions are detected, the contention window is enlarged to reduce collision probability; when fewer transmissions are detected, the contention window is reduced to improve access efficiency. This adaptive parameter adjustment resolves the contradiction by optimizing channel access behavior according to actual channel conditions.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The terminal apparatus performs channel sensing to detect sidelink transmissions from other terminals, uses this detection information as feedback to determine the number of ongoing transmissions, and adjusts its contention window size accordingly. This feedback mechanism enables the system to adapt channel access parameters based on real-time channel state, improving both coexistence and efficiency.

Inventive Principle:

Principle #23Feedback

2Device complexity

If the contention window size is fixed, then device complexity is reduced, but adaptability to varying channel conditions and coexistence performance deteriorate

Engineering Contradiction:

Improvecontention window managementVSAvoidchannel access adaptability

Core Design Contradiction:

Device complexityVSAdaptability or versatility

Solution Approach 1:

The patent transforms the static contention window size into a dynamic parameter that automatically adjusts based on the number of detected sidelink transmissions. The terminal counts transmissions during channel sensing and selects appropriate contention window sizes from a predefined set, enabling the system to adapt to varying channel conditions without requiring complex real-time optimization algorithms.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The contention window size parameter is changed adaptively based on channel conditions. When the number of detected transmissions is high, a larger contention window is selected to reduce collisions; when the number of transmissions is low, a smaller contention window is selected to improve access efficiency. This parameter adaptation resolves the contradiction between simplicity and adaptability.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS20260100784A1Terminal apparatus and communication method

Publication Date: 2026.04.09 SHARP KK

AI summary

A terminal apparatus including a transmitter configured to perform, for sidelink transmission with HARQ-ACK feedback disabled, channel sensing while maintaining a contention window size last applied, wherein in a case that the number of times that the contention window size is maintained reaches a prescribed number of times, the contention window size is configured to a next larger value.