Base Station Contention Window Size Determination in LAA-LTE
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Solution Overview
Problem
In Licensed-Assisted Access using Long Term Evolution (LAA-LTE) systems, determining a contention window size (CWS) for downlink transmission is inaccurate due to the consideration of HARQ status from UEs that do not occupy the uplink subframe, leading to an increased waiting time for the base station.
Innovation Solution
A method and apparatus for determining CWS in clear channel assessment (CCA) where only the HARQ status of UEs occupying the uplink subframe is considered, ignoring the HARQ status of UEs that do not occupy the uplink subframe, to improve accuracy and reduce excessive waiting times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the base station determines CWS based on HARQ status from all scheduled UEs, then the determination process is simple, but the accuracy of CWS determination decreases due to inclusion of UEs that did not perform LBT
Solution Approach 1:
The patent segments the set of scheduled UEs into two groups: UEs that successfully performed LBT and occupied the uplink subframe, and UEs that failed LBT and did not occupy the uplink subframe. The base station selectively uses HARQ status only from the first group for CWS determination, thereby improving accuracy while managing complexity through structured classification of UE states.
Solution Approach 2:
The patent applies local quality by treating different UEs differently based on their LBT outcome. Instead of uniformly considering all UEs' HARQ status, the system selectively weights or excludes HARQ status from specific UEs (those that failed LBT) depending on their local condition (whether they occupied the uplink subframe), thereby improving overall CWS determination accuracy.
2Quantity of substance
If the base station considers HARQ status from UEs that did not occupy the uplink subframe, then more feedback information is available, but the waiting time increases due to excessively large CWS
Solution Approach 1:
The patent extracts and excludes HARQ status information from UEs that did not occupy the uplink subframe (i.e., UEs that failed LBT) from the CWS determination process. By taking out this potentially misleading information, the system prevents excessive CWS enlargement that would otherwise occur, thereby reducing base station waiting time while still utilizing HARQ feedback from successful UEs.
Solution Approach 2:
Instead of the conventional approach of using all available HARQ feedback, the patent inverts the logic by deliberately excluding certain HARQ status (from UEs that failed LBT) to achieve better performance. This inversion prevents the system from being misled by false NACK indications, thereby optimizing the balance between utilizing feedback information and maintaining efficient channel access timing.
3Ease of operation
If the base station directly determines CWS based on HARQ status without verifying LBT success, then the process is straightforward, but the probability of incorrect CWS determination increases
Solution Approach 1:
The patent performs a preliminary check to determine whether each UE successfully performed LBT and occupied the uplink subframe before using its HARQ status for CWS determination. This preliminary action (verifying LBT success) is executed prior to the CWS calculation, ensuring that only reliable HARQ feedback is included, thereby maintaining operational simplicity while significantly improving determination reliability.
Solution Approach 2:
The patent introduces an additional feedback mechanism where the base station verifies whether UEs successfully performed LBT by checking if they occupied the uplink subframe. This feedback loop ensures that only UEs with successful channel access contribute their HARQ status to CWS determination, thereby enhancing reliability without substantially complicating the overall process through structured verification steps.
Data Source
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AI summary
Embodiments of the present invention provide a method for determining a contention window size in clear channel assessment. The method includes: determining, by a base station, at least one user equipment UE that occupies an uplink subframe on an unlicensed carrier and that is in at least one UE scheduled in a reference subframe, where the uplink subframe is an uplink subframe in which at least one UE scheduled by the base station in the reference subframe feeds back a hybrid automatic repeat request HARQ status for the reference subframe; and determining, by the base station, a CWS in CCA for downlink transmission based on a HARQ status of the at least one UE that occupies the uplink subframe. The embodiments of the present invention further provide an apparatus for determining a contention window size in clear channel assessment and a base station. The embodiments of the present invention have the following benefits: Accuracy of determining a CWS for downlink transmission can be improved, and a probability of increasing a waiting time of a base station due to an adjusted excessively large CWS can be reduced.