Contention Window Adjustment for FeLAA Uplink
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Solution Overview
Problem
The uplink performance in unlicensed spectrum for LTE systems is degraded due to double Listen-Before-Talk (LBT) requirements at both evolved NodeB and user equipment, leading to UL starvation when scheduled systems coexist with unscheduled systems like Wi-Fi, necessitating improvements in autonomous uplink transmission mechanisms.
Innovation Solution
The proposed solution involves adjusting the contention window size (CWS) based on HARQ-ACK feedback and introducing specific rules for resetting or increasing CWS values, including timing mechanisms and AUL-specific offsets to optimize resource utilization and reduce collisions, enabling efficient autonomous uplink transmissions within the maximum channel occupancy time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If double LBT requirements are implemented at both eNB and UE, then fair coexistence with incumbent systems is achieved, but uplink transmission performance is degraded
Solution Approach 1:
The patent segments the LBT procedure into different types (Type 1 for eNB, Type 2 for UE) with different contention window sizes and backoff mechanisms. This segmentation allows the system to maintain fair coexistence through Type 1 LBT while improving uplink performance by using Type 2 LBT with smaller contention windows at the UE side, reducing the impact of the double LBT requirement.
Solution Approach 2:
The patent introduces dynamic contention window adjustment mechanisms where the contention window size is adapted based on channel conditions, HARQ-ACK feedback, and transmission success rates. This dynamic adjustment allows the system to optimize the balance between fair coexistence and uplink transmission performance by reducing contention window sizes when channel conditions are favorable, thereby mitigating the performance degradation caused by double LBT.
2Reliability
If contention window size is increased to reduce collisions, then coexistence with Wi-Fi is improved, but uplink transmission latency increases
Solution Approach 1:
The patent implements periodic contention window adjustments based on transmission attempts and HARQ-ACK feedback. Instead of using a fixed large contention window size, the system periodically adapts the CW size based on recent transmission success rates and channel occupancy, allowing it to reduce latency when conditions permit while maintaining coexistence when competition is high.
Solution Approach 2:
The patent changes the contention window size parameter dynamically based on multiple factors including HARQ-ACK feedback, channel occupancy time, and transmission success rates. This parameter adaptation allows the system to optimize the trade-off between coexistence and latency by using smaller CW sizes when transmission success is high and larger CW sizes when collisions are frequent.
3Productivity
If autonomous uplink transmission is enabled to improve performance, then uplink starvation is reduced, but collision probability with unscheduled systems increases
Solution Approach 1:
The patent implements preliminary LBT procedures and contention window setup before autonomous uplink transmissions. By performing Type 2 LBT with pre-configured contention window sizes before AUL transmissions, the system prepares the channel access parameters in advance, reducing the probability of collisions with unscheduled systems while enabling improved uplink performance through autonomous transmission opportunities.
Data Source
AI summary
An apparatus of a Fifth Generation NodeB (gNB) to operate in a License Assisted Access (LAA) system configures a transmission initiation time interval contention window size (CWS) of N number of subframes between Category 4 Listen Before Talk (LBT) uplink (UL) transmissions by a user equipment (UE) operating in the LAA system, and a memory to store a value of N which can have a value 6 or greater or 10 or greater. An apparatus of a UE to operate in an LAA system decodes a configuration from the gNB of a transmission initiation time interval contention CWS of N number of subframes between Category 4 LBT UL transmissions in the LAA system. The CWS is increased to a next higher value when an UL grant or an autonomous UL (AUL) downlink feedback indicator (DFI) is not received before the expiration of a timer.