LAA eNB Contention Window Adjustment via HARQ-ACK Feedback
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Solution Overview
Problem
Current wireless communication systems face challenges in improving communication capacity, speed, flexibility, and efficiency, particularly in licensed-assisted access (LAA) scenarios, where collision detection and channel access mechanisms are inefficient due to high NACK probabilities and delayed HARQ-ACK feedback, leading to exaggerated channel congestion estimates and fairness issues.
Innovation Solution
The implementation of dynamic and semi-static contention window size adjustments based on HARQ-ACK feedback, collision status, and channel conditions, using methods such as exponential backoff and look-up tables, to optimize channel access and reduce false collision detection in LAA systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional channel access mechanisms are used in LAA systems, then channel access procedures can be implemented, but false collision detection occurs due to high NACK probabilities and delayed HARQ-ACK feedback
Solution Approach 1:
The patent implements feedback mechanisms where the eNB monitors HARQ-ACK feedback from UEs and uses this information to adjust contention window sizes dynamically. This feedback loop allows the system to distinguish between actual collisions and false collisions caused by high NACK probabilities, thereby improving collision detection accuracy while maintaining channel access reliability
Solution Approach 2:
The patent introduces dynamic contention window size adjustment based on collision status and channel conditions. By making the contention window size variable rather than fixed, the system can adapt to changing channel conditions and reduce false collision detection while maintaining reliable channel access under varying traffic loads and interference conditions
2Adaptability or versatility
If contention window size is increased to reduce collision, then channel access fairness improves, but communication efficiency decreases due to longer backoff periods
Solution Approach 1:
The patent dynamically adjusts contention window sizes based on real-time collision status and channel conditions rather than using fixed or uniformly increased window sizes. This allows the system to maintain fairness by increasing CW size when collisions are detected while preserving efficiency by using smaller CW sizes when channel conditions are good, thus balancing fairness and communication efficiency
Solution Approach 2:
The patent changes the contention window size parameter based on monitored channel conditions and collision status. By adjusting this critical parameter dynamically, the system can optimize the trade-off between channel access fairness (achieved through larger CW sizes during congestion) and communication efficiency (maintained through smaller CW sizes during clear channel conditions)
3Measurement precision
If HARQ-ACK feedback is used for collision detection, then collision status can be determined, but false-alarm collisions occur due to delayed feedback and high NACK probabilities
Solution Approach 1:
The patent performs preliminary actions by monitoring multiple HARQ-ACK feedback results over time and accumulating collision status information before making contention window size adjustments. This preliminary monitoring phase allows the system to distinguish between temporary NACKs and actual collisions, reducing false-alarm collisions while utilizing the available HARQ-ACK feedback effectively
Solution Approach 2:
The patent implements a feedback-based collision detection mechanism that accumulates HARQ-ACK feedback results over multiple transmission opportunities. By analyzing the pattern of feedback rather than relying on single delayed feedback instances, the system improves collision status determination accuracy while mitigating the impact of feedback delay and high NACK probabilities
Data Source
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AI summary
An evolved NodeB (eNB) is described. The eNB includes a processor and memory in electronic communication with the processor. Instructions stored in the memory are executable to maintain a contention window size. The instructions are also executable to increase the contention window size according to hybrid automatic request acknowledgement/negative acknowledgment (HARQ-ACK) value(s) corresponding to physical downlink shared channel (PDSCH) transmission(s) in a first subframe. The first subframe is a starting subframe of a previous downlink transmission burst on a licensed-assisted access (LAA) carrier for which HARQ-ACK has been fed back.