Wireless Spectrum Access via HARQ Feedback
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Solution Overview
Problem
LTE-LAA devices face challenges in replicating Wi-Fi's exponential backoff mechanism due to multiple receivers and delayed acknowledgments, leading to inefficient spectrum access and potential interference with other technologies in unlicensed shared spectrum.
Innovation Solution
Implementing a method that uses Hybrid Automatic Repeat Request (HARQ) feedback to modify Clear Channel Assessment (CCA) and Extended Clear Channel Assessment (ECCA) defer intervals through penalty functions, based on the ratio of Negative Acknowledgment (NAK) signals, to determine the duration of these intervals and ensure fair sharing of unlicensed spectrum.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If LTE-LAA devices use a fixed backoff mechanism similar to Wi-Fi, then spectrum access simplicity is improved, but transmission efficiency deteriorates due to delayed acknowledgments and multiple receivers
Solution Approach 1:
The patent applies dynamics by making the backoff mechanism adaptive rather than fixed. The clear channel assessment (CCA) interval duration is dynamically adjusted based on HARQ feedback from previous transmissions. When acknowledgments are received, the CCA interval is shortened, allowing faster reaccess. When negative acknowledgments occur, the interval is extended to reduce collisions. This dynamic adjustment resolves the contradiction by maintaining operational simplicity while significantly improving spectrum access efficiency.
2Reliability
If LTE-LAA devices extend the clear channel assessment interval to account for delayed feedback, then collision avoidance is improved, but spectrum access delay increases
Solution Approach 1:
The patent applies parameter changes by adjusting the CCA interval duration based on HARQ feedback parameters. Instead of using a fixed extended interval, the system modifies the assessment time parameter dynamically: shorter intervals when feedback indicates successful transmissions, and longer intervals when collisions are detected. This resolves the contradiction by maintaining reliable collision avoidance only when necessary, thereby reducing unnecessary delays.
Solution Approach 2:
The patent implements feedback mechanisms where HARQ acknowledgments from receivers are used to adjust future CCA interval durations. This closed-loop feedback system allows the transmitter to learn from past transmission outcomes and optimize the clear channel assessment timing accordingly, achieving both collision avoidance and minimal delay.
3Area of stationary object
If LTE-LAA devices use multiple receivers with delayed acknowledgments, then communication coverage is improved, but backoff mechanism accuracy deteriorates
Solution Approach 1:
The patent applies merging by combining feedback from multiple receivers into a unified channel assessment decision. Instead of treating each receiver's feedback separately, the system aggregates HARQ acknowledgments from all receivers to determine the overall channel status and adjust the CCA interval accordingly. This resolves the contradiction by maintaining accurate channel assessment despite multiple delayed feedback sources, thereby preserving both coverage and precision.
Data Source
AI summary
A first wireless device determines the duration of a clear channel assessment interval based on feedback signals before transmitting data to a second wireless device. The first wireless device receives feedback signals, such as acknowledgement (ACK) and negative acknowledgement (NAK) signals, from one or more second wireless devices. The first wireless device determines a ratio of NAK/ACK signals in the feedback signals for a predetermined amount of time. The first wireless device determines whether the wireless medium is free by monitoring for wireless signals during a clear channel assessment interval. The duration of the clear channel assessment interval is based on the ratio of NAK/ACK signals. If the wireless medium is free for the duration of the clear channel assessment, the first wireless device wirelessly transmits data to at least one of the second wireless devices.