HARQ Feedback Transmission in Unlicensed Spectrum
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Solution Overview
Problem
In LTE and LTE-Advanced wireless communication systems, the uncertainty of available resources in unlicensed serving cells hinders the reliable transmission of hybrid automatic repeat request (HARQ) feedback, affecting communication between user equipment (UE) and evolved Node-B (eNB).
Innovation Solution
A communication device is configured to perform downlink receptions in specific subframes and transmit HARQ feedbacks in subsequent subframes determined by a combination of predetermined timing and HARQ timing, with the option to check availability using listen before talk (LBT) to ensure clear subframes for transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If unlicensed serving cell is used to offload network traffic, then network capacity and throughput are improved, but resource availability uncertainty increases causing HARQ feedback transmission failures
Solution Approach 1:
The patent performs LBT (Listen Before Talk) procedure in advance before transmitting HARQ feedback to check if the unlicensed resource is available. This preliminary action prevents transmission failures by identifying available resources beforehand, resolving the contradiction between using unlicensed cells for throughput improvement and maintaining reliable feedback transmission.
2Loss of energy
If HARQ feedback is transmitted in unlicensed serving cell, then network load is reduced, but communication regularity deteriorates due to resource uncertainty
Solution Approach 1:
The system performs LBT procedure beforehand to determine resource availability, then decides whether to transmit HARQ feedback in the unlicensed cell or fallback to licensed cell. This preliminary check ensures communication regularity is maintained while still utilizing unlicensed resources to reduce network load.
Solution Approach 2:
The LBT procedure acts as an intermediary mechanism that mediates between the desire to use unlicensed resources for load reduction and the need for communication regularity. Based on LBT results, the system dynamically selects transmission path, ensuring stable communication while benefiting from offloading.
3Productivity
If eNB uses unlicensed serving cell for DL transmission, then system capacity increases, but HARQ resource availability decreases due to LBT failures
Solution Approach 1:
The UE performs LBT procedure in advance to check unlicensed resource availability before HARQ feedback transmission. This preliminary action ensures that even when eNB uses unlicensed cells for DL transmission to increase system capacity, the HARQ feedback can still be transmitted reliably by verifying resource availability first.
Solution Approach 2:
The LBT mechanism serves as an intermediary that bridges the gap between increased system capacity from unlicensed cell usage and maintained HARQ resource availability. It dynamically determines whether unlicensed resources are available for HARQ feedback, ensuring both goals are achieved.
Data Source
AI summary
A communication device for handling a hybrid automatic repeat request (HARQ) transmission comprises a storage unit for storing instructions and a processing circuit coupled to the storage unit. The processing circuit is configured to execute the instructions stored in the storage unit. The instructions comprise performing a first downlink (DL) reception in a first subframe from a serving cell; and transmitting a first HARQ feedback in response to the first DL reception in a second subframe to the serving cell, wherein the second subframe is determined according to the first subframe and a sum of a predetermined timing and a first HARQ timing.