HARQ CSI Feedback Selection Over Unlicensed Carriers
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Solution Overview
Problem
In LTE systems, the increasing number of carriers for carrier aggregation poses challenges in reliably transmitting Hybrid Automatic Repeat Request (HARQ) and Channel State Information (CSI) feedback, especially when there are not enough licensed uplink carriers available, necessitating the use of unlicensed carriers, whose availability is unpredictable.
Innovation Solution
Configuring backup Component Carriers (CCs) for HARQ and CSI feedback, allowing the wireless device to select an available backup CC when the primary unlicensed CC is unavailable, with the base station capable of blindly decoding feedback on both primary and backup CCs, ensuring continuous feedback transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If unlicensed carriers are used for HARQ/CSI feedback transmission, then the capacity for feedback transmission is improved, but the reliability deteriorates due to unpredictable channel availability
Solution Approach 1:
The base station pre-configures multiple backup component carriers for feedback transmission before the unlicensed carrier becomes unavailable. When the primary unlicensed carrier is occupied, the wireless device can immediately switch to a pre-configured backup carrier without delay, ensuring continuous feedback transmission.
Solution Approach 2:
The system prepares multiple backup carriers in advance as a cushion against the unpredictable unavailability of unlicensed carriers. This proactive preparation ensures that feedback transmission reliability is maintained by having alternative carriers ready before the primary carrier fails.
2Reliability
If multiple backup Component Carriers are configured, then the reliability of feedback transmission is improved, but the device complexity increases
Solution Approach 1:
The wireless device autonomously selects an appropriate backup carrier from the pre-configured list based on channel availability conditions, without requiring complex base station coordination or additional signaling. This self-service approach reduces system complexity while maintaining reliability.
Solution Approach 2:
The backup carriers are configured with simplified parameters and selection criteria, treating them as readily available resources that can be quickly switched to without extensive configuration or management overhead.
3Reliability
If backup CCs are configured for all downlink carriers, then the reliability is improved, but the signaling overhead increases
Solution Approach 1:
Backup carriers are selectively configured based on local conditions - specifically for downlink carriers that use unlicensed spectrum and have unpredictable availability. Licensed carriers with stable availability do not require backup configurations, reducing overall signaling overhead while maintaining reliability where needed.
Solution Approach 2:
The system dynamically adjusts the number and configuration of backup carriers based on the specific characteristics of each downlink carrier, such as whether it uses licensed or unlicensed spectrum, rather than applying a uniform backup configuration to all carriers.
Data Source
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AI summary
Systems and methods relating to the use of an unlicensed Component Carrier (CC) for Hybrid Automatic Repeat Request (HARQ) and/or Channel State Information (CSI) feedback for a downlink CC or a downlink CC group are disclosed. In some embodiments, a method of operation of a wireless device in a cellular communications network comprises selecting, from a plurality of uplink CCs configured for the wireless device for HARQ and/or CSI feedback of a downlink CC or a downlink CC group, an uplink CC for HARQ and/or CSI feedback of the downlink CC or the downlink CC group based on channel availability. The method further comprises transmitting HARQ and/or CSI feedback of the downlink CC or the downlink CC group over the uplink CC selected from the plurality of uplink CCs configured for the wireless device.