Adaptive Downlink Scheduling for Carrier Aggregation Link Adaptation
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Solution Overview
Problem
In LTE-Advanced networks, carrier aggregation scenarios face challenges with ambiguous HARQ-ACK feedback, leading to inefficient link adaptation and increased BLER, particularly in TDD CA scenarios where the number of UL component carriers is less than or equal to the DL carriers, causing unnecessary retransmissions and reduced throughput.
Innovation Solution
Implementing adaptive downlink scheduling and outer loop link adaptation by determining an initial modulation and coding scheme (MCS) for subframes and adjusting the MCS pattern based on channel conditions, using PUCCH feedback to set the update rate of the outer loop link adaptation, and employing inner and outer link adaptation loops to optimize MCS allocation for each subframe, thereby reducing ambiguity and improving decoding accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If carrier aggregation is used to increase bandwidth and throughput, then downlink throughput is improved, but ambiguous HARQ-ACK feedback increases leading to higher BLER and unnecessary retransmissions
Solution Approach 1:
The patent segments the HARQ-ACK feedback by introducing separate feedback channels: PUCCH for downlink HARQ-ACK and PUSCH for uplink HARQ-ACK. This segmentation resolves the ambiguity in TDD carrier aggregation scenarios where UL and DL component carriers are aggregated, allowing the system to maintain high throughput while improving link adaptation accuracy through clear, dedicated feedback paths for each direction.
2Device complexity
If the number of UL component carriers is reduced to match TDD requirements, then system complexity is reduced, but feedback ambiguity increases and retransmissions increase
Solution Approach 1:
The patent introduces an intermediary mechanism - the PUSCH channel - to carry uplink HARQ-ACK feedback separately from downlink feedback. This intermediary allows the system to maintain the reduced UL carrier configuration for TDD while preventing feedback ambiguity, as the PUSCH provides a dedicated path for uplink acknowledgments, thereby maintaining throughput without increasing complexity.
3Reliability
If outer loop link adaptation updates frequently to adapt to channel changes, then link adaptation accuracy is improved, but feedback overhead and processing complexity increase
Solution Approach 1:
The patent implements dynamic outer loop link adaptation where the update frequency and aggressiveness are adjusted based on current channel conditions and feedback quality. When channel conditions are stable or feedback is reliable, updates are performed more frequently to maintain accuracy. When conditions are volatile or feedback is ambiguous, updates are tempered to avoid unnecessary complexity and processing overhead, allowing the system to adapt dynamically to varying operational contexts.
Data Source
AI summary
Described herein are apparatuses, systems and methods for adaptive downlink scheduling and link adaptation. The methods including, at a base station connected to a user equipment (“UE”), determining an initial modulation and coding scheme (“MCS”) for a plurality of subframes to be transmitted to the UE, wherein each MCS relates to a coding rate value for the subframes, determining an MCS pattern for the plurality of subframes based on the initial MCS, wherein an MCS for one of the subframes has a higher coding rate value than the initial MCS, and transmitting the plurality of subframes to the UE according to the MCS pattern.