Carrier Aggregation HARQ Timeline for Downlink Throughput
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Solution Overview
Problem
Wireless communication systems face a tradeoff between downlink throughput and response latency due to the requirement for longer transmission time intervals (TTIs) when implementing carrier aggregation, which limits the number of component carriers that can be supported.
Innovation Solution
The implementation of modified hybrid automatic repeat request (HARQ) timelines that utilize shorter TTIs for uplink transmissions, allowing for longer TTIs on the downlink while reducing HARQ feedback latency by aligning HARQ timing with the shorter uplink TTIs, thereby enhancing downlink throughput.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If longer TTI is used for downlink carrier aggregation, then downlink throughput is improved, but response latency increases
Solution Approach 1:
The patent applies dynamics by allowing the TTI length to vary dynamically between downlink and uplink directions. The downlink can use longer TTIs for high throughput while the uplink uses shorter TTIs for low latency feedback, with the system adapting TTI lengths based on directional requirements rather than using a fixed TTI length for both directions.
Solution Approach 2:
The patent segments the TTI configuration by direction, creating independent TTI length parameters for downlink and uplink. This segmentation allows each direction to have optimized TTI lengths tailored to its specific requirements, resolving the contradiction between downlink throughput and uplink response latency.
2Productivity
If more component carriers are supported for carrier aggregation, then downlink throughput is enhanced, but the number of supported carriers is limited by transmission mode
Solution Approach 1:
The patent changes the TTI length parameter independently for downlink and uplink, allowing the system to support more component carriers by using shorter uplink TTIs that can accommodate the increased number of carriers while maintaining longer downlink TTIs for high throughput on each carrier.
3Loss of time
If shorter TTI is used for uplink, then HARQ feedback latency is reduced, but coordination between downlink and uplink timing becomes complex
Solution Approach 1:
The patent introduces HARQ timing indicators as intermediaries that mediate between the downlink TTI and uplink TTI. These indicators provide the necessary coordination information to align HARQ feedback timing with the shorter uplink TTI while maintaining compatibility with the longer downlink TTI, reducing the complexity of direct timing coordination.
Data Source
AI summary
Methods, systems, and devices for wireless communications are described. In some wireless communications systems, devices may implement carrier aggregation and shortened transmission time intervals (sTTIs) for downlink transmissions. To improve downlink throughput with a reduced feedback latency, the system may implement a modified hybrid automatic repeat request (HARQ) timeline. For example, a base station may configure a first component carrier with a TTI or sTTI for downlink that is longer than an sTTI for a second uplink component carrier. The base station and a user equipment (UE) may operate using a HARQ timing for the first component carrier that is based on the shorter sTTI for the second component carrier. The base station may transmit a downlink transmission using the longer TTI or sTTI for greater carrier aggregation, and the UE may send a downlink HARQ acknowledgment (ACK) message in response according to the HARQ timing for reduced latency.