Dynamic HARQ Rescheduling for LTE Uplink Latency
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Solution Overview
Problem
The standardized approach to TTI bundling in LTE networks faces limitations in reducing uplink physical layer delay for VoIP services, leading to increased packet overhead and reduced coverage due to larger packet sizes and lower coding gains, especially when dealing with delay-sensitive applications.
Innovation Solution
Dynamic rescheduling of HARQ retransmissions by temporarily remapping subframes from one HARQ process to another, using control signaling within the Downlink Control Information (DCI) to accelerate retransmissions and optimize resource allocation, thereby reducing latency and improving coverage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If TTI bundling is used to improve coverage, then uplink coverage is improved, but transmission delay increases due to multiple HARQ retransmissions
Solution Approach 1:
The patent applies dynamic TTI bundling by enabling the network to flexibly configure and activate/deactivate TTI bundling based on real-time channel conditions and service requirements. This dynamic approach allows the system to adaptively switch between bundled and non-bundled transmissions, optimizing both coverage and delay performance rather than using static bundling configurations.
Solution Approach 2:
The patent changes key parameters including the bundling size (number of TTIs per bundle), the activation state of bundling, and the HARQ process configuration. By dynamically adjusting these parameters based on channel quality indicators and service type, the system can optimize the trade-off between coverage enhancement and transmission delay.
2Reliability
If multiple HARQ retransmissions are performed to ensure successful reception, then reception reliability is improved, but latency increases which is intolerable for delay-sensitive applications
Solution Approach 1:
The patent employs preliminary actions by pre-configuring multiple HARQ processes and pre-establishing TTI bundle structures. When a transmission fails, the system can quickly switch to pre-prepared retransmission resources and configurations, reducing the decision and setup time for retransmissions compared to traditional sequential HARQ processes.
Solution Approach 2:
The patent introduces an intermediary mechanism where the network controller dynamically manages HARQ process states and coordinates retransmission timing. This intermediary control enables optimized retransmission scheduling that balances reliability requirements with latency constraints for delay-sensitive services.
3Loss of time
If segmented transmission is used to meet delay requirements, then latency is reduced, but packet overhead increases and coding gain decreases
Solution Approach 1:
The patent dynamically adjusts the transport block size and segmentation level based on channel conditions and delay requirements. When delay is critical, the system can transmit smaller blocks that fit within delay constraints while maintaining adequate coding gains, avoiding excessive segmentation. When channel conditions are poor, larger bundled transmissions can be used to improve reliability without unnecessary overhead.
4Reliability
If larger packet sizes are used in TTI bundling, then coverage is improved through better energy accumulation, but packet overhead increases and coding efficiency decreases
Solution Approach 1:
The patent dynamically changes packet size parameters including transport block size, resource allocation, and coding rate based on channel quality indicators. This allows the system to optimize the balance between energy accumulation for coverage and overhead efficiency, transmitting appropriately sized packets rather than always using maximum size bundling.
Data Source
AI summary
The teachings herein disclose methods (600, 700) and apparatuses (36, 50) for dynamically rescheduling retransmissions from a selected Hybrid Automatic Repeat reQuest, “HARQ”, process, based on temporarily remapping the selected HARQ process to one or more subframes (12) that are by default scheduled for another HARQ process running synchronously with the first HARQ process. One advantage of dynamic rescheduling is that a retransmission for a given HARQ process can be accelerated in time, as compared to when the retransmission would occur absent the remapping. In another advantageous aspect, in at least some embodiments, the control signalling (20) for dynamic rescheduling is included in the Downlink Control Information, “DCI”, used to send scheduling grants for the HARQ processes, such that dynamic rescheduling uses control signalling (20) that is compatible with existing scheduling grant signalling.