Variable TTI Duration Scheduling for Lower-Latency HARQ Feedback
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Solution Overview
Problem
Latency in wireless networks is caused by factors such as the use of Hybrid Automatic Repeat Request (HARQ), which can lead to increased transmission times due to retransmissions and processing delays, particularly in systems like LTE where timing relationships between transmissions and feedback are fixed, affecting overall system efficiency.
Innovation Solution
The solution involves dynamically adjusting the Transmission Time Interval (TTI) duration based on various factors such as data availability, type of data, and channel characteristics, allowing for variable TTI durations for different channels and feedback processes, thereby optimizing processing times and reducing latency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If fixed TTI duration is used in LTE systems, then timing relationships between transmissions and feedback are stable, but latency increases due to retransmissions and processing delays
Solution Approach 1:
The patent implements dynamic TTI duration adjustment where the TTI length is no longer fixed but varies based on channel conditions, data priority, and traffic type. The system can switch between short and long TTI durations to optimize both latency for time-sensitive data and reliability for stable transmissions, directly resolving the contradiction between fixed timing stability and variable latency reduction
Solution Approach 2:
The invention changes the TTI duration parameter dynamically based on multiple factors including channel quality indicators, data priority levels, and traffic patterns. By adjusting this critical timing parameter, the system achieves lower latency when conditions permit while maintaining stability when needed, eliminating the need for a fixed TTI duration
2Reliability
If HARQ retransmissions are implemented, then error correction capability is improved, but transmission time increases due to feedback processing delays
Solution Approach 1:
The patent applies dynamic HARQ timing adjustment where feedback timing is no longer fixed but adapts based on channel conditions and data priority. High-priority data can trigger immediate retransmissions with shortened feedback delays, while lower-priority data follows standard HARQ timing, thus reducing overall transmission time while maintaining error correction capability
Solution Approach 2:
The invention segments HARQ processes into different priority levels and channel conditions, allowing independent timing optimization for each segment. Critical data receives aggressive retransmission timing with minimal delays, while non-critical data uses conventional HARQ timing, thereby reducing the average transmission time across all data types without compromising error correction for any segment
3Loss of time
If variable TTI durations are used for different channels, then processing time is optimized, but system complexity increases
Solution Approach 1:
The patent manages the complexity of variable TTI durations by establishing standardized parameter sets and selection criteria. Rather than allowing arbitrary TTI lengths, the system uses predefined duration options with clear selection rules based on channel type, data priority, and traffic characteristics, making the complexity manageable while still achieving processing time optimization
Solution Approach 2:
The invention creates a universal TTI duration selection mechanism that can be applied across different channel types and data priorities through a common framework. This multi-functional approach allows the same variable TTI mechanism to serve multiple purposes - reducing latency for urgent data, optimizing processing for different channel conditions, and maintaining compatibility with existing LTE structures, thereby managing complexity through consolidation
Data Source
AI summary
Devices and techniques for determining a transmission time interval (TTI) duration and/or varying the TTI duration are contemplated. The TTI duration may be varied based on one or more of: the timing a transmission, the amount of data available for transmission, or the type of data to be transmitted. The TTI duration may be for one or more of: the Enhanced Physical Downlink Control Channel (EPDCCH), the Physical Downlink Shared Channel (PDSCH), and/or the Physical Uplink Control Channel (PUCCH). One or more different TTI durations may be achieved by modifying OFDM symbols per TTI and/or symbol duration (e.g., subcarrier spacing). One or more variable time-slot boundaries are contemplated. TTI duration per set of subcarriers is contemplated. One or more timing rules to deal with different processing time(s) are contemplated.