Variable TTI Duration Scheduling for Low-Latency Wireless HARQ
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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 be exacerbated by the fixed duration of transmission time intervals (TTIs) and the need for additional processing and feedback times, leading to inefficiencies in data transmission.
Innovation Solution
A wireless transmit/receive unit (WTRU) dynamically adjusts the TTI duration based on factors like transmission timing, data availability, and data type, allowing for variable TTI durations and additional processing rules to manage HARQ processes and channel assignments, thereby optimizing transmission times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If fixed TTI duration is used, then system stability is maintained, but latency increases due to inability to adapt to varying data transmission requirements
Solution Approach 1:
The patent implements dynamic TTI duration adjustment by introducing multiple TTI length configurations (e.g., 1ms, 0.5ms, 0.25ms) that can be selected and applied based on current network conditions, data type, and service requirements. This transforms the static TTI system into a dynamic one that adapts its time interval to optimize latency for different scenarios.
Solution Approach 2:
The invention changes the TTI duration parameter from a fixed value to a variable parameter with multiple configurable options. The system can switch between different TTI durations (e.g., changing from 1ms to 0.25ms) to adjust latency characteristics, thereby resolving the contradiction between maintaining stability and achieving low latency adaptability.
2Loss of time
If shorter TTI duration is used, then latency is reduced, but processing complexity increases due to tighter timing constraints and additional rules required
Solution Approach 1:
The patent segments the TTI duration into multiple discrete levels (e.g., 1ms, 0.5ms, 0.25ms, 0.125ms) rather than allowing continuous adjustment. This segmentation simplifies processing by providing predefined options that reduce the complexity of timing management while still enabling latency optimization for different service requirements.
Solution Approach 2:
The system dynamically selects appropriate TTI durations based on service type and network conditions, applying different processing rules only when necessary. This dynamic approach reduces overall processing complexity by avoiding the need to handle all possible TTI configurations simultaneously, while still achieving low latency when required.
3Productivity
If variable TTI durations are implemented for different channels, then transmission efficiency is improved, but system complexity increases due to multiple timing rules and HARQ process management
Solution Approach 1:
The patent applies different TTI durations to different channels and service types based on their specific requirements. For example, control channels may use one TTI duration while data channels use another, and different QoS requirements may trigger different TTI selections. This local differentiation improves transmission efficiency without requiring the entire system to operate with maximum complexity.
Solution Approach 2:
The invention creates a universal TTI management framework that handles multiple service types, channels, and QoS requirements through a unified mechanism. The same TTI adjustment principles and selection logic are applied across different channels and services, reducing system complexity by avoiding the need for separate management mechanisms for each channel type.
4Speed
If TTI duration is decreased, then data transmission speed is improved, but reliability may deteriorate due to reduced processing and feedback time
Solution Approach 1:
The system dynamically adjusts TTI duration based on channel conditions and service requirements rather than using a fixed short duration. When channel conditions are good and latency is critical, shorter TTIs are used to improve speed. When reliability is more important or channel conditions are poor, longer TTIs are selected to allow sufficient processing and feedback time, thus maintaining reliability while optimizing speed when possible.
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.