Downlink HARQ Timing for Short TTI in TDD Systems
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Solution Overview
Problem
Current LTE systems face challenges in reducing packet data latency, particularly due to the limitations of Transmission Time Interval (TTI) lengths, which affect radio resource efficiency and throughput, especially with the introduction of short TTIs that are not optimized for downlink Hybrid Automatic Repeat Request (HARQ) timing in Time Division Duplexing (TDD) configurations.
Innovation Solution
The implementation of a new downlink HARQ timing table that supports short Transmit Time Intervals (sTTIs) in TDD systems, using either a latency optimization or load balancing approach, allowing for the determination and utilization of downlink HARQ timing that aligns with uplink sTTIs, thereby optimizing latency and resource allocation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If short TTI is introduced to reduce latency, then packet data latency is reduced, but downlink HARQ timing is not optimized for TDD configurations causing radio resource efficiency degradation
Solution Approach 1:
The patent introduces new downlink HARQ timing tables specifically designed for short TTI operations in TDD systems. These tables define new k values (e.g., k=4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100) that represent the time offset between downlink sTTI and uplink sTTI for HARQ feedback, optimized for short TTI durations and TDD configurations to simultaneously achieve low latency and high resource efficiency
2Productivity
If short TTI is used to improve throughput, then system throughput is enhanced, but HARQ timing alignment with uplink sTTIs becomes problematic
Solution Approach 1:
The patent defines new downlink HARQ timing parameters k for short TTI operations, where k represents the time offset in sTTI units between a downlink sTTI and the corresponding uplink sTTI for HARQ feedback transmission. The timing tables provide specific k values (e.g., k=4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100) that ensure proper timing alignment between downlink data transmission and uplink HARQ feedback in short TTI TDD systems, enabling straightforward implementation without complex timing calculations
Solution Approach 2:
The patent segments the HARQ timing relationship into discrete sTTI units, where each downlink sTTI is associated with a specific uplink sTTI for feedback based on the timing offset k. This segmentation allows independent optimization of downlink and uplink timings while maintaining proper synchronization, facilitating efficient resource allocation and simplifying the management of multiple HARQ processes in short TTI TDD operations
Data Source
AI summary
Systems and methods for determining and utilizing downlink Hybrid Automatic Repeat Request (HARQ) timing when using short Transmit Time Intervals (sTTIs) are disclosed. In some embodiments, a method of operation of a wireless device in a cellular communications network comprises determining a downlink HARQ timing k for transmission of downlink HARQ feedback for a downlink transmission received in a downlink sTTI nDL based on a Time Division Duplexing (TDD) uplink/downlink configuration and transmitting, in an uplink sTTI nDL+k, downlink HARQ feedback for the downlink transmission received in the downlink sTTI nDL. In this manner, downlink HARQ timing is determined and utilized when using sTTIs.