ACK/NACK Bundling Window Sub-Bundling for LTE TDD
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Solution Overview
Problem
In LTE wireless networks, especially in TDD mode, the one-to-one mapping of allocated resources to ACK/NACK signals is challenging due to the imbalance between downlink and uplink subframes, leading to reduced spectral efficiency and increased retransmissions, particularly for dual-layer MIMO configurations where correlation between subframes is limited.
Innovation Solution
The implementation of sub-bundling algorithms that split the ACK/NACK bundling window into smaller sub-bundling windows, allowing for flexible use of ACK/NACK bits to generate resource-specific reply bits based on the pattern of allocated downlink resources, enabling efficient ACK/NACK signaling even when subframes have different PRB resources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If one-to-one mapping of allocated resources to ACK/NACK signals is used, then control signaling accuracy is improved, but spectral efficiency deteriorates due to imbalance between downlink and uplink subframes
Solution Approach 1:
The patent segments the ACK/NACK feedback by introducing resource-specific bits that identify which downlink resource each ACK/NACK corresponds to. This segmentation allows multiple ACK/NACK signals to be transmitted in uplink subframes without requiring a one-to-one mapping, thereby resolving the contradiction between control signaling accuracy and spectral efficiency.
2Productivity
If ACK/NACK bundling is used to handle downlink-uplink subframe imbalance, then spectral efficiency is improved, but reliability deteriorates due to limited correlation between subframes
Solution Approach 1:
The patent applies local quality by making ACK/NACK bits resource-specific, where each ACK/NACK bit is associated with a particular downlink resource. This allows the bundling to be performed locally for each resource type while maintaining the ability to distinguish between different resources, thereby improving reliability without sacrificing spectral efficiency.
3Productivity
If dual-layer MIMO configuration is used, then data throughput is improved, but ACK/NACK signaling complexity increases due to limited correlation between subframes
Solution Approach 1:
The patent introduces resource-specific bits as an intermediary element that mediates between the dual-layer MIMO configuration and the ACK/NACK signaling. These bits provide the necessary information to distinguish ACK/NACK signals for different layers and resources, reducing signaling complexity while maintaining high data throughput capability.
Data Source
AI summary
An allocation of downlink resources is received, which are monitored on l layers for data. A resource-specific bit (ACK/NACK) is generated for each of those resources. From a pattern of those resources is selected an algorithm from among a first algorithm that bundles them in a first mode and a second algorithm that bundles them in a second mode. The selected algorithm is used on the generated resource-specific bits that correspond to the downlink resources, bundled according to the selected mode, to generate l reply bits which are then transmitted. At the network side a NACK reply bit is received, based on a pattern of the allocated downlink resources, a first algorithm that bundles them in a first mode or a second algorithm that bundles them in a second mode is selected. A bundling window and layer combination are determined from the selected algorithm, which gives the resource for retransmitting the NACK'd data.