ACK/NACK Bundling for Wireless HARQ Error Reduction
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Solution Overview
Problem
In LTE-based wireless communication systems, hybrid automatic repeat request (HARQ) errors occur due to mismatched serving cell configurations between user equipment (UE) and base stations, leading to data loss or service delays in multiple carrier systems.
Innovation Solution
A method for transmitting reception acknowledgments in a time division duplex (TDD) system that reduces HARQ errors by using a downlink assignment index (DAI) and optimizing ACK/NACK bit transmission through spatial bundling and cell index prioritization, ensuring accurate HARQ processing even with mismatched cell configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If carrier aggregation is used to increase system capacity and data rate, then network throughput is improved, but the complexity of HARQ process management increases and HARQ errors occur due to configuration mismatches
Solution Approach 1:
The base station performs preliminary actions by determining the total number of ACK/NACK bits required before transmitting downlink data. The DAI (Downlink Assignment Index) is prepared in advance in the downlink control information to indicate this total number, allowing the user equipment to pre-configure its ACK/NACK feedback structure and avoid configuration mismatches during HARQ processing.
Solution Approach 2:
The invention implements a feedback mechanism where the base station provides information about the expected number of ACK/NACK bits through the DAI in downlink control information. The user equipment uses this feedback to adjust its ACK/NACK feedback configuration, ensuring that the feedback matches what the base station expects to receive, thereby resolving configuration mismatches.
2Productivity
If the number of serving cells is increased in carrier aggregation, then system capacity is improved, but the likelihood of configuration mismatch between UE and base station increases
Solution Approach 1:
Before transmitting data across multiple serving cells, the base station determines in advance the total number of ACK/NACK bits required from the user equipment. This preliminary determination is communicated through the DAI, allowing the user equipment to pre-configure its feedback structure and avoid mismatches that could occur with dynamic serving cell additions or modifications.
Solution Approach 2:
The invention dynamically adjusts the ACK/NACK feedback parameters based on the actual number of downlink assignments received. The DAI provides a reference parameter that allows the user equipment to modify its feedback configuration to match the base station's expectations, even when the number of serving cells changes.
3Reliability
If ACK/NACK bits are transmitted for each serving cell independently, then HARQ accuracy is improved, but uplink control channel overhead increases
Solution Approach 1:
The invention merges multiple ACK/NACK bits from different serving cells into a single uplink control channel transmission. By using the DAI to indicate the total number of bits required, the system combines the feedback for multiple serving cells into one unified feedback message, reducing uplink control channel overhead while maintaining HARQ accuracy through proper bit positioning and identification.
Data Source
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AI summary
Provided arc a method and an apparatus for transmitting a reception confirmation in a wireless system. A terminal determines at least one downlink sub-frame for ACK/NACK feedback from each of a plurality of serving cells and determines the number of ACK/NACK bits for the plurality of serving cells. The terminal generates bundled ACK/NACK bits by arraying the ACK/NACK bits in the ascending order of the cell index of the plurality of serving cells, and transmits the bundled ACK/NACK bits.