HARQ ACK/NACK Transmission in TDD-FDD Carrier Aggregation
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Solution Overview
Problem
In wireless communication systems employing TDD-FDD carrier aggregation, there is a challenge in effectively transmitting HARQ ACK/NACK signals across all subframes of a second serving cell configured as FDD, due to asymmetrical resource allocation and timing differences between TDD and FDD modes.
Innovation Solution
A method and apparatus that bundle HARQ ACK/NACK signals with a new associated subframe, using a 2-bit downlink assignment index field in the DL DCI format, allowing for efficient transmission of ACK/NACK signals through one uplink subframe of the first serving cell, which supports TDD mode, thereby facilitating effective communication between the base station and user equipment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If TDD-FDD carrier aggregation is implemented to support wideband bandwidth and higher data rates, then system capacity and data rate are improved, but difficulty in transmitting HARQ ACK/NACK signals increases due to asymmetrical resource allocation and timing differences
Solution Approach 1:
The patent segments the HARQ ACK/NACK transmission by separating TDD and FDD component carriers into different serving cells with distinct uplink-downlink configurations. The first serving cell (TDD) handles ACK/NACK transmission while the second serving cell (FDD) focuses on data transmission, dividing the complex multi-carrier HARQ problem into manageable cell-specific segments that can be handled independently
Solution Approach 2:
The patent introduces an intermediary mechanism where the first serving cell acts as a mediator for HARQ ACK/NACK transmission. Instead of requiring direct ACK/NACK transmission from the second FDD serving cell, the system uses the first TDD serving cell as an intermediate transmitter, which has the flexibility to handle the timing and resource allocation for ACK/NACK signals across both carriers
2Adaptability or versatility
If multiple serving cells are aggregated with different TDD and FDD configurations, then frequency resource utilization is improved, but difficulty in aligning HARQ timings across all subframes increases
Solution Approach 1:
The patent applies local quality by allowing different serving cells to have different uplink-downlink configurations tailored to their specific requirements. The first serving cell is configured with TDD mode suitable for control signal transmission, while the second serving cell uses FDD mode optimized for data transmission. Each cell's resource allocation and timing are optimized locally for its function rather than forcing a uniform configuration across all cells
Solution Approach 2:
The patent implements preliminary action by pre-configuring the first serving cell as the designated ACK/NACK transmission cell before data transmission begins. The network establishes the TDD-FDD carrier aggregation configuration and identifies the first serving cell as the mediator for HARQ feedback, allowing the system to prepare timing and resource allocation in advance rather than reacting to timing conflicts during active transmission
3Productivity
If a single uplink subframe is used for transmitting HARQ ACK/NACK across multiple downlink subframes, then resource efficiency is improved, but reliability of ACK/NACK transmission decreases due to increased burden on single uplink subframe
Solution Approach 1:
The patent merges the HARQ ACK/NACK transmission function across multiple downlink subframes into a single uplink subframe of the first serving cell. Instead of requiring separate ACK/NACK transmissions for each downlink subframe, the system combines all feedback into one consolidated transmission opportunity, improving resource efficiency by eliminating redundant transmissions while maintaining reliability through the dedicated mediator cell
Data Source
AI summary
Provided is a method and apparatus for transmitting an HARQ ACK/NACK. The method includes: in a TDD-FDD CA scheme; recognizing a 2-bit downlink (DL) downlink assignment index (DAI) field configured in a DL downlink control information (DCI) format, the DL DCI format indicating a Physical Downlink Shared Channel (PDSCH) transmission on the second serving cell, and the 2-bit DL DAI field indicating that ten downlink subframes for the second serving cell are associated with one uplink subframe; in response to received data, generating a Hybrid Automatic Repeat reQuest (HARQ) Acknowledgement/Negative Acknowledgement (ACK/NACK) signal, the HARQ ACK/NACK signal being indexed based on a value of the 2-bit DL DAI field; and transmitting the HARQ ACK/NACK signal through one uplink subframe of the first serving cell.