HARQ ACK/NACK Bundling for Limited TDD Uplink Feedback
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Solution Overview
Problem
In wireless communication systems, especially in TDD mode, the inefficiency in transmitting ACK/NACK signals due to the limited uplink resources results in restricted feedback, leading to potential packet loss and reduced recovery capability when the number of ACK/NACK signals is less than the number of downlink packets.
Innovation Solution
A method where a user equipment (UE) receives a bundling indicator for downlink subframes, generates a representative ACK/NACK signal based on successful reception of codewords, and transmits this signal on an uplink channel, allowing for efficient use of resources by associating the uplink resource with the last detected bundled downlink subframe or its scheduling resource.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If TDD mode with asymmetrical allocation of downlink and uplink subframes is used, then adaptability to asymmetric services is improved, but the number of ACK/NACK signals that can be transmitted is limited
Solution Approach 1:
The patent applies ACK/NACK bundling to combine multiple individual ACK/NACK signals into a single bundled signal. Multiple downlink subframes are grouped together, and their corresponding ACK/NACK feedbacks are merged into one unified signal transmitted on the uplink, thereby resolving the contradiction between limited uplink resources and the need to feedback multiple downlink packets
Solution Approach 2:
The bundled ACK/NACK signal serves multiple functions simultaneously: it provides feedback for multiple downlink subframes, indicates reception status of multiple codewords, and enables the system to maintain adaptability to asymmetric service requirements while operating within TDD constraints
2Loss of energy
If a single UE transmits fewer ACK/NACK signals than the number of received downlink packets, then uplink radio resource usage is reduced, but packet loss increases and recovery capability decreases
Solution Approach 1:
Multiple ACK/NACK signals are merged into a single bundled signal that carries information about multiple downlink subframes. This consolidation reduces the number of separate uplink transmissions needed while preserving the ability to indicate reception status for all bundled subframes, thereby reducing resource usage without sacrificing reliability
Solution Approach 2:
The bundled ACK/NACK signal provides comprehensive feedback about the reception status of multiple downlink subframes transmitted in previous downlink slots. This feedback mechanism enables the base station to identify which packets were successfully received and which require retransmission, maintaining recovery capability while using fewer uplink resources
3Productivity
If ACK/NACK bundling is implemented to reduce uplink resource usage, then efficiency is improved, but the complexity of signal generation and transmission increases
Solution Approach 1:
The downlink subframes are segmented into bundles, and the ACK/NACK feedback is segmented into codeword-level signals that can be independently processed. This segmentation allows the complex task of generating bundled feedback to be broken down into manageable steps: identifying bundled subframes, determining reception status for each codeword, and constructing the final bundled signal
Solution Approach 2:
The patent changes the parameter of signal aggregation by transitioning from individual per-subframe ACK/NACK signals to a bundled signal format. This parameter change involves modifying how feedback is structured and transmitted, using techniques such as multiplexing multiple feedback bits into a single signal carrier, thereby improving efficiency while managing complexity through standardized processing rules
Data Source
AI summary
A method of performing HARQ performed by a user equipment (UE) is provided. The method includes receiving a bundling indicator which indicates the number of bundled downlink subframes, determining whether at least one bundled downlink subframe is missed by comparing the bundling indicator with the number of detected bundled downlink subframes, generating a representative ACK/NACK signal when no bundled downlink subframe is missed, and transmitting the representative ACK/NACK signal on an uplink channel. Recovery capability is maximized and the packet loss is reduced in such a situation that less number of ACK/NACK signals are fed back than that of downlink packets.