LTE TDD Downlink Feedback Mode Selection
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Solution Overview
Problem
In LTE TDD systems, the existing methods for downlink receiving status feedback, such as ACK/NACK bundling and multiplexing, lead to unnecessary retransmissions and reduced system throughput due to the imbalance between uplink and downlink subframes, particularly when there are more downlink subframes than uplink subframes, causing coverage and throughput issues.
Innovation Solution
A downlink receiving status feedback method that allows a base station to dynamically configure either ACK/NACK bundling or multiplexing mode for each user equipment (UE) based on its uplink signal quality, using a control parameter in RRC signaling to ensure optimal feedback mode selection, with ACK/NACK bundling for edge UEs to maintain uplink performance and multiplexing for central UEs to enhance throughput.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ACK/NACK bundling is used to reduce the number of feedback bits, then uplink coverage is improved, but system throughput deteriorates due to unnecessary retransmissions
Solution Approach 1:
The patent dynamically selects between ACK/NACK bundling and multiplexing modes based on uplink signal quality metrics (RSRP, SINR, path loss). The base station configures the appropriate mode via RRC signaling, allowing the system to adapt feedback mechanism to current channel conditions. This dynamic approach resolves the contradiction by using bundling only when coverage is critical (edge UEs) and multiplexing when throughput can be prioritized (central UEs).
Solution Approach 2:
Different feedback modes are applied to different user equipment based on their local channel conditions. Edge UEs with poor uplink signal quality use ACK/NACK bundling to ensure reliable feedback delivery, while central UEs with good signal quality use ACK/NACK multiplexing to maximize throughput. This localized quality approach allows each UE to operate in the optimal mode for its specific situation.
2Productivity
If multiple ACK/NACK bits are transmitted in one UL subframe, then downlink throughput is improved, but ACK/NACK detection performance deteriorates
Solution Approach 1:
The patent extracts the problem of multiple ACK/NACK bit transmission by separating it into two distinct feedback modes. Instead of always transmitting multiple bits (which causes detection issues), the system extracts only the necessary feedback information based on channel conditions. When using bundling mode, multiple bits are compressed into fewer transmitted bits, reducing detection complexity and improving reliability while maintaining throughput through selective retransmission.
Solution Approach 2:
The patent changes the parameter of feedback bit representation based on channel conditions. For edge UEs, the system changes from transmitting multiple individual ACK/NACK bits to transmitting bundled feedback bits, altering the information encoding parameter. This parameter change reduces the number of bits that need to be detected, thereby improving detection performance while still conveying the necessary feedback information for maintaining downlink throughput.
3Productivity
If ACK/NACK multiplexing is used to maintain throughput, then system throughput is improved, but uplink coverage deteriorates
Solution Approach 1:
The system dynamically switches between multiplexing and bundling modes based on real-time uplink signal quality measurements. When signal quality degrades below thresholds (RSRP < -105dBm or SINR < -3dB), the system transitions from multiplexing to bundling mode, automatically adapting to maintain coverage. This dynamic adjustment ensures that throughput is maximized when conditions permit while coverage is protected when conditions deteriorate.
4Productivity
If the number of ACK/NACK bits is increased to support more DL subframes, then downlink capacity is improved, but feedback reliability deteriorates
Solution Approach 1:
The patent segments the feedback mechanism into two distinct modes: ACK/NACK bundling for reliability and ACK/NACK multiplexing for capacity. Instead of always using high-capacity multiplexing that compromises reliability, the system segments the approach based on channel conditions. For edge UEs, bundling segments multiple feedback bits into fewer transmitted bits, improving reliability. For central UEs, multiplexing allows more bits to be transmitted, increasing downlink capacity. This segmentation resolves the contradiction by allowing both modes to coexist in the same system.
Data Source
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AI summary
A downlink receiving status feedback method is disclosed. The method comprises: a control parameter, which is used for indicating a feedback mode used by a terminal for feeding back downlink receiving status, is carried in a radio resource control (RRC) signaling which is transmitted to the terminal (1) by a base station (2). The terminal feeds data receiving status corresponding to PDSCHs in multiple downlink sub-frames back to the base station in one uplink sub-frame according to the current feedback mode, current configurations of uplink sub-frames and downlink sub-frames, and an uplink feedback timing relation defined by a system.