Multi-Level Feedback Link Adaptation for Wireless Retransmission Latency
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Solution Overview
Problem
In wireless communication systems like HSPA and LTE, non-adaptive modulation schemes during retransmissions lead to increased latency and reduced data throughput due to the inability to change transport block size, modulation scheme, or channelization codes, especially in deteriorating channel conditions, which affects applications requiring low latency like voice services.
Innovation Solution
Implementing an explicit adaptive modulation and coding scheme selection method in mobile devices, where acknowledgments or negative acknowledgments are sent based on the quality of received transport blocks, allowing the network to adjust modulation and coding schemes accordingly, rather than relying on implicit link adaptation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If non-adaptive modulation scheme is used during retransmission, then the transport block size and modulation scheme remain fixed, but latency increases and data throughput decreases in deteriorating channel conditions
Solution Approach 1:
The patent implements dynamic modulation and coding scheme adaptation during HARQ retransmissions by introducing a multi-level feedback mechanism. The mobile device evaluates channel quality and provides feedback (ACK, NAK, or DTX) that triggers adaptive changes in modulation order and code rate for subsequent retransmissions, transforming the static retransmission process into a dynamic adaptive system that responds to channel conditions.
Solution Approach 2:
The patent changes the parameters of modulation and coding schemes during retransmission based on channel quality feedback. When channel conditions deteriorate, the system transitions to lower-order modulation (e.g., from 16QAM to QPSK) and adjusts code rate to ensure successful decoding, thereby reducing latency by avoiding repeated failed transmissions with inadequate parameters.
2Device complexity
If non-adaptive modulation scheme is used during retransmission, then the system is simpler to implement, but data throughput decreases in deteriorating channel conditions
Solution Approach 1:
The patent introduces a multi-level feedback mechanism where the mobile device evaluates channel quality and sends feedback (ACK for successful reception, NAK for unsuccessful but detectable, or DTX for poor quality) to the network. This feedback drives adaptive modulation and coding scheme adjustments, enabling the system to maintain high data throughput by selecting appropriate transmission parameters based on real-time channel conditions.
Solution Approach 2:
The mobile device performs self-evaluation of channel quality and generates appropriate feedback messages without requiring complex network-side channel estimation. This self-service approach allows the receiving device to actively participate in the adaptation process, reducing network complexity while maintaining high data throughput through informed parameter selection.
3Reliability
If lower order modulation scheme is used, then reception robustness improves and error tolerance increases, but data throughput decreases
Solution Approach 1:
The patent dynamically selects modulation order based on real-time channel quality evaluation. The system starts with higher-order modulation for maximum throughput and adapts to lower-order modulation only when channel conditions deteriorate, as indicated by multi-level feedback. This dynamic adaptation ensures optimal balance between reception robustness and data throughput throughout the transmission process.
Solution Approach 2:
The patent changes modulation parameters (order, code rate) based on channel quality feedback. When feedback indicates poor channel conditions, the system transitions to more robust lower-order modulation schemes with lower code rates to ensure successful decoding. This parameter adaptation maintains the optimal trade-off between robustness and throughput by matching transmission parameters to current channel capabilities.
4Stability of the object's composition
If rate control is not applicable during retransmission, then the transport format remains fixed, but unnecessary retransmissions continue in degrading channel conditions
Solution Approach 1:
The patent makes the transport format dynamic during retransmission by enabling adaptation of transport block size, modulation scheme, and code rate based on channel quality feedback. This dynamic adjustment allows the system to respond to degrading channel conditions by selecting more appropriate transport parameters, preventing unnecessary retransmissions and reducing overall retransmission delay while maintaining format consistency when channel conditions are stable.
Data Source
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AI summary
A method and apparatus for explicit adaptive modulation and coding scheme selection, the method receiving, at a mobile device, a transport block targeted to the mobile device, and if a quality of the received transport block exceeds a threshold, providing an acknowledgment or negative acknowledgment to a network element; and if the quality of the received transport block is below the threshold, suppressing the acknowledgment or negative acknowledgement.