HARQ Feedback Constellation Swapping for URLLC Decoding

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Solution Overview

Problem

In LTE wireless communications, the existing modulation constellations for HARQ feedback are not optimally balanced, leading to reduced decoding performance due to skewed constellations when subframe ACK/NACK reporting is not available, particularly in Ultra-Reliable Low Latency Communications (URLLC) scenarios.

Innovation Solution

A modified modulation constellation is applied for HARQ feedback, where the ACK/NACK assignments of constellation points are swapped to achieve a balanced distribution, improving the constellation points' separation and reducing error rates.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a normal modulation constellation is used for HARQ feedback, then the implementation is simple and standard-compliant, but the decoding performance deteriorates due to skewed constellations when subframe ACK/NACK reporting is not available

Engineering Contradiction:

Improvedecoding performanceVSAvoidconstellation modification complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent applies parameter changes by modifying the modulation constellation mapping parameters. Specifically, it swaps the ACK/NACK assignments between different constellation points (e.g., swapping the meanings of 00/01 versus 10/11) to transform a skewed constellation into a balanced one, thereby improving decoding performance without changing the physical transmission mechanism

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent applies inversion by reversing the conventional ACK/NACK mapping approach. Instead of using the standard constellation assignment, it inverts the mapping by swapping which constellation points represent ACK versus NACK, effectively correcting the skewness caused by unavailable subframe feedback

Inventive Principle:

Principle #13The other way round (Inversion)

2Loss of information

If subframe ACK/NACK reporting is enabled, then complete feedback information is available, but the latency increases and resource consumption increases

Engineering Contradiction:

Improvefeedback information completenessVSAvoidfeedback latency

Core Design Contradiction:

Loss of informationVSLoss of time

Solution Approach 1:

The patent extracts only the essential HARQ feedback information (ACK/NACK for current subframe) while discarding or omitting the subframe ACK/NACK reporting. This selective extraction maintains the critical feedback functionality for URLLC while eliminating the latency and resource overhead associated with complete subframe-level feedback

Inventive Principle:

Principle #2Taking out (Extraction)

3Reliability

If a balanced modulation constellation is used, then the decoding performance is optimized, but the standard compliance and implementation simplicity are reduced

Engineering Contradiction:

Improvedecoding performanceVSAvoidimplementation simplicity

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent modifies existing standard constellation parameters through controlled swapping of ACK/NACK assignments. This approach maintains compatibility with standard QPSK modulation while achieving balanced constellation distribution, thus improving decoding performance without requiring fundamental implementation changes

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS11329858B2Quardrature phase-shifting keying reception for non-equiprobable bit reception

Publication Date: 2022.05.10 TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

AI summary

A method is performed by a wireless device for transmitting Hybrid Automatic Repeat Request (HARQ) feedback. The wireless device, for an uplink transmission to be transmitted on an uplink channel, applies a modified modulation constellation for a HARQ feedback. The modified modulation constellation has a modified Acknowledgment/Non-Acknowledgment (ACK/NACK) assignment as compared to a normal modulation constellation having a normal ACK/NACK assignment. The wireless device further transmits HARQ feedback in the uplink transmission according to the modified modulation constellation.