HARQ ACK/NACK Feedback Using a Second Frequency Band in TDD

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Solution Overview

Problem

In time-division duplex (TDD) wireless communication networks, the delayed and inefficient transmission of Hybrid Automatic Repeat Request (HARQ) acknowledgments (ACK/NACK) due to limited uplink capacity and asynchronous timing in LTE frame structures increases latency and buffer occupancy, especially in scenarios where uplink and downlink subframes are not evenly distributed.

Innovation Solution

A receiver configured to evaluate downlink data and transmit evaluation data, including ACK/NACK, in a second frequency band outside the primary frequency band during downlink-only subframes of TDD-frames, utilizing unused bandwidth in TDD schemes, such as NB-IoT channels, to enable early transmission of feedback.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If HARQ ACK/NACK is transmitted in the uplink frequency band following TDD frame structure, then the transmission follows standard protocol timing, but the latency increases and buffer occupancy increases due to limited uplink capacity and asynchronous timing

Engineering Contradiction:

ImproveHARQ acknowledgment transmissionVSAvoidlatency

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent transmits HARQ ACK/NACK feedback in the downlink frequency band instead of the traditional uplink band, utilizing the reverse link dimension. This allows the receiver to send feedback during downlink subframes when the transmitter is listening, effectively using an alternative communication dimension to reduce latency without conflicting with uplink capacity constraints

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Solution Approach 2:

The feedback is transmitted earlier than traditional TDD timing would allow by utilizing downlink subframes immediately following the data transmission, rather than waiting for the next uplink subframe. This preliminary action reduces the waiting time and buffer occupancy while maintaining protocol reliability

Inventive Principle:

Principle #10Preliminary action

2Reliability

If HARQ ACK/NACK is transmitted in the uplink frequency band following TDD frame structure, then the transmission follows standard protocol timing, but the buffer occupancy increases due to delayed feedback

Engineering Contradiction:

ImproveHARQ acknowledgment transmissionVSAvoidbuffer occupancy

Core Design Contradiction:

ReliabilityVSQuantity of substance

Solution Approach 1:

Inventive Principle:

Principle #10Preliminary action

3Productivity

If unused bandwidth in TDD schemes is utilized for feedback transmission, then resource utilization is optimized, but the feedback transmission must occur during downlink-only subframes

Engineering Contradiction:

Improveresource utilizationVSAvoidfeedback transmission timing

Core Design Contradiction:

ProductivityVSEase of operation

Solution Approach 1:

The downlink frequency band serves dual purposes: transmitting downlink data during downlink subframes and carrying HARQ ACK/NACK feedback during the same downlink subframes. This multi-functionality allows unused downlink capacity to be utilized for feedback transmission, optimizing resource utilization without requiring separate dedicated feedback resources

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS12580719B2Fast ACK/NACK in wireless communication networks

Publication Date: 2026.03.17 KONINKLIJKE PHILIPS NV

AI summary

A receiver is configured to receive and process a radio signal. The radio signal includes a first frequency band including a first signal, the first signal including a plurality of TDD-frames. The receiver is configured to evaluate reception of downlink data to obtain evaluation data. The receiver is further configured to transmit the evaluation data in a second frequency band outside of the first frequency band.