DRX Timer Handling for HARQ Feedback Dropped in 5G SPS

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Solution Overview

Problem

In wireless communication systems, particularly in 5G networks, the DL HARQ feedback for DL SPS can be dropped due to overlapping with DL slot/sub-slot/symbol in a TDD configuration, leading to missed retransmission DL assignment DCI commands.

Innovation Solution

The UE initiates the drx-HARQ-RTT-TimerDL and drx-RetransmissionTimerDL timers at specified symbols even if the DL HARQ feedback is not transmitted, ensuring continuous PDCCH monitoring and enabling the network to immediately transmit retransmission assignments.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the UE follows existing specifications and does not start timers when HARQ feedback is dropped, then the UE conserves energy by avoiding unnecessary PDCCH monitoring, but the UE misses retransmission DL assignment DCI commands from the network

Engineering Contradiction:

Improveretransmission reception reliabilityVSAvoidpacket delay

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The UE proactively starts the drx-HARQ-RTT-TimerDL and drx-RetransmissionTimerDL timers at specified symbols even when HARQ feedback is dropped, before the potential retransmission occurs. This preliminary action ensures the UE is in the correct monitoring state to receive retransmission assignments without waiting for explicit network signaling.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent introduces a feedback mechanism where the UE monitors whether HARQ feedback was successfully transmitted. When feedback is dropped (detected through timer expiration or collision detection), the UE triggers alternative behavior (starting timers) to ensure retransmission monitoring, creating a closed-loop response to the feedback failure condition.

Inventive Principle:

Principle #23Feedback

2Reliability

If the UE continuously monitors PDCCH to ensure reception of retransmission assignments, then the UE receives retransmissions reliably, but the UE consumes excessive energy due to continuous reception

Engineering Contradiction:

Improveretransmission reception reliabilityVSAvoidUE energy consumption

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The UE employs periodic PDCCH monitoring based on DRX cycle configurations rather than continuous monitoring. The drx-HARQ-RTT-TimerDL and drx-RetransmissionTimerDL create structured monitoring intervals, allowing the UE to sleep during inactive periods while maintaining reliability during critical retransmission windows.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The PDCCH monitoring behavior dynamically adapts based on the DRX state and timer conditions. The UE transitions between active monitoring and sleep states, with the monitoring intensity and timing adjusted according to whether HARQ feedback was transmitted successfully or dropped, optimizing the balance between reliability and energy consumption.

Inventive Principle:

Principle #15Dynamics

Data Source

PatentUS20250150220A1Discontinuous reception timer handling with semi-persistent scheduling hybrid automatic repeat request feedback

Publication Date: 2025.05.08 TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

AI summary

A communication device of a communications network can receive a downlink (“DL”) hybrid automatic repeat request (“HARQ”) message for DL semi-persistent scheduling (“SPS”) from a network node in the communications network. The communication device can determine that HARQ feedback has not been transmitted to the network node in response to the DL HARQ message within a period of time. The communication device can, responsive to determining that the HARQ feedback has not be transmitted to the network node within the period of time, initiate a timer associated with monitoring for retransmission of the DL HARQ message.