HARQ Transmission Failure Recovery Using Dual Processes
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Solution Overview
Problem
In communications networks, especially for real-time services like VoLTE, HARQ transmission failures due to PDCCH failures result in packet loss and delayed data transfer, which degrades service quality, particularly when wireless devices are configured with low DRX settings, leading to missed retransmissions and inconsistent NDI bits.
Innovation Solution
Implementing a method where the network node detects HARQ failures and transmits data using two mutually different HARQ processes, with toggled NDI values, to ensure robustness and prevent packet loss, allowing for successful retransmissions even during DRX periods and minimizing NDI inconsistencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If a wireless device uses low DRX settings (low drx-onDurationTimer and low drx-inactivityTimer values) to reduce power consumption and minimize delays, then battery efficiency and real-time service responsiveness improve, but HARQ retransmission reliability deteriorates because the device stops monitoring PDCCH during DRX periods, causing missed retransmissions
Solution Approach 1:
The network node proactively transmits the transport block using two different HARQ processes before the device enters DRX mode, ensuring that at least one transmission is received during the device's active monitoring period. This preliminary action prevents packet loss without requiring the device to maintain extended DRX timers.
Solution Approach 2:
The system changes the HARQ process parameters by using two mutually different HARQ processes with toggled NDI values for retransmission. This parameter change allows the network to adapt to the device's DRX behavior, ensuring reliable delivery despite the device's intermittent PDCCH monitoring.
2Device complexity
If the network node uses a single HARQ process for retransmission, then the transmission protocol remains simple and easy to implement, but transmission reliability deteriorates when PDCCH failures occur, leading to packet loss
Solution Approach 1:
The transmission is segmented into two separate HARQ processes, each handling different transmissions of the same transport block. This segmentation allows the network to distribute transmission attempts across multiple HARQ processes, increasing the probability of successful delivery while maintaining clear separation between the processes for manageable complexity.
Solution Approach 2:
The network node prepares cushioning measures by having a second HARQ process ready to immediately take over if the first HARQ process fails. This beforehand cushioning ensures that packet loss is prevented without requiring complex real-time decision-making, as the fallback mechanism is pre-configured.
3Device complexity
If the NDI bit is not toggled consistently during retransmissions, then the HARQ process maintains simplicity, but transmission accuracy deteriorates due to NDI inconsistencies, causing the device to misinterpret retransmissions
Solution Approach 1:
The network node implements feedback control by monitoring HARQ acknowledgments and adjusting NDI bit toggling accordingly. When a retransmission is detected, the system ensures the NDI bit is properly toggled to signal the device to discard old data and accept the new transmission, preventing misinterpretation while maintaining simple control logic.
Data Source
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AI summary
There is provided mechanisms for hybrid automatic repeat request (HARQ) transmission of a transport block from a network node to a wireless device. A method is performed by the network node. The method comprises detecting a HARQ failure upon having transmitted the transport block to the wireless device, wherein the transport block has been transmitted using a HARQ process. The method comprises transmitting data of the transport block to the wireless device using two mutually different HARQ processes as a result of having detected the HARQ failure. There is also provided a network node configured to perform such a method.