Uplink PDU Repackaging for TTI Duration Mismatch in 5G NR
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Solution Overview
Problem
In 5G New Radio (NR) systems, uplink HARQ retransmissions often fail due to mismatched numerology and TTI durations, leading to wasted radio resources and energy consumption when user equipment (UE) ignores unsuitable grants to maintain Quality of Service (QoS), resulting in dropped grants and inefficient resource allocation.
Innovation Solution
The method involves repackaging a packet data unit (PDU) by determining unsuitable service data units (SDUs) for retransmissions and either using data from other logical channels, inserting padding bits, or not transmitting in the free bits, ensuring that only suitable SDUs are retransmitted, thus maintaining QoS and optimizing resource use.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the UE ignores unsuitable uplink grants to maintain QoS, then QoS is preserved, but radio resources are wasted and energy consumption increases
Solution Approach 1:
The network performs preliminary action by signaling TTI duration information in advance through downlink grants or MAC control elements before the UE makes transmission decisions. This allows the UE to proactively determine whether to transmit or ignore uplink grants based on pre-received TTI duration information, avoiding unnecessary energy consumption from transmitting on unsuitable grants while maintaining QoS requirements.
2Productivity
If the UE transmits on long TTI duration to avoid dropping grants, then resource utilization improves, but QoS breakdown occurs for delay-sensitive traffic
Solution Approach 1:
The system implements dynamic adaptability by allowing the UE to flexibly switch between transmitting and ignoring uplink grants based on real-time TTI duration information received from the network. The UE dynamically adjusts its transmission behavior to match the TTI duration requirements of different logical channels, ensuring that delay-sensitive traffic always uses appropriate short TTI durations while maximizing resource utilization when suitable grants are available.
3Adaptability or versatility
If the scheduler allocates resources without advance TTI duration signaling, then scheduling flexibility is maintained, but UE cannot determine suitable grants for retransmission
Solution Approach 1:
The TTI duration information acts as an intermediary that bridges the network scheduler and the UE. The network signals TTI duration information through downlink grants or MAC control elements as an intermediate message, which then enables the UE to correctly interpret and select appropriate uplink grants for retransmission. This intermediary information maintains network scheduling flexibility while providing the UE with the necessary guidance to make informed grant selection decisions.
Data Source
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AI summary
A method is provided in a user equipment for retransmitting a packet data unit, PDU, that has previously been transmitted in an uplink to a receiver, the previously transmitted PDU comprising one or more service data units, SDUs. The method comprises receiving an uplink grant for retransmission, wherein the uplink grant for retransmission comprises a time transmission interval, TTI, duration associated therewith. The method comprises determining whether a SDU of the one or more SDUs of the previously transmitted PDU comprises a TTI duration which is not suited to the TTI duration associated with the uplink grant for retransmission, and, if so repackaging the PDU for retransmission.