IAB Network Packet Loss Prevention via Centralized PDCP ARQ
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Solution Overview
Problem
Integrated Access Backhaul systems in mobile communication networks face challenges in preventing or mitigating packet loss, particularly in multi-hop scenarios where hop-by-hop Automatic Repeat Request (ARQ) is employed, leading to increased latency and throughput degradation.
Innovation Solution
A method involving a base station centralized unit (CU) and integrated access backhaul (IAB) nodes using packet data convergence protocol (PDCP) with hop-by-hop ARQ, where the CU detects missing PDCP packets and sends an uplink data delivery status report to IAB nodes, instructing retransmission and configuring UE to delay radio link failure declaration, thereby preventing packet loss without involving higher layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hop-by-hop ARQ is employed in multi-hop IAB scenarios, then packet loss is prevented through retransmission, but latency increases due to multiple retransmission hops
Solution Approach 1:
The patent combines multiple ARQ retransmission hops into a single end-to-end retransmission mechanism at the PDCP layer. Instead of performing separate ARQ operations at each IAB node hop, the PDCP entity at the donor gNB performs a unified ARQ operation that spans the entire multi-hop path, thereby maintaining reliability while reducing the cumulative latency of multiple sequential retransmission attempts.
Solution Approach 2:
The PDCP layer acts as an intermediary that manages retransmissions end-to-end across the multi-hop IAB network. The PDCP entity receives packets from upper layers and manages their transmission through multiple RLC layers at different hops, coordinating retransmissions centrally rather than allowing each hop to independently perform ARQ, thus reducing overall latency while ensuring packet delivery.
2Reliability
If path switching is performed in multi-hop IAB networks, then link failure is recovered, but packet loss occurs during the transition
Solution Approach 1:
The patent implements preliminary actions before path switching by maintaining packet buffers at the PDCP entity and RLC entities during link failure events. When a link failure is detected, the system prepares for path switching by preserving transmitted packets in buffers, then performs the path switch while ensuring packets are not lost during the transition, and finally manages retransmission after the new path is established.
Solution Approach 2:
The patent implements a mechanism where packets are temporarily held in buffers during path switching rather than being discarded or lost. The PDCP entity and RLC entities coordinate to recover packets that were transmitted but not yet acknowledged during the path transition, ensuring that no packets are permanently lost even though the path changes occur.
3Speed
If radio link failure declaration is performed immediately, then link failure is detected quickly, but unnecessary failures are declared due to temporary disruptions
Solution Approach 1:
The patent implements preliminary counter-actions to prevent premature radio link failure declarations by introducing a delay mechanism and alternative path verification. When link degradation is detected, instead of immediately declaring failure, the system waits for a configured period and checks whether packets can still be delivered through alternative IAB nodes, thereby preventing false failure declarations while maintaining quick detection of genuine failures.
Data Source
AI summary
A method is performed by a base station centralized unit (CU) node that is in communication, using a packet data convergence protocol (PDCP), with a user equipment (UE) via one or more intermediate integrated access backhaul (IAB) nodes of a radio access network (RAN). The CU node receives one or more PDCP packets over a radio link control (RLC) layer utilizing hop-by-hop automatic repeat request (ARQ) at each intermediate IAB node. In response to a trigger, the CU node sends an uplink (UL) data delivery status report to at least one of the intermediate IAB nodes.