IAB Adapt Layer Flow Control for HFN Synchronization
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current Integrated Access and Backhaul (IAB) networks in cellular communication systems lack effective flow control mechanisms, leading to issues like HFN desynchronization, lossless handover challenges, and congestion-related SDU discards, which affect the efficiency and fairness of data transmission in NR (New Radio) systems.
Innovation Solution
Implementing end-to-end and hop-to-hop flow control within the IAB network using an adaptation layer to provide flow control information in the opposite direction of data flow, allowing IAB nodes to manage memory availability and scheduling fairness among UEs, thereby preventing HFN desynchronization and reducing congestion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If flow control mechanism is not implemented in IAB network, then data transmission can proceed without explicit control protocols, but HFN desynchronization occurs and lossless handover cannot be achieved
Solution Approach 1:
The patent implements feedback mechanisms where the receiving PDCP entity sends acknowledgments about the highest in-sequence PDCP PDU received to the transmitting PDCP entity. This feedback allows the transmitter to track delivery status and maintain HFN synchronization without complex explicit flow control protocols, resolving the contradiction between reliability and device complexity.
Solution Approach 2:
The transmitting PDCP entity autonomously tracks the highest in-sequence PDCP PDU delivered to the receiving entity using internal state variables and feedback information. This self-service approach eliminates the need for external flow control mechanisms while maintaining HFN synchronization, thereby improving reliability without increasing device complexity.
2Device complexity
If implicit flow control mechanism is used on Uu radio interface, then implementation is simpler, but congestion-related SDU discards occur at intermediate IAB nodes
Solution Approach 1:
The patent introduces an intermediary flow control mechanism at intermediate IAB nodes that monitors buffer status and sends flow control feedback to upstream nodes. This intermediary approach prevents congestion-related SDU discards by enabling proactive flow control without requiring complex end-to-end protocols, thus improving reliability while maintaining reasonable device complexity.
3Speed
If PDCP transmitter transmits more than half of PDCP SN space without delivery confirmation, then transmission speed increases, but HFN desynchronization issue occurs
Solution Approach 1:
The transmitting PDCP entity uses feedback from the receiving entity about the highest in-sequence PDCP PDU delivered to dynamically adjust transmission pacing. This feedback mechanism allows the transmitter to maintain high transmission speed while preventing HFN desynchronization by ensuring delivery confirmation before advancing the transmission window beyond half of PDCP SN space.
4Productivity
If network scheduler at parent IAB node schedules packets without visibility on downstream blockage, then scheduling efficiency is high, but packets are discarded at congested links
Solution Approach 1:
The patent implements feedback loops where intermediate IAB nodes monitor downstream link status and send congestion information upstream to parent schedulers. This feedback enables the scheduler to maintain high productivity by efficiently allocating resources while preventing packet discards at congested links through proactive flow control based on real-time network conditions.
Data Source
Figure 1
Figure 2
Figure 3a)~3c)
AI summary
A method of data flow control in an IAB network at the Adapt layer is provided. The method comprises the steps of, for each UE of a plurality of UEs: in a downlink (DL) context, transferring a polling request, the polling request being configured to facilitate requesting PDCP status information; or in an uplink (UL) context, transferring PDCP status information; the PDCP status information including sequence data indicative of: a highest in-sequence PDCP SN or PDCP COUNT of PDCP PDUs successfully delivered or transmitted to the UE, or a first missing PDCP SN or PDCP COUNT based on PDCP PDUs successfully delivered or transmitted to the UE. An IAB network configured to perform the method of data flow control is also provided. The network comprises an IAB-donor CU configured to implement NUPP and configured for polling the PDCP status information; an IAB-donor DU configured for forwarding the polling request in the Adapt layer; and, optionally one or more intermediate IAB-nodes configured for forwarding polling requests and/or PDCP status information between the DU and MT sides.