Dangling Data Recovery in NR Split Bearer UL Leg Switching
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Solution Overview
Problem
In split bearer networks, uplink leg switching in LTE or NR can cause data to dangle due to fluctuating network conditions, leading to data loss and throughput degradation, as the network may suspend or resume UL grants, resulting in PDCP sequence number gaps and Radio Link Failures.
Innovation Solution
The system allows User Equipment (UE) to predict UL leg switching by monitoring grant allocation and retransmissions, preventing PDCP from pushing data to NR RLC and MAC after a switch is predicted, and sending Buffer Status Reports to clear the NR buffer, with network indications using MAC Control Elements to facilitate data recovery by transferring dangling data to LTE RLC and MAC.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the network stops providing UL grants on the NR UL leg to switch to LTE UL leg, then the UL channel condition can be improved by using a better leg, but data that has been sent to NR RLC and MAC layers will dangle and may be lost
Solution Approach 1:
The network performs preliminary actions by sending an indication message to the UE before actually suspending UL grants on the NR leg. This allows the UE to proactively clear dangling data from NR RLC and MAC layers, transfer it to LTE leg, and prevent data loss before the switch occurs. The indication message triggers a timer that gives the UE advance warning to prepare for the upcoming leg switch.
Solution Approach 2:
The indication message acts as an intermediary between the network's decision to switch legs and the actual execution of the switch. It enables coordinated action between network and UE, allowing the UE to clear dangling data and transfer it to the target leg before the NR leg is actually suspended, thus preventing data loss during the transition.
2Adaptability or versatility
If the network frequently varies UL grant allocation in both LTE and NR legs to adapt to fluctuating network conditions, then network adaptability is improved, but PDCP sequence number gaps occur and data dangles frequently
Solution Approach 1:
The network uses feedback mechanisms by monitoring UL channel conditions and grant allocation status, then sends indication messages to the UE when leg switching is anticipated. This feedback loop allows the network to maintain adaptability while preventing data loss through coordinated action with the UE, who can clear dangling data based on the indication before the actual switch occurs.
3Productivity
If the UE sends multiple Scheduling Requests to obtain UL grants after NR leg switch, then the UE can attempt to recover data transmission, but Radio Link Failure may occur if maximum SRs are reached
Solution Approach 1:
The UE performs preliminary action by clearing dangling data and transferring it to the target LTE leg before the NR leg is actually suspended, upon receiving the indication message. This proactive approach prevents data loss and eliminates the need for multiple SR attempts, thereby maintaining connection stability while ensuring data transmission recovery.
Data Source
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AI summary
A method for handling data, dangling in a new radio (NR) leg of a split bearer, by a user equipment (UE) is disclosed. The method comprises predicting occurrence of NR uplink (UL) leg switch; sending a buffer status report (BSR) pertaining to protocol data units (PDUs) in radio link control (RLC) layer and media access control (MAC) layer in the NR leg based on predicting the occurrence of NR UL leg switch; and initiating recovery of dangling PDUs in the NR leg after the occurrence of the NR UL leg switch, wherein the recovery includes sending the dangling PDUs to a long term evolution (LTE) leg of the split bearer.