PDCP Handover Handling for Lossless Data Transfer
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Solution Overview
Problem
In mobile telecommunications networks, particularly those operating under 3GPP standards, the handover process of User Equipment (UE) from one base station to another poses challenges in maintaining seamless data transmission, minimizing packet loss, and optimizing data delivery, especially during hard handovers, where conventional methods may result in data loss and increased interruption times.
Innovation Solution
The proposed solution involves a method for handover handling that includes appending sequence numbers to PDCP Service Data Units, ciphering, segmenting, and managing these units through Outer ARQ entities to ensure lossless and seamless data transfer between source and target nodes, with mechanisms for synchronizing data transmission status and minimizing duplicate packet transmission by stopping data flows at optimal times during handover.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional handover methods are used, then handover speed is improved, but packet loss increases and data transmission reliability deteriorates
Solution Approach 1:
The source base station performs preliminary actions by buffering PDCP SDUs and maintaining their sequence numbers before handover occurs. This allows the source station to prepare data for seamless forwarding to the target base station, ensuring no packet loss during the handover transition while maintaining fast handover speed.
Solution Approach 2:
The PDCP sequence number acts as an intermediary mechanism that enables the target base station to correctly reorder and reconstruct data packets received during handover. This intermediary element ensures reliable data transmission by providing a reference framework for packet sequencing across the handover boundary.
2Productivity
If data transmission continues during handover, then throughput is maintained, but duplicate packet transmission increases and data integrity deteriorates
Solution Approach 1:
The target base station uses PDCP sequence numbers as feedback information to determine which packets have been successfully received and which need retransmission. This feedback mechanism prevents duplicate packet transmission by allowing the target station to identify and discard redundant packets while maintaining continuous throughput.
Solution Approach 2:
The handover mechanism changes the transmission parameter by switching from source base station transmission to target base station transmission while maintaining the same PDCP sequence number space. This parameter change allows seamless continuation of data flow without duplication, as the target station continues the sequence numbering from where the source left off.
3Productivity
If PDCP layer is moved to eNodeB, then data transmission efficiency is improved, but system complexity increases
Solution Approach 1:
The system segments functionality by placing the PDCP layer at the eNodeB, separating it from the core network. This segmentation improves data transmission efficiency by enabling local processing of PDCP functions such as sequence numbering and handover management, while the core network handles higher-level functions, thus managing system complexity through functional decomposition.
4Reliability
If sequence numbers are appended to PDCP SDUs, then packet reordering capability is improved, but processing overhead increases
Solution Approach 1:
The PDCP SDUs carry their own sequence numbers as self-identifying information, enabling the target base station to autonomously reorder packets without requiring complex external coordination. This self-service approach improves packet reordering capability while minimizing processing overhead, as each packet contains the necessary information for its own proper sequencing.
Data Source
AI summary
A system is proposed to provide handover in a mobile telecommunications environment, particularly applicable to 3GPP networks, which does not increase signalling overhead but minimises user data loss during handover. In the modified system, PDCP SDUs with Sequence numbers are buffered and retransmitted as necessary. At the time of handover, SDUs not received by the user device are forwarded to the target base station for forward transmission to the UE. The handover procedure is designed to minimise packet loss whilst keeping to a minimum the duplication of packet transmission over the air interface.