PDCP Status Report for LTE Handover Interruption
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Solution Overview
Problem
In 3GPP LTE wireless communication systems, during enhanced Node B (eNB) re-pointing, the Radio Link Control (RLC) Protocol Data Units (PDUs) are not forwarded from the source eNB to the target eNB, leading to potential user plane interruptions and wastage of radio capacity, as incomplete Service Data Units (SDUs) need to be retransmitted at the target eNB.
Innovation Solution
A method where a mobile device sends a Packet Data Convergence Protocol (PDCP) status report to the target eNB, allowing only missing RLC SDUs to be resent, thereby avoiding duplication and conserving bandwidth by informing the target eNB which PDCP packets to send using the X2 logical network, and the source eNB stops sending RLC SDUs once handoff begins.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If RLC PDUs are not forwarded from source eNB to target eNB during re-pointing, then device complexity is reduced and handover is simplified, but user plane interruptions occur and radio capacity is wasted due to retransmission of incomplete SDUs
Solution Approach 1:
The patent introduces a new entity called the Lower PDCP layer that acts as an intermediary between the RLC layer and the upper PDCP layer. This intermediary layer is responsible for forwarding RLC SDUs from the source eNB to the target eNB during handover, ensuring continuity of user plane data while keeping the RLC layer simple and avoiding complex forwarding mechanisms in the RLC protocol itself.
Solution Approach 2:
The patent segments the data transmission function into multiple layers: the RLC layer handles reliable delivery within a single eNB, while the new Lower PDCP layer handles the forwarding function during handover. This segmentation allows each layer to focus on its specific function without complexity, while the Lower PDCP layer specifically manages the handover data forwarding to maintain user plane continuity.
2Reliability
If all RLC SDUs are retransmitted at target eNB, then reliability is improved by ensuring complete data delivery, but bandwidth is wasted due to duplication of already received packets
Solution Approach 1:
The patent implements a feedback mechanism where the mobile device sends a PDCP status report to the target eNB indicating which PDCP packets have been successfully received. The Lower PDCP layer at the target eNB uses this feedback information to determine which RLC SDUs need to be forwarded from the source eNB and which can be skipped, avoiding retransmission of duplicate data and optimizing radio capacity utilization.
Solution Approach 2:
The patent performs preliminary actions by establishing the Lower PDCP layer before handover occurs, which pre-configures the forwarding mechanism. The status report feedback is processed in advance to determine the exact set of packets that need forwarding, allowing the handover to proceed efficiently without unnecessary retransmissions and ensuring complete data delivery.
3Ease of operation
If RLC operation is reset at each re-pointing event, then ease of operation is improved by simplifying protocol state management, but loss of information occurs as incomplete SDUs must be retransmitted
Solution Approach 1:
The patent introduces the Lower PDCP layer as an intermediary that preserves RLC SDU data during handover. While the RLC layer can be reset at the target eNB to simplify state management, the Lower PDCP layer maintains the forwarding function, retrieving incomplete SDUs from the source eNB and delivering them to the target eNB, thus preventing information loss while keeping protocol state management simple.
Data Source
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AI summary
A method used in a wireless communication system including a plurality of cells, the method includes transmitting to a mobile device from a source enhanced node B, and sending a Packet Data Convergence Protocol (PDCP) status report to a target enhanced node B. Another method includes transmitting to a mobile device from a source enhanced node B, and sending a Packet Data Convergence Protocol (PDCP) status report to the source enhanced node B prior to a re-pointing to a target enhanced node B.