PDCP Layer Enhancements for Small Cell Data Offload
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Solution Overview
Problem
The complexity of mobility management in heterogeneous networks, particularly due to frequent handovers of mobile devices between small cells, leads to increased signaling traffic and a higher possibility of dropped calls, exacerbated by backhaul latency issues between macro and small cells.
Innovation Solution
Implementing a method where the small cell periodically sends PDCP PDU delivery status reports to the macro cell, allowing for efficient data delivery indication and reducing backhaul signaling, while also relocating the PDCP discard timer to the small cell to account for backhaul latency, thereby minimizing packet loss and handover disruptions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If data is offloaded from macro cell to small cell with RLC layer acknowledgements, then data delivery reliability is improved, but backhaul signaling traffic increases and latency causes timeouts
Solution Approach 1:
The patent extracts the acknowledgment function from the RLC layer and relocates it to the PDCP layer. Instead of requiring RLC acknowledgments to traverse the backhaul link between small cell and macro cell, the PDCP layer directly generates and processes delivery status reports, eliminating the need for backhaul signaling for acknowledgments while maintaining delivery reliability
Solution Approach 2:
The PDCP layer acts as an intermediary that directly manages data delivery status between the small cell and the core network. By having the PDCP layer generate delivery status reports based on PDCP PDU reception status at the small cell, it mediates the acknowledgment process without requiring RLC layer involvement, thus reducing backhaul signaling traffic while maintaining reliable data delivery
2Extent of automation
If PDCP discard timer is kept at macro cell, then centralized control is maintained, but backhaul latency causes packet loss during handovers
Solution Approach 1:
The patent segments the discard timer function from the centralized macro cell control and relocates it to the distributed small cell. Each small cell independently maintains and enforces the PDCP discard timer for its local PDCP PDUs, eliminating the need for centralized timer management over the backhaul link. This segmentation allows immediate local enforcement of discard policies, preventing packet loss during handovers while maintaining adequate control through standardized timer values configured by the network
3Productivity
If small cell footprint is reduced for frequency reuse, then system capacity increases, but mobility management complexity increases due to frequent handovers
Solution Approach 1:
The patent implements self-service mechanisms at the small cell level for mobility management. The small cell autonomously generates PDCP delivery status reports and enforces discard timers based on local PDCP PDU reception status, without requiring complex centralized coordination for each handover event. This self-service approach simplifies mobility management by enabling independent local decision-making while maintaining network-wide consistency through standardized protocols
Data Source
AI summary
A method at a first wireless network element, the method receiving, from a second wireless network element, a plurality of packet data units (PDUs) for a user equipment; transmitting the PDUs to the user equipment (UE); compiling a PDU delivery status report in response to the transmitting of the PDUs; and sending the compiled PDU delivery status report to the second wireless network element.