PDCP Layer HFN Synchronization for LTE Handover
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Solution Overview
Problem
In LTE-Advanced systems, a mismatch occurs between the Hyper Frame Number (HFN) used in the PDCP layer on the transmitting and receiving sides during handover or reconnection procedures, leading to failures in deciphering processing and decreased throughput due to unconfirmed delivery of PDCP-PDUs.
Innovation Solution
Implementing a mechanism in mobile stations and radio base stations to manage and report the HFN and COUNT values, ensuring synchronization by transmitting the most recently used or upcoming HFN/COUNT values when specific triggers are detected, thereby preventing mismatches and ensuring successful deciphering processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the PDCP layer on the transmitting side transmits PDCP-PDUs ciphered by using the COUNT value with HFN=0 while multiplexing the PDCP-PDUs on a single RLC-PDU, then the throughput is improved, but a mismatch occurs between the HFN used in the PDCP layer on the transmitting side and the HFN used in the PDCP layer on the receiving side after handover
Solution Approach 1:
The transmitting side performs ciphering processing on PDCP-PDUs in advance using COUNT values with HFN=0 before handover, and multiplexes them on a single RLC-PDU. This preliminary action allows the receiving side to successfully decipher and update its receive window to HFN:1, PDCP-SN:0 to 2047, ensuring HFN synchronization is established before the handover completes
Solution Approach 2:
The receiving side updates its HFN value based on the successful receipt and deciphering of PDCP-PDUs. This feedback mechanism ensures that when handover occurs, both transmitting and receiving sides synchronize their HFN values, preventing the mismatch problem that would otherwise occur
Data Source
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AI summary
A mobile station comprising a receiver unit configured to receive a PDCP-PDU with a PDCP-SN added as a header at a PDCP layer from a radio base station; and a transmitter unit configured to transmit the PDCP-PDU at the PDCP layer to the radio base station. The receiver unit is configured to perform deciphering processing on the PDCP-PDU by using a COUNT value composed by an HFN and the PDCP-SN added as the header to the received PDCP-PDU. The transmitter unit is configured to, if a report trigger is detected, send the radio base station a PDCP Status Report including the COUNT value most recently used in the deciphering processing on the PDCP-PDU. Or, the transmitter unit is configured to, if a report trigger is detected, send the radio base station a PDCP Status Report including the COUNT value to be used in the deciphering processing on the next PDCP-PDU. A radio base station comprising a receiver unit configured to receive a PDCP-PDU with a PDCP-SN added as a header at a PDCP layer from a mobile station; and a transmitter unit configured to transmit the PDCP-PDU at the PDCP layer to the mobile station. The receiver unit is configured to perform deciphering processing on the PDCP-PDU by using a COUNT value composed by an HFN and the PDCP-SN added as the header to the received PDCP-PDU. The transmitter unit is configured to, if a report trigger is detected, send the mobile station a PDCP Status Report including the COUNT value most recently used in the deciphering processing on the PDCP-PDU.