Transmitter Sequence Number Adjustment for Handover Alignment
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Solution Overview
Problem
During a handover in a radio access network, the transmitter and receiver may become misaligned with respect to their hyper frame numbers (HFNs), leading to incorrect determination of new or repeated data units, resulting in data misalignment and potential decryption errors.
Innovation Solution
The sequence numbers of data units are selectively adjusted after a handover to ensure alignment, using status reports to determine whether a data unit is new or repeated, thereby maintaining alignment between the transmitter and receiver.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If sequence numbers are regularly looped over from 4095 to 0 every 4096 PDCP PDUs, then the sequence number range is efficiently utilized, but the transmitter and receiver may become misaligned with respect to HFNs during handover
Solution Approach 1:
The patent applies preliminary action by having the receiver send a status report indicating the sequence number of the last correctly received PDU before handover. This allows the transmitter to proactively adjust its sequence number assignment after handover to ensure the receiver can correctly identify new PDUs versus repeated PDUs, preventing misalignment before it occurs.
Solution Approach 2:
The patent changes the sequence number parameter dynamically after handover based on the status report received from the receiver. Instead of continuing with the regular loop pattern, the transmitter adjusts the starting sequence number to ensure it falls within a range that the receiver's reordering window can correctly process, thus maintaining reliability while preserving productivity.
2Productivity
If the reordering window uses sequence numbers to determine new or repeated data units, then data unit identification is efficient, but handover causes misalignment leading to incorrect determination
Solution Approach 1:
The patent implements feedback by having the receiver send a status report to the transmitter indicating the sequence number of the last correctly received PDU. This feedback mechanism allows the transmitter to adjust its sequence number assignment after handover, ensuring that the reordering window at the receiver can accurately determine whether incoming PDUs are new or repeated, thus maintaining measurement precision.
3Device complexity
If HFN is kept track of locally at both transmitter and receiver, then ciphering/deciphering alignment is maintained, but handover disrupts this local tracking causing misalignment
Solution Approach 1:
The patent introduces an intermediary mechanism in the form of a status report exchanged between transmitter and receiver during handover. This intermediary communication allows both parties to synchronize their HFN tracking after handover, ensuring that the ciphering alignment is maintained without increasing the complexity of the local tracking mechanisms themselves.
Data Source
AI summary
A method, a transmitter and a computer program product for processing data units at the transmitter are disclosed. In one embodiment, data units are transmitted to a receiver according to a protocol and with respective sequence numbers. The protocol indicates that the receiver is to use a reordering window to determine whether a data unit which is newly received from the transmitter is a new or repeated data unit the data stream by comparing the sequence numbers of the newly received data unit and a previously received data unit. A status report is received and based thereon, the sequence number of a next data unit to be transmitted in a new cell following a handover is selectively adjusted such that the next data unit will be determined to be a new data unit. The next data unit is transmitted with the adjusted sequence number to the receiver.