RLC Ciphering Sequence Number Segmentation for LTE Retransmission
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Solution Overview
Problem
The existing wireless communication technologies face challenges in designing efficient and low-complexity user plane architectures for ciphering operations, particularly in LTE systems, where RLC re-segmentation complicates the construction of ciphering sequence numbers and is dependent on various numbering schemes used for ARQ and reordering functions.
Innovation Solution
A method and apparatus for ciphering and de-ciphering packet units in the RLC layer during retransmission, involving buffering, re-segmentation, and performing ciphering processes on re-segmented packet units, with different variants for constructing ciphering sequence numbers using RLC sequence numbers and identifiers to reduce overhead and optimize reassembly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If RLC re-segmentation is performed for retransmission, then retransmission efficiency is improved, but ciphering sequence number construction complexity increases
Solution Approach 1:
The ciphering sequence number is segmented into two independent parts: a short sequence number (from RLC PDU header) and a long sequence number (hyper frame number). This segmentation allows the short sequence number to be reused for re-segmented PDUs without complex reconstruction, while the long sequence number provides the necessary uniqueness for ciphering operations.
Solution Approach 2:
The hyper frame number (long sequence number) is pre-incremented by the transmitting entity before retransmission. This preliminary action ensures that re-segmented PDUs have a different long sequence number than the original PDU, enabling secure re-ciphering without complex real-time sequence number generation during retransmission.
2Reliability
If re-ciphering of re-segmented PDUs is performed, then security is maintained, but processing overhead increases
Solution Approach 1:
The ciphering process is segmented into two independent stages: initial ciphering of the original PDU and re-ciphering of re-segmented PDUs. Each stage uses its own sequence number components, allowing efficient independent processing without requiring complex coordination or re-computation of the entire ciphering process.
Solution Approach 2:
The sequence number parameters are changed between initial transmission and retransmission: the long sequence number (hyper frame number) is incremented while the short sequence number is reused. This parameter change enables secure re-ciphering with minimal processing overhead, as only the long sequence number needs to be updated and used in the re-ciphering operation.
3Reliability
If hyper frame number is incremented for retransmission, then sequence number uniqueness is maintained, but sequence number management complexity increases
Solution Approach 1:
The sequence number management is segmented into two independent counters: a short sequence number for identifying PDU segments within a hyper frame, and a long sequence number (hyper frame number) for identifying different hyper frames. This segmentation simplifies management by allowing each counter to operate independently with its own increment rules.
Solution Approach 2:
The hyper frame number is pre-incremented by the transmitting entity before retransmission of re-segmented PDUs. This preliminary action ensures uniqueness without requiring complex real-time coordination between transmitter and receiver, as both entities independently maintain and increment their hyper frame numbers according to the same rules.
Data Source
AI summary
A method and apparatus are disclosed relating to ciphering and de-ciphering of packet units in wireless devices during retransmission in wireless communications. The packet units are re-segmented with the ciphering done on the re-segmented packet unit or on a radio link control protocol data unit (RLC PDU) with or without segmentation. Alternatively, the re-segmentation is done on the radio link control service data unit (RLC SDU) with or without segmentation. Alternatively, the ciphering process and multiplexing of the RLC PDU is done in the medium access control (MAC) layer of a MAC PU before undergoing a hybrid automatic repeat request (HARQ) process for retransmission. Further, the ciphering process in the RLC is done on a packet data convergence protocol packet data unit (PDCP PDU).