PDCP Layer Ciphering and Sequence Number Management in LTE
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Solution Overview
Problem
The existing UMTS L2 protocol fails to support selective re-transmission during handover, flexible RLC PDU size, and reduces overhead in the ciphering process, particularly in the LTE system, which requires explicit PDCP sequence numbers for efficient data transmission and ciphering.
Innovation Solution
A new L2 protocol design for LTE that includes explicit PDCP sequence numbers for selective re-transmission and variable PDU size, with the PDCP layer performing ciphering and using indicators to differentiate ciphered and non-ciphered data, reducing the need for RLC layer ciphering and optimizing data transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the existing UMTS L2 protocol is used, then the system maintains backward compatibility, but it fails to support selective re-transmission during handover and flexible RLC PDU size
Solution Approach 1:
The patent segments the protocol functionality by introducing a new L2 protocol structure with distinct PDCP and RLC layers, each with specific responsibilities. The PDCP layer handles sequence numbering and ciphering, while the RLC layer handles segmentation and reassembly, enabling selective re-transmission without requiring complete protocol redesign
Solution Approach 2:
The patent introduces dynamic parameters including variable RLC PDU sizes that can be adjusted based on channel conditions, and explicit PDCP sequence numbers that enable flexible re-transmission control during handover, making the protocol adaptable to different operational requirements
2Reliability
If explicit PDCP sequence numbers are added for selective re-transmission, then re-transmission control is improved, but overhead in the ciphering process increases
Solution Approach 1:
The patent extracts the ciphering function from the RLC layer and places it in the PDCP layer, where it can operate on the complete PDCP PDU including the explicit sequence number. This separation allows the sequence numbers to be used for both re-transmission control and ciphering synchronization, reducing overall overhead
Solution Approach 2:
The explicit PDCP sequence number serves multiple functions: it enables selective re-transmission control, provides ciphering synchronization, and facilitates in-order delivery. This multi-functionality reduces the need for separate mechanisms, thereby reducing overall overhead despite the addition of explicit sequence numbers
3Reliability
If RLC layer performs ciphering for each PDU, then data security is maintained, but processing overhead and complexity increase
Solution Approach 1:
The patent merges the ciphering function with the PDCP layer's sequence number management, so that a single ciphering operation at the PDCP layer protects the entire PDCP PDU. This eliminates the need for separate RLC layer ciphering operations, reducing processing overhead while maintaining security
Solution Approach 2:
The PDCP layer performs ciphering on the complete PDCP PDU before passing it to the RLC layer for segmentation. This preliminary ciphering ensures that when the RLC layer segments the data, the ciphering overhead is calculated once at the higher layer, reducing overall processing complexity
Data Source
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AI summary
An apparatus and method for performing procedures (protocols) of a PDCP (Packet Data Convergence Protocol) layer and an RLC (Radio layer in an E-UMTS (Evolved Universal Mobile Telecommunications System) which has evolved from UMTS, among radio protocols of a mobile communication system. The PDCP layer performs ciphering on data (i.e., PDCP SDU) received from an upper layer, generates an indicator discriminating ciphered data and non-ciphered data (i.e., an ROHC feedback packet directly generated by the PDCP layer), and transmits the same to a lower layer (i.e., MAC layer). A PDCP SN (Sequence Number) is defined as an algorithm for ciphering the data in the PDCP layer to perform ciphering in the PDCP layer.