RLC Unacknowledged Mode Header Optimization for VoIP Delay Reduction
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Solution Overview
Problem
In radio link control (RLC) unacknowledged-mode protocol data units (PDUs) for WCDMA systems, there is a challenge in accurately indicating the boundaries of service data units (SDUs) when they are two octets smaller than the PDU size, leading to uncertainty about the completeness of SDUs if a PDU is lost, which affects real-time packet switched services like VoIP.
Innovation Solution
The method involves inserting service data units into protocol data units of appropriate sizes and using length indicators to clearly define the boundaries, including changing the meaning of specific length indicator values to indicate that an SDU starts and ends within a PDU, thereby allowing for immediate delivery to higher layers even if the next PDU is missing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If RLC PDU size is fixed and RLC SDU size varies, then RLC overhead can be optimized, but boundary indication becomes ambiguous when SDU is two octets smaller than PDU
Solution Approach 1:
The patent changes the parameter interpretation of the length indicator field. When the length indicator equals the PDU size minus two octets, it now indicates that the SDU starts and ends within the PDU, rather than indicating that the previous PDU was completely filled. This parameter redefinition resolves the ambiguity in boundary indication while maintaining optimized overhead.
2Loss of information
If length indicator is used to indicate SDU boundaries, then boundary definition is provided, but uncertainty remains when PDU is lost and next PDU indicates incomplete SDU
Solution Approach 1:
The patent applies preliminary action by explicitly indicating in the current PDU that the SDU starts and ends within this PDU (using length indicator = PDU size - 2). This preliminary indication within the PDU itself eliminates the need to wait for or rely on the next PDU to verify SDU completeness, thereby improving reliability without requiring additional PDUs.
3Reliability
If additional PDU is added to indicate end of SDU, then SDU completeness is confirmed, but delay increases for real-time services
Solution Approach 1:
The patent extracts the boundary indication function from the next PDU and places it within the current PDU itself. By using the length indicator to explicitly state that the SDU starts and ends within the current PDU, the indication is taken out of the future (next PDU) and placed in the present (current PDU), eliminating the delay associated with waiting for the next PDU.
Data Source
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AI summary
A system and method is provided for inserting, in a radio link control entity, at least one service data unit to a protocol data unit of an appropriate size. The method also includes providing at least one indicator including a length indicator for indicating that a first data octet of the protocol data unit is a first octet of a first service data unit and at least one other octet of the protocol data unit is the last octet of another service data unit, the first service data unit being either the same or different from the other service data unit.