HARQ Protocol Synchronization via Explicit Reset and Grants
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Solution Overview
Problem
Existing automatic retransmission protocols, such as HARQ, face issues with link layer protocol synchronization due to misinterpretation of feedback messages, leading to residual errors and loss of synchronization.
Innovation Solution
The solution involves detecting lost synchronization errors in NDI-based retransmission protocols by sending an explicit RESET message to restore synchronization. Additionally, explicit scheduling grants are used to prevent protocol synchronization errors by ensuring that each PDU transmission is authorized.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If HARQ protocol uses feedback messages (ACK/NACK) for error control, then transmission reliability is improved, but protocol synchronization between transmitter and receiver may be lost due to misinterpretation of feedback messages
Solution Approach 1:
The patent implements a feedback mechanism where the receiver sends ACK/NACK messages to the transmitter to indicate successful reception or request retransmission. This feedback loop enables the transmitter to adapt its transmission strategy, improving reliability while maintaining synchronization through proper state management at both ends.
Solution Approach 2:
The patent uses a New Data Indicator (NDI) bit that is toggled in advance to indicate whether a transmission is a new PDU or a retransmission. This preliminary indication allows the receiver to properly interpret incoming packets and maintain synchronization without waiting for feedback, preventing the loss of synchronization state.
2Reliability
If the transmitter retransmits PDUs based on NACK feedback, then error correction capability is improved, but residual errors occur when feedback messages are misinterpreted
Solution Approach 1:
The ACK/NACK feedback mechanism enables the receiver to request retransmission of erroneous PDUs. When the transmitter receives a NACK, it retransmits the specific PDU that failed, improving error correction. The feedback loop ensures that retransmissions are properly coordinated between transmitter and receiver, reducing residual errors from misinterpretation.
Solution Approach 2:
The NDI bit is toggled in advance to mark new transmissions versus retransmissions. This preliminary action prevents the receiver from misinterpreting retransmitted PDUs as new data, eliminating residual errors that would occur from incorrect PDU identification and ensuring proper error correction processing.
3Measurement precision
If soft combining is used to combine multiple PDUs for decoding, then decoding performance is improved, but combining errors occur when synchronization is lost
Solution Approach 1:
The NDI bit provides preliminary information to the receiver about whether an incoming PDU is new data or a retransmission. This allows the receiver to correctly identify and group PDUs for soft combining, ensuring that only appropriate PDUs are combined together. Without this preliminary indication, synchronization loss would cause incorrect PDUs to be combined, resulting in combining errors.
Data Source
AI summary
A method and apparatus according to the present invention addresses and/or prevents lost protocol synchronization in HARQ systems caused by ACK/NACK errors. One embodiment detects lost synchronization errors for NDI-based retransmission protocols and restores synchronization by sending an explicit RESET message. In response to the RESET message, the transmitter aborts the transmission of a current PDU and transmits a new PDU and corresponding NDI. Another embodiment prevents protocol synchronization errors by sending scheduling grants on a packet by packet basis. The receiver sends a subsequent explicit scheduling grant to the transmitter based on an error evaluation of a received PDU. The transmitter will not send the next PDU unless it receives the subsequent explicit scheduling grant.