Outer Erasure Code for HARQ Retransmission
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Solution Overview
Problem
Current wireless communication systems face inefficiencies in Hybrid Automatic Repeat Request (HARQ) retransmissions, particularly in managing errors and reducing overhead, especially when soft combining fails due to pre-empted traffic or high-speed scenarios, and existing erasure codes are complex or inefficient for correcting multiple code blocks.
Innovation Solution
The implementation of an outer erasure code with a nested HARQ protocol that computes parity blocks through XOR operations on information blocks or their cyclic shifts, allowing for the correction of an arbitrary number of code blocks with reduced redundancy and simpler decoding, and feedback indicating only the number of failed code blocks, rather than specific indices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If soft combining is used for HARQ retransmission, then throughput is improved, but reliability deteriorates when pre-empted traffic or high-speed scenarios cause decoding failures
Solution Approach 1:
The code block group (CBG) is segmented into individual code blocks (CBs) for independent error detection and correction. Each CB is processed separately with its own CRC check, allowing selective retransmission of only failed CBs rather than retransmitting the entire TB or relying on soft combining that may fail in pre-empted traffic scenarios.
Solution Approach 2:
The invention changes the HARQ feedback parameter from soft combining metrics to explicit CB failure indicators. By transmitting CBG index information that identifies specific failed code blocks, the system transitions from implicit soft combining to explicit error identification, improving reliability in scenarios where soft combining fails.
2Productivity
If CBG based retransmission is implemented, then retransmission efficiency is improved, but feedback overhead increases due to CBG index requirements
Solution Approach 1:
The invention extracts only the essential failure information (CBG index of failed code blocks) from the complete CBG state, transmitting minimal feedback data. Instead of sending detailed information about all CBs in a CBG, only the indices of failed CBs are transmitted, reducing feedback overhead while maintaining retransmission efficiency.
Solution Approach 2:
The system transmits partial feedback information (only failed CBG indices) rather than complete information about all code blocks. This partial action approach reduces feedback overhead significantly while providing sufficient information for efficient retransmission of only the necessary portions.
3Device complexity
If TB based HARQ retransmission is used, then implementation complexity is reduced, but retransmission efficiency deteriorates when only some FEC blocks fail
Solution Approach 1:
The transport block (TB) is segmented into multiple forward error correction (FEC) blocks that can be independently decoded and evaluated. This segmentation allows the system to identify and retransmit only the specific failed FEC blocks rather than retransmitting the entire TB, improving retransmission efficiency while maintaining manageable complexity through structured organization.
Solution Approach 2:
Instead of retransmitting the complete TB when any error occurs, the system transmits only the partial set of failed FEC blocks identified through individual CRC checks. This partial retransmission approach significantly improves efficiency by avoiding unnecessary retransmission of correctly received blocks while keeping implementation complexity reasonable.
Data Source
AI summary
Systems and methods disclosed herein provide an outer code for HARQ applications, which may be an erasure code. In some embodiments, the outer code has a relatively simple decoding algorithm, increased decoding probability with no extra redundancy packets needed and can correct an arbitrary number of code blocks. In some embodiments, the outer code may be implemented as part of the 5G air interface, also known as new radio (NR), and/or in applications such as vehicle-to-everything (V2X) and/or ultra-reliable low latency communication (URLLC). Some embodiments provide a nested HARQ protocol for HARQ transmission with an outer code.