HARQ Soft Decision Scaling for Memory Overflow Control
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Solution Overview
Problem
In communications systems employing HARQ error correction, combining re-transmitted and stored information blocks can lead to memory overflow or clipping due to increased dynamic range with each re-transmission, resulting in inaccurate decoding.
Innovation Solution
Calculating a scaling factor prior to combining the blocks to produce a scaled combined information block, using statistical properties of the blocks to determine a limiting value that ensures efficient storage and reduces clipping, thereby controlling memory overflow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If soft decisions from multiple re-transmitted blocks are simply added together, then the accuracy of decoding improves through error correction, but the dynamic range of the combined result increases with each re-transmission causing memory overflow or clipping
Solution Approach 1:
The patent applies preliminary action by calculating the scaling factor before the combining operation. The receiver determines the scaling factor based on the number of re-transmissions and applies it to the soft decisions prior to addition. This prevents memory overflow from occurring during the combining process, as the dynamic range is controlled in advance rather than requiring additional memory capacity to accommodate the unbounded growth of the combined result.
Solution Approach 2:
The patent changes the parameter of the soft decisions by applying a scaling factor that adjusts their magnitude. Instead of directly adding the original soft decisions which would cause unbounded dynamic range growth, the receiver transforms them by multiplying with a scaling factor (e.g., 0.5, 0.25, 0.125) that decreases exponentially with the number of re-transmissions. This parameter transformation maintains the relative relationships between soft decisions while keeping the absolute values within the representable range of the memory system.
2Reliability
If a scaling factor is applied after combining the blocks, then memory overflow is controlled, but additional memory or processing resources are required to perform the combining operation twice or store intermediate results
Solution Approach 1:
The patent eliminates the need for post-combining scaling by performing the scaling operation preliminarily, before the combining takes place. The receiver calculates the appropriate scaling factor based on the number of re-transmissions and applies it to each soft decision block before addition. This approach avoids the need to store intermediate combining results or perform a second combining operation, thereby reducing both memory requirements and processing complexity compared to methods that apply scaling after combining.
Data Source
AI summary
A device and method of combining a first version of an information block and a second version of the information block is disclosed. The method comprises calculating, prior to combining the first and second versions of the information block, a scaling factor to be applied in combining the first and second versions of the information block to produce a scaled combined information block.