Scrambled Symbol Demodulation for Low-Complexity QAM Decoding
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Solution Overview
Problem
Conventional methods for demodulation, especially for QAM, require complex memory storage and multiple processes for descrambling and bit likelihood calculation, making them inefficient and difficult to implement, particularly when dealing with soft decisions and turbo equalization.
Innovation Solution
A wireless communication device and method that generates a reference point using a transmission symbol number, allowing for simple demodulation and soft symbol calculation for both PSK and QAM by scrambling the symbol mapping number, reducing the complexity and memory requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional QAM demodulation methods are used with complete descrambling and bit likelihood calculation, then accurate demodulation is achieved, but device complexity and memory requirements increase significantly
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing only the necessary reference point mapping numbers in a lookup table before demodulation. Instead of performing complete descrambling and calculating all possible bit likelihood combinations during reception, the system prepares the essential reference data in advance, significantly reducing the computational complexity and memory requirements during actual demodulation while maintaining accurate bit likelihood calculation.
2Reliability
If all symbol mapping points are stored in ROM for reference, then complete descrambling can be performed, but memory usage increases
Solution Approach 1:
The patent extracts only the essential reference point mapping numbers from the complete set of symbol mapping points and stores them in a compact lookup table. Instead of storing all possible symbol mappings in ROM, the system identifies and stores only the critical reference points needed for accurate descrambling and bit likelihood calculation, significantly reducing memory usage while maintaining descrambling reliability.
Solution Approach 2:
The system performs preliminary identification and storage of necessary reference points before the demodulation process. By pre-calculating which mapping numbers are essential for reference and storing only those in the lookup table, the patent reduces memory requirements while ensuring that all necessary information for complete and accurate descrambling is available when needed.
Data Source
AI summary
SISO decoding of a reception signal having a scrambled symbol arrangement is realized using a process having reduced complexity. Coordinates are generated for a reference point obtained by scrambling and mapping a symbol number not a symbol reference point position. This reference point simulates transmission-side scrambling and is generated for each symbol number by a first mapping unit. Because the binary expression of a corresponding original signal number is retained, a bit likelihood calculation unit can easily calculate a bit likelihood based on the distance between the reference point and a reception signal. The calculated bit likelihood is then deinterleaved and subjected to SISO error-correcting decoding. The thus obtained bit likelihood is then reinterleaved and used to calculate a symbol probability. Soft symbols are generated through the multiplication of all the calculated symbol probabilities by corresponding reference points output by a second mapping unit similar to the first mapping unit.