OFDMA Demodulation Apparatus Using Preliminary QAM Mapping
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Solution Overview
Problem
Existing OFDMA systems experience significant time delays during signal demodulation due to the need to analyze frame prefix and MAP information, which hinders efficient packet processing and increases hardware requirements.
Innovation Solution
A demodulation apparatus and method that utilizes a QAM demapper and slot buffers to perform QAM demapping and channel decoding, allowing for the analysis of modulation methods for each sub-channel, and selectively reads and outputs valid data based on these analyses, reducing the need for pre-analysis buffers and minimizing delay.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the conventional OFDMA demodulation process waits for frame prefix and MAP information analysis before QAM demapping, then the modulation method for each sub-channel can be correctly identified, but significant time delay occurs (about 11 symbols delay)
Solution Approach 1:
The patent performs QAM demapping in advance on all sub-channels assuming maximum modulation ratio (64-QAM) before the frame prefix and MAP information are fully analyzed. The demapped data is stored in buffers, and after the modulation methods are identified, only the valid portions are selected and processed further. This preliminary action eliminates the need to wait for MAP analysis before starting demapping, reducing delay from 11 symbols to approximately 3 symbols.
Solution Approach 2:
The patent divides the demodulation process into two independent stages: (1) preliminary QAM demapping on all sub-channels using maximum modulation ratio, and (2) selective validation and processing based on later identified modulation methods. This segmentation allows the first stage to proceed without waiting for MAP information, while the second stage ensures correctness by validating against actual modulation methods.
2Reliability
If buffers are used to store data during frame prefix and MAP analysis, then data can be processed after modulation methods are identified, but hardware complexity and buffer memory requirements increase
Solution Approach 1:
The patent uses a single buffer structure that serves multiple purposes: storing demapped data from all sub-channels, holding both valid and invalid data temporarily, and enabling selective retrieval based on identified modulation methods. This multi-functional buffer reduces the need for separate buffers for different stages of processing, thereby reducing overall hardware complexity while maintaining reliability.
3Measurement precision
If sequential processing is used where each stage waits for the previous stage to complete, then processing accuracy is maintained, but overall processing speed decreases
Solution Approach 1:
The patent implements preliminary QAM demapping on all sub-channels before the frame prefix and MAP information analysis is complete. This allows the demapping stage to proceed in parallel with the analysis stage rather than sequentially waiting, significantly improving processing speed while maintaining accuracy through subsequent validation.
Solution Approach 2:
The patent maintains continuous demapping operations across all sub-channels without interruption or waiting for MAP information. The useful action of demapping continues uninterrupted, and the results are validated later, ensuring both high productivity and maintained accuracy.
Data Source
AI summary
Disclosed is a demodulation apparatus for receiving signals by an adaptive modulation and coding method, and demodulating the signals, in an OFDMA based packet communication system, comprising: a QAM demapper for performing QAM demapping to the received signals by a modulation method using a maximum modulation ratio, until modulation methods for each of sub-channels are analyzed; a slot buffer for storing the data outputted from the QAM demapper; a channel decoder for decoding the data stored in the slot buffer and analyzing modulation methods for each sub-channels and transferring the analyzed modulation methods to the QAM demapper; and in at the same time, reading valid data from the data stored in the slot buffer, based on the analyzed modulation methods for each sub-channels, and demodulating the valid data.