Soft Decision Value Correction for OFDM Signal Amplitude Control
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Solution Overview
Problem
Conventional reception apparatuses in radio communications face characteristic degradation due to inappropriate amplitude control of the AGC amplifier, leading to ineffective utilization of reception signals, especially with OFDM signals, where peak-to-average power ratio is high, and are prone to setting inappropriate weighting factors influenced by noise.
Innovation Solution
A method for correcting soft decision values by demodulating reception signals, estimating the amplitude of the reception signal in predetermined measurement periods, and variably setting the weight factor in symbol units to ensure the corrected soft decision values fall within a predetermined amplitude range, thereby suppressing characteristic degradation and improving reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the AGC amplifier gain is increased to amplify weak reception signals, then the signal amplitude becomes sufficient for A/D conversion, but the signal exceeds the input full scale range and gets clipped causing waveform distortion
Solution Approach 1:
The patent changes the parameter of soft decision values by applying different gain coefficients based on the estimated signal amplitude. When the signal amplitude is too large, a gain coefficient less than 1 is applied to reduce the amplitude of soft decision values, preventing clipping distortion while maintaining the reliability of signal reception.
2Object-affected harmful factors
If the AGC amplifier gain is decreased to avoid signal clipping, then waveform distortion is reduced, but the signal amplitude becomes too small resulting in insufficient resolution and large quantization errors
Solution Approach 1:
The patent adjusts the parameter of soft decision values by applying gain coefficients based on estimated signal amplitude. When the signal amplitude is too small, a gain coefficient greater than 1 is applied to increase the amplitude of soft decision values, ensuring sufficient resolution and reducing quantization errors without requiring actual signal amplification that could cause clipping.
3Measurement precision
If the weighting factor is set based on instantaneous reception amplitude to correct soft decision values, then quantization errors are reduced, but the weighting factor is influenced by noise causing inappropriate correction
Solution Approach 1:
The patent performs preliminary action by estimating the signal amplitude over a predetermined measurement period before setting the weighting factor. This averaging process filters out instantaneous noise fluctuations, ensuring that the weighting factor is set based on a reliable estimate of the true signal amplitude, thereby improving both precision and reliability.
4Productivity
If OFDM modulation is used to increase transmission capacity, then data rate is improved, but the peak-to-average power ratio becomes large causing frequent amplitude control errors
Solution Approach 1:
The patent applies a dynamic weighting factor that is adjusted based on the estimated amplitude of the reception signal. This dynamic adjustment compensates for the large peak-to-average power ratio characteristics of OFDM signals, ensuring that soft decision values are appropriately scaled even when the signal amplitude varies significantly, thereby maintaining reliable decoding performance.
Data Source
AI summary
A method for correcting a soft decision value includes: demodulating a reception signal, which is coded by an error correction code and modulated in order to represent one or multiple bits with one symbol; generating the soft decision value, which is used in decoding of the error correction code; multiplying the soft decision value by a weight factor to correct the soft decision value; estimating an amplitude of the reception signal in every predetermined measurement time period; and variably setting the weight factor in a symbol unit in accordance with an estimating result so that a corrected soft decision value approaches to a predetermined amplitude range.