Method for generating log-likelihood ratio for QAM-OFDM modulating signal

Abstract

The invention provides a method for producing log likelihood ratio of a quadrature amplitude modulation-orthogonal frequency-division multiplexing (QAM-OFDM) modulating signal. The method comprises the following steps: allowing an OFDM receiver to estimate the frequency domain channel factor of each QAM sub-carrier symbol; performing the channel compensation of each QAM sub-carrier symbol by utilizing the estimated frequency domain channel factor; normalizing the estimated frequency domain channel factor; multiplying the normalized frequency domain channel factor by a specified scaling factor that is selected from a look-up table; subjecting the compensated QAM symbol to the QAM de-mapping to obtain a basic bit measurement information; multiplying the basic bit measurement information by a scaling factor that is subjected to the normalization and the scaling treatment; and searching a pre-emphasis look-up table by utilizing the scaled soft information to obtain the final bit likelihood ratio and outputting the bit likelihood ratio. The method is universal, can obviously improve the system performance, and is applied to various modern broadband wireless multimedia communication systems. Additionally, the method is simple and free of complex calculation and is adaptive to the hardware implementation.

Description

technical field [0001] The present invention relates to communication systems, and more particularly, the present invention relates to demodulation and decoding techniques in receivers of communication systems. Background technique [0002] As technologies with efficient spectrum utilization, Orthogonal Frequency Division Multiplexing (OFDM) and high-order Quadrature Amplitude Modulation (M-QAM) technologies are often used in multimedia broadband wireless communication systems [1. Mobile Multimedia Broadcasting Part 1: Broadcast channel frame structure, channel coding and modulation. People's Republic of China radio, television and film industry standard GY / T 200.1-2006; 2. Digital TV terrestrial broadcast transmission system frame structure, channel coding and modulation, People's Republic of China national standard GB20600-2006, 2006.]; this type of system generally also uses powerful error control coding techniques such as Turbo codes or LDPC codes to improve the anti-jam...

AI Technical Summary

Problems solved by technology

This error will seriously degrade the performance of the Turbo / LDPC iterative decoder, especially when it uses nonlinear operations, the performance degradation will be more serious

Accurate LLR computation is very important for this type of decoder, because the inaccuracies of the input LLR values ​​are amplified when passed through non-linear operations, resulting in unacceptable decoding performance

[0021] (2) The range of the approximate LLR is greatly affected by the magnitude of the channel factor, and the channel conditions vary greatly, which will lead to the instability of the decoding result under different channel conditions

[0022] (3) Some methods are applied to single-carrier CDMA systems with low-order QAM modulation, but not suitable for OFDM systems with high-order QAM modulation

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