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| Adaptive Demodulation Scheme of High Order QAM Based on Log-likelihood Ratio Threshold |
| LEI Weijia SONG Haina XIE Xianzhong |
| (Chongqing Key Laboratory of Mobile Communications Technology, Chongqing University of Posts and Telecommunications, Chongqing 400065, China) |
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Abstract The order of the modulation used in existing adaptive demodulation schemes is no higher than 16, and the decoding of channel codes is not taken into consideration in the analysis and design. In this paper, an adaptive demodulation algorithm used for higher order Quadrature Amplitude Modulation (QAM) is studied. A rate adaptive scheme at receiver is proposed which combines this algorithm and rateless error correcting codes. The bits in received symbols with absolute log-likelihood ratio value higher than demodulation threshold are demodulated, otherwise, deleted. In the scheme, the length of the codeword for the rateless codes decoding is fixed, and error performance is achieved by adjusting the demodulation threshold. Based on the analysis of the average mutual information of the demodulation bits, the calculation method is given of the log-likelihood ratio demodulation threshold and demodulation bits ratio under different signal-to-noise ratio. A sample design scheme employing 256-QAM constellations and Raptor codes is provided, and the simulation results of this sample are consistent well with those of the theoretical analysis, which confirms the effectiveness of the scheme.
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Received: 03 August 2016
Published: 07 March 2017
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| Fund: The National Natual Science Foundation of China (61471076), The Chongqing Research Program of Basic Research and Frontier Technology (cstc2015jcyjA40047), The Program for Changjiang Scholars and Innovative Research Team in University (IRT1299), The Special Fund of Chongqing Key Laboratory (CSTC) |
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Corresponding Authors:
SONG Haina
E-mail: songhn_cqupt@163.com
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