M-QAM调制的OFDM系统峰均比较高,而放大器的非线性会导致系统性能的下降.分析放大器非线性对M-QAM调制的OFDM系统性能的影响,将非线性影响总结为两类:星座图旋转和非线性噪声.采用训练序列来估计星座图的旋转角度,并仿真非线性噪声的统计特性和不同静态工作点条件下的误码率曲线,最后给出一种输出功率与信噪比损失的权衡方法.工程应用中,当已知功放的特性曲线和调制参数时,可依照该方法快速计算链路的解调信噪比损失和总体性能损失,并确定功放的最佳静态工作点.%PAPR (Peak to Average Power Ratio) of M-QAM modulated OFDM is usually high, and the nonlinearity of amplifier may cause the performance degradation. In this paper, the impact of amplifier nonlinearity on M-QAM modulated OFDM is discussed. The impact of nonlinearity is summarized as two types, i.e., constellation rotation and nonlinear noise, the constellation rotation may be estimated with training sequence, while the statistics of nonlinear noise and BER (Bit Error Ratio) curves with different static operating point of amplifier are simulated. And finally a trade-off of between the output power and the SNR loss is given. In engineering applications, both the signal-to-noise ratio loss and total performance loss can be calculated quickly in accordance with the method when the characteristic curve and the modulation parameters are known, and the optimal static operating point of the power amplifier could thus be determined.
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