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高输入信号功率时的交调失真是降低星间微波光子链路接收灵敏度的主要因素。考虑输入N路四相相移键控(QPSK)调制信号的情形,建立了强度调制/直接检测(IM/DD)星间微波光子链路模型。利用傅里叶级数展开、傅里叶变换/逆傅里叶变换和Graf加法定理,推导出了接收信号任意谐波和交调分量的解析表达式,在确定三阶交调失真个数的基础上,得到了接收光功率与信号噪声失真比(SNDR)之间的关系。着重分析了不同调制方式下链路接收灵敏度与信道数和调制系数之间的关系。当调制系数较小时,接收灵敏度对信道数变化不敏感。随着调制系数的增大,接收灵敏度先增大后减小,存在最佳的调制系数可以使链路接收灵敏度最高。
Intermodulation distortion at high input signal power is a major factor in reducing the receiver sensitivity of an intermicapillary photonic photonic link. Taking into account the case of inputting N quadrature phase shift keying (QPSK) modulated signals, an intermimic microwave photonic link model of intensity modulation / direct detection (IM / DD) is established. Using the Fourier series expansion, Fourier transform / inverse Fourier transform and Graf addition theorem, the analytic expression of arbitrary harmonic and intermodulation components of the received signal is derived. After determining the number of third order intermodulation distortion Based on this, the relationship between received optical power and signal noise distortion ratio (SNDR) is obtained. The relationship between link receiving sensitivity and channel number and modulation factor under different modulation schemes is emphatically analyzed. When the modulation factor is small, the receiving sensitivity is not sensitive to the change of the number of channels. As the modulation factor increases, the receiver sensitivity first increases and then decreases, and there is an optimal modulation factor to maximize the link reception sensitivity.