交调失真影响下星间微波光子链路接收灵敏度优化

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。

Receiver Sensitivity Optimization of Intersatellite Microwave Photonics Link Considering the Effect of Intermodulation Distortion

The intermodulation distortion greatly deteriorates the receiver sensitivity of intersatellite microwave photonics link in the range of high input signal power. The situation of N quadrature phase shift keying (QPSK) modulation signal input is considered and the intensity modulation/direct detection (IM/DD) intersatellite microwave photonics link model is presented. An exact analytical solution for any harmonic and intermodulation components of receiver signal is deduced with the method of Fourier expansion, Fourier transform/inverse Fourier transform and Graf addition theory. Combined with the number of third-order intermodulation distortion, the relationship formula between receiver optical power and signal-to-noise and distortion ratio (SNDR) is derived. The analysis concentrates on the relationship between receiver sensitivity of intersatellite microwave photonic link and the number of channels, the modulation index under different modulation modes. When the modulation index is small, the receiver sensitivity is robust against the change of channel number. The receiver sensitivity increases and then decreases as the increase in modulation index. It shows that an optimum modulation index can maximize the receiver sensitivity of link.