Research On Methods Of Intermodulation Distortion Suppression In Microwave Photonics

Microwave photonics link technology is the conjunction of microwave communication and optical communication. It makes good use of optical fiber link to transmit microwave signals because of the advantages of optical fiber link, which are low loss, high bandwidth and the characteristic of resistance to electromagnetic interference. At present, microwave photonic link technology is mainly used in military and civil radar, high-definition digital TV, high speed mobile communications and high-speed wireless access, etc.The main parameters of microwave photonic link system include noise factor, link gain, Spurious Free Dynamic Range (SFDR). In which, SFDR is a parameter which combines nonlinear distortion and noise. It is the SNR of one fundamental frequency at the link output. The link input consists of two equal-power fundamental frequencies and when the power of.the link input is at a level that produces intermodulation distortion products with output powers equal to the output noise, The SNR of the fundamental frequency output is SFDR. SFDR determines the scope of signal power that the system can receive, ROF communication system with large dynamic range has a larger coverage area of signal and greater tolerance for severe environment. And it is clear that the larger the value of SFDR of the system is the better the performance of the system plays. Thus it is of great significance to improve the performance of the system and the quality of communication to study how to improve the SFDR of the system link.With the high-speed development of communication, communication users have increased dramatically, which leads to high rate of occupation of communication at low frequency. In order to avoid crosstalk in communication, the development of communication frequency to high frequency is the inevitable trend of the future. As a result of the limitation of device, the generation of high-frequency millimeter-wave often has a higher cost. In order to overcome this limitation, the researchers find the methods of frequency multiplication to generate millimeter-wave signal. In this way, the cost of generation of the millimeter-wave signal is greatly reduced. And these methods are very effective in the experiment. In the frequency multiplication system, the existence of frequency multiplication and the nonlinear factors lead to the result that the constellation diagram of the received signal is of serious distortion while the vector signal is applied in the frequency multiplication system. The way to reduce or avoid this kind of distortion is becoming a significant subject of microwave photonics.This paper mainly studies and discusses the principle of microwave photonics link, methods of distortion suppression and the realization of the frequency multiplication system. On this based, we propose a method of phase and amplitude pre-coding of the vector signal16QAM used in the frequency doubling system, which is based on MZ modulator. The change of phase and amplitude of the vector signal in the frequency doubling system are analyzed theoretically, and thus the reason of distortion that the signal is forced is found. In this way, the pre-coding rule of the phase and amplitude is proposed and simulation and experiment are carried out respectively to validate the proposed system. At the last, the pre-coding rule of vector signal in other frequency multiplication system has carried on the further discussion, and the corresponding conclusions are presented.