RF Interference Cancellation Based On Microwave Photonics

In continuous wave(CW) radars and full duplex wireless communication systems, when the isolation between the transmitter and receiver is not enough, the self-interference signal will come into being, causing a series of serious consequences. So, how to suppress the leakage signal and improve the isolation has become a key factor in improving system performances. In order to solve this problem, various schemes have been proposed, where the RF cancellation is regarded as the most solutions. However, traditional schemes based on electronics components which suffer from electronic bottlenecks, and limited precision. Therefore, the cancellation depth cannot be further increased. Recently the optical RF cancellation schemes have been put forward. Benefiting from the large bandwidth and excellent precision of optics devices, the cancellation depth in optical system can be greatly increased. Under this circumstance, an in-depth study in optical RF cancellation system has been made. The main work of this paper is shown in the following three aspects:1. The principle of the RF interference cancellation technology was analyzed, and the graphs of the cancellation depth were simulated with MATLAB to analyze the influence of delay and phase error on the cancellation depth.2. In order to solve the problem of the dispersion-induced RF power fading in the optical link, a new scheme based on the two polarization modulators was proposed, by which the cancellation signal and the leak signal can be counter-phase modulated into the optical carriers. The delay and amplitude of the two signals could be matched by finely tuning the optical tunable delay line and the optical variable attenuator, so that the interference cancellation could be realized. The feasibility of the interference cancellation of this scheme was proved by the formulas, and the principle of dispersion compensation by polarization modulator was also analyzed. Finally, the experiments for the cancellation of the leak signal and the compensation of the dispersion-induced RF power fading were demonstrated.3. In order to solve the problem of the multipath interference caused by the different transmission channels of the leak signal, a new scheme based on a tunable dispersion compensation module was proposed. In this scheme, the two signals from the transmitted and received antennas were also counter-phase modulated into the optical carriers by the two polarization modulators. With the purpose of realizing interference cancellation, the delay and amplitude could be matched by finely adjusting the wavelength and the optical power of each tunable laser. The relationships between the delay and the dispersion value could be got from the principle of the tunable dispersion compensation module. The single path interference and the multipath interference were simulated by the experiments and the cancellation depth in different interference conditions was demonstrated. In order to get the advantages and disadvantages of the proposed scheme when compared with the performances of the existing schemes, the basic performance parameters of the link were measured.