Research On Radio Frequency Interference Cancellation By Using Direct Modulation Based Microwave Photonic Technology

Facing the increasing demands of mobile communication for spectrum resources and data transmission,the co-frequency co-time full-duplex mode has the characteristics of high spectrum utilization and fast transmission speed,so it has good application prospects.However,the high-power transmitted signal in full-duplex mode will affect the reception of low-power signal of interest of the same frequency at the receiving end,forming radio frequency(RF)self-interference.Since it is impossible to filter out the interference signals of the same frequency with filters,self-interference has become the primary problem faced by the co-frequency co-time full-duplex.Compared with the traditional electrical interference cancellation method,the interference cancellation method based on microwave photonics has the advantages of large processing bandwidth and high control precision,which has attracted the attention of many scholars at home and abroad,and obtained a lot of research progress.This paper aims at the practical application of microwave photonic radio frequency interference cancellation technology,and studies the radio frequency interference cancellation scheme based on the direct modulated microwave photonic link.This solution uses a direct modulated laser,which simultaneously serves as a laser light source and an electro-optical modulation unit to achieve electro-optical conversion of radio frequency signals.It has the advantages of small size,low power consumption,high integration,and good matching of electro-optic modulation response.Using the adjustable optical attenuator and adjustable optical delay line to adjust the amplitude and delay of the light-borne RF signal in the optical domain can have a very high adjustment accuracy.Based on differential balance detection,photoelectric conversion and radio frequency interference cancellation are completed,and the signal of interest is recovered from the interference signal.For the proposed interference cancellation scheme,the ratio of the power of the interference signal after cancellation to that before cancellation is defined as the interference suppression ratio.The impact of the mismatch of amplitude,delay and phase on the interference suppression ratio is simulated and analyzed,which provides a theoretical basis for the construction and testing of the system prototype.The transmission characteristic of the system to signal of interest is analyzed by means of simulation,which plays a guiding role in system performance optimization.A prototype of direct modulation microwave photon interference cancellation system is designed and made,and the analysis of the cancellation effect of RF interference and the recovery ability of signal-of-interest are analyzed.The experimental results show that the RF interference cancellation of 51 dB is achieved at a center frequency of 2.4GHz with a bandwidth of 20MHz;The signal-of-interest can be recovered with an interference to signal ratio of 38 dB when the signal's EVM after demodulated is lower than 30%.The interference cancellation performance of the system and the matching conditions between the two links at different center frequencies and different bandwidths are measured and analyzed,which provides a useful reference for the optimization of system.