Research On Technology And Application Of In-Band Full-Duplex Based Adaptive Optical Self-Interference Cancellation

With the development of B5G/6G research and the emergence of new services and technologies such as webcasting and virtual reality,users’ demand for higher communication speed and capacity is experiencing unprecedented explosive growth.Compared with the traditional half-duplex communication mode,in-band full duplex communication(In-band full-duplex,IBFD)can realize two-way communication between users simultaneously at the same frequency,which owns the advantages of doubling communication capacity and improving spectrum utilization efficiency.It is regarded as one of the important technologies of next-generation wireless mobile communication,and has received extensive attention from scientific researchers in recent years.However,due to the close proximity between the co-located transmitting and receiving antennas,the receiving antenna which is supposed to receive the remote signal of interest(SOI)will inevitably be capturing the nearby transmitting RF signal as an in-band selfinterference(SI)signal.Since the transmitting antenna is so close to the receiving antenna,the presence of the transmitting RF signal,i.e.,in-band SI signal,is so strong that the SOI will be completely buried underneath the SI signal in both spectral and temporal domains.Since the SI signal and SOI are spectrally overlapping,even a conventional RF bandpass filter cannot be used to remove the SI signal.To address this problem,self-interference cancellation(SIC)systems have been intensively investigated to ensure IBFD communication.Microwave photonics based Optical SIC(OSIC)systems have shown superior cancellation performance over RF electronics approaches due to its wider bandwidth,higher operating frequency and adjustment accuracy,accordingly serving as the crucial technology for analog SIC cancellation.However,the basic OSIC system is usually in a static mode,that is,the delay and amplitude matching of the reference signal and the SI signal is manually adjusted,and the adaptive feedback adjustment cannot be made in time according to the sudden change of the wireless IBFD channel.This has greatly limited the application of OSIC system and does not meet the practical requirements of IBFD technology.The dynamic adaptive OSIC system will implement an adaptive feedback adjustment algorithm according to the current cancellation results of the system,dynamically adjust its own parameters,and update in real time.The best cancellation performance will be attained when the algorithm stops and reaches convergence.However,how to realize the adaptive OSIC system at the fastest speed and recover the SOI in the IBFD communication scenario is a key issue in the current adaptive OSIC research.Therefore,this paper is mainly focusing on studying and improving the adaptive speed of adaptive OSIC system based on IBFD communication,exploring the application of adaptive OSIC technology in different systems to upgrade system performance.The main research can be divided into the following parts:1.The principle of adaptive OSICThis paper analyzes the principle of OSIC system based on the Dual-Drive MachZehnder Modulator(DDMZM)OSIC system and Electro-absorption modulated distributed feedback laser(EML)OSIC system.By theoretically studying and simulating the relationship between the cancellation depth,signal frequency,delay deviation and amplitude deviation,the process of adaptive OSIC can be uniformly modeled as a twodimensional,unconstrained convex optimization problem within the adjustment range of delay and amplitude.The establishment of the optimization model lays a theoretical foundation for the subsequent proposal of the adaptive OSIC algorithm.2.The adaptive OSIC technology based on IBFD communicationBased on the model,an adaptive OSIC technology based on the Basic Regular Triangle(BRT)algorithm is proposed with the system output power as the objective function.The BRT algorithm adjusts the delay and amplitude of the reference signal according to the current change of output signal power,that is,the cancellation performance change of the OSIC system.By doing this,the reference signal and the self-interference signal are matched precisely and adaptively and the best cancellation status is obtained when the algorithm stops.Back-to-back IBFD experiment is carried out to verify and compared with the existing adaptive OSIC technologies,the proposed BRT algorithm can achieve correct and stable convergence with the least sampling times(≤15 times)with self-interference signal being cancelled completely.The adaptive convergence speed of the OSIC system is upgraded up to 60%,greatly decreasing the self-adjustment time of the adaptive OSIC system when the wireless chanel changes and makes itself more suitable for the IBFD communication system.Moreover,in order to comply with the nature of IBFD communication mode and measure the transmission quality of SOI directly,SOI is firstly introduced to the adaptive OSIC process and an adaptive OSIC technology based on Improved Regular Triangle(IRT)algorithm is proposed with the bit error rate(BER)of the SOI is used as the objective function.By setting the training phase in advance before real transmission,the IRT algorithm is able to calculate the BER and observe the recovery condition of SOI while doing cancellation.IBFD wireless(18.35 GHz center frequency)experiment is conducted to show that the IRT algorithm can accurately and efficiently complete the optimal convergence of the adaptive OSIC system with the least sampling times(≤11 times).It is the first adaptive OSIC technology that implemented under wireless high-frequency IBFD communication,in accordance with the actual IBFD communication application scenario.The adaptive feedback speed of the adaptive OSIC system is further improved by 15%,enabling the OSIC system to quickly adjust itself and return to the best cancellation status when the wireless environment change leads to poor cancellation performance.3.The interference cancellation of multipath IBFD-RoF system based on adaptive OSIC technologyThe IBFD radio-over-fiber(IBFD-RoF)system is the combination of IBFD communication mode and the basic optical transmission system.The adaptive OSIC technology is applied into the multipath IBFD-RoF system,and the adaptive OSIC preprocessing method is also utilized to improve the multipath SIC performance and RoF transmission bandwidth.On the one hand,the IRT algorithm based adaptive OSIC technology is adopted to improve the system’s ability to deal with more complex timevarying multipath channels and finish the basic analog cancellation.On the other hand,an adaptive OSIC preprocessing method based on the Least Mean Square(LMS)algorithm is introduced to pre-process the reference signal according to the recovery of SOI and increase the matching degree of the reference signal and the multipath SI signal to further improve the cancellation effect.32 d B cancellation depth is achieved over 2.7GHz cancellation bandwidth at 1.65 GHz center frequency through experiment,which is to the best of our knowledge,the widest cancellation bandwidth in the multipath OSIC system.The transmission bandwidth of the multipath IBFD-RoF system is accordingly enlarged,which is more consistent with the development trend of larger capacity and broader band in communication system.Since the SOI is fully recovered in optical domain before fiber transmission,the BER of SOI is substantially decreased,achieving the high reliability transmission of multipath IBFD-RoF system.4.The optical analog noise encryption based on adaptive OSIC technologyThe optical analog noise encryption system based on the principle of IBFD and OSIC is a physical layer encryption technology.In order to improve the flexibility and security of this system under dynamic key changing scenario and expand its encryption bandwidth to make it safer,DDMZM based OSIC architecture for encryption at transmitter and EML based OSIC system for decryption at receiver is proposed.With the help of adaptive OSIC technology and pre-sharing the two fingerprints—analog noise and training data in advance for only once,the legal receiver is able to run the IRT algorithm to adjust and recover the two-dimensional encryption keys according to the decrypted signal condition,remove the encryption noise and complete the adaptive reception of the sensitive signal.In this way,key distribution is no longer needed and the encryption system can work more securely under the dynamic key update scenario,avoiding the risk of interception during troublesome key distribution.In the experiment,not only the encryption keys are adaptively recovered for the first time in the optical analog noise encryption system based on IBFD and OSIC,but also the wideband noise encryption is attained with the bandwidth increased by 500 MHz to 3.5GHz,which is by far the best performance.