Research On Digital Domain Full-duplex Self-interference Cancellation Method

With the further development and improvement of The Fifth Generation(5G),wireless communication will usher in a brand new stage,and the instantaneous transmission of data will increase exponentially.However,the number of devices connected to the communications network is also increasing geometrically,and the available spectrum resources for wireless communications are still limited.There is great value in improving the utilization of spectrum.Full-duplex communication technology means that two parties in a communication send and receive signals simultaneously in the same frequency band.Compared with the traditional half duplex,the spectrum utilization rate can be doubled in theory,which is undoubtedly a powerful tool to solve the problem of spectrum resources.However,self-interference(SI)is the biggest obstacle to the full duplex(FD)from theory to practice.In this thesis,the SI elimination of FD radio is studied.The specific work is as follows:Firstly,the performance of ADC dynamic range limited full-duplex system and non-uniform sampling problems are discussed.In this thesis,a forced zero sampling(ZF)method SI elimination method is proposed.In this method,an auxiliary signal is designed and added to the received signal,so that the sum of the SI signal and the auxiliary signal is zero at the time of ADC sampling.Secondly,the mapping relationship between the time domain and the complex domain is established by using the Z transform,and the SI signal is expanded into the form of polynomial,so that the roots of the polynomial in the complex domain and the sampling time correspond one to one.Therefore,the design of auxiliary functions is transformed into solving the problem of linear polynomials in complex domain.Thirdly,the traditional reconstruction subtraction and offset method ignores the desired signal(DS)problem.The orthogonal pilot structure is used for the first time in a full duplex system.Based on the comb-shaped pilot,the pilot symbols of the self-jamming and the desired signals are interleft in two adjacent OFDM symbols,so as to realize an orthogonal pilot structure,so that the influence of the desired signals on the self-jamming channel estimation is completely eliminated.Finally,this paper verifies the effectiveness of the proposed method from two aspects of SI elimination level and received error bit rate.Experimental results show that the cancellation effect of the ZF method is up to 60d B,and the bit error rate is lower than that of the similar non-uniform sampling method under the same channel estimation condition.With the orthogonal pilot structure,the expected bit error rate of the signal is between10^-3and10^-4.