Design And Implementation Of A Full-Duplex Relay System Based On Self-Interference Cancellation

Co-time co-frequency full duplex(CCFD)technology enables wireless communication devices to transmit and receive signals in the same frequency band at the same time,which significantly increases the spectrum efficiency of the wireless communication system and effectively mitigates the problem of lack of spectrum resources.Therefore,combining fullduplex(FD)technology with wireless communication systems is a new trend in the development of mobile communications.However,the FD wireless communication has selfinterference(SI),which dramatically degrades the performance of the communication system,so it is necessary to suppress the SI signal.This paper focuses on FD relay application scenarios.On the basis of researching the existed propagation domain and digital domain self-interference cancellation(SIC)technology,this paper proposes a cross-domain SIC algorithm assisted by the digital domain in the radio frequency(RF)domain,and finally completes the hardware implementation of the CCFD relay system.The main contents of this paper is summarized as follows:1.Algorithm design and simulation.First,the transmission frame structure and baseband processing algorithm of the physical layer are designed,and a direct down-sampling synchronization algorithm is proposed to replace the traditional sampling synchronization algorithm,which reduces the complexity of hardware implementation.The entire baseband system is simulated by Matlab.The bit error rate meets the design requirements.Next,a digital domain cancellation algorithm based on SI channel estimation is designed.The principle of this algorithm is to estimate the SI channel by using the transmitted pilot information extracted after receiving frame synchronization,and reconstruct the SI signal from the known transmitted signal.The reconstructed signal is subtracted from the received signal to implement the SIC in the digital domain.Simulation has verified that only 1d B bit error rate loss is caused when 30 d B SI is present.Finally,in the aspect of SIC in the RF domain,a digital domain correlator is designed to support the reconstruction of the auxiliary channel in the RF domain,and the inverse SI signal of the auxiliary channel is added to the received signal to implement the SIC in the RF domain.In case of SI suppression in the propagation domain,a directional antenna is designed and verified by the high frequency structural simulator(HFSS).2.Engineering implement.Based on ZC706 and AD9361,a CCFD relay communication system is built,the simulation of the communication system is carried out by Vivado,and the correctness of FPGA implementation is verified.In order to mitigate the SI signal in the FD relay system,a SIC circuit in the RF domain is built to implement the mitigation of SI in the RF domain.The Vivaldi directional antenna that meets the frequency requirements of the system is designed to implement the SI suppression in the propagation domain.3.Testing and verification.The wireless transmission performance of the relay system in the case of continuous frames and burst frames is tested outdoors,and the stability of the CCFD relay system is verified.Based on the practical test,the SIC performance in the propagation domain is 44 d B,and the SIC performance in the RF domain is 28 d B.After considering the SIC in the digital domain,the total SI suppression performance of the system can reach102 d B.