Research Of Digital Self-interference Suppression Technology In Full-duplex LTE Systems

Transmitting and receiving information can be implemented simultaneously is called duplex communication in wireless communication. Current duplex modes include time-division duplex and frequency-division duplex, which are both half duplex. As the sending and receiving equipment can work at the same frequency simultaneously in a full duplex communication system, the spectrum resource utilization is double that of half duplex communication systems.However, the main technical obstacle is that useful signals from the remote device decay so rapidly after the space environment, that transmission signals of the local device will interfere strongly with useful ones in the full duplex communication. Some techniques are used in order to suppress local self-interference signals, which mainly include antenna self-interference suppression, RF self-interference suppression and digital self-interference suppression. Digital self-interference suppression in full duplex is mainly researched in this paper based on LTE systems, which focuses on three technologies including the technology of digital self-interference suppression based on self-interference rebuilding, the adaptive digital self-interference suppression based on RLS algorithm, and the adaptive digital self-interference suppression based on QRD-LS algorithm. Effects of researched suppression technologies are simulated by Simulink.First of all, digital self-interference suppression in frequency-domain is researched.The main procedures include estimating the channel impulse response of self-interference signal, rebuilding the received self-interference signal and removing it from the hybrid signal which is received. Effects of the technology in single-antenna full-duplex mode are simulated by Simulink.Secondly, technology of RLS algorithm applied to time-domain adaptive digital self-interference suppression is researched. According to single-antenna full-duplex mode and dual-antenna full-duplex mode, this paper presents details of signal processing and verifications by Simulink, and simulates the effects of the algorithm and the factors which affect the algorithm. Following conclusions can be obtained from the simulation: under the conditions of SNR equaling 20 dB and ISR ranging from 10 dB to70dB, the RLS algorithm can ensure the ratio of signal to interference up to 18.5dB at least in AWGN channel in single-antenna mode; It can ensure the ratio of signal to interference up to 17.0dB at least in Rayleigh multipath channel in dual-antenna mode.Finally, adaptive digital self-interference suppression technology in time-domain based on the QR decomposition RLS algorithm is discussed, and the algorithm is implemented through Systolic array. The article analyzes the timing of signal processing of the algorithm, and verifies effects of self-interference suppression in single-antenna full-duplex mode and dual-antenna full-duplex mode by Simulink. Following conclusions can be obtained from the simulation: under the conditions of SNR equaling20 dB and ISR ranging from 10 dB to 70 dB, the QRD-LS algorithm can ensure the ratio of signal to interference up to 18.7dB at least in AWGN channel in single-antenna mode;The algorithm can ensure the ratio of signal to interference up to 17.3dB at least in Rayleigh multipath channel in dual-antenna mode.Three different techniques of digital self-interference suppression in full-duplex communication based on LTE in time-domain and frequency-domain are researched in this paper. In time-domain, the article extends adaptive digital self-interference suppression technology of single-antenna mode to dual-antenna full-duplex mode, and provides a theory basis for the implementing of full-duplex digital self-interference suppression.