Research On The Technology Of The Co-site Interference Cancellation

Wireless communication technology has developed rapidly in recent years.The bandwidth and the quantity of communication devices are increasing enormously with the emerging of new services and applications.The electromagnetic interference is becoming more and more serious since the wide usage of communication equipment will increase the intensity of the electromagnetic field around it.Co-site interference refers to electromagnetic interference caused by the situation that multiple devices work at the same time in a relatively small space in which the antenna space isolation is small.For the problem of the co-site interference,adaptive interference cancellation technology is an ideal solution.The main idea of the technology is to couple a portion of the sampled signal,the part that is to gain the interference reconstructed signal through an adaptive filter,from the known transmitting signal.The reconstructed signal will be as equal as possible to the received interference signal by adjusting the filter coefficient.At the receiving antenna,the goal of the interference cancellation could be achieved as the reconstructed signal is subtracted.Currently,interferences are cancelled mainly from the airspace domain,analog domain and digital domain.Co-time Co-frequency Full Duplex(CCFD),one of the candidates of 5G,is supposed to double the spectrum utilization theoretically,which makes it a new research topic.Nevertheless,the high-power self-interference signal must be cancelled for achieving the technology,which has a higher demand for the cancellation ability of co-site interference cancellation technology.This thesis introduces the research background,significance and the development of the interference cancellation technology in recent years firstly,followed by the introduction of existing interference cancellation technology and the basic theory of CCFD,the latest application direction of the technology.Then a self-interference cancellation system combined with the airspace domain,analog domain and digital domain cancellation is proposed,where the airspace uses the antenna isolation to obtain a certain amount of self-interference signal attenuation,the analog domain uses the direct coupling method to reconstruct the self-interference signal and the digital domain reconstructs the self-interference signal by using the adaptive cancellation technique on the basis of the preconditioning.Finally,the system simulation model is built and the whole scheme is simulated.It is concluded that the system combined with the airspace domain,analog domain and digital domain can realize the self-interference cancellation with about 90 d B,verifying the feasibility of the scheme theoretically.For those results whose digital domain cancellation performance are poor,non-ideal factors in practice are analyzed.The non-linear distortion of the most influential factor on the power amplifier is modeled and the non-linear digital domain cancellation algorithm based on interference reconstruction is proposed.The result of the simulation of the algorithm shows that the non-linear digital domain cancellation algorithm has a better performance than linear digital domain cancellation,which can increase the interference cancellation ratio of the digital domain by about 9d B.In conclusion,the self-interference cancellation system with the combination of airspace domain,analog domain and digital domain cancellation can solve the problem of co-site interference in CCFD system.The non-linear digital domain cancellation algorithm based on interference reconstruction is able to improve the self-interference cancellation capability in digital domain.The study above demonstrates that CCFD has the possibility of achieving,which might be valuable for those researches on self-interference cancellation of CCFD system in the future.