Research On Technologies Of Co-time Co-frequency Full-duplex

At present,the fifth generation(5G)wireless communication work is in full swing,a series of related regulations and key technologies have been proposed.With the rapid growth of 5G wireless communication traffic,the current situation of wireless spectrum resources allocation becomes increasingly tense.At the same time,as one of the eight key technologies of 5G,the Co-time Co-frequency Full Duplex(CCFD)can transmit and receive signals in the same time using the same frequency channel.Compared with the traditional half duplex technology,that is Time Division Duplexing(TDD)technology and Frequency Division Duplexing(FDD)technology,CCFD can double the spectrum utilization theoretically,which effectively solves the problem of spectrum resource shortage in the new generation wireless mobile communication systen.However,in order to realize the technology of CCFD,the problem of strong self-interference(SI)signal between local receiver and transmitter must be solved at first.At present,the cancellation of SI signal is mainly from the three aspects of antenna domain,radio frequency(RF)domain and digital domain,and has made some progress and achievements.In this paper,the SI signal cancellation methods from the RF domain and digital domain will be studied and discussed.Aiming at the mutual restriction between convergence speed and steady-state error(SSE)in the existing SI suppression methods,some improved schemes are proposed.The main research works in this paper are as follows.First of all,we study and discuss the existing SI cancellation methods in the CCFD system,mainly in the RF domain and the digital domain,and analyze the current common problems in the algorithm effectiveness and reliability,and the CCFD system model is constructed to more vividly describe the process of SI signal cancellation.In the CCFD system with two nodes,the remote and near nodes can be defined,so that both sides of the communication can transmit data in the same frequency band at the same time.In this paper,when designing the transceiver model of the CCFD system,a near-end receiver is taken as an example,and a direct RF coupling cancellation(DRFCC)structure including mutually orthogonal double taps is adopted.After receiving the desired signal,the full duplex receiver first needs to cancel the SI signal in the RF domain.After RF interference suppression,the received signal goes into baseband processing unit after low-noise amplifier(LNA),down conversion and analog-to-digital conversion(ADC)for subsequent digital domain SI elimination processing.Secondly,aiming at the problems existing in the process of SI cancellation in RF domain,an improved scheme of SI cancellation in RF domain is proposed.CCFD transceiver transmits and receives data at the same time in the same frequency band,and the received signal is interfered by the high power of the local transmitted signal.Due to the limitation of dynamic range of ADC,in order to avoid the remote desired signal being submerged in the quantization noise of ADC,the received high-power SI signal must be suppressed in RP domain.In order to solve the problem of mutual restriction among convergence speed,channel tracking ability and SSE in the existing RP domain SI cancellation methods,this paper proposes a convergence parameters decay gradually with time-varying Least Mean Square(DTV-LMS)adaptive filtering algorithm.By using the improved arctangent function,the control step length is coordinated with the relationship between time parameters and error signal correlation value.And the characters such as convergence,channel tracking ability and Interference Cancellation Ratio(ICR)can be maintained in an ideal state under the low computational complexity,which enables the SI signal in the RF domain of CCFD system is effectively suppressed.Finally,aiming at the problem of cancelling the SI signal in the digital domain and proposes a scheme of digital domain SI cancellation based on spectrum estimation.In CCFD system,if antenna SI cancellation or RP SI cancellation are used alone,the ability of SI cancellation is limited,so the remaining SI signals need to be further reduced in the digital domain.In view of the problems of wide band and power loss in the current adaptive digital SI cancellation scheme based on channel estimation,this paper proposes a digital SI cancellation algorithm based on spectrum estimation,and proposes to build a spectrum estimation SI signal model,and then reconstruct the SI signal and SI cancellation through the second-order cyclic statistical information of the signal.By combining spectrum estimation and adaptive tracking interference channel,the algorithm can effectively eliminate residual SI signals and improve the effectiveness of CCFD system bandwidth.