Convergence Performance Of Self-interference Suppression For Co-time Co-frequency Full Duplexcommunication

In a co-time co-frequency full duplex(CCFD)radio,which simultaneously transmits and receives on the same frequency resources,the received signal contains not only the desired signal from remote radio,but also the interference from itself,which need to be sufficiently suppressed.However,the current research on CCFD communication technologies mainly focuses on the self-interference(SI)suppression algorithm design and experimental verification,lacks convergence performance analysis of the SI suppression.This thesis focuses on the convergence performance of the SI suppression for CCFD radio.The contributions are summarized as follows.Firstly,a quick SI suppression algorithm at the radio frequency(RF)domain based on dimensionality reduction is proposed,and its convergence performances,inclusive of convergence time and SI suppression ratio,are analyzed.Considering a single-path SI channel,the proposed algorithm adopts the direct-coupled single tap SI suppression structure at the RF domain,converts the two-dimensional search of adjustable attenuator and phase shifter parameters to the one-dimensional estimations of in-phase and quadrature components.Thus,the proposed algorithm realizes rapid SI suppression at the RF domain by avoiding the slow search of adjustable attenuator and phase shifter parameters.The simulation results show that the convergence time is 20 ?s and SI suppression ratio is 67 d B,when the carrier frequency is 2 GHz,signal bandwidth is 10 MHz,interference to signal ratio is 50 d B and measured time per iteration is 100 symbol periods.Secondly,an adaptive algorithm for SI suppression at the RF domain is presented,and its convergence performances,inclusive of convergence speed and SI suppression ratio,are analyzed.Considering a single-path SI channel,the proposed algorithm utilizes a novel SI suppression structure,which contains an in-phase and quadrature branches.Therefore,the two-dimensional parameters optimization problem of adjustable attenuator and phase shifter in the conventional SI suppression structure is transformed into that of two adjustable attenuators of the in-phase and quadrature branches in the novel structure.Then,the two adjustable attenuators parameters are searched based on the criterion of minimum mean square.Since the transformed optimization problem is a convex problem with quadratic form,the convergence speed of proposed algorithm is fast.The simulation results show that the SI suppression ratio is almost 80 d B,when the carrier frequency is 2.4 GHz,signal bandwidth is 5 MHz,signal to noise ratio is 0 d B,interference to signal ratio is 60 d B,normalization step is 0.3 and measured time per iteration is 50 symbol periods.Thirdly,considering a CCFD multi-user system,the optimal digital precoding scheme under the scenario of strongly correlated SI channels is studied,and its convergence performance is analyzed.By utilizing the strong correlation of the SI channels,the downlink rate maximization problem subject to a targeted uplink rate is transformed into a convex problem,which can be solved by the standard convex optimization tools.Afterwards,the optimal precoding and system capacity can be concluded.Numerical results and performance analysis show that with randomly generated parameters about the uplink,downlink channel vectors and strong correlated SI channel matrix,the time complexity of a single iteration is O(43)and the sum rate is increased by 1.35 bit/s/Hz compared with the conventional suboptimal precoding scheme,when the numbers of transmitted and received antennas in the base station are 4,the transmitted signal powers for the uplink and downlink are 40 d Bm and interference to signal ratio of the received signal in the base station is 3 d B.Finally,the optimal convergence performance of the generic RF multi-tap SI suppression architecture in the broadband CCFD communication system is studied.Assuming perfect channel estimation,the optimal values of the multi-tap parameters is calculated by analysis of the residual SI power.Then the convergence time of the adaptive multi-tap SI suppression at the RF domain is discussed,and the optimal SI suppression performance of the generic RF multi-tap SI suppression architecture is analyzed.Assuming the carrier frequency is 2.4 GHz and signal bandwidth is 100 MHz,a SI channel consisting of 9 paths is generated by Matlab,and the numerical and simulation results show that the generic RF multi-tap SI suppression architecture with 9 taps acquires almost 80 d B SI suppression ratio.In summary,the SI suppression algorithms in CCFD communication systems are studied and the corresponding convergence performances are also analyzed.In practical engineering applications,these results could be applied to help design SI suppression scheme and evaluate the performance of the CCFD communication systems in theory.