Full Duplex Technology In Wireless Communication

With explosive growth in mobile data traffic,wireless communication network is in rapid and constant development.Half-duplex technology is adopted in the traditional wireless communication networks,which transmits and receives electromagnetic waves in an orthogonal time domain or frequency domain in order to avoid interference between uplink and downlink signals.Full-duplex technology is able to transmit and receive electromagnetic waves at the same frequency simultaneously when the self-interference is effectively suppressed.Compared with half-duplex technology,full-duplex technology can theoretically improve the spectral efficiency by up to 2 times.Hence,it is a field worth of exploring that full-duplex technology is applied in wireless communication networks for efficient transmission and security performance improvement.In this dissertation,we study the achievable rate of full-Duplex relaying-based device-to-device systems,the physical-layer secrecy of full-duplex one-way and two-way systems,and the ultra-low power physical-layer security aided by ambient backscattering full-duplex technology,respectively.1)Considering the achievable rate for full-duplex relaying-based device-to-device systems,a novel beamforming scheme is proposed.The proposed schemes can capture a balance between useful signal improvement and self-interference suppression for further achievable rate improvement.To solve the nonconvex optimization problem,an iterative algorithm with proven convergence is developed.Specifically,at each iteration of the two sub-problems,an optimal solution derived by semidefinite relaxation and an efficient sub-optimal closed-form solution derived by linear combinations are presented,respectively.The simulation results show that the proposed design outperforms the schemes based on singular value decomposition and joint-nulling method.2)Considering the physical-layer secrecy of full-duplex one-way systems,to improve the system security performance,a strategy is proposed that a full-duplex receiver assigns part of its antennas to emit jamming signals to confound the passive eavesdropper.The maximal secure degree of freedom is obtained by optimizing antenna allocation at the receiver with two conditions,i.e.the condition of nulling out self-interference and the condition of balancing the contradicting effects of jamming signals acting as self-interference signals for the receiver and confusing signals for the eavesdropper,respectively.The non-convex coupled problem is translated into an integer programming problem by generalized singular value decomposition method.Closed-form solutions and corresponding beamforming matrixes are provided.Furthermore,the general design guidelines,i.e.,the feasibility and optimality conditions,for the considered system are revealed.Numerical results verify the effect of different antenna allocation schemes on system security performance and demonstrate the superior performance of the proposed scheme.3)Considering the physical-layer secrecy of full-duplex two-way systems,a novel strategy is propose that the secure degree of freedom is obtained when the subspace spanned by the useful signals from two full-duplex transceivers are aligned with each other at eavesdropper.To solve the problem,it is simplified to a single variable integer programming problem with the self-interference complete cancellation assumption.Then,the optimal antenna allocations of two full-duplex transceivers and the feasibility condition of the strategy are provided in closed-form,respectively.Numerical results show that the theoretical analysis is in good agreement with the Monte Carlo simulation curve,verify the superior performance of the proposed scheme,and demonstrate the validity of the feasibility condition.4)Considering the physical-layer secrecy of ultra-low power systems,a novel full-duplex node aided by ambient backscatter technology is adopted to emit jamming signals at eavesdropper.The novel communication system model is established,which integrates backscatter full duplex technology with traditional communication system.The accurate expression of achievable secrecy rate is provided.The effect of the position of backscatter full duplex node,reflection coefficient of backscatter full duplex node,antenna gain of backscatter full duplex node,and power of the transmitter are analyzed,respectively.Then,the upper or lower bounds of achievable secrecy rate and the feasibility condition of the strategy are provided in closed-form with the worst environment,respectively.Numerical results show the validity of the theoretical analysis,and the superior performance of the proposed scheme.