Research On Beamforming Technology For Multiple-antenna Secure Communications

The broadcast nature of the wireless channel makes information security problems more serious.Traditionally,wireless security is guaranteed through high layer encryption.With the development of computer technologies and interception techniques,encryption becomes increasingly cannot meet the requirements for information security.Inspired by information theory,physical layer security is introduced into wireless communications to guarantee secure communication by using wireless channel characteristics.Multiple-antenna beamforming technology becomes one of the most popular technologies in the area of physical layer security due to it can enhance desired signal and suppress eavesdropping signal at the same time.This paper mainly considers the physical layer security problems about cognitive radio networks and simultaneously wireless information and power transfer networks.Firstly,this paper introduces artificial noise aided technology into the secure cognitive radio networks.To obtain the maximum secrecy rate,we propose an algorithm to jointly design the information beam and artificial noise beam.Simulation results show that the proposed algorithm can improve the security of the system effectively and can address the short distance interception problems.Then,the relay technology is introduced into the secure cognitive radio networks,which combines the independent main network and secondary network together.In cognitive relay network,the secondary network assists the communication of main network by the means of relaying.This paper establishes the model of the secure cognitive relay network.Considering the cases that secondary transmitter knows the perfect and imperfect CSI,we propose two optimization algorithms to obtain the minimum total transmit power by jointly design the transmit matrix,information beam and power splitting ratios.Next,we study the physical layer security problems for simultaneously wireless information and power transfer over interference channels.Under a practical assumption that only imperfect eavesdropper CSI is available,we formulate the two equivalent optimization problems–the total transmit power minimization problem and the secrecy rate maximization problem.An optimal robust secure beamforming and power splitting scheme of each problem is obtained via the aid of one-dimensional search.Moreover,in order to decrease the algorithm complexity,we also propose corresponding zero-forcing beamforming schemes.Finally,simulation results show that the proposed robust optimal scheme outperforms the conventional artificial noise aided scheme.We also demonstrated that the optimal scheme can obtain larger performance gains than zero-forcing beamforming scheme under the same conditions.Finally,in order to increase the energy transfer efficiency and the information transmit security of wireless powered communication networks simultaneously and considering both cases that the eavesdropper is an internal or external node,we design two effective joint resource allocation schemes.Simulation results show that the proposed schemes outperform than the fixed resource allocation scheme,and have a better anti-short-distance interception performance.