能量收集全双工中继系统中的安全波束成形研究

针对节点具有能量收集能力的全双工中继窃听信道保密速率的优化问题,提出了一种基于信息和能量联合传输的人工噪声辅助的安全波束成形方法。该方法在满足节点传输功率和中继节点收集能量等约束条件下,通过联合优化波束成形矩阵、人工噪声协方差矩阵和功率分配因子等参数实现系统安全速率最大化(Secrecy Rate Maximization,SRM)。由于SRM问题是一个非凸的优化问题,为了有效解决该问题,文中采用分步优化方法将原始问题转化成两个子问题。首先,设计一种双层优化算法来优化波束成形矩阵和人工噪声协方差矩阵,其中,外层优化问题使用一维搜索方法解决,内层优化问题使用半定松弛技术解决;然后,固定波束成形矩阵和人工噪声协方差矩阵,再次使用一维搜索方法求解功率分配因子。理论推导证明了内层优化问题总是存在秩为1的最优解,即使用的松弛技术是紧的。仿真结果表明,所提方法能将系统安全性能提升2~3倍。

Study on Secure Beamforming for Full-duplex Energy Harvesting Relaying System

The optimization of secrecy rate is studied in the full-duplex relay-eavesdropper channel in which the nodes harvest energy.For guaranteeing the secure communications,an artificial noise aided secure beamforming design is proposed under simultaneous wireless information and power transfer method.An optimization problem is considered aiming to maximize the secrecy rate(SRM)of the system by jointly optimizing the beamforming matrix,artificial noise covariance matrix and the power splitting ration at the relay subject to the transmission power and energy harvesting requirement for relay.Because this problem is a non-convex secrecy rate maximization problem,the objective problem is decoupled into two subproblems.First,this paper recasts this SRM as a two-level optimization problem to optimize the beamforming matrix and artificial noise covariance matrix.The outer optimization problem is solved by one-dimensional search,and the inner optimization problem is solved by semidefinite relaxation technique.Then,it fixes the value of beamforming matrix and artificial noise covariance matrix,and once again uses the one-dimensional search to solve the power splitting ration.Theoretical derivation proves that there always exists a rank-one optimal solution for the SDR problem,the relaxation technique adopted is tight.The simulation results show that the proposed method can effectively improve the security performance of the system by 2 to 3 times.