In this paper, we investigate beamforming design for cooperative secure transmission in cognitive two-way relay networks, where the cognitive transmitter (CT) with multiple antennas helps to forward the signals of two primary transmitters (PTs) and tries to protect the PTs from wiretapping by a single-antenna eavesdropper. With the objective of maximizing the secrecy sum rate (SSR) for PTs, we jointly design the beamforming matrix for the PTs' signals, the beamforming vector for the cognitive receiver (CR)'s signal, and the artificial noise (AN)'s beamforming matrix, under the quality of service constraint at the CR and the transmit power constraint at the CT. We propose the monotonic optimization-based algorithm to obtain the global optimal solution to the SSR maximization problem, which is a double-layer iterative algorithm and has very high complexity. To balance the complexity and the performance, we also propose a sequential parametric convex approximation-based single-layer iterative algorithm and a zero-forcing-based closed-form algorithm, the latter of which has the lowest complexity. Furthermore, we derive the asymptotic achievable secrecy sum rate when the CT transmit power goes to infinity. We present the numerical results to verify the effectiveness of our proposed algorithms.

中文翻译：

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认知双向中继网络中协作安全传输的波束成形

在本文中，我们研究了用于认知双向中继网络中协作安全传输的波束成形设计，其中具有多个天线的认知发射机（CT）有助于转发两个主要发射机（PT）的信号，并尝试保护PT免受窃听通过一个单天线窃听器。为了最大程度地提高PT的保密总和（SSR），我们共同设计了PT信号的波束形成矩阵，认知接收器（CR）信号的波束形成矢量和人工噪声（AN）的波束成形矩阵，在CR处的服务质量约束下，在CT处的发射功率约束下。我们提出了基于单调优化的算法来获得SSR最大化问题的全局最优解，这是一个双层迭代算法，具有很高的复杂度。为了平衡复杂性和性能，我们还提出了一种基于顺序参数凸近似的单层迭代算法和一种基于零强迫的闭式算法，后者具有最低的复杂度。此外，当CT发射功率达到无穷大时，我们得出了渐近可实现的保密和率。我们提出了数值结果，以验证我们提出的算法的有效性。当CT发射功率达到无穷大时，我们得出了渐近可达到的保密和率。我们提出了数值结果，以验证我们提出的算法的有效性。当CT发射功率达到无穷大时，我们得出了渐近可达到的保密和率。我们提出了数值结果，以验证我们提出的算法的有效性。