In this paper, we investigate the problem of joint power allocation and collaborative beamforming for physical layer security in underlay cognitive radio non-orthogonal multiple access relay systems. We consider two relaying schemes, i.e., amplify-and-forward and decode-and-forward, with the goal of maximizing the secrecy rate for the central user subjective to the transmit power constraint at the source node, individual transmit power constraints at relays, rate requirements at the cognitive users and the interference power constraint at the primary receiver. The optimization problems are nonconvex and hard to solve. We propose an efficient iterative algorithm by the constrained concave–convex procedure to solve the nonconvex optimization problems. For a comparison, we provide another method, namely alternating optimization (AO) algorithm. In addition, simulations are provided to show the superiority of our proposed methods with comparison to the AO algorithm and traditional orthogonal multiple access schemes.

在本文中，我们研究了底层认知无线电非正交多址中继系统中物理层安全的联合功率分配和协作波束成形问题。我们考虑两种中继方案，即放大转发和解码转发，目标是最大化中心用户的保密率，受源节点的发射功率约束，中继的个体发射功率约束，认知用户的速率要求和主接收机的干扰功率限制。优化问题是非凸的，很难解决。我们通过约束凹凸过程提出了一种有效的迭代算法来解决非凸优化问题。为了进行比较，我们提供了另一种方法，即交替优化 (AO) 算法。