In this paper, an intelligent reflecting surface (IRS) assisted spectrum sharing underlay cognitive radio (CR) wiretap channel (WTC) is studied, and we aim at enhancing the secrecy rate of secondary user in this channel subject to total power constraint at secondary transmitter (ST), interference power constraint (IPC) at primary receiver (PR) as well as unit modulus constraint at IRS. Due to extra IPC and eavesdropper (Eve) are considered, all the existing solutions for enhancing secrecy rate of IRS-assisted non-CR WTC as well as enhancing transmission rate in IRS-assisted CR channel without eavesdropper fail in this work. Therefore, we propose new numerical solutions to optimize the secrecy rate of this channel under full primary, secondary users’ channel state information (CSI) and three different cases of Eve’s CSI: full CSI, imperfect CSI with bounded estimation error, and no CSI. To solve the difficult non-convex optimization problem, an efficient alternating optimization (AO) algorithm is proposed to jointly optimize the beamformer at ST and phase shift coefficients at IRS. In particular, when optimizing the phase shift coefficients during each iteration of AO, a Dinkelbach based solution in combination with successive approximation and penalty based solution is proposed under full CSI and a penalty convex-concave procedure solution is proposed under imperfect Eve’s CSI. For no Eve’s CSI case, artificial noise (AN) aided approach is adopted to help enhancing the secrecy rate. Simulation results show that our proposed solutions for the IRS-assisted design greatly enhance the secrecy performance compared with the existing numerical solutions with and without IRS under full and imperfect Eve’s CSI. And positive secrecy rate can be achieved by our proposed AN aided approach given most channel realizations under no Eve’s CSI case so that secure communication also can be guaranteed. All of the proposed AO algorithms are guaranteed to monotonic convergence.

中文翻译：

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通过智能反射表面实现安全认知无线电通信


本文研究了一种智能反射面（IRS）辅助频谱共享底层认知无线电（CR）窃听信道（WTC），目的是在二级发射机总功率约束下提高该信道中二级用户的保密率(ST)、主接收器 (PR) 处的干扰功率约束 (IPC) 以及 IRS 处的单位模数约束。由于考虑了额外的IPC和窃听者(Eve)，所有现有的提高IRS辅助的非CR WTC保密率以及在没有窃听者的情况下提高IRS辅助的CR信道传输速率的解决方案都失败了。因此，我们提出了新的数值解决方案，以在完整的主、次用户信道状态信息（CSI）和 Eve CSI 的三种不同情况下优化该信道的保密率：完整的 CSI、有界估计误差的不完美 CSI 和无 CSI。为了解决困难的非凸优化问题，提出了一种高效的交替优化（AO）算法来联合优化 ST 处的波束形成器和 IRS 处的相移系数。特别是，在AO每次迭代期间优化相移系数时，在完全CSI下提出了基于Dinkelbach的解决方案，结合逐次逼近和基于惩罚的解决方案，并在不完美Eve的CSI下提出了惩罚凸凹过程解决方案。对于No Eve的CSI案例，采用人工噪声（AN）辅助方法来帮助提高保密率。仿真结果表明，在完整和不完善的 Eve CSI 下，与现有的具有和不具有 IRS 的数值解决方案相比，我们提出的 IRS 辅助设计解决方案大大提高了保密性能。 考虑到大多数信道在 no Eve 的 CSI 情况下实现，我们提出的 AN 辅助方法可以实现正保密率，从而也可以保证安全通信。所有提出的 AO 算法都保证单调收敛。