Analog Beamforming for Wideband Secure Communications

Physical layer security (PLS), bolstered by multi-antenna beamforming, plays a vital role in securing information exchange. The evolution towards sixth-generation (6G) ultra-high speed communications has introduced distinctive challenges in ensuring secure transmissions, primarily due to the beamsplit effect caused by wideband transmission and the costly fabrication of a fully digital massive antenna array. Although previous studies have employed analog beamforming to achieve cost-effective secure transmission, their designs were limited to narrowband transmission. Against this backdrop, this paper proposes analog beamforming to enhance wideband PLS in the presence of beamsplit. Specifically, an alternating optimization framework is developed to efficiently design power allocation and the analog beamformer, maximizing the secrecy rate. Furthermore, we apply this framework to enable another fully-digital solution-facilitated analog beamforming design, which is achieved in two stages. Numerical results demonstrate the superiority of the proposed analog beamforming strategies in enhancing the secrecy rate of wideband transmission in a low-cost manner.