Secure Transmission of Integrated Sensing and Communication Systems With Eavesdropper: From Mainlode to Sidelode Deployment

In this article, we explore the security transmission issues of Multiple Input Single Output (MISO) integrated sensing and communication (ISAC) system, focusing on the communication security transmission in radar-embedded communication systems. This system simultaneously detects and tracks target when transmitting communication information to downlink users. However, in the presence of hostile eavesdropping devices, the communication transmission security of ISAC system cannot be guaranteed. We have considered two common deployment scenarios: deployment of eavesdropper within the main lobe (DEML) and deployment of eavesdropper within the side lobes (DESL). In DEML scenario, the sensing target is considered as eavesdropper, we introduce cooperative jamming (CJ) device to disrupt the eavesdropper and ensure the transmission security. Through a combination of traversal search and a series of semidefinite relaxation methods, we optimize the covariance matrices of the transmission signal and CJ signal, ensuring both sensing and communication performance requirements while enhancing the overall system secrecy rate. In DESL scenario, we mainly focus on the situation where the eavesdropper is located on the transmission channel between the ISAC system and the user, the intelligent reflecting surfaces (IRS) is proposed to enhance the ISAC system communication security. We employ a combined approach of alternating optimization and fractional programming to jointly solve for the covariance matrix of the transmission signal and the reflection phase shift matrix, optimizing the system's secrecy rate. The numerical results validate the effectiveness of the proposed algorithms under both deployment scenarios and compare the advantages and disadvantages of the two methods. The results demonstrate that the designs of both CJ and IRS under the two deployment scenarios significantly enhance the system's secure communication rate, and the IRS scheme can provide higher performance gains, which is attributed to the IRS's rational utilization of energy losses in other directions.