Multi-Beam Index Modulation with Cooperative Legitimate Users Schemes Based on Frequency Diverse Array

In this paper, a novel multi-beam transmission scheme is proposed to enhance physical layer (PHY) security. This scheme utilizes index modulation (IM) based on frequency diverse array (FDA) beamforming with cooperative legitimate users (LUs). By leveraging IM based on FDA, the indices associated with multiple LUs are directly used as additional sources to transmit information. Using this scheme, the confidential messages can be retrieved only if all the index information and the corresponding symbols are obtained. This adds an extra level of PHY security hence reduces the possibility of information interception by eavesdroppers (Eves). Here instead of maximizing the secrecy rate, we propose a minimum message transmission power criterion to design the FDA beamforming vector, subject to prescribed minimum received power at each of the LUs, in addition to the orthogonality constraints of the remaining LUs. This provides a reliable and accurate transmission assurance for the LUs to obtain the corresponding messages under minimum message transmission power. To further deteriorate the quality of the received signals at Eves, we also add artificial noise (AN). Moreover, by elaborating the time-variant characteristics, we provide a new and more accurate perspective for the range-time dimension secure transmission. Numerical simulations confirm the effectiveness of the proposed scheme.