Reconfigurable Intelligent Surfaces Assisted Secure Multicast Communications

Reconfigurable Intelligent surface (RIS) can enhance the desired signals and suppress the undesired signals by adjusting the phase shifts of its reflector elements. This letter considers secure multicast communication with the help of RIS. A multiple-antennas transmitter multicasts the common messages to a group of single-antenna receivers in the presence of a single-antenna eavesdropper, where an RIS is set up to enhance the desired signals for the receivers and suppress the signals for the eavesdropper. First, the equivalent multicast and wiretap channels are analyzed, and a secrecy capacity maximization problem is formulated. Next, this letter obtains the necessary conditions that the optimal solution needs to satisfy. Finally, a logarithmic barrier algorithm is proposed to obtain a local optimal solution.