Improper Gaussian Signaling for STAR-RIS assisted Multiuser MISO Interference Channels

In this paper, we focus on simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) assisted multiuser multiple-input single-output (MISO) interference channels (ICs), where the RIS can serve the users in both forward and backward half-spaces at the same time by transmitting and reflecting incident signals. To suppress the inevitable inter-user interference, we adopt improper Gaussian signaling (IGS) and propose to jointly optimize the beamforming vectors of APs and the passive transmission and reflection coefficients of RIS to maximize the minimum achievable information rate among these users. In order to address the non-convex optimization problem, we provide an efficient iterative optimization algorithm to attain high-quality solutions. Numerical results demonstrate the superiority of IGS over conventional proper Gaussian signaling in STAR-RIS assisted MU-MISO ICs.