In this paper, we investigate the covert communication performance and sensing performance of integrated sensing and communication (ISAC) systems enhanced by simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS). A novel non-orthogonal multiple access (NOMA) enabled covert framework is proposed, where the covert transmission can be enhanced by eliminating the interference of public signals and sensing signals at the covert user. The large system analytic estimation is employed to effectively decouple the correlation of the warden’s channel fading gains and derive a closed-form expression for the minimum average detection error probability of the warden. Both sensing and covert rate optimization problems are investigated through jointly designing base station transmit beamforming and STAR-RIS passive beamforming. To optimize sensing performance, we aim at minimizing the Cramér-Rao bound (CRB) while satisfying the covert rate requirement. Conversely, when maximizing the covert rate, the CRB is incorporated as a constraint in the sensing. To address these challenging optimization problems, an iterative algorithm based on penalty methods and semidefinite programming are proposed to obtain the transmit beamforming and the beamforming of STAR-RIS. Simulation results indicate that the CRB and covert rate of the proposed ISAC systems, assisted by STAR-RIS and NOMA, outperform the ISAC systems enhanced by orthogonal multiple access and conventional RIS.
Zheng Yang, Haoyang Li, Gaojie Chen et al.· IEEE Transactions on Wireles...· 0 citations
In this paper, we consider a backscatter communication (BackCom)-assisted uplink pinching-antenna system in Internet of Things (IoT), where a non-energy-constrained IoT device provides radio frequency signals to support multiple energy-constrained IoT devices, with multiple pinching antennas deployed on a waveguide. We formulate a joint optimization problem to select a energy-constrained device and simultaneously design its power reflection coefficient and pinching antenna locations. The objective is to maximize the achievable rate of the selected device, subject to the quality of service requirements of the non-energy-constrained device, minimum energy harvesting at energy-constrained devices, and collision-free constraints imposed on the pinching antennas. The problem is non-convex and analytically intricate, due to the strong interdependence among device selection, power reflection coefficients, and antenna positions. To overcome these challenges, we propose a block coordinate descent-based successive convex approximation algorithm that iteratively transforms the original non-convex problem into a series of convex subproblems that can be solved efficiently. Additionally, we analyze a special case with a single pinching antenna, deriving the optimal antenna location along with an approximate outage probability expression and the corresponding diversity order. Simulation results demonstrate that the proposed system achieves higher achievable rates, lower outage probability, and improved diversity gain compared to conventional uplink fixed-antenna systems.
Zheng Yang, Jingjing Cui, Gaojie Chen et al.· IEEE Transactions on Wireles...· 0 citations
