Simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) is becoming a prospective technology in realizing extremely low power transmission and seamless coverage for the sixth generation (6G) wireless communication era. Motivated by this, we study the secrecy performance of the STAR-RIS assisted non-orthogonal multiple access (NOMA) networks. To be more practical, we assume that all nodes suffer from residual hardware impairments (RHIs). To characterize the performance of the considered network, the analytical expressions of the secrecy outage probability (SOP) for NOMA users over the Nakagami- $m$ fading channels are derived. Meanwhile, the asymptotic behaviors of SOP at high signal-to-noise ratio (SNR) are also studied. The numerical results show that: 1) The existence of the RHIs reduces the secrecy performance of the network under consideration. 2) The increase in the number of configurable elements $K$ will improve the system secrecy performance.

This work studies a simultaneous wireless information and power transfer based downlink non-orthogonal multiple access (NOMA) network. The near user is equipped with a non-linear energy harvester, whose non-linear property is depicted by a piecewise linear model. An incremental cooperative NOMA (ICN) protocol is proposed to improve the performance of the considered network. Specifically, based on no more than 2-bit feedback from the far and near users, respectively, the network determines to work in the direct NOMA transmission (DNT), conventional point-to-point communications, or conventional cooperative NOMA (CCN) modes. The outage probabilities and throughput for both the far and near users are derived. Numerical results compare the differences among the proposed ICN, CCN, DNT and orthogonal multiple access protocols in terms of outage performance and system throughput, and exhibit the superior performance of the proposed ICN protocol.

This letter investigates a simultaneous wireless information and power transfer (SWIPT) based cooperative non-orthogonal multiple access (NOMA) system, where the near user close to the source node serves as a relay to help the far user. The near user adopts the power splitting (PS) protocol for harvesting energy and decoding the signals of both users. To ensure the user fairness, we propose a joint design for the power allocation coefficients and the PS factor to enhance the outage performance of the near user, and thereby to improve the system performance. Analytical expressions for the outage probabilities and diversity orders of both the far user and the near user are derived. Numerical results are exhibited to verify our analysis and further show that the proposed scheme significantly enhances the performance of the near user, and consequently enjoys a larger system throughput compared to the existing scheme.

In this letter, we propose a tag selection scheme to enhance the security transmission in a passive backscatter communication system with multiple tags and one eavesdropper, and analyze the secrecy outage probability (SOP). In particular, considering a practical non-linear energy harvesting model, we first determine the optimal dynamic reflection coefficient to maximize the power of the backscattered signal while satisfying the energy-causality constraint of tags, and then select the tag that can maximize the instantaneous secrecy capacity. The closed-form analytical expression of the SOP corresponding to the proposed tag selection scheme over the independent but not necessarily identically distributed Rayleigh fading channels is derived and the diversity gain is analyzed. Numerical simulations corroborate the theoretical analysis and exhibit the superior performance of the proposed scheme compared to other schemes.

With the development of the mobile communication and intelligent information technologies, the intelligent transportation systems driven by the sixth generation (6G) has many opportunities to achieve ultralow latency and higher data transmission rate. Nonetheless, it also faces the great challenges of spectral resource shortage and large-scale connection. To solve the above problems, non-orthogonal multiple access (NOMA) and cognitive radio (CR) technologies have been proposed. In this regard, we study the reliable and ergodic performance of CR-NOMA assisted intelligent transportation system networks in the presence of imperfect successive interference cancellation (SIC) and non-ideal channel state information. Specifically, the analytical expressions of the outage probability (OP) and ergodic sum rate (ESR) are derived through a string of calculations. In order to gain more insights, the asymptotic expressions for OP and ESR at high signal-to-noise ratio (SNR) regimes are discussed. We verify the accuracy of the analysis by Monte Carlo simulations, and the results show: i) Imperfect SIC and channel estimation errors (CEEs) have negative impacts on the OP and ESR; ii) The OP decreases with the SNR increasing until convergence to a fixed constant at high SNR regions; iii) The ESR increases with increasing SNR and there exists a ceiling in the high SNR region.

In this letter, we propose an opportunistic source selection based two-way cooperative ambient backscatter communication (CABC) system, in which two sources convey information to each other via a decode-and-forward enabled relay node and the tag embedded in the relay utilizes the power difference produced by the two hops to accomplish backscatter communication (BC) concurrently. The proposed system can achieve the bidirectional information flow for both the relaying transmission (RT) and BC at the same time. The analytical results of the outage probabilities for both RT and BC are derived. Numerical results verify the theoretical analysis and show that the proposed scheme can increase the throughput of the BC while maintaining the same power consumption and not degrading the performance of RT, compared to the existing one-way CABC system.