This paper investigates the secrecy communications of a downlink wireless-powered cooperative non-orthogonal multiple access (NOMA) system with a source node, a relay, a pair of near and far users, and an eavesdropper (Eve). A wireless-powered relay assists the transmission from the source to the far user, and the Eve intends to wiretap the confidential message transmitted to the near user. We propose a dynamic power allocation and friendly jamming based secure transmission scheme. Specifically, the optimal power allocation factors at the source node for the paired NOMA users are obtained to guarantee the perfect successive interference cancellation performance and improve the transmission reliability of the pair of NOMA users. In the direct transmission phase, the source transmits a superimposed signal to the near user and the wireless-powered relay, and the far user serves as a friendly jammer to emit artificial noise to confuse the Eve. In the cooperative transmission phase, the relay utilizes the harvested energy to assist the transmission to the far user. By applying the Gaussian-Chebyshev and Gaussian-Laguerre quadratures, closed-form expressions for the secrecy outage probability of the near user and the connection outage probability of the far user are derived. Simulation results verify the correctness of our theoretical analysis. The superiority of the proposed scheme is also demonstrated for improving the secrecy performance, as compared to the existing cooperative NOMA schemes. © 2024 IEEE.

In this paper, we investigate the robust resource allocation and relay selection in wireless-powered full-duplex (FD) multi-relay networks, where a self-energy recycling relay node is selected from N candidates to assist the transmission from the source node to the destination node. With imperfect channel state information (CSI), an optimization problem is formulated to minimize the outage probability, and the optimal values of time and power allocation coefficients are obtained. Moreover, on the basis of the optimal time and power allocation coefficients, a two-stage relay selection scheme is proposed. In addition, the analytical expressions of outage probability and diversity order are derived to characterize the performance of the proposed scheme. Finally, simulation results are provided to verify the theoretical analysis and demonstrate the effectiveness of the proposed scheme in different scenarios. © 2023 IEEE.

This paper investigates a simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) assisted downlink non-orthogonal multiple access (NOMA) system, consisting of a base station (BS), a STAR-RIS, a transmission user and a reflection user, where STAR-RIS uses mode switching protocols. Under the proposed transmission model, the base station serves the two users via the STAR-RIS and a direct link exists from the base station to the reflection user. By using the Beaulieu series, the statistical property of the Nakagami-m fading cascaded channel is characterized. Based on this, closed-from expressions of outage probability and diversity order for the reflection user and transmission user are obtained, respectively. In addition, to ensure the maximum gain in system throughput, a component allocation scheme is proposed, and the optimal allocation interval between the transmission and reflection components is obtained. Numerical results verify the theoretical analysis and demonstrate the superiority of the proposed scheme in terms of outage probability and system throughput compared to existing schemes. © 2023 IEEE.

This paper proposes transmission mode switching for the simultaneous wireless information and power transfer enabled non-orthogonal multiple access (NOMA) systems with imperfect successive interference cancellation (SIC) and random user locations. The system is composed of a base station (BS) and multiple near and far users. The location of the near and far users follows a homogeneous Poisson point process. The near users adopt incremental relay protocol and the simultaneous wireless information and power transfer enabled system can switch between cooperative and non-cooperative transmission mode based on 1-bit feedback of the far users. Due to the decoding errors of practical SIC process, imperfect SIC is considered at the near user. Under the proposed mode switching scheme, the closed-form expressions for the outage probability and system throughput are obtained considering random user locations. Numerical results demonstrate the correctness of the theoretical analysis and show that the proposed scheme outperforms the traditional cooperative and non-cooperative NOMA schemes in terms of outage and throughput performance. © 2023 IEEE.

This paper proposes a novel video caching and transmission scheme in cache and full-duplex (FD) relay assisted wireless networks, where parts of the contents to be requested are stored in the local caches of relay nodes. To provide diversified viewing qualities to multimedia users, we combine scalable video coding (SVC) with edge caching in this work. With the aid of SVC, each video is encoded into multiple layers, including a base layer (BL) and multiple enhancement layers (ELs). The super layers, each of them containing one BL and several successive ELs, are cached and transmitted to users to bring diversified viewing experiences. Under the proposed caching and transmission policies, we conduct comprehensive performance analysis. By using the tool of stochastic geometry, we obtain the analytical expressions for successful transmission probabilities (STPs) in cache hit and miss cases. After obtaining STPs, the cache-aided data rate (CADR) is derived. Simulation results validate the derived STPs and demonstrate that the proposed SVC-based random caching scheme with FD relays has great potential to increase the data transmission rate. © 2023 IEEE.

This paper studies the secure communications of a wireless-powered full-duplex cooperative non-orthogonal multiple access (CoNOMA) system with a source node, a group of near users, a far user and an external eavesdropper. In particular, the eavesdropper intends to wiretap the transmitted signals from the source. Two of the near users are picked up, served as a wireless-powered relay and a wireless friendly jammer, respectively. We propose a user selection and cooperative jamming based secure transmission scheme. Specifically, the source transmits a superimposed signal to the selected near user. The selected near user, who is employed as a relay, can harvest energy from the radio frequency signals and decode the information simultaneously. The harvested energy are then utilized to forward the signal to the far user. The jammer also collects energy from the source, and emits artificial noise by using the harvested energy to confuse the eavesdropper. Based on the proposed scheme, the closed-form expression for secrecy outage probability (SOP) and effective secrecy throughput (EST) are derived. The correctness of our theoretical analysis is verified by Monte-Carlo simulations, and the superiority of the proposed scheme in improving the system secure performance is also validated. © 2023 IEEE.

Due to the different propagation characteristics such as large path loss and susceptibility to blockage, the coverage of mmWave base stations (BSs) is more irregular and complex than that of the legacy wireless frequency band. As a consequence, the traditional network planning method will not satisfy the demand for mmWave system. To address this issue, this paper proposes a predicting algorithm for the layout of mmWave BSs leveraging the Sub-6GHz band. Specifically, the mapping relationship between the channel information in the Sub-6GHz band and the layout of mmWave BSs is utilized. To approximate this implicit and highly nonlinear mapping relationship, a deep neural network (DNN) is employed, leveraging the strong approximation capability of DNN. To train the DNN by the training data set, an integer programming (IP) algorithm is used as a supervisor, which obtains the BSs layout outcomes by solving an optimization problem. Moreover, to improve the generalization and scalability performance of the proposed scheme in large-scale scenarios, the candidate BS locations are clustered by environment features in addition to the wireless features. Simulation results show that the proposed algorithm can achieve a near-optimal network coverage even only Sub-6 GHz channel information is used. And the time consumption is less than 0.3% compared with the reference algorithm. © 2023 IEEE.

In this paper, we investigate the physical layer security for simultaneous transmission and reflection (STAR) reconfigurable intelligent surface (RIS) aided systems. We consider a more practical case where multiple eavesdroppers can wiretap the transmitted signals from the access point (AP) to the legitimate users located in the transmission and reflection regions, respectively. An artificial noise (AN) aided secrecy transmission scheme is then proposed, aiming to improve the secrecy performance. The transmit beamforming and AN vectors of AP as well as the transmission and reflection coefficients are jointly optimized to maximize the sum secrecy rate. To effectively solve the formulated problem, it is firstly divided into two subproblems, and then the methods of semi-definite relaxation and Sion's minimax theorem are employed to deal with the subproblems. By alternatively solving the sub-problems, the optimal solutions are obtained. Simulation results demonstrate the effectiveness of the proposed scheme compared to the conventional scheme without AN and STAR-RIS, and also bring useful insights into the design of secrecy communications in STAR-RIS aided systems with multiple eavesdroppers. © 2023 IEEE.

In this paper, we study a distributed reconfigurable intelligent surface-aided downlink multiple-input multiple-output non-orthogonal multiple access systems with random distributed users, where the signal alignment can be achieved within the paired users by controlling discrete phase shifts. In particular, a unified precoder and decoder are provided to cancel inter-cluster interference. To evaluate the performance of proposed framework, the near and far users' channel statistics with Nakagami-m fading are derived. Further, the approximate expressions of average outage probability are obtained by utilizing the proposed channel statistics, and the corresponding diversity orders can also be obtained to acquire more insights. Finally, simulation results reveal that not only discrete phase shifts design by selecting a 3bit resolution can realize the near optimal performance but also the diversity gain can be significantly improved by increasing the number of reflection elements. © 2022 IEEE.