Intelligent reflecting surfaces (IRS) has become a transformative technology to enable smart, reconfigurable, and cost-efficient wireless communication environments. Prior work has primarily focused on distributed IRS models, which require joint IRS design for both energy transfer and information transfer. This approach requires complex phase-shift reconfiguration and leads to suboptimal resource utilization. This work is a novel attempt to consider dedicated IRS for energy harvesting (EH) and information transfer in wireless powered communication networks (WPCN). Specifically, IRS-I is used to assist EH in the downlink (DL) at devices through a power station. A separate IRS-II is installed between devices and the data sink (DS) for information transfer using non-orthogonal multiple access (NOMA). We investigated a non-linear EH model alongside dedicated IRS deployment, surpassing the limitations of the simplified linear EH approach. Our objective is to maximize the sum-rate (SR) problem while optimizing the active beamforming vector, transmit time, power allocation, and IRS phase-shifts considering NOMA-enabled WPCN. This non-convex optimization problem is solved using the proposed alternating optimization (AO) algorithm and simultaneously optimizes the resource allocation and IRS phase-shifts using semidefinite relaxation. The numerical results demonstrate the advantages of integrating dedicated IRS into WPCNs and show the notable performance gains of the proposed algorithm over benchmark schemes.

Non-orthogonal multiple access (NOMA) offers a promising solution to enhance spectral efficiency and support massive connectivity in future wireless systems. However, most NOMA research assumes ideal conditions, neglecting the impact of imperfect successive interference cancellation (SIC) and relying on conventional decoding order based on channel gains. In this work, we address these limitations by considering all possible decoding order combinations for a two-user NOMA system and developing a systematic approach for joint optimization of decoding order and power allocation. Our goal is to maximize the sum-rate and fairness under realistic conditions, including imperfect SIC. We formulate a joint optimization problem to maximize sum-rate while ensuring each user's data rate meets a minimum quality-of-service (QoS) requirement, and tackle the max-min fairness problem to ensure fairness. The optimal decoding order is proven analytically, and global optimal power allocation solutions are derived. Extensive simulations validate our theoretical results, showing that the proposed scheme outperforms conventional methods in sum-rate and fairness.

The advancement of industrial Internet of Things (IIoT) networks has brought challenges in terms of connectivity, efficient spectrum usage, and low latency. To tackle these challenges, advanced multiple access techniques have been developed. Non-orthogonal multiple access (NOMA) is a promising multiple access technique due to its high energy efficiency and fairness for devices. However, NOMA has inherent security issues due to wireless transmission and complex successive interference cancellation (SIC) based decoding, which can negatively impact system performance. Furthermore, achieving perfect SIC is also a challenging task due to implementation complexity. This study investigates the effects of imperfect SIC in a dual-device cooperative NOMA system. Our system includes direct links between the source and devices and uses both decode-and-forward and amplify-and-forward relays. The overall objective is to optimize decoding order and power allocation coefficients in order to maximize the near or priority device’s secrecy rate while meeting the quality-of-service (QoS) requirements of the far or normal device. Observing the underlying optimization problems to be non-convex, a low-complexity algorithm yielding optimal solutions is developed. Our findings reveal how imperfect SIC can impact massive access systems and secrecy performance. Extensive simulations provide novel design insights into the achievable secrecy rate and optimal power allocation coefficients. We also explore the trade-off between the priority device’s secrecy rate and the normal device’s rate, along with the impact of residual interference. Finally, our proposed solution has been shown to significantly improve the QoS-constrained secrecy rate of priority devices when compared to relevant benchmarks.

Rate-splitting multiple access (RSMA) is a technique that is widely used in next-generation wireless systems to efficiently manage multiple users. RSMA splits the transmission into two parts using rate splitting, which increases spectral efficiency. However, this technique also makes a portion of the transmission vulnerable to eavesdropping, which can compromise information security. This vulnerability is not limited to external eavesdroppers but also includes internal eavesdropping among users who share the same transmission. Therefore, there is an increasing need to develop secure RSMA systems to address these critical security issues among untrusted users. This paper focuses on a single-antenna RSMA downlink system with multiple untrusted users undergoing Rician channel fading. In this novel system framework considered for performance analysis, each user interprets its own common and private streams while attempting to eavesdrop on the private streams of other users. We evaluate the system-level performance in practical settings involving line-of-sight (LoS) paths using the Rician channel model and derive a tight closed-form approximate expression of the ergodic secrecy rate. Finally, we conduct numerical simulations to validate the theoretical analysis and provide valuable insights into the critical system parameters that impact the achievable ergodic secrecy performance of the RSMA system with untrusted users.

Non-Orthogonal Multiple Access (NOMA) is a wireless communication technique that uses the Successive Interference Cancellation (SIC) strategy to achieve high efficiency. However, SIC can pose security risks in an untrusted NOMA environment where users can suffer from internal eavesdropping. In this research paper, we propose security solutions for downlink NOMA transmission involving two untrusted user terminals and imperfect SIC. Specifically, we investigate the ergodic secrecy rate performance in NOMA for two user terminals against mutual eavesdropping. To achieve the maximum weighted ergodic sum secrecy rate of the system while meeting the quality of service (QoS) requirements of both user terminals, we formulate an optimization problem for power allocation. Our solution approach considers a decoding order that yields the best possible outcome and employs an iterative method to obtain the optimal power allocation. Simulation results confirm the analytical claims and provide key insights on the optimal design parameters. Lastly, we numerically demonstrate that our proposed power control and decoding order design outperforms the benchmark schemes in terms of weighted ergodic sum secrecy rate performance.

Non-orthogonal multiple access (NOMA) has been recognized as a promising multiple access technique for enhanced spectral efficiency in the current and next-generation wireless networks. In this paper, we examine a realistic NOMA model where users, assisted by a regenerative relay, cannot be fully trusted. We address the challenge of ensuring secure access for these users while accounting for the error propagation in successive interference cancellation (SIC) during the decoding process. For such, we formulate and solve two optimization problems, viz. maximizing the minimum secrecy rate of the users and maximizing the sum secrecy rate of the users, while accounting for SIC errors and the constraint on the power budget. For each case, we derive the optimal power allocation solution to achieve positive secrecy rates despite imperfect SIC. Simulation results provide key insights on the obtained secrecy rates and power allocations, factoring in residual interference. The joint optimal solution for the decoding order and power allocation is compared with different benchmark schemes: optimal decoding order and equal power allocation, fixed decoding order and equal power allocation, fixed decoding order and optimal power allocation, and optimal decoding order and channel-based power allocation. Our proposed framework demonstrates average performance gains of about 47.62 dB, 50.79 dB, 54.02 dB and 39.83 dB over these schemes and, hence, the fact that the proposed framework can substantially improve the secrecy performance.

The security of confidential information associated with devices in the industrial Internet of Things (IIoT) network is a serious concern. This article focuses on achieving a non orthogonal multiple access (NOMA)-enabled secure IIoT network in the presence of untrusted devices by jointly optimizing resources, such as decoding order and power allocated to devices. Assuming that the devices are resource-constrained for performing perfect successive interference cancellation, we characterize the residual interference at receivers with the linear model. Firstly, considering all possible decoding orders in an untrusted scenario, we obtain secure decoding orders that are feasible to obtain a positive secrecy rate for each device. Then, under the secrecy fairness criterion, we formulate a joint optimization problem of maximizing the minimum secrecy rate among devices. Since the formulated problem is non-convex and combinatorial, we first obtain the optimal secure decoding order and then solve it for power allocation by analyzing Karush–Kuhn–Tucker points. Thus, we provide the closed-form global-optimal solution of the formulated optimization problem. Numerical results validate the analytical claims and demonstrate that the conventional decoding order and assigning more power allocation to weak devices, as presumed in many NOMA works, is not an optimal strategy from the secrecy fairness viewpoint. Also, average percentage gain of about 22.75%, 50.58%, 94.59%, and 98.16%, respectively, is achieved by jointly optimized solution over benchmarks ODEP (optimal decoding order, equal power allocation), ODFP (optimal decoding order, fixed power allocation), FDEP (fixed decoding order, equal power allocation), and FDFP (fixed decoding order, fixed power allocation).

Non-orthogonal multiple access (NOMA) has been recognized as a promising multiple access technique to improve the spectral efficiency of the fifth-generation (5G) and beyond networks. However, the successive interference cancellation (SIC) based decoding used at the receivers makes NOMA prone to critical security risks. In this paper, we consider a regenerative relay-assisted dual-user downlink NOMA communication model. To ensure the robustness of the model, we also take into account the error propagation in SIC occurring in the decoding process. Our design goal being to provide security to both users, we propose an optimal power management strategy, so as to maximize the secrecy rate of the users under the impact of imperfect SIC. The optimal power allocation solution is obtained such that positive secrecy rate is achieved at both of the end receivers, while accounting for SIC errors. Analytical expressions of the secrecy rates are derived to analyze the secrecy performance. Simulation results are also presented, and provide key insights on the obtained secrecy rate and power allocation coefficients with residual interference. The achieved gains prove that the proposed model can substantially improve the secrecy performance.

Non-orthogonal multiple access (NOMA) has emerged as an enabling solution for 5th generation and beyond networks, but the often-neglected issues due to successive interference cancellation (SIC) based decoding might seriously hamper its performance. In this paper, we study a downlink NOMA system with cooperative half-duplex relaying with imperfect SIC, where the base station is communicating with two untrusted users with the aid of a trusted decode-and-forward relay while also considering the availability of direct links from the source. An optimization problem is formulated for maximizing the secrecy rate of the near user while fulfilling the quality-of-service requirements of the far user. The optimal power allocation solution is derived while considering the impact of SIC error. The simulation results illustrate the exactness of the theoretical analysis alongside insightful discussions to investigate the impact of imperfect SIC.

Non-orthogonal multiple access (NOMA) has been considered as a promising solution to provide spectrally efficient communications in the 5th generation and beyond networks. Cooperative communication, on the other hand, helps in improving the coverage and reliability of the communications. In this paper, we consider a cooperative NOMA communication system with two untrusted users and a trusted amplify-and-forward relay. Maximization of the secrecy rate of the near user while considering the service requirements of the far user is tackled. Closed-form expressions are obtained for the optimal power sharing between the source and the relay, along with the optimal power allocation for both users. Numerical results are also provided, which verify the exactness of the theoretical analysis and provide insights on the design of secure NOMA-based cooperative communication networks.

Non-orthogonal multiple access (NOMA) has been recognized as one of the key enabling technologies for future generation wireless networks. Sharing the same time-frequency resource among users imposes secrecy challenges in NOMA in the presence of untrusted users. This paper characterizes the impact of user-pair selection on the secrecy performance of an untrusted NOMA system. In this regard, an optimization problem is formulated to maximize the secrecy rate of the strong user while satisfying the quality of service (QoS) demands of the user with poorer channel conditions. To solve this problem, we first obtain optimal power allocation in a two-user NOMA system, and then investigate the user-pair selection problem in a more generalized four user NOMA system. Extensive performance evaluations are conducted to validate the accuracy of the proposed results and present valuable insights on the impact of various system parameters on the secrecy performance of the NOMA communication system.

To develop a cyber-physical artificial intelligence enabled wireless network, it is essential to support unprecedented high throughput and efficient spectrum utilization in a practically unknown channel. In this regard, we need to investigate the design aspects of the network exploiting deep learning-based non-orthogonal multiple access (NOMA) for a model-free environment. In this work, a model-free deep learning algorithm based on deep deterministic policy gradient is proposed that provides a continuous course of actions under the optimal policy for an untrusted NOMA network. Utilizing the concept of physical layer security, we focus on maximizing the sum secrecy rate of the system in terms of decoding order and transmitting power allocation to users under the limited energy constraint at the base station. Via extensive simulations, while training, we measure the performance of the deep learning algorithm in terms of cumulative sum secrecy rate, convergence rate and stability. Also, after the training, we obtain various insights on the performance of the obtained optimal policy by varying the independent system parameters and compare the algorithm against a benchmark that provides the improvement of nearly 55% in the noisy channel.

Non-orthogonal multiple access (NOMA) has come to the fore as a spectral-efficient technique for fifth-generation and beyond communication networks. We consider the downlink of a NOMA system with untrusted users. In order to consider a more realistic scenario, imperfect successive interference cancellation is assumed at the receivers during the decoding process. Since pair outage probability (POP) ensures a minimum rate guarantee to each user, it behaves as a measure of the quality of service for the pair of users. With the objective of designing a reliable communication protocol, we derive the closed-form expression of POP. Further, we find the optimal power allocation that minimizes the POP. Lastly, numerical results have been presented which validate the exactness of the analysis, and reveal the effect of various key parameters on achieved pair outage performance. In addition, we benchmark optimal power allocation against equal and fixed power allocations with respect to POP. The results indicate that optimal power allocation results in improved communication reliability.

This paper presents a novel joint transmit power sharing and relay placement scheme for decode-and-forward relay assisted secure communication to a legitimate user in presence of external eavesdropper. Observing that secrecy outage minimization problem for the trusted user is non-convex, key insights on optimal power sharing between source and relay are first presented to derive an equivalent single variable problem. Next, tight analytical bounds for optimal relay placement are discoursed to ultimately come up with a computationally-efficient jointly global optimization algorithm. Finally, selected numerical results validate analysis, present key insights, and demonstrate performance gains of around 30dB over benchmark schemes.

Non-orthogonal multiple access (NOMA) serves multiple users simultaneously via the same resource block by exploiting superposition coding at the transmitter and successive interference cancellation (SIC) at the receivers. Under practical considerations, perfect SIC may not be achieved. Thus, residual interference (RI) occurs inevitably due to imperfect SIC. In this work, we first propose a novel model for characterizing RI to provide a more realistic secrecy performance analysis of a downlink NOMA system under imperfect SIC at receivers. In the presence of untrusted users, NOMA has an inherent security flaw. Therefore, for this untrusted users' scenario, we derive new analytical expressions of secrecy outage probability (SOP) for each user in a two-user untrusted NOMA system by using the proposed RI model. To further shed light on the obtained results and obtain a deeper understanding, a high signal-to-noise ratio approximation of the SOPs are also obtained. Lastly, numerical investigations are provided to validate the accuracy of the desired analytical results and present valuable insights into the impact of various system parameters on the secrecy rate performance of the secure NOMA communication system.

The amalgamation of non-orthogonal multiple access (NOMA) and physical layer security is a significant research interest for providing spectrally-efficient secure fifth-generation networks. Observing the secrecy issue among multiplexed NOMA users, which is stemmed from successive interference cancellation based decoding at receivers, we focus on safeguarding untrusted NOMA. Considering the problem of each user’s privacy from each other, the appropriate secure decoding order and power allocation (PA) for users are investigated. Specifically, a decoding order strategy is proposed which is efficient in providing positive secrecy at all NOMA users. An algorithm is also provided through which all the feasible secure decoding orders in accordance with the proposed decoding order strategy can be obtained. Further, in order to maximize the sum secrecy rate of the system, the joint solution of decoding order and PA is obtained numerically. Also, a sub-optimal decoding order solution is proposed. Lastly, numerical results present useful insights on the impact of key system parameters and demonstrate that average secrecy rate performance gain of about 27 dB is obtained by the jointly optimized solution over different relevant schemes.

Spectrally-efficient secure non-orthogonal multiple access (NOMA) has recently attained a substantial research interest for fifth generation development. This work explores crucial security issue in NOMA which is stemmed from utilizing the decoding concept of successive interference cancellation. Considering untrusted users, we design a novel secure NOMA transmission protocol to maximize secrecy fairness among users. A new decoding order for two users' NOMA is proposed that provides positive secrecy rate to both users. Observing the objective of maximizing secrecy fairness between users under given power budget constraint, the problem is formulated as minimizing the maximum secrecy outage probability (SOP) between users. In particular, closed-form expressions of SOP for both users are derived to analyze secrecy performance. SOP minimization problems are solved using pseudoconvexity concept, and optimized power allocation (PA) for each user is obtained. Asymptotic expressions of SOPs, and optimal PAs minimizing these approximations are obtained to get deeper insights. Further, globally-optimized power control solution from secrecy fairness perspective is obtained at a low computational complexity and, asymptotic approximation is obtained to gain analytical insights. Numerical results validate the correctness of analysis, and present insights on optimal solutions. Finally, we present insights on global-optimal PA by which fairness is ensured and gains of about 55.12%, 69.30%, and 19.11%, respectively are achieved, compared to fixed PA and individual users' optimal PAs.

In resource allocation for secure cooperative communication systems, along with power allocation, relay placement also has equal importance in improving the system performance. In this paper, we study the joint optimization of relay placement and power allocation to minimize the secrecy outage probability (SOP) for a four-node cooperative system with a trusted randomize-and-forward relay in the presence of an external eavesdropper. Initially, we derive the expression of SOP, and then formulate an optimization problem to minimize SOP under given power budget and relay placement (RP) constraints. By providing analytical insights on power allocation (PA) between source and relay, we obtain closed form expressions of optimal PA (OPA) for a given RP that minimizes the SOP. Next, we propose a low complexity algorithm to obtain the near-optimal RP (ORP) for a given PA. Finally, we obtain optimal SOP with joint RP and PA. Numerical results present validation of analytical SOP through Monte Carlo simulations, optimal PA for a given RP, optimal RP for a given PA, and joint PA and RP for a given secrecy threshold rate. Finally, we highlight the significant performance gains achieved by the joint design over the conventional scheme.

In this paper, we consider the problem of resource allocation in the orthogonal frequency division multiple access system with single source and M untrusted users in presence of a friendly jammer. The jammer is used to improve either the weighted sum secure rate or the overall system fairness. The formulated optimization problem in both the cases is a mixed integer non-linear programming problem, belonging to the class of NP-hard. In the sum secure rate maximization scenario, we decouple the problem and first obtain the subcarrier allocation at source and the decision for jammer power utilization on a per-subcarrier basis. Then, we do joint source and jammer power allocation using primal decomposition and alternating optimization framework. Next, we consider fair resource allocation by introducing a novel concept of subcarrier snatching with the help of jammer. We propose two schemes for jammer power utilization, called proactively fair allocation (PFA) and on-demand allocation (ODA). PFA considers equitable distribution of jammer power among the subcarriers, while ODA distributes jammer power based on the user demand. In both cases of jammer usage, we also present suboptimal solutions that solve the power allocation at a highly reduced complexity. Asymptotically optimal solutions are derived to benchmark optimality of the proposed schemes. We compare the performance of our proposed schemes with equal power allocation at source and jammer. Our simulation results demonstrate that the jammer can indeed help in improving either the sum secure rate or the overall system fairness.

We consider the problem of resource allocation among M untrusted mobile users with a source and a friendly jammer in a secure OFDMA system. The jammer can be utilized to improve either the sum secure rate or the fairness of the system. Since the optimization problem is combinatorial and belongs to the class of NP hard, we propose two independent suboptimal schemes to solve the resource allocation problem. Our simulation results demonstrate that the use of jammer helps trade between secure rate and fairness performance.