Secure Transmission in HARQ-Assisted Non-Orthogonal Multiple Access Networks

In this letter, we carry out the performance analysis of the simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) in the hybrid automatic repeat request (HARQ) assisted cognitive non-orthogonal multiple access (NOMA) networks, where a security-required user (SRU) with secure transmission requirements is paired with a quality of service (QoS)-sensitive user (QSU) with low delay requirements to perform NOMA. To characterize the performance of secure transmission, we derive the analytical expressions for connection outage probability (COP), average number of transmission (ANT) and secrecy outage probability (SOP) for the SRU in randomized retransmission NOMA (RR-NOMA) scheme, while a cognitive power allocation scheme is developed to meet QSU’s QoS requirement. To obtain deeper insights, the asymptotic expressions of COP and SOP are also derived. Furthermore, some significant results are drawn from simulations: 1) There exist a balance between COP and ANT, COP and SOP, which are denoted by the security-reliability balance (SRB) and reliability-delay balance (RDB), respectively. 2) HARQ is benefit to improve the RDB and SRB performance of SRU. 3) The increase in the number of STAR-RIS elements <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${K}$ </tex-math></inline-formula> improves the system reliability performance, while the secrecy performance deteriorates.

Nowadays the Internet of Things (IoT) still does not have global policies and standards to deal with the interaction and the development of applications. There are huge of security issues relevant to the application layer of IoT becoming very urgent. On the other hand, it is important for addressing the development of security algorithm to protect the IoT system from malicious attack. In this article, a fusion diversity scheme adopts maximum ratio combining (MRC) and selection combining (SC) schemes with trust management (TM) security algorithm are proposed. In MRC stage, specified parameters first extracted and they weighted by one estimation value before combined with the control information. The fused information generated from MRC passed forward to the SC in order to calculate the final trust value. What degree of the quality of service (QoS) will provide with IoT technologies is dependent on the trust value comes from the previously step. The simulation results from experiments deployed with physical assessment show that the security has more reliability after the MRC and SC schemes fused into the TM procedure. That is, the proposed fusion diversity scheme is more reliable in terms of security. Furthermore, the mechanism fusing MRC and SC methods with the TM can enhance the efficiency and solve the security problem of application layer. Alternatively, the reducing in QoS degree, such as the data rate, the packet capacity for the requester is the penalty.

In view of the scarce spectrum resources and inconvenient deployment in wireless communications, this work focuses on an unmanned aerial vehicle (UAV) enabled non-orthogonal multiple access (NOMA) system where a UAV deployed as a base station serves two users by NOMA. A joint power allocation and aerial jamming (PAAJ) scheme is proposed to achieve reliable and secure communications for the system in the presence of a malicious eavesdropper. To be specific, dynamic power allocation is adopted to ensure the reliability of the system and another friendly UAV jammer is introduced to improve the security of the system. The closed-form expressions of connection outage probability (COP), secrecy outage probability (SOP), and effective secrecy throughput (EST) are derived to evaluate the performance of the security-required user in the practical condition of probabilistic line-of-sight (LoS) and non-line-of-sight (NLoS) air-to-ground (A2G) channels. Moreover, the asymptotic EST is analyzed to obtain further insights. Numerical results show the validity of theoretical derivations and the superiority of the proposed PAAJ scheme over benchmark schemes. The EST of the UAV-enabled NOMA communication system outperforms the conventional terrestrial NOMA system at the low transmitting power from the UAV base station. There exists an optimal height of the UAV base station to maximize the EST, which provides a useful framework for designing UAV-enabled communication systems with heterogeneous service requirements.

In this study, the secrecy outage probability (SOP) of a dual-hop energy harvesting (EH) non-orthogonal multiple access (NOMA) system is investigated. In order to improve the signal quality at the transmitter node, the transmitter antenna selection (TAS) method is applied, while the generalized selection combining (GSC) technique is used to increase the reliability at the users and maximum ratio combining (MRC) is utilized at eavesdropper (EVE). In the system, the relay node harvests energy from the signals received from the base station (BS) and transmits messages to the users with the amplify-and-forward (AF) protocol. In the study, the findings for the SOP are presented with Monte Carlo simulations. The study shows that there is a trade-off between harvested energy, data rate and SOP performance, while power allocation factors have an impact on secrecy performance.

This paper investigates a hybrid framework that combines free space optics (FSO) and terahertz (THz) technologies for a backhaul network. In this hybrid configuration, the FSO and THz systems are empowered by reconfigurable intelligent surface (RIS) and are combined at the receiver using either maximal ratio combining (MRC) or selection combining (SC). The performance of the RIS-assisted hybrid FSO/THz system is evaluated under multiple impairments for FSO and THz links. The exact closed-form expressions for probability density function (PDF), cumulative distribution function (CDF), and moment-generating function (MGF) of the output signal-to-noise ratio (SNR) of both RIS-assisted FSO and THz links are derived. Leveraging these SNR statistics, we compute the outage probability and the average symbol error rate (SER) of the proposed hybrid FSO/THz system with MRC and SC schemes. Additionally, this paper conducts an asymptotic analysis at high SNR levels, yielding asymptotic expressions for outage and average SER, which not only reduce computational complexity but also provide insights into the system’s diversity gain. In the numerical results, the performance of the proposed hybrid FSO/THz system is compared against other state-of-the-art wireless systems, including direct link FSO without RIS, RIS-aided FSO, and the hybrid FSO/THz systems without RIS using diversity combining techniques.

SummaryIn this paper, the performance of an underlay cognitive radio system with random mobility and imperfect channel state information (CSI) is investigated. The mobile user (MU) utilises maximum ratio combining (MRC) and selection combining (SC) diversity techniques as signal reception to improve the quality of received signal‐to‐noise ratio (SNR). Under the Rayleigh fading, random waypoint mobility model is employed to characterised the effect of the MU random mobility on the system performance. Thus, novel probability density function (PDF) and cumulative distribution function (CDF) for the two considered diversity techniques are derived. Through these, the outage probability and average bit error rate (ABER) closed‐form analytical expressions are then obtained to quantify the system performance under the MRC and SC schemes. The results illustrate the effect of imperfect CSI, user mobility which is characterised by pathloss and the network topology on the system performance. Also, the results depict that MRC offers the system better performance compared with SC under the same system conditions. The accuracy of the derived analytical expressions is verified through Monte‐Carlo simulations.

Millimeter-wave (mmWave) communication is one of the key enabling technologies for fifth generation (5G) mobile networks. In this paper, we study the problem of secure communication in a mmWave wiretap network, where directional beamforming and link blockages are taken into account. For the secure transmission in the presence of spatially random eavesdroppers, an adaptive transmission scheme is adopted, for which sector secrecy guard zone and artificial noise (AN) are employed to enhance secrecy performance. When there exists no eavesdroppers within the sector secrecy guard zone, the transmitter only transmits information-bearing signal, and, conversely, AN along with information-bearing signal are transmitted. The closed-form expressions for secrecy outage probability (SOP), connection outage probability (COP) and secrecy throughput are derived under stochastic geometry. Then, we evaluate the effect of the sector secrecy guard zone and AN on the secrecy performance. Our results reveal that the application of the sector secrecy guard zone and AN can significantly improve the security of the system, and blockages also can be utilized to improve secrecy performance. An easy choice of transmit power and power allocation factor is provided for achieving higher secrecy throughput. Furthermore, increasing the density of eavesdroppers not always deteriorates the secrecy performance due to the use of the sector secrecy guard zone and AN.

In this paper, we studied the secure transmission of a hybrid automatic repeat request with chase combining (HARQ-CC) system, under the existence of multiple eavesdroppers and limited latency. First, we analyzed some critical performance metrics, including connection outage probability (COP), secrecy outage probability (SOP) and effective secrecy throughput (EST). Then, to maximize the EST, three optimization problems of rate adaption were discussed: (i) optimizing the code rate with a given secrecy redundancy rate by a parameterized closed-form solution; (ii) optimizing the secrecy redundancy rate with a given code rate by a fixed-point method; (iii) optimizing both code rate and secrecy redundancy rate by an iterative optimization algorithm. We also considered COP and SOP constraints among the problems while corresponding solutions were deduced. Finally, numerical and simulated results verified our conclusions that the approximated SOP matches well with Monte–Carlo simulation for a strict reliable constraint, and that the optimized transmitting rate enhances EST efficiently with multiple eavesdroppers and retransmissions. Moreover, the influence of the number of eavesdroppers on secrecy performance was analyzed. Briefly, secrecy performance inevitably deteriorates with increasing number of eavesdroppers due to raised information leakage.

In the fifth generation (5G) wireless communication system, the non‐orthogonal multiple access (NOMA) scheme has recently been proposed as a possible candidate for improving spectral efficiency. We look at power‐domain NOMA in this study, in which, multiple simultaneous transmissions are allowed at the same channel with different transmission powers. To achieve reliable transmissions in NOMA, the hybrid automatic repeat request (HARQ) scheme can be integrated into NOMA. The performance of a downlink NOMA system using the Type I HARQ method is investigated in this research. This type of HARQ does not entail expensive device which is considered one of the requirements for a massive 5G‐based Internet of Things network. Unfortunately, in the literature, it has been shown that deriving closed‐form expressions for the outage probabilities of HARQ‐aided NOMA systems is intractable due to the incorporation of multiple fractional random variables. Consequently, in this article, we follow a simple yet efficient methodology to study our considered HARQ‐aided NOMA system. The HARQ‐assisted NOMA system on the downlink is modeled as an absorbing discrete‐time Markov chain (DTMC). Thereafter, under perfect and imperfect channel estimation, we use this model to examine system performance in terms of outage probability and estimated number of retransmissions. Interestingly, we demonstrate that our DTMC‐based analysis is straightforward, repeatable, and accurate. Moreover, in this article, we propose a cooperative HARQ (CHARQ) scheme for the downlink NOMA system. According to CHARQ, the users cooperate with the base station in the retransmission process that will result in improving the performance of NOMA. Monte Carlo simulations have been conducted to not only verify the accuracy of our DTMC‐based analysis, but also manifest the superiority of CHARQ over HARQ.

This letter investigates secure transmission in non-orthogonal multiple access networks with an untrusted amplify-and-forward relay. In order to enhance secrecy performance, a cooperative jamming strategy is designed to confuse the relay. The new exact and asymptotic expressions for effective secrecy throughput (EST) are derived over Nakagami- ${m}$ fading channels, which demonstrates that jamming plays an important role for obtaining nonzero EST and should be carefully designed for achieving better secrecy performance. In addition, simulations are presented to provide some insights into parameters, i.e., transmit powers and fading parameters, on the secrecy performance.

We develop an analytical framework to derive the meta distribution and moments of the conditional success probability (CSP), which is defined as success probability for a given realization of the transmitters, in large-scale co-channel uplink and downlink non-orthogonal multiple access (NOMA) networks with one NOMA cluster per cell. The moments of CSP translate to various network performance metrics such as the standard success or signal-to-interference ratio (SIR) coverage probability (which is the 1-st moment), the mean local delay (which is the −1st moment in a static network setting), and the meta distribution (which is the complementary cumulative distribution function of the success or SIR coverage probability and can be approximated by using the 1st and 2nd moments). For the uplink NOMA network, to make the framework tractable, we propose two point process models for the spatial locations of the inter-cell interferers by utilizing the base station (BS)/user pair correlation function. We validate the proposed models by comparing the second moment measure of each model with that of the actual point process for the inter-cluster (or inter-cell) interferers obtained via simulations. For downlink NOMA, we derive closed-form solutions for the moments of the CSP, success (or coverage) probability, mean local delay, and meta distribution for the users. As an application of the developed analytical framework, we use the closed-form expressions to optimize the power allocations for downlink NOMA users in order to maximize the success probability of a given NOMA user with and without latency constraints. Closed-form optimal solutions for the transmit powers are obtained for two-user NOMA scenario. We note that maximizing the success probability with latency constraints can significantly impact the optimal power solutions for low SIR thresholds and favor orthogonal multiple access.

ABSTRACTIn this paper, we consider the physical layer security of a downlink cooperative multiple-input single-output (MISO) non-orthogonal multiple access (NOMA) network over Nakagami-m fading. The network consists of a multi-antenna source, multiple decode-and-forward (DF) relays, and two users with different priority, in the presence of a passive eavesdropper. Specifically, we investigate the secure transmission from the source to the users via the help of the relays, in which the signals of the users might or might not be successfully decoded at the relays. Thus, we aim to design secure communication protocols for the considered system, where transmit antenna selection (TAS), maximal ratio transmission (MRT), and relay selection are employed based on the source-to-relays channel conditions. To characterize the secrecy performance, analytical and asymptotic expressions for the secrecy outage probability (SOP) of the overall system are derived. Our analytical results validated by Monte-Carlo simulations show that the secrecy performance of cooperative NOMA networks can be improved by increasing the number of antennas at the source and the number of relays. Comparing TAS and MRT, we conclude that TAS has lower complexity but can achieve the secrecy performane comparable with MRT. Finally, the results also indicate that our proposed protocol bring more general and practical insights with similar secrecy performance compared with the conventional solution.

Due to the successive interference cancellation (SIC) technique, Non orthogonal multiple Access (NOMA) users have the capability of decoding the other paired users sharing the same resource bloc. As a result, NOMA technique is not only exposed to external eavesdropping, but also to internal eavesdropping which raises security risks regarding NOMA users' privacy. Therefore, this research aims to analyse a Multi-antenna cooperative NOMA system where both Decode and Forward (DF) and Amplify and Forward (AF) strategies are studied. In this context, we investigate the secrecy performance of our system with both internal and external eavesdropping scenarios. Closed-form expressions of the secrecy outage probability (SOP) and the strictly positive secrecy capacity (SPSC) metrics are derived. Numerical results are given to illustrate the validity of the obtained theoretical results.

In this paper, we focus on non-orthogonal multiple access (NOMA) network with power-domain user multiplexing at the transmitter side and successive interference cancellation (SIC) on the receiver side. The main problem presented in NOMA network is the design of the precoder. It has to be applied to users with weak channel conditions to effectively mitigate interference between cells. We propose a coordinated operation access scheme between OMA and NOMA that removes the precoder and increases the performance of the system. The channel gain is analyzed by order statistics obtaining its probability density function. System level simulation results are provided. We show, under multiple configurations, that the transmission rate achieved by our scheme is higher by more than 42% compared to NOMA on the edge of the cell.

In this research work, the authors propose an error constrained data transmission approach using non-orthogonal multiple access (NOMA) protocol with hybrid automatic repeat request (HARQ) and different packet combining schemes. In this proposed work, the transmitter simultaneously transmits two data packets to the users (UEs) by considering the superposition coding technique in the power domain. The decoding scheme of the receiver changes according to the message decoding status in the previous rounds. This combined protocol has the capability of realizing ultra-reliability, error correction power in high error prone wireless links. The receiver adopts successive interference cancelation (SIC) to decode its own packet. Retransmission process is performed when the data is erroneously received by the destination and the receiver corrects the error by applying HARQ with Packet Combining (HARQ-PC) and HARQ with Aggressive Packet Combining (HARQ-APC) schemes. This paper analyzes the data rates, outage probabilities and bit error rates of UEs for downlink NOMA systems with respect to the transmit power using some basic parameters. The proposed schemes can greatly outperform the conventional NOMA with HARQ (NOMA-HARQ) in terms of data rates, outage probability and bit error rate in dynamic wireless channels.