Secrecy performance analysis for a NOMA based FSO-RF system with imperfect CSI

This paper proposes a unified performance analysis framework of asymmetric dual-hop radio-frequency/free-space optical (RF/FSO) transmission systems. The generalized independent and identically distributed (i.i.d.) <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\alpha -\mu$</tex-math></inline-formula> distribution is considered for each branch in the RF link, whereas the FSO link is assumed to experience Málaga ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathcal {M}$</tex-math></inline-formula> ) fading with pointing error impairments. With amplify-and-forward (AF) and decode-and-forward (DF) relaying, the imperfect channel state information (CSI) of both links is considered. For the considered system, we first derive exact and novel analytical expressions for the probability density function (PDF) and cumulative distribution function (CDF) of the end-to-end signal-to-noise ratio (SNR). Furthermore, we obtain key performance metrics such as outage probability (OP), average bit-error-rate (ABER), and effective capacity (EC). The important effects of channel parameters on the system are disclosed from mathematical analysis and are further validated by Monte-Carlo simulations.

In this paper, an exact errors rate analysis of the hybrid free-space optical/radio frequency (FSO/RF) system based on combining diversity is presented. The system’s errors rate is analyzed under the effects of the atmospheric turbulence, foggy weather, and the multipath fading channel. The Gamma-Gamma and the Nakagami-m models are used to characterize the atmospheric turbulence through the FSO link and the multipath fading over the RF link respectively. The performance of the hybrid system is examined by a new closed-form expression for the averaged bit errors rate under the considered channel effects. The simulation results show that the hybrid FSO/RF system can outperform both FSO and RF link only systems under different fog densities of the channel. The accuracy of the new analytical results is demonstrated by computer-based Monte-Carlo simulations.

The increase in number of cellular users had lead to the evolution from the traditional cellular networks to the more efficient heterogeneous cellular networks (HetNet) to handle the traffic. Offloading plays a vital role in handling the traffic from the congested macro base station by handing users to the less congested femto base stations (FBS). Further, non-orthogonal multiple access (NOMA) has proved to be efficient for the future generation networks. In this work, we study the offloading in HetNets, where the FBS tier serves the users using NOMA. Imperfect channel state information (CSI) is considered to analyze the outage probability of offloaded user, since, in practice CSI estimation requires significant system overhead, especially when the number of users are large. Hence, for practical systems, the analyses with imperfect CSI is more relevant. Some important observations regarding offloading to FBS tier with NOMA based on imperfect CSI are drawn. The analytical results are validated using Monte Carlo simulations.

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, a downlink single-cell non-orthogonal multiple access (NOMA) network with uniformly deployed users is considered and an analytical framework to evaluate its performance is developed. Particularly, the performance of NOMA is studied by assuming two types of partial channel state information (CSI). For the first one, which is based on imperfect CSI , we present a simple closed-form approximation for the outage probability and the average sum rate, as well as their high signal-to-noise ratio (SNR) expressions. For the second type of CSI, which is based on second order statistics (SOS) , we derive a closed-form expression for the outage probability and an approximate expression for the average sum rate for the special case two users. For the addressed scenario with the two types of partial CSI, the results demonstrate that NOMA can achieve superior performance compared to the traditional orthogonal multiple access (OMA). Moreover, SOS-based NOMA always achieves better performance than that with imperfect CSI, while it can achieve similar performance to the NOMA with perfect CSI at the low SNR region. The provided numerical results confirm that the derived expressions for the outage probability and the average sum rate match well with the Monte Carlo simulations.

This paper investigates the performance analysis of dual-hop free-space optical/radio frequency (FSO/RF) communication systems. In this system, we study aims to improve users' spectral efficiency by applying non-orthogonal multiple access (NOMA) under the situation of perfect successive interference cancellation (SIC). At the first hop, the FSO link suffers Gamma-Gamma fading technique, which can significantly advance the anti-fading performance of the FSO link. For the second hop, use the RF technique over Rayleigh fading channel. We derived the closed-form expressions for outage probability (OP) of secondary users through the effect of atmospheric turbulence and performance metrics of the system. The main study results are to ensure fairness between users of NOMA. Monte-Carlo simulations are performed to verify the proposed analytical results in hybrid wireless communications.

SummaryThe simultaneous wireless information and power transfer or energy harvesting (EH) can be combined in nonorthogonal multiple access (NOMA) as green applications towards 5G. This paper investigates a new cooperative EH‐NOMA protocol, where the intermediate relay has not equipped the fixed power source and acts as a wireless powered relay to help signal transmission to representative weak user and strong user in NOMA. However, impacts of imperfect channel estimation contribute to outage system performance evaluations. We formulate the power resource assignment paradigms as two schemes, namely, fixed power allocation and dynamic power allocation, by considering imperfect channel state information (CSI). To solve this problem, we derive the closed‐form expressions of outage probability under imperfect CSI and the power allocation constraints. The expected numerical results related to the derived expressions for the outage probability are examined that numerical and the Monte Carlo simulations are strictly matching lines.

Security performance and the impact of imperfect channel state information (CSI) in underlay cooperative cognitive networks (UCCN) is investigated in this paper. In the proposed scheme, relay R uses non-orthogonal multiple access (NOMA) technology to transfer messages , from the source node S to User 1 (U1) and User 2 (U2), respectively. An eavesdropper (E) is also proposed to wiretap the messages of U1 and U2. The transmission’s security performance in the proposed system was analyzed and performed over Rayleigh fading channels. Through numerical analysis, the results showed that the proposed system’s secrecy performance became more efficient when the eavesdropper node E was farther away from the source node S and the intermediate cooperative relay R. The secrecy performance of U1 was also compared to the secrecy performance of U2. Finally, the simulation results matched the Monte Carlo simulations well.

The fifth generation (5G) of wireless communication accompanied by the advancement of mobile internet and the Internet of Things (IoT) will create stormy data traffic. The 5G challenges like higher spectral efficiency, massive connectivity, and low latency are addressed by the Non-Orthogonal Multiple Access (NOMA) in recent years. NOMA is proven to be a promising technique from its capability to accommodate a larger number of users in contrast to the conventional orthogonal multiple access (OMA) schemes. NOMA comprises two distinct techniques such as Power-Domain NOMA and Code-Domain NOMA. The non-orthogonal resource allocation in Power-Domain NOMA is practically realized by the Superposition Coding (SC) at the Base Station (BS) and an advanced Successive Interference Cancellation at the User Equipment (UE). In this manuscript, the basic concepts of NOMA, on comparing its channel gain with OMA are discussed first. Specifically, a comprehensive survey of various SIC techniques applied under perfect and imperfect Channel State Information (CSI) uncertainties are summarized in terms of outage probability, ergodic capacity, and system performance. In addition, the sophisticated SIC techniques, when NOMA is integrated with modern wireless communication technologies such as multiple-input multiple-output (MIMO-NOMA) and Cooperative (C-NOMA) communications are investigated. Furthermore, the challenges to be solved with their corresponding opportunities and future research directions of NOMA are explored.

This paper investigates a non-orthogonal multiple access (NOMA) technique by employing device-to-device (D2D) transmission in small-cell networks. More specifically, the D2D transmission combines the relay selection model from a group of macro base stations (MBS) with the D2D mode in in small-cell network to form a D2D-NOMA system. Such D2D transmission needs assistance from multiple MBS and the small-cell base station (SBS) using decode-and-forward (DF) techniques. In this context, full-duplex (FD) is adopted at intermediate nodes. Furthermore, there are two possible scenarios in practice including perfect channel state information (CSI) and imperfect CSI that need to be studied to examine performance degradation in such considered network. To evaluate system performance, we derive expressions of outage probability for D2D user. Our study results show that the proposed network with more MBSs selection can improve the outage performance compared to the conventional orthogonal multiple access (OMA) scheme. Finally, numerical results confirms the accuracy of the derived expressions.

ABSTRACTFuture communications networks, including sixth‐generation (6G) and the internet of things (IoT), are expected to support higher capacity, quality of service, and user demands. However, serving a massive number of users in future networks poses the bandwidth limitation challenge. Non‐orthogonal multiple access (NOMA) has been proposed for the future IoT and 6G networks to address the mentioned problem by serving multiple users in one resource block. However, the practical approach for a multi‐cell network is to consider inter‐network interference and imperfect channel state information (CSI), which significantly deteriorates NOMA performance. This paper analyzes NOMA performance in terms of network outage probability, base station (BS) activity detection, and network sum rate under imperfect CSI and the presence of interference. In this regard, it proposes a method to improve the BS activity detection and network sum rate of NOMA networks, which exploits a lower computation complexity compared to similar research in the literature. The analytical and simulation results demonstrate the superiority of the proposed method over conventional NOMA and orthogonal multiple access (OMA) schemes in terms of network sum rate and base station detection activity.

SummaryIn this paper, we analyze the performance of maximum‐ratio combining (MRC) receivers for single‐input multiple‐output (SIMO) non‐orthogonal multiple access (NOMA) system. We explore the aforesaid system performance in presence of impairments like imperfect channel state information (CSI) and successive interference cancellation (SIC) errors. In general, receive diversity provides diversity gain and helps to maintain quality of service (QoS), while the NOMA system achieves higher spectral efficiency compared to orthogonal multiple access (OMA). Power‐domain NOMA system transmits superimposed‐coded signal, which utilize SIC detection method at the receiving users. Here, we derive the closed‐form expression of the average bit error rate (BER) for the MRC‐based NOMA system. We also analyze the performance of the system in high signal‐to‐noise ratio (SNR) regime through derived asymptotic expression. Furthermore, the outage probability, diversity order, and sum rate comparison between NOMA and OMA system are also presented. Simulation results also validate the derived theoretical expressions and confirm the diversity gain achieved for the considered system.

One of the main reasons for switching to the next generation of communication systems is the demand of increasing capacity and network connections. This goal can be achieved using massive multiple input - multiple output (massive-MIMO) systems in combination with Non-orthogonal multiple access (NOMA) technique. NOMA technology uses the successive interference cancellation (SIC) receiver to detect user's signals which imposes an additional complexity on the system. In this paper, we proposed two methods to reduce the system complexity. The proposed method despite imperfect channel state information (CSI) in the receiver, there is not significantly reduction in the system performance. Since the computation of matrices inverse has a high computational complexity, we used the Neumann series approximation method and the Gauss-Seidel decomposition method to compute matrices inverse in the SIC receiver. Simulation results are provided at the end of the paper in terms of bit error rate (BER) at the receiver which show, these methods have lower computational complexity in comparison with the traditional methods while they cause a slight performance reduction in the SIC receiver. Also, we examined the increasing and decreasing value of imperfect channel state information in the system performance which shows the increasing value of imperfect channel state information, cause a slight performance reduction in SIC receiver.

In this paper, we evaluate system performances of a multi-hop relay protocol with presence of an active eavesdropper. In the proposed protocol, a source attempts to transmit its data to a destination with assistance of multiple intermediate relays. From the eavesdropping Channel State Information (CSI) estimated, the source and relays adjust their transmit power so that the eavesdropper cannot overhear the transmitted data. Moreover, to enhance throughput for the proposed system, Non-Orthogonal Multiple Access (NOMA) technique with a simple power allocation is also proposed. We derive exact closed-form expressions of the Outage Probability (OP) and throughput for the data transmission over Rayleigh fading channel. In addition, when the CSI estimation is imperfect, Intercept Probability (IP) at the eavesdropper is derived. Finally, Monte Carlo simulations are presented to verify the theoretical derivations.

In this paper, we investigate the physical layer security for an asymmetric dual-hop radio frequency-free space optical (RF-FSO) communication system, in which a source transmits information to a multi-aperture destination (D) through a best relay under the wiretapping of a multi-aperture eavesdropper (E). The best relay is selected by a partial relay selection scheme in terms of maximum instantaneous channel gain for the RF link. Moreover, equal gain combining scheme is also used to process the multiple copies of receiving signal at D and E. Assuming all the RF channels are subject to independent and identical distributed (i.i.d.) Nakagami-m fading and all the FSO channels are modeled by i.i.d. Gamma-Gamma process, the secrecy performance in terms of secrecy outage probability and the probability of strictly positive secrecy capacity are studied, and the accuracy of the analytical results is verified by Monte-Carlo simulations.