Secured communication in cognitive MIMO schemes under hardware impairments

We study the fundamental capacity trade-off between full-duplex and half-duplex transmission modes in a two- hop communication system with a fixed infrastructure-based amplify-and-forward relay. First, we derive closed-form expressions for the average end-to-end capacity in the relay link. We show that it may be better to tolerate some loop interference with the full-duplex mode than to consume channel resources by allocating two orthogonal channels with the half-duplex mode. Furthermore, we evaluate the maximum loop interference power levels that still allow the full-duplex mode to achieve the same capacity as the half-duplex mode. Our results indicate that with practical signal-to-noise ratio values, the full-duplex mode is preferable in terms of capacity.

In this paper, we propose a transmit antenna selection (TAS) protocol exploiting Fountain codes for secure communication. In the proposed protocol, a base station (BS) selects its best antenna to transmit Fountain packets to a legitimate user (US). Moreover, a cooperative jammer (JA) is used to generate artificial noises to an eavesdropper (EA). The transmission between BS and US will terminate as soon as US can receive a sufficient number of the encoded packets for decoding the original message. To obtain a secure communication, US must receive enough the number of the packets before EA can. Under impact of hardware noises at all of the nodes, we derive expressions of probability of successful and secure communication (SSC), intercept probability (IP) and average number of the packets transmitted by BS over Rayleigh fading channel. Monte Carlo simulations are presented to verify the theoretical results.

Multi-antenna relay assisted NOMA network with multiple imperfect factors

In this paper, we propose an adaptive spectrum access protocol for secondary users (SUs) be used to access licensed bands in cognitive radio networks. Specifically, if the primary network, which uses multicast communication to transmit data from one primary source to multiple primary destinations, satisfies a required system quality of service (QoS), SUs can access the licensed bands, follows an underlay spectrum sharing. Otherwise, a secondary base (SB) station must assist the primary network in obtaining the QoS so that it can find opportunities to use the bands, i.e., cooperation-based spectrum access. To enhance the performance for the secondary network, in terms of outage probability (OP), various best-user selection methods are proposed. Moreover, we take into consideration the impact of hardware impairments on the OP of both primary and secondary networks. We derive exact and asymptotic closed-form expressions of the OP over Rayleigh fading channel. From the analytical results, an optimal value of maximal interference threshold and an optimal fraction of the SBs' transmit power to the primary data are obtained when the secondary network operates on the underlay and the cooperation-based spectrum access modes, respectively. Finally, Monte Carlo simulations are performed to verify the theoretical derivations.

This paper investigates impact of hardware impairments on the probability of Non-zero Secrecy Capacity (NSC) of multi-hop relay networks. In the considered protocol, multiple eavesdroppers attempt to overhear the data that is relayed from a source to a destination via multiple intermediate relay nodes. To enhance the secrecy performance, the multi-hop randomize-and-forward (RF) strategy is used to confuse the eavesdroppers. We derive exact expressions of the NSC probability in integral forms over Rayleigh fading channels. Moreover, these formulas are then expressed by sums of infinite series of exponential functions and exponential integral functions. Finally, Monte Carlo simulations are performed to verify our derivations.

This article explores a practical scenario with hardware impairments (HIs) in a multireconfigurable intelligent surface (RIS) assisted wireless system. This approach is based on a mathematical analysis of the performance of the HI‐RIS system. To this end, a closed‐form expression of the energy efficiency (EE) and its asymptotic behavior, particularly in regions with high transmit power, are derived. Next, an analysis was conducted to compare the EE of the HI‐RIS system with those of relevant systems: the ideal hardware (ID)‐RIS system, HI‐point‐to‐point (P2P) system (without RISs), and ID‐P2P system (without RISs). The numerical findings unequivocally demonstrate that the incorporation of RISs substantially enhances the EE of the HI‐RIS system, particularly at high transmit rates. However, at low transmit rates, the EE of the HI‐RIS system less than that of the HI‐P2P system. This trend is also reflected in the EEs of the ID‐RIS and ID‐P2P systems. Moreover, the significant impact of HI on the EEs of the HI‐RIS and HI‐P2P systems is analyzed. The effects of crucial system parameters, such as the number of reflecting elements, frequencies of WiFi networks, and fading order, are comprehensively determined to provide insights into the behaviors of the HI‐RIS system. The outage probability and throughput behaviors of the HI‐RIS system are also evaluated to comprehensively analyze of the benefits of RISs and the effects of HI. Finally, the accuracy of the derived expressions was verified using Monte Carlo simulations.

Reconfigurable intelligent surface (RIS) is a revolutionary passive radio technique to facilitate capacity enhancement beyond the current massive multiple-input multiple-output (MIMO) transmission. However, the potential hardware impairment (HWI) of the RIS usually causes inevitable performance degradation and the amplification of imperfect CSI. These impacts still lack full investigation in the RIS-assisted wireless network. This paper developed a robust joint RIS and transceiver design algorithm to minimize the worst-case mean square error (MSE) of the received signal under the HWI effect and imperfect channel state information (CSI) in the RIS-assisted multi-user MIMO (MU-MIMO) wireless network. Specifically, since the proposed robust joint RIS and transceiver design problem yields non-convex characteristics under severe HWI, an iterative three-step convex algorithm is developed to approach the optimality by relaxation and convex transformation. Compared with the state-of-the-art baselines that ignore the HWI, the proposed robust algorithm inhibits the destruction of HWI while raising the worst-case MSE effectively in several numerical simulations. Moreover, due to the properties of the HWI, the performance loss is notable under the magnification of the number of reflected elements in the RIS-assisted MU-MIMO wireless network.

The effects of hardware impairments with imperfect channel estimation for cache-enabled UAV networks are studied in this paper. The effects of the setup parameters, such as the number of cached or relaying nodes, the hardware impairment factor, the channel estimation error, and the transmission SNR, on the outage probability are present by deriving the exact closed-form expressions on outage probability. Also, the asymptotic results are present when the transmission SNR is large enough. From the asymptotic analysis, we can see that there is an error floor introduced by the hardware impairments and imperfect channel estimation. Specifically, the error floor is dependent on the channel estimation error factor, the hardware impairment distortion factor, and the QoS requirements. And the diversity order of the error floor for the cached/relaying links is equal to the number of cached/relaying UAV nodes.

Space information networks are proposed to broaden the observation area and realize continuous information acquisition using satellites and high-altitude platform stations. Space information networks are able to enhance detection and transmission capabilities compared to the current single Earth observation satellite. The satellite–terrestrial network is an important component of the space information networks. Hence, the major contribution of this article is to propose a new transmitted link selection scheme in a satellite–terrestrial network. Switch-and-stay combining scheme is used by destination to have a trade-off between the complexity and efficiency. The satellite, terrestrial relays, and destination user are influenced by hardware impairments, respectively. The closed-form expressions for the outage probability and throughput are derived. In order to analyze the system performance at high signal-to-noise rate, the asymptotic expressions for the system performance are also derived to give a special view on the impact of hardware impairments on the considered network. What is more, numerical results are derived to verify the correctness of our analytical results.

In this paper, we investigate the impact of hardware impairments on the outage performance and the instantaneous capacity of dual-hop decode-and-forward (DF) satellite relay networks in the presence of co-channel interference. Specifically, the exact closed-form expression for the outage probability and the analytical expression for the instantaneous capacity of the system are derived over a shadowed-Rician fading channel, which provides a fast means to evaluate the impact of hardware impairments on the system performance. Our results demonstrate that the outage floor occurs and the capacity upper bound appears when the hardware impairments exist. In addition, simulation results were provided to verify the correctness of the analytical results.

The non‐orthogonal multiple access (NOMA) technique is a prospective solution to support the massive connectivity of an ever‐increasing number of wirelessly connected devices and address the spectrum scarcity issue. In this article, the outage probability and ergodic capacity of a two‐hop cooperative NOMA network with an energy‐limited relaying node are quantified over a generalizedstatistical model. The relay acts in an amplify‐and‐forward mode and performs energy harvesting (EH) using the time‐switching and power splitting relaying protocols. Moreover, the impact of hardware impairments (HIs) is incorporated into the performance evaluation. The obtained results prove the importance of HIs and allow one to evaluate the outage probability and ergodic capacity over various statistical models and system parameters. Finally, the results suggest that the optimal performance at a specific scenario depends on the combination of multiple factors, such as channel conditions, HI level, transmit power, and EH protocol.

Given that fifth generation (5G) networks suggest heterogeneous networks (HetNets) design and millimeter-wave (mmWave) transmission as promising technologies to achieve its vision, we consider the downlink of a multi-user multiple-input multiple-output (MU-MIMO) HetNet operating at the region of mmWave frequencies. Actually, by focusing on a realistic assessment, the proposed framework includes the effects of channel aging, residual additive transceiver hardware impairments (RATHIs), and amplified thermal noise (ATN). After providing the definition of the coverage probability for this novel synergy between HetNets and mmWave transmission with its special characteristics under realistic conditions, we proceed with its derivation. Monte Carlo simulations verify the analytical results that allow to quantify the degradation obtained in this new paradigm, and provide interesting design insights. Hence, among others, we determine the degradation of the system due to channel aging, and we demonstrate that the RATHIs play a significant role in the high signal-to-noise ratio (SNR) regime.

In this paper, we consider an overlay cognitive satellite-terrestrial relay network comprising a primary satellite source-receiver pair and a secondary transmitter-receiver pair on the ground while taking into account the practical relay transceiver hardware impairments. Herein, a primary satellite source communicates with its terrestrial user by utilizing both direct and relay links, using an amplify-and-forward based cooperative communication technique. Considering distortion noises in relay signal processing, we obtain new closed-form expressions for the outage probability of primary satellite network and secondary terrestrial network and explicitly derive the asymptotic outage behaviour for primary network by adopting pertinent heterogeneous fading models. Both primary and secondary networks satisfy their quality-of-service criteria for the low data rate requirements only. However, for the high data rate requirements, a ceiling effect is shown to occur which eventually makes the spectrum sharing infeasible.

In this paper, we analyze the performance of underlay communication between full-duplex capable device-to-device (D2D) nodes transmitting in the cellular band. The D2D nodes use peak interference type of power control to restrict the overall interference at the cellular base station below a statistically determined interference temperature limit (ITL), thereby ensuring its quality of service for uplink cellular users. From the derived analytical expressions, sum-throughput optimal strategies are evolved to choose between full-duplex and half-duplex modes of operation for the D2D nodes. Since both D2D nodes transmit simultaneously in full-duplex mode, the ITL needs to be apportioned between the D2D terminals. A closed-form expression is presented for the optimum ITL apportioning that maximizes D2D sum-throughput. It is shown that switching to half-duplex mode is advantageous when the target rate is above a certain critical target-rate, for which an expression is derived. Computer simulations are presented that demonstrate accuracy of the derived expressions.

Hybrid duplex wireless networks, use half duplex (HD) as well as full duplex (FD) modes to utilize the advantages of both technologies. This paper tries to determine the proportion of the network nodes that should be in HD or FD modes in such networks, to maximize the overall throughput of all FD and HD nodes. Here, by assuming imperfect self-interference cancellation (SIC) and using ALOHA protocol, the local optimum densities of FD, HD and idle nodes are obtained in a given time slot, using Karush–Kuhn–Tucker (KKT) conditions as well as stochastic geometry tool. We also obtain the sub-optimal value of the signal-to-interference ratio (SIR) threshold constrained by fixed node densities, using the steepest descent method in order to maximize the network throughput. The results show that in such networks, the proposed hybrid duplex mode selection scheme improves the level of throughput. The results also indicate the effect of imperfect SIC on reducing the throughput. Moreover, it is demonstrated that by choosing an optimal SIR threshold for mode selection process, the achievable throughput in such networks can increase by around 5%.