Underlay Cognitive Radio Networks Research Articles

End-to-end performance of Hybrid DF/AF (HDAF) relayed underlay cognitive radio networks

In the presented work, the performance analysis of an underlay cognitive relay network with a hybrid-decode/amplify-and-forward relaying protocol is undertaken. Since the system is an underlay system, the secondary network will communicate simultaneously with the primary network. Hence interference temperature will act as a constraint to keep the secondary communication from interfering with the primary transmission. To ensure this, secondary transmit powers need to be kept below a pre-defined threshold level. Severe multi-path fading and shadowing or a long distance between the secondary source and the destination make a direct link between the two infeasible. These nodes can only be linked by a relay between the two. All the radio links in the system are characterized by the extended generalized-K fading distribution. The closed form expressions for the outage probability and ergodic channel capacity of the system are derived. The system outage performance and capacity with hybrid-decode/amplify-and-forward relay is compared to the performance with amplify-and-forward and decode-and-forward relays. Optimum relay position for best outage performance is also investigated. Further, the results of the performance analysis of the system are also illustrated by the numerical plots.

Outage and Throughput Analysis of Cognitive Users in Underlay Cognitive Radio Networks With Handover

Interference characterization in cognitive networks with handover has received less attention in stochastic geometry-based interference management and control, especially in cognitive radio networks, because of the possibility of complicating the analysis of various performance metrics of interest, such as outage probability and throughput. However, because of the possible mobility that is observed in real practical systems, some of the receivers may be located outside the coverage regions of their paired transmitters. In order to ensure that any receiver located outside the coverage region of its paired transmitter continues to receive its required service from its paired transmitter while still achieving tractable analysis for various performance metrics of interest, we adopted multiuser diversity via packet relaying. With this approach, any secondary nodes waiting to transmit can be used to sustain coverage between any typical active transmitter and receiver pair, while reducing their own waiting period in the process. We obtained tractable analysis for outage probability, spectral efficiency and throughput and showed the effect of handover rate over the network performance. The outcomes of the numerical results show that the proposed approach is capable of improving the overall network performance by improving coverage and throughput among network users in the cognitive radio networks.

A Two-Phase Transfer Learning-Based Power Spectrum Maps Reconstruction Algorithm for Underlay Cognitive Radio Networks

In the underlay cognitive radio networks, the power spectrum maps (PSMs) estimation is the main challenge in sensing the idle wireless radio resources. Traditional deep learning-based algorithms achieve good estimation performance, under the hypothesis that the training data must be independent and identically distributed (i.i.d.) with the PSMs in the target region. However, collecting the PSMs training data is not an easy task, which is time-consuming and requires a numerous number of sensing devices. For this reason, we propose a two-phase transfer learning generative adversarial network (TPTL-GAN) for the PSMs reconstruction task. The proposed algorithm relaxes the i.i.d. assumption in traditional deep learning-based algorithms, allowing us to estimate the PSMs based on the simulated or previously collected training data, which share similar rather than strictly identical distribution with the target data. In the first phase of the TPTL-GAN algorithm, we design a domain projecting (DP) framework to project the source domain to the adjacent domain. In the second phase, we propose a domain completing (DC) framework, which extracts helpful radio environment features from the adjacent domain and reconstructs the PSMs in the target domain. Through the above two phases, the proposed algorithm provides a more accurate PSMs reconstruction performance than the traditional methods, as verified by the simulation results.

Analysis of Underlay Cognitive Radio Networks based on Interference Cancellation Mechanism

In this paper, we investigate the performance of secondary transmission scheme based on Markov ON-OFF state of primary users in Underlay cognitive radio networks. We propose flexible secondary cooperative transmission schemewith interference cancellation technique according to the ON-OFF status of primary transmitter. For maximal ratio combining (MRC) at destination, we have derived exact closed-form expressions of the outage probability in different situations. The numerical simulation results also reveal that the proposed scheme improve the secondary transmission performance compared with traditional mechanism in terms of secondary outage probability and energy efficiency.

Physical Layer Security in NOMA-Enabled Cognitive Radio Networks With Outdated Channel State Information

In this article, we investigate physical layer security (PLS) in non-orthogonal multiple access-enabled (NOMA-enabled) underlay cognitive radio networks (CRNs) with outdated channel state information (CSI). Considering the influence of outdated CSI on the interference of secondary transmitter (Alice) to primary user (PU), the constraint for the power is adopted to guarantee the quality-of-service (QoS) of PU over Nakagami-m channels. To further analyze the NOMA-enabled underlay CRNs with outdated CSI in PLS perspective, the secrecy performance is evaluated by the closed-form expressions for connection outage probability (COP), the intercept probability (IP) and effective secrecy throughput (EST). In addition, Monte Carlo simulations are provided to verify the derived analytical results. From the analytical results and simulations, it is concluded that a) with the increment of the channel parameter m, the secrecy performance of the considered networks increases in the low SNR region and decreases in the high SNR region, b) the connection performance with the outdated CSI of the interference links only reduce in the high SNR region, because the power margin factor changes significantly in this region, c) considering the impact of the constraint for the power, the secrecy performance and EST performance of the considered networks with the outdated CSI of the interference links increase in the high SNR region, d) the considered networks with NOMA scheme can achieve higher EST than that with orthogonal multiple access (OMA) scheme.

Best Relay Selection Schemes for NOMA Based Cognitive Relay Networks in Underlay Spectrum Sharing

Cognitive Radio and the emerging Non-Orthogonal Multiple Access (NOMA) techniques hold the potential to fulfill the increasing demands of radio spectrum by 5G-and-B5G wireless systems. It is a usual practice in underlay cognitive radio networks to take assistance from intermediate relays to reach the remote destination. Putting together, NOMA based Cognitive Relay Networks (NCRNs) have recently gained tremendous research attention to improve the spectrum utilization efficiency. This article studies the application of best relay selection (BRS) in downlink scenario of NCRNs in which a base station (BS) being unable to communicate directly with the far user U2 takes assistance from the near user U1 and from the best Decode-and-Forward (DF) relay selected from the potential NCRN operating in underlay environment. Three BRS schemes are proposed selecting a relay which (i) maximizes signal-to-noise ratio (SNR) on relayU2 link, (ii) minimizes interference on relay-primary user (PU) link, (iii) maximizes the quotient of relay-U2 link's SNR and relay-PU link's interference power. Scheme 3 considers the existence of U1 -U2 link as well whereas the other two schemes do not. To characterize the performance of the proposed schemes assuming Rayleigh channel model, closed-form expressions of probability distribution function (PDF) of received SNR at U2, average number of reliable relays, outage probability and bit error rate are obtained. For insight analysis, analytical results are validated through simulations which reveal that relay selection in NCRNs is different from non-cognitive networks and is feasible in low-to-medium SNR regions. The signal from near user further improved the outage performance.

On Residual Energy Maximization in DF Cognitive Radio Networks With Multiple Eavesdroppers

This paper explores the issues of energy harvesting (EH) and multiple eavesdropping in an underlay cognitive radio network (CRN) that comprises of a secondary transmitter ( $SU_{\mathcal {T}}$ ) and destination ( $SU_{\mathcal {D}}$ ) node connected through a decode-forward (DF) relay ( $S_{\mathcal {R}}$ ). CRN is operated following a frame structure that includes three non-overlapping slots where in the first one, the relay harvests energy from the information signal of $SU_{\mathcal {T}}$ and the interference signal of primary user (PU). During the second slot, $SU_{\mathcal {T}}$ transmits data to the relay node. In the last slot, $S_{\mathcal {R}}$ forwards the same to $SU_{\mathcal {D}}$ and $SU_{\mathcal {T}}$ does EH from PU signal. Residual energy maximization is done under the constraints of energy causality for $SU_{\mathcal {T}}$ and $S_{\mathcal {R}}$ , interference to PU, secondary outage probability and secrecy outage probability. Analytical expressions of ergodic secrecy capacity and secrecy outage probability are derived for non-colluding (NCE) and colluding eavesdropping (CE) scenarios. Closed form expressions for the optimal transmit power of $SU_{\mathcal {T}}$ and $S_{\mathcal {R}}$ along with the time slot for EH are derived and their impacts on the residual energy, secondary outage probability and secrecy outage probability are analysed. Simulation results show a gain on the maximum value of the residual energy by ~8.13% for CE and ~4.72% for NCE over the existing works.

A PHY Layer Security Analysis of Uplink Cooperative Jamming-Based Underlay CRNs With Multi-Eavesdroppers

In this paper, the physical layer security of a dual-hop underlay uplink cognitive radio network is investigated over Nakagami- ${m}$ fading channels. Specifically, multiple secondary sources $(S_{i})_{1\leq i \leq N}$ are taking turns in accessing the licensed spectrum of the primary users and communicating with a multi-antenna secondary base station ( ${D}$ ) through the aid of a multi-antenna relay ${R}$ in the presence of ${M}$ eavesdroppers $(E_{k})_{1\leq k \leq M}$ that are also equipped with multiple antennas. Among the remaining nodes, one jammer is randomly selected to transmit an artificial noise to disrupt all the eavesdroppers that are attempting to intercept the communication of the legitimate links, i.e., $S_{i}$ - ${R}$ and ${R}$ - ${D}$ . The received signals at each node are combined using maximum-ratio combining. Secrecy analysis is provided by deriving closed-form and asymptotic expressions for the secrecy outage probability. The impact of several key parameters on the system’s secrecy, e.g., transmit power of the sources, number of eavesdroppers, maximum tolerated interference power, and the number of diversity branches is investigated. Importantly, by considering two scenarios, namely (i) absence and (ii) presence of a friendly jammer, new insights are obtained for the considered communication system. Especially, we tend to answer to the following question: Can better secrecy be achieved without jamming by considering a single antenna at eavesdroppers and multiple-ones at the legitimate users (i.e., relay and end-user) rather than sending permanently an artificial noise and considering that both the relay and the destination are equipped with a single antenna, while multiple antennas are used by the eavesdroppers? The obtained results are corroborated through Monte Carlo simulation and show that the system’s security can be enhanced by adjusting the aforementioned parameters.

Harvest-or-Transmit Policy for Cognitive Radio Networks: A Learning Theoretic Approach

We consider an underlay cognitive radio network where the secondary user (SU) harvests energy from the environment. We consider a slotted-mode of operation where each slot of SU is used for either energy harvesting or data transmission. Considering block fading with memory, we model the energy arrival and fading processes as a stationary Markov process of first-order. We propose a harvest-or-transmit policy for the SU along with optimal transmit powers that maximize its expected throughput under three different settings. First, we consider a learning-theoretic approach where we do not assume any a priori knowledge about the underlying Markov processes. In this case, we obtain an online policy using Q-learning . Then, we assume that the full statistical knowledge of the governing Markov process is known a priori . Under this assumption, we obtain an optimal online policy using infinite horizon stochastic dynamic programming . Finally, we obtain an optimal offline policy using the generalized Benders decomposition algorithm. The offline policy assumes that for a given time deadline, the energy arrivals and channel states are known in advance at all the transmitters. Finally, we compare all policies and study the effects of various system parameters on the system performance.

Secrecy outage probability of inter‐vehicular cognitive radio networks

SummaryHerein, we consider an underlay cognitive radio network (CRN) where mobile secondary user wishes to transmit a confidential information to the secondary destination in the presence of an illegitimate eavesdropper which is trying to steal the classified message signal. The proposed scenario can be viable for a secondary safety task force working with a primary regiment, which wishes to transmit the confidential information to the commander while an eavesdropper is trying to intercept the classified information. In the analysis, two novel power allocation methods are considered by assuming perfect and limited feedback channels of the primary network, and for both methods, exact and asymptotic expressions of secrecy outage probability (SOP) are derived for N*Nakagami‐m fading channels which are used to model fading channels such as mobile‐to‐mobile/vehicle‐to‐vehicle communication systems where the nodes are moving into a rich scattering environment. We further verified our analytic results through Monte‐Carlo simulations. It is shown from the numerical results that the cascading degree of the channels has a worsening effect on the secrecy outage performance of the CRN systems.

Secure transmission in underlay cognitive radio network with outdated channel state information

This paper investigates the secrecy performance of an underlay cognitive radio network (CRN) with outdated channel state information (CSI) for two practical scenarios, i.e., scenario 1: the CSI of an eavesdropper’s channel is unavailable at the secondary transmitter and scenario II: the CSI of an eavesdropper is available at the secondary transmitter. The selection combining (SC) and maximal ratio combining (MRC) techniques are utilized at the secondary receiver while MRC is also employed at both eavesdropper and primary receiver. For the scenario I, the compact expressions of exact and asymptotic secrecy outage probability (SOP), intercept probability and ϵ- outage secrecy capacity are derived, and simulations are conducted to verify analytical results. Our results reveal that the secrecy performance of the system degrades when the CSI of the main channel is outdated. Additionally, in scenario II, a comprehensive analysis of average secrecy capacity is performed, and new closed-form expressions for exact and asymptotic average secrecy capacity are derived which are valid for an arbitrary number of antennas at secondary receiver and eavesdropper. Finally, we investigate the high signal to noise ratio (SNR) slope and high SNR power offset which characterize the impact of the outdated CSI of the main channel and eavesdropper’s channel on average secrecy capacity.

On end-to-end performance of variable gain AF relayed cognitive underlay networks

ABSTRACTThe objective of this work is to analyse the performance of an underlay cognitive radio network which incorporates a variable-gain amplify-and-forward relay to enhance its performance. The system is based on extended generalised-K fading distribution and works under the constraint of interference temperature. As a result, the secondary source and the relay transmit powers will be curbed to avoid secondary signal interfering with the primary transmission when both the networks communicate simultaneously. This is the basic principle of an underlay system where both primary and secondary networks are active at the same time. The influence of fading and shadowing on the different radio links of the system is also taken into account. The analysis begins with finding the end-to-end signal-to-noise-ratio and then derives its cumulative distribution function and moment generating functions. This is followed by the derivation of the analytic closed form expressions for the outage probability, the channel capacity and the error probability of the dual-hop AF relayed underlay cognitive radio network. Numerical plots following the mathematical analysis illustrate the effects of various parameters on the system performance under the constraints of interference temperature and the secondary transmit powers.

Energy Efficiency Optimization for Secure Transmission in MISO Cognitive Radio Network with Energy Harvesting

In this paper, we investigate different secrecy energy efficiency (SEE) optimization problems in a multiple-input single-output underlay cognitive radio (CR) network in the presence of an energy harvesting receiver. In particular, these energy efficient designs are developed with different assumptions of channels state information (CSI) at the transmitter, namely perfect CSI, statistical CSI and imperfect CSI with bounded channel uncertainties. In particular, the overarching objective here is to design a beamforming technique maximizing the SEE while satisfying all relevant constraints linked to interference and harvested energy between transmitters and receivers. We show that the original problems are non-convex and their solutions are intractable. By using a number of techniques, such as non-linear fractional programming and difference of concave (DC) functions, we reformulate the original problems so as to render them tractable. We then combine these techniques with the Dinkelbach's algorithm to derive iterative algorithms to determine relevant beamforming vectors which lead to the SEE maximization. In doing this, we investigate the robust design with ellipsoidal bounded channel uncertainties, by mapping the original problem into a sequence of semidefinite programs by employing the semidefinite relaxation, non-linear fractional programming and S-procedure. Furthermore, we show that the maximum SEE can be achieved through a search algorithm in the single dimensional space. Numerical results, when compared with those obtained with existing techniques in the literature, show the effectiveness of the proposed designs for SEE maximization.

Design of Asymptotically Optimal Improper Constellations With Hexagonal Packing

This paper addresses the problem of designing asymptotically optimal improper constellations with a given circularity coefficient (correlation coefficient between the constellation and its complex conjugate). The designed constellations are optimal in the sense that, at high signal-to-noise-ratio (SNR) and for a large number of symbols, yield the lowest probability of error under an average power constraint for additive white Gaussian noise channels. As the number of symbols grows, the optimal constellation is the intersection of the hexagonal lattice with an ellipse whose eccentricity determines the circularity coefficient. Based on this asymptotic result, we propose an algorithm to design finite improper constellations. The proposed constellations provide significant SNR gains with respect to previous improper designs, which were generated through a widely linear transformation of a standard $M$ -ary quadrature amplitude modulation constellation. As an application example, we study the use of these improper constellations by a secondary user in an underlay cognitive radio network.

Secrecy outage performance analysis of MIMO underlay cognitive radio networks with delayed CSI and transmitter antenna selection

SummaryCognitive radio network is an emerging solution to deal with spectrum scarcity and to utilize the radio spectrum in opportunistic and efficient manner. Secure data transmission is one of the important issues in these kind of networks. This work studies the secrecy outage performance of a multiple‐input multiple‐output underlay cognitive wiretap radio network system over Rayleigh fading channel with delayed channel state information. This work considers that the secondary transmitter is equipped with multiple antennas and confidential information is transmitted from to multiantenna receiver in the presence of multiantenna eavesdropper. Further, the transmit antenna selection scheme is considered at secondary transmitter to reduce the complexity of antenna selection and to make it more practicable. To improve the quality of signal, this work considers maximal ratio combining (MRC) at secondary receiver, while selection combining and MRC techniques are utilized at the eavesdropper. The closed form expression for exact, asymptotic, and intercept secrecy outage probability has been derived, and the simulation is done for the validation of analytical results. The derived results reveal deterioration of channel secrecy performance with outdated channel state information, and the eavesdropper with outdated channel state information has also an adverse effect. Moreover, the diversity order that can be achieved in underlay cognitive radio network with outdated channel state information is unity.

Performance Analysis of a Secondary User in Cognitive Radio over Generalized-Gamma Fading Channels

DOI : 10.26650/electrica.2019.19017 In this paper, the performance of a secondary user (SU) in an underlay cognitive radio (CR) network over a generalized-gamma (GG) fading channel in terms of three performance metrics, namely, outage probability, ergodic capacity, and bit error rate (BER), is investigated. According to the underlay approach, the transmit power of the SU should be limited to avoid interference to primary users (PUs). The performance metrics of the SU in the underlay CR network are theoretically derived and also obtained with Monte Carlo simulations for a GG fading channel with different fading parameters. To demonstrate the effect of limited power on the performance metrics, three different maximum transmit power levels (Pmax), namely, 10, 20, and 30 dB, are used. The simulation results lead to three conclusions: First, when high values are chosen for the fading parameters (α, c), the fading channel gets less distorted and the performance metrics improve. The second conclusion is that the BER performance gets better as the limited power increases. The final conclusion is that the BER performance of SUs improves as the interference power that PUs can tolerate increases. Cite this article as : Aldirmaz Colak S. Performance Analysis of a Secondary User in Cognitive Radio over Generalized-Gamma Fading Channels. Electrica, 2019; 19(2): 166-172.

CSI Based Multiple Relay Selection and Transmit Power Saving Scheme for Underlay CRNs Using FRBS and Swarm Intelligence

In this article, a multiple relay selection (MRS) scheme for signal-to-noise ratio (SNR) enhancement is proposed for underlay relay-assisted cognitive radio networks (RCRNs). A secondary source-destination pair experiencing deep fading on direct path is assisted by amplify-and-forward (AF) relays in an underlay mode. In this energy-constrained scenario, the aim is to maximize the secondary network's end-to-end SNR through an intelligent power-saving method incorporated with MRS. In contrast to the prior relay selection (RS) schemes, the relay-selection factor is the difference of SNR of the source-relay link and corresponding relay-destination link for each relay along with its corresponding interference channel coefficient. The difference factor aims to achieve the SNR upper bound while performing minimum power amplification, eventually resulting in interference mitigation as well. The proposed algorithm has been implemented using Fuzzy Rule Based System (FRBS), Artificial Bee Colony (ABC) and Particle Swarm Optimization (PSO) and their performance has been compared through simulations.

Multi-population coevolutionary dynamic multi-objective particle swarm optimization algorithm for power control based on improved crowding distance archive management in CRNs

This paper aims to resolve the problem of power control in underlay CRNs better. Firstly, a multi-objective optimization problem of maximizing the throughput of PUs and SUs is proposed, which satisfied the constraints of PU’ interference temperature, the normal communication quality of all users and the transmission power limitation of users. Moreover, according to the theory of penalty function and particle swarm optimization (PSO), an improved multi-objective particle swarm optimization (IMOPSO) algorithm is proposed based on the archives management, which can achieve the maximum throughput of PUs and SUs as well as the minimum penalty constraints term. On this basis, in order to improve the boundary searching ability and diversity of the power control scheme, an improved coevolutionary multi-objective particle swarm optimization (ICMOPSO) in multiple population is proposed based on crowding distance archival management. Further, in order to adapt to the dynamic communication environment well, three different dynamic response schemes are presented correspondingly to cope with the instability of three types of environment. In the end, simulation results show that ICMOPSO and IMOPSO algorithm based on the archives management can obtain the maximum throughput compared with the conventional PSO. Through comparing with the performances in IMOPSO and ICMOPSO, it can be concluded that ICMOPSO algorithm has good abilities of stability, diversity and local search ability, which can provide more throughput optimal allocation schemes for decision makers and ensure the quality of customer service. On the basis of ICMOPSO algorithm, dynamic response strategy is better than the static response strategy at computational cost compared with the average number of iterations. And it can cope with the dimensional change of decision space in dynamic communication environment.

Performance analysis of nonorthogonal multiple access‐based underlay cognitive relay network

SummaryThis paper considers cooperative non‐orthogonal multiple access (NOMA) scheme in an underlay cognitive radio (CR) network. A single‐cell downlink cooperative NOMA system has been considered for the secondary network, consisting of a base station (BS) and two secondary users, ie, a far user and a near user. The BS employs NOMA signaling to send messages for the two secondary users where the near user is enabled to act as a half‐duplex decode‐and‐forward (DF) relay for the far user. We derive exact expressions for the outage probability experienced by both the users and the outage probability of the secondary system assuming the links to experience independent, nonidentically distributed Rayleigh fading. Further, we analyze the ergodic rates of both the users and the ergodic sum rate of the secondary network. The maximum transmit power constraint of the secondary nodes and the tolerable interference power constraint at the primary receiver are considered for the analysis. Further, the interference caused by the primary transmitter (PT) on the secondary network is also considered for the analysis. The performance of the proposed CR NOMA network has been observed to be significantly better than a CR network that uses conventional orthogonal multiple access (OMA) scheme. The analytical results are validated by extensive simulation studies.

Intercept Probability Analysis of Cognitive Radio Threshold-Based System With Diversity Reception

The intercept probability performance of decode-and-forward (DF) underlay cognitive radio threshold-based network is investigated in this paper. Here, a secondary source is transferring data to secondary destination via secondary relay cooperation. There are interference limitations on secondary user of cognitive system from the primary licensed users. The DF relays are not assumed to correctly decode the message always and only those relays which can satisfy the predetermined threshold are successful in decoding the source message. The worst case scenario has been studied, where Maximal Ratio Combining (MRC) and Selection Combining (SC) diversity reception schemes have been applied only at eavesdropper. We have obtained asymptotic and diversity analysis for balanced and unbalanced system. The secrecy of the system is shown to be significantly affected by eavesdropper link quality, predetermined threshold and interference power limitations. Furthermore, the optimal relay selection scheme (OS) is presented and the improvement in secrecy performance is shown with the increase in relay number.