Intercept Probability of Underlay Uplink CRNs with Multi-Eavesdroppers

Cooperative communication is regarded as a key technology in wireless networks, including cognitive radio networks (CRNs), which increases the diversity order of the signal to combat the unfavorable effects of the fading channels, by allowing distributed terminals to collaborate through sophisticated signal processing. Underlay CRNs have strict interference constraints towards the secondary users (SUs) active in the frequency band of the primary users (PUs), which limits their transmit power and their coverage area. Relay selection offers a potential solution to the challenges faced by underlay networks, by selecting either single best relay or a subset of potential relay set under different design requirements and assumptions. The best relay selection schemes proposed in the literature for amplify-and-forward (AF) based underlay cognitive relay networks have been very well studied in terms of outage probability (OP) and bit error rate (BER), which is deficient in multiple relay selection schemes. The novelty of this work is to study the outage behavior of multiple relay selection in the underlay CRN and derive the closed-form expressions for the OP and BER through cumulative distribution function (CDF) of the SNR received at the destination. The effectiveness of relay subset selection is shown through simulation results.

A hybrid overlay/underlay cognitive radio network (CRN) is demonstrated to provide high spectrum efficiency and channel capacity. Decision‐making in joining CRNs is one of the major issues of secondary users (SUs). Each SU has the option of joining the spectrum or balking according to the trade‐off between the service profit and the delay cost. In this study, the decision‐making problem in accessing the hybrid overlay/underlay CRN is addressed using queuing models and game theory. An almost unobservable queuing server is used to model hybrid overlay/underlay CRN. The interaction between the cognitive users is treated as a non‐cooperative game. A closed‐form expression for the average number of cognitive users as well as associated expected waiting time in both overlay and underlay CRNs is derived. The strategic behaviour for spectrum access of cognitive users in hybrid overlay/underlay CRN is investigated and the existence of symmetric Nash equilibrium is proved as well. Finally, we provide extensive validation results using a wide range of realistic simulation scenarios. The proposed model gives detailed guidance to the decision makers to deploy the suitable strategy according to the available channel situation.

In this paper, we propose a cooperative spectrum sharing protocol for cognitive radio networks (CRNs) which operate in underlay mode with an automatic repeat-request (ARQ)-based primary user (PU) including primary transmitter (PT) and primary receiver (PR) and a bidirectionally communicating secondary user (SU) which consists of the nodes S1 and S2. In ARQ-based PU, ACKnowledgement/Negative-ACKnowledgement (ACK/NACK) messages are sent from PR to PT and listened by S1 and S2 to control the PU's packet success. Si (i=1 or 2) alerts both PT and PR if its reception from PT is successed or failed and PR considers the link from Si or PT, respectively. PU transmits its packet by accessing the spectrum alone or by cooperating with SU or under an interference caused by SU. If PT transmits alone its packet successfully, in the next time slot it transmits a new packet in underlay mode during which SU access the spectrum simultaneously with a tolerable interference level to improves the PU's performance. Conversely, if PT fails to transmit alone its packet and at least one of the nodes S1 and S2 success to decode it, then S1 or S2 cooperates with PT attending as a relay to enhance the PU's throughput in the next time slot during which PT stays silent. If both of S1 and S2 fail to decode PT's packet, PT retransmits its packet in underlay mode. When the first transmission of PT's packet is failed in underlay mode, PT retransmits this packet alone. We derive analytical expressions for the throughputs of PU and SU and show that the proposed protocol significantly improves the PU's throughput compared to non-CR scheme while stabilizing the SU's throughput at high SNR values.

This paper investigates the performance of Multisource Multirelay Cognitive Radio Network (MMCRN). Underlay spectrum sharing is used to achieve efficient spectrum utilization while limiting the interference level on the Primary User (PU) with an average interference power constraint. One source and one relay are selected for Secondary User (SU) transmission based on maximizing the SU effective capacity (EC) of the transmission channel. Practically, this paper studies the MMCRN with assuming Imperfect Channel State Information (ICSI) of the interference link between the SU source (SS) and the PU destination (PD). Performance analysis measurement in terms of SU EC is derived for the proposed system model when there is an average interference power constraint and with considering ICSI. The proposed numerical analysis demonstrates the quasi-optimal number of relays that should be used to obtain an efficient SU EC. In addition, the obtained results investigate the effect of the interference channel imperfection on the measurement metric with different parameters such as the number of SUs and the SU statistical delay QoS constraint.

In this paper, the performance of asecondary user (SU) in an underlay cognitive radio (CR) network over ageneralized-gamma (GG) fading channel in terms of three performance metrics,namely, outage probability, ergodic capacity, and bit error rate (BER), isinvestigated. According to the underlay approach, the transmit power of the SUshould be limited to avoid interference to primary users (PUs). The performancemetrics of the SU in the underlay CR network are theoretically derived and alsoobtained with Monte Carlo simulations for a GG fading channel with different fadingparameters. To demonstrate the effect of limited power on the performancemetrics, 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 fadingchannel gets less distorted and the performance metrics improve. The secondconclusion is that the BER performance gets better as the limited powerincreases. The final conclusion is that the BER performance of SUs improves asthe interference power that PUs can tolerate increases. Cite this article as: Aldırmaz Çolak S.Performance Analysis of a Secondary User in Cognitive Radio overGeneralized-Gamma Fading Channels. Electrica, 2019; 19(2): 166-172.

In this paper, we introduce a new cooperative paradigm for secure communication in cognitive radio networks (CRNs) where secondary users (SUs) are allowed to access the spectrum of primary users (PUs) as long as they preserve the secure communication of PUs in the presence of malicious eavesdroppers. To do so, the SU transmission is divided into two hops: at first hop, the SU transmitter sends the information to a relay set and the SU receiver acts as a friendly jammer to disturb the overhearing of eavesdroppers and at the second hop, one of the relays is selected to pass the information to the SU receiver and the SU transmitter acts as a friendly jammer for the PU. In this new setup, the time duration for each hop, the power transmissions of all nodes in CRN, and relay selection at the second hop are allocated in such a way that the secrecy rate of the SU is maximized subject to the minimum required PU's secrecy rate. From primary service perspective, this transforms the possibly disturbing secondary service activities into a beneficial network element. We investigate instantaneous and ergodic resource allocation problems for perfect and imperfect channel state information (CSI). Since these problems are non-convex, we propose a solution based on decomposition of main optimization problem into three subproblems related to the power allocation, time allocation, and relay selection. We show that the power allocation problem can be transformed into a generalized geometric programming (GGP) model via the so-called scaled algorithm and it can be solved very efficiently. Simulation results indicate that in terms of the secondary secrecy rate, the proposed setup outperforms the conventional setup in which the secrecy rate of the PU is not guaranteed.

In this study, the problem of robust adaptive power control (PC) in an underlay cognitive radio network with multiple secondary users (SUs) and primary users (PUs) is considered. Due to the effects of uncertainties (i.e. estimation errors, delays), the optimal PC (resource allocation) cannot guarantee the quality of service of SUs and PUs under imperfect channel state information and interference power of PUs. A robust resource allocation problem is formulated to maximise sum throughput of SUs under individual power constraints and signal-to-interference-and-noise ratio constraints of SUs as well as interference temperature constraints of PUs, whereas channel uncertainties and interference uncertainties induced into the secondary system are modelled by multiplicative uncertainties. Under the worst-case approach, the problem is transformed into a geometric programming problem solved by Lagrange dual methods. The performance of the different algorithms and the impact of uncertainties are discussed according to several simulation results.

In cognitive radio networks (CRNs), secure information transfer is of paramount importance for primary users (PUs), while secondary users (SUs) mainly desire to ease the starvation for transmission opportunities. To meet such different requirements, cooperation between PUs and SUs can be leveraged and therefore create a win-win situation. In this paper, we investigate cooperative spectrum access for CRNs, which targets to improve the secure transmission of PUs via cooperating SUs that would be incented by certain transmission opportunities. Two types of cooperation schemes are proposed, whereby the PU either cooperates with two individual SUs or a cluster of SUs, which are referred to as relay-jammer (R-J) scheme and cluster-beamforming (C-B) scheme, respectively. In R-J scheme, two individual SUs act as a relay and a friendly jammer to improve the PU's secrecy; In return, the PU allocates a fraction of access time for the SUs' transmission. To achieve the maximum secrecy rate, joint time and power allocation is considered. Particularly, the cooperating relay and jammer determine the optimal transmission power, while the PU decides the optimal time allocation strategy. In C-B scheme, the PU cooperates with a cluster of SUs to enhance the secrecy of the primary link via collaborative beamforming, where three different approaches are proposed for the scenarios with one eavesdropper, with multiple eavesdroppers, and without eavesdroppers' information, respectively. To maximize the secrecy rate, the weight selection and time allocation are also studied. Simulation results are given to validate the proposed schemes and demonstrate that the PU can significantly enhance the secrecy through cooperation.

Unlike in overlay cognitive radio networks, secondary users in underlay cognitive radio networks can access licensed spectrum even at the presence of a primary user, given that the interference caused by the secondary transmission is lower than a pre‐specified threshold. Based on this underlay access principle, we propose in this paper a dynamic channel access strategy for multi‐channel cognitive radio networks. Different from existing underlay access techniques, channel assembling, spectrum adaptation and restricted channel occupancy are also considered in the proposed strategy in order to achieve better performance in the secondary network. Accordingly, a partial channel occupancy mode, which allows secondary users to access a portion of a channel when co‐existing with a primary user, is introduced in this study. The size of this portion is adjusted by selecting an appropriate value of a configurable parameterαin the partial channel occupancy mode. The system performance is evaluated for both primary and secondary networks, and a comparison analysis is carried out to assess the cost against the gain. Numerical results demonstrate that the proposed underlay channel access strategy outperforms the corresponding overlay strategy in terms of secondary network capacity, blocking probability and dropping probability. The cost and gain analysis identifies appropriate traffic conditions under which the overall system performance could be improved by employing the proposed underlay strategy. Copyright © 2015 John Wiley & Sons, Ltd.

We consider a network of cognitive users (also referred to as secondary users (SUs)) coexisting and sharing the spectrum with primary users (PUs) in an underlay cognitive radio network (CRN). Specifically, we consider a CRN wherein the number of SUs requesting channel access exceeds the number of available frequency bands and spatial modes. In such a setting, we propose a joint fast optimal resource allocation and beamforming algorithm to accommodate maximum possible number of SUs while satisfying quality of service (QoS) requirement for each admitted SU, transmit power limitation at the secondary network basestation (SNBS) and interference constraints imposed by the PUs. Recognizing that the original user maximization problem is a nondeterministic polynomial-time hard (NP), we use a mixed-integer programming framework to formulate the joint user maximization and beamforming problem. Subsequently, an optimal algorithm based on branch and bound (BnB) method has been proposed. In addition, we propose a suboptimal algorithm based on BnB method to reduce the complexity of the proposed algorithm. Specifically, the suboptimal algorithm has been developed based on the first feasible solution it achieves in the fast optimal BnB method. Simulation results have been provided to compare the performance of the optimal and suboptimal algorithms.

Energy-efficient power allocation for multi-user single-AF-relay underlay cognitive radio networks

The optimal admission control for secondary users (SUs) using blockchain technology in a cognitive radio (CR) network is investigated in this paper. When an SU comes to the system, it will decide to either enter the system, or give up its service and then leave the system based on the current number of PU and SU users in the network. SUs are linked as a block in the waiting area to access the spectrum in an opportunistic way without interfering the operations of PUs. When a PU arrives, if the band is occupied by SU(s), the SU service on the band is interrupted and SU(s) is then placed back to the waiting queue. Admitting an SU would bring a reward to the system provider but holding an SU in the system would also incur an expense to the provider. We concentrate on the optimization problem of when to admit or reject an arriving SU in order to achieve the maximum total discounted expected reward for any initial state. By establishing a discounted Continuous Time Markov Decision Process (CTMDP) model, we verify that the optimal policies for admitting SUs are state-related control limit policies. An extensive numerical analysis is implemented to show how to determine the value of optimal threshold and of the corresponding maximum objective function. Especially, a simulation by using the idea of the neural network and machine learning is implemented to show how to determine the optimal threshold value for any new input parameters through learning process for a given input parameters. The idea and the corresponding result of this paper can be applied in designing optimal cognitive radio networks.

Empowered by the cognitive radio technology, and motivated by the sporadic channel utilization, both spatially and temporally, dynamic spectrum access networks (also referred to as cognitive radio networks and next generation wireless networks) have emerged as a solution to improve spectrum utilization and provide more flexibility to wireless communication. A cognitive radio network is composed of wireless users, referred to as secondary users, which are allowed to use a given licensed spectrum band as long as there are no primary, licensed, users occupying this band in their vicinity. This restricted spectrum access strategy leads to heterogeneity in channel availability among secondary users. Heterogeneity in channel availability forms a significant source of performance degradation for cognitive radio networks, and poses a great challenge on protocol design. In this dissertation, we propose spectrum allocation algorithms that take this heterogeneity property and its effect on the network performance into consideration. The spectrum allocation solutions proposed in this dissertation address three major objectives in cognitive radio mesh networks. The first objective is maximizing the network coverage, in terms of the total number of served clients, and at the same time simplifying the communication coordination function. To address this objective, we proposed a received based channel allocation strategy that alleviates the need for a common control channel, thus simplifying the coordination function, and at the same time maximizes the number of clients served with link reliability guarantees. We show the superiority of the proposed allocation strategy over other existing strategies. The second objective is improving the multicast throughput to compensate for the performance degradation caused by the heterogeneity in channel availability. We proposed a

In cognitive radio networks, security issues arise when intelligent malicious users can attack and decrease the permitted channel for unlicensed users (secondary users). In this paper, we propose a novel scheme, based on friend or foe (FoF) detection technique with physical layer network coding, to enable discrimination between secondary users and intelligent malicious users. Theoretical expressions are derived for probabilities of detection of secondary user, miss detection, and false alarm. In addition, the effectiveness of the proposed approach is evaluated by theoretical analysis and Monte Carlo simulation. Furthermore, an algorithm is proposed for distinguishing between secondary user and intelligent malicious user. Finally, based on the outcome of simulation of probabilities and normalised cross-correlation, it is determined that the proposed scheme outperforms in terms of orthogonal frequency-division multiplexing (OFDM) signal compared with quadrature phase-shift keying (QPSK) signal over cognitive radio network.

In this paper, the power allocation of Non-orthogonal multiple access (NOMA) for secondary users in underlay cognitive radio is studied. In underlay cognitive radio networks, the interference, which is produced by secondary users (SUs), should be less than predefined threshold. On the other hand, their SINR should be greater than certain threshold, otherwise outage occurs. Accordingly, the total rate of downlink SUs can be maximized under the SUs SINR and interference limits constraints. The optimum power allocation coefficients of users are derived. Due to the low complexity of this new method for power allocation, it can be simply implemented in the practical systems. Simulation results show that the proposed scheme achieves a higher rate and lower outage compared to the previous NOMA schemes with fixed power allocation coefficients as well as conventional orthogonal multiple access.