Primary User Nodes Research Articles

CR-IoTNet: Machine learning based joint spectrum sensing and allocation for cognitive radio enabled IoT cellular networks

In recent years, the Internet of Things (IoT) paradigm has gained much popularity due to its potential ability to integrate the physical world with the digital world. However, this digital revolution is driving an insatiable demand for wireless spectrum, leading the upcoming novel personal, social and industrial IoT applications competing for limited spectrum resources. One of the main challenges that may hinder the vision of IoT is the scarcity of radio spectrum. Therefore, in order to cope with the challenge of spectrum scarcity brought about by the unprecedented number of IoT devices, this paper proposes to integrate cognitive radio (CR) technology with the IoT paradigm (CR-IoTNet). The CR is realized as a promising solution to improve the spectrum utilization and alleviate the spectrum scarcity in wireless networks. In CR, spectrum sensing is widely recognized as a key technology that enables secondary users (SUs) to detect spectrum holes and have the opportunity to access unoccupied spectrum. The CR-IoTNet, which is composed of multiple primary user (PU) base-stations and SU devices as IoT smart objects, performs the joint spectrum sensing and optimal allocation of spectrum to the requesting SU-IoT devices in the network through an intelligent fusion center (IFC). Furthermore, we employ support vector machines (SVM) in CR-IoTNet, enabling it to learn and adapt to the changing network dynamics, and identify the PU spectrum usage based on the established multi-class (J×6)-D feature set. The performance of CR-IoTNet is evaluated across several key factors, where simulation results validate the efficacy of the proposed framework in achieving high reliable identification, classification and allocation of unoccupied frequency bands in PU spectrum, especially in key areas of low signal-to-noise ratio (SNR). In addition, the trained SVM classifier obtained 95.11% accuracy, with 92.67% true positive rate and 96.34% true negative rate in CR-IoTNet, reflecting the optimal allocation of PU nodes for spectrum access.

An integrated service model to support user specific QoS routing in cognitive radio ad hoc network

Routing in Cognitive Radio Ad Hoc Network (CRAHN) is a challenging task due to limited spectrum availability. To overcome this problem several researchers have proposed various routing schemes based on Quality of Service (QoS) and spectrum availability. These schemes choose a path that gives maximum QoS and spectrum level ignoring the required QoS level for a particular application which may be quite less than the maximum level. Thus, this paper proposes an integrated service model having eight classes instead of two for CRAHN to envisage the admission control at Primary User (PU) nodes thus reducing overhead on Secondary Users (SU) for various applications. The PU node first examines the spectrum availability and then checks whether the received packet can be granted user specific Quality of Service (QoS) or not to support Elastic plus Real Time Applications for (SU) nodes. To prove the efficacy of proposed scheme comparison with Cognitive Ad hoc On-demand Distance Vector (CAODV) or shortest spectrum aware path routing mechanism is done. The result exhibits that high performance rate for good reliability, low latency and high throughput with fair load distribution among all the nodes of the network.

Secure Distance Based Improved Leach Routing to Prevent Puea in Cognitive Radio Network

Routing in cognitive radio networks (CRNs) faces numerous limitations in misbehaving activities and secure the routing requests and reply messages. In this research work, Secure Distance based Improved LEACH Routing (SDILR) protocol is presented to avoid the primary user emulation attack (PUEA) in CRN. Initially, the nodes in the cognitive radio network are clustered by using distance based improved Low- energy adaptive clustering hierarchy (ILEACH). After the formation of clusters, secure routing is presented using support value based signature authentication to avoid PUEA. The proposed secure ILEACH routing results the secure data sharing through the primary user nodes PUEA.

Cognitive MIMO-RF/FSO Cooperative Relay Communication With Mobile Nodes and Imperfect Channel State Information

This paper analyzes the performance of an underlay cognitive radio based decode-and-forward mixed multiple-input multiple-output radio frequency/free space optical cooperative relay system with multiple mobile secondary and primary user nodes. The effect of imperfect channel state information (CSI) arising due to channel estimation error is also considered at the secondary user transmitters (SU-TXs) and relay on the power control and symbol detection processes respectively. A unique aspect of this paper is that both fixed and proportional interference power constraints are employed to limit the interference at the primary user receivers. Analytical results are derived to characterize the exact and asymptotic outage and bit error probabilities of the above system under practical conditions of node mobility and imperfect CSI, together with impairments of the optical channel, such as path loss, atmospheric turbulence, and pointing errors, for orthogonal space-time block coded transmission between each SU-TX and relay. Finally, simulation results are presented to yield various interesting insights into the system performance such as the benefits of a midamble versus preamble for channel estimation.

Performance Analysis of Co-Operative Beacon Sensing Strategies for Spatially Random Cognitive Users

Primary user (PU) beacons must be detected by cognitive users (CUs) to access spectrum holes, and misdetection results in interference on PUs. To alleviate this problem, sensing results of spatially separated CUs can be combined to make a final decision. In this paper, we analyze several such co-operative beacon sensing (CBS) strategies given spatial randomness of CU and PU nodes, which is modeled via independent homogeneous Poisson point processes. We consider two cases of beacon emitter placement: 1) at PU-transmitters and 2) at PU-receivers. We analyze three separate local beacon detection schemes and propose five CBS schemes. They require the sharing of CU results via a control channel subject to Rayleigh fading and path loss, and making a final decision via the OR rule. By using stochastic geometry, we derive both the misdetection probability, the false alarm probability, and the primary outage and show that impressive gains are achievable. For example, with PU-receiver beacons, CBS reduces misdetection by a factor of 104. In contrast, with PU-transmitter beacons, the reduction diminishes with the increased cell radii, but there exists an optimum cooperation radius.

Artificial Noise-Aided Physical Layer Security in Underlay Cognitive Massive MIMO Systems with Pilot Contamination

In this paper, a secure communication model for cognitive multi-user massive multiple-input multiple-output (MIMO) systems with underlay spectrum sharing is investigated. A secondary (cognitive) multi-user massive MIMO system is operated by using underlay spectrum sharing within a primary (licensed) multi-user massive MIMO system. A passive multi-antenna eavesdropper is assumed to be eavesdropping upon either the primary or secondary confidential transmissions. To this end, a physical layer security strategy is provisioned for the primary and secondary transmissions via artificial noise (AN) generation at the primary base-station (PBS) and zero-forcing precoders. Specifically, the precoders are constructed by using the channel estimates with pilot contamination. In order to degrade the interception of confidential transmissions at the eavesdropper, the AN sequences are transmitted at the PBS by exploiting the excess degrees-of-freedom offered by its massive antenna array and by using random AN shaping matrices. The channel estimates at the PBS and secondary base-station (SBS) are obtained by using non-orthogonal pilot sequences transmitted by the primary user nodes (PUs) and secondary user nodes (SUs), respectively. Hence, these channel estimates are affected by intra-cell pilot contamination. In this context, the detrimental effects of intra-cell pilot contamination and channel estimation errors for physical layer secure communication are investigated. For this system set-up, the average and asymptotic achievable secrecy rate expressions are derived in closed-form. Specifically, these performance metrics are studied for imperfect channel state information (CSI) and for perfect CSI, and thereby, the secrecy rate degradation due to inaccurate channel knowledge and intra-cell pilot contamination is quantified. Our analysis reveals that a physical layer secure communication can be provisioned for both primary and secondary massive MIMO systems even with the channel estimation errors and pilot contamination.

Exact Outage Probability Analysis of a Dual-Hop Cognitive Relaying Network Under the Overhearing of an Active Eavesdropper

In this paper, we study the secure communication of dual-hop cognitive relaying networks. An eavesdropper can combine two received signals from two hops by using the maximum ratio combining technique. The data transmission from the secondary source to the secondary destination is assisted by the best decode-and-forward relay, which is selected from four relay selection schemes. The first scheme, MaSR, is based on the maximum channel gain from the source to the relays. In the second scheme, MaRD, the best relay is selected on the basis of the maximum channel gain from the relays to the destination. In the third scheme, MiRE, the gain to the eavesdroppers is instead minimized. Finally, optimal relay selection is considered as the fourth scheme. For these four schemes, we study the system security performance by deriving the exact analytical secrecy outage probability. These analytical expressions are then verified by comparing them with the results of Monte Carlo simulations. Herein, we evaluate and discuss the outage performance of the schemes while varying important system parameters: the number and locations of the relay nodes, primary user node, and eavesdropper; the transmit power threshold; and the target secure rate.

Cognitive Decode-and-Forward MIMO-RF/FSO Cooperative Relay Networks

This letter considers decode-and-forward (DF) based mixed multiple-input multiple-output radio frequency/free space optical (MIMO-RF/FSO) cooperative relay systems for underlay cognitive radio scenarios. Subsequently, a performance analysis is presented and closed-form expressions are derived for the per-frame outage probability considering both orthogonal space-time block coded transmission and transmit antenna selection at the secondary user. The analysis assumes the RF links between the secondary user-relay and secondary user-primary user to be Nakagami- $m$ fading in nature, while the FSO link between the relay and destination eNodeB is assumed to be affected by optical channel impairments, such as path loss, atmospheric turbulence, and pointing errors, thus incorporating the key characteristics of both the links. Further, the impact of primary user node mobility on the performance of the cognitive radio network is also analyzed. Results demonstrate an improved outage performance of the cognitive MIMO-RF/FSO DF cooperative relay system with multiple antennas in comparison to amplify-and-forward based single-input single-output systems proposed in the existing literature.

Maximum Lifetime Communication Topologies of Secondary User Nodes in Cognitive Radio Ad hoc Networks

A Cognitive radio ad hoc network (CRAHN) is an ad hoc network of primary user (PU) nodes and secondaryuser (SU) nodes, wherein the SU nodes use the licensed channels of the PU nodes when not in use. As theavailability of the PU channels fluctuates with time, communication topologies spanning the SU nodes have tobe dynamically and frequently reconfigured. Given the complete knowledge of the availability of the PUchannels, we propose a generic benchmarking algorithm that determines a sequence of stable communicationtopologies spanning all of the SU nodes such that the number of transitions from one instance of the topology toanother is the global minimum. At any time instant t when we need a stable communication topology spanningthe entire network, we look for the largest value of k such that the intersection of the static SU graphs from timeinstants t to t+k, defined as the mobile graph Gt...t+k(SU) = Gt(SU) ? Gt+1(SU) ? .... ? Gt+k(SU), is connected andthat the mobile graph Gt...t+k+1(SU) is not connected. We repeat the above procedure for the entire network sessionto determine a sequence of longest-living instances of the mobile graphs and the corresponding instances of thecommunication topology of interest (say a shortest path tree rooted at a source SU node) such that the number oftopology transitions is the minimum. We prove the theoretical correctness of the algorithm and evaluate itseffectiveness by implementing it to determine a sequence of shortest path trees of the maximum lifetime.

Robust Two-Way Cognitive Relaying: Precoder Designs under Interference Constraints and Imperfect CSI

We present various robust precoder designs for two-way relaying in a cognitive radio network, where a pair of cognitive (or secondary) transceiver nodes communicate with each other assisted by a set of cognitive two-way relays. The secondary nodes share the spectrum with a licensed primary user (PU) node while keeping the interference to the PU below a specified threshold. The PU node and the cognitive transceivers employ single transmit/receive antennas whereas the secondary relay nodes employ multiple transmit/receive antennas. The proposed precoder designs ensure robust performance in the presence of errors in the channel state information (CSI). Such robust designs are of significant interest since in practice it is very difficult to obtain perfect CSI. We consider CSI errors with two different types of characterization and corresponding robust designs. First, we consider robust relay precoder designs that are applicable when CSI errors have known first and second moments. Next, we consider robust designs that are applicable when the CSI error can be characterized in terms of spherical uncertainty region. We show that the proposed designs can be reformulated as convex optimization problems that can be solved efficiently. Through numerical simulations and comparisons we illustrate the performance of the proposed designs.

A fuzzy-based routing protocol for cognitive radio networks

With the growing spectrum demand over the last decade, the use of cognitive radio networks (CRN) has provided a viable solution to spectrum scarcity problem. These networks basically employ two types of users: primary user (PU) and secondary user (SU). The PUs are allocated a license to use the spectrum at their will. On the other hand the SUs communicates via other SUs or through the licensed spectrum of PU nodes opportunistically. In such a scenario it is important that routing protocol that is deployed must take into consideration the stability of the route. Therefore, this paper proposes a novel fuzzy-based routing strategy with this objective in mind. Further, an attempt has been made to evaluate the performance of proposed routing strategy in realistic environment. The simulation results shows that the path selection utilising the fuzzy theory presents far better results when compared with shortest path routing protocol employing CR capabilities.

Optimal power allocation for cognitive relay networks: amplify-and-forward versus selection relay

We consider a cognitive relay network which is defined by a source, a destination, and cognitive relay nodes and primary user nodes. In this network, a source is assisted by cognitive relay nodes which allow coexisting with primary user nodes by imposing severe constraints on the transmission power so that they operate below the noise floor of primary user nodes. In this paper, we mainly study the power allocation strategies of this system to minimize the outage probability subject to total and individual power constraints for cognitive relay nodes and subject to interference constraints for primary user nodes. A relay transmission scheme, namely amplify-and-forward (AF), is considered. We first present an optimal power allocation (OPA) scheme to minimize the system outage probability, based on instantaneous channel state information among the source, destination and relay nodes and mean channel gains between primary user nodes and cognitive relays. Next, we propose a selection AF scheme (S-AF) where the single best relay is chosen to assist in the transmission and study power allocation strategy for S-AF to minimize outage probability. The analytical power allocation strategies have been validated through numerical simulations. The results indicate that the AF with OPA and S-AF with OPA have significantly better outage behavior and average throughput than AF and S-AF schemes respectively. We also find that S-AF with OPA achieves a higher throughput, and hence lower outage probability than AF with OPA.