Secondary User Nodes Research Articles

An energy efficient fair node selection for cooperative in-band and out-of-band spectrum sensing

In a cooperative cognitive network, multiple secondary user (SU) nodes are selected for spectrum sensing to detect the presence of primary user (PU) nodes in the currently used channel as well as identify other available unused licensed channels. Periodic sensing of such in-band (IB) and out-of-band (OB) channel consumes a considerable amount of energy which is a huge liability to an energy constrained networks. Additionally, SU nodes are selected to meet the requirements such as detection and false alarm probabilities. This results the consecutive selection of same nodes, which depletes the energy of those nodes rapidly shortening the lifetime of nodes and network itself. In this paper, we propose a fair and energy efficient node selection scheme for joint IB and OB spectrum sensing. The SU nodes are grouped based on the energy stored in it referred as residual energy. A joint optimization problem is formulated to minimize energy consumption while ensuring the selected nodes belong to specific group depending on whether sensing is IB or OB. Considering the nature of formulated problem, we use particle swarm optimization to solve it. The results show that proposed scheme not only consumes relatively less energy and reduces the number of dead nodes, but also allows to maintain fair distribution residual energy within the network. Consequently, the network can prolong its spectrum sensing activities for longer duration.

A Context-Aware Trust Framework for Resilient Distributed Cooperative Spectrum Sensing in Dynamic Settings

Cognitive radios enable dynamic spectrum access where secondary users (SUs) are allowed to operate on the licensed spectrum bands on an opportunistic noninterference basis. Cooperation among the SUs for spectrum sensing is essential for environments with deep shadows. In this paper, we study the adverse effect of insistent spectrum sensing data falsification (ISSDF) attack on iterative distributed cooperative spectrum sensing. We show that the existing trust management schemes are not adequate in mitigating ISSDF attacks in dynamic settings where the primary user (PU) of the band frequently transitions between active and inactive states. We propose a novel context-aware distributed trust framework for cooperative spectrum sensing in mobile cognitive radio ad hoc networks (CRAHN) that effectively alleviates different types of ISSDF attacks (Always-Yes, Always-No, and fabricating) in dynamic scenarios. In the proposed framework, the SU nodes evaluate the trustworthiness of one another based on the two possible contexts in which they make observations from each other: PU absent context and PU present context. We evaluate the proposed context-aware scheme and compare it against the existing context-oblivious trust schemes using theoretical analysis and extensive simulations of realistic scenarios of mobile CRAHNs operating in TV white space. We show that in the presence of a large set of attackers (as high as 60% of the network), the proposed context-aware trust scheme successfully mitigates the attacks and satisfy the false alarm and missed-detection rates of $10^{-2}$ and lower. Moreover, we show that the proposed scheme is scalable in terms of attack severity, SU network density, and the distance of the SU network to the PU transmitter.

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.

Spectrum-sharing DF generalized order relay selection with interference and multiple primary users using orthogonal spectrums

In this paper, we propose and evaluate the performance of cognitive decode-and-forward (DF) generalized order relay selection network where the primary user (PU) receivers utilize orthogonal spectrums in the presence of interference. We consider a new scenario where the primary receivers utilize orthogonal spectrum bands and the spectrum of the primary receiver whose channel enhances the performance of the secondary system is shared with the secondary user (SU) nodes. Using orthogonal spectrum bands in cellular networks aims to reduce the interference between users as in the downlink transmission where orthogonal frequency bands are used by the base station (BS) in transmitting the data for the different users. The generalized order relay selection scheme is efficient in situations where the opportunistic relaying scheme could fail such as in conditions of imperfect channel-state-information, outdated channel information, and in cases where the best relay is busy in some scheduling and load balancing duties in other parts of the network. Closed-from expression is derived for the end-to-end (e2e) outage probability assuming Rayleigh fading channels. Furthermore, to get more insights about the system behavior, the performance is studied at the high signal-to-noise ratio (SNR) regime where the diversity order and coding gain are derived. Monte-Carlo simulations are given to verify the achieved results. The main results show that the number of primary receivers affects the system performance through affecting the coding gain and not the diversity order. Unlike the existing papers where the same spectrum band is assumed to be shared by the primary receivers with the secondary users, our findings demonstrate that increasing the number of primary receivers in the proposed scenario enhances the system performance. Finally, results illustrate that when the interference at the secondary relays or destination or at both scales with SNR, the system achieves a zero diversity order and a noise floor appears in the results due to the effect of interference on the system performance.

Performance Analysis and Power Allocation for Underlay Cognitive MIMO Relaying Networks with Transmit Antenna Selection Under Antenna Correlation

In this paper, we examine transmit antenna selection with receiver maximal ratio combining (TAS/MRC), and selection combining (TAS/SC) in underlay multiple-input multiple-output cognitive relay networks with decode-and-forward relaying protocol, considering optimal and suboptimal cases. The considered secondary user (SU) network consists of a source, a relay and a destination each equipped with multiple correlated antennas. On the other hand, the primary network is composed of L primary users (PU) destinations, each of which is equipped with multiple correlated antennas. The SU transmission power is limited to the minimum between the maximum allowable power for transmission and the maximum interference power allowed by the PU network. In the analysis, all the channel coefficients between the PU and SU networks and between the SU nodes are assumed to follow independent and identically distributed (i.i.d.) Rayleigh fading distribution. Hence, new exact closed-form expressions are derived to study the outage performance of the considered CRN system. Moreover, for the high SNR values, simple asymptotic expressions for the outage probability are obtained to get more insights on the characterization of the achievable diversity orders and coding gains. The impact of antenna correlation on the system outage probability is investigated for special correlation cases. To enhance SU network performance, a power allocation optimization problem is formulated to minimize the SU asymptotic outage probability by optimally distributing the SU power budget between the SU source and SU relay under the constraints of total allowable SU transmission power and maximum allowable PU interference limit. The derived analytical formulas herein are supported by numerical and simulation results to clarify the main contributions. The results show that although the antenna correlation harms the system coding gain, the considered system can still achieve a full diversity order. Also, The results show that although the outage performance of optimal case outperforms the suboptimal case, the optimal case is more complicated compared to the suboptimal one. Moreover, the optimal power allocation solutions enhance the system outage performance compared to equal distribution model.

Resource allocation in cooperative cognitive radio networks towards secure communications for maritime big data systems

In this paper, an innovative framework labeled as cooperative cognitive maritime big data systems (CCMBDSs) on the sea is developed to provide opportunistic channel access and secure communication. A two-phase frame structure is applied to let Secondary users (SUs) entirely utilize the transmission opportunities for a portion of time as the reward by cooperation with Primary users (PUs). Amplify-and-forward (AF) relaying mode is exploited in SU nodes, and Backward induction method based Stackelberg game is employed to achieve optimal determination of SU, power consumption and time portion of cooperation both for non-secure communication scenario and secure communication. Specifically, a jammer-based secure communications scheme is developed to maximize the secure utility of PU, to confront of the situation that the eavesdropper could overheard the signals from SU i and the jammer. Close-form solutions for the best access time portion as well as the power for SU i and jammer are derived to realize the Nash Equilibrium. Simulation results validate the effectiveness of our proposed strategy.

Eigenvector centrality-based stable path routing protocol for cognitive radio ad hoc networks

We propose to use eigenvector centrality (EVC) as the basis for determining stable paths and arrive at benchmarks for the number of path transitions incurred with stability-based routing in cognitive radio ad hoc networks (CRAHNs) wherein secondary users (SUs) use the available (idle) licensed channels of primary users (PUs). We model a time-variant network graph (at any time instant) of SU nodes whose adjacency matrix indicates the number of common available PU channels in the mutually intersecting neighbourhoods of any two SU nodes at the time instant. Such an adjacency matrix is used as the basis to compute the EVC of the vertices in the network graph of SU nodes and determine an end-to-end source-destination path whose constituent SU nodes have a higher EVC. Simulation results indicate EVC-based paths between any two SU nodes incur significantly fewer transitions without any appreciable increase in the average hop count per path.

Wireless Energy Harvesting in Cognitive Massive MIMO Systems with Underlay Spectrum Sharing

The achievable sum rate of a wireless-powered multi-cell/multi-user cognitive radio massive multiple-input multiple-output system with underlay spectrum sharing is investigated. The secondary user nodes can harvest energy from the primary user transmissions, and then access and utilize the primary network spectrum for information transmission. The signal-to-interference-plus-noise ratio and achievable sum rate are derived for two specific antenna configurations: 1) unlimited base-station antenna arrays and 2) limited base-station antenna arrays. Furthermore, the optimal time-switching factor and the energy-rate trade-off are quantified in closed-form. The asymptotic analysis reveals that the secondary system can be operated by using its maximum harvested energy when the number of primary base-station antennas grows without bound without hindering the primary transmission.

Route selection for interference minimization to primary users in cognitive radio ad hoc networks: A cross layer approach

An opportunistic routing problem in a cognitive radio ad hoc network is investigated with an aim to minimize the interference to primary users (PUs) and under the constraint of a minimum end-to-end data rate for secondary users (SUs). Both amplify-and-forward (AF) and decode-and-forward (DF) relaying techniques are considered for message forwarding by SU nodes in the network. Unlike popular transmit power control based solutions for interference management in cognitive radio networks, we adopt a cross layer approach. The optimization problem is formulated as a joint power control, channel assignment and route selection problem. Next, closed form expression for transmission power is derived and corresponding channel selection scheme and routing metric are designed based on this solution. The proposed route selection schemes are shown to depend not only on gains of the interference channels between SUs and PUs but also on the values of the spectrum sensing parameters at the SU nodes in the network. Two distributed routing schemes are proposed based on our analysis; (i) optimal_DF and (ii) suboptimal_AF. The routing schemes could be implemented using existing table driven as well as on demand routing protocols. Extensive simulation results are provided to evaluate performance of our proposed schemes in random multihop networks. Results show significant reduction in PUs’ average interference experience and impressive performance as opportunistic routing schemes can be achieved by our schemes compared to traditional shortest path based routing schemes. Performance improvement is also reported over prominent recent schemes.

Joint Opportunistic Spectrum Access and Optimal Power Allocation Strategies for Full Duplex Single Secondary User MIMO Cognitive Radio Network

This paper introduces a full duplex single secondary user multiple-input multiple-output (FD-SSU-MIMO) cognitive radio network, where secondary user (SU) opportunistically accesses the authorized spectrum unoccupied by primary user (PU) and transmits data based on FD-MIMO mode. Then we study the network achievable average sum-rate maximization problem under sum transmit power budget constraint at SU communication nodes. In order to solve the trade-off problem between SU`s sensing time and data transmission time based on opportunistic spectrum access (OSA) and the power allocation problem based on FD-MIMO transmit mode, we propose a simple trisection algorithm to obtain the optimal sensing time and apply an alternating optimization (AO) algorithm to tackle the FD-MIMO based network achievable sum-rate maximization problem. Simulation results show that our proposed sensing time optimization and AO-based optimal power allocation strategies obtain a higher achievable average sum-rate than sequential convex approximations for matrix-variable programming (SCAMP)-based power allocation for the FD transmission mode, as well as equal power allocation for the half duplex (HD) transmission mode.

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.

A Distributed Approach to Construct Minimum Spanning Tree in Cognitive Radio Networks

Abstract The minimum spanning tree is useful for data disseminating or broadcasting where a leader node can regulate the data with minimum cost and time. The article presents an algorithm to construct minimum spanning tree in cognitive radio networks. The cognitive radio network works differently with single channel or multi-channel wireless networks than conventional wireless networks. The cognitive radio (or secondary user) nodes have multi-channel accessing capabilities during run time by adjusting the radio parameters according to the available spectrum. The primary user or licensed user holds the spectrum and if it is free, the secondary user can use this for any purpose. Initially, we identify the challenges related to formation of logical structure in cognitive radio network. Then, we present our time and message constrained based cost (or weight) estimation distributed algorithm to construct minimum spanning tree. We describe our algorithm with the help of state diagram representation. The correctness proof of the algorithm is also included.

Outage performance of cognitive AF relay networks with direct link and heterogeneous non‐identical constraints

AbstractAlthough there have been many interesting works on outage performance analysis of cognitive AF relay networks, we have not found works taking into consideration all the following issues: multiple primary users (PUs), the existence of the direct link from secondary user (SU) source to SU destination, non‐identical, independent Rayleigh‐fading channels, non‐identical interference power limits of PUs, and non‐identical noise powers in signals. Additionally, in outage performance analysis for such networks, the correlation issue, which results from the channel gain of interference links from the SU nodes to the PU, requires elaborate treatments. Hence, analyzing outage performance of non‐identical‐parameter networks (where all channels are fully non‐identical Rayleigh‐fading channels, the PUs have different interference power limits, and received signals have different noise powers) from the beginning is highly complicated. To overcome this problem, we conduct the analysis in two steps. In the first step, expressions of both exact and asymptotic outage probability of identical‐parameter cognitive AF relay networks (where all channels are fully non‐identical Rayleigh‐fading channels but all other parameters are identical) are obtained. Then in the second step, we propose a method for transforming a network with all non‐identical parameters into a new identical‐parameter network, meanwhile guaranteeing that outage performance of the two networks before and after the transformation are the same. Hence, OP of the original non‐identical‐parameter network can be obtained indirectly by using the analysis results obtained in the first step. Our analysis results are validated through numerical simulations. The effects of the number of PUs and the diversity level of channel parameters (which means the range of the channel parameter values) are also inspected by simulations. The results show that taking these factors into consideration is of key importance in obtaining a more accurate estimation of outage performance of such networks. Copyright © 2014 John Wiley & Sons, Ltd.

Cognitive Opportunistic DF Relay Networks with Interference and Multiple Primary Receivers Using Orthogonal Spectrums

Most of existing papers on cognitive relay networks with multiple primary user (PU) receivers consider the scenario where the PU receivers utilize the same spectrum band. In this paper, we consider a new scenario where the PU receivers utilize orthogonal spectrum bands and the spectrum of a PU receiver whose channel enhances the performance of the secondary system is shared with the secondary user (SU) nodes. Using orthogonal spectrum bands in cellular networks aims to reduce the interference between users as in the downlink transmission where orthogonal frequency bands are used by the base station in transmitting the data for the different users. In this paper, we study the outage performance of cognitive opportunistic decode-and-forward relaying operating in the secondary network with multiple PU receivers and in the presence of interference from a PU transmitter. A closed-form expression is derived for the outage probability with all system links following Rayleigh distribution. Furthermore, to get more insights about the system behavior, the performance is studied at the high signal-to-noise ratio (SNR) regime where approximate expressions for the outage probability, diversity order, and coding gain are obtained. Monte Carlo simulations are given to validate the achieved results. Main findings illustrate that with fixed interference power, the diversity order of the secondary system equals the number of relays and it is not affected by the number of PU receivers. Also, results show that the number of PU receivers affects the system performance through affecting only the coding gain. Unlike the existing papers where the same spectrum band is assumed to be shared by the PU receivers, our findings demonstrate that increasing the number of PU receivers in the proposed scenario enhances the system performance. Finally, results illustrate that when the interference at the SU relays or at SU destination or at both scales with SNR, the system achieves a zero diversity order and a noise floor appears in the results due to the effect of interference on the system performance.

Optimal Energy-Efficient Power Allocation and Outage Performance Analysis for Cognitive Multi-Antenna Relay Network Using Physical-Layer Network Coding

In this paper, we investigate power allocation scheme and outage performance for a physical-layer network coding (PNC) relay based secondary user (SU) communication in cognitive multi-antenna relay networks (CMRNs), in which two secondary transceivers exchange their information via a multi-antenna relay using PNC protocol. We propose an optimal energy-efficient power allocation (OE-PA) scheme to minimize total energy consumption per bit under the sum rate constraint and interference power threshold (IPT) constraints. A closed-form solution for optimal allocation of transmit power among the SU nodes, as well as the outage probability of the cognitive relay system, are then derived analytically and confirmed by numerical results. Numerical simulations demonstrate the PNC protocol has superiority in energy efficiency performance over conventional direct transmission protocol and Four-Time-Slot (4TS) Decode?and-Forward (DF) relay protocol, and the proposed system has the optimal outage performance when the relay is located at the center of two secondary transceivers.

Performance Analysis of the Primary User in the Secondary User Relay Assisted Spectrum Sharing Networks

In this paper, inaccurate spectrum detecting by the secondary user (SU) is taken into account. The impact of the interference caused by the SUs due to miss detection on the primary user (PU) in a spectrum sharing network is analyzed, and those SU nodes of correct detection are assumed to act as potential relays to assist the PU transmission process based on two proposed cooperative transmission schemes, referred to as, the distance based and the signal-to-noise-ratio (SNR) based schemes. We utilize stochastic geometry to analyze the impact of the secondary network parameters and cooperative transmission schemes on a typical primary source–destination (S–D) pair for the SU relay assisted spectrum sharing networks in Rayleigh fading environment. Using this approach, closed-form expressions for the primary system success probabilities with those cooperative transmission schemes as well as the PU direct re-transmission scheme are derived respectively. Simulations confirm our analytical derivations and results demonstrate that significant improvement on the PU success probability by using SU cooperative transmission schemes, and the SNR based scheme is superior to the distance based scheme.

An Incentivized Cooperative Architecture for Dynamic Spectrum Access Networks

The existing dynamic spectrum access network architecture fails to offer incentives to primary users (PUs). Therefore, PUs are unwilling to cooperate with secondary users (SUs) and intend to set up stringent requirements on SUs' spectrum access. This diminishes the benefit of dynamic spectrum access and hinders its commercialization success. In this paper, we propose a novel architecture for dynamic spectrum access networks, termed incentivized cooperative dynamic spectrum access network (IC-DSAN), to motivate PUs to cooperate with SUs, such that both PUs and SUs achieve significantly higher performance. In an IC-DSAN, SU nodes serve as relays between PU nodes and while relaying PU packets, utilize network coding to encode SU packets onto PU packets, i.e., SU packets get a `free ride' via network coding. To further improve the performance, we propose a new network coding scheme termed coding over coded packets. At last, an optimization model is developed to analyze the throughput gain of IC-DSAN. The performance evaluation indicates that the throughputs of both PUs and SUs significantly increase.

Dynamic Spectrum Sharing for OFDMA-Based Multi-hop Cognitive Radio Networks with Priority

In this paper, we propose a resource assignment scheme of a secondary user (SU) for a multi-hop cognitive radio network. In multi-hop networks, since each link has different SNR because of their different distance between stations and multipath fading, the link of the smallest SNR is the bottleneck. For overcoming this problem, it is proposed to give a priority to each link based on the link SNR and to assign the resource blocks (RBs) in ordering of instantaneous SNR on the link. This link priority information is shared among nodes through a control channel. Then, we assign the selected SU RB to each SU node according to the SNR ordering with distributed manner. We confirm the effectiveness of the proposed SU RB assignment by using computer simulation.

Cognitive Relaying with Frequency Incentive for Multiple Primary Users

This work is directed towards a symbiotic architecture called cognitive relaying with frequency incentive for multiple primary users (CRFI-M). The rationale of CRFI-M is that the primary users (PUs) of a cognitive radio (CR) network, with weak transmission links, seek cooperation from the secondary user (SU) nodes in their vicinity to achieve as much throughput as they can get from their direct links. In return they reward the SUs with incentive frequency bands for their own communication. Each PU has its own distinct bandwidth of operation; however, when relaying through the SU network it can also use the bandwidth of the other PUs to enhance its throughput. Furthermore, the incentive frequency bands may be offered as a complete band-set or interleaved bands. Cross-layer optimization problems are formulated for each of these variants of the CRFI-M paradigm in a multi-hop multi-channel SU network. The frequency incentive that should be awarded to the SUs by each PU is analyzed by means of a utility-based decision-making process, and its efficient utilization is proposed. To make the CRFI-M scheme practically realizable, a MAC scheduling protocol is described. Simulation results are furnished to demonstrate the proof of concept.

Distributed execution of cognitive relaying with time incentive: multiple PU scenario

The prime focus of this study is in developing distributed algorithms for cognitive relaying with time incentive for multiple primary users (CRTI-M). CRTI-M is a symbiotic paradigm in which the incumbent primary users (PUs) of the spectrum, with weak transmission links, seek cooperation from the cognitive secondary user (SU) nodes in their vicinity, and in return reward them with an incentive time for the latter’s own communication. When relaying through the SU network, each PU can either use its own spectrum or that of the other PUs. Cross-layer optimization problems are formulated to enable both these possibilities in a multi-hop multi-channel cognitive radio network with the objective of maximizing the cumulative time incentive for the SUs. Corresponding distributed algorithms are developed, which face the challenge of meeting the constraints of the formulated problems with only local information and the lack of a centralized controller. Further, to make the CRTI-M schemes practically realizable, a MAC scheduling protocol is suggested, which gives emphasis to the distributed implementation and provides a unified framework for the PUs and SUs. Simulation results are furnished to demonstrate the effectiveness of the proposed algorithms.