Secondary User Network Research Articles

Adaptive Full-Duplex Communications in Cognitive Radio Networks

In this paper, we propose a novel adaptive scheme for full-duplex communication of secondary users (SUs) in a cognitive radio network. The secondary network operates adaptively in three modes; cooperative sensing (CS), full duplex transmit and sensing (FDTS), and in-band bidirectional full duplex transmit and receive (FDTR). In the CS mode, the secondary nodes will detect the signal of a primary user (PU) through a novel cooperative medium access control (MAC) protocol and will decide the system's mode of operation in the subsequent spectrum hole. This adaptive decision is based on dual-threshold detection introduced for the first time. When the PU's signal at SU's receivers is weak, the system switches to the FDTS mode to avoid higher collisions probability and long or endless collision durations. In the FDTS mode, one of SUs senses the PU activity continuously while transmitting to another node. When the channel conditions allow, the system switches to the FDTR mode, in which the SUs would communicate bidirectionally in an asynchronous full duplex manner. The novel idea of asynchronous transmission in this mode will result in decreased maximum and average collision durations. Analytical closed forms for probability of collision, average collision duration, and cumulative collision duration, as well as throughput of the SU network are derived, and performance of the proposed scheme in terms of the above-mentioned metrics, effectiveness, and advantages over conventional methods of sensing and transmission are verified via simulations.

Physical layer security in cognitive radio network with energy harvesting relay and jamming in the presence of direct link

In this paper, we examine the physical (PHY) layer security in terms of secrecy outage of an energy harvesting (EH) relay based underlay cognitive radio network (CRN) in the presence of an eavesdropper. A dual hop communication network consisting of an energy harvesting relay that harvests energy from radio transmission of secondary user (SU) network using a time switching relay (TSR) scheme is studied. The relay works in decode and forward (DF) mode and forwards the confidential message to the destination, if it is successfully decoded at the relay. The advantage of the direct link between source to destination is exploited, if the relay link is in outage. Furthermore, simultaneous transmission of message signal and jamming signal to the legitimate nodes and illegitimate node respectively degrades the eavesdropping link capacity. We evaluate the secrecy outage probability (SOP) of the network under study. It is found that exploiting the direct link at the destination increases the secrecy in transmission as compared to the case of only relay based transmission without direct link. The impact of interference threshold, energy harvesting time, power allocation factor, target data rate, target secrecy rate and direct link on SOP of this proposed network is investigated.

Approximating the largest connected topology in cognitive radio networks

Connection between two secondary users (SUs) in cognitive radio networks (CRNs) is not only determined by their transmission power and distance, it also depends on the availability of a common channel for both SUs to open it for communication. In CRN, each SU is equipped with a number of antennas, denoted as β, which is the maximum number of channels that an SU can open simultaneously, known as antenna budget constraint. As each SU has a limit on the maximum number of channels it can open simultaneously, so network may not be connectable. But, it is desirable to connect the largest subset of SUs while minimizing the interference introduced due the nearby transmissions among SUs on the same channel, this problem is called the largest-connected minimum-interference topology control (LMTC) problem in CRNs. In this paper, we model the network of SUs as a potential graph PG=(V(PG),E(PG)), where V(PG) is set of SUs and E(PG) is set of potential edges. First, we show that the LMTC problem is NP-hard then we propose an approximation algorithm to address LMTC problem with min (m/log n, n.β/2log n) ratio, where n and m are the number of nodes and edges in potential graph respectively. We also propose a distributed algorithm called distributed-LMTC with message complexity O(n2), to address the LMTC problem. To address this NP-hard problem, we combine both topology control and channel assignment phase. In topology control phase, a network subgraph is derived with satisfying antenna budget constraints. In channel assignment phase, we assign channel to link to minimize interference. Simulation results show that the constructed topology can achieve higher connectivity and throughput than other competitive topology control algorithms.

Multiband Spectrum Sensing in Cognitive Radio Networks With Secondary User Hardware Limitation: Random and Adaptive Spectrum Sensing Strategies

Hardware limitation at the secondary user (SU) terminal makes multiband (wideband) spectrum sensing more challenging. This paper considers spectrum sensing under SU hardware limitation, where the SU can only sense a small portion of the multiband spectrum for a given time period. This introduces a design issue of selecting channels to sense at a given time. A random spectrum sensing strategy (RSSS) is presented to select the subchannels to sense in a totally random fashion. Considering the Markov property of the state transition of a primary user (PU), an adaptive spectrum sensing strategy (ASSS) is then proposed to take advantage of the PU traffic patterns in determining the subchannels to sense. In the proposed ASSS, a novel decision rule is designed and two decision combinations are obtained. The ASSS decision rule adaptively selects a decision combination to determine the subchannels to sense for SU such that the selected subchannels are more likely to be available for the SU network. A metric called spectrum sensing capability (SSC) is defined to evaluate the performance of any spectrum sensing strategies. The SSC expressions for both RSSS and ASSS are derived. Numerical results show significant performance gain of ASSS as compared to RSSS.

Performance of cognitive relay network with energy harvesting relay under imperfect CSI

SummaryThis paper evaluates the performance of an underlay cognitive relay network under imperfect channel state information (CSI) where a secondary user (SU) transmits using a secondary relay (SR) based on decode and forward scheme. The outage probability (OP) of SU is investigated in a scenario where the decode and forward relay harvests energy from radio frequency signal of SU. The relay uses a fraction of time for harvesting in time switching–based relaying (TSR) while a fraction of received power is used for harvesting in power splitting–based relaying (PSR) scheme. The SU and relay control their transmit power using a scaling factor, based on CSI of the interfering links (ie, links from SU transmitter and SR to the primary user [PU] receiver) to protect the quality of service of PU. The available CSI at the SU and SR are imperfect due to practical limitation. Analytical expressions of the OP are derived for TSR‐ and PSR‐based schemes. The impact of harvesting time, power splitting ratio, imperfect CSI, PU outage constraint and interference threshold on the OP of the SU network, and average transmit power of SR is indicated. Further, the impact of multiple SRs is also shown.

Secrecy Outage of a Cognitive Radio Network with Selection of Energy Harvesting Relay and Imperfect CSI

This paper investigates the physical layer security of an underlay cognitive radio network with relay selection scheme under threats of an eavesdropper. We consider a set of intermediate relays working in decode and forward mode. The relays harvest energy from radio frequency signal transmission of secondary user (SU) using a time switching relaying. We evaluate the secrecy outage probability (SOP) of secondary relay network assuming that the channel state information (CSI) of the interfering links from both the SU and relay transmitter to primary user (PU) receiver are imperfect. The transmit power of the SU as well as relay is controlled by the maximum tolerable interference at PU because of underlay environment and outage constraint of PU as demanded by quality of service of PU. The impact of several network parameters such as maximum tolerable interference threshold, number of relays, time for energy harvesting, imperfection in CSI and primary outage constraint on the secrecy outage of the SU network is indicated. The influence of relay selection scheme on SOP with energy harvesting and imperfect CSI is indicated.

Power Allocation Scheme and Performance Analysis for Multiuser Underlay Full-Duplex Cognitive Radio Networks With Energy Harvesting

This paper introduces a comprehensive wireless energy harvesting model applied for multiple secondary users (SUs) in full-duplex cognitive radio networks. In this proposed model, SUs harvest energy from a hybrid base station (HBS), in addition to the primary user (PU) network on the downlink and transmit their data on the uplink. The opportunistic user selection scheme is employed in the SU network to achieve a better SU performance. Considering the underlay spectrum sharing paradigm, the total SU transmitted powers are limited to the maximum allowable PU interference threshold. Moreover, the proposed SU system suffers from self-interference from the transmitting antenna of the HBS and co-channel interference from the PU transmitter. Closed-form expressions for the SU system outage probability, average symbol error probability, and ergodic capacity are derived. Obtained exact expressions are then simplified to their asymptotic results in the high signal-to-noise-ratio regime. Based on these results, a power allocation optimization problem is formulated to reduce the SU outage probability under the constraints of performance indices. Computer-aided numerical and simulation work is performed to validate the exact expressions.

A Study of Redundancy of Time Dilation in Theory of Relativity

Objectives: In this Paper a generic approach of ISM band channel scanner design module is proposed to identify available free white spaces to utilize under secondary communication network. Method/Analysis: The feature of opportunistic spectrum access (OSA) is to identify free channel to deployment purpose, the channel is compared on the basis of RSSI level individually amongst total available channel were in normally 80% channel are mostly vacant due to dominating nature of channel. The output of the OSA based ISM band channel brings a free channel identification and noise free path to continue communication in between other ISP. Findings: The result indicates that the available channels are having bunch of availability of total 14 no of channels in general. In which channel no 1-6 and 11 are comes under high dominating index ratio. The channel always forcing every new SSID/service provider to accommodate in between these three channels only; due to this a normal channel Co-channel conjunction/Interference occurs in crowed area. This may lead to call/request lost data packets in bulk! As a result users always share more data beyond a normal, causing more power consumption/ battery in cell phone/laptop. So for channel identification OSA technique is implemented which is actually determines dynamic spectrum access by comparing received power in –dB on -90dB to -20dB range were on results comparison above -50dB range signal is mostly having week strength/the origin of base channel is on far distance to other nearby channels. Once the low signal channel or non operational channel is detected it effectively deployed for secondary user network communication. Novelty/Improvements: In this novel design, portable OSA channel estimator-indicator is actively scanned in real time in live data fields; in future it helps to bi-pass the used channel to remove interference. Keywords: Bending of Light, Caesium Atomic Clock, Perihelion of Mercury, Shapiro Delay, Space-time Fabric, Time Dilation, Theory of Relativity

A Novel OSA Based ISM Band Channel Scanner Design for Identification and Deployment of White-Spaces

Objectives: In this Paper a generic approach of ISM band channel scanner design module is proposed to identify available free white spaces to utilize under secondary communication network. Method/Analysis: The feature of opportunistic spectrum access (OSA) is to identify free channel to deployment purpose, the channel is compared on the basis of RSSI level individually amongst total available channel were in normally 80% channel are mostly vacant due to dominating nature of channel. The output of the OSA based ISM band channel brings a free channel identification and noise free path to continue communication in between other ISP. Findings: The result indicates that the available channels are having bunch of availability of total 14 no of channels in general. In which channel no 1-6 and 11 are comes under high dominating index ratio. The channel always forcing every new SSID/service provider to accommodate in between these three channels only; due to this a normal channel Co-channel conjunction/Interference occurs in crowed area. This may lead to call/request lost data packets in bulk! As a result users always share more data beyond a normal, causing more power consumption/ battery in cell phone/laptop. So for channel identification OSA technique is implemented which is actually determines dynamic spectrum access by comparing received power in –dB on -90dB to -20dB range were on results comparison above -50dB range signal is mostly having week strength/the origin of base channel is on far distance to other nearby channels. Once the low signal channel or non operational channel is detected it effectively deployed for secondary user network communication. Novelty/Improvements: In this novel design, portable OSA channel estimator-indicator is actively scanned in real time in live data fields; in future it helps to bi-pass the used channel to remove interference.

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.

Carrier Aggregation for Cooperative Cognitive Radio Networks

The ever-increasing demand for mobile Internet and high-data-rate applications poses unique challenging requirements for 5G mobile networks, including spectrum limitations and massive connectivity. Cognitive radio and carrier aggregation (CA) have recently been proposed as promising technologies to overcome these challenges. In this paper, we investigate joint relay selection and optimal power allocation in an underlay cooperative cognitive radio with CA, taking into account the availability of multiple carrier components in two frequency bands, subject to outage probability requirements for primary users (PUs). The secondary user network employs relay selection, where the relay that maximizes the end-to-end sum rate is selected, assuming both decode-and-forward and amplify-and-forward relaying. The resulting optimization problems are optimally solved using convex optimization tools, i.e., dual decomposition and an efficient iterative method, allowing their application in practical implementations. Simulation results illustrate that the proposed configuration exploits the available degrees of freedom efficiently to maximize the SU rate, while meeting the PU average outage probability constraints.

New Bandwidth Efficient Relaying Schemes in Cooperative Cognitive Two-Way Relay Networks With Physical Layer Security

In this paper, a new cooperative two-way cognitive relaying scheme is proposed. In this model, a primary user (PU) network consisting of two PU sources communicate with each other via a single amplify-and-forward (AF) relay. In addition, a secondary user (SU) source transmits its data to an SU destination via the same PU relay node. To mitigate the SU interference caused to the PU network, the PU network considers the SU network pairs as two additional relay nodes helping the original PU relay node in improving the PU network performance. As a reward for its cooperation, the PU network allows the SU network to communicate simultaneously via the PU relay node by using the decode-and-forward protocol. The proposed system allows the transmission of four PU symbols and one SU symbol in four/three time slots resulting in a bandwidth efficiency of $1.25/1.67$ based on the cooperative scheme, respectively. Two power allocation optimization problems are formulated: the first problem minimizes the weighted sum of the average symbol error probability of both PU and SU systems, whereas the second problem maximizes the total achievable sum rate of the PU and SU networks. Lagrangian multiplier method is used to find the optimal solutions for both problems under the constraint of maximum allowable power budget. In addition, the paper investigates how the proposed model improves the PU physical layer security performance against a single passive eavesdropper. The results show that the error performance of the proposed relay selection model outperforms the conventional two-way relaying networks with AF protocol. Moreover, findings illustrate that the total achievable sum rate of the proposed relay elimination model is higher than the total achievable rate of the conventional two-way relaying model. From secrecy point of view, the proposed model is shown to achieve a nonzero secrecy rate that improves the PU system security against eavesdropping attacks.

Distributed Dynamic Resource Allocation for Cooperative Cognitive Radio Networks With Multi-Antenna Relay Selection

A cognitive radio scenario is considered where the signals transmitted by a secondary user (SU) are relayed by multi-antenna relays using an amplify-and-forward cooperation protocol. In this paper, the optimal power allocation and beamforming scheme is derived for the SU transmitters (SU-TXs), which minimizes the exact outage probability of the SU network with relay selection, under both a transmit power constraint and a constraint on the interference power generated at every primary user receiver. After deriving the optimal structure of the beamforming matrix, several distributed resource allocation algorithms are obtained for different levels of channel state information (CSI) at the SU-TXs: perfect CSI and imperfect CSI are considered, along with the case where only channel distribution information is available. The numerical results show that the multi-antenna relays can significantly improve the performance of the SU network, which would otherwise be severely limited by the harsh interference constraints. Furthermore, we also investigate how the number of relays, the number of antennas, and the level of CSI impact the performance of the SU network. Finally, we point out that the proposed algorithms outperform several algorithms presented in the literature.

Collaborative Spectrum Sharing Through Non-Collaborative Gaming for Next-Generation Small Cells

Existing spectrum-sharing schemes either allow the secondary-network users (SUs) to utilize the spectrum when primary-network users (PUs) remain idle, or require the SUs to coordinate with the PUs, causing signaling overhead. In this paper, we propose a game-theoretic spectrum-sharing scheme, which enables the SUs and PUs to utilize the spectrum simultaneously, without compromising the quality of service (QoS) of the PUs and ensuring reduced signaling overhead. We formulate a multi-priority non-cooperative power-control game by considering a scenario where multiple small cell base stations belonging to either the primary network or secondary network utilize the available spectrum resources at the same time. The base stations are empowered to adjust their transmit powers in an automated manner based on measured interference, until their transmit powers are stabilized. As a key idea, a game parameter, dynamic price coefficient, is designed to give the primary network priority over the secondary network for accessing the spectrum. We determine appropriate bounds for the game parameters to ensure the existence and uniqueness of the Nash equilibrium of the proposed game. Furthermore, we propose a novel dual-mode solution to reduce the real-time signaling overhead between the networks, by minimizing the information exchange during the game required to reach an equilibrium point. Extensive simulation results are presented to prove the convergence of the game to a Nash equilibrium, along with a throughput performance analysis.

Agent-Based Model of the Spectrum Auctions with Sensing Imperfections in Dynamic Spectrum Access Networks

Cognitive radio (CR) is the underlying platform for the application of dynamic spectrum access (DSA) networks. Although the auction theory and spectrum trading mechanisms have been discussed in the CR related works, their joint techno-economic impact on the efficiency of distributed CR networks has not been researched yet. In this paper we assume heterogeneous primary channels with network availability statistics unknown to each secondary user (SU) terminal. In order to detect the idle primary user (PU) network channels, the SU terminals trigger regularly the spectrum sensing mechanism and make the cooperative decision regarding the channel status at the fusion center. The imperfections of the spectrum mechanism create the possibility of the channel collision, resulting in the existence of the risk (in terms of user collision) in the network. The spectrum trading within SU network is governed by the application of the sealed-bid first-price auction, which takes into account the channel valuation as well as the statistical probability of the risk existence. In order to maximize the long-term payoff, the SU terminals take an advantage of the reinforcement comparison strategy. The results demonstrate that in the investigated model, total revenue and total payoff of the SU operator (auctioneer) and SU terminals (bidders) are characterized by the existence of the global optimum, thus there exists the optimal sensing time guaranteeing the optimum economic factors for both SU operator and SU terminals.

Adaptive coding and modulation using imperfect CSI in cognitive BIC-OFDM systems

This work investigates adaptive coding and modulation (ACM) algorithms under the realistic assumption that the available channel state information (CSI) at the transmitter is imperfect due to estimation errors and/or feedback delays. First, we introduce an optimal performance metric for the secondary user (SU) bit-interleaved coded orthogonal frequency division multiplexing (BIC-OFDM) system, called the expected goodput (EGP). By using an accurate modeling approximation, we succeed in deriving a tractable and very accurate approximation for the EGP. This approximate EGP (AEGP) is then used for the derivation of several ACM algorithms which optimize the code rate and bit and energy allocation under a constraint on the interference caused to the PU network. In the numerical results, we show that the AEGP is far more accurate than previous attempts to model the GP in the presence of imperfect CSI. Further, we verify that, in spite of the imperfect nature of the available CSI, the derived ACM algorithms significantly increase the goodput of the SU network, compared to a non-adaptive selection of the transmission parameters.

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.

How to Increase Energy Efficiency in Cognitive Radio Networks

In this paper, we investigate the achievable energy efficiency of cognitive radio networks where two main modes are of interest, namely, spectrum sharing (known as underlay paradigm) and spectrum sensing (or interweave paradigm). In order to improve the energy efficiency, we formulate a new multiobjective optimization problem that jointly maximizes the ergodic capacity and minimizes the average transmission power of the secondary user network while limiting the average interference power imposed on the primary user receiver. The multiobjective optimization will be solved by first transferring it into a single objective problem (SOP), namely, a power minimization problem, by using the $\varepsilon$ -constraint method. The formulated SOP will be solved using two different methods. Specifically, the minimum power allocation at the secondary transmitter in a spectrum sharing fading environment are obtained using the iterative search-based solution and augmented Lagrangian approach for single and multiple secondary links, respectively. The significance of having extra side information and also imperfect side information of cross channels at the secondary transmitter are investigated. The minimum power allocations under perfect and imperfect sensing schemes in interweave cognitive radio networks are also found. Our numerical results provide guidelines for the design of future cognitive radio networks.

Performance analysis of amplify‐and‐forward cognitive relay networks with interference power constraints over Nakagami‐m fading channels

With the wide-spread wireless applications and services, the spectrum scarcity has become a challenging problem. Thus, it is necessary to find a solution to have more spectrum bands. One from these solutions is the cognitive relay network, where we can increase the spectrum utilization by combining the cognitive radio (CR) with cooperative spectrum sharing systems. In this paper, the performance of cognitive relay networks under interference power constraints from the primary user (PU) is studied. Here, the system models are studied by utilizing different scenarios. The first scenario is by using a single amplify-and-forward (AF) relay, and the second one is by using a single AF relay with selection diversity. Tabulated expressions for the outage probability (OP) are derived over independent and non-identically distributed Nakagami-m fading channels. Numerical results show that the cooperative spectrum sharing transmission with a single AF relay and selection diversity outperforms both the direct transmission and the transmission using a single AF relay for the underlay cognitive relay networks. Furthermore, the results show that the outage performance depends on the minimum fading severity parameters of the two hops of the secondary user (SU) and the OP decreases as the PU moves away from the SU network.

Secondary User Aggressiveness Optimization in Sensing-Transmission Scheduling for Cognitive Radio Networks

The constraint of limited frequency spectrum for wireless communication is very daunting. The radio spectrum licensed to permanent users is wasted at times when not used continuously. Cognitive radio technology involves a change in regulation of radio spectrum. In cognitive radio networks a secondary user network is designed for efficiently using gaps in spectrum and not causing at the same time harmful interference to license holding primary users. There is a continuous tradeoff between the opposing goals of Primary User transmission protection and Secondary User throughput maximization. For a Secondary User, both sensing and transmitting is important so as to avoid collisions, packet loss and improve throughput. This paper presents optimization of Secondary User packet length in sensing-transmission scheduling for dynamically accessing the spectrum in cognitive radios. The need to maximize the Secondary User access is achieved by optimizing its packet length with respect to collision cost in a threshold based sensing-transmission structure using Matlab simulations. The results are presented in the form of traces of thresholds for different packet lengths and collision costs. This scheme optimizes Secondary User aggressiveness and throughput while safeguarding Primary User interests