Secondary User Destination Research Articles

Effective cooperative spectrum sensing using deep recurrent reinforced learning‐based Q‐routing in multihop cognitive radio networks

SummaryCognitive radio network (CRN) is a promising technology that mitigates the scarcity of spectrum. The main challenge faced in the opportunistic CRN is the spectrum sensing (SS). The traditional methods of SS use detectors to find the available bands, which appear to provide unreliable performance in the case of actual environment where noise is predominant. Literature has proved that employing an artificial intelligence (AI) model for routing overcomes the lack of network knowledge and lack of human intervention and helps to learn robust patterns. Reinforced learning (RL) is a dynamically learning process that selects the actions based on continuous feedback received from the dynamic environment to maximize the reward. Deep reinforcement learning (DRL) models have proven to be successful at learning control policies image inputs. However, they struggle with learning policies that require longer term information. Recurrent neural network (RNN) architectures have been used in tasks dealing with longer term dependencies between data points. Motivated by the performance of AI models, these architectures are investigated in this work to overcome the difficulties arising from learning policies with long‐term dependencies. Thus, a deep recurrent reinforced learning‐based Q‐routing (DRRL‐based Q‐routing) is developed. The proposed study suggests a multihop CRN operated in an interweave mode. This algorithm finds optimal routing path between the secondary user transmitter (SUT) and the secondary user destination (SUD), optimal SS duration, and individual secondary user (SU) power requirements for SS and data transmission process while minimizing the end‐to‐end outage under the constraints of energy causality, SS reliability, interference threshold, and individual link throughput.

A route stability-based multipath QoS routing protocol in cognitive radio ad hoc networks

Secondary user (SU) mobility, primary user activity, and spectrum sensing inaccuracy are the main challenges to the stability of a quality of service (QoS) route in cognitive radio ad hoc networks (CRAHNs). In this work, a new routing protocol for CRAHNs, referred to as the route stability based multipath QoS routing protocol (SMQRP), is proposed. The proposed protocol finds the optimal primary and alternative paths between an SU source and an SU destination and guarantees the use of the optimal primary and alternative channels along the paths. A proposed routing metric (SMQ) used for path and channel decisions is applied to the proposed protocol. The main idea is to use different routing metrics to select QoS paths with higher stability. The SMQRP was compared in this category with other routing protocols and was evaluated based on CRAHNs parameters. The results of the simulations show significant improvements with respect to the average end-to-end delay, packet drop probability, and throughput.

Performance Analysis and Power Optimization for Spectrum-Sharing Mixed RF/FSO Relay Networks With Energy Harvesting

In this paper, the energy harvesting in mixed multiple-input-single-output radio frequency (RF)/free space optical (FSO) networks is studied. Assuming underlay mode, the secondary user (SU) source with limited battery communicates with its destination via a hybrid SU relay. The SU source harvests energy from both the hybrid relay and the primary network. The hybrid SU relay node is equipped with two antennas; one for energy transmission to the secondary user and the other for data reception. The SU source transmits its data over an RF link to the relay. Then, the relay decodes the SU data before retransmitting it to the SU destination over an optical link. The RF/FSO channels are assumed to follow Nakagami-m/Malaga-M fading models with pointing errors on the FSO link. Closed-form expressions for the exact outage probability, average bit error rate, and ergodic capacity are derived. For high signal-to-noise ratio values, closed-form expressions for the asymptotic outage probability and average bit error rate are derived. Based on the asymptotic results, a power allocation model is proposed to enhance the system outage performance. Some simulation and numerical results are employed to validate the derived expressions.

Joint Relay Selection and Power Allocation through a Genetic Algorithm for Secure Cooperative Cognitive Radio Networks

In cooperative cognitive radio networks (CCRNs), there has been growing demand of transmitting secondary user (SU) source information secretly to the corresponding SU destination with the aid of cooperative SU relays. Efficient power allocation (PA) among SU relays and multi-relay selection (MRS) are a critical problem for operating such networks whereas the interference to the primary user receiver is being kept below a tolerable level and the transmission power requirements of the secondary users are being satisfied. Subsequently, in the paper, we develop the problem to solve the optimal solution for PA and MRS in a collaborative amplify-and-forward-based CCRNs, in terms of maximizing the secrecy rate (SR) of the networks. It is found that the problem is a mixed integer programming problem and difficult to be solved. To cope with this difficulty, we propose a meta-heuristic genetic algorithm-based MRS and PA scheme to maximize the SR of the networks while satisfying transmission power and the interference requirements of the networks. Our simulation results reveal that the proposed scheme achieves near-optimal SR performance, compared to the exhaustive search scheme, and provides a significant SR improvement when compared with some conventional relay selection schemes with equal power allocation.

Cooperative spectrum sharing with multi-antenna based adaptive hybrid relay in presence of multiple primary users

Performance analysis of cooperative spectrum sharing network using multi-antenna based Adaptive Hybrid Relay (AHR) scheme in presence of multiple primary users under non-identical Rayleigh fading channel has been studied in this paper. An Adaptive Hybrid Relay equipped with multiple antennas at the input employs selection combining (SC) on the signals received from secondary user source (S) via multiple receiving antennas at the input and forwards the received signal to secondary user destination (D). The outage probability has been evaluated at the secondary destination where best relay selection (BRS) scheme is used. The comparison between outage performances of cooperative spectrum sharing for Amplify-and-Forward (AF), Decode-and-Forward (DF) and Adaptive Hybrid Relay (AHR) scheme is also presented. The effects of number of relay antennas (L), number of relays (K) and number of primary users (M) on the system performance have also been studied. It is seen that the outage performance improves considerably with increase in number of primary users (PUs). It is also observed that increase in number of primary users compensate the negative impact of high channel rate (R). A trade-off between number of relay and number of antenna at each relay is also shown.

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.

Secrecy Performance Analysis of Cognitive Decode-and-Forward Relay Networks in Nakagami- $m$ Fading Channels

This paper investigates the physical layer security problem of cognitive decode-and-forward relay networks over Nakagami-m fading channels. We consider the relaying communication between one secondary user (SU) source and one SU destination by using an opportunistic relay selection from multiple SU relays and sharing the licensed spectrum of multiple primary users (PUs) in the underlay network. While the transmission between the SUs imposes interference on each PU, the relayed transmission is intercepted by one SU eavesdropper. In the absence of the eavesdropper's channel state information, the relay selection is based on the largest channel gain of relay-to-destination link, which is assumed to be outdated due to feedback delay. We derive the exact probability of non-zero secrecy capacity and the exact secrecy outage probability (SOP) in the closed form. Furthermore, we derive the asymptotic SOP in two different cases, and explicitly show the effects of system parameters on the secrecy diversity order and the secrecy diversity gain, respectively. Both asymptotic analysis and simulation results show that the secrecy performance can be improved by increasing either the number of relays or the Nakagami parameter of the legitimate relay channels, whereas the secrecy diversity gain deteriorates as the number of the PUs increases.

Throughput and Outage Probability of Wireless Energy Harvesting Based Cognitive DF Relaying Network

This paper evaluates the throughput performance and outage probability of a secondary user (SU) in a decode-and-forward (DF) relaying network based on wireless energy harvesting under cognitive radio constraint. The energy constrained relay node first harvests energy through radio-frequency (RF) signals from the source node. Next, the relay node uses the harvested energy to forward the decoded source information to the destination node. The power transmitted by source and relay node is constrained by the tolerable interference threshold of the primary unit receiver. The source node transfers energy and information to the relay node through power splitting-based relaying (PSR). In PSR, the relay splits the received power for energy harvesting and information processing. The interference caused by a primary unit transmitter at the SU relay and destination nodes is also considered. Considering wireless energy harvesting constraint at the relay node, we analyse the achievable throughput and outage performance of a cognitive DF relaying network. We study the impact of different system parameters such as power splitting ratio, primary transmitter power and tolerable interference threshold of PU receiver on the throughput and outage performance of SU.

Transceiver Design for Nonregenerative MIMO Cognitive Relay Networks With Tomlinson–Harashima Precoding

Transceiver with Tomlinson-Harashima (TH) precoding outperforms the linear minimum mean-square-error (MSE) architecture in terms of minimum achievable MSE. In this paper, we investigate transceiver design optimization problem for nonregenerative multiple-input multiple-output cognitive relay networks (CRNs) with TH precoding. In the CRN, a secondary user (SU) source, an SU relay and an SU destination employ a TH precoder, a relay precoder, and a linear equalizer, respectively. For scenario in which SUs know perfect channel state information (CSI) from SUs to primary users, we propose an alternating optimization (AO)-based suboptimal algorithm. Given TH precoder and relay precoder, we derive a closed-form optimal solution of linear equalizer. Given relay precoder, TH precoder can be found by convex optimization. Given TH precoder, we transform nonconvex relay precoder design problem into a difference of convex programming and propose a constrained concave convex procedure-based iterative algorithm to find its local optimum. For scenario in which SUs know imperfect CSI, the channel uncertainties are modeled by worst case model. We derive equivalent worst case interference power constraints and extend the proposed AO-based suboptimal algorithm to cope with the worst case interference power constraints. Simulation results demonstrate that the proposed transceiver design with TH precoding outperforms linear transceiver designs.

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.

Multiuser and Multirelay Cognitive Radio Networks Under Spectrum-Sharing Constraints

In this paper, the outage behavior of dual-hop multiuser multirelay cognitive radio networks under spectrum-sharing constraints is investigated. In the proposed cognitive radio network, the secondary network is composed of one secondary-user (SU) source that communicates with one out of L destinations through a direct link and also via the help of one out of N relays by using an efficient relay-destination selection scheme. Additionally, a selection combining (SC) scheme to select the best link (direct or dual-hop link) from the SU source is employed at the selected SU destination. Adopting an underlay approach, the SU communication is performed accounting for an interference constraint, where the overall transmit power is governed by the interference at the primary-user (PU) receiver, as well as by the maximum transmission power available at the respective nodes. Closed-form expressions for the outage probability are derived, from which an asymptotic analysis reveals that the diversity order of the considered system is not affected by the interference and is equal to N + L for both decode-and-forward (DF) and amplify-and-forward (AF) relaying protocols. The analytical results are corroborated by Monte Carlo simulations, and insightful discussions are provided.

Cognitive Amplify-and-Forward Relaying with Best Relay Selection in Non-Identical Rayleigh Fading

This paper investigates several important performance metrics of cognitive amplify-and-forward (AF) relay networks with a best relay selection strategy and subject to non-identical Rayleigh fading. In particular, assuming a spectrum sharing environment consists of one secondary user (SU) source, K SU relays, one SU destination, and one primary user (PU) receiver, closed-form expressions for the outage probability (OP), average symbol error probability (SEP), and ergodic capacity of the SU network are derived. The correctness of the proposed analysis is corroborated via Monte Carlo simulations and readily allows us to evaluate the impact of the key system parameters on the end-to-end performance. An asymptotic analysis is also carried out and reveals that the diversity gain is defined by the number of relays pertaining to the SU network (i.e., K), being therefore not affected by the interference power constraint of the PU network.

Capacity Analysis of Cognitive Relay Networks with the PU's Interference

In this letter, with the primary user's (PU's) interference, we investigate the performance of the secondary user (SU) in spectrum sharing cognitive relay networks. Considering the correlation among the received interference plus noise ratios (SINRs) at the relays and SU destination, closed-form expressions for the outage probability and capacity of the SU are derived. It is shown that, though the interference from the PU badly degrades the SU's performance, an increase of the number of relays can compensate the loss. Finally, simulation results are provided to validate our theoretical analysis.

An Adaptive Cooperation Communication Strategy for Enhanced Opportunistic Spectrum Access in Cognitive Radios

To guarantee the continuity of secondary transmission (ST) in cognitive radio networks (CRNs), a beamforming-based cognitive cooperative communication protocol, referred to as BCC, is proposed in this paper. In BCC, a secondary user (SU) can increase the transmit power to reach its destination directly when the primary users (PUs) are absent. On the other hand, when new PUs come in, the SU will reduce its power and choose an intermediate relay to reach its destination to avoid the impact on the primary transmission (PT); in this case, the SU destination will leverage beamforming to receive data from both the SU and relay respectively. We analyze the performance of BCC and obtain the closed-form expressions of the ST outage probability. Simulation results are presented to validate the theoretical analysis and demonstrate that BCC achieves lower SU outage probability than the traditional cognitive radio scheme without using beamforming-based cooperation.