Overlay Cognitive Radio Networks Research Articles

Many-to-one matching based cooperative spectrum sharing in overlay cognitive radio networks

Cooperative Spectrum Sharing (CSS) is a Dynamic Spectrum Access mechanism aimed at providing incentives for both primary users (PUs) and secondary users (SUs) through cooperative communication. This paper addresses the pairing problem among multiple PUs and SUs to allocate optimal fractions of spectrum resources in terms of access time, using the CSS technique. Inspired by Matching Theory, we model the CSS between PUs and SUs as a Two-sided Matching Market and explore different market equilibria. Cooperative strategies among SUs are employed to maximize the gross utility of cooperative SUs and overall utility of the secondary network, in exchange for relay services rendered to PUs. We propose a polynomial-time based many-to-one matching scheme that favors groups of collaborative SUs to attract favorable PUs from the opposite side, leading to optimal matching for SUs. On the other hand, each PU achieves stable matching when paired with a group of cooperative SUs. We provide necessary proofs for the achieved matching equilibrium. Furthermore, we formulate an optimization framework for the optimal usage of PU access time among stable PU-SU pairs and propose a near-optimal solution, achieving 96% accuracy compared to the optimal allocation yield from the benchmark method (analytical). Our proposed many-to-one matching scheme outperforms similar existing schemes and the one-to-one matching scheme in terms of SU utility, satisfaction, participation, and throughput fairness index.

Cooperative NOMA in cognitive radio networks: A study on imperfect CSI, SIC and hardware impairments over Nakagami-m fading channel

This paper proposes a cooperative uplink–downlink non orthogonal multiple access (NOMA) in an overlay cognitive radio network (CR). We examine the impact of imperfect channel state information (impCSI), imperfect successive interference cancellation (impSIC) and residual hardware impairments (RHI) on the cooperative cognitive radio network over Nakagami-m fading channels. We derive the exact outage probabilities of primary user (PU) and multicast secondary users (SUs) under perfect/imperfect conditions for fixed and adaptive power allocations. We show that the use of multiple relays enhances the diversity order, but with fixed power allocation in perfect/imperfect case and adaptive power allocation in imperfect case both suffer from an error floor, which reduces the diversity order to zero. On the other hand, the adaptive power allocation for the perfect case achieves full diversity gain. We validate the analytical results with Monte Carlo simulations and demonstrate the diversity gains of the considered schemes.

Full‐duplex jamming for physical layer security improvement in NOMA‐enabled overlay cognitive radio networks

AbstractIn this paper, we analyze the physical layer security (PLS) performance of nonorthogonal multiple access (NOMA)‐enabled overlay cognitive radio networks (NOMA‐OCRNs) in the presence of an external passive eavesdropper. Here PLS is expressed in terms of the secrecy outage probabilities (SOPs) experienced by the primary user (PU) and secondary user (SU). We obtain approximate expressions for the SOPs of both PU as well as SU assuming a jamming‐free environment, where both primary and secondary destination nodes are half‐duplex devices. To improve the SOP performance, we propose a jamming‐assisted framework, where full‐duplex destination nodes are employed, which are capable of transmitting jamming signals to confound the eavesdropper. Approximate expressions for the SOPs of PU and SU are derived for the jamming‐assisted framework as well. It is demonstrated that the proposed jamming‐assisted framework significantly reduces the SOPs compared to the jamming‐free scenario. We also determine optimal power allocation coefficients (OPACs) for PU and SU at the secondary transmitter that maximizes the total secrecy throughput of the jamming‐assisted NOMA‐OCRN with FD destinations. It is shown that the suggested OPAC significantly enhances the total secrecy throughput, compared to the default selection of the PAC.

Covert Communications Aided by Cooperative Jamming in Overlay Cognitive Radio Networks

Covert Communications Aided by Cooperative Jamming in Overlay Cognitive Radio Networks

Multi-objective optimization for energy efficient cooperative communication in energy-constrained overlay Cognitive Radio Networks

With the rapid proliferation of wireless devices, energy efficiency and addressing spectrum scarcity have become critical global concerns. To address these challenges, this paper explores radio-frequency energy harvesting in Cognitive Radio Networks (CRNs) as a solution which can significantly extend the battery life of mobile devices. In this setup, energy-constrained secondary users (SUs) use Simultaneous Wireless Information and Power Transfer (SWIPT) technology to harvest energy from primary signals and aid primary transmission. We propose a joint time-switching and power-splitting technique to maximize energy harvesting, achieving a 97.7% accurate sub-optimal solution compared to the optimal (benchmark) result. Furthermore, we investigate optimal power allocation during cooperative communication and secondary transmission, resulting in a near-optimal solution with 98.5% accuracy. We also introduce a cooperative communication framework using the Hedonic game concept, enabling SUs to establish preferred partnerships with suitable primary users (PUs). Numerical results indicate that this cooperative framework enhances the secondary network’s overall utility, average SU satisfaction, and SU participation when compared to the non-cooperative approach.

Robust precoder design with transmit antenna selection for overlay cognitive radio massive MIMO system

Massive MIMO systems were utilized in overlay Cognitive Radio (CR) networks to allow simultaneous primary and secondary data transmission while enhancing the spectral efficiency. However, the precoder design of a massive MIMO system especially in the overlay CR paradigm usually has a trade-off between achieved data rate and complexity. In this paper, the precoder design for overlay Cognitive Radio (CR) massive MIMO system is introduced, where a two-stage precoder that accommodates Transmit Antenna Selection (TAS) is proposed for the Secondary Base Station (SBS). The unselected antennas in the cognitive base station are proposed to be utilized to relay the data of the Primary Users (PUs) to maximize the network sum rate. The proposed precoder design for primary data aims to cancel the interference inflicted on Secondary Users (SUs) as a result of relaying the primary data. Moreover, a fast algorithm is proposed which aims to select and distribute the SBS antennas for primary and secondary data transmission to achieve better data and convergence rates, this algorithm is called Transmit Antenna Selection and Distribution (TASD). Simulation results show that the proposed precoders' design and the TASD algorithm enhance the total system sum rate (primary and secondary rates) compared to the conventional TAS (where the unselected antennas were not used to relay PUs' data). This enhancement was achieved by relaying primary data without affecting the rate of SUs. As a result, the computational time of the TASD algorithm is reduced by 52% compared to the full array case while the total sum rate of the algorithm is only 3% less than the full array scenario. Furthermore, the results in case of using a practical correlated channel proved the robustness of the proposed TASD algorithm, as it achieved nearly the same results compared to uncorrelated channels.

DDPG-Based Joint Time and Energy Management in Ambient Backscatter-Assisted Hybrid Underlay CRNs

Ambient backscatter (AB) communications and radio frequency (RF)-powered cognitive radio networks (CRNs) address the concerns of energy and spectrum scarcities from different perspectives, and the integration of them has potential benefits for throughput. Motivated by this fact, we study the RF-powered AB-assisted hybrid underlay CRN (ABHU-CRN), and optimize the long-term secondary throughput. Based on the channel states, secondary users choose to perform different actions, and two action spaces are accordingly designed. Due to dynamic and unpredictable environment states, we jointly control the time scheduling and energy management of secondary users, and propose two algorithms, i.e., adjusted-deep deterministic policy gradient (A-DDPG) and combination of A-DDPG and convex optimization (C-ADCO), for the long-term secondary throughput. A-DDPG, a deep reinforcement learning algorithm with continuous spaces, is extended from DDPG to adapt to the design of two action spaces. C-ADCO utilizes the convex optimization that can find the optimal solution to assist A-DDPG to accelerate the convergence. In simulations, the ABHU-CRN under A-DDPG and C-ADCO achieves higher throughput than the optimal throughput of AB-assisted overlay CRN and AB-assisted underlay CRN, which indicates the advantage of the hybrid transmission mode in the ABHU-CRN.

NOMA-based cognitive radio network with hybrid FD/HD relay in industry 5.0

The continued growth of the industrial Internet of Things (IoT) paves the way for the fifth industrial revolution (Industry 5.0), which is expected to further enhance the wireless connectivity and human machine collaboration. Nonetheless, Industry 5.0 will inevitably face the great challenges such as large scale connectivity and explosive data traffic because of the proliferation of IoT devices. To meet these challenges, we propose a novel non-orthogonal multiple access (NOMA)-based overlay cognitive radio (OCR) network for Industry 5.0. Specifically, the hybrid full-duplex (FD)/ half-duplex (HD) mode at the secondary user (SR) is adopted and in-phase and quadrature phase imbalance (IQI) is introduced to better comply with the practical scenarios. We investigate the outage probability (OP) and ergodic sum rate (ESR) of the considered network with the Nakagami-m channels. Extensive simulation experiments are performed to verify the accuracy of the analysis. From the simulation results, we can conclude: i) Increasing the signal-to-noise ratio (SNR), OP decreases but ESR increases and tends to a fixed value at high SNR regimes, indicating that the existence of IQI leads to a ceiling for the ESR; ii) The primary system has higher reliable performance at low SNR regions when SR is in FD mode, and for ergodicity, the system with FD relay is superior to HD relay; iii) The reliable performance of OMA system for primary users will be better since there is no interference at the relay.

Joint spectrum sensing and resource allocation against byzantine attack in overlay cognitive radio networks

AbstractCognitive radio (CR) technology has emerged as a viable solution to solve the dilemma of spectrum scarcity and underutilization. It allows secondary users (SUs) to opportunistically access the primary user (PU) channel. Cooperative spectrum sensing (CSS) further improves the accuracy of detecting spectrum availability by exploiting spatial diversity gain. However, the open nature of CR networks (CRNs) makes CSS process be prone to Byzantine attack, resulting in the excessive interference to the PU and the waste of spectrum resources. To this end, we propose a joint spectrum sensing and resource allocation scheme to defend against Byzantine attack. Specifically, we develop a probabilistic Byzantine attack model to characterize attack behaviors from malicious users (MUs) and evaluate its negative impact on the CSS performance. Then, the delivery evaluation mechanism is designed to evaluate the sensing performance of SUs and distinguish between normal users and MUs. Based on this, we propose a selection‐majority algorithm to improve CSS performance by exploiting sensing reports from MUs. To further solve the Byzantine attack, we propose a spectrum resource allocation algorithm, which allocates corresponding spectrum resources according to the historical behavior of SUs. By reducing the resources allocated to poorly performing SUs, this scheme incentivizes them to report correct sensing results and drive MUs to stop attacking or leave CRN. Extensive simulation results corroborate the correctness and effectiveness of our theoretical analysis and show that our proposed scheme can effectively resist Byzantine attack.

DDPG-Based Throughput Optimization with AoI Constraint in Ambient Backscatter-Assisted Overlay CRN.

The combination of ambient backscatter (AB) communications (ABCs) and RF-powered cognitive radio networks (CRNs) deals with challenges of both energy supply and spectrum shortage, and improves the network performances. With the expansion of wireless networks, many applications raise requirements for both high-throughput and timely data. Driven by these facts, we study the long-term throughput optimization of the secondary network in the AB-assisted overlay CRN (ABO-CRN), ABCs, and CRNs with the age of information (AoI) constraint, which is a novel metric for measuring the freshness of data received by receivers. Due to the dynamic environment, complete knowledge of the environment could not be obtained. Then, the deep deterministic policy gradient (DDPG), a deep reinforcement learning (DRL) method that addresses decision issues in both continuous and discrete spaces, is deployed to address the throughput optimization. We consider the impacts of time and energy allocation on the reward when the AoI constraint can not be satisfied, and develop the corresponding reward functions. Furthermore, we analyze the impacts of the minimum throughput requirement and maximum allowable AoI on the throughput and AoI of the secondary networks in the ABO-CRN, ABCs, and CRNs. We compare the throughput optimization scheme under the AoI constraint with two baseline schemes (i.e., throughput-optimal (T-O) and AoI-optimal (A-O) baseline schemes), and the simulation results show that the throughput of the ABO-CRN is close to the optimal throughput of the T-O baseline scheme, and the AoI of the ABO-CRN is close to the optimal AoI of the A-O baseline scheme.

Primary-User-Friendly Dynamic Spectrum Anti-Jamming Access: A GAN-Enhanced Deep Reinforcement Learning Approach

This letter studies the problem of deep reinforcement learning (DRL)-based dynamic spectrum anti-jamming access in overlay cognitive radio networks. To prevent secondary user (SU) from interfering with primary user (PU) and being jammed by jammer, we propose a PU-friendly dynamic spectrum anti-jamming access scheme. First, a generative adversarial network (GAN)-based virtual environment is proposed to simulate spectrum environment. Then, a DRL-based channel decision network (CDN) is trained to learn the optimal spectrum access policy in the virtual environment. Finally, SU accesses spectrum environment under the guidance of the trained CDN. Simulation results show that the proposed scheme is able to elude both PU signals and jamming completely and converges much faster than the scheme that trains the CDN in spectrum environment from scratch.

Overlay Cognitive Radio Networks Enabled Energy Harvesting With Random AF Relays

In this paper, we investigate an overlay cognitive radio network (CRN) in which one user is selected among multiple secondary users (SUs) to harvest energy from primary transmissions using a time-switching protocol. Based on a power allocation scheme, the selected user utilizes a portion of the harvested energy to assist the primary user (PU) in forwarding its messages to a primary receiver, while the remaining portion is used to transmit its own information in exchange for this cooperation. Specifically, we evaluate the reliability of both the primary and secondary networks in terms of the outage probability. Moreover, both the time switching and power allocation factors that maximize the users’ data rate are optimized.

Linear Precoding for the Downlink of Cognitive Radio Network

In this paper, a multiple-input–single-output (MISO) overlay cognitive radio (CR) network is considered in which a primary base station (PBS) and a cognitive base station (CBS) share the same spectrum to transmit the information. We consider a novel linear precoding technique to cannel the interferences which is bring about by the CBS’s transmission. Three theorems about the design of the precoding and decoding matrices are put forward. With the linear precoding and decoding, the BER performance of the PBS and CBS are improved significantly. At the same time, the capacity of the PBS and CBS channels are analyzed.

Throughput and Outage Probability Analysis for Cognitive Radio-Non-Orthogonal Multiple Access in Uplink and Downlink Scenarios

Non orthogonal multiple access (NOMA) in cognitive radio (CR) network has been recognized as potential solution to support the simultaneous transmission of both primary and secondary users. In addition, CR-NOMA can also be used to serve multiple secondary networks in overlay cognitive radio networks. The aim of our work is to increase the secondary user’s throughput without compromising in QoS requirements of the primary users. Our presented work analyses the performance of power domain NOMA in cognitive radio networks for both uplink and downlink scenarios. The primary aspect of the work is to investigate the impact of power allocation on spectrum efficiency and fairness performance of CR-NOMA. Objective function is to maximize the overall throughput under the QOS constraints of the users. We have derived closed form expressions for optimized power allocation coefficient(α) for CR-NOMA uplink and downlink communications. Parameters causing the channel outage, have been examined and conditions for outage probability is derived for CR-NOMA communication. Finally, we have presented the simulation results to validate the mathematical models that are developed for power allocation coefficient and outage probability.

Achieving Covert Communication in Overlay Cognitive Radio Networks

In this paper, we investigate the covert communications in an overlay cognitive radio (CR) network, where multiple secondary transmitters (STs) opportunistically send confidential information to a secondary receiver (SR). In contrast to current studies with ensuring security of information transmitted, we are motivated to protect communication behavior in CR network, which is considered as a higher-level security. To address covert rate and fairness performance, three joint user-jammer scheduling schemes are proposed, namely, rate-oriented secondary user scheduling (R-SUS), link-oriented secondary user scheduling (L-SUS), and fairness oriented secondary user scheduling (F-SUS). Numerical results show that the minimal detection error probability at eavesdropper (Eve) can be effectively impacted by creating channel uncertainty with the jamming signal. Further, it can be seen that under the same covert constraint, the R-SUS scheme achieves the best covert rate performance, full diversity can be obtained by the L-SUS scheme, while the F-SUS scheme exploits an advantage of better fairness.

Secure cooperative spectrum sharing in full-duplex multi-antenna cognitive radio networks with jamming

We consider a secure overlay cognitive radio network with an eavesdropper wherein a multi-antenna secondary transmitter performs transmission in primary spectrum, on the condition that it helps primary system to perform secure and reliable transmission via cooperative relaying and jamming. To improve secrecy performance of primary network, we propose full-duplex jammer protocol and zero-forcing based beamforming design, which completely cancels the interferences at the primary and secondary users and simultaneously avoids the leakage of confidential information to eavesdropper. Moreover, we present new expressions for the average secrecy rate and a lower bound for the secrecy outage probability. Furthermore, an asymptotic analysis in the high signal-to-noise ratio regime is carried out to obtain closed-form average secrecy rate. Our analytical findings reveal that by exploiting beamforming and full-duplex at the secondary transmitter secrecy outage probability can be significantly reduced and a diversity order of min (NR-1,NT-2) can be achieved where NR and NT are the number of received and transmit antennas at secondary transmitter. Simulation results also demonstrate that as compared to the half-duplex scenario without jamming, the proposed cooperative FD overlay CR scheme with jamming can improve the average secrecy rate up to 224%.

Performance Analysis and Optimization of Bidirectional Overlay Cognitive Radio Networks With Hybrid-SWIPT

This paper considers a cooperative cognitive radio network with two primary users (PUs) and two secondary users (SUs) that enables two-way communications of primary and secondary systems in conjunction with non-linear energy harvesting based simultaneous wireless information and power transfer (SWIPT). With the considered network, SUs are able to realize their communications over the licensed spectrum while extending relay assistance to the PUs. The overall bidirectional end-to-end transmission takes place in four phases, which include both energy harvesting (EH) and information transfer. A non-linear energy harvester with a hybrid SWIPT scheme is adopted in which both power-splitting and time-switching EH techniques are used. The SUs aid in relay cooperation by performing an amplify-and-forward operation, whereas selection combining technique is adopted at the PUs to extract the intended signal from multiple received signals broadcasted by the SUs. Accurate outage probability expressions for the primary and secondary links are derived under the Nakagami-$m$ fading environment. Further, the system behavior is analyzed with respect to achievable system throughput and energy efficiency. Since the performance of the considered system is strongly affected by the spectrum sharing factor and hybrid SWIPT parameters, particle swarm optimization is implemented to optimize the system parameters so as to maximize the system throughput and energy efficiency. Simulation results are provided to corroborate the performance analysis and give useful insights into the system behavior concerning various system/channel parameters.

Channel-Aware Power Allocation and Decoding Order in Overlay Cognitive NOMA Networks

To further improve spectral efficiency, this paper considers a non-orthogonal multiple access (NOMA)-assisted overlay cognitive radio network consisting of a pair of primary users and a pair of secondary users. In this network, communication between the pair of primary users is achieved with the help of the secondary transmitter (ST). In return, ST can communicate with the secondary receiver by sending a superimposed signal consisting of its own message and the received primary message. We intend to minimize the outage probability of the secondary system under quality-of-service constraints of the primary system by jointly optimizing the power allocation (PA) factor at ST and the decoding order (DO) at the receivers. When full channel state information (CSI) is available at ST, the optimal PA and DO are derived in closed form under the constraint that the target rate of the primary system should be guaranteed. When only statistical CSI is available at ST, the optimal PA and DO are derived in closed form or by using a bisection method, under the constraints that the outage probability of the primary system is not more than a predetermined threshold and is not larger than that of the secondary system. For the proposed strategies, outage probability expressions of the primary and secondary systems are derived in closed form or semi-closed form. Numerical results are shown to verify our analysis and demonstrate the superiority of the proposed strategies in different CSI-availability scenarios.

BER Performance of Full-Duplex Cognitive Radio Network With Nonlinear Energy Harvesting

In this paper, the bit error rate (BER) performance of a full-duplex (FD) overlay cognitive radio (CR) network with linear/nonlinear energy harvesting (EH) capability is investigated. The considered overlay CR network consists of a primary transmitter/receiver (PT/PR) pair, a secondary transmitter (ST) and an FD mode operated secondary receiver (SR) where ST harvests energy from both PT and SR during the first communication time slot. In the second communication time slot, SR receives its intended signal from ST while cooperating with PT by transmitting its signal to PR. The bit error probability (BEP) expressions for the primary/secondary users (PU/SU) are analytically derived and validated through Monte-Carlo simulations according to both linear and nonlinear EH models applied at ST. In addition, the optimum distance value between PT and ST is determined considering the objective of minimizing BER of both PU and SU. Moreover, corresponding system performances are obtained regarding a power allocation coefficient at SR to obtain the trade-off between EH and information processing. The results show that the proposed FD-CR system with nonlinear EH improves the PU BEP performance compared to the non-cooperative (direct transmission) case while the SU benefits from the spectrum of PU with a significant BER performance.

Performance of Wireless Powered Cognitive Radio Sensor Networks With Nonlinear Energy Harvester

This letter analyzes the performance of simultaneous wireless information-and-power transfer (SWIPT) in an overlay cognitive radio network (CRN) under Nakagami-$m$ fading. A pair of secondary users (SUs) is considered in which one SU facilitates relay cooperation for communications between two primary users (PUs). In return, SUs make use of primary users' signals for energy harvesting (EH) and realize their own communications. In such a network, end-to-end bidirectional communications between the two PUs and unidirectional information exchange between the SUs can be performed in three phases. A power splitting (PS) based approach is adopted for enabling SWIPT. The relaying SU applies an amplify-and-forward (AF) protocol to broadcast primary and secondary signals, whereas the PUs perform selection combining to access the active direct link. Accurate expressions of the outage probability (OP) and throughput are derived for the primary system by considering a nonlinear energy harvester at the relaying SU under Nakagami-m fading