Underlay Cognitive Radio System Research Articles

Physical-layer security for primary users in 5G underlay cognitive radio system via artificial-noise-aided by secondary users

The advent of the Internet of Things (IoT) has revolutionized connectivity by interconnecting a vast array of devices, underscoring the critical need for robust data security, particularly at the Physical Layer Security (PLS). Ensuring data confidentiality and integrity during wireless communications poses a primary challenge in IoT environments. Additionally, within the constrained frequency bands available, Cognitive Radio Networks (CRNs) has emerged as an urgent necessity to optimize spectrum utilization. This technology enables intelligent management of radio frequencies, enhancing network efficiency and adaptability to dynamic environmental changes. In this research, we focus on examining the PLS for the primary channel within the underlying CRNs. Our proposed model involves a primary source-destination pair and a secondary transmitter-receiver pair sharing the same frequency band simultaneously. In the presence of a common eavesdropper, the primary concern lies in securing the primary link communication. The secondary user (SU) acts as cooperative jamming, strategically allocating a portion of its transmission power to transmit artificial interference, thus confusing the eavesdropper and protecting the primary user's (PU) communication. The transmit power of the SU is regulated by the maximum interference power tolerated by the primary network's receiver. To evaluate the effectiveness of our proposed protocol, we develop closed-form mathematical expressions for intercept probability ( P int ) and outage probability (OP) along the primary communication link. Additionally, we derive mathematical expressions for OP along the secondary communications network. Furthermore, we investigate the impact of transmit power allocation on intercept and outage probabilities across various links. Through both simulation and theoretical analysis, our protocol aims to enhance protection and outage efficiency for the primary link while ensuring appropriate secondary OP, thereby contributing to advancements in IoT security and spectrum management.

Deep-Q Learning for Distributed Spectrum Reuse Maximization in Underlay Cognitive Radio Systems

Deep-Q Learning for Distributed Spectrum Reuse Maximization in Underlay Cognitive Radio Systems

Ensemble deep learning based resource allocation for multi-channel underlay cognitive radio system

This paper proposes a resource allocation strategy for multi-channel underlay cognitive radio (CR) systems by means of an ensemble deep learning framework. The transmit power of secondary users (SUs) allocated to each channel is determined to maximize the overall spectral efficiency (SE), whilst meeting the interference constraint on the primary user (PU). To this end, a deep neural network (DNN) structure is developed, in which multiple DNN units are jointly utilized, to obtain the diversity over different DNNs. Our simulation results confirm that the proposed scheme can achieve near-optimal performance with a low computation time of less than 1.5 ms.

RF Precoding for Cognitive Radio Systems

In this letter, a precoding framework in the radio-frequency (RF) domain is developed for the downlink of a multiuser multiple-input single-output underlay cognitive radio (CR) system. Firstly, a low hardware complexity analog multiantenna architecture is proposed for the system’s transmitter. The proposed analog architecture is based on a phase-shifting network driven by an variable gain amplifier and has low power consumption since it avoids the use of energy hungry components such as digital-to-analog converters (DACs). Secondly, a novel RF precoder for the design of the transmit signals is developed such that the performance of the CR system is optimized and the constraints related to both the system’s architecture and the employed underlay CR paradigm are satisfied. The corresponding nonconvex and difficult optimization problem is formulated and solved via a novel algorithmic solution based on the saddle point method. The convergence of the proposed algorithmic solution is theoretically studied. The proposed approach is shown to be much more energy efficient than existing approaches based on fully digital transceivers.

Outage and Error-Rate Analysis of NOMA-Inspired Multicarrier Underlay Cognitive Radio System

In this paper, the performance of a multicarrier underlay cognitive radio system is analyzed considering that the successive interference cancellation (SIC) method is used for detection. In the proposed system model, a multicarrier-based secondary user (SU) uses all the subcarriers of the primary user (PU) in underlay mode, guaranteeing the quality of service (QoS) to the primary system. The power allocation strategy is modified accordingly. With a fixed PU transmit power, power is allocated to the SU subcarriers to maximize its throughput while ensuring minimum throughput to PU. The system is analyzed for its performance considering an L-tap multipath Rayleigh fading channel. Analytical expression for outage probability at SU is derived in closed-form. Also, analytical expressions and closed-form approximations for average symbol error rates (SER) per subcarrier of PU and SU are obtained. The derived expressions are validated with the Monte-Carlo (MC) simulations. Further, the proposed scheme was implemented in an orthogonal frequency division multiplexing (OFDM)-based system with different detection schemes used at the receiver. SERs were compared through extensive simulations and it was noticed that SIC with channel estimation based on minimum-mean-squared-error (MMSE) often performed better than that based on least squares (LS) estimation. Observations reveal that the nominal error rates were achieved on the optimal choice of the parameters. The proposed system ensures sufficient throughput to SU, meanwhile eliminating the need for opportunistic sensing.

On the secrecy outage analysis of underlay cognitive radio systems with buffer‐aided relaying under Nakagami‐ m channels

In this work, the physical layer security performance of an underlay cognitive buffer-aided relay network over the general Nakagami-m fading channel model is addressed, where a primary source communicates with a destination via a decode-and-forward relay node in the presence of an eavesdropper and a secondary communication system. The relay is equipped with a finite-size storage equipment or buffer which can store the sequence of received data packets from source and forward it immediately or subsequently in an adequate time-slot. In this way, the buffer relay enables to adopt a link selection scheme in order to detect the best available link, (i.e. the one with higher secrecy rate) among the available data at source or at the relay buffer. The closed-form expression for the secrecy outage probability (SOP), which is a widely adopted performance metric in the considered scenario, is also derived. Numerical results confirm the accuracy of the derived closed-form analytic expression for SOP and indicates the interaction between secrecy performance and the Nakagami channel parameter m. In particular, it is shown that the SOP experiences a significant drop as the Nakagami channel parameter increases for a predefined target secrecy rate.

Joint power allocation and collaborative beamforming for physical layer security in underlay CR NOMA relay systems

In this paper, we investigate the problem of joint power allocation and collaborative beamforming for physical layer security in underlay cognitive radio non-orthogonal multiple access relay systems. We consider two relaying schemes, i.e., amplify-and-forward and decode-and-forward, with the goal of maximizing the secrecy rate for the central user subjective to the transmit power constraint at the source node, individual transmit power constraints at relays, rate requirements at the cognitive users and the interference power constraint at the primary receiver. The optimization problems are nonconvex and hard to solve. We propose an efficient iterative algorithm by the constrained concave–convex procedure to solve the nonconvex optimization problems. For a comparison, we provide another method, namely alternating optimization (AO) algorithm. In addition, simulations are provided to show the superiority of our proposed methods with comparison to the AO algorithm and traditional orthogonal multiple access schemes.

Performance Analysis of Underlay Cognitive Radio System with Self-Sustainable Relay and Statistical CSI

The relentlessly increasing number of small-sized devices with limited powering and computational capabilities requires the adoption of new approaches to spectrum access. In this paper, we analyze an underlay cooperative cognitive wireless system based on available statistical channel state information (CSI) that is applicable to the cognitive system with limited computational resources due to its low complexity. We considered the scenario where the primary and the cognitive network coexist in the same spectrum band, under the constraints of interference threshold and maximal tolerable outage permitted by the primary user. The communication in the secondary decode-and-forward (DF) relaying system is established via a self-sustainable relay, which harvests energy from both cognitive and primary transmitters. The closed-form expressions for the outage probability of the cognitive network are derived, which are valid for both time-switching relaying (TSR) and power-splitting relaying (PSR) protocols. We analyze the influence of both cognitive and primary systems as well as the impact of channel parameters on the cognitive system outage performance. The derived analytical results are corroborated by an independent simulation method.

Rate Maximization of Wireless-Powered Cognitive Massive MIMO Systems

In order to combat the challenges of scarce spectrum bandwidth and energy supply in the Internet-of-Things networks, this article investigates a wireless-powered massive multiple-input-multiple-output (MIMO) underlay cognitive radio (CR) system, where the secondary user (SU) harvests the energy from the primary network through a time-switching (TS) strategy. Moreover, the detection technique of maximum-ratio combining (MRC) is applied at base stations (BSs) due to its low complexity. Thereon, the achievable rate of the secondary network is thoroughly analyzed by accounting for spatial correlations at both users and BSs, which significantly differentiates the analysis from the prior literature. With the analytical results, the impacts of the number of antennas and the spatial correlations are quantified. In particular, the negative impact of the spatial correlation on the achievable rate is theoretically proved based on the majorization theory. Furthermore, the TS factor and/or power allocation coefficients are optimally designed based on the statistical channel state information (CSI) only to maximize the achievable rate while ensuring the maximum endurable interference constraint. It is found that the optimal power allocation matrix is a variant of water-filling solution with two water levels associated with sum power constraint and sum weighted power constraint, respectively. The weighting matrix is aligned with the transmit spatial correlation in the SU. The joint design of TS factor and power allocation coefficients is also shown to reach a superior performance over the algorithms-based solely on TS factor or power allocation coefficients optimizations. Finally, the analytical results are validated by conducting simulations.

Energy Efficient Power Allocation with Antenna Selection for Interference Alignment based MIMO-OFDM Cognitive Radio Networks

Energy efficient communications in cognitive radio (CR) networks has been of great interest. In order to address the power consumption problem and to maximise the energy efficiency (EE) in MIMO-OFDM underlay CR systems, power allocation (PA) and antenna selection (AS) algorithms are proposed. Interference alignment, which helps in mitigating the interference at primary and secondary receivers, is considered for setting-up the underlay CR scenario. The AS transmit is employed for the secondary users (SUs) on a per-subcarrier basis to improve their QoS. Further, to improve the QoS of both primary user (PU) and SUs, the AS is followed by energy efficient PA. Due to the fractional nature of EE, the EE maximisation problem is transformed into an equivalent parametric optimisation problem based on Dinkelbach method. Simulation results confirm that the proposed EE aware algorithms can improve the EE performance of both PU and SUs than the SE aware algorithms.

Energy efficient power allocation with antenna selection for interference alignment-based MIMO-OFDM cognitive radio networks

Energy efficient communications in cognitive radio (CR) networks has been of great interest. In order to address the power consumption problem and to maximise the energy efficiency (EE) in MIMO-OFDM underlay CR systems, power allocation (PA) and antenna selection (AS) algorithms are proposed. Interference alignment, which helps in mitigating the interference at primary and secondary receivers, is considered for setting-up the underlay CR scenario. The AS transmit is employed for the secondary users (SUs) on a per-subcarrier basis to improve their QoS. Further, to improve the QoS of both primary user (PU) and SUs, the AS is followed by energy efficient PA. Due to the fractional nature of EE, the EE maximisation problem is transformed into an equivalent parametric optimisation problem based on Dinkelbach method. Simulation results confirm that the proposed EE aware algorithms can improve the EE performance of both PU and SUs than the SE aware algorithms.

Joint Power Allocation and Power Splitting for MISO-RSMA Cognitive Radio Systems With SWIPT and Information Decoder Users

In this article, we investigate the rate-splitting multiple access (RSMA) framework in a multiuser multiple-input single-output (MISO) underlay cognitive radio system with power-splitting secondary users and information secondary users by using simultaneous wireless information and power transfer. The RSMA framework is a novel multiple access method based on linearly precoded rate splitting at the secondary base station, and successive interference cancellation at the secondary receivers, which has shown better performance compared with the traditional space-division multiple access (SDMA) method. In particular, the objective is to minimize the transmit power at the secondary base station subject to the constraints of minimum energy harvesting, minimum data rate, and a maximum power level for allowable interference with the primary users. The challenging problem under consideration is nonconvex, and the solution relies on dividing it into outer and inner optimization problems. Then, we propose a particle-swarm-optimization-based algorithm to solve the outer problem, with the inner problem managed by the semidefinite relaxation method. In addition, we present a comparative scheme based on the successive convex approximation method and a scheme based on SDMA. Finally, simulation results confirm the superior performance of the proposed approach in comparison with the other schemes.

Analysis and outage performance evaluation of a fair scheduling for independent non‐identically distributed users in a cognitive radio using OSTBC with equally correlated transmit antennas

In this study, a fair user-scheduling method is considered for an underlay cognitive radio system, in which the secondary users (SUs) are sharing the licenced frequency spectrum of a single primary user (PU), where the PU and SUs utilise Alamouti orthogonal space-time block coding (OSTBC). The impacts of some important practical issues are investigated in the system. First, it is assumed that the signal-to-noise-ratios of the SUs are independent non-identically distributed. Second, the transmit antennas for OSTBC corresponding to the SUs are assumed to be equally correlated. Third, the interference from the PU to SUs as well as the interferences from SUs to the PU are taken into consideration. To investigate the outage performance of the SUs, a closed-form expression for the cumulative distribution function of the SUs signal-to-interference-noise-ratio is obtained and then used to derive an expression for evaluating the secondary system outage performance. The numerically evaluated results, validated by computer simulations, provide insights about system outage performance under various practical situations on the impacts of the spatial antennas correlation and the PU interference on to SUs.

On the performance of underlay cognitive radio system with random mobility under imperfect channel state information

SummaryIn this paper, the performance of an underlay cognitive radio system with random mobility and imperfect channel state information (CSI) is investigated. The mobile user (MU) utilises maximum ratio combining (MRC) and selection combining (SC) diversity techniques as signal reception to improve the quality of received signal‐to‐noise ratio (SNR). Under the Rayleigh fading, random waypoint mobility model is employed to characterised the effect of the MU random mobility on the system performance. Thus, novel probability density function (PDF) and cumulative distribution function (CDF) for the two considered diversity techniques are derived. Through these, the outage probability and average bit error rate (ABER) closed‐form analytical expressions are then obtained to quantify the system performance under the MRC and SC schemes. The results illustrate the effect of imperfect CSI, user mobility which is characterised by pathloss and the network topology on the system performance. Also, the results depict that MRC offers the system better performance compared with SC under the same system conditions. The accuracy of the derived analytical expressions is verified through Monte‐Carlo simulations.

Performance Analysis of Overlay Cognitive NOMA Systems With Imperfect Successive Interference Cancellation

Non-orthogonal multiple access (NOMA) and cognitive radio (CR) are envisioned as promising solutions to achieve high spectral efficiency for future wireless networks. This work investigates the outage performance of an overlay cognitive NOMA system with imperfect successive interference cancellation (SIC). The outage probability of primary user and secondary user are derived in closed forms. To obtain further insights, asymptotic expressions of outage probability and system throughput are evaluated when the transmit signal-to-noise ratio approaches infinity. An optimal power allocation coefficient is provided to maximize the system throughput. Moreover, the overlay cognitive NOMA system is compared with the underlay CR system and the overlay cognitive orthogonal multiple access (OMA) system in terms of outage probability. Finally, the performance analysis is validated by simulations. The simulation results demonstrate that the outage performance and system throughput of overlay cognitive NOMA system are superior to those of overlay cognitive OMA system and underlay CR system when the imperfect SIC satisfies certain conditions.

Ensuring equal outage performance for down‐link secondary users in full/half duplex cognitive NOMA systems

This study considers an underlay cognitive radio (CR) system, where the secondary network employs cooperative non-orthogonal multiple access (NOMA) to transfer information for downlink secondary users (SUs). Here the near user is enabled to act as a full duplex/half duplex (FD/HD) decode-and-forward (DF) relay for the far user. We derive analytical expressions for the outage probabilities experienced by the SUs in the considered FD/HD – CR-NOMA network. The maximum transmit power constraint of the secondary nodes and the tolerable interference power constraints at the primary receiver are considered for the analysis. We provide numerical and simulation results to identify the impact of key system parameters on the outage performance of SUs. Further, we provide insights on the selection of key system parameters such as NOMA power allocation coefficient for ensuring that both the SUs experience equal outage performance. Finally, we derive an analytical expression for the system outage probability of the FD-CR-NOMA network. We determine the optimal power allocation (OPA) factor at the secondary transmitter that minimises the system outage probability. We establish that OPA can reduce the system outage significantly as compared to the default choice of power allocation factor. The analytical results are validated by extensive simulation studies.

Relay Selections for Cooperative Underlay CR Systems With Energy Harvesting

In this paper, we consider a cooperative underlay cognitive radio system in which one secondary user ( ${S}$ ) transmits its data to a secondary receiver with the assistance of multiple relays. In the considered underlay spectrum sharing scenario, the transmit power levers at ${S}$ and forwarding relays are adjusted simultaneously according to a given threshold interference power that the primary user can tolerate. We also consider that relays adopt threshold decode-and-forward relay scheme and harvest energy from the primary transmitter with finite energy storage capacity under time switching scheme. Three best relay selection (RS) schemes, optimal source-relay link with wireless energy harvesting (WEH), optimal relay-destination link with WEH and optimal source-relay-destination link with WEH schemes, are proposed and studied. Closed-form analytical expressions for the outage probability of these three best RS schemes are derived, respectively. Finally, our analytical results are verified by Monte-Carlo simulations.

Impact of Multiple Primaries and Partial CSI on Transmit Antenna Selection for Interference-Outage Constrained Underlay CR

Transmit antenna selection is a low-complexity multiple-antenna technique that exploits spatial diversity using only one radio frequency chain. We investigate it for an underlay cognitive radio system that operates in the presence of multiple primary receivers and is subject to a constraint on the interference outage it causes at any of the primary receivers. The selection is based on a practically motivated and general partial channel state information (CSI) model in which the secondary transmitter (STx) only knows the channel power gains to a subset of the primary receivers. We derive a novel and general antenna selection rule that provably minimizes the symbol error probability (SEP) of the secondary system. We also derive insightful analytical expressions for its average SEP and interference-outage probability. These apply to a general class of channel fading models and any number of transmit and receive antennas, and include the special cases in which the STx knows channel power gains of all or none of the primary receivers. Our numerical results bring out a new insensitivity of the average SEP of the optimal rule to the interference power threshold when the CSI available is partial.

Asymptotic Performance Analysis of Generalized User Selection for Interference-Limited Multiuser Secondary Networks

We analyze the asymptotic performance of a generalized multiuser diversity scheme for an interference-limited secondary multiuser network of underlay cognitive radio systems. Assuming a large number of secondary users and that the noise at each secondary user's receiver is negligible compared to the interference from the primary transmitter, the secondary transmitter transmits information to the $k$-th best secondary user, namely, the one with the $k$-th highest signal-to-interference ratio (SIR). We use extreme value theory to show that the $k$-th highest SIR converges uniformly in distribution to an inverse gamma random variable for a fixed $k$ and large number of secondary users. We use this result to derive asymptotic expressions for the average throughput, effective throughput, average bit error rate and outage probability of the $k$-th best secondary user under continuous power adaptation at the secondary transmitter, which ensures satisfaction of the instantaneous interference constraint at the primary receiver caused by the secondary transmitter. Numerical simulations show that our derived asymptotic expressions are accurate for different values of system parameters.

A compact wide-slot UWB antenna with reconfigurable and sharp dual-band notches for underlay cognitive radio applications

This paper presents a compact wide-slot ultrawide-band (UWB) antenna with reconfigurable and sharp dual-band notches compatible with the underlay cognitive radio systems. The antenna slot and tuning stub are reshaped in such a way that the proposed antenna operating bandwidth extends along the frequency band specified for UWB applications (3.1-10.6 GHz). In spite of their sharpness, the generated band notches perfectly cancel the interference with the entire 5 GHz wireless local area network (WLAN) frequency band (5.15-5.725 GHz) and that of the military X-band satellite communications downlink (7.25-7.745 GHz). The WLAN band notch is presented by attaching a pair of quarter wavelength parasitic elements to the antenna ground plane, while the other band notch is produced by engraving another pair of half wavelength parasitic elements within the antenna wide slot along the circumference of the antenna tuning stub. The reconfiguration of the band notches is achieved by inserting a pair of PIN diodes for each pair of parasitic elements. The simulated and measured results accentuate the UWB coverage of the proposed antenna, and also verify the reconfigurability and the sharpness of the antenna band notches. Moreover, the antenna has a noticeably stable radiation pattern over the entire band of operation with omnidirectional pattern convenient for portable UWB gadgets.