Primary User Receiver Research Articles

Joint sensing interval and channel access optimization in energy harvesting hybrid active/passive symbiotic networks

The radio frequency spectrum became crowded because of the huge number of wireless devices, hence cognitive radio networks (CRNs) should increase the efficiency of spectrum utilization. Moreover, energy-saving techniques are becoming essential to prolong the devices’ life. Consequently, this work considers a hybrid active/passive (interweave/backscatter) symbiotic network while adopting the energy harvesting technology and applying the sensing interval concept. The sensing interval concept helps the secondary users (SUs) to transmit their data for consecutive time slots depending on the sensing result of the first time slot. This concept helps the SUs to reduce the consumed energy in sensing the channel each time slot. The hybrid transmission mode improves the spectrum utilization. The energy harvesting technology, the sensing interval concept, and the backscatter mode improve the energy efficiency. These spectrum utilization and energy efficient techniques are combined, for the first time, in one model. To deal with the mixed system state (the energy of the SUs which is fully observable state and the primary users activity which is partially observable state due to the imperfect sensing) and take the future rewards into consideration, a mixed observable Markov decision process is proposed. Moreover, we derive a closed form expression for the data outage probability of the backscatter transmission with/without spectrum sensing. The numerical results show that the proposed model prevails over the other models in the literature in terms of throughput and energy efficiency. Moreover, the interference on the primary user receiver due to applying the sensing interval concept is reduced by introducing a new penalty parameter.

Empirical Mode Decomposition Based Amplify and Forward Technique for Cooperative Cognitive Radio System

The rapid growth in the mobile industry due to increase in number of users accessing diverse services causes a high demand for radio spectrum. Nonetheless, the radio spectrum allocated for different wireless communication services is restricted. Cooperative Cognitive Radio (CCR) technique with Amplify and Forward (AF) relaying protocol used to address the problem suffers from noise amplification resulting in poor reception at the destination. Hence, in this paper, Empirical Mode Decomposition (EMD) based AF technique for CCR system was carried out to improve the performance of the existing CCR with AF relaying protocol. The transmitted signal from Primary User (PU) was received at the Secondary User (SU) where SU superimposed its own signal using Exclusive OR (XOR) rule. The combined signal from XOR was made to pass through EMD and amplified using AF by multiplying with the relay gain. The amplified signal was radiated to PU and SU receivers during the second hop transmission. The multiple copies of the receive signal at the SU receiver at different number of path (L = 2, 4) were combined at destination using Maximal Ratio Combiner (MRC). Mathematical expression for Bit Error Rate (BER) and Throughput (TP) were derived using the Probability Density Function (PDF) of the Nakagami-m fading distribution. Extensive simulations using MATLAB R2021a were employed to assess the effectiveness of the proposed technique and evaluated using BER and TP by comparing with the existing AF CCR. The EMD based AF technique proposed gave better performance with 75.2% reduction in BER and 21.86% increase in TP over the existing AF technique for CCR. The proposed technique can be deployed to improve the performance of cooperative cognitive radio system.

Performance Analysis of Dual-Hop AF Cognitive Relay Networks with Best Selection and Interference Constraints

In this paper, a dual-hop underlay cognitive relay network (CRN) with a best-relay selection (BRS) scheme under spectrum-sharing constraints from the primary user (PU) is investigated. The system model in this work consists of one PU, one secondary user (SU) and a few SU relays. Both users exchange the information using a half-duplex mode through amplify-and-forward (AF) SU relays. Moreover, all channels are modelled using the Nakagami-m fading model. In this work, the outage probabilities (OPs) are derived for the proposed system model under several scenarios to investigate the network performance under interference power constraint Ip at the PU receiver. In addition, the impacts of the number of relays and the channel fading severity parameters are investigated as well. Furthermore, the system performance is investigated for several PU locations. The various numerical results are verified using a Monte Carlo simulation. Overall, the obtained results show that several factors such as the number of relays, channel fading severity parameters and PU location have a major impact on the outage performance of the SU. The simulation and analytical results are perfectly matched, confirming the accuracy of the analytical derivations.

Performance analysis of overlay cognitive NOMA network with imperfect SIC and imperfect CSI

In this paper, we investigate a multiple users cooperative overlay cognitive radio non-orthogonal multiple access (CR-NOMA) network in the presence of imperfect successive interference cancellation (SIC) and imperfect channel state information (CSI). In the context of cellular network, cell-center cognitive secondary users act as relays to assist transmission from the primary user (PU) transmitter to the cell-edge PU receiver via NOMA. According to the received signals between the primary transmitter and multiple cognitive secondary center users, the best cell-center cognitive SU with the maximum signal to noise ratio (SNR) is selected to transmit the PU’s signals and its own signal to cell-edge users through NOMA principle. Then, the PU cell-edge user combine the signals received from direct transmission in the first phase and relay transmission from the best cell-center cognitive SU in the second phase by selection combining (SC). To measure the performance of the system quantitatively, we derive the end-to-end outage probability and capacity for the primary and secondary networks by taking the imperfect SIC and CSI into consideration. Finally, the performance analysis is validated by the simulations, and show that serious interference caused by imperfect SIC and (or) imperfect CSI reduce the system performance.

Jamming in Eavesdropping on Throughput Maximization in Green Cognitive Radio Networks

This work considers a cognitive radio (CR) network consisting of a set of CR transmit-receive node pairs, one fusion center (FC), multiple primary user emulation attack (PUEA) nodes, an eavesdropper ( <inline-formula><tex-math notation="LaTeX">$E_{av}$</tex-math></inline-formula> ) node and a set of friendly jammers used for protection of CR data transmission from eavesdropping. At the initial time slot of the frame, simultaneous energy harvesting (EH) and spectrum sensing are done through power splitting (PS) mode. CR transmit nodes then amplify and forward the sensed samples of both the primary user (PU) and the PUEA to the FC for cooperative spectrum sensing (CSS). Based on the CSS decision, CR transmit nodes either perform EH over the entire duration or make an opportunistic data transmission in time division mode. The closed form expressions of the optimal sensing duration, power allocation factor and transmit power for each secondary user (SU) are found. The sum secondary throughput of the network is maximized under the constraints of meeting the sensing reliability of the PU, individual energy causality for each SU and the best selected jammer, interference at the PU receiver, individual secondary and secrecy outage probability. Simulation results show a performance gain on the maximum value of the sum secondary throughput by <inline-formula><tex-math notation="LaTeX">$\sim$</tex-math></inline-formula> 17.56 and <inline-formula><tex-math notation="LaTeX">$\sim$</tex-math></inline-formula> 49.69 percent over the existing works.

Enhancing multicast security of cognitive radio networks with antenna correlations over Nakagami-m fading channels

In this paper, we investigate the impact of diversity and antenna correlations on the secrecy capacity and outage performance of a cognitive radio multicast network over Nakagami-m fading channels analytically. The proposed network consists of single primary and secondary user, multiple primary and secondary receivers, and multiple eavesdroppers. It is assumed that each user is equipped with single antenna while all the primary and secondary receivers, and eavesdroppers are equipped with multiple antennas. The primary and secondary users transmit their common messages to the respective receivers in the presence of multiple eavesdroppers. A mathematical model is developed to ensure successful reception of confidential information to the primary receivers protecting the activities of eavesdroppers neglecting the effect of interference due to secondary user. In order to analyze the security of the proposed model, closed-form analytical expressions have been derived for the secrecy multicast capacity, the secure outage probability for multicasting and the probability of non-zero secrecy multicast capacity. Analytical results are justified via Monte-Carlo simulations.

Enhanced interpolation-based interference rejection combining for black-space cognitive radio in time-varying channels

In this paper, we investigate multi-antenna interference rejection combing (IRC)-based black-space cognitive radio (BS-CR) operation in time-varying channels. The idea of BS-CR is to transmit secondary user (SU) signal in the same frequency band with the primary user (PU) such that SU’s power spectral density is clearly below that of the PU, and no significant interference is inflicted on the PU receivers. We explore the effects of interpolation and mobility on the novel blind IRC technique which allows such operation mode for effective reuse of the PU spectrum for relatively short-distance CR communication. We assume that both the PU system and the BS-CR use orthogonal frequency division multiplexing (OFDM) waveforms with common numerology. In this case, the PU interference on the BS-CR signal is strictly flat-fading at subcarrier level. Sample covariance matrix-based IRC adaptation is applied during silent gaps in CR operation. We evaluate the effect of the gap length on the link performance, using known PU channel-based interference covariance estimation as reference. We also propose an interpolation-based scheme for tracking the spatial covariance in time-varying channels, demonstrating significantly improved robustness compared to the earlier scheme. The performance of the proposed IRC scheme is tested considering terrestrial digital TV broadcasting (DVB-T) as the primary service. Also joint PU and co-channel CR interference cancellation is included in the study. The resulting interference suppression capability is evaluated with different PU interference power levels, silent gap durations, data block lengths, and CR device mobilities.

Intelligent Reflecting Surface-Assisted Cognitive Radio System

Cognitive radio (CR) is an effective solution to improve the spectral efficiency (SE) of wireless communications by allowing the secondary users (SUs) to share spectrum with primary users (PUs). Meanwhile, intelligent reflecting surface (IRS), also known as reconfigurable intelligent surface (RIS), has been recently proposed as a promising approach to enhance energy efficiency (EE) of wireless communication systems through intelligently reconfiguring the channel environment. To improve both SE and EE, in this paper, we introduce multiple IRSs to a downlink multiple-input single-output (MISO) CR system, in which a single SU coexists with a primary network with multiple PU receivers (PU-RXs). Our design objective is to maximize the achievable rate of SU subject to a total transmit power constraint on the SU transmitter (SU-TX) and interference temperature constraints on the PU-RXs, by jointly optimizing the beamforming at SU-TX and the reflecting coefficients at each IRS. Both perfect and imperfect channel state information (CSI) cases are considered in the optimization. Numerical results demonstrate that IRS can significantly improve the achievable rate of SU under both perfect and imperfect CSI cases.

Physical layer security and energy efficiency driven resource optimisation for cognitive relay networks

In this study, a resource allocation problem considering physical layer security and power consumption for cognitive relay networks is studied. In a secondary network, the ratio of secret rate to power consumption is defined as a secret rate per watt (SRW). Fixed circuit power, dynamic circuit power, and transmit power are all considered in the power consumption model. Under the constraints of the maximum total transmit power of secondary user transmitters and relay nodes, minimum secret rate requirement of secondary user receiver and tolerable interference threshold of each primary user receiver, the authors propose a SRW maximisation algorithm to maximise SRW. The resource allocation problem is formulated as a non-linear fractional programming and it is transformed into an equivalent subtraction based on the Dinkelbach method. They incorporate the non-convex constraints into the objective function to convert the feasible region into a convex set and achieve an optimal resource allocation scheme with the nested loop iteration algorithm through the Lagrange dual theory and the difference of convex programming. By the Dinkelbach method and the nested loop iteration algorithm, the optimal SRW is obtained. Simulation results demonstrate the effectiveness and the out-performance of the proposed algorithm comparing with other algorithms.

Secrecy analysis of a Cognitive Radio Network with an adaptive path selection based transmission scheme and JTAPS relay

This paper investigates the secrecy outage performance of a Cognitive Radio Network (CRN), where we propose an adaptive path selection based transmission scheme to transmit the information from the source to destination. The transmit power of the secondary user (SU) and relay is limited due to underlay CRN to maintain the maximum acceptable interference at the primary user (PU) receiver. The secondary network uses an intermediate relay between source and destination to harvest energy from the transmission of the radio frequency (RF) signal of SU following a joint time allocation and power splitting (JTAPS) protocol. Here we use the hybridization of two known energy harvesting (EH) protocols by combining the time allocation (TA) and power splitting (PS) factor to make more efficient use of the EH method in evaluating physical layer secrecy. We develop analytical expressions for secrecy outage under JTAPS and the effect of time allocation (TA) and power splitting (PS) factor on the secrecy outage probability (SOP) is investigated. Our proposed JTAPS scheme yields 12% reduction in SOP with respect to TSR scheme at an energy harvesting factor α=0.6.

Statistical Modelling of Dynamic Interference Threshold and Its Effect on Network Capacity

In this paper, we present the case of utilizing interference temperature (IT) as a dynamic quantity rather than as a fixed quantity in an orthogonal frequency division multiple access (OFDMA) based spectrum sharing systems. The fundamental idea here is to reflect the changing capacity demand of primary user (PU) over time in setting the interference power threshold for secondary user (SU). This type of dynamic IT will allow the SU to opportunistically have higher transmit power during relaxed IT period, thereby resulting in higher network capacity. The cognitive radio network (CRN) considered in this paper has an underlay network configuration in which the available spectrum of the PU is accessed concurrently by SU provided that the interference power at the PU receiver from SU is under a certain power threshold. This power threshold is set to maintain and guarantee a certain level of quality of service (QoS) for PU network. Theoretical expressions for outage probability and mean capacity for SU network are derived, and validated with simulation results, and it is observed that utilizing dynamic IT results in high network performance gains as compared to utilizing a fixed IT in cognitive radio system.

Discrete Exclusion Zone for Dynamic Spectrum Access Wireless Networks

The implementation of a geographic exclusion zone (GEZ) has been a scheme in regulations developed to protect a primary user (PU) in dynamic spectrum access wireless networks, where secondary users (SUs) can transmit only outside the exclusion zone region centered at the PU receiver. After determining the radius of the GEZ, the number of operable nodes in actual deployment is quite uncertain due to the random location of nodes. This poses certain difficulty for SU spectrum sharing planning. In this paper, we propose an alternative PU protection scheme called the discrete exclusion zone (DEZ), which is shapeless. The PU protection is achieved by switching off the first <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$k-1$ </tex-math></inline-formula> nearest neighboring SUs surrounding the PU. Building on the stochastic geometry of wireless node locations, the conditions under which the mean and the variance of the aggregate interference from SUs to the PU exist are obtained. These conditions define the minimum size of the DEZ. Then, we obtain the closed-form expressions for the mean and the variance as a function of the DEZ size <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$k$ </tex-math></inline-formula> for a given number of SUs <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N$ </tex-math></inline-formula> , including <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N\rightarrow \infty $ </tex-math></inline-formula> . Since it is challenging to obtain a closed-form expression of the density function, we resort to the Gamma distribution to approximate the distribution of the aggregate interference, which is validated by simulations. Finally, the performances of the GEZ and DEZ are investigated in terms of the number of operable SUs outside the GEZ and DEZ, respectively, for achieving a given PU protection requirement. The results show that the DEZ gives a fixed number of operable nodes in the presence of topology randomness associated with the actual SU network deployment.

Secrecy and throughput performance of an energy harvesting hybrid cognitive radio network with spectrum sensing

In this paper, we evaluate the secrecy outage performance and throughput of a hybrid cognitive radio network, where a secondary user (SU) accesses the primary spectrum either in underlay or overlay mode based on spectrum sensing decision. In underlay, the transmit power of the SU as well as the relay is limited by the maximum acceptable interference at primary user (PU) receiver as required by an PU outage constraint, a quality of service for PU. The secondary network employs a decode and forward relay which harvests energy from the radio frequency signal of SU following a time switching relaying protocol. We develop analytical expressions for secrecy outage considering the impact of sensing decision and sensing time. Impact of sensing time, imperfect channel state information of interfering link, energy harvesting time, acceptable interference threshold and PU outage constraint on the secrecy outage probability, as well as throughput of SU are investigated. Further, an interplay between throughput performance and secrecy outage of the network is highlighted.

A Hybrid Framework for Spectrum Sharing in Cognitive Radio Systems With Dynamic Users

In this letter, we present a hybrid spectrum sharing approach in cognitive radio (CR) systems with dynamic users in which the secondary users (SU) may not accurately detect the presence of primary users (PU). As a consequence, there is an increased probability of collision between PU and SU transmissions, resulting in interference at the PU receiver. The proposed hybrid framework combines the interweave and underlay spectrum sharing paradigms, and limits interference to the PU through a mathematical expression that provides bounds on the SU power based on its sensing performance. The framework requires that the PU only share this expression and does not require that the PU reveal its waveform or other operating parameters to the SU. An example illustrating the proposed approach is also presented.

Beam Selection and Discrete Power Allocation in Opportunistic Cognitive Radio Systems With Limited Feedback Using ESPAR Antennas

We consider an opportunistic cognitive radio (CR) system consisting of a primary user (PU), secondary transmitter (SUtx), and secondary receiver (SUrx), where SUtx is equipped with an electrically steerable parasitic array radiator (ESPAR) antenna with beam steering capability for sensing and communication, and there is a limited feedback channel from SUrx to SUtx. Taking a holistic approach, we develop a framework for integrated sector-based spectrum sensing and sector-based data communication. Upon sensing the channel busy, SUtx determines the beam corresponding to PU's orientation. Upon sensing the channel idle, SUtx transmits data to SUrx, using the selected beam corresponding to the strongest channel between SUtx and SUrx. We formulate a constrained optimization problem, where SUtx- SUrx link ergodic capacity is maximized, subject to average transmit power and interference constraints, and the optimization variables are sensing duration, thresholds of channel quantizer at SUrx, and transmit power levels at SUtx. Since this problem is non-convex we develop a suboptimal computationally efficient iterative algorithm to find the solution. Our numerical results quantify the capacity improvement provided by the ESPAR antenna and demonstrate that our CR system yields lower outage and symbol error probabilities, compared with a CR system that its SUtx has an omni-directional antenna.

Overlay Cognitive Radio Based on OFDM with Channel Estimation Issues

Cognitive radio (CR) has been proposed as a technology to improve the spectrum efficiency by giving an opportunistic access of the licensed-user spectra to unlicensed users. We consider an overlay CR consisting of a primary macro-cell and cognitive small cells of cooperative secondary base stations (SBS). We suggest studying a CR where an orthogonal frequency division multiplexing is used for both the primary users (PU) and the secondary users (SU). In order to cancel the interferences, a precoding is required at the SBS. Therefore, we first derive the interferences expression due to SU at the PU receiver. Then, zero forcing beamforming (ZFBF) is considered to cancel the interferences. However, applying ZFBF depends on the channels between the SBS and the PU. A channel estimation is hence necessary. For this purpose, we propose to approximate the channel by an autoregressive process (AR) and to consider the channel estimation issue by using a training sequence. The received signals, also called the observations, are considered to be disturbed by an additive white measurement noise. In that case, the AR parameters and the channel can be jointly estimated from the received noisy signal by using a recursive approach. Nevertheless, the corresponding state space representation of the system is non-linear. Then, we propose to carry out a complementary study by compare non-linear Kalman filter based approaches.

Throughput Optimization for Interference Aware Underlay CRN

Minimization of interference to primary user (PU), maximizing the throughput and connectivity of secondary users (SUs) while providing the quality of service are the major challenges for success of an underlay mode cognitive radio network (CRN). In this work we propose a model for addressing channel sharing problem for an ad-hoc underlay CRN. The objective is to maximize the throughput of the SUs while keeping the level of interference caused to the PU by the SUs under a given PU threshold. During the underlay communication, each SU receives certain signal strength based on their distances from the PU. A head node is chosen amongst the SUs using a technique based on received signal strength by the SUs. The head collects the information from all the other SUs in terms of data rate requirement, interference produced to PU and the SNR level of the SUs through a common control channel. Using the information received a dynamic programming based model is proposed to decide which SUs can be selected to access a channel for underlay mode communication. A channel is allowed to be accessed such that the throughput of the network is maximized while the overall interference to the PU receiver is kept within the specified tolerable limit. The head node dynamically assigns the channel among the selected SUs. The efficacy of the proposed model has been evaluated with numerical evaluation and simulation study. A greedy algorithm has been formulated which selects the SUs based on their data rate to interference ratio for simulation and comparative study with the proposed model. The results show that the proposed model outperforms the greedy algorithm while increasing the overall connectivity.

Achievable Rates With Cooperative Spectrum Sharing in the Modulation-Based Dimension

Cooperative spectrum sharing (CSS) is a joint spectrum access technique that involves collaboration between primary user (PU) and secondary user (SU) systems. An instance of CSS occurs when the SU transmitter acts as a relay for the PU system. In forwarding the PU signal, the SU transmitter deliberately superimposes the signal intended for the SU receiver. This process unfortunately causes mutual interferences at both PU and SU receivers. Achievable rates for both systems are typically analyzed by assuming Gaussian signals and interferences. Unlike most of previous work, this paper studies the use of practical digital modulation schemes in CSS. The novelty of the proposed CSS approach lies on the smart alignment and superimposition of the SU's pulse amplitude modulated signal to the PU's phase-shift keying signal. It is shown that the SU signal does not interfere with the PU signal, it actually improves the PU signal strength. This paper then focuses on deriving the approximated theoretical transmission rates for both the PU and SU. Interestingly, the analysis shows superior transmission rates for both systems, compared to that achieved by conventional signal superimposition approaches. Simulation results then confirm the matching with the analytical results and validate the performance advantages of the proposed CSS approach.

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.

Outage analysis for multiuser underlay cognitive TWRN with antenna selection and user scheduling

This paper investigates the outage performance of cellular two-way amplify-and-forward (AF) cooperative spectrum sharing systems in the presence of primary user (PU) network and multiple secondary user (SU) destinations. A general Nakagami-m fading environment has been used, where distinct fading parameters, as well as unequal average fading powers between the interference and relaying links, are assumed. Focusing on the cooperation process among the SU nodes and making use of the underlay cognitive approach, an approximate closed-form expression for the overall outage probability (OOP) of the secondary network is derived. In this analysis, an opportunistic scheduling and transmit antenna selection (TAS) algorithm in the secondary network has been employed. Considering the interference constraints due to the presence of PU receiver, power allocation of secondary user is done. The effects of fading severity, secondary network relay placement, the number of PU & SU transmit antenna, and number of SUs on the end-to-end system performance are examined through some representative numerical plots. Moreover, to minimize the secondary network OOP, we investigate the optimization problems of relay position. Monte Carlo simulation results are presented to corroborate the proposed analysis.