Secondary Transmitter-receiver Pair 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.

Joint relay selection and power allocation for NOMA‐based multicast cognitive radio networks

In this study, the problem of joint relay selection and power allocation (J-RS-PA) for NOMA-based multicast cognitive radio networks is considered. In particular, the aim is to simultaneously maximise the end-to-end SINR/SNR of the primary and secondary transmitter–receiver (TR) pairs, subject to quality-of-service (QoS) constraints. Communication between the primary and secondary TR pairs is performed over two-phases, namely, the broadcasting phase, and the cooperation phase. In the broadcasting phase, the primary and secondary transmitters broadcast their data symbols; while in the cooperation phase, the selected relay forwards the decoded symbols to their intended receivers. However, the formulated J-RS-PA problem happens to be non-convex, resulting in computationally-prohibitive complexity. Consequently, an optimal low-complexity two-stage relay selection and power allocation (TS-RS-PA) algorithm is devised, which is based on the solution of linear programming problem reformulations. Simulation results are presented to validate the proposed TS-RS-PA algorithm, which is shown to yield the optimal SINR/SNR values in comparison to the J-RS-PA scheme, but with lower computational complexity, while satisfying QoS constraints.

On the Performance of NOMA-Assisted Overlay Multiuser Cognitive Satellite-Terrestrial Networks

In this letter, we investigate the performance of an overlay cognitive satellite-terrestrial network comprising a primary satellite source with its multiple terrestrial receivers and a secondary transmitter-receiver pair on the ground. Herein, the primary satellite source employs a non-orthogonal multiple access (NOMA) scheme to simultaneously serve its all users, while the secondary transmitter assists the primary communication through cooperative relaying technique in exchange for spectrum access. For this overall set-up, we obtain the closed-form expressions for the outage probability of primary satellite network and secondary terrestrial network by adopting pertinent heterogeneous fading models. Further, we derive the asymptotic outage behaviour at high signal-to-noise-ratio (SNR) for the primary and secondary networks, and thereby calculate the achievable diversity orders. Our analytical findings are corroborated through various numerical and simulation results.

BER analysis of non‐orthogonal multiple access‐based cognitive butterfly network

In this Letter, the non-orthogonal multiple access (NOMA) technique is applied to the cognitive butterfly network, where a secondary relay assists a primary transmitter–receiver pair in the lack of a direct link between them to realise spectrum sharing for a secondary transmitter–receiver pair. In this network, the uplink and downlink NOMA principles are combined and the side information from the nearer transmitters is exploited for better successive interference cancellation (SIC) at the receivers. The end-to-end bit error probability (BEP) is analytically derived for both users and the results are approved via computer simulations by considering imperfect SIC. The better BEP performance provided by NOMA compared to a reference orthogonal multiple access protocol is demonstrated.

Performance Analysis of Hardware-Impaired Overlay Cognitive Satellite–Terrestrial Networks With Adaptive Relaying Protocol

In this article, we consider an overlay cognitive hybrid satellite-terrestrial network consisting of a primary satellite source-receiver pair and a secondary transmitter-receiver pair on the ground while taking into account the practical hardware impairments (HIs) at the user devices. Herein, a secondary terrestrial user acts as a cooperative relay to assist the transmission of primary satellite user. In return for this kind of favor, the secondary user gets access to the primary's spectrum for its own communication. Further, we consider the distortion noises induced by all the hardware-impaired terrestrial nodes and demonstrate their detrimental impact on the system performance. We manifest analytically that, for the higher data rates, the HIs invoke ceiling effects which reprehensibly cap the fundamental capacity of the system. To mitigate the effect of HIs, we propose an adaptive relaying (AR) protocol for both amplify-and-forward and decode-and-forward operations and compare its performance with the competitive fixed relaying schemes. The proposed AR protocol efficiently utilizes the available degrees-of-freedom to enhance the system performance. We comprehensively analyze the overall system performance by deriving closed-form expressions for the outage probability of the primary and secondary networks under heterogeneous fading environments. Our theoretical developments are corroborated through various numerical and simulation results.

Joint source and relay precoder design for energy‐efficient MIMO‐cognitive relay networks

This study addresses the energy efficiency (EE) maximisation problem in multi-input multi-output cognitive relay networks, where a secondary transmitter–receiver pair communicates through an amplify-and-forward relay using the licenced spectrum of a primary user. The authors aim to maximise the EE of the secondary system by jointly designing the source and relay precoding matrices, subject to transmit power, interference, and quality-of-service constraints. The resultant problem is non-convex in the precoding matrices; it is converted into a much simpler vector-valued problem using singular value decomposition. A combination of iterative optimisation, fractional programming, and Lagrangian multiplier is used to further tackle the problem. Numerical results are presented to evaluate the EE performance of the proposed scheme. Impact of transmit power, interference threshold, and minimum rate requirement on the EE is analysed.

Capacity Maximization for an RF Energy-harvesting Cooperative Cognitive Radio Network

This work considers a cooperative cognitive radio network including a primary system with a primary transmitter-receiver pair (PT-PR) and a secondary system with a secondary transmitter-receiver pair (ST-SR). In order to access the licensed band allocated to primary users, the ST plays the role of a decode-and-forward relay in order to forward primary signals to the PR. In particular, after receiving the primary signals, the ST first uses a power-splitting energyharvesting method to harvest energy and decode the primary signals. Then, the ST superimposes its information on the decoded primary signals, and use the harvested power to transmit the superimposed signal to the PR and the SR. We here devote our efforts to formulating and solving an optimization problem aimed at maximizing the capacity obtained by secondary users while also guaranteeing quality of service for the primary users. Simulation results clearly show that our solution significantly improves the achievable capacity of secondary users.

Secure Beamforming for Untrusted MISO Cognitive Radio Networks

In this paper, we study the secure beamforming design for a cognitive radio network (CRN), where a primary transmitter-receiver pair coexists with an untrusted secondary transmitter-receiver pair. Each pair constitutes a multiple-input single-output link. We consider an underlay scheme and a cooperative scheme. For the underlay scheme, the secondary user (SU) is allowed to transmit simultaneously in the presence of the primary transmission. For the cooperative scheme, the secondary transmitter acts as a relay to forward the secrecy information of the primary transmission in exchange for its own transmission. For both schemes, the SU is untrusted and considered a potential eavesdropper. Our goal is to minimize the total power consumption while satisfying the primary user's required secrecy rate and the SU's required information rate. Using suitable optimization tools, we design the jointly optimal secure beamforming for the underlay scheme and an alternative optimizing algorithm for the cooperative scheme. To further reduce the complexity, we also design suboptimal zero-forcing beamformers for both schemes. The simulation results verify the proposed schemes.

On physical‐layer security for primary system in underlay cognitive radio networks

In this study, the authors consider the physical-layer security for transmission in underlay cognitive radio networks, where consisting of a primary source–destination pair, a secondary transmitter–receiver pair and a common eavesdropper (E). To transmit data in a secure and reliable manner, they propose a transmission protocol for an underlay cognitive radio network. In particular, the secondary user is allowed to operate on the primary spectrum bandwidth when the interference threshold is satisfied. To protect the transmission confidentiality of primary system, PS node transmits a signal, which is linearly combined with the jamming signal (as artificial noise) and expectation signal, to interfere E. Furthermore, they propose a superimposed coding to combine with the artificial noise and expectation signal at PS node. We also analyse the performance of the proposed transmission protocol. We obtain the outage probability of secondary and primary systems. Simultaneously, they derive the closed-form expression of intercept probability for primary system. In addition, they verify the performance of their proposed transmission protocol by numerical experiment. The numerical results show that their proposed transmission protocol not only has the better outage performance for secondary system but also has the better intercept performance for primary system.

Cognitive Relaying Cooperation in Satellite-Terrestrial Systems With Multiuser Diversity

This paper investigates the outage performance of an overlay multiuser hybrid satellite-terrestrial spectrum sharing system. Herein, we exploit both direct and relay links from a primary satellite source to multiple terrestrial users with the coexistence of a secondary transmitter–receiver pair on the ground. Based on an overlay approach, the secondary transmitter provides an amplify-and-forward-based relay cooperation to the primary satellite network that employs opportunistic scheduling of multiple users. The underlying user scheduling strategy is based on satisfying the criterion of minimal outage probability (OP) for the primary network and, eventually, exploring more opportunities of the spectrum sharing for the secondary terrestrial network. By considering the widely adopted Shadowed-Rician fading model for the satellite links while the Nakagami- $m$ fading model for the terrestrial links, we derive the analytical expressions for the OP of the primary satellite network and the secondary terrestrial network and further highlight the corresponding achievable diversity orders. We also examine the impact of power splitting factor for spectrum sharing between primary and secondary networks.

Maximum Secondary Stable Throughput of a Cooperative Secondary Transmitter–Receiver Pair: Protocol Design and Stability Analysis

In this paper, we investigate the impact of cooperation between a secondary transmitter–receiver pair and a primary transmitter on the maximum stable throughput of the primary–secondary network. Each transmitter, either primary or secondary, has a buffer for storing its own traffic. In addition to its own buffer, the secondary transmitter has a buffer for storing a fraction of the undelivered primary packets due to channel impairments. Moreover, the secondary destination has a relaying queue (buffer) for storing a fraction of the undelivered primary packets. In our proposed cooperative system, the secondary transmitter and the secondary destination increase the spectrum availability for the secondary packets by relaying the unsuccessfully transmitted packets of the primary transmitter. We consider two multiple-access strategies to be used by the secondary transmitter and the secondary destination to utilize the silence sessions of the primary transmitter. Numerical results demonstrate the gains of our proposed cooperative system over the noncooperation case and the systems when the secondary transmitter is the only cooperating node in the network.

Secure Transmission Design for Cognitive Radio Networks With Poisson Distributed Eavesdroppers

In this paper, we study physical layer security in an underlay cognitive radio (CR) network. We consider the problem of secure communication between a secondary transmitter–receiver pair in the presence of randomly distributed eavesdroppers under an interference constraint set by the primary user. For different channel knowledge assumptions at the transmitter, we design four transmission protocols to achieve the secure transmission in the CR network. We give a comprehensive performance analysis for each protocol in terms of transmission delay, security, reliability, and the overall secrecy throughput. Furthermore, we determine the optimal design parameter for each transmission protocol by solving the optimization problem of maximizing the secrecy throughput subject to both security and reliability constraints. Numerical results illustrate the performance comparison between different transmission protocols.

Downlink Capacity and Optimal Power Allocation in Hybrid Underlay–Interweave Secondary Networks

In this paper, the downlink capacity region of a secondary network in a multiuser spectrum sharing system is obtained for a hybrid underlay-interweave paradigm, where the current channel side information (CSI) of the channel between a secondary transmitter-receiver pair is assumed at the secondary transmitter, whereas the outdated CSI of the interference channel is available to the secondary transmitter. In the hybrid paradigm, the secondary network cycles through the interweave or the underlay paradigms depending on whether spectrum holes are detected or the primary network is active, respectively. The outdated CSI is described via a correlation model, and the interference outage probability constraint (IOPC) and the average interference power constraint are considered. In general, determining the boundary of this region is a nonconvex problem. To navigate around solving this nonconvex problem, we replace the IOPC with its equivalent constraint on the peak transmit power, and we propose a power allocation algorithm for solving the latter problem. Simulations show that utilizing the outdated CSI of the interference channel reduces the secondary network's capacity as compared with when the current CSI is utilized. This reduction is a function of the correlation between the current and outdated CSI values, the interference outage probability in the primary network, and imperfect spectrum sensing.

Distributed Channel Assignment in Cognitive Radio Networks: Stable Matching and Walrasian Equilibrium

We consider a set of secondary transmitter-receiver pairs in a cognitive radio setting. Based on channel sensing and access performances, we consider the problem of assigning channels orthogonally to secondary users through distributed coordination and cooperation algorithms. Two economic models are applied for this purpose: matching markets and competitive markets. In the matching market model, secondary users and channels build two agent sets. We implement a stable matching algorithm in which each secondary user, based on his achievable rate, proposes to the coordinator to be matched with desirable channels. The coordinator accepts or rejects the proposals based on the channel preferences which depend on interference from the secondary user. The coordination algorithm is of low complexity and can adapt to network dynamics. In the competitive market model, channels are associated with prices and secondary users are endowed with monetary budget. Each secondary user, based on his utility function and current channel prices, demands a set of channels. A Walrasian equilibrium maximizes the sum utility and equates the channel demand to their supply. We prove the existence of Walrasian equilibrium and propose a cooperative mechanism to reach it. The performance and complexity of the proposed solutions are illustrated by numerical simulations.

Distributed spectrum sharing scheme for multiuser orthogonal frequency-division multiplexing cognitive radio networks

This paper presents a novel spectrum sharing design aiming at optimising the performance of a Multiuser Orthogonal Frequency-Division Multiplexing (MU-OFDM) Cognitive Radio Network (CRN) that consists of multiple secondary Transmitter-Receiver (Tx-Rx) pairs. For most MU-OFDM systems, the Exclusive Subchannel Assignment (ESA) is an efficient resource allocation method. Nonetheless, it is inappropriate for the network considered in this paper, because subchannels sharing among secondary Tx-Rx pairs can further improve the system performance. We investigate the Weighted Sum Rate (WSR) maximization problem under the Shared Subchannel Assignment (SSA), where each subchannel is shared by multiple secondary Tx-Rx pairs. With Lagrangian duality technique, we decompose the original resource allocation problem into several sub-problems on each subchannel and propose a duality-based subchannel sharing approach. For practical realisation in the cognitive systems without central control entity, a distributed duality-based WSR maximization scheme is presented. Simulation results manifest that the proposed scheme achieves significantly better performance than ESA duality scheme.

Spectrum Sharing through Contracts for Cognitive Radios

Development of dynamic spectrum access and allocation techniques recently have made feasible the vision of cognitive radio systems. However, a fundamental question arises: Why would licensed primary users of a spectrum band allow secondary users to share the band and degrade performance for them? And how can we design incentive schemes to enable spectrum sharing using cooperative communication schemes? We consider a principal-agent framework, and propose a contracts-based approach. First, a single primary and a single secondary transmitter-receiver pair with a Gaussian interference channel between them are considered. The two users may contract to cooperate in doing successive-interference cancellation. Under full information, we give equilibrium contracts for various channel conditions. These equilibrium contracts yield Pareto-optimal rate allocations when physically possible. We then allow for time-sharing and observe that in equilibrium contracts there is no actual time-sharing. We show that the designed contracts can be made robust to deviation by either user post-contract. We also show how these can be extended to multiple secondary users. We show that under hidden information, when the primary user has a dominant role, neither user has an incentive to lie about their direct channel coefficients, or manipulate the cross channel measurements, and Pareto-optimal outcomes are achieved at equilibrium.

Hybrid Spectrum Sharing with Cooperative Secondary User Selection in Cognitive Radio Networks

In this paper, we propose a cooperative hybrid spectrum sharing protocol by jointly considering interweave (opportunistic) and underlay schemes. In the proposed protocol, secondary users can access the licensed spectrum along with the primary system. Our network scenario comprises a single primary transmitter-receiver (PTx-PRx) pair and a group of M secondary transmitter-receiver (STx-SRx) pairs within the transmission range of the primary system. Secondary transmitters are divided into two groups: active and inactive. A secondary transmitter that gets an opportunity to access the secondary spectrum is called “active”. One of the idle or inactive secondary transmitters that achieves the primary request target rate R PT will be selected as a best decode-and-forward (DF) relay (Re) to forward the primary information when the data rate of the direct link between PTx and PRx falls below R PT . We investigate the ergodic capacity and outage probability of the primary system with cooperative relaying and outage probability of the secondary system. Our theoretical and simulation results show that both the primary and secondary systems are able to achieve performance improvement in terms of outage probability. It is also shown that ergodic capacity and outage probability improve when the active secondary transmitter is located farther away from the PRx.

Dynamic Cooperative Secondary Access in Hierarchical Spectrum Sharing Networks

We address the challenge of energy efficiency in hierarchical spectrum sharing networks with dynamic traffic. We consider a primary and a cognitive secondary transmitter–receiver pair, where the secondary transmitter can utilize cooperative transmission to relay primary traffic while superimposing its own information. The secondary user meets a dilemma in this scenario. By choosing cooperation, it can transmit a packet immediately, but it has to bear the additional cost of relaying. Otherwise, it can wait for the primary user to become idle, which increases the queuing delay that secondary packets experience. To solve this dilemma and trade off delay and energy consumption, we propose dynamic cooperative secondary access control that takes the state of the spectrum sharing network into account. We formulate the problem as a Markov decision process and prove the existence of a stationary policy that is average cost optimal. We evaluate reinforcement learning to find optimal transmission strategy when the traffic and link statistics are not known. We demonstrate that dynamic cooperation is necessary for the secondary system to be able to adapt to changing network conditions and show that optimal sequential decision can significantly improve the tradeoff of the energy consumption and the delay.

Interference alignment for MIMO cognitive networks: a complex FDPM-based subspace tracking approach

Interference alignment (IA) for multiple-input multiple-output (MIMO) cognitive networks is considered by modelling the unlicensed secondary transmitter-receiver pairs which coexist with the licensed multi-antenna primary user as a K-user MIMO interference channel. Starting from investigating the constraint conditions of IA scheme in MIMO cognitive networks, a practical IA algorithm is developed by using a subspace tracking approach based on the complex fast data projection method (FDPM). In the proposed algorithm, first, each secondary transmitter aligns its transmitted signal into the null space of the channel matrix from itself to the primary user without causing any interference to the primary user. Then secondary transmitters and receivers, requiring no channel knowledge of secondary networks, alternately design the precoding and postprocessing matrices through a training period which exploits the complex FDPM-based minor subspace tracking, thus eliminating interference among secondary users. Moreover, the case where secondary transmitters have partial knowledge of channels from themselves to the primary user is also discussed. Simulation results reveal that the proposed algorithm can achieve a high sum rate performance while requiring low computational complexity.

Impact of Cognition and Cooperation on MAC Layer Performance Metrics, Part I: Maximum Stable Throughput

In this paper, we consider a broadband secondary transmitter-receiver pair which interferes with N narrowband primary users and study the effect of cognition and cooperation on the maximum stable throughput. In our study we focus on four transmission protocols as well as two channel types, i.e., flat fading and frequency selective fading. In the cooperative protocols, the broadband transmitter relays the packets of the primary users which have not correctly decoded at the primary receiver. The analysis includes random packet arrivals at the transmitters which may impact on the maximum stable throughput. Moreover, sensing errors at the secondary user are considered. In this paper, we derive the exact stability region for non-cooperative protocols and inner bounds for cooperative ones. The results reveal that depending on the channel states, the cooperative protocols may provide significant performance gains over non-cooperative protocols. Numerical results indicate that in the frequency selective channel, independent and simultaneous parallel transmissions in the available subbands are preferred, while in the flat fading channel, a non-parallel transmission in the total available bandwidth is recommended. In part II of our paper, we investigate the impact of cognition and cooperation on the delay performance of the protocols introduced in this paper.