Primary Transmitter-receiver Pair Research Articles

Overlay Cognitive IoT-Based Full-Duplex Relaying NOMA Systems With Hardware Imperfections

Energy harvesting with cognitive radio and nonorthogonal multiple access (NOMA) techniques offer a promising solution to enhance the spectral and energy efficiency in Internet of Things (IoT) networks. This article investigates the performance of an overlay cognitive NOMA (OCNOMA) system tailored for IoT applications. Herein, the primary network includes a primary transmitter-receiver pair, whereas the secondary network comprises an energy-constrained full-duplex (FD) relaying-based secondary transmitter (ST) with its intended multiple receivers. Accordingly, ST employs a time-switching (TS)/power-splitting (PS)-based receiver architecture to harvest the energy from the radio-frequency signal of primary transmission and, thereby, uses this energy to relay the primary signal and to transmit its own signals simultaneously using the OCNOMA principle. For this, we propose a cooperative spectrum-sharing transmission (CSST) scheme using the decode-and-forward relaying strategy, while considering the realistic assumptions of FD-based loop self-interference, NOMA-based imperfect successive interference cancelation, and the transceiver hardware impairments in IoT devices. Adopting Nakagami- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${m}$ </tex-math></inline-formula> fading environments, we comprehensively analyze the performance by deriving the expressions of the outage probability for the primary and secondary networks for the FD-based CSST scheme under both TS and PS protocols. Thereby, we disclose some apposite ceiling effects and provide an insight on deciding the value of the OCNOMA power allocation factor for efficacious spectrum-sharing cooperation. We further quantify throughput and energy efficiency for the overall system. Our results demonstrate the performance advantages of the proposed FD CSST scheme over the benchmark schemes and provide useful guidelines for the practical design of cognitive IoT networks.

Multiple Access-Enabled Relaying with Piece-Wise and Forward NOMA: Rate Optimization under Reliability Constraints.

The increasing proliferation of Internet-of-things (IoT) networks in a given space requires exploring various communication solutions (e.g., cooperative relaying, non-orthogonal multiple access, spectrum sharing) jointly to increase the performance of coexisting IoT systems. However, the design complexity of such a system increases, especially under the constraints of performance targets. In this respect, this paper studies multiple-access enabled relaying by a lower-priority secondary system, which cooperatively relays the incoming information to the primary users and simultaneously transmits its own data. We consider that the direct link between the primary transmitter–receiver pair uses orthogonal multiple access in the first phase. In the second phase, a secondary transmitter adopts a relaying strategy to support the direct link while it uses non-orthogonal multiple access (NOMA) to serve the secondary receiver. As a relaying scheme, we propose a piece-wise and forward (PF) relay protocol, which, depending on the absolute value of the received primary signal, acts similar to decode-and-forward (DF) and amplify-and-forward (AF) schemes in high and low signal-to-noise ratio (SNR), respectively. By doing so, PF achieves the best of these two relaying protocols using the adaptive threshold according to the transmitter-relay channel condition. Under PF-NOMA, first, we find the achievable rate region for primary and secondary receivers, and then we formulate an optimization problem to derive the optimal PF-NOMA time and power fraction that maximize the secondary rate subject to reliability constraints on both the primary and the secondary links. Our simulation results and analysis show that the PF-NOMA outperforms DF-NOMA and AF-NOMA-based relaying techniques in terms of achievable rate regions and rate-guaranteed relay locations.

On the Performance of Secure Underlay Cognitive Radio Networks With Energy Harvesting and Dual-Antenna Selection

In this letter, we consider a secure underlay cognitive radio network consisting of a secondary source-destination pair and a primary transmitter-receiver pair in the presence of a primary passive eavesdropper. Herein, a secondary multi-antenna full-duplex destination node acts as a jammer to the primary eavesdropper in an effort to improve the physical layer security of the primary network. In return for this favor, the energy constrained secondary source gets access to the primary network to transmit its own information so long as the interference to the latter is below a certain level. In light of the aforementioned, we evaluate the system performance in terms of the outage probability for the secondary network, the secrecy outage probability, and the probability of non-zero secrecy capacity for the primary network. Numerical results are provided to verify the correctness of the proposed analytical framework.

Performance Analysis of Energy Harvesting-Assisted Overlay Cognitive NOMA Systems With Incremental Relaying

In this paper, we analyze the performance of an energy harvesting (EH)-assisted overlay cognitive non-orthogonal multiple access (NOMA) system. The underlying system consists of a primary transmitter-receiver pair accompanied by an energy-constrained secondary transmitter (ST) with its intended receiver. Accordingly, ST employs a time switching (TS) based receiver architecture to harvest energy from radio-frequency signals of the primary transmissions, and thereby uses this energy to relay the primary information and to transmit its own information simultaneously using the NOMA principle. For this, we propose two cooperative spectrum sharing (CSS) schemes based on incremental relaying (IR) protocol using amplify-and-forward (AF) and decode-and-forward (DF) strategies, viz., CSS-IAF and CSS-IDF, and compare their performance with the competitive fixed relaying based schemes. The proposed IR-based schemes adeptly avail the degrees-of-freedom to boost the system performance. Thereby, considering the realistic assumption of the NOMA-based imperfect successive interference cancellation, we derive the expressions of outage probability for the primary and secondary networks under both CSS-IAF and CSS-IDF schemes subject to the Nakagami-m fading. In addition, we quantify the throughput and energy efficiency for the considered system. The obtained theoretical findings are finally validated through numerous analytical and simulation results to reveal the advantages of the proposed CSS schemes over the baseline direct link transmission and orthogonal multiple access schemes.

Underlay spectrum‐sharing non‐orthogonal multiple access network with imperfect successive interference cancellation

This study investigates the performance of a cooperative non-orthogonal multiple access cognitive network with imperfect successive interference cancellation under Rayleigh fading conditions. Specifically, the authors consider an underlay cognitive network that consists of a primary transmitter–receiver pair and a secondary system where a source node communicates with two destinations nodes directly and indirectly through a relay node selected from a set of decode-and-forward relays. A partial relay selection scheme is used to determine the best relay. The authors present an analytical framework, with closed-form analytical expressions for the outage probabilities at the two destinations as well the primary destination. Moreover, to simplify the analysis and to provide further insights into the impact of key system parameters, asymptotic studies of the outage probabilities were carried out. To this end, the authors focus on two cases: (i) the maximum allowable transmit power of the secondary network grows sufficiently large and (ii) the interference power approaches infinity. Finally, Monte Carlo simulations are provided in an effort to assess the accuracy of the proposed mathematical framework.

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.

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.

On outage secrecy minimisation in an energy harvesting relay assisted cognitive radio networks

This work considers an energy harvesting (EH) based two-hop relay assisted cognitive radio system that consists of a secondary transmitter, a relay node and a cooperative jammer operated in an underlay mode with a primary transmitter–receiver pair. An optimisation problem is formulated to minimise the secrecy outage probability under the constraints of simultaneously meeting the energy causality of the secondary transmit nodes, interference to the primary receiver and secondary outage probability. An analytical expression of the secrecy outage probability is developed followed by deriving the closed-form expressions to determine the optimal transmit power of the source, the relay node and the fraction of the time slot for EH. Simulation results show that the minimum value of the secrecy outage probability is and less over the existing works.

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.

Secrecy Capacity in CRN With Malicious Energy Harvester Using Game Theoretic Techniques

In this paper, an underlay-based cognitive radio network (CRN) consisting of a secondary transmitter (ST), a secondary receiver (SR), an energy harvesting node (EHN), and a primary transmitter-receiver pair, is considered. The EHN is an energy constrained node and is thereby, assumed to have a power splitter at its receiver to decode information and harvest energy simultaneously from the received RF signal. The EHN behaves maliciously and decodes ST’s messages when it is granted with a permission to (only) harvest energy from the received RF signal, thereby reducing the secrecy capacity of the ST-SR link. Since both ST and EHN are selfish with conflicting interests, we model the interaction between them as a Stackelberg game (SG). Further, we analyze the behavior of the nodes in a non-cooperative game (NCG) theoretic framework and prove the existence of a unique Nash equilibrium (NE) strategy. Simulation results show that the SG framework performs better than the NCG framework, in terms of the achievable secrecy capacity of the ST-SR link. Thereby the proposed SG model is applied to the considered CRN with multiple STs and a unique equilibrium is found. In case the STs possess limited channel state information (CSI), we model the competition among the STs as a Bayesian game and found its equilibrium solution, known as Bayesian NE (BNE). Simulation results demonstrate that BNE performs better than the NE when the STs possess limited CSI.

Achievable DoF of an Underlay Two-User Gaussian Interference Channel in Heterogeneous Networks

This paper studies a new symmetric two-user Gaussian interferencechannel (IC) in heterogeneous networks where twotransmitter-receiver pairs are underlaid with one primarytransmitter-receiver pair. When underlay transmitters must restricttheir transmission to guarantee target degrees of freedom (DoF) of aprimary receiver, the achievable DoF of the underlay receivers inheterogeneous networks is investigated. Either transmit power ortransmission time is regulated to secure the target DoF of a primaryreceiver and their effects on the achievable DoF are analyzed for thesimple Han-Kobayashi scheme. Our analytical results show that theachievable DoF of the underlay two-user IC is substantiallydifferent from that of a conventional two-user IC due to the imposedrestriction on the underlay users. It is also shown that jointdecoding capability at the primary receiver using common codebookrelaxes the restriction imposed on the underlay users and henceimproves the achievable DoF of the underlay receivers.