On hybrid cooperation in underlay cognitive radio networks

In this paper, we propose frequency allocation and path selection scheme in underlay cognitive radio (CR) networks using network coding. In the proposed scheme, we choose the path with consideration of network coding and interference temperature in underlay CR networks and propose an optimization problem to maximize the system throughput of secondary users (SUs). Then, we represent the proposed optimization problem as the multi-dimensional multiple-choice knapsack problem and give the theoretical upper bound for the system throughput of SUs by using linear programming. Finally, we compute the system throughput of SUs by using brute-force search (BFS) and link quality first (LQF) scheme in underlay CR networks. Simulation results show that the system throughput of SUs with BFS is higher than that with LQF in underlay CR networks with and without application of network coding, respectively.

Cooperative communication is a promising strategy to enhance the performance of a communication network as it helps to improve the coverage area and the outage performance. However, such enhancement comes at the expense of increased resource utilization, which is undesirable; more so in the case of opportunistic wireless systems such as cognitive radio networks. In order to balance the performance gains from cooperative communication against the possible over-utilization of resources, we propose and analyze an adaptive-cooperation technique for underlay cognitive radio networks, termed as hybrid-cooperation. Under the proposed cooperation scheme, secondary users in a cognitive radio network cooperate adaptively to enhance the spectral efficiency and the error performance of the network. The bit error rate, the spectral efficiency and the outage performance of the network under the proposed hybrid cooperation scheme with amplify-and-forward relaying are analyzed in this paper, and compared against conventional cooperation technique. Findings of the analytical performance analyses are further validated numerically through selected computer-based Monte-Carlo simulations. The proposed scheme is found to achieve significantly better performance in terms of the spectral efficiency and the bit error rate, compared to the conventional amplify-and-forward cooperation scheme.

This paper investigates the physical layer security of non-orthogonal multiple access (NOMA) with decode-and-forward (DF) relays in underlay cognitive radio (CR) network. Secondary transmitter communicates with legitimate users via the aid of relays, while the eavesdroppers try to intercept the message. To safeguard legitimate communications against eavesdropping, the joint of artificial-noise (AN) and relay selection (RS) is applied. We derive the secrecy outage probability (SOP) and the secrecy throughput to evaluate the secrecy performance. In addition, the asymptotic floor of SOP is derived. Numerical results verify that cooperative NOMA in underlay CR (CRNOMA) significantly outperforms the conventional orthogonal multiple access (OMA) in underlay CR network (CROMA) in terms of the secrecy outage performance. Furthermore, the effect of some critical parameters on the secrecy performance has been studied.

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.

This paper discusses transmission performance and power allocation strategies in an underlay cognitive radio (CR) network that contains relay and massive multi-input multi-output (MIMO). The downlink transmission performance of a relay-aided massive MIMO network without CR is derived. By using the power distribution criteria, the kth user's asymptotic signal to interference and noise ratio (SINR) is independent of fast fading. When the ratio between the base station (BS) antennas and the relay antennas becomes large enough, the transmission performance of the whole system is independent of BS-to-relay channel parameters and relates only to the relay-to-users stage. Then cognitive transmission performances of primary users (PUs) and secondary users (SUs) in an underlay CR network with massive MIMO are derived under perfect and imperfect channel state information (CSI), including the end-to-end SINR and achievable sum rate. When the numbers of primary base station (PBS) antennas, secondary base station (SBS) antennas, and relay antennas become infinite, the asymptotic SINR of the kth PU and SU is independent of fast fading. The interference between the primary network and secondary network can be canceled asymptotically. Transmission performance does not include the interference temperature. The secondary network can use its peak power to transmit signals without causing any interference to the primary network. Interestingly, when the antenna ratio becomes large enough, the asymptotic sum rate equals half of the rate of a single-hop single-antenna K-user system without fast fading. Next, the PUs' utility function is defined. The optimal relay power is derived to maximize the utility function. The numerical results verify our analysis. The relationships between the transmission rate and the antenna number, relay power, and antenna ratio are simulated. We show that the massive MIMO with linear pre-coding can mitigate asymptotically the interference in a multi-user underlay CR network. The primary and secondary networks can operate independently.

In this paper, the impact of co-channel interference (CCI) on the performance of an underlay cognitive radio (CR) network over Nakagami-m fading channels is presented and analyzed. More precisely, a decode-and-forward (DF) relay protocol for a dual-hop cognitive cooperative network is considered. In this study, the impact of both the primary transmitter and CCI on the secondary system performance are considered. First, an exact expression for the equivalent signal-to-interference-plus-noise ratio (SINR) of the secondary system is obtained. Then, the corresponding exact and asymptotic cumulative distribution function (CDF) are derived. From this, the exact outage performance for the secondary network is investigated. From the results, it can be inferred that the presence of the CCI and primary network interference severely degrades the system performance. Moreover, a higher value of the shape parameter of the desired channel gives better performance and diversity gain. Finally, the analytically derived results have been supported by providing numerical and Monte Carlo simulations results.

In this letter, we investigate the multi-user diversity (MUD) in an underlay cognitive radio (CR) network where multiple secondary transmitters and primary receivers exist. Many studies on MUD in the underlay CR network have assumed that the secondary transmitters adaptively control their transmit power in order to achieve the {optimal} MUD gain, maintaining the interference at the primary receivers below a pre-determined level. We, however, prove the optimal MUD gain can be also achieved by the fixed power transmission strategy. In contrast to the adaptive power transmission strategy, the fixed power operation in the secondary transmitters relaxes the coordination constraint between the primary and secondary networks, and significantly reduces the signaling and feedback overhead from the secondary transmitters to the secondary receiver.

In this paper, non-orthogonal multiple access (NOMA) is applied to\nlarge-scale underlay cognitive radio (CR) networks with randomly deployed\nusers. In order to characterize the performance of the considered network, new\nclosed-form expressions of the outage probability are derived using\nstochastic-geometry. More importantly, by carrying out the diversity analysis,\nnew insights are obtained under the two scenarios with different power\nconstraints: 1) fixed transmit power of the primary transmitters (PTs), and 2)\ntransmit power of the PTs being proportional to that of the secondary base\nstation. For the first scenario, a diversity order of $m$ is experienced at the\n$m$-th ordered NOMA user. For the second scenario, there is an asymptotic error\nfloor for the outage probability. Simulation results are provided to verify the\naccuracy of the derived results. A pivotal conclusion is reached that by\ncarefully designing target data rates and power allocation coefficients of\nusers, NOMA can outperform conventional orthogonal multiple access in underlay\nCR networks.\n

SummaryCognitive radio network is an emerging solution to deal with spectrum scarcity and to utilize the radio spectrum in opportunistic and efficient manner. Secure data transmission is one of the important issues in these kind of networks. This work studies the secrecy outage performance of a multiple‐input multiple‐output underlay cognitive wiretap radio network system over Rayleigh fading channel with delayed channel state information. This work considers that the secondary transmitter is equipped with multiple antennas and confidential information is transmitted from to multiantenna receiver in the presence of multiantenna eavesdropper. Further, the transmit antenna selection scheme is considered at secondary transmitter to reduce the complexity of antenna selection and to make it more practicable. To improve the quality of signal, this work considers maximal ratio combining (MRC) at secondary receiver, while selection combining and MRC techniques are utilized at the eavesdropper. The closed form expression for exact, asymptotic, and intercept secrecy outage probability has been derived, and the simulation is done for the validation of analytical results. The derived results reveal deterioration of channel secrecy performance with outdated channel state information, and the eavesdropper with outdated channel state information has also an adverse effect. Moreover, the diversity order that can be achieved in underlay cognitive radio network with outdated channel state information is unity.

This work studies the impact of a multi-relay scheme and co-channel interference (CCI) on the performance of a dual-hop underlay cognitive radio (CR) network. An amplify-and-forward (AF) relay protocol is considered at the relay nodes. Besides the effect of CCI on the secondary network, the interference from the primary transmit node is also considered. Based on opportunistic selection, the best relay is selected to establish the transmission between source and destination node. First, the equivalent per hop signal-to-interference-plus-noise ratio (SINR) is obtained. Then, an exact per hop cumulative distribution function (CDF) for the equivalent SINR is derived. From this, the outage probability performance is investigated. The results show that considering a multi-relay scheme is an efficient way to combat the impact of the interference power constraint and CCI. In addition, they show that CCI could severely degrade the system performance, especially when its power linearly increases with the secondary transmit powers. To validate the theoretical results, Monte Carlo simulations are also provided.

In this paper, the performance of asecondary user (SU) in an underlay cognitive radio (CR) network over ageneralized-gamma (GG) fading channel in terms of three performance metrics,namely, outage probability, ergodic capacity, and bit error rate (BER), isinvestigated. According to the underlay approach, the transmit power of the SUshould be limited to avoid interference to primary users (PUs). The performancemetrics of the SU in the underlay CR network are theoretically derived and alsoobtained with Monte Carlo simulations for a GG fading channel with different fadingparameters. To demonstrate the effect of limited power on the performancemetrics, three different maximum transmit power levels (Pmax), namely, 10, 20,and 30 dB, are used. The simulation results lead to three conclusions: First,when high values are chosen for the fading parameters (α, c), the fadingchannel gets less distorted and the performance metrics improve. The secondconclusion is that the BER performance gets better as the limited powerincreases. The final conclusion is that the BER performance of SUs improves asthe interference power that PUs can tolerate increases. Cite this article as: Aldırmaz Çolak S.Performance Analysis of a Secondary User in Cognitive Radio overGeneralized-Gamma Fading Channels. Electrica, 2019; 19(2): 166-172.

Wireless communication has nowadays become one of the major worldwide causes of energy consumption in the field of ICT, with a devastating impact in terms of pollution and energy waste. As a result, the past decade has witnessed tremendous efforts and progress made by both the industry and academia for improving energy and power efficiency in current and emerging wireless communication networks, among which cognitive and cooperative communication are proposed as key technologies to increase both spectrum and energy efficiency. With cognitive and cooperative communication, the use of larger spectrum band and the opportunistic adaptation of the spectrum use lead to more effective interference management, better spatial and temporal reuse, thus reducing the power consumption. Despite the ever growing interests, the research on green cognitive and cooperative communication and networking is still in its infancy. Some fundamental problems are still open and require immediate studies. This special issue is intended to provide a forum for presenting, exchanging and discussing the recent advances on green cognitive and cooperative communication and networking. In response to the call for paper, we have received 26 paper submissions from both academia and industries that covered a variety of topics. Two rounds of careful review by the guest editors and experts in the field led to 5 papers for inclusion in this issue. In the first article, “Green Cooperative Cognitive Communication and Networking: A New Paradigm for Wireless Networks”, the authors (Lin Chen, Wei Wang, Alagan S. Anpalagan, Athanasios V. Vasilakos, Kandasamy Illanko, Honggang Wang, Muhammad Naeem) provide a comprehensive survey of the green cognitive and cooperative communication and networking techniques from its characteristics point of view to operational details in the eventual deployment. They present a systematic overview on the tools and techniques that can be used to solve problems arising in energy efficiency optimization problem in this context. The need to incorporate green concepts such as multi-input and multi-output, multirate, and multi-carrier systems, short-range low-power communication using small cell networks, and machine to machine communication in emerging and advanced wireless communication technologies is also addressed. Finally, the paper highlights design challenges and open issues in embracing green technologies in different and cross layers of communication and networking. In the second paper titled “Towards Energy-Efficiency in Selfish, Cooperative Networks”, the authors (Chi Harold Liu, Jun Fan, Zhengguo Sheng, Xiumei Fan, Kin K. Leung) propose an adaptive multi-relay selection with power allocation mechanism to offer energy fairness at each node for a cooperative network. Unlike traditional approaches where all nodes are considered to transmit in a collaborative manner, they explicitly consider the situation where nodes exhibit some degree of selfish behavior. Specifically, they introduce a novel concept of the selfishness index and incorporate it into a utility function which denotes the degree a node can benefit from cooperative transmission. Theoretical analysis and simulation results are supplemented to show advantages inmaximizing the network lifetime and guaranteeing the QoS in realistic wireless environments. They also consider the practical situation when nodes consume energy in mode switching, and study the L. Chen (*) Department of Computer Science, University of Paris-Sud, Orsay, France e-mail: Lin.Chen@lri.fr

Cognitive Radios have been proposed as a novel technology to improve the spectrum utilization in wireless transmissions. In self-organized network such ad-hoc cognitive radio networks (AHCRNs), the resource allocation (e.g., power, and channel) rise up several challenges due to rapid utilization of the available spectrum. In this paper, we consider noncooperative game theory to solve the power allocation problem in an underlay ad-hoc cognitive radio networks (AHCRNs) via interference compensations in order to provide good quality of service to CR nodes, on one hand, and to protect the transmission of PUs, on the other hand. Moreover, numerical simulations are presented to shows the existence and uniqueness of the NE for power control algorithm.

In this paper, we investigate the optimal power allocation strategy in the joint spectrum overlay and underlay cognitive radio network where a licensee and multiple unlicensed users coexist and operate in the same spectrum. We propose an optimal power allocation scheme which achieves the maximum system utility while satisfying the QoS requirement of SUs and interference constrains of the PU. Particularly, since the unlicensed users adopting the overlay strategy do not necessarily have perfect sensing knowledge regarding the licensee, we modify the optimal power allocation scheme with the imperfect sensing knowledge. Moreover, we propose a QoS sensitivity based admission control algorithm to deal with the case that the optimal power allocation scheme is infeasible. The simulation results show that the proposed algorithm achieves better performance.

In this paper, we study the resource allocation problem, including the joint consideration of user grouping and power allocation, of an, underlay cognitive radio (CR) network employing non-orthogonal multiple access (NOMA), which is referred to as the NOMA-CR network. Based on the non-transferable utility coalition formation game theory, the so-called distributed sequential coalition formation (DSCF) algorithm is leveraged to solve the user grouping problem, where multiple cognitive users within a group can access the primary user's spectrum band while satisfying a minimum rate requirement of the primary user. The simulation results show that a near-optimal performance can be achieved by implementing the proposed DSCF as well as the optimal power allocation algorithms. Furthermore, the results validate that NOMA-CR can significantly outperform the traditional orthogonal multiple access CR, in terms of throughput. Finally, it is shown that by applying a novel adaptive trellis turbo coded modulation technique to the underlay NOMA-CR network, a significant throughput gain can be achieved.