A DISTRIBUTED COOPERATIVE RELAYING OPTIMIZATION SCHEME FOR SECONDARY TRANSMISSION IN COGNITIVE RADIO NETWORKS

In Cognitive Radio(CR) networks,cooperative communication has been recently regarded as a key technology for improving the spectral utilization efficiency and ensuring the Quality of Service(QoS) for Primary Users(PUs).In this paper,we propose a distributed joint relay selection and power allocation scheme for cooperative secondary transmission,taking both Instantaneous Channel State Information(I-CSI) and residual energy into consideration,where secondary source and destination may have different available spectrum.Specifically,we formulate the cognitive relay network as a restless bandit system,where the channel and energy state transition is characterized by the finite-state Markov chain.The proposed policy has indexability property that dramatically reduces the computation and implementation complexity.Analytical and simulation results demonstrate that our proposed scheme can efficiently enhance overall system reward,while guaranteeing a good tradeoff between achievable date rate and average network lifetime.

Effects of multiple transmission pathways on Zika dynamics

Although the Zika virus is transmitted to humans primarily through the bite of infected female Aedes aegypti mosquitoes,it can also be sexually and vertically transmitted within both populations.In this study,we develop a new mathematical model of the Zika virus which incorporates sexual transmission in humans and mosquitos,vertical transmission in mosquitos,and mosquito to human transmission through bites.Analysis of this deterministic model shows that the secondary transmission routes of Zika increase the basic reproductive number(R0)of the virus by 5%,shift the peak time of an outbreak to occur 10%sooner,increase the initial growth of an epidemic,and have important consequences for control strategies and estimates of R0.Furthermore,sensitivity analysis show that the basic reproductive number is most sensitive to the mosquito biting rate and transmission probability parameters and reveal that the dynamics of juvenile mosquito stages greatly impact the peak time of an outbreak.These discoveries deepen our understanding of the complex transmission routes of ZIKV and the consequences that they may hold for public health officials.

Novel pricing model for spectrum leasing in secondary spectrum market

According to the property rights model of cognitive radio,primary users who own the spectral resource have the right to lease or trade part of it to secondary users in exchange for appropriate profit.In this paper,an implementation of this framework is investigated,where a primary link can lease the owned spectrum to secondary nodes in exchange for cooperation （relaying）.A novel pricing model is proposed that enables the trading between spectrum and cooperation.Based on the demand of secondary nodes,the primary link attempts to maximize its quality of service （QoS） by setting the price of spectrum.Taking the price asked by primary link,the secondary nodes aim to obtain most profits by deciding the amount of spectrum to buy and then pay for it by cooperative transmission.The investigated model is conveniently cast in the framework of seller/buyer （Stackelberg） games.Analysis and numerical results show that our pricing model is effective and practical for spectrum leasing based on trading spectral resource for cooperation.

Microstructure and secondary phases in epitaxial LaBaCo_2O_(5.5 + δ) thin films

Aberration-corrected scanning transmission electron microscopy was employed to investigate the microstructures and secondary phases in LaBaCo2O5.5＋δ（LBCO） thin films grown on SrTiO3 （STO） substrates. The as-grown films showed an epitaxial growth on the substrates with atomically sharp interfaces and orientation relationships of [100]LBCO//[100]STO and （001）LBCO//（001）STO. Secondary phases were observed in the films, which strongly depended on the sample fabrication conditions. In the film prepared at a temperature of 900 ℃, nano-scale CoO pillars nucleated on the substrate, and grew along the [001] direction of the film. In the film grown at a temperature of 1000 ℃, isolated nano-scale C0304 particles appeared, which promoted the growth of {111 } twinning structures in the film. The orientation relationships and the interfaces between the secondary phases and the films were illustrated, and the growth mechanism of the film was discussed.