Multiuser Diversity for Secrecy Communications Using Opportunistic Jammer Selection -- Secure DoF and Jammer Scaling Law

In this paper, we propose opportunistic jammer selection in a wireless security system for increasing the secure degrees of freedom (DoF) between a transmitter and a legitimate receiver (say, Alice and Bob). There is a jammer group consisting of $S$ jammers among which Bob selects $K$ jammers. The selected jammers transmit independent and identically distributed Gaussian signals to hinder the eavesdropper (Eve). Since the channels of Bob and Eve are independent, we can select the jammers whose jamming channels are aligned at Bob, but not at Eve. As a result, Eve cannot obtain any DoF unless it has more than $KN_j$ receive antennas, where $N_j$ is the number of jammer's transmit antenna each, and hence $KN_j$ can be regarded as defensible dimensions against Eve. For the jamming signal alignment at Bob, we propose two opportunistic jammer selection schemes and find the scaling law of the required number of jammers for target secure DoF by a geometrical interpretation of the received signals.Comment: Accepted with minor revisions, IEEE Trans. on Signal Processin

Bishop-Phelps-Bolloba's theorem on bounded closed convex sets

This paper deals with the \emph{Bishop-Phelps-Bollob\'as property} (\emph{BPBp} for short) on bounded closed convex subsets of a Banach space $X$, not just on its closed unit ball $B_X$. We firstly prove that the \emph{BPBp} holds for bounded linear functionals on arbitrary bounded closed convex subsets of a real Banach space. We show that for all finite dimensional Banach spaces $X$ and $Y$ the pair $(X,Y)$ has the \emph{BPBp} on every bounded closed convex subset $D$ of $X$, and also that for a Banach space $Y$ with property $(\beta)$ the pair $(X,Y)$ has the \emph{BPBp} on every bounded closed absolutely convex subset $D$ of an arbitrary Banach space $X$. For a bounded closed absorbing convex subset $D$ of $X$ with positive modulus convexity we get that the pair $(X,Y)$ has the \emph{BPBp} on $D$ for every Banach space $Y$. We further obtain that for an Asplund space $X$ and for a locally compact Hausdorff $L$, the pair $(X, C_0(L))$ has the \emph{BPBp} on every bounded closed absolutely convex subset $D$ of $X$. Finally we study the stability of the \emph{BPBp} on a bounded closed convex set for the $\ell_1$-sum or $\ell_{\infty}$-sum of a family of Banach spaces

Do anti-discrimination laws alleviate labor market duality? Quasi-experimental evidence from Korea

Labor market segmentation is a growing phenomenon in many countries across different continents. In 2007, the Korean government undertook a labor reform prohibiting undue discriminatory treatment against fixed-term, part-time, and dispatched workers in an attempt to address income inequality arising from labor market duality. By exploiting a gradual introduction of the anti-discrimination law by firm size, I identify the treatment effects of the anti-discrimination law on gaps in wage and non-wage benefits between regular and non-regular workers, taking a difference-indifferences approach, a quasi-experimental design. My findings suggest that the imposition of the anti-discrimination law has significantly narrowed gaps in labor conditions between regular and non-regular workers. Labor conditions of targeted nonregular workers did not improve at the expense of those of non-targeted non-regular workers. Nevertheless, non-targeted non-regular workers being treated in a less favorable way raises another concern about the possibility of overusing non-targeted non-regular workers

Does Hagwon Curfew Work? Effect of a Regulation over Operating Hours of Private Tutoring Institutions on Private Tutoring Expenditures in Korea

This investigation aims at estimating the effect of a regulation over operating hours of hagwon on private tutoring expenditures in Korea. The average treatment effect is measured with a difference-in-differences (DD) estimator using data from the survey of private education expenditure, conducted by the Statistics Korea (KOSTAT). By exploiting the fact that all education offices have placed a restriction on operating hours of hagwon in their ordinances since 2009 and some of them changed their curfew on hagwon in 2011 and 2012, the DD estimator measures the average treatment effect of the policy. The main finding of this study is that the reinforcement of the curfew on operating hours of hagwon does not generate a significant reduction in hours spent on private tutoring and that the policy is only successful in significantly decreasing middle school students’ private tutoring costs. The standard economic theory suggests that the policy increases high school students’ private tutoring costs due to their inelastic demands for private tutoring services. Furthermore, when the analysis is restricted to the group of students most likely to be affected by the policy, i.e. those who receive private tutoring intensively, the policy causes a sizable decrease in private tutoring expenses at all school levels. Given that those with intensive private tutoring tend to have higher socio-economic backgrounds, this evidence implies that the policy may be producing fruitful consequences in terms of a reduction in inequality of educational opportunities