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Short-term fading model for signals reflected by ocean surfaces in underwater acoustic communication
Joonsuk Kim,Il-Suek Koh,Yongshik Lee IET 2015 IET COMMUNICATIONS Vol.9 No.9
<P>A short-term fading model based on rough surface theory is proposed to estimate stochastic characteristics of signals reflected by time-varying ocean surfaces in underwater acoustic channels. With this method, probability density functions of the fluctuations in the propagation delay and magnitude, and the Doppler spectral densities are provided with respect to wind speeds. After conducting several experiments and verifying them by comparing with the measurements, it is shown that the model accurately estimates the stochastic characteristics. The proposed model is valid when the transmitter and receiver locate sufficiently far away from the ocean surface.</P>
( Joonsuk Bae ) 홍익대학교 법학연구소 2015 동북아법 Vol.9 No.-
As most of the countries in the world approach an aging society, security for the aged emerges as one of the most important goals for a government to pursue. There are two primary areas related to retirement income security: pension systems and inflation-indexed bonds. Pension systems fall into three categories: public, corporate, and individual pensions. Public pensions, such as Social Security in the United States, are showing their limitation in securing retirement income because it is no longer easy to maintain their solvency as the ratio of workers-to-retirees goes down. Because of this limitation of public pensions, private pensions are gaining attention as methods to secure retirement income. A characteristic of retirement savings is long-term investment. It is furthermore difficult to earn additional income after retirement. For these reasons, retirees are exposed to inflation risk more than anyone else. The only financial products that guarantee returns exceeding the inflation level are inflation-indexed bonds. They guarantee the bonds’ purchasing power by indexing principal and interest to inflation. Therefore, investing in inflation-indexed bonds is essential to secure the real income of retirees. Financial markets are another significant factor for retirement income security because they are where pension funds and individual retirement savers invest to secure retirement income. Pension systems, inflation-indexed bonds, and financial markets develop by influencing one another. Therefore, facilitating the interaction of the three factors is essential to strengthening retirement income security. The primary goal of this article is to suggest reform measures for Korean pension systems and inflation-indexed bonds. The article examines the related systems with which the United States has had an extensive experience compared with Korea. Based on this examination, several suggestions are offered regarding how these systems can be implemented efficiently and effectively in Korea.