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- 저자 : Stapleton, Ann (검색결과 22 건)
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Roy, J.Stapleton 한국전략문제연구소 2001 전략연구 Vol.8 No.3
One of the most positive aspects of the post Cold War period is that trends on the Korean peninsula during the 1990s have made it possible for the first time since World War II realistically to contemplate the emergence of a unified Korea within a foreseeable time frame. This is a remarkable development that would have been unthinkable a few years earlier. Nevertheless, realistic observers recognize that there are still formidable obstacles hindering progress toward the goal of a unified Korea. Foremost among these is the nature of the regime in the Democratic People's Republic of Korea (DPRK). Moreover, while the progress achieved in establishing a productive dialogue between the Republic of Korea and the DPRK, and in improving communications between the United States and North Korea, is highly significant, it has not yet resulted in a significant lowering of the military posture along the demilitarized zone dividing North and South Korea. As long as these circumstances remain unchanged, progress toward Korean unification will face many impediments, and the process is likely to be prolonged and difficult. There are, therefore, sound reasons to begin considering the nature of the security arrangements for the Korean peninsula that will be needed if and when Korean unification occurs. Factors that need to be addressed include whether or not there will be a need for modifications to the U.S.-ROK alliance; the size, role, and functions of U.S. forces in Korea; the likely responses of other major powers; and the agenda items that should be addressed in U.S.-ROK consultations. This paper is intended to make a modest contribution to this process. Korean unification will both be influenced by and have a profound impact on the strategic environment of Northeast Asia. The geopolitical characteristics of this region have no parallel elsewhere in the world. The Korean peninsula lies at the intersection of three great powers - China, Japan, and Russia - and for much of the last century the United States has been a major factor in the balance of power in Northeast Asia as well. In the space of barely two decades, there was a dramatic transformation of great power relationships in East Asia that made it possible to think seriously about Korean unification as an achievable goal. The United States has had a long-standing interest in lowering tensions on the Korean peninsula and preventing the emergence of security threats. Because of their common interests in this regard, the United States has maintained close ties with the ROK for a half century and would wish these to continue even under the altered circumstances that would result from Korean unification. Realistically speaking, however, the United States will face difficult adjustments in its security posture that it will wish to consider carefully. The United States will need to assess developments from the standpoint of the overall power balance in Asia. In particular, the United States will give special attention to ensuring that Korean unification does not adversely affect the ability of the United States to continue to playa stabilizing role in the region. All four can be profoundly affected by the manner in which Korean unification occurs, and each will wish to see its interests accommodated to the maximum extent possible. Clearly, the process of unification will be greatly facilitated if relations among the major affected powers are harmonious. This cannot be taken for granted. Accordingly, undue pessimism is no more justified than naive optimism in assessing whether great power relationships will facilitate or hinder progress toward unification on the Korean peninsula. Expecially, if not managed carefully, Korean unification could have a profound impact on Sino-U.S. relations. The impact of Korean unification on Sino-U.S. relations would depend on the process by which unification was achieved. Also, Korean unification would confront Japan with an entirely new situation that would force it to undertake a fundamental review of its security posture. The extent of the worries in Japan would depend on the nature of the security arrangements worked out for the Korean peninsula. In Japanese eyes, a neutral Korea would almost certainly end up in China's orbit and thus severely compromise Japan's security interests. An additional consideration needs attention, which is the nature of the great power alignments at the time of Korean unification and the possibility that Korean unification itself could be a precipitating factor causing the emergence of new alignments. This is an important consideration in assessing the security arrangements that should accompany Korean unification. The post-unification U.S. force presence in Korea cannot be viewed in isolation from other considerations. First, will be the quality of the mutual understanding and cooperation that the United States and the Republic of Korea have been able to maintain throughout the unification process. A second issue of great importance will be the degree to which the ROK and DPRK have been able to develop growing confidence in each other. There is a critical point beyond which U.S. forces cannot be reduced without compromising their integrity as a defensive force. This could be the case under circumstances where military disengagement has only partially been achieved, and where reciprocal confidence between the North and the South is still in question. Accordingly, the timing of any adjustments of U.S. forces in Korea will be vitally important. The circumstances that will affect the nature of the U.S. force presence in Korea following unification differ markedly, depending on the manner in which unification occurs. The key question that would need to be addressed would be whether a unified Korea should remain within the U.S. alliance structure. The United States would be reluctant to make sweeping changes in its security arrangements until it had assessed the implications and consequences of Korean unification. Nevertheless, changes in the U.S. security role in Korea would be only a question of time. In all probability such changes would be accompanied by adjustments in the U.S. security presence in Japan as well. The Korean unification, if properly prepared and wisely implemented, could have a significant positive impact on the security environment in East Asia and remove the Korean peninsula as a potential "hot spot" in relations among the major powers with interests in Northeast Asia. However, if pursued without regard to the factors discussed here, a unification process could easily be caught up in conflicting interests among these powers and precipitate unintended consequences. Continued close relations between the United States and the Republic of Korea, a healthy U.S.-ROK security alliance, and detailed consultations between Seoul and Washington on all relevant aspects of unification will remain vitally important to a successful outcome.
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기지국 안테나 배열을 이용한 FDD 방식의 무선통신 시스템에서 송신 빔 형성을 위한 주파수 변환 방식
오성근,Shawn P.Stapleton 대한전자공학회 1997 電子工學會論文誌, S Vol.s34 No.5
We consider transmission beamforming techniques for frequency-division-duplex (FDD) wireless communication systems using adaptive arrays to improve the signal quality of the array transmission link. We develop a simple effective transmission beamforming technique based on an approximated frequency tranlsation (AFT) to derive the tranmsiion beamforming weights from the uplink channel vector. This technique exploits the invariance of the short-time averaged fast fading statistics to small frequency translations. A simple approximate relationship that relates the transmission channel vector to the reception channel vector is derived. We have developed its practical alternative in which the frequency translation of the channel vector is performed at the principal angle of arrival (AOA) of the u;link synthestic angular spectrum instead of the mean AOA. To analyze the performance of the proposed methods, we consider the power loss incurred by applying the estimated channel vector instead of the true downlink channel vector. The performance is analyzed as a function of the mean AOA, the angular spread, the number of elements, frequncy difference between the uplink and the downlink, and the angle distribution. Their performance is also compared with that of the direct weight reuse method and the AOA based methods.
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Doherty Feed-Forward Amplifier Performance Using a Novel Crest Factor Reduction Technique
Kim, Wan-Jong,Cho, Kyoung-Joon,Stapleton, Shawn P.,Kim, Jong-Heon THE INSTITUTE OF ELECTRICAL ENGINEERS 2007 IEEE MICROWAVE AND WIRELESS COMPONENTS LETTERS Vol. No.
<P>This letter describes a novel iterative crest factor reduction (CFR) technique applied to a Doherty feedforward linear power amplifier (DFFLPA). This novel CFR technique is based on repeated peak cancellations and uses a scaling factor to reduce complexity. According to our results, only three iterations result in over 4-dB reduction for a two carrier WCDMA signal. Experimental results demonstrate that the proposed algorithm was able to enhance the DFFLPA system efficiency from 11.5% to 18.3%</P>
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Piecewise pre-equalized linearization of the wireless transmitter with a Doherty amplifier
Kim, Wan-Jong,Cho, Kyoung-Joon,Stapleton, S.P.,Kim, Jong-Heon Professional Technical Group on Microwace Theory a 2006 IEEE transactions on microwave theory and techniqu Vol.54 No.9
This paper describes a predistorter (PD) based on piecewise pre-equalizers for use in multichannel wideband applications. The predistortion linearizer consists of piecewise pre-equalizers along with a look-up-table-based digital PD that together compensate for nonlinearities, as well as memory effects of power amplifiers (PAs). It takes advantage of multiple finite-impulse-response filters that significantly reduce the complexity when compared to memory polynomial methods. The proposed method was also compared with the conventional Hammerstein structure. A 300-W peak envelope power Doherty PA was first modeled by measured time-based samples in order to verify the adjacent channel power ratio (ACPR) performance in simulation using a multitone and single wideband code-division multiple-access (W-CDMA) carrier. Furthermore, the experimental results applying two W-CDMA carriers verify that the proposed method provided similar improvement to that of the memory polynomial approach. The experimental results verified the complexity reduction and superior ACPR performance over the conventional Hammerstein structure.
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