IEEE 802.16e 에서 멀티캐스트 MAP 의 효율적 전송 기법

The IEEE 802.16e suggests the use of multicast sub-MAPs whose messages are differently encoded according to the operating condition. In this case, it is desired for the base station to properly choose a modulation and coding set (MCS) associated with operating condition. In this paper, we consider the use of an adaptive modulation coding (AMC) scheme for the multicast sub-MAP that achieves the same MAP coverage as the broadcast MAP while minimizing the signaling overhead. We consider the adjustment of the threshold for the AMC according to the channel condition without explicit information on the channel condition, significantly reducing the amount of the signaling overhead. Simulation results show that when it is applied to voice-over-IP (VoIP) services, the proposed scheme can enhance the VoIP capacity

Mitigation of inter-cell interference in the WiMAX system

The Worldwide Interoperability for Microwave Access (WiMAX) can provide wireless services at high rates even in high mobility, but it can suffer from serious inter-cell interference (ICI) near the cell boundary. To mitigate the ICI problem in the downlink of mobile-WiMAX, we consider combined use of interference avoidance and cancellation techniques in addition to inter-sector coordination, maximizing the user capacity in a seamless manner. To make the proposed scheme realizable, we maximize the geometry capacity. Simulation results show that the proposed scheme can improve the capacity of users near the cell boundary over the conventional schemes and provide flexibility in resource allocation.KT research projec

Inter-sector Beamforming with MMSE Receiver in the Downlink of TDD Cellular Systems

The use of beamforming is effective for users in limited power environments. However, when it is applied to the downlink of a cellular system with universal requency reuse, users near the sector boundary may experience significant interference from more than one sector. The use of a minimum mean square error (MMSE)-type receiver may not sufficiently cancel out the interference unless a sufficient number of receive antennas are used. In this paper, we consider the use of inter-sector beamforming that cooperates with a neighboring sector in the same cell to mitigate this interference problem in time-division duplex (TDD) environments. The proposed scheme can avoid interference from an adjacent sector in the same cell, while enhancing the transmit array gain by using the TDD reciprocity. The performance of the proposed scheme is analyzed in terms of the output signal-to-interference-plus-noise power ratio (SINR) and the output capacity when applied to an MMSE-type receiver. The beamforming mode can be analytically switched between the inter-sector and the single-sector mode based on the long-term channel information. Finally, the effectiveness of the proposed scheme is verified by computer simulation.IT R&D program of MKE/IITA (2008- F-007-0

Usefulness of prone cross-table lateral radiographs in vertebral compression fractures

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.Background: Dynamic radiographs are recommended to investigate non-healing evidence such as the dynamic mobility or intravertebral clefts in osteoporotic vertebral compression fractures (VCFs). However, it is difficult to examine standing flexion and extension lateral radiographs due to severe pain. The use of prone cross-table lateral radiographs (PrLRs) as a diagnostic tool has never been proposed to our knowledge. The purpose of this study is to clarify the usefulness of PrLRs in diagnosis and treatment of VCFs. Methods: We reviewed 62 VCF patients examined with PrLRs between January 1, 2008 and June 30, 2011. To compare the degree of pain provoked between standing extension lateral radiographs (StLRs) and PrLRs, numeric rating scale (NRS) scores were assessed and compared by a paired t-test. Vertebroplasty was done for 40 patients and kyphoplasty was done for 9 patients with routine manners. To assess the degree of postural reduction, vertebral wedge angles (VWA) and vertebral height ratios (VHR) were calculated by using preoperative StLRs, PrLRs, and postoperative lateral radiographs. Two variables derived from changes in VWA and VHR between preoperative and postoperative radiographs were compared by a paired t-test. Results: The average NRS scores were 6.23 ± 1.67 in StLRs and 5.18 ± 1.47 in PrLRs. The degree of pain provocation was lower in using PrLRs than StLRs (p < 0.001). The average changes of VWA between preoperative and postoperative status were 5.24° ± 6.16° with PrLRs and 3.46° ± 3.47° with StLRs. The average changes of VHR were 0.248 ± 0.178 with PrLRs and 0.148 ± 0.161 with StLRs. The comparisons by two variables showed significant differences for both parameters (p = 0.021 and p < 0.001, respectively). The postoperative radiological status was reflected more precisely when using PrLRs than StLRs. Conclusions: In comparison with StLR, the PrLR was more accurate in predicting the degree of restoration of postoperative vertebral heights and wedge angles, and provoked less pain during examination. The PrLR could be a useful diagnostic tool to detect intravertebral cleft or intravertebral dynamic instability.OAIID:oai:osos.snu.ac.kr:snu2013-01/102/0000004226/12ADJUST_YN:YEMP_ID:A079510DEPT_CD:801FILENAME:clin orthop surg-2013_cho_usefulness of prone cross-table lateral radiographs in vertebral compression fractures.pdfDEPT_NM:의학과CONFIRM:

A New Hardware Correlator in Korea: Performance Evaluation using KVN observations

We report results of the performance evaluation of a new hardware correlator in Korea, the Daejeon correlator, developed by the Korea Astronomy and Space Science Institute (KASI) and the National Astronomical Observatory of Japan (NAOJ). We conducted Very Long Baseline Interferometry (VLBI) observations at 22~GHz with the Korean VLBI Network (KVN) in Korea and the VLBI Exploration of Radio Astrometry (VERA) in Japan, and correlated the aquired data with the Daejeon correlator. For evaluating the performance of the new hardware correlator, we compared the correlation outputs from the Daejeon correlator for KVN observations with those from a software correlator, the Distributed FX (DiFX). We investigated the correlated flux densities and brightness distributions of extragalactic compact radio sources. The comparison of the two correlator outputs show that they are consistent with each other within $<8\%$, which is comparable with the amplitude calibration uncertainties of KVN observations at 22~GHz. We also found that the 8\% difference in flux density is caused mainly by (a) the difference in the way of fringe phase tracking between the DiFX software correlator and the Daejeon hardware correlator, and (b) an unusual pattern (a double-layer pattern) of the amplitude correlation output from the Daejeon correlator. The visibility amplitude loss by the double-layer pattern is as small as 3\%. We conclude that the new hardware correlator produces reasonable correlation outputs for continuum observations, which are consistent with the outputs from the DiFX software correlator.Comment: 13 pagee, 9 figures, 3 tables, to appear in JKAS (received February 9, 2015; accepted March 16, 2015