77 research outputs found
IEEE 802.16e ์์ ๋ฉํฐ์บ์คํธ MAP ์ ํจ์จ์ ์ ์ก ๊ธฐ๋ฒ
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
๋ชจ๋ฐ์ผ ์์ด๋งฅ์ค ์์คํ ์์ ์ฃผ๋ณ ์ ์ ์ ํธ ์ธ๊ธฐ ์ ๋ณด๋ฅผ ์ด์ฉํ ์ธ์ ์ ๊ฐ์ญ ๊ฐ์ ๊ธฐ๋ฒ
The Mobile-Worldwide Interoperability for Microwave Access (m-WiMAX) can provide wireless services
at high rates even in high mobility. However, the performance of m-WiMAX can seriously be degraded near
the cell boundary due to inter-cell interference (ICI). To mitigate the ICI problem in the downlink of m-
WiMAX, we consider combined use of ICI mitigation techniques with macro beamforming to maximize the
user capacity in response to the change of interference environment. The proposed scheme optimally
determines the configuration of ICI mitigation techniques using the geometrical information (e.g., the longterm
received signal strength of neighboring cells). Simulation results show that the proposed scheme can
accurately estimate the user capacity and thus improve the capacity of users near the cell boundary.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
TDD ๊ธฐ๋ฐ์ ์ ๋ฃฐ๋ผ ์์คํ ์์ ํํฅ๋งํฌ ๋ค์ค ์นํฐ ๋นํฌ๋ฐ ๊ธฐ๋ฒ
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 frequency 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 when a small number of receive
antennas is 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) with combined use of an
MMSE receiver. The effectiveness of the proposed scheme is verified by computer simulation
First Phase Development of Korea-Japan Joint VLBI Correlator and Its Current Progress
The first phase of the Korea-Japan Joint VLBI Correlator (KJJVC) development has been completed and installed to correlate the observed data from KVN (Korean VLBI Network) and VERA (VLBI Exploration of Radio Astrometry) in October 2009. KJJVC is able to process 16 stations, a maximum of 8 Gbps/station, and 8,192 output channels for VLBI data. The system configuration, the experimental results, and future plans are introduced in this paper
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 ยฑ 1.67 in StLRs and 5.18 ยฑ 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 5.24ยฐ
ยฑ 6.16ยฐ with PrLRs and 3.46ยฐ ยฑ 3.47ยฐ with StLRs. The average changes of VHR were 0.248 ยฑ 0.178 with PrLRs and 0.148 ยฑ 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:์ํ๊ณผCONFIRM:
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 ,
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
- โฆ