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An ATM-Based Multicast Intersatellite Routing for LEO Satellite Networks
Umehara, Daisuke,Ebiko, Keisuke,Kobayashi, Toshihito,Kawai, Makoto,Morihiro, Yoshiteru 통신위성우주산업연구회 2000 Joint Conference on Satellite Communications Vol.2000 No.-
Low Earth Orbit (LEO) satellite communication systems with InterSatellite Links (ISLs) are promising as a world-wide multimedia core network infrastructure. As satellites come to higher latitudes in polar orbit constellation, the degradation of ISL transmission quality becomes large because of ISL interference and relative angular velocity between satellites in adjacent orbits. This paper deals with the transmission quality of ISLs based on the general transmission model. We propose an ATM-based multicast routing approach with link weight which overcomes the degradation of transmission quality and show that this approach enhances transmission quality significantly by computer simulation.
Umehara Takuya,Inukai Ayaka,Kuwahara Daisuke,Kaneyashiki Ryo,Kaneguchi Akinori,Tsunematsu Miwako,Kakehashi Masayuki 대한척추외과학회 2022 Asian Spine Journal Vol.16 No.3
Study Design: A prospective cohort study.Purpose: This study aimed to reveal physical functions and comorbidity affecting collapse at ≥4 weeks after hospital admission of patients with osteoporotic vertebral fracture.Overview of Literature: Only a few studies have investigated the influence of physical function and activity on collapse in patients with osteoporotic vertebral fractures.Methods: This prospective cohort study analyzed patients with osteoporotic vertebral fractures admitted to the hospital between March 2018 and October 2019. Logistic regression analysis was performed to explore the predictors of vertebral collapse at >4 weeks after admission. Model 1 used basic medical information and physical functions at admission; model 2 used basic medical information and physical function and activity at >4 weeks after admission.Results: In the model 1 results of logistic regression analysis, cardiovascular disease (odds ratio [OR], 12.27; 95% confidence interval [CI], 1.28–117.91) was extracted as a factor affecting vertebral collapse at ≥4 weeks after admission. In the model 2 results of logistic regression analysis, cardiovascular disease (OR, 34.57; 95% CI, 2.53–471.74), movement control during one leg standing at 4 weeks (OR, 7.25; 95% CI, 1.36–38.71), and Pain Catastrophizing Scale score at 4 weeks (OR, 1.11; 95% CI, 1.01–1.21) were extracted as factors affecting vertebral collapse at ≥4 weeks after admission.Conclusions: Our results indicate that physical functions and comorbidity affect collapse at ≥4 weeks after admission in patients with osteoporotic vertebral fractures.
Quasi-Synchronous CDMA Performances Using Orthogonal Cyclic Shift M-Sequences
Sugano, Kiminobu,Umehara, Daisuke,Morihiro, Yoshiteru,Kawai, Makoto 통신위성우주산업연구회 2003 Joint Conference on Satellite Communications Vol.2003 No.-
CDMA (Code Division Multiple Access) is one of the attractive multiple access schemes for satellite data communications. In terms of chip synchronization, CDMA can be classified into asynchronous, synchronous, and quasi-synchronous (QS) CDMA. In this paper, we propose the QS-CDMA using the orthogonal cyclic shift M-sequences for satellite data communications. We investigate the number of sequences which have zero cross-correlation property each other within the prescribed chip timing errors by computer simulation and show the results. Furthermore, we show the throughput performances of the QS-CDMA with the orthogonal cyclic shift M-sequences and then compare it with that of the synchronous CDMA.
A Synchronization Method for Synchronous CDMA Systems with GEO Satellites
Sakamoto, Takuya,Umehara, Daisuke,Kawai, Makoto 통신위성우주산업연구회 2001 Joint Conference on Satellite Communications Vol.2001 No.-
High-speed core networks with optical fibers are globally being installed. However, it is very difficult to access these core networks from rural districts such as remote places among mountains and solitary islands. Synchronous CDMA systems with GEO satellite links are very attractive to solve this problem, since such systems have wide service areas and are suitable for packet-based networks due to their statistically multiplexing effect. Furthermore, their statistically multiplexing effect leads to effective frequency and power efficiency. In synchronous CDMA systems, each transmitted signal from a fixed earth station must be controlled to be synchronized with each other. However, the broadband systems require extremely precise timing control. In this paper, we discuss synchronization methods and evaluate their timing accuracy for the broadband systems quantitatively. First, we point out defects of two fixed filter methods and a Kalman filter method. Then, we propose a new synchronization method, which is robust to random noise and trend components. As a result, we conclude that the proposed synchronization method can make it possible to synchronize lGchip/sec CDMA systems with GEO satellites.
Performance Analysis of a Two-hop Wireless Relay Network with CSMA / CA and Network Coding
Chun-Hsiang Huang,Daisuke Umehara,Satoshi Denno,Masahiro Morikura,Takatoshi Sugiyama 대한전자공학회 2009 ITC-CSCC :International Technical Conference on Ci Vol.2009 No.7
In this paper, we provide an analytical model to compute the approximate throughput of a two-hop wireless relay network in which stations employ carrier sense multiple access with collision avoidance (CSMA/CA) protocol and network coding on the MAC layer. In addition, this model can be applied to the conventional CSMA/CA wireless relay network without network coding. Network coding is a highly regarded technology that is able to enhance the system capacity of multiple unicast and multisource multicast networks. Based on the assumption of no hidden terminals, we show that the proposed analytical model works well with the parameters of IEEE 802.11a and the difference in throughput between theoretical analysis and computer simulation is at most 2 percent.
Nakamura, Junichi,Makishima, Akihito,Umehara, Daisuke,Kawai, Makoto 통신위성우주산업연구회 2002 Joint Conference on Satellite Communications Vol.2002 No.-
TCP is generally used for data transmission on a geo-synchronous satellite link. It is known that the throughput increase corresponding to the increase of transmission speed can not be expected on a geo-synchronous satellite link since TCP was originally designed as a protocol for terrestrial cable networks. We established a computer simulation system and an experimental system using a Ka-band satellite to investigate the TCP performance on a high speed satellite communication link. This paper describes the throughput performances obtained by both systems using Window Scaling Option which is expected to improve the conventional TCP performances and shows the relationship between bit error rate and throughput.