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Proceedings of the Global Communications Conference, 2007. GLOBECOM '07, Washington, DC, USA, 26-30 November 2007; 01/2007
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IEICE Transactions. 01/2007; 90-B:700-703.
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ABSTRACT: Scheduling is a widely used technique in recent wireless communication systems to utilize radio resource efficiently and adaptively according to varying radio channel conditions. In this paper, scheduling-based systems in Rayleigh fading channels are analyzed mathematically. First, a scheduling-based system and signal models are described. Then, the signal-to-noise ratio (SNR) distribution is formulated and the joint distribution of SNR, distance, and selected user is also derived. Using the derived joint distribution, we evaluate the selection probability and the distribution of selected users' SNR values. Finally, system capacity is evaluated from the derived formulation. The analysis results and evaluated performance show that a multiuser diversity gain increases the system capacity and the scheduling-based systems take advantage of radio fading channel variation efficiently
Personal, Indoor and Mobile Radio Communications, 2006 IEEE 17th International Symposium on; 10/2006
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ABSTRACT: The aim of this study was to determine the outcome of the neoaortic valve after the arterial switch operation for transposition of the great arteries.
A retrospective review of arterial switch operations that were performed during the period from 1991 to 2003 was conducted. We followed patients with echocardiography. When regurgitation of the neoaortic valve was observed we analyzed the risk factors.
One hundred and three patients underwent a successful arterial switch operation. Eighty-one males and 22 females participated in the study. Follow-up period was 77+/-42 months. The age and body weight at the time of the arterial switch operation were 1.4+/-2.8 months and 3.8+/-1.0 kg, respectively. Preoperative pulmonary valve regurgitation was found in six patients (two patients had grade I and four patients had grade II). In the postoperative echocardiography, 52 patients demonstrated neoaortic valve regurgitation (26 patients had grade I, 25 patients had grade II, and 1 patient had grade III). At the last follow-up visit, 61 patients demonstrated neoaortic regurgitation (18 patients had grade I, 37 patients had grade II, 5 patients had grade III, and 1 patient had grade IV). Neoaortic valve regurgitation increased progressively with follow-up (p-value<0.01). The size discrepancy between the aorta and the pulmonary artery was correlated with neoaortic valve regurgitation (p-value=0.02). The age and body surface area, relationship of the great arteries, coronary arterial pattern, pulmonary artery banding, use of trap-door technique, myocardial ischemic time, use of total circulatory arrest, and existence of ventricular septal defect were not significant risk factors.
Neoaortic valve regurgitation progressed after the arterial switch operation. The degree of regurgitation was more severe in patients with a size discrepancy between the aorta and the pulmonary artery preoperatively.
European Journal of Cardio-Thoracic Surgery 02/2006; 29(2):162-7. · 2.55 Impact Factor
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ABSTRACT: There has been an increasing demand for wireless data services due to the popularity of Internet services and circuit-switched (CS) systems are not appropriate for accommodating bursty data traffic. The wireless data services can be efficiently supported in the packet-switched (PS) system and General Packet Radio Service (GPRS) is a representative PS system which is being serviced widely. In GPRS, three mobile station (MS) mobility management states, i.e., idle, ready, and standby are defined in order to accommodate bursty traffic characteristics of data services, and thus, GPRS results in efficient management of radio resources and signaling networks. In order to analyze the performance of GPRS mobility management, we develop an analytical model to derive the steady-state probability of the MS states, which is essential in the performance analysis. The analytical model is validated by using a simulation model. The effect of various input parameters on the steady-state probability and the effect of variances of cell residence time, RA residence time, and packet transmission time are analyzed. Then, location update signaling and paging signaling loads are investigated based on the steady-state probability. Our study provides guideline for proper selection of PS system parameters and can be used to analyze the performance of mobility management schemes for PS systems.
Computer Communications. 01/2006;
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ABSTRACT: Mobile hosts (MHs) in all IP-based mobile networks must update their current location to receive incoming packets. The MHs are idle for most of time. Both registration of approximate location information and paging can facilitate efficient power management for the idle MHs. Furthermore, the MHs can be in switch-off state for battery power conservation. Mobile IP, the current standard for IP-based mobility management, needs to be enhanced for use in all IP-based mobile networks. Mobility management in all IP-based mobile networks should consider idle and detached MH states as well as active MH state. A mobility management scheme for all IP-based mobile networks is introduced in this paper. This scheme includes management of communicating, attentive, idle, and detached states. We model MH behavior in the networks when the binding-lifetime-based registrations are utilized as a means of identifying that an MH is switched off. The steady-state probabilities for MH state transitions are derived, and an optimal rate of binding-lifetime-based registrations that results in minimum network cost is derived.
IEEE Transactions on Vehicular Technology 12/2004; · 1.92 Impact Factor
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ABSTRACT: We reviewed our long-term results of complete repair of tetralogy of Fallot (TOF) in infant. One hundred and sixty infants diagnosed as TOF underwent complete repair between January 1990 and April 2002. Mean age at the operation was 8.1+/-2.6 months. Correction was accomplished through a short right ventriculotomy of less than 30% of the ventricular height in all patients. A transannular patch was used in 78 patients (49%). There were four early deaths and no late death. Follow-up was complete in all survivors. All patients are currently in New York Heart Association functional class I or II. Actuarial freedom from reoperation at 1 and 10 years were 94.0 and 87.5%, respectively. Echocardiographic studies at follow-up showed excellent right ventricular function in most patients. Our results suggest that early complete repair of TOF yielded acceptable results with low mortality and morbidity. Transventricular repair of intracardiac pathology can be safely applied to yield good postoperative right ventricular function.
Interactive cardiovascular and thoracic surgery 10/2004; 3(3):470-4.
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ABSTRACT: Mobile communication networks can provide various types of services, such as voice, data, video, and multimedia as they evolve toward 3G networks. To increase the efficiency of limited resources in the UTRAN Iub interface, AAL2/ATM link transmission schemes with multiplexing have been introduced. As an all-IP based network technology develops, the AAL2/ATM link transmission schemes will be replaced by IP based link transmission schemes in future to reduce large protocol overheads. Accordingly, CIP, LIPE and PPPmux have been proposed in 3GPP standards. In this paper, we describe a link transmission model in the UTRAN Iub interface and evaluate the performance of ATM based and IP based link transmission schemes in terms of link efficiency and average link transmission delay. Simulation results show that the IP based transmission schemes perform better than the ATM based transmission scheme as the number of users increases.
Wireless Communications and Networking Conference, 2004. WCNC. 2004 IEEE; 04/2004
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ABSTRACT: Three patients with type III Takayasu's arteritis were referred to us because of the upper extremity hypertension and vascular claudication of the lower extremities. They underwent extra-anatomic ascending aorta-abdominal aorta bypass with vascular graft under a median sternotomy and a splitted midline laparotomy incision without cardiopulmonary bypass. The postoperative course was uneventful. Upper extremity hypertension and vascular claudication were completely resolved.
Asian cardiovascular & thoracic annals 01/2004; 11(4):357-8.
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ABSTRACT: Recently, mobile communication systems have supported various services including voice, data, video, and multimedia services as they evolve toward 3G. An AAL2 multiplexing scheme is introduced for transmission link efficiency in the UTRAN (UMTS terrestrial radio access network). However, limited radio resources and various quality of services (QoS) make it difficult to guarantee QoS requirements at radio access networks. The conventional AAL2/ATM multiplexing systems focused on link efficiency in multiplexing real-time voice and nonreal-time data traffic. In this paper, we classify various services into four classes according to QoS requirements and propose AAL2/ATM multiplexing schemes using statistical multiplexing and scheduling to guarantee the given requirements. Simulation results show that the proposed schemes perform better than the conventional schemes in guaranteeing QoS requirements of various services.
Personal, Indoor and Mobile Radio Communications, 2003. PIMRC 2003. 14th IEEE Proceedings on; 10/2003
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ABSTRACT: A multisector antenna based access point (AP) network architecture with omni-directional mobile nodes (MNs) is proposed. We investigate the effect of hidden nodes and power control on the system performance, and compare the performance of the proposed network architecture with that of an omni-directional AP/MNs network architecture in terms of throughput, delay, probability of collision, and power consumption per throughput. The data throughput in the multisector antenna based AP network architecture with power control (PC) is approximately 5.65 and 6.59 times higher than for the conventional omni-directional AP network architecture with PC and without PC, respectively, at an aggregate offered load of 1.0 (2.0 Mbps). The peak data throughput of the proposed network architecture with PC is approximately 1.9 (3.8 Mbps) for an aggregate offered load of about 2.1 (4.2 Mbps). Furthermore, the power consumption of MNs per throughput in the proposed network architecture with PC is only 1.02% and 2.25% of those of the omni-directional AP network architecture without PC and with PC, respectively, at an aggregate offered load of 1.0 (2.0 Mbps). The proposed network architecture with PC yields a significant improvement in system throughput and power saving in comparison with the conventional omni-directional AP/MNs network architecture.
Personal, Indoor and Mobile Radio Communications, 2003. PIMRC 2003. 14th IEEE Proceedings on; 10/2003
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ABSTRACT: For data communication services gradually dominating in future wireless networks, one crucial problem is to save battery power of data terminals usually requiring much power. A mobility management scheme in IP-based wireless networks is proposed to reduce battery power consumption of mobile hosts. The proposed scheme manages six states: communicating, attention/cell-connected, attention/PA-connected, idle, off/attached, and detached states for efficient management of battery power, radio resources, and network load. Steady state probabilities for mobile host (MH) state transitions are derived using a semi-Markov process approach, and the power-saving effect of the proposed scheme is analyzed. The effects of various input parameters on the steady state probabilities and power consumption are also investigated. The proposed mobility management scheme yields significant power saving in comparison with the current mobility management schemes for Mobile IP-based wireless networks.
Global Telecommunications Conference, 2002. GLOBECOM '02. IEEE; 12/2002
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ABSTRACT: We propose a network architecture with a multi-sector antenna based access point (AP) and omni-directional antenna based mobile nodes (MNs) in order to mitigate a hot spot problem in a single cell environment. In order to investigate the effect of carrier sensing range on the system performance we compare the performance of the proposed network architecture with that of an omni-directional antenna based AP/MNs network architecture in terms of throughput, probability of collision, power consumption, and power consumption per throughput for varying the carrier sensing range. As the carrier sensing range increases, the occurrence of fewer hidden nodes improves the overall network performance in the conventional omni-directional AP/MNs network architecture. On the other hand, in the proposed network architecture, the occurrence of more hidden nodes increases the possibility of multiple concurrent transmissions. Therefore, the performance of the proposed network architecture is generally improved, as the carrier sensing range decreases. The proposed network architecture with a proper carrier sensing range yields a significant improvement in system capacity and power saving in comparison with the conventional omni-directional AP/MNs network architecture. The peak data throughput of the proposed network architecture at the power level threshold of MNs for carrier sensing, ϒ<sub>cs</sub>= -80 dBm is approximately 2.39, 3.59, and 3.85 times higher than for the conventional omni-directional AP/MNs network architecture at ϒ<sub>cs</sub>= -88 dBm, ϒ<sub>cs</sub>= -84 dBm, and ϒ<sub>cs</sub>= -80 dBm, respectively. And, the power consumption of MNs per throughput in the proposed network architecture at ϒ<sub>cs</sub>= -80 dBm is only 1.90%, 2.15%, and 9.79% of those of the conventional omni-directional AP/MNs network architecture at ϒ<sub>cs</sub>= -80 dBm, ϒ<sub>cs</sub>= -84 dBm, and ϒ<sub>cs</sub>= -88 dBm, respectively, at an aggregate offered load of 1.0 (2.0 Mbps).
Communications, 2004 and the 5th International Symposium on Multi-Dimensional Mobile Communications Proceedings. The 2004 Joint Conference of the 10th Asia-Pacific Conference on;
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ABSTRACT: Emerging ubiquitous wireless networks are being spread widely. Ubiquitous wearable computers (UWCs) which may contain various communication protocol modules such as WLAN, Bluetooth, ZigBee, Wibro, and CDMA can be a solution in this era to support the ubiquitous wireless network environment. In ubiquitous wireless environments, ubiquitous wearable computers(UWCs) with multiple communication mod-ules can control each communication module as a coordinator and communicate with other devices containing WLAN and Zig-Bee modules in the surrounding networks. Since IEEE802.15.4 ZigBee and IEEE802.11b WLAN share the same 2.4GHz ISM band, WLAN causes severe interference to ZigBee devices due to higher transmission power in a large bandwidth of 22MHz. We propose a UWC-aided coexistence algorithm in an overlaid network environment of WLAN and ZigBee networks to solve this problem, and measure the performance of WLAN and ZigBee communication modules for two scenarios in a real network testbed in terms of frame error rate (FER) and goodput.
