Chul-Hee Kang

Design of hierarchical crossconnect WDM networks employing a two-stage multiplexing scheme of waveband and wavelength

The authors propose a design method for hierarchical crossconnect wavelength-division-multiplexed networks employing a two-stage multiplexing scheme of waveband and wavelength, in order to reduce the complexity and size of optical crossconnect at the nodes. The waveband is formed by grouping lightpaths with the same destination in a network. The authors present an integer linear programming formulation for the routing and grouping of lightpaths, and a heuristic design method is also proposed as a practical method to find a design solution for general large-scale networks. It is found that the proposed design method can largely reduce crossconnect requirements, although it slightly increases the wavelength requirements.

An implementation of wireless sensor network

In recent years, the advances in wireless communication and electronics have accelerated to develop many wireless network solutions to replace existing wired networks. A wireless network solution can support mobility and flexibility of nodes in a network. Especially in sensor networks, it has many advantages to replace cables with wireless logical links. On the other hand, Bluetooth is generally considered as a promising short-range wireless technology because of its inexpensive cost, low power and small size, and thus Bluetooth has been gaining increasing interest from various industries. For the above reasons, we adopt Bluetooth technology for a wireless sensor network, which is designed for security systems. Since Bluetooth will continue to be a feature found in many devices, it is worthwhile to investigate its use in wireless sensor networks. In this paper, we describe a Bluetooth wireless sensor network for security systems, which includes the implementation issues about system architecture, power management, self-configuration of network, and routing. We think that the methods or algorithms described in this paper can be easily applied to other embedded Bluetooth applications for wireless networks.

An adaptive resource allocation mechanism including fast and reliable handoff in IP-based 3G wireless networks

The aim of the all-IP architecture in third-generation wireless networks is to allow operators to deploy IP technology in delivering third-generation services, that is, an architecture based on packet technologies and IP telephony for simultaneous real-time and non-real-time services. We present a new handoff management scheme that utilizes simultaneous multiple bindings in IP-based 3G wireless networks. The proposed handoff scheme minimizes packet losses and incurs negligible delays during handoff. We also present an adaptive resource allocation scheme that allocates connection resources to incoming calls depending on the network conditions. The resources accumulated by bandwidth degradation for on-going calls are utilized to minimize dropping probability of handoff calls and blocking probability of new calls.

Priority-Based Service-Differentiation Scheme for IEEE 802.15.4 Sensor Networks in Nonsaturation Environments

In this paper, we propose two mechanisms, i.e., 1) backoff exponent differentiation (BED) and 2) contention window differentiation (CWD), to provide multilevel differentiated services for IEEE 802.15.4 sensor networks. The beacon-enabled mode with the slotted carrier-sense multiple-access mechanism with collision avoidance (CSMA/CA) algorithm is considered for nonsaturation. A mathematical model based on a discrete-time Markov chain is presented and analyzed to measure the performance of the proposed mechanisms. Numerical results show the effects of varying parameters. It shows that BED is better for service differentiation and channel utilization, regardless of the number of devices and the packet-arrival rate. It also shows that the throughput depends on the backoff exponent (BE), contention window (CW), and packet size and that the relative delay for successfully transmitted packets for BED is longer than that for CWD, which enables a higher relative gain for CWD. In addition, we obtain the number of unit backoff periods required to process all of the head packets of devices. Based on the numerical results, we obtain a criterion that provides guidelines for choosing a mechanism that is suitable for the objective function and determining the optimal length of the superframe to process the packets in the system.

Quick Local Repair Scheme using Adaptive Promiscuous Mode in Mobile Ad Hoc Networks

In mobile ad hoc networks (MANETs), there is frequently disconnected a route consisting of multi- hop from a source to a destination because of the dynamic nature such as the topology change caused by nodes’ mobility. To overcome this situation, existing routing protocols for MANETs have performed route repair scheme to repair the disconnected route. However, existing reactive routing protocols have the problem which is that a source node unnecessarily performs re-discovers the whole path when just one node moves, even if the rest of path needs not to be re-arranged. Therefore, the time for re-discovery of the whole path may often take too long. To solve the problem, we propose a new local repair scheme using promiscuous mode. Our scheme is mainly composed of two parts: adaptive promiscuous mode and quick local repair scheme. Adaptive promiscuous mode is to repeat the switching processes between promiscuous mode and nonpromiscuous mode to overcome energy limit caused by using promiscuous mode in overall time and quick local repair scheme is to fast perform the local re-route discovery process with the information of the active connection in the local area acquired by promiscuous mode. With simulation in the various number of connection, We demonstrate the better network performances achieved with the proposed schemes as compared with AODV as reference model that do not provide local repair scheme.

Asynchronous inter-network interference avoidance for wireless body area networks

This paper considers the internetwork interference problem in environments with multiple wireless body area networks (WBANs). We propose an asynchronous internetwork interference avoidance scheme (abbreviated as AIIA), which is based on the hybrid multiple access of carrier sense multiple access with collision avoidance (CSMA/CA) and time division multiple access (TDMA). In AIIA, the gateway device of each WBAN maintains a table, called an AIIA table, which includes the timing offset and TDMA transmission schedule information corresponding to the interfering WBANs. By referring to the table, the conflicting TDMA schedule can be checked and updated by itself, in asynchronous and distributed manners. Extensive simulations are conducted to demonstrate the feasibility and effectiveness of AIIA.

QoS support in mobile/wireless IP networks using differentiated services and fast handoff method

In the mobile/wireless IP network where frequent mobility is encountered, it is required to accommodate Internet quality of service (QoS) mechanisms such as differentiated services (DiffServ) for mobile hosts. We consider the issue of integration of mobile IP and DiffServ including handoff condition and propose the schemes with a hierarchical agent architecture for supporting QoS in mobile/wireless IP networks. To support DiffServ for mobile hosts, we configure foreign agent to have pre-allocated resources in advance for static service level agreement (SLA) case. In case foreign network has no pre-configured SLA or enough resources for mobile host, we configure new SLA among bandwidth brokers to be set up using dynamic SLA. Also, we propose the signaling and data procedures with DiffServ with respect to fast handoff.

Dynamic adaptation of contention window for consumer devices in WiMedia home networks

WiMedia ultra-wideband technology is an attractive transmission solution for high-data-rate multimedia streaming and high-quality consumer electronic devices in wireless multimedia home networks. However, the contention-based protocol of WiMedia medium access control (MAC) may cause channel collisions and throughput degradation as the number of consumer devices in the network increases. In order to resolve this problem and to reduce channel access latency, we propose a dynamic adaptation of contention window (DACW) scheme in which the contention window size for the optimal transmission probability is derived after traffic information has been obtained by means of distributed beaconing procedures. The trace-driven simulation results demonstrate that the DACW scheme outperforms the existing channel access schemes (i.e., prioritized channel access) in WiMedia MAC under different situations, especially when the number of contending nodes is large.

A Group-aware Multicast Scheme in 60GHz WLANs

The relation of multicast transmission and directional antennas is an open problem that has been debated for a long period of time. In this paper, we propose a group-aware multicast scheme of efficient multicast communication using the directional antennas for 60㎓ millimeter wave wireless networks. For this purpose, we first derive the relation among beamwidth, distance between devices and most suitable data rate in the 60㎓ frequency-based wireless network. In addition, for the dynamic beamforming of multicast communication, the x and y coordinates of any point with sender device at the center is generated, and a best-chosen group is deduced based on the Euclidean distance. Then the most suitable data rate for the group is obtained using the law of cosine. Using the Standard IEEE 802.11ad MAC protocol as an example, extensive simulation results demonstrate that the proposed scheme outperforms the existing multicast communication schemes with directional antennas under different situations.

Telemedicine with digital video transport system in Asia-Pacific area

We have established a medical network in Asia-Pacific area with high-quality moving image on a super broad-banded Internet line since February 2003. Broadcasting real-time surgery and teleconference with medical-quality videos with digital video transport system (DVTS) were so useful to learn surgical techniques and other medical procedures beyond borders. We have conducted 20 events in categories of teleconference (8 times), live transmission of medical procedure (6 times), and remote attendance to scientific medical meetings (6 times) until September 2004. We had teleconferences among 3 countries in APAN-Hawaii in January 2004 (Japan, Korea and USA), and in APAN-Cairns in July 2004 (Japan, Korea and Australia). There have been no serious transmission/ethical problems so far. With these experiences and current achievements, we hope to extend this advanced network system to whole Asia-Pacific countries to share medical skills and knowledge.