Moo Wan Kim

Adaptive QoS Mechanism for Wireless Mobile Network

Wireless mobile multimedia communications have been greatly increased in the number of users, diversity of applications and interface technologies. Wireless mobile networks are being evolved and integrated into IP based core network, so it is necessary to provide sufficient QoS (Quality of Service) mechanism to provide enhanced user’s satisfaction. In this paper, we propose a new adaptive QoS mechanism based on utility function borrowed from the field of microeconomics, call setup and handover signaling mechanism integrating QoS and mobility management. Through a simulation, we show that adaptive resource allocation based on user preferences can be realized in the wireless mobile network with some considerations.

Validation of VoIP System for University Network

This paper propose an example of FMC based on IMS. Then the outline of the VoIP system which has been experimentally developed for the university network based on the proposed FMC is described.

Asymmetric RTS/CTS for Exposed Node Reduction in IEEE 802.11 Ad Hoc Networks

One interesting problem regarding wireless local area network (WLAN) ad-hoc networks is the effective mitigation of hidden nodes. The WLAN standard IEEE 802.11 provides request to send/clear to send (RTS/CTS) as mitigation for the hidden node problem; however, this causes the exposed node problem. The first 802.11 standard provided only two transmission rates, 1 and 2 Mbps, and control frames, such as RTS/CTS assumed to be sent at 1 Mbps. The 802.11 standard has been enhanced several times since then and now it supports multi-rate transmission up to 65 Mbps in the currently popular 802.11n (20 MHz channel, single stream with long guard interval). As a result, the difference in transmission rates and coverages between the data frame and control frame can be very large. However adjusting the RTS/CTS transmission rate to optimize network throughput has not been well investigated. In this paper, we propose a method to decrease the number of exposed nodes by increasing the RTS transmission rate to decrease RTS coverage. Our proposed method, Asymmetric Range by Multi-Rate Control (ARMRC), can decrease or even completely eliminate exposed nodes and improve the entire network throughput. Experimental results by simulation show that the network throughput in the proposed method is higher by 20% to 50% under certain conditions, and the proposed method is found to be effective in equalizing dispersion of throughput among nodes.

Sensor Network to collect Data in Field to match Satellite Data

In this paper, the wireless ubiquitous network architecture is described based on IMS which has been standardized by 3GPP (3rd generation partnership program). Then the field data collection system to match the satellite data using location information is described based on the wireless ubiquitous network.

Experiment of IMS core network enabling ubiquitous network

IMS provides a mean that integrates heterogeneous networks into an IP based network enabling ubiquitous network. In this paper, we describe the experiment of IMS core network inevitable before the system deployment to the current network, in terms of system architecture, experiment configuration and switching mode conversion

A Task Scheduling Method after Clustering for Data Intensive Jobs in Heterogeneous Distributed Systems

Several task clustering heuristics are proposed for allocating tasks in heterogeneous systems to achieve a good response time in data intensive jobs. However, one of the challenging problems is the process in task scheduling after task allocation by task clustering. We propose a task scheduling method after task clustering, leveraging worst schedule length (WSL) as an upper bound of the schedule length. In our proposed method, a task in a WSL sequence is scheduled preferentially to make the WSL smaller. Experimental results by simulation show that the response time is improved in several task clustering heuristics. In particular, our proposed scheduling method with the task clustering outperforms conventional list-based task scheduling methods.

Ad hoc WLAN throughput improvement by reduction of RTS range

In this paper, we evaluate a novel method for reducing exposed nodes in IEEE 802.11 ad hoc WLANs using asymmetric transmission ranges for RTS and CTS frames. The RTS/CTS handshake communication control mechanism used in IEEE 802.11 networks solves the hidden node problem but causes the exposed node problem. Our proposed method uses asymmetric transmission ranges for RTS and CTS control frames to solve the exposed node problem. Simulations using the Network Simulator 2 (NS-2) show that asymmetric transmission of RTS and CTS frames improves overall network throughput compared to the standard RTS/CTS method.

Evaluation of task clustering algorithm by FFT for heterogeneous distributed system

In this paper, the evaluation result of a task clustering heuristic algorithm proposed for heterogeneous distributed systems is shown. The proposed heuristic algorithm is based on our original concept, known as “Worst Schedule Length (WSL)”. It derives the lower bound of the total execution time of the cluster for each processor using WSL, then the processor which contributes to minimize WSL is chosen as an assignment target. Task clustering is then performed to get minimal response time (i.e., minimal schedule length). We show that our proposed method has advantages over existing conventional approaches through the evaluation results.

Optimizing RTS/CTS to improve throughput in ad hoc WLANs

IEEE 802.11 WLANs use carrier sense multiple access with collision avoidance (CSMA/CA) to initiate the Request to Send / Clear to Send (RTS/CTS) handshaking mechanism that solves the hidden node problem. However RTS/CTS also causes the exposed node problem where a node is unnecessarily prevented from accessing the wireless channel even when such access will not disrupt another nodes ongoing transmission. In this paper, we present continuing evaluation of a method for reducing exposed nodes in 802.11 ad hoc WLANs using asymmetric transmission ranges for RTS and CTS frames. NS-2 simulations show that the proposed method improves overall network throughput in a topology scenario of a 3-D network faced with ceiling/floor obstructions.

Throughput improvement by adjusting RTS transmission range for W-LAN Ad Hoc network

The W-LAN Ad Hoc network tends to cause problems called “Hidden Node” and “Exposed Node”. RTS/CTS mechanism has been introduced to mitigate Hidden Node and most of existing researches assume that RTS and CTS are sent at the same transmission range. This paper describes a new method to improve the network throughput by adjusting the RTS transmission range. The simulation result showed that the proposed method achieved higher throughput in some degree.