Won-Ik Kim

Ping-Pong Avoidance Algorithm for Vertical Handover in Wireless Overlay Networks

In this paper, we propose a ping-pong avoidance algorithm capable of effectively alleviating the unnecessary vertical handovers between 3G cellular and WLAN hotspots. The proposed algorithm determine the appropriate time at which a terminal should initiate a handover. It can be classified into two major schemes: One is designed to separate the single vertical handover threshold; the other to estimate the transition of the beacon signal strengths received by the terminal from WLAN hotspots on the basis of the least square approach. The aim of this study is to prevent such performance degradations as the increase of the service interruption time which follows unnecessary vertical handovers.

Dynamic Network Selection using Kernels

We present a new algorithm for vertical handover and dynamic network selection, based on a combination of multi- attribute utility theory, kernel learning and stochastic gradient descent. We show that this new method is able to improve network selection in a non-stationary mobile environment. Furthermore, since the kernel employed is based on the utility functions for attributes such as Availability, Quality and Cost, the kernel regression in fact gives interpretable results. We present simulation results that demonstrate our algorithm being able to dynamically learn utilities and efficiently select networks.

An adaptive soft handover algorithm for traffic-load shedding in the WCDMA mobile communication system

In a mobile communication environment, an abrupt increase of mobile users in a specific cell causes an unbalanced traffic-load distribution. When the increased traffic-load exceeds the link capacity of a WCDMA system, it significantly degrades the traffic quality of the mobile users. In this paper, we propose an adaptive soft handover algorithm (ASHA) to efficiently alleviate the overloaded traffic in a cell by adjusting handover parameters. The proposed algorithm virtually reduces the service coverage of the overloaded cell without adjustment of base station transmission power. Consequently, mobile users located in the area farthest away from the heavily loaded cell site are handed over to lightly loaded neighboring cells, so that the traffic-load of the overloaded cell is decreased. The performance of the proposed algorithm is analyzed in path loss and shadow fading environments and is compared with that of a conventional soft handover algorithm.

A new traffic-load shedding scheme in the WCDMA mobile communication systems

In a mobile telecommunication environment, an abrupt increase of mobile users in a specific cell causes an unbalanced traffic-load distribution. When the increased traffic-load exceeds the link capacity of a WCDMA system, it significantly degrades the traffic quality of the mobile users. In this paper, we propose an adaptive soft handover algorithm (ASHA) to efficiently alleviate the overloaded traffic in a cell by adjusting handover parameters. The proposed algorithm virtually reduces the service coverage of the overloaded cell without adjustment of base station transmission power. Consequently, mobile users located in the area farthest away from the heavily loaded-cell site are handed over to the lightly loaded neighboring cells, so that the traffic-load of the overloaded cell is decreased. The performance of the proposed algorithm is analyzed in path loss and shadow fading environments and is compared with that of a conventional soft handover algorithm.

Location Aided Location Update in IEEE 802.16e Wireless MANs

IEEE 802.16 is one of the standards for Broadband Wireless Access (BWA) in Metropolitan Area Networks (MANs). IEEE 802.16e is the extension of IEEE 802.16 to enhance the mobility of Mobile Stations (MSs). In IEEE 802.16e Wireless MANs, idle mode, which allows MSs to become periodically available for downlink broadcast messaging without registration at a specific Base Station (BS), is proposed in order to conserve power and operation resource of MS. The idle mode MS performs idle mode location update to establish location to the network and acknowledge message decoding. How to minimize the total cost of location update is one of the most important and challenging issues in wireless mobile networks. In this paper, we propose two schemes of Location Aided Location Update (LALU) to conserve power more efficiently. Our simulation results show that the proposed schemes provide better performance than that of previous location update of IEEE 802.16e.

Performance Evaluation of WCDMA-to-CDMA2000 Handover

Cellular service providers in Korea have started WCDMA commercial service since 2004. The initial deployment has been done in highly-crowded urban districts. Therefore, inter-RAT handover from WCDMA to cdma2000 (hereafter, called as the inter-RAT handover) should be developed to provide seamless service in out-of-service areas. We develop some handover procedures and set conditions for the inter-RAT handover. For the purpose of performance analysis, we build an inter-RAT handover performance simulator. Using the simulator, we determine proper handover conditions and parameter ranges for the inter-RAT handover. Through simulation results, we assess the handover failure rate and the border cell utilization for WCDMA systems. From simulation results, we define the cost function to evaluate performance of handover for each scenario. Based on the values of the cost function, we suggest optimal handover scenarios and parameter sets in the view of users and service-providers, respectively