Kyung-Yul Cheon

Relay Selection and Resource Allocation Schemes for Effective Utilization of Relay Zones in Relay-Based Cellular Networks

In relay-based cellular networks, total system throughput and cell-edge user throughput are affected by relay selection (RS) and resource allocation (RA) schemes. In this letter, we propose an RS scheme and two RA schemes (optimal and heuristic) for relay-based cellular networks. Via simulation, we show that the proposed RS and RA schemes improve total throughput of relay-based cellular networks while maintaining cell-edge user throughput comparable to existing schemes.

A femtocell power control scheme to mitigate interference using listening TDD frame

Due to the rapid growth of indoor wireless communications, many of the telecommunication industries recently are interested in femtocell. Femtocell is low power and low cost indoor base-station to cover indoor traffics. Before using femtocell in current wireless environments, interference problem between macrocell and femtocell should be solved since the interference affects the performance of both macrocell and femtocell. In order to reduce the interference, in this paper, we suggest a new time-division-duplex (TDD) frame structure called listening-TDD frame (LTDDF) for femtocells. In LTDDF, femtocell has both downlink and uplink periods during downlink period in macrocell. The uplink period in macrocell is used as listening period in femtocell that is used to overhear signals from surrounding macrocell users to obtain their channel quality information (CQI). Based on the CQI of macrocell users, femtocell base-station adaptively adjusts its transmission power. Thus, LTDDF can effectively reduce interference on macrocell users. By simulations, we evaluate the performance of LTDDF in terms of capacity of macrocell and femtocell in both downlink and uplink.

Analysis of WLAN to UMTS Handover

Generally, in UMTS-WLAN overlay networks, when a UE moves from UMTS to WLAN, it can make a choice of handover to WLAN on its own initiative and break off the UMTS connection after finishing the initial WLAN access operations such as an association, a subscriber authentication, etc. Therefore, the UE can seamlessly switch to the new access system and the handover delay is not significant problem. However, when the handover is happened from WLAN to UMTS, the UE is apt to lose the WLAN signal without warning because it can suddenly stray from the WLAN coverage. As the UE cannot communicate with any systems until it accesses to a UMTS system or another WLAN system, the current session in use may be abruptly terminated if the handover is too delayed and hence the handover delay has a great effect on the seamless mobility. This paper represents a UMTS-WLAN overlay network model and describes our developed UMTS-WLAN handover testbed. We show the test results and the analysis of handover delay happened during handover from WLAN to UMTS.

Mobility-based handover decision mechanism to relieve ping-pong effect in cellular networks

In order to guarantee quality of service (QoS) and seamless communications to nomadic users, it is important to prevent unnecessary handovers occurred during a short interval, so-called ping-pong effect. Considering mobility is one of the useful methods to relieve ping-pong effect in cellular networks since a mobile device can efficiently determine whether it should perform handover or not through the estimation of its moving direction or velocity. In this paper, we propose a mobility estimation method that estimates radial velocity of mobile device directed to the neighboring base stations based on the received signal strength (RSS). In addition, we propose an efficient handover decision mechanism based on the estimated mobility to relieve ping-pong effect. From performance evaluation based on simulations, we find that the proposed mobility estimation mechanism can accurately estimate mobility of moving devices and the proposed handover mechanism can effectively relieve ping-pong effect and reduce handover delay.

3GE-WLAN Vertical Handover Experience using Fast Mobile IPv6

Recently, seamless vertical handover has become one of the challenging issues in wireless networks. Seamless handover enables mobile users to access on-going services without interruption as moving across various wireless networks. The vertical handover requires fast and efficient handover control over various wireless technologies to realize the service continuity and seamless mobility. In this paper, we propose novel vertical handover platform for 3G evolution which has characteristics of FMIPv6 based mobility management. The experimental result shows that our vertical handover platform is well-designed and suitable for seamless vertical handover.

Seamless Handover Using FMIPv6 with Effective Tunnel Management Scheme

Fast Mobile IPv6 has been proposed to reduce latency and packet loss inherent to the handover process. However the previous research did not consider the packet loss according to the tunnel management for Fast Mobile IPv6. In the procedure of binding updates and fast binding updates, a mobile node has to establish new tunnels after receiving binding acknowledgement messages. While completing the tunnel creation and routing update, the mobile node can not handle packets incoming and outgoing through the new tunnels. This drawback causes packet loss of impeding the seamless handover. To reduce this packet loss, we have developed an effective tunnel management scheme called Dual Mode Tunneling (DMT). It employs decapsulation-only tunnels before using typical tunnels which can do an encapsulation and decapsulation. Through implementation and experimental study for vertical handover between 3G long term evolution and wireless local area network, we have evaluated the performance of the proposed scheme.

Channel assignment and jammer mitigation for military MANETs with multiple interfaces and multiple channels

The capability of accessing multiple channels through multiple interfaces improves the network capacity, which attracted the attention of the future military networks. However, due to the presence of jammers as well as mobility and ad-hoc features, they require distributed and efficient resource management and channel assignment. Due to the NP hardness of the channel assignment problem, we propose a heuristic algorithm termed CA-JAM (Channel Assignment and JAmmer Mitigation) that requires each station to exchange control messages through beacon frames on every individual interface. CA-JAM assigns a distinct channel for each interface of a station and use the information in the beacon received from the neighbors, to improve the network throughput by reducing the number of stations using the same channel to avoid interference and mitigate the effect of jamming while maintaining the connectivity. Simulation results are obtained through OPNET to compare CA-JAM algorithm with existing protocols.

Overhead analysis on beacon broadcasting for self-organizing MIMC ad-hoc networks

In self-organizing mobile ad-hoc networks with multi-interface and multi-channel (MIMC), nodes need to rendezvous on a channel using any interface, when there is neither a dedicated channel nor a common control channel. To design such mission-critical combat networks that are alike cognitive radio networks, we modified the existing IEEE 802.11 MAC protocol by extending beacons, such that each interface randomly generates a beacon that includes its channel information. As multiple interfaces of many nodes generate beacons within a transmission range, there is a possibility of beacon collisions on the same channel at a certain node. Through the results based on our implementation with the OPNET simulator, we verify that the system works well while the probability of beacon collisions is very small.

Dual Tunnelling Mechanism for Mobile IP Based 3G LTE-WLAN Handover

Mobile IPv6 (MIPv6) used to support IP mobility in heterogeneous network such as the universal mobile telecommunications system (or long term evolution system) and 802.11 wireless local area networks (WLANs). But MIPv6 has well-known packet loss during movement detection and binding update, but it has another packet loss while creating new tunnel and updating routing path. That is, when the home agent sends a binding acknowledgement (BA) message to mobile node after receiving a binding update (BU) message, the new tunneled packets are also sent to MN with the BA message. After receiving the BA message, the MN creates new tunnel and modifies routing information. But while completing these procedures, the MN can not handle new tunneled packets incoming together the BA message. To solve this problem, this paper proposes the dual tunneling mechanism(DTM) to reduce the additional loss using the reception- only tunnel. In this paper, we analyze the packet delay time in overlay and non-overlay network in case of general mobile IPv6 and DTM, and observe the handover experimental result for the 3G LTE-WLAN network.