Hyeyeon Kwon

Handover prediction strategy for 3G-WLAN overlay networks

In 3G-WLAN overlay network environments, a UE is apt to lose the WLAN signal without any notice by moving while it connects to WLAN because it can be apart from the WLAN coverage suddenly. In this case the on-going services are disrupted by unexpected link corruption. Hence, it needs to execute quickly the handover to 3G network as soon as it detects the lost of WLAN signal. However, as the 3G access has many network signaling operations additionally including IP mobility operations for service continuity, it requests more enough processing time for the operations, which increases the handover latency causing the service interruption. Therefore it is important to predict the time when the UE will get out of the WLAN coverage. By the handover prediction, the UE can prepare the connection to 3G network before breaking off the WLAN connection. This paper shows several handover prediction algorithms to reduce the handover latency by fast handover triggering. The correctness of the algorithms is compared by simulation.

Consideration of UMTS-WLAN seamless handover

By mutual complemented reason of wide coverage and high data transmission, the integration and handover of SG network and WLAN is regarded as an important function for 3G beyond (B3G) mobile communication systems. The seamless mobility is one of the basic requirements for handover between these heterogeneous networks. In this paper, we present a seamless handover mechanism for UMTS and WLAN within the framework of handover architecture, IP mobility and authentication mechanism. Firstly, we review the 3GPP-specific integration architecture of UMTS and WLAN, WLAN UE-initiated tunnel mechanism, IP mobility and authentication mechanisms of both networks. Then we propose the configuration of mobile IPv6 based UMTS-WLAN overlay network and the security mechanism for reducing the handover delay. Lastly we show the operation of seamless handover in our proposed network model.

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.

UMTS-WLAN Interworking Strategies for Reducing Handover Delays

During handover between heterogeneous networks such as the 3G mobile telecommunication systems and the Wireless LAN systems, a subscriber authentication, the Mobile IP operations for IP mobility and an accessing to a data gateway are heavy burdens due to its time-taken operations and overheads. So they are main factors of handover delays. This paper proposes the handover strategies for reducing handover delays in the UMTS (Universal Mobile Telecommunications System) and the Wireless LAN overlay networks. For decreasing the delays, mandatory use of a fast re-authentication is applied and newly added features of one for the UMTS are introduced. And simplified MIPv6 operations and an optimized gateway approach to minimize the network access time are proposed. These proposed approaches are analyzed and evaluated with the results of an authentication test bed and a network simulation.

End-to-End qos guaranteed service in WLAN and 3GPP interworking network

In this paper, we model the end-to-end QoS provisioning mechanisms in the WLAN and 3GPP interworking network. For the end-to-end QoS guaranteed service, we model the control plane and user plane considering the WLAN and 3GPP interworking network. And we propose the QoS parameter/class mapping and DPS packet scheduler. By the simulation results, DPS can provide the low end-to-end delay of voice traffic, even though a traffic load increases by 96%. Especially, the end-to-end delay of voice is much smaller when the QoS parameter/class mapping and DPS are applied to the interworking network.

Optimum transmission of secondary user for spectrum sharing on interference channel

This paper presents optimum transmission strategies in terms of the number of transmission antennas and pilot symbols for secondary users of multiple-input and multiple-output system. By complying with the restriction of transmission power from geo-location database, secondary users can protect primary users. However, the receiver of secondary users can suffer from the interference by primary users. We derive a closed-form expression on achievable throughput of zero-forcing linear processing in the presence of channel estimation error due to interference and noise. In addition, we provide optimal values for transmission parameters in the condition of permitted power level and frame duration. With numerical results, we verify our analysis and discuss the effect of the transmission parameters.