Ae-Soon Park

Machine-Type-Communication (MTC) Device Grouping Algorithm for Congestion Avoidance of MTC Oriented LTE Network

Machine-Type-Communication (MTC) is a new paradigm in mobile wireless network domains such as Mobile WiMAX (IEEE 802.16e) and 3GPP LTE (3rd Generation Partnership Project Long Term Evolution). We explain the background for MTC environments, and its key issues. Then we focus on the uplink traffic aggressiveness characteristics in major applications such as Smart Grid. Then, we propose a new congestion avoidance algorithm to reduce the congestion of the uplink intensive applications.

Load balancing among internet gateways in ad hoc networks

Since Internet gateways route all packets to and from the Internet, they are likely to become the traffic bottleneck between Ad Hoc networks and the Internet. Although multiple Internet gateways can be used to distribute the traffic load, the possibility of congestion in some Internet gateway still exists in case of uneven traffic distribution if the default Internet gateway selection scheme based on hop-distance is used. In this paper, we propose a load-based Internet gateway selection scheme to distribute the traffic load over multiple Internet gateways. The proposed Internet gateway selection scheme is applied during the on-demand route discovery and the Mobile IP agent discovery procedure. To allow mobile nodes to select less congested Internet gateway as their default Internet gateway, the proxy route reply and solicited agent advertisement messages are adaptively delayed according to Internet gateways load.

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.

Gateway discovery and routing in ad hoc networks with NAT-based Internet connectivity

The paper presents gateway discovery and routing schemes for ad hoc networks with NAT-based Internet connectivity. To maintain a reachable gateway set (RGS) and up-to-date routes to gateways, an extended HELLO (e-HELLO) message is used. A mobile node includes its RGS in the e-HELLO message and periodically broadcasts it to neighbors. On receiving the e-HELLO message, a mobile node updates its RGS and routes to gateways. To prevent on-going sessions from being broken, the current default gateway is maintained as long as it is in the RGS and there exists any on-going session. A proxy route reply (p-RREP) message is used to allow a source node to change its default gateway during route discovery. Also, a packet routing scheme for subnet-based ad hoc networks with Internet connectivity is presented. The proposed gateway discovery and routing schemes can efficiently support NAT-based Internet connectivity in ad hoc networks.

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.

System Coverage and Capacity Analysis on Millimeter-Wave Band for 5G Mobile Communication Systems with Massive Antenna Structure

The use of a millimeter-wave band defined as a 30–300 GHz range is significant element for improving performance of 5th generation (5G) mobile communication systems. However, since the millimeter-wave signal has peculiar propagation characteristics especially toward non-line-of-sight regions, the system architecture and antenna structure for 5G mobile communications should be designed to overcome these propagation limitations. For realization of the 5G mobile communications, electronics and telecommunications research institute (ETRI) is developing central network applying various massive antenna structures with beamforming. In this paper, we have introduced the central network and evaluated the system coverage and capacity through C

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.

Design of Session and Bearer Control Signaling in 3GPP LTE System

3GPP long term evolution (LTE) system targets a packet optimized system which provides higher data rate and lower delay with improved coverage and spectrum efficiency. The LTE system requires optimized signaling as well as optimized radio transmission and radio access network. Key LTE system features related to signaling optimization have been proposed in 3GPP and these should be considered in designing the LTE signaling protocols. In this paper, we propose an LTE radio interface signaling for session and bearer control, which adopts key LTE features agreed in 3GPP such as network-controlled service, QoS aggregation, and default IP access service. We analyze the session setup delay with the proposed signaling. The session setup delay is much reduced when compared to the pre-LTE signaling.