Seungwan Ryu

Research activities on next-generation mobile communications and services in Korea

In this article we present a perspective on next-generation mobile communications and services. As a preliminary research work on next-generation mobile communications, we exploit what next-generation mobile services will be (S. Ryu et al., May 2003). We define next-generation mobile services as a hierarchy of services consisting of three different service levels: the service areas, the service functionalities, and the service technologies. We derive these service levels by means of scenario-based analysis. Next we propose conceptual reference network architecture, focusing on the realization of the service technologies. We divide the network into four different parts: a user equipments and access part, a network service provisioning layer part, a network control layer part, and non-mobile network operator service pan, according to characteristics of information and service flows within a network. In this reference network architecture, service elements such as servers, processors, and gateways are placed in each network part to support the derived next-generation mobile services. Finally, we give a brief introduction of research and development activities for next-generation mobile communication systems and services in Korea.

Multi-Hop Relay Based Coverage Extension in the IEEE802.16j Based Mobile WiMAX Systems

In this paper, we investigate various issues of cost- effective coverage extension in a multi-hop relay based WiBro/WiMAX systems. Since the coverage extension problem may occur in metropolitan areas as well as suburban or rural areas where user density is relatively low or moderate, we first introduce several topologies and the resulting cost-effective coverage extension methods for each case. Secondly, we propose two cost-effective coverage extension methods using two sectorized cellular approaches, one using the wide-beam tri-sector cell (WBTC) and the other using the narrow-beam tri-sector cell (NBTC). Finally, we present a practical deployment scenario consisting of three phases depending on user traffic density.

Performance analysis of a cellular network using frequency reuse partitioning

In this paper, we propose an analytical model to evaluate the performance of Frequency Reuse Partitioning (FRP) based cellular systems. In an FRP scheme, a channel with a smaller reuse factor is assigned to Mobile Stations (MSs) located near the serving Base Station (BS), whereas a channel with a larger reuse factor is assigned to MSs located near the edge of a cell. In this manner, FRP can reduce the effect of Co-Channel Interference (CCI) and improve system throughput. In order to establish an analytical model for FRP based cellular systems, we introduce a model for traffic analysis using a two dimensional Markov chain and approximate CCI levels with the power sum of multiple log-normal random components in a multi-cell environment. The performance of the FRP based system is presented in terms of channel utilization, call blocking probability, outage probability and effective throughput. The analytical results are compared with computer simulations.

Development of device-to-device(D2D) communication based new mobile proximity multimedia service business models

Mobile and wireless technology is advancing forward to deliver more connected devices and richer multimedia content and applications. The number of mobile subscriptions continues to grow along with an explosive increase in the mobile data traffic demand. Thereby, it creates a significant network capacity shortage concerns for mobile network operators. In order to address this problem, it is essential to increase the network capacity at a low additional cost. The device-to-device (D2D) communication based proximity service is believed to have a promising future mobile communication technology that is capable to create new mobile service opportunities and offload traffic to the eNB. In this article, we present perspectives, possibilities and challenging issues of the D2D communication based new mobile proximity multimedia services. Based on the scenario analysis process, we propose three types of D2D services, an Ad hoc D2D type, an agent-based D2D type and a mesh D2D type. Finally, we argue on the several challenging issues that are essential in provisioning the D2D based proximity services.

Vertical handover between LTE and wireless LAN systems based on common resource management (CRRM) and generic link layer (GLL)

It is expected that many heterogeneous wireless networking systems such as 3GPP Long-term Evolution (LTE) systems, WiMAX/WiBro systems and WLAN systems will be exist in next generation wireless communication environment. Under such environment, various communication services will be introduced by integrating heterogeneous wireless networking technologies, especially at the radio access networks. In order to provide such integrated communication services, integrated radio resource management and seamless vertical handover across such heterogeneous access networks should be supported. In this paper, to tackle these problems, we propose a Generic Link Layer (GLL) based common radio resource management (CRRM). In particular, we propose the network architecture and functions of each network element for integrated radio resource management among heterogeneous access networks. Then, we propose policy-based and multi criteria decision making (MCDM) based seamless vertical handover schemes between LTE and next generation WLAN systems. Performance of the proposed vertical handover schemes are evaluated via extensive simulation studies. Simulation results show that the proposed VHO schemes outperform other VHO schemes such as received signal strength (RSS) based VHO scheme in terms of throughput, handover success rate and the service cost.

Next generation mobile service environment and evolution of context aware services

Context aware service which provides best suitable services for a user by analyzing users needs and situational information, will be one of the promising next generation (NG) mobile services. In this paper, we propose the NG mobile service environment based on the NG mobile service platform and evolutional phases of context aware services in the NG mobile service environment. We then introduce the Context Aware Follow-me (CAF) service developed as a prototype of promising NG context aware mobile service followed by introduction of testbed system developed to investigate feasibility of the CAF service

Performance analysis of single-frame mode and multi-frame mode in IEEE 802.16j MMR system

In this paper, we investigate the performance of MMR system in non-transparent mode. The IEEE 802.16j MMR system has two mode of operation, single-frame mode and multi-frame mode. In the analysis, we assume that channel interference between MR-BS and RS, or between RSs anywhere in the given area is negligible. The performance is presented in terms of frame efficiency by varying number of RS and BS coverage to RS coverage ratio and maximum coverage area of a BS by varying traffic density. Analytical results show that the single-frame mode is more efficient than multi-frame mode in frame efficiency and coverage extension.

Scenario Decomposition based Analysis of Next Generation Mobile Services

The next-generation mobile communication, the so called fourth generation, is a system capable to provide a variety of multimedia services such as multimedia moving pictures, movies, and television broadcasts with high-speed and high quality via the converged network of wireless and wired infrastructures. However, the next generation mobile services have not been studied actively yet because there is no clear definition what the next generation mobile communication and its services will be. In this paper, we exploit a perspective of the next generation mobile communication services and its characteristics. We then propose a service analysis framework for eliciting key service functionalities and core technologies when various future mobile service scenarios are given. The proposed analysis framework, called scenario based service analysis process (2SAP), consists of 4 sequential analysis steps, a scenario transformation, a scenario decomposition, an analysis of functions for each situation, and an elicitation of service functionalities.

Secure and Smart Media Sharing Based on a Novel Mobile Device-to-Device Communication Framework with Security and Procedures

Cellular network service providers are trying to expand their capacity to accommodate the increasing mobile traffic demand by adopting new mobile technologies like user proximity based Device-to-Device (D2D) communication underlying existing Long Term Evolution-Advanced (LTE-A) cellular network, which is a promising technology to overcome legacy cellular networks congestion. D2D communication is a new paradigm to enhance legacy LTE-A cellular network performance. However, there are several challenges to be overcome: 1) what will be the trending technology for overcoming cellular network data traffic congestion? 2) How can we overcome security threats and high pricing for data services? And 3) how can users earn revenue by media sharing? We propose a secure and smart D2D communication framework that answers the three challenges thereby enhancing efficiency of D2D communications in a smart and secure manner. Our framework demonstrates that the proposed application level security and procedures provide reduced network congestion, better pricing schemes, and less or no security threats than the current legacy non-D2D communication model.

Performance analysis of LTE enterprise femtocell using cooperative downlink transmission scheme

In this paper, we propose a cooperative transmission scheme (CTS) for system throughput enhancement in enterprise femtocell downlink systems. In our scheme, the user equipment (UE) is capable of receiving the desired signal from the serving femtocell base station (fBS) as well as from an adjacent fBS. Thus, the UE achieves an improved signal-to-interference ratio (SIR) by using two time synchronized signals. Performances of the proposed scheme are evaluated in terms of the call-level quality of service (QoS) (i.e., call blocking probability) and the packet-level QoS (i.e., outage probability). We first measure the resource utilization and call blocking probability for the downlink resources for various offered load in femtocell. Based on that, we obtain the outage probability and effective throughput of the system via computer simulations. Simulation results show that compared to the conventional scheme, the proposed scheme can reduce the UEs outage probability in the enterprise femtocell environment. In particular, a significant performance improvement can be achieved with the proposed CTS for UEs located at the cell edge.