• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.35 no.11A
• /
• pp.1085-1090
• /
• 2010

Ultra wideband (UWB) technologies have been developed to exploit a new spectrum resource in substances and to realize ultra-high-speed communication, high precision geolocation, and other applications. The energy of UWB signal is extremely spread from near DC to a few GHz. This means that the interference between conventional narrowband systems and UWB systems is inevitable. However, the interference effects had not previously been studied from UWB wireless systems to conventional mobile wireless systems sharing the frequency bands such as Cellular CDMA and Korean PCS. This paper experimentally evaluates the interference from two kinds of UWB sources, namely a direct-sequence spread-spectrum UWB source and an impulse radio UWB source, to a Cellular CDMA and K-PCS digital transmission system. The average frame error rate degradation of each system arc presented. From these experimental results, we show that in all practical cases UWB system can coexist with Cellular CDMA and K-PCS terminal without causing any dangerous interference.

• Journal of Communications and Networks
• /
• v.15 no.1
• /
• pp.45-53
• /
• 2013

Multi-hop cellular networks (MCNs), which reduce the transmit power, mitigate the inter-cell interference, and improve the system performance, have been widely studied nowadays. The relay selection scheme is a key technique that achieves these advantages, and inappropriate relay selection causes frequent relay switchings, which deteriorates the overall performance. In this study, we analyze the conditions for relay switching in MCNs and obtain the expressions for the relay switching rate and relay activation time. Two mobile-based relay selection schemes are proposed on the basis of this analysis. These schemes select the relay node with the longest relay activation time and minimal relay switching rate through mobility prediction of the mobile node requiring relay and available relay nodes. We compare the system performances via simulation and analyze the impact of various parameters on the system performance. The results show that the two proposed schemes can obtain a lower relay switching rate and longer relay activation time when there is no reduction in the system throughput as compared with the existing schemes.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.6 no.1
• /
• pp.203-228
• /
• 2012

It is expected that device-to-device (D2D) communication is allowed to underlay future cellular networks such as IMT-Advanced for spectrum efficiency. This article studies the mechanisms of D2D communication and interference avoidance when the D2D subsystem reuses uplink resources and downlink spectrums with a cellular system, respectively. We firstly propose an effective scheme to establish and maintain D2D communication. Moreover, a novel method to deal with the resource allocation and interference avoidance issues by utilizing the network peculiarity of a hybrid network to share the uplink resource is proposed. Most research focuses on reusing the uplink spectrums, but how to share the downlink frequency bands is seldom addressed. To share the downlink spectrums and avoid the interference to the primary cellular devices, a labeled time slots based mechanism is proposed. Implementation details are described in a real cellular system and simulation results prove that satisfying performance can be achieved by using the proposed mechanisms.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.44 no.12
• /
• pp.54-62
• /
• 2007

Mobile IPv6 is the representative standard protocol proposed to offer mobility of mobile hosts, but it has drawbacks such as high handover latency and packet loss during handover. To complement these drawbacks, several protocols have been proposed and they can support faster handover than the Mobile IPv6, but there still exists inevitable packet loss during handover in those protocols. In this paper, we propose a new handover procedure of mobile host who has a dual link for minimizing packet loss rate during micro handover to improve mobility capability of Cellular Ethernet system that supports mobility at layer 2. And we derive the superiority of proposed scheme by comparing in terms of packet loss rate, handover latency and throughput of proposed scheme with those of Hierarchical Mobile IPv6 which is the representative IP-layer micro mobility protocol by simulation.

• Journal of Communications and Networks
• /
• v.7 no.2
• /
• pp.192-206
• /
• 2005

Integration of mobile networks and Internet has started with 2.5 generation of mobile cellular networks. Internet traffic is today dominant traffic type worldwide. The hanger for higher data rates needed for data traffic and new IP based services is essential in the development of future wireless networks. In such situation, even 3G with up to 2 Mbit/s has not provided data rates that are used by Internet users with fixed broadband dial-up or through wired local area networks. The solution to provide higher bit rates in wireless access network has been found in wireless LAN although initially it has been developed to extend wired LAN into wireless domain. In this paper, we propose and describe a solution created for interoperability between mobile cellular network and WLAN. The integration between two networks, cellular and WLAN, is performed on the authentication, authorization, and accounting, i.e., AAA side. For that purpose we developed WLAN access controller and WLAN AAA gateway, which provide gateway-type access control as well as charging and billing functionalities for the WLAN service. In the development process of these elements, we have considered current development stadium of all needed network entities and protocols. The provided solution provides cost-effective and easy-to-deploy PLMN-WLAN Internetworking scenario.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.30 no.1B
• /
• pp.47-51
• /
• 2005

Mobile number portability(MNP) means currently number portability among the 2G cellular phone in Korea and subscriber can change his mobile phone system operator without change his phone number. MNP system use QoR(Query on Release) method in call processing. We shows that the realization and performance of MNP system and the problems that is related with MNP system.

• Journal of Communications and Networks
• /
• v.8 no.1
• /
• pp.13-20
• /
• 2006

In cellular mobile communications, how to achieve optimum system capacity with limited frequency spectrum is one of the main research issues. Many dynamic channel assignment (DCA) schemes have been proposed and studied to allocate the channels more efficiently, thus, the capacity of cellular systems is improved. Reuse partitioning (RP) is another technique to achieve higher capacity by reducing the overall reuse distance. In this paper, we present a network-based DCA scheme with the implementation of RP technique, namely dynamic reuse partitioning with interference information (DRP-WI). The scheme aims to minimize the effect of assigned channels on the availability of channels for use in the interfering cells and to reduce their overall reuse distances. The performance of DRP-WI is measured in terms of blocking probability and system capacity. Simulation results have confirmed the effectiveness of DRP-WI scheme. Under both uniform and non-uniform traffic distributions, DRP-WI exhibits outstanding performance in improving the system capacity. It can provide about 100% capacity improvement as compared to conventional fixed channel assignment scheme with 70 system channels.

• Journal of Sensor Science and Technology
• /
• v.18 no.5
• /
• pp.337-342
• /
• 2009

This paper describes a robust mobile u-healthcare system with multiple physiological signs measurement capability in real time with integration of WSN(wireless sensor network) technology and CDMA(code division multiple access) network. A cellular phone receives health data in WSN and performs local physiological signs analysis at a phone processor, and then transmits abnormal data to server for further detail or precise health signal evaluation by a medical doctor over a CDMA network. Physiological signs of the patients are continuously monitored, processed and analyzed locally at cellular phone process to produce useful medical information for diagnosis and tracking purposes. By local simple analysis in cellular phone processor we can save the data transmission cost in CDMA network. By using the developed integrate ubiquitous healthcare service architecture, patients can realize self-health checking so that the prevention actions can be taken earlier. Appropriate self-monitoring and self-management can cure disease and relieve pain especially for patients who suffer from chronic diseases that need long term observation.

• Journal of Information Processing Systems
• /
• v.8 no.3
• /
• pp.521-538
• /
• 2012

As the knowledge society matures, not only distant, but also off-line universities are trying to provide learners with on-line educational contents. Particularly, high effectiveness of mobile devices for e-Learning has been demonstrated by the university sector, which uses distant learning that is based on blended learning. In this paper, we analyzed previous m-Learning scenarios and future technology prospects. Based on the proposed m-Learning scenario, we designed cellular phone-based educational contents and service structure, implemented m-Learning system, and analyzed m-Learning service satisfaction. The design principles of the m-Learning service are 1) to provide learners with m-Learning environment with both cellular phones and desktop computers; 2) to serve announcements, discussion boards, Q&A boards, course materials, and exercises on cellular phones and desktop computers; and 3) to serve learning activities like the reviewing of full lectures, discussions, and writing term papers using desktop computers and cellular phones. The m-Learning service was developed on a cellular phone that supports H.264 codex in 3G communication technology. Some of the functions of the m-Learning design principles are implemented in a 3G cellular phone. The contents of lectures are provided in the forms of video, text, audio, and video with text. One-way educational contents are complemented by exercises (quizzes).

• Journal of Industrial Technology
• /
• v.21 no.A
• /
• pp.65-71
• /
• 2001

In this paper, we propose handoff scheme for BT(Bluetooth) IP and define signaling for the handoff scheme. In local area, BT IP use the concept of Cellular IP and the operation property of Bluetooth system. In case of accessing external internet, use the concept of Mobile IP. IP-based Mobility of Bluetooth Terminal provides efficient and rapid mobility in local area and flexibility on the internet.