• Journal of Advanced Navigation Technology
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• v.14 no.2
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• pp.198-205
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• 2010

Any user in Ubiquitous environments have to be able to access networks in anywhere and anytime. Thus interests and researches are increasing. In this paper, we propose an interface selection scheme that adaptively utilizes a proper interface, as the wireless channel condition changes, instead of utilizing only one interface while the node is in move. The proposed scheme can determine which interface would be the most proper one by measuring data rate, packet error rate (PER), and end-to-end delay of each interface. From the simulation results, it is verified that the proposed scheme is able to enhance packet transmission about 20% better.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.12
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• pp.4269-4292
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• 2014

Currently, increasing numbers of access points (AP) are being deployed in enterprise offices, campuses and municipal downtowns for flexible Internet connectivity, but most of these access points are idle or redundant most of the time, which causes significant energy waste. Therefore, with respect to power conservation, applying energy efficient strategies in WIFI networks is strongly advocated. One feasible method is dynamically managing network resources, particularly APs, by powering devices on or off. However, when an AP is powered on, the device is initialized through a long boot time, during which period clients cannot be associated with it; therefore, the network performance would be greatly impacted. In this paper, based on a global view of an entire WLAN, we propose an AP selection technology, known as Temporary Access Selection (TAS). The criterion of TAS is a fusion metric consisting of two evaluation indexes which are based on throughput and battery life, respectively. TAS is both service and clients' preference specific through balancing the data rate, battery life and packet size. TAS also works well independently in traditional WLANs in which no energy efficient strategy is deployed. Moreover, this paper demonstrates the feasibility and performance of TAS through experiments and simulations with Network Simulator version 3 (NS3).

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.3
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• pp.652-663
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• 1996

In this paper, we analyze the blocking probability of a call in a PC communication network. In a PC communication network, a call generated from the PSTN (public switched telephone network) requests the connection to the ICPS(information communication processing system) which interconnects the the PSTN and the PSDN(packet switched data network). Then, as a second step, a packet call is requested to the specific service database attached in the PSDN. The call blocking probabilies are analyzed for these two interface points, the PSTN interface ports of the ICPS and the PSDN interface link of the database. We also present some numerical results to show the effects of the system parameters on the performance of the network. The results show the effects of the capacity of each interface point on the performance point.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.47 no.10
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• pp.27-35
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• 2010

In wireless packet networks, energy and wireless resource efficiency is critical issue to addressed for wide deployment. To achieve the both goals of saving the mobile station's energy and increasing the wireless capacity, transmission power control is introduced to wireless packet networks. In the transmission power controled networks, it is not deeply studied on unfairness among transmissions with different power levels that reaches starvation. Through the performance analysis, this paper explains the throughput unfairness of high power transmission with the unfair media access probability owing to the contending node number difference and proposes a simple PHY-MAC cross layer approach.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.12
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• pp.2871-2877
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• 2014

Real-time communication and diversification of multimedia application services using high-capacity data over the Internet demand high speed connection, and real-time and high-speed access internet service such as multimedia make Internet traffic increase rapidly. Meanwhile, QoS (Quality of Service) of internet service is not satisfied. In this situation, ISP (Internet Service Provider) has been required to improve service quality and extend network according to the user's needs. This request includes issue of extending network focused on increasing router and the number of routing table as well as simply extending bandwidth.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.8B
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• pp.1333-1340
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• 2000

This paper shows that the Kronecker sequence, the rapid acquisition spreading code, can be used in packet wireless data communication systems. The general properties of the Kronecker sequence such as construction and correlation characteristics are described, and it is shown that the Kronecker sequence can use a partial-period correlation for a faster acquisition. Based on above Properties, it can be expected that the Kronecker sequence can be used in packet communication systems because the probability of false alarm for the Kronecker sequence is lower and flatter(that is, less sensitive to Ec/No variations) than that for the PN sequence under the assumption that both sequences have the same acquisition time.

• Journal of Communications and Networks
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• v.13 no.1
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• pp.70-76
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• 2011

This paper presents the unified user equipment (UE) baseband modulation and demodulation (modem) hardware platform architecture to support multiple radio access technologies. In particular, this platform selectively supports two systems; one is HEDGE system, which is the combination of third generation partnership project (3GPP) Release 7 high speed packet access evolution (HSPA+) and global system for mobile communication (GSM)/general packet radio service (GPRS)/enhanced data rates for GSM evolution (EDGE), while the other is LEDGE system, which is the combination of 3GPP Release 8 long term evolution (LTE) and GSM/GPRS/EDGE. This is done by applying the flexible pin multiplexing scheme to a hardwired pin mapping process. On the other hand, to provide stable connection, high portability, and high debugging ability, the stacking structure is employed. Here, a layered board architecture grouped by functional classifications is applied instead of the conventional one flatten board. Based on this proposed configuration, we provide a framework for the verification step in wireless cellular communications. Also, modem function/scenario test and inter-operability test with various base station equipments are verified by system requirements and scenarios.

• Journal of Communications and Networks
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• v.13 no.2
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• pp.160-166
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• 2011

In u-healthcare services based on wireless body sensor networks, reliable connection is very important as many types of information, including vital signals, are transmitted through the networks. The transmit power requirements are very stringent in the case of in-body networks for implant communication. Furthermore, the wireless link in an in-body environment has a high degree of path loss (e.g., the path loss exponent is around 6.2 for deep tissue). Because of such inherently bad settings of the communication nodes, a multi-hop network topology is preferred in order to meet the transmit power requirements and to increase the battery lifetime of sensor nodes. This will ensure that the live body of a patient receiving the healthcare service has a reduced level of specific absorption ratio (SAR) when exposed to long-lasting radiation. We propose an efficientmethod for delivering delay-intolerant data packets over multiple hops. We consider forward error correction (FEC) in an erasure correction mode and develop a mathematical formulation for packet-level scheduling of delay-intolerant FEC packets over multiple hops. The proposed method can be used as a simple guideline for applications to setting up a topology for a medical body sensor network of each individual patient, which is connected to a remote server for u-healthcare service applications.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.10B
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• pp.1168-1174
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• 2011

The IEFT has recently considered to provide flow mobility for multi-interface MN in the PMIPv6. In this paper, we proposed an extended BCE of the LMA and a novel mechanism for flow mobility of PMIPv6. With our proposal BCE and mechanism, the LMA can route packets by the flow label and hence packet loss during handover can be eliminated. Also, to validate our flow mobility scheme, we designed and implemented the PMIPv6 packet data unit and database of both LMA and MAG, and configured a testbed for flow mobility in PMIPv6. And the support of flow mobility was configured with the network connectivity test in our testbed. According to the Wireshark results, we can see that our proposed scheme works wells for flow mobility in PMIPv6.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.5C
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• pp.485-497
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• 2009

In this paper, we described DVB-S2 system for mobility. cross layer coding technique are needed to maintain the performance in deep fading channel. Cross layer coding is divided into two kinds of level. First level is Physical layer coding and, second layer is link layer or upper layer coding. Fixed on DVB-S2 short frame coding method as a physical layer, we simulated the various coding method as an upper layer coding. Furthermore, we analyzed the performance of each coding method on according to mobile vehicle speed, data rate, interleaving memory size, and IP packet size.