Youngkyu Choi

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Automatic Repeat reQuest (ARQ) is one of the effective techniques against the transmission error at the medium access control (MAC) layer. An erroneous MAC protocol data unit (MPDU) can be typically retransmitted within a given limit. In order to improve the IP-level performance, which directly affects the user-perceived quality-of-service (QoS), we propose(More)
— This paper considers two issues arising in an integrated IEEE 802.16e/802.11 network: 1) finding a possible network, which mobile station (MSTA) can switch to, and 2) making a decision whether to execute a vertical handoff (VHO). For this purpose, we propose that 802.16e Base Stations (BSs) periodically broadcast the information about the density of(More)
In this paper, we evaluate and enhance the performance of a Forward Error Correction (FEC) scheme for IEEE 802.11 Medium Access Control (MAC). A novel retransmission combining technique is proposed to enhance the performance of the MAC-level FEC scheme. We also identify the problem with the IEEE 802.11a physical (PHY) layer when it is used with the(More)
A wireless LAN (WLAN)-based Internet service, called NESPOT, of Korea Telecom (KT), the biggest telecommunication and Internet service company in Korea, has been operational since early 2002. As the numbers of subscribers and deployed access points (APs) increase, KT has been endeavoring to improve its service quality as well as the network management. In(More)
—Femto BS (Base Station) is emerging as a key technology to secure the coverage and capacity in indoor environments. However, since the existing macrocell network is overlaid on femtocell networks utilizing the same set of frequency channels, femtocell networks can originate severe co-channel interference to the macrocell network unless the femtocell(More)
We consider an issue arising in a vertical handoff (VHO) between IEEE 802.16e and IEEE 802.11 networks, i.e., how efficiently the scanning operation can be controlled to find a target wireless local area network (WLAN) access point (AP). For this purpose, we propose that the 802.16e Base Stations (BSs) periodically broadcast the information about the(More)
The energy consumption in transmitting an information bit, i.e., energy-per-bit, has been known to decrease monotonically as the transmission time increases [1]. However, when considering the power amplifier (PA) characteristics, we learn that the energy-per-bit starts to increase as the transmission time becomes long over a certain threshold. This is(More)
The ideal design for VoIP should be able to maximize the number of concurrent users while each admitted user enjoys the satisfactory quality of voice communication. In a recent packet-based wireless system, the quality-of-service (QoS) provisioning for VoIP raises several challenging issues including correlated delay performance among users and the(More)