Hyong-Woo Lee

Bio: Hyong-Woo Lee is an academic researcher from Korea University. The author has contributed to research in topics: Throughput & Random access. The author has an hindex of 10, co-authored 72 publications receiving 469 citations.

Performance analysis of sleep mode operation in IEEE 802.16e

Abstract: The paper investigates the queueing behavior of the sleep mode operation in IEEE 802.16e for conserving the power of an mobile station (MS) in terms of the dropping probability and the mean waiting times of packets in the base station (BS) queue. In the sleep mode, when an MS wakes up at the end of each sleep interval and there is traffic addressed to it, this is notified in the listening interval immediately following the sleep interval. Otherwise, an MS again enters the sleep mode with a sleep interval which is double the length of the previous one. We modeled this sleep mode operation as M/GI/1/N with multiple vacations whose periods depend on the previous one. Our work may be a rough guide to understanding the BS queueing behavior according to parameters such as the minimum and maximum sleep interval, the BS queue size and the arrival rate of packets at a BS.

RFID MAC Performance Evaluation Based on ISO/IEC 18000-6 Type C

Abstract: This paper evaluates a new RFID reservation MAC protocol that utilizes tree based collision avoidance Performance evaluation is conducted for tag read latency and read efficiency as a function of link parameters defined in ISO/IEC 18000-6 Type C standard

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

Abstract: 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

An adaptive QoS provisioning distributed call admission control using fuzzy logic control

Abstract: Faced with limited radio spectrum and increased demand for broadband multimedia services in an advanced wireless network, it is becoming important to carefully manipulate handoff calls as well as new calls. In particular, there is a need for well designed call admission control (CAC) schemes that enable one to provide guaranteed QoS while efficiently utilizing the scarce radio spectrum. There have been CAC methods called distributed call admission control (DCAC) which take into consideration the traffic pattern in its adjacent cells, in addition to that in the cell where a new call request is made. However, DCAC tends to be conservative in QoS provisioning to the point that it excessively restricts access of new calls. We propose an adaptive algorithm named fuzzy logic controller for DCAC (FDCAC) which is an adaptive version of DCAC. We show by the simulation that it is possible to manage radio spectrum more flexibly than DCAC while guaranteeing the required QoS. The performance of the proposed algorithm in terms of new call blocking probability, handoff dropping probability, and channel utilization is analyzed and compared with that of previously known algorithm.

Device-to-device-based heterogeneous radio access network architecture for mobile cloud computing

Abstract: The emerging heterogeneous mobile network architecture is designed for an increasing amount of traffic, quality requirements, and new mobile cloud computing demands. This article proposes a hierarchical cloud computing architecture to enhance performance by adding a mobile dynamic cloud formed by powerful mobile devices to a traditional general static cloud. A mobile dynamic cloud is based on heterogeneous wireless architecture where device-to-device communication is used for data transmission between user devices. The main advantage of the proposed architecture is an increase in overall capacity of a mobile network through improved channel utilization and traffic offloading from Long Term Evolution-Advanced to device-to-device communication links. Simulations show that the proposed architecture increases the capacity of a mobile network by up to 10 percent depending on the conditions and amount of offloaded data. The offloading probability is also evaluated by taking into consideration the number of devices in the cloudlet and the content matching values. We have gained insight into how content similarity affects offloading probability much more than the number of devices in a cloudlet.

RFID: From Supply Chains to Sensor Nets

Abstract: The next generation internet will be the internet of things (and not just of computing devices like PCs, PDAs); this is presumed to be enabled by integrating simple computing plus communications capabilities into common objects of everyday use. Radio-frequency identification (RFID) is a compelling technology for creation of such pervasive sensor networks due to its potential for ubiquitous, low-cost/low-maintenance use. However, the current drivers for RFID deployment emphasize supply chain management using passive tags, implying that RFID sensor nets require advances beyond the components and system designs aimed at supply chain applications. This work provides a glimpse of how this may be achieved.

Energy-Efficient Multicasting of Scalable Video Streams Over WiMAX Networks

Abstract: The Multicast/Broadcast Service (MBS) feature of mobile WiMAX network is a promising technology for providing wireless multimedia, because it allows the delivery of multimedia content to large-scale user communities in a cost-efficient manner. In this paper, we consider WiMAX networks that transmit multiple video streams encoded in scalable manner to mobile receivers using the MBS feature. We focus on two research problems in such networks: 1) maximizing the video quality and 2) minimizing energy consumption for mobile receivers. We formulate and solve the substream selection problem to maximize the video quality, which arises when multiple scalable video streams are broadcast to mobile receivers with limited resources. We show that this problem is NP-Complete, and design a polynomial time approximation algorithm to solve it. We prove that the solutions computed by our algorithm are always within a small constant factor from the optimal solutions. In addition, we extend our algorithm to reduce the energy consumption of mobile receivers. This is done by transmitting the selected substreams in bursts, which allows mobile receivers to turn off their wireless interfaces to save energy. We show how our algorithm constructs burst transmission schedules that reduce energy consumption without sacrificing the video quality. Using extensive simulation and mathematical analysis, we show that the proposed algorithm: 1) is efficient in terms of execution time, 2) achieves high radio resource utilization, 3) maximizes the received video quality, and 4) minimizes the energy consumption for mobile receivers.

Packet Switching in a Multiaccess Broadcast Channel: Performance Evaluation

Abstract: In this paper, the rationale and some advantages for multiaccess broadcast packet communication using satellite and ground radio channels are discussed. A mathematical model is formulated for a slotted ALOHA random access system. Using this model, a theory is put forth which gives a coherent qualitative interpretation of the system stability behavior which leads to the definition of a stability measure. Quantitative estimates for the relative instability of unstable channels are obtained. Numerical results are shown illustrating the trading relations among channel stability, throughput, and delay. These results provide tools for the performance evaluation and design of an uncontrolled slotted ALOHA system. Adaptive channel control schemes are studied in a companion paper.