Yeonchul Shin - Academia.edu (original) (raw)

Papers by Yeonchul Shin

2018 15th Annual IEEE International Conference on Sensing, Communication, and Networking (SECON)

Recently, WiFi has become irreplaceable wireless technology to support increasing mobile applicat... more Recently, WiFi has become irreplaceable wireless technology to support increasing mobile applications and data traffic. While today's smartphone users frequently use WiFi on the move, smartphone does not perform WiFi handoff to nearby access points (APs) even if signal quality is severely degraded. Such undesired operation of smartphone is known as sticky client problem. In this work, we focus on resolving sticky client problem through fast WiFi handoff. First, we analyze the causes of sticky client problem based on experiments with commercial Android smartphones by focusing on WiFi scanning and handoff operations. Note that smartphones and state-of-the-art APs are equipped with Bluetooth Low Energy (BLE), we propose a practical solution, called BLEND, utilizing BLE to enable fast WiFi handoff. Smartphone acquires information about nearby APs through BLE advertising packet sent by APs, and then judiciously performs WiFi handoff. We implement BLEND on Android smartphones and demonstrate that BLEND achieves up to 61% and 111% higher throughput and video bitrate, respectively, compared with a commercial Android application. We also validate that BLEND operates on smartphone with negligible energy overhead.

IEEE INFOCOM 2017 - IEEE Conference on Computer Communications

Multicast is a major solution in supporting the explosive growth of the wireless video traffic de... more Multicast is a major solution in supporting the explosive growth of the wireless video traffic demand. Also, power saving is a key technology to extend battery life of mobile devices. To meet both purposes, IEEE 802.11 wireless local area network (WLAN) supports power save mode (PSM) for station (STA) while receiving multicast packets. According to recent studies, off-the-shelf chipsets configured to use PSM show un-desired functions, thus resulting in many multicast packet losses. From our extensive measurement, we also verify degradation of multicast performance with widely-used off-the-shelf chipsets using PSM, and present previously-unknown undesired functions. Without modification of the chipsets, STA in PSM cannot enjoy reliable multicast service. Given this, we develop a practical and readily-applicable AP-side solution, called ACT-AP, which avoids multicast packet losses by preventing STA from operating in PSM. Our prototype implementation with off-the-shelf chipsets demonstrates that ACT-AP improves packet delivery ratio by up to 216% with little additional protocol overhead. To our best knowledge, ACT-AP is the first practical effort to support multicast to real devices with undesired functions in PSM.

2017 14th Annual IEEE International Conference on Sensing, Communication, and Networking (SECON)

Multi-rate forward erasure correction (FEC)-applied wireless multicast enables reliable and effic... more Multi-rate forward erasure correction (FEC)-applied wireless multicast enables reliable and efficient video multicast with intelligent selection of physical (PHY) layer data rate and FEC rate. The optimal PHY/FEC rates depend on the cause of the packet losses. However, previous approaches select the PHY/FEC rates by considering only channel errors even when interference is also a major source of packet losses. We propose InFRA, an interference-aware PHY/FEC rate adaptation framework that (i) infers the cause of the packet losses based on received signal strength indicator (RSSI) and cyclic redundancy check (CRC) error notifications, and (ii) determines the PHY/FEC rates based on the cause of packet losses. Our prototype implementation with off-the-shelf chipsets demonstrates that InFRA enhances the multicast delivery under various network scenarios. InFRA enables 2.3x and 1.8x more nodes to achieve a target video packet loss rate with a contention interferer and a hidden interferer, respectively, compared with the state-of- the-art PHY/FEC rate adaptation scheme. To our best knowledge, InFRA is the first work to take the impact of interference into account for the PHY/FEC rate adaptation.

2016 IEEE International Conference on Communications (ICC), 2016

In video multicast, it is a challenging task to deliver video at a satisfactory level to multiple... more In video multicast, it is a challenging task to deliver video at a satisfactory level to multiple receivers with different channel quality and different battery capacities. In order to resolve such receiver heterogeneity, we propose a video multicast system that integrates scalable video coding (SVC) and flexible multicast service (FMS). The system is designed to transmit the base layer (BL) and the enhancement layer (EL) of an SVC-encoded video at different delivery traffic indication maps (DTIMs) such that each receiver can freely select either energy-intensive high quality video or energy-saving baseline quality video. Moreover, we enhance reliability by adding a functionality of intra-flow network coding (NC). As a measure of user satisfaction, we develop a multi-attribute utility model, and then, based on the utility model, we develop a Stakelberg game-based optimization framework to determine modulation and coding scheme (MCS) and the number of NC-generated packets for each layer. Through simulations, we confirm that the proposed scheme achieves higher user satisfaction by exhibiting performance gain of 16.4% to 47% over the legacy 802.11 scheme.

2015 IEEE Global Communications Conference (GLOBECOM), 2015

The Journal of Korean Institute of Communications and Information Sciences, 2015

Random linear network coding (RLNC) is widely employed to enhance the reliability of wireless mul... more Random linear network coding (RLNC) is widely employed to enhance the reliability of wireless multicast. In RLNC encoding/decoding, Galois Filed (GF) arithmetic is typically used since all the operations can be performed with symbols of finite bits. Considering the architecture of commercial computers, the complexity of arithmetic operations is constant regardless of the dimension of GF , if  is smaller than 32 and pre-calculated tables are used for multiplication/division. Based on this, we show that the complexity of RLNC inversely proportional to . Considering additional overheads, i.e., the increase of header length and memory usage, we determine the practical value of . We implement RLNC in a commercial computer and evaluate the codec throughput with respect to the type of the tables for multiplication/division and the number of original packets to encode with each other.

2011 Third International Conference on Ubiquitous and Future Networks (ICUFN), 2011

Video multicast service is becoming one of the most important applications over WiFi, due to the ... more Video multicast service is becoming one of the most important applications over WiFi, due to the increasing popularity of WiFi for multimedia communication. On the one hand, energy efficient operation is required to WiFi technology due to the limited battery power of most WiFi-equipped devices. In this paper, we empirically study the video multicast operation, especially, along with power management operation in two aspects: (1) whether commercial WiFi devices correctly operate as defined in IEEE 802.11 standard and (2) what problem the standard-compliant operation can induce. From our experimental results, we first figure out that some of commercial WiFi devices do not follow the standard with respect to the power saving operation, and this noncompliance worsens interoperability. We also find that the standard-compliant operation may cause significant delay of voice over IP (VoIP) traffic, when video multicast coexists with VoIP. Through this experimental study, we provide the guidelines for energy-efficient video multicast service.

IEEE Communications Magazine, 2014

Wi-Fi has become an essential wireless technology in our daily lives, although the original inten... more Wi-Fi has become an essential wireless technology in our daily lives, although the original intention of its introduction was to replace the Ethernet cable. In this article, we outline the most remarkable features introduced during its ongoing technological evolution in terms of three major directions, i.e., throughput enhancement, long-range extension, and greater ease of use. By stitching these advanced features together, we also envision a promising future that Wi-Fi technology will bring us in terms of the spectrum heterogeneity, seamless service provisioning, and possible relations with cellular networks.

2013 Fifth International Conference on Ubiquitous and Future Networks (ICUFN), 2013

In enterprise wireless networks where Access Points (APs) are densely deployed, the importance of... more In enterprise wireless networks where Access Points (APs) are densely deployed, the importance of Dynamic Channel Assignment (DCA) is more emphasized since the network is under severe inter-cell interference. In this paper, we propose Contention Factor (CF) as a metric for DCA in enterprise wireless networks. The metric is designed to minimize the performance degradation by separating collision domains of APs. Simulation results demonstrate that the proposed metric precisely predicts the network performance so that DCA utilizing the proposed metric improves the overall network throughput.

Proceeding of IEEE International Symposium on a World of Wireless, Mobile and Multimedia Networks 2014, 2014

Various packet-based simulation tools (e.g., NS-3) have been employed for design, validation, and... more Various packet-based simulation tools (e.g., NS-3) have been employed for design, validation, and evaluation of new protocols for WiFi networks since they offer cost efficiency, scalability, and reproducibility. These benefits come, however, at the expense of lack of realism compared to live testbed experiments. This is attributed in a major part to the difficulty of capturing detailed characteristics of channel dynamics, bit-level protocol specification (PHY layer), and application/user behaviors in a high-fidelity manner. The performance gap predicted by simulation and live testbed becomes even more pronounced when one considers a wide diversity of device characteristics and the way each device is used by end users. For example, smartphones generally show worse WiFi performance than other WiFi devices (e.g., laptops and tablets) because smartphones suffer from additional signal loss due to hand-grips and the low antenna gains of their embedded antennas. The goal of this study is to significantly close the gap by incorporating survey- and measurement-based smartphone WiFi characteristics and realistic hand-grip models into traditional WiFi network simulators (NS-3 in this study). The enhanced WiFi simulation tool's performance prediction capability is validated through an comparative study between testbed experiments and simulations.

2019 IEEE 16th International Conference on Mobile Ad Hoc and Sensor Systems (MASS)

Video multicast over wireless local area network (WLAN) has been gaining attraction for applicati... more Video multicast over wireless local area network (WLAN) has been gaining attraction for applications sharing a venue-specific common video with multiple users. However, wireless multicast is limited by a receiver that has the weakest communication link to the source. Collaborative relaying could overcome this challenge by enabling selected receiver nodes to relay the packets from the source to other receivers. We propose EV-CAST, an interference and energy-aware video multicast system using collaborative relays, which entails (i) online topology management based on interference-aware link characterization, (ii) joint selection of relay nodes and transmission parameters, and (iii) polling-based relay protocol. Our proposed algorithm, the core of EV-CAST, judiciously selects the relay nodes and transmission parameters in consideration of interference, battery status, and spatial reuse. Our prototype-based experiment results demonstrate that EV-CAST enhances video multicast delivery under various network scenarios. EV-CAST enables 2x more nodes to achieve a target video packet loss ratio with 0.59x shorter airtime than the state-of-the-art video multicast scheme.