Kwangsue Chung

An Energy Efficient Multi-channel MAC Protocol for wireless ad hoc networks

The IEEE 802.11 [1] provides multiple channels for wireless communications at the Physical Layer, but the Medium Access Control (MAC) protocol is only designed for a single channel. If the multiple channels can be exploited by multi-channel MAC protocol, there can be multiple transmissions on different channels. Besides that, the power control algorithm can improve the spatial reuse of wireless channels. In this paper, we combine the multi-channel MAC protocol and the power control algorithm together to exploit multiple channels and improve frequency reuse. The main idea of our proposal is to use IEEE 802.11 Power Saving Scheme (PSM) with different transmission power levels in the ATIM window and the data window. All nodes transmit ATIM/ATIM-ACK/ATIM-RES messages with the maximum power while contending the data channel during the ATIM window, and use the minimum required transmission power in the data window on their negotiated channels. The simulation results show that the proposed E-MMAC improve the performance of the network: aggregate throughput, average delay and energy efficiency.

Video quality adaptation scheme for improving QoE in HTTP adaptive streaming

HTTP (Hypertext Transfer Protocol) adaptive streaming is easy to configure in existing Internet infrastructure. Also, it is typically granted traversal of firewalls and NAT (Network Address Translator). Because of these advantages, HTTP adaptive streaming has been the subject of much attention. However, because conventional video quality adaptation schemes based on bandwidth measurement are too aggressive to respond to short-term network bandwidth variation, frequent changes of video quality occur. Also, because conventional schemes based on bandwidth measurement do not reflect buffer occupancy, buffer underflow that freezes playback occurs. Due to these problems, conventional schemes can hardly guarantee the appropriate level of QoE (Quality of Experience) in HTTP adaptive streaming. In this paper, we propose a client-side video quality adaptation scheme for improving the QoE of HTTP adaptive streaming. To provide seamless and smooth video streaming, the proposed scheme adapts video quality by considering both network bandwidth variation and buffer occupancy of client. We evaluate the performance of the proposed scheme in the ns-3 (Network Simulator-3). Simulation results show that the proposed scheme provides a better QoE than conventional video quality adaptation schemes.

Context-aware multimedia quality adaptation for smart streaming

The proliferation of the Internet technology has contributed to an increasing demand for streaming applications. The adaptation of multimedia streaming content according to context information is essential to supporting these applications. In this paper, we design a context-aware multimedia quality adaptation framework for smart streaming. The proposed framework seamlessly provides multimedia data inputs from multimedia sensors. It also controls the quality of multimedia content according to variations in the context information such as content, device, and network. The implementation results show that our framework adaptively transmits the multimedia content to various mobile devices.

DASH-Based Multi-View Video Streaming System

With the rapid development of electronic and computing technology, multi-view video transmission has attracted significant attention from the research and industrial communities. A multi-view video service provides a user with various viewpoints according to the user’s input. Alongside the recent trend of shifting video streaming service platforms to HTTP adaptive streaming, dynamic adaptive streaming over HTTP (DASH)-based multi-view video services has been widely studied. However, DASH-based multi-view video streaming suffers from high view-switching delay. The delay between a request for view switching and the rendering of the target view adversely affects the quality of experience. This paper provides an analysis of the view-switching delay of DASH-based multi-view video streaming. Based on the analysis, a novel DASH-based multi-view video streaming system is proposed. It can minimize the view-switching delay by employing a buffer control, parallel streaming, and server push schemes. The results obtained from the implementation of this solution show that the proposed system significantly reduces the view-switching delay while guaranteeing the quality of multi-view video.

Short paper: Context-aware adaptive streaming in web of objects environments

The proliferation of various objects and explosive development of the Internet technologies such as Web of Objects (WoO) have contributed to an increasing demand for multimedia streaming applications. The adaptation of multimedia content according to context information is essential to supporting these applications in the WoO environments. In this study, we design a context-aware adaptive streaming framework. The proposed framework seamlessly manages multimedia content inputs from multimedia sensors. It also controls the quality of multimedia content based on the various context information such as content, device, and network. The implementation result shows that our framework adaptively transmits multimedia content to various mobile devices.

Client-side rate adaptation scheme for HTTP adaptive streaming based on playout buffer model

HTTP Adaptive Streaming (HAS) is an adaptive bitrate streaming technique which is able to adapt to the network conditions using conventional HTTP web servers. An HAS player periodically requests pre-encoded video chunks by sending an HTTP GET message. When the downloading a video chunk is finished, the player estimates the network bandwidth by calculating the goodput and adjusts the video quality based on its estimates. However, the bandwidth estimation in application layer is pretty inaccurate due to its architectural limitation. We show that inaccurate bandwidth estimation in rate adaptation may incur serious rate oscillations which is poor quality-of-experience for users. In this paper, we propose a buffer-based rate adaptation scheme which eliminates the bandwidth estimation step in rate adaptation to provide a smooth playback of HTTP-based streaming. We evaluate the performance of the HAS player implemented in the ns-3 network simulator. Our simulation results show that the proposed scheme significantly improves the stability by replacing bandwidth estimation with buffer occupancy estimation.

Dynamic segment duration control for live streaming over HTTP

Due to the prevalence of various mobile devices and the growth of wireless network technologies, HTTP adaptive streaming has become a new trend in video delivery. In HTTP adaptive streaming, the client pulls the video as a sequence of files called media segments from a server and adjusts the video quality. In order to maintain seamless playback with acceptable video quality, the client needs large receive buffers. However, the buffering delay is critical in live streaming. Therefore, it is important to provide the balance between buffering delay and seamless playback. In this paper, we propose a DSDC (Dynamic Segment Duration Control) scheme for live streaming over HTTP. The proposed DSDC scheme determines the segment duration according to the device information and network status. Through the simulation, we prove that our scheme significantly reduce the playback discontinuity while maintaining the low buffer delay.

A client side buffer management algorithm to improve QoE

In networks, streaming of multimedia content is a challenging issue. Video streaming services make up a large proportion of Internet traffic throughout the world. Adaptive streaming allows for dynamical adaptation of the bitrate with varying network conditions, to guarantee the best user experience. Recently, to guarantee a promised quality of experience (QoE), multiple rate adaptive algorithms have been proposed. In this paper, a rate adaptive algorithm is proposed that improves video quality by observing the available throughput and managing the playback buffer. The existing schemes download the segments quickly to avoid playback interruption which may fill the buffer with low quality segments and degrade the user experience. The proposed scheme manages the playback buffer and keeps the buffer filled with high quality segments. Furthermore, the proposed algorithm randomizes the segment request time to mitigate the client’s biased view of network conditions in the presence of competing TCP traffic. The experimental results show that the proposed algorithm significantly improves the video streaming quality.

Adaptive packet transmission scheme to improve video streaming for multi-homed devices

Because of the explosive development of different wireless technologies, mobile users can now access multiple wireless networks simultaneously. In this environment, a multiple path scheduling algorithm can improve the performance of the wireless networks and ensure high quality of video streaming for mobile users. This may not be the case, however, for TCP flows. One key reason is the occurrence of out-of-order packets resulting from different delays in alternative paths. Another is packet loss stemming from the unstable channel status of wireless networks. To better exploit multiple path scheduling for TCP flows, this paper proposes a new scheduling algorithm called Adaptive Packet Transmission Scheme (APTS) for multi-homed devices. Our scheme accurately estimates the available bandwidth of wireless networks using a TCP-Friendly Rate Control for Wireless Networks (TFRC-WN) scheme. APTS also distributes TCP packets to the multiple paths simultaneously according to the estimated available bandwidth. Our scheme effectively reduces the number of out-of-order packets by predicting the receiving sequences. Through simulation results, we prove that our scheme improves the performance of TCP and the video quality of mobile users.

Content-aware rate adaptation scheme to improve stability in HTTP Adaptive Streaming

HTTP-based adaptive streaming (HAS) has recently been widely deployed on the Internet. In the HAS approach, a video content is encoded at multiple bitrates and the encoded video content is segmented into small parts of fixed durations. The HAS client requests a video segment, and stores it in the playout buffer. Many studies have shown a robust rate adaptation algorithm is critical to ensuring quality-of-experience in HAS systems. However, most existing algorithms use a poorly designed bandwidth estimation method to adjust video bitrates. In this paper, we propose a novel content-aware rate adaptation algorithm that improves stability of the HAS system. In our method, the playout buffer is modeled with content characteristics. Different from previous works, we propose to adapt video bitrates based on the variance in playout buffer length, rather than static buffer information. We evaluate the performance of the proposed algorithm by simulation and subjective tests. Through extensive simulations, we demonstrate that the proposed scheme achieves very high quality smoothness, even under variations of network bandwidth.