Hulya Seferoglu

Opportunistic network coding for video streaming over wireless

In this paper, we study video streaming over wireless networks with network coding capabilities. We build upon recent work, which demonstrated that network coding can increase throughput over a broadcast medium, by mixing packets from different flows into a single packet, thus increasing the information content per transmission. Our key insight is that, when the transmitted flows are video streams, network codes should be selected so as to maximize not only the network throughput but also the video quality. We propose video-aware opportunistic network coding schemes that take into account both aspects, namely (i) the decodability of network codes by several receivers and (ii) the distortion values and playout deadlines of video packets. Simulation results show that our schemes significantly improve both video quality and throughput.

I 2 NC: Intra- and inter-session network coding for unicast flows in wireless networks

In this work, we are interested in improving the performance of constructive network coding schemes in lossy wireless environments. We propose I2NC - an approach that combines inter-session and intra-session network coding and has two strengths. First, the error-correcting capabilities of intra-session network coding make our scheme resilient to loss. Second, redundancy allows intermediate nodes to operate without knowledge of the decoding buffers of their neighbors. Based only on the knowledge of the loss rates on the direct and overhearing links, intermediate nodes can make decisions for both intra-session (i.e., how much redundancy to add in each flow) and inter-session (i.e., what percentage of flows to code together) coding. Our approach is grounded on a network utility maximization (NUM) formulation of the problem. We propose two practical schemes, I2NC-state and I2NC-stateless, which mimic the structure of the NUM optimal solution. We also address the interaction of our approach with the transport layer. We demonstrate the benefits of our schemes through simulation in GloMoSim.

Video-aware opportunistic network coding over wireless networks

In this paper, we study video streaming over wireless networks with network coding capabilities. We build upon recent work, which demonstrated that network coding can increase throughput over a broadcast medium, by mixing packets from different flows into a single packet, thus increasing the information content per transmission. Our key insight is that, when the transmitted flows are video streams, network codes should be selected so as to maximize not only the network throughput but also the video quality. We propose video-aware opportunistic network coding schemes that take into account both the decodability of network codes by several receivers and the importance and deadlines of video packets. Simulation results show that our schemes significantly improve both video quality and throughput. This work is a first step towards content-aware network coding.

Cooperative video streaming on smartphones

Video applications are increasingly popular over smartphones. However, in current cellular systems, the downlink data rate fluctuates and the loss rate can be quite high. We are interested in the scenario where a group of smartphone users, within proximity of each other, are interested in viewing the same video at the same time and are also willing to cooperate with each other. We propose a system that maximizes the video quality by appropriately using all available resources, namely the cellular connections to the phones as well as the device-to-device links that can be established via Bluetooth or WiFi. Key ingredients of our design are: (i) the cooperation among users, (ii) network coding, and (iii) exploiting broadcast in the mobile-to-mobile links. Our approach is grounded on a network utility maximization formulation of the problem. We present numerical results that demonstrate the benefit of our approach, and we implement a prototype on android phones.

Network coding-aware queue management for TCP flows over coded wireless networks

In this paper, we are interested in improving the performance of TCP flows over wireless networks with a given constructive intersession network coding scheme. We are motivated by the observation that TCP does not fully exploit the potential of the underlying network coding opportunities. In order to improve the performance of TCP flows over coded wireless networks, without introducing changes to TCP itself, we propose a network-coding aware queue management scheme (NCAQM) that is implemented at intermediate network coding nodes and bridges the gap between network coding and TCP rate control. The design of NCAQM is grounded on the network utility maximization (NUM) framework and includes the following mechanisms. NCAQM: 1) stores coded packets at intermediate nodes in order to use the buffer space more efficiently; 2) determines what fraction of the flows should be coded together; and 3) drops packets at intermediate nodes so that it matches the rates of parts of different TCP flows that are coded together. We demonstrate, via simulation, that NCAQM significantly improves TCP throughput compared to TCP over baseline queue management schemes.

Network coding-aware rate control and scheduling in wireless networks

In this paper, we study rate control and scheduling over wireless networks with intersession network coding, as a utility maximization problem. We demonstrate that making rate control and scheduling aware of the underlying network coding increases throughput. The key intuition is that network coding introduces new network coded flows and eventually new conflicts between nodes, which should be taken into account both in rate control and in scheduling. We compare the network coding-aware to the network coding-unaware schemes in two cases: (i) optimal control and (ii) practical, suboptimal control. Our main goal is to make the case for network coding-aware rate control and scheduling, via simulation of representative examples. Along the way, we also propose a practical scheme that approximates the optimal control.

Delay-Optimized Network Coding for Video Streaming over Wireless Networks

In this paper, we study delay-optimized network coding for video streaming over wireless networks with network coding capabilities. It has been demonstrated that network coding can increase throughput in wireless networks, by mixing packets from different flows into a single packet, thus increasing the information content per transmission. However, network coding potential is not always fully exploited in this setting, because there may not be enough packets at intermediate nodes to do network coding due to bursty nature of transport protocols, packet losses, and difference in path delays. One way to deal with this problem is to delay packets at intermediate nodes in order to create more network coding opportunities. However, introducing large or varying delays eventually hurts video traffic, which requires low delay and delay jitter. In this paper, we study this tradeoff in coded wireless networks, and we propose a packet delaying scheme at intermediate nodes to maximize video quality.

Diff-Max: Separation of routing and scheduling in backpressure-based wireless networks

Backpressure routing and scheduling, with throughput-optimal operation guarantee, is a promising technique to improve throughput in wireless multi-hop networks. Although backpressure is conceptually viewed as layered, the decisions of routing and scheduling are made jointly, which imposes several challenges in practice. In this work, we present Diff-Max, an approach that separates routing and scheduling and has three strengths: (i) Diff-Max improves throughput significantly, (ii) the separation of routing and scheduling makes practical implementation easier by minimizing cross-layer operations; i.e., routing is implemented in the network layer and scheduling is implemented in the link layer, and (iii) the separation of routing and scheduling leads to modularity; i.e., routing and scheduling are independent modules in Diff-Max, and one can continue to operate even if the other does not. Our approach is grounded in a network utility maximization (NUM) formulation and its solution. Based on the structure of Diff-Max, we propose two practical schemes: Diff-subMax and wDiff-subMax. We demonstrate the benefits of our schemes through simulation in ns-2.

MicroCast: Cooperative Video Streaming Using Cellular and Local Connections

We consider a group of mobile users, within proximity of each other, who are interested in watching the same online video. The common practice today is that each user downloads the video independently on her mobile device using her own cellular connection, which wastes access bandwidth and may also lead to poor video quality. We propose a novel cooperative system where each mobile device uses simultaneously two network interfaces: (i) cellular to connect to the video server and download parts of the video and (ii) WiFi to connect locally to all other devices in the group to exchange those parts. Devices cooperate to efficiently utilize all network resources and to adapt to varying wireless network conditions. In the local WiFi network, we exploit overhearing, which we further combine with network coding. The end result is savings in cellular bandwidth and improved user experience. We follow a complete approach, from theory to practice. First, we formulate the problem using a network utility maximization (NUM) framework, decompose the problem, and provide a distributed solution. Then, based on the structure of the NUM solution, we design a system called MicroCast, and we implement a prototype as an Android application. We provide both simulation results of the NUM solution and experimental evaluation. We demonstrate that the proposed approach brings significant performance benefits (namely, faster download on the order of the group size) without battery penalty.

Congestion state-based dynamic FEC algorithm for media friendly transport layer

TCP-friendliness has been adopted as the most important property for the design of new media-specific transport layers in the Internet. The TCP protocol is mainly concerned with achieving as much throughput as possible while preventing long-term congestion. Various TCP protocol designs do this by inducing brief episodes of network congestion, measuring it, then reducing the offered load quickly to remove the congestion. Media flows, on the other hand, are very sensitive to even brief episodes of congestion. The question therefore arises: how can we protect media flows against TCP-induced network congestion? In this paper, we focus on combining the TCP Friendly Rate Control (TFRC) protocol with Forward Error Correction (FEC) to achieve such protection. We observe that FEC methods that solely rely on loss statistics generate significant overhead in terms of the redundant parity packets transmitted over the network. Accordingly, we investigate the loss and delay characteristics in several TCP-induced congestion scenarios in order to identify potential periods of increased congestion and apply FEC protection during those periods judiciously. We find out that indeed efficient models can be developed and incorporated into a dynamic FEC framework which can achieve substantially better overhead vs. reliability tradeoff (e.g., up to 60% improvement at high reliability region) than an FEC approach that uses fixed coding rate to satisfy a given reliability.