Antonios Argyriou

Wireless network coding with improved opportunistic listening

Network coding has been shown to be a very promising technique for increasing the throughput in wireless ad hoc networks. In this paper, we set to define simple extensions for distributed medium access control (MAC) protocols that optimize the transmission of network-coded packets independently of the actual network coding algorithm. The main characteristic of the proposed protocol is that it improves the efficiency of coding decisions and allows verifying the decodability of packets before they are transmitted. The aforementioned goals are achieved first by adopting minor extensions to the channel access scheme, and second by introducing a new algorithm that manages intelligently the data packets that are stored at the MAC queue of each network node. The later algorithm improves the knowledge of a node regarding the available correct coding opportunities by the use of opportunistic acknowledgments, and by maintaining virtual buffers for the overheard data packets. For the proposed protocol, we also develop an analytical performance model that is used for evaluating its performance in conjunction with simulations. Extensive simulations are presented for several ad hoc network topologies that test all the features of the proposed protocol. Significant throughput improvement can be observed when our protocol is compared with network coding schemes that do not exploit the full potential of opportunistic listening.

Cooperative Protocol for Analog Network Coding in Distributed Wireless Networks

The concept of analog network coding (ANC) considers the concurrent transmission of signals over the wireless medium so that they intentionally interfere. Higher network throughput can be achieved with ANC when an intended transmission that a receiver desires to receive is made to interfere with a concurrent transmission of a signal known a priori at the receiver. In this paper, we present a cooperative protocol that exploits ANC. We consider a system with cooperative relaying of overlapped transmissions from two independent users. More specifically, we explore the case that network nodes may allow the transmitted signals to interfere both at the final destination node, and also at an intermediate node that acts subsequently as a relay. The relay employs a cooperative and multicast amplify-and-forward protocol so that the two destinations can use the interfered signals in order to recover the desired packet. We analyze this protocol in terms of the achieved rate and present an algorithm to recover signals from the overlapped transmissions. We study the impact of overlapping in signal transmissions on the throughput of the system. We show that even with considerable overlapping, the throughput under the proposed protocol is better in comparison to an orthogonal amplify-and-forward protocol.

Cross-Layer Error Control for Multimedia Streaming in Wireless/Wireline Packet Networks

In this paper, we propose a cross-layer error control framework for robust and low delay multimedia streaming in tandem-connected IEEE 802.11 wireless LANs and the Internet. For this network configuration, we model the end-to-end delay and packet loss rate as a function of the automatic repeat request (ARQ) and forward error correction (FEC) error control mechanisms that are employed at the application and wireless link layers. The analytical model is used as the basis of a delay-constrained error control algorithm that adapts the protection level at the application and link layers so that the end-to-end packet loss rate is minimized. With extensive simulations, we validate the efficiency of the proposed cross-layer error control methodology for delay-sensitive pre-compressed video streaming.

Streaming H.264/AVC video over the Internet

We propose a novel end-to-end architecture for streaming H.264/AVC (advanced video coding) unicast video over the Internet. The proposed video streaming architecture is based primarily on a new transport layer protocol, the stream control transmission protocol (SCTP). We show that the network-friendly specification of H.264/AVC and the novel technical characteristics of SCTP, when coupled together are able to provide a highly adaptive and flexible system for unicast video streaming. With simulation results we prove (1) that our system is capable of maintaining good perceptual quality under various loss conditions and (2) that the proposed system maintains TCP-friendliness.

Bandwidth aggregation with SCTP

We present a number of modifications to the stream control transmission protocol (SCTP) recently adopted by IETF; they allow bandwidth aggregation over the multiple interfaces of a host. We show that it is possible to implement a number of algorithms for bandwidth aggregation, with only a small number of modifications to the basic SCTP. Our simulation results clearly depict the efficiency of our approach in terms of bandwidth utilization. Furthermore, we implement and evaluate a mechanism for identifying bottlenecks that are shared by flows from the same aggregate connection. Our purpose is to show that SCTP is a good candidate for building a practical protocol for bandwidth aggregation that is fair and supportive of TCP.

Using a new protocol to enhance path reliability and realize load balancing in mobile ad hoc networks

In this paper we introduce a novel end-to-end approach for achieving the dual goal of enhanced reliability under path failures, and multi-path load balancing in mobile ad hoc networks (MANETs). These goals are achieved by fully exploiting the presence of multiple paths in mobile ad hoc networks in order to jointly attack the problems of frequent route failures and load balancing. More specifically, we built a disjoint-path identification mechanism for maintaining multiple routes between two endpoints on top of the Stream Control Transmission Protocol (SCTP), and the Dynamic Source Routing (DSR) protocol. A number of additional modifications are incorporated to the SCTP protocol in order to allow its smooth operation. The proposed approach differs from previously related work since it consists of an entirely end-to-end scheme built on top of a transport layer protocol. We provide both analytical and simulation results that prove the efficiency of our approach over a wide range of mobility scenarios.

Error-Resilient Video Encoding and Transmission in Multirate Wireless LANs

In this paper, we present a cross-layer approach for video transmission in wireless LANs that employs joint source and application-layer channel coding, together with rate adaptation at the wireless physical layer (PHY). While the purpose of adopting PHY rate adaptation in modern wireless LANs like the IEEE 802.11a/b is to maximize the throughput, in this paper we exploit this feature to increase the robustness of wireless video. More specifically, we investigate the impact of adapting the PHY transmission rate, thus changing the throughput and packet loss channel characteristics, on the rate-distortion performance of a transmitted video sequence. To evaluate the video quality at the decoder, we develop a cross-layer modeling framework that considers jointly the effect of application-layer joint source-channel coding (JSCC), error concealment, and the PHY transmission rate. The resulting models are used by an optimization algorithm that calculates the optimal JSCC allocation for each video frame, and PHY transmission rate for each outgoing transport packet. The comprehensive simulation results obtained with the H.264/AVC codec demonstrate considerable increase in the PSNR of the decoded video when compared with a system that employs separately JSCC and PHY rate adaptation. Furthermore, our performance analysis indicates that the optimal PHY transmission rate calculated by the proposed algorithm, can be significantly different when compared with rate adaptation algorithms that target throughput improvement.

Optimizing Data Forwarding from Body Area Networks in the Presence of Body Shadowing with Dual Wireless Technology Nodes

In this paper we are concerned with the problem of data forwarding from a wireless body area network (WBAN) to a gateway when body shadowing affects the ability of WBAN nodes to communicate with the gateway. To solve this problem we present a new WBAN architecture that uses two communication technologies. One network is formed between on-body nodes, and is realized with capacitive body-coupled communication (BCC), while an IEEE 802.15.4 radio frequency (RF) network is used for forwarding data to the gateway. WBAN nodes that have blocked RF links due to body shadowing forward their data through the BCC link to a node that acts as a relay and has an active RF connection. For this architecture we design a network layer protocol that manages the two communication technologies and is responsible for relay selection and data forwarding. Next, we develop analytical performance models of the medium access control (MAC) protocols of the two independent communication links in order to be used for driving the decisions of the previous algorithms. Finally, the analytical models are used for further optimizing energy and delay efficiency. We test our system under different configurations first by performing simulations and next by using real RF traces.

Cross-Layer and Cooperative Opportunistic Network Coding in Wireless Ad Hoc Networks

In this paper, we present a cross-layer framework for optimizing the performance of opportunistic network coding in wireless multihop networks. The target scenario considers a wireless ad hoc network (WANET) with backlogged nodes and with multiple unicast packet flows. Initially, we focus on modeling the expected network-coded throughput individually for each wireless station as a function of parameters at the lower layers, like the maximum number of link-layer retransmissions and the transmission mode at the physical layer (PHY). Based on this analysis, we develop a network-coding algorithm that opportunistically and locally optimizes the expected information content of individual packet transmissions. To address the problem in a multihop setting, we focus on controlling the air time that is consumed by the resulting transmissions of coded packets. More specifically, we devise a distributed-cooperation algorithm that allows nodes to select the optimal PHY transmission mode by also considering the PHY selection of their neighbors. Nodes use only a partial view of the link contention relationships up to their interference range. Compared with existing works on opportunistic network coding and scheduling in ad hoc networks, our approach can yield significant throughput gains without employing complex link-scheduling algorithms.

Real-time and rate-distortion optimized video streaming with TCP

In this paper we explore the use of a new rate-distortion metric for optimizing real-time Internet video streaming with the transmission control protocol (TCP). We lay out the groundwork by developing a simple model that characterizes the expected latency for packets send with TCP-Reno. Subsequently, we develop an analytical model of the expected video distortion at the decoder with respect to the expected latency for TCP, the packetization mechanism, and the error-concealment method used at the decoder. Characterizing the duo protocol/channel more accurately, we obtain a better estimate of the expected distortion and the available channel rate. This better knowledge is exploited with the design of a new algorithm for rate-distortion optimized encoding mode selection for video streaming with TCP. Experimental results for real-time video streaming depict improvement in PSNR in the range of 2dB over metrics that do not consider the behavior of the transport protocol.