In recent years, Cognitive Radio (CR) technology has received significant attention from the research community as it enables on-demand spectrum utilization, based on the requests of the end-users. An interesting application area of CR technology is Vehicular Ad Hoc Networks (VANETs). In such networks, several innovative services and applications based on inter-vehicular communication have strict requirements in terms of bandwidth and delay, which might not be guaranteed by a fixed spectrum allocation paradigm. In this paper, we propose two key contributions pertaining to CR-VANETs: (i) an experimental study of the spectrum availability and sensing accuracy in a moving vehicle and (ii) a collaborative spectrum management framework (called Cog-V2V), which allows the vehicles to share spectrum information, and to detect spectrum opportunities in the licensed band. As part of this framework, we design a collaborative sensing and decision algorithm, enabling the vehicles to share spectrum information and to know in advance the spectrum availability at future locations along their motion paths. The simulation results, produced through a novel integrated simulation platform for CR networks, reveal significant improvements of Cog-V2V in sensing accuracy and pair-wise communication performance compared to classical fixed spectrum approaches.

Cooperative spectrum management in cognitive Vehicular Ad Hoc Networks

Recently, the IEEE 1609.4 Standard for Wireless Access in Vehicular Environments (WAVE) has been proposed to enhance the performance of vehicular networks with multi-channel operations that allow for the coexistence of safety-related and non-safety related vehicular applications. However, while the benefits of the multi-channel approach are clear, the impact of the IEEE 1609.4 channel scheduler on the performance of delay-constrained vehicular applications remains to be well explored by researchers. At present, the evaluation of 1609.4-based Vehicular Ad Hoc Networks (VANETs) constitutes an open issue due to the lack of simulation tools that can provide a complete modeling of the IEEE WAVE 802.11p/1609.4 stack. In this paper, we provide three key contributions pertaining to multi-channel VANETs. First, we describe our implementation of the IEEE 1609.4 protocol in the ns2 simulator, and we detail its current integration with the existing ns2 implementation of the 802.11p MAC protocol. Second, using our simulation model we propose an evaluation study of 1609.4-based VANETs, and we show that the tight channel synchronization issues foreseen by the protocol might have a dramatic impact on the performance of safety-related applications with strict delivery ratio and delay requirements. Third, we propose two new enhancements for the WAVE protocol stack to favor the dissemination of safety messages in multi-channel VANETs. The suggested algorithms are shown to greatly improve packet delivery ratio and delay of safety applications in single and multi-hop topologies, while preserving the synchronization scheme of the IEEE 1609.4 protocol.

Modeling and simulation of WAVE 1609.4-based multi-channel vehicular ad hoc networks

A method of delivering an encoded data stream to a plurality of recipient end- user nodes of a network The method comprises: receiving an incoming encoded data stream at a first recipient node from a transmitting node over the network; during ongoing receipt of the incoming encoded data stream at the first recipient node from the transmitting node, decoding the incoming encoded data stream at the first recipient node to produce a decoded data stream and outputting the decoded data stream for consumption at the first recipient node; using the decoded data stream to generate a modified encoded data stream being a modified version of the incoming encoded data stream; and, still during ongoing receipt of the incoming encoded data stream at the first recipient node from the transmitting node, relaying the modified encoded data stream from the first recipient node to one or more second recipient nodes over the network

Coding data streams

Video dissemination capabilities are crucial for the deployment of many services over VANETs. These services range from enhancing safety via the dissemination of video from the scene of an accident, to advertisement of local services or businesses. This work considers the infrastructure-less scenario of VANETs and dissemination of video content over this network environment, which is extremely challenging mainly due to its dynamic topology and stringent requirements for video streaming. This study discusses issues and challenges that need to be tackled for disseminating high-quality video over VANETs. Furthermore it surveys and analyzes the suitability of different existing solutions aimed towards effective and efficient techniques for video dissemination in vehicular networks. As a result, a set of the most promising techniques are selected, described in detail and evaluated based on standard terms in quality of service. This thesis also discusses efficiency and suitability of these techniques for video dissemination and compares their performance over the same network condition. In addition, a detailed study on the effect of network coding on video dissemination protocols has been conducted to guide how to employ this technique properly for video streaming over VANETs. From this study, a summary of the observations was obtained and used to design a new hybrid solution by deploying robust and efficient techniques in number of existing protocols in an optimal manner. The proposed hybrid video dissemination protocol outperforms other protocols in term of delivery ratio and complies with other quality-of-service requirements for video broadcasting over vehicular environments.

Video Streaming and Multimedia Broadcasting Over Vehicular Ad Hoc Networks

Layered video streaming in peer-to-peer (P2P) networks has drawn great interest, since it can not only accommodate large numbers of users, but also handle peer heterogeneity. However, there’s still a lack of comprehensive studies on chunk scheduling for the smooth playout of layered streams in P2P networks. In these situations, a playout smoothing mechanism can be used to ensure the uniform delivery of the layered stream. This can be achieved by reducing the quality changes that the stream undergoes when adapting to changing network conditions. This paper complements previous efforts in throughput maximization and delay minimization for P2P streaming by considering the consequences of playout smoothing on the scheduling mechanisms for stream layer acquisition. The two main problems to be considered when designing a playout smoothing mechanism for P2P streaming are the fluctuation in available bandwidth between peers and the unreliability of user-contributed resources—particularly peer churn. Since the consideration of these two factors in the selection and scheduling of stream layers is crucial to maintain smooth stream playout, the main objective of our smoothing mechanism becomes the determination of how many layers to request from which peers, and in which order. In this work, we propose a playout smoothing mechanism for layered P2P streaming. The proposed mechanism relies on a novel scheduling algorithm that enables each peer to select appropriate stream layers, along with appropriate peers to provide them. In addition to playout smoothing, the presented mechanism also makes efficient use of network resources and provides high system throughput. An evaluation of the performance of the mechanism demonstrates that the proposed mechanism provides a significant improvement in the received video quality in terms of lowering the number of layer changes and useless chunks while improving bandwidth utilization.

https://hal.archives-ouvertes.fr/hal-00875223/document

An efficient playout smoothing mechanism for layered streaming in P2P networks

Peer-to-peer (P2P) is a powerful platform for a variety of multimedia streaming applications over the Internet such as video-on-demand, video conferencing, live broadcasting, etc. A P2P system is extremely cost-effective since it utilizes the resources (CPU cycles, storage space, and uplink bandwidth) of peer machines. Recently, there has been significant development in desiging video conferencing systems. Video conferencing requires substantial network bandwidth in order to be able to transport high volume video data. This is particularly true for multiparty (MP) video conferencing system. One way to address the demand of high bandwidth is to use a network-based device called Multipoint Control Units (MCU). However, MCUs’ high cost and maintenance complexities make it only feasible for large business enterprises. Alternatively, the low cost P2P video conferencing services allow participants to establish pair-wise video communication. However, using this technology in a MP video conferencing system greatly reduces the video quality experienced by the user. The decentralized and shared bandwidth nature of a P2P network, therefore, makes it an effective choice for implementing video conferencing applications. In this work we present Vanets, a P2P based video conferencing system that takes advantage of transcoding to optimally allocate streaming rates for all participating peers. Our solution distinguishes between active and passive participants and enhances the video quality of the active participant. The remainder of this proposal is organized as follows. In Sec. II, we present an overview of the Vanets interface, network model, tree construction algorithm, and video adaptation procedure. In Sec. III we present our demonstration plan.

Vanets: Case Study of a Peer-to-Peer Video Conferencing System

Layered streaming is an effective solution to address receiver heterogeneity in a Peer-to-peer (P2P) network. This paper addresses the problem of rate allocation for layered video stream in p2p mesh networks. We present a distributed rate allocation algorithm that achieves close to optimal layer allocation among peers receiving the same video. We use load balancing technique that evenly distributes layer requests to a parent peer. Weight based layer allocation technique ensures that a child peer with higher children receives higher priority in servicing layer allocation request from its parents. Results show that for up to seven layers streamed by a server, the algorithm maintains a layer delivery ratio of 88% or more among all peers in a network. I. INTRODUCTION

On the Optimality of Layered Video Streaming Rate in a P2P Mesh Network

This paper addresses the problem of optimal rate allocation for video streaming in a multi-path peer-to-peer mesh network. We present a distributed rate allocation algorithm that minimizes the total rate distortion among receiving peers. The scheme assumes that video streams can be transcoded/requantized at intermediate peers. We deploy a double pricing solution that simultaneously incorporates both the network and the relay constraints. We compare it with a single pricing solution where the relay constraint is applied only after all the communicating peers have converged. Our simulation shows that the double pricing solution consistently achieves a smaller aggregate distortion for all peers in comparison to the single pricing solution and thus achieves higher video quality.

Rate Distortion Optimization for Mesh-Based P2P Video Streaming

This paper addresses the problem of optimal rate allocation for video stream in peer-to-peer networks. We present a distributed rate allocation algorithm with the goal of minimizing the total video distortion among peers receiving the same video. The scheme assumes that video streams can be transcoded/re-quantized at intermediate peers. We deploy a double pricing solution that simultaneously incorporates the network and the relay constraints in the peer-to-peer network and compare it with a single pricing solution where the relay constraint is applied only after all the communicating peers converge to optimality. We combine our solution with two video adaptation techniques: transcoding using x264 and scalable coding using H.264 SVC (scalable video coding) extension. Our experiment shows that the double pricing solution consistently achieves a smaller aggregate distortion for all peers over the single pricing solution.

Minimizing Rate Distortion in Peer-to-Peer Video Streaming

Receiver heterogeneity of a P2P network can be effectively addressed by scalable video streams. Due to the discontinuous nature of scalable video, traditional convex-optimization approach is not applicable. We propose a message-passing based approach for optimization using the sum- product update algorithm. Advantage of this simple but elegant approach over other heuristic-based algorithm is that the optimization algorithm itself is independent of the underlying constraints. The algorithm iteratively updates layer allocation decision based on a given set of codewords. The codewords are binary representation of various network and video constraints. Therefore, any number of constraints can be used to generate a set of codewords without modifying the algorithm. To the best of our knowledge, this is the first work that systematically addresses the scalable video optimization problem. Preliminary simulation with up to 8 layers shows that the sum- product update process achieves an average layer delivery of 95% or higher.

Tareq Hossain

Papers

Vanets: Case Study of a Peer-to-Peer Video Conferencing System

On the Optimality of Layered Video Streaming Rate in a P2P Mesh Network

Rate Distortion Optimization for Mesh-Based P2P Video Streaming

Minimizing Rate Distortion in Peer-to-Peer Video Streaming

Sum-Product Based Optimization for Scalable Video Streams in Peer-to-Peer Mesh Network