We design and analyze the performance of a redundancy management mechanism for peer-to-peer backup applications . Armed with the realization that a backup system has peculiar requirements – namely, data is read over the network only during restore processes caused by data loss – redundancy management targets data durability , i.e. guaranteeing that data is not lost, rather than attempting to make each piece of information available at any time. In our approach each peer determines, in an on-line manner, an amount of redundancy sufficient to counter the effects of peer deaths, while preserving acceptable data restore times. Our experiments, based on trace-driven simulations, indicate that our mechanism can reduce the redundancy by a factor between two and three with respect to redundancy policies aiming for data availability. These results imply an according increase in storage capacity and decrease in time to complete backups, at the expense of longer times required to restore data. We believe this is a very reasonable price to pay, given the nature of the application. We complete our work with a discussion on practical issues, and their solutions, related to which encoding technique is more suitable to support our scheme.

We propose a redundancy management mechanism for peer-to-peer backup applications. Since, in a backup system, data is read over the network only during restore processes caused by data loss, redundancy management targets data durability rather than attempting to make each piece of information availabile at any time. Each peer determines, in an on-line manner, an amount of redundancy sufficient to counter the effects of peer deaths, while preserving acceptable data restore times. Our experiments, based on trace-driven simulations, indicate that our mechanism can reduce the redundancy by a factor between two and three with respect to redundancy policies aiming for data availability. These results imply an according increase in storage capacity and decrease in time to complete backups, at the expense of longer times required to restore data.We believe this is a very reasonable price to pay, given the nature of the application.

In this paper, we propose a framework for user/operator utility-based infrastructure deployment in vehicular networks. We extend the well known maximum coverage problem to consider the following four complementary aspects: (i) a non-circular polygon-based coverage representing measured heterogeneous any-directional communication conditions (ii) a generic intensity-based utility function reflecting variations of the intensity of a desired metric over the polygonal area (iii) comparable metrics either by normalizing the utility over the coverage, or by an intensity threshold maintaining a minimal utility regardless of coverage, (iv) a joint user/operator utility optimization minimizing the infrastructure deployment. We finally illustrate the benefits of our framework over related coverage-based approaches in an exemplary study.

The IEEE Task Group has approved recently the 802.11p amendment to enable efficient short range communications for vehicular networks by introducing multiple enhancements at the physical and MAC layer. It defines a control frequency channel for control and most critical data packets and one or several service frequency channels for less critical packets. In this paper, we propose an analytical model for the 802.11p operations in the control frequency. It captures all suggested enhancements important for exchanging data packets generated by road safety applications. We showed through diverse simulations scenarios that our proposed model is able to reproduce expected results. We consider this work as an important step toward understanding the performance of 802.11p-based vehicular communications and the model can be employed in the simulations of safety applications in large scenarios.

In the near future vehicular networks based on wireless technology will be part of our lives. Efficient and robust routing algorithms will play a key role in the success of such technology. In this paper we present TrafRoute, an efficient and robust routing scheme for vehicular networks, suitable for both Vehicle-to-Vehicle and Vehicle-to-Infrastructure communications. TrafRoute introduces a novel approach to routing that involves landmark-based routes and forwarder self-election, exploiting the knowledge of the underlying road network. We demonstrate TrafRoute's efficiency and robustness through simulation studies performed with accurate mobility and propagation models.

Digital fountain codes have emerged as a low-complexity alternative to Reed-Solomon codes for erasure correction. The applications of these codes are relevant especially in the field of wireless video, where low encoding and decoding complexity is crucial. In this paper, we introduce a new class of digital fountain codes based on a sliding-window approach applied to Raptor codes. These codes have several properties useful for video applications, and provide better performance than classical digital fountains. Then, we propose an application of sliding-window Raptor codes to wireless video broadcasting using scalable video coding. The rates of the base and enhancement layers, as well as the number of coded packets generated for each layer, are optimized so as to yield the best possible expected quality at the receiver side, and providing unequal loss protection to the different layers according to their importance. The proposed system has been validated in a UMTS broadcast scenario, showing that it improves the end-to-end quality, and is robust towards fluctuations in the packet loss rate.

Overcoming problems associated with network dynamicity and unreliable channels has been a challenge for data dissemination protocols in vehicular networks. In this paper, we present an overview on the most interesting solutions that have been proposed to perform data dissemination in this environment. Starting from this analysis, we present a novel approach that can efficiently address a reliable communication even in high dynamic networks. The new approach is based on the exploitation of a peculiar characteristic of rateless codes. In particular, the proposed method uses the orthogonality of the encoded sets of symbols generated by different random seeds. In this way, portions of the information can be disseminated even if this has not been decoded yet. In fact, an easy management of the communication of these sets among nodes enhances the reliability of the communication as well as the speed of the information dissemination. In this work, we present the idea of this innovative approach and we provide results that show the advantages of using it over other solutions.

Digital fountain codes are becoming increasingly important for multimedia communications over networks subject to packet erasures. These codes have significantly lower complexity than Reed-Solomon ones, exhibit high erasure correction performance, and are very well suited to generating multiple equally important descriptions of a source. In this paper we propose an innovative scheme for streaming multimedia contents by using digital fountain codes applied over sliding windows, along with a suitably modified belief-propagation decoder. The use of overlapped windows allows one to have a virtually extended block, which yields superior performance in terms of packet recovery. Simulation results using LT codes show that the proposed algorithm has better performance in terms of efficiency, reliability and memory with respect to fixed-window encoding.