Elena Fasolo

In-network aggregation techniques for wireless sensor networks: a survey

In this article we provide a comprehensive review of the existing literature on techniques and protocols for in-network aggregation in wireless sensor networks. We first define suitable criteria to classify existing solutions, and then describe them by separately addressing the different layers of the protocol stack while highlighting the role of a cross-layer design approach, which is likely to be needed for optimal performance. Throughout the article we identify and discuss open issues, and propose directions for future research in the area

An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad hoc Networks

In this paper, we focus on a vehicular ad hoc network (VANET) that makes use of 802.11-like wireless interfaces for Inter Vehicular Communication (IVC). We propose a distributed position-based broadcast protocol, named Smart Broadcast (SB), that aims at i) maximizing the progress of the message along the propagation line, and ii) minimizing the re-broadcast delay. The protocol is analyzed through a mathematical model that permits to determine the optimal parameter setting for a given scenario. Simulations are then used to validate the mathematical model and to compare SB with other broadcast algorithms.

Network Coding meets MIMO

In this paper, MIMO techniques are applied to network coding in order to exploit the spatial diversity inherent in packet combining. This is possible because network coding and MIMO solve similar problems, namely to decode a vector of transmitted symbols given a vector of received samples. This observation leads to a new approach for NC coding/decoding. Our basic idea is to move network coding functionalities towards the physical layer in order to jointly perform NC decoding and MIMO detection and gain the advantages of the two approaches. We refer to this new strategy as MIMO_NC. Theoretical analysis and simulations prove that our system is more robust than traditional network coding to fading and packet losses.

Toward network coding-based protocols for data broadcasting in wireless Ad Hoc networks

In this paper we consider practical dissemination algorithms exploiting network coding for data broadcasting in ad hoc wireless networks. For an efficient design, we analyze issues related to the use of network coding in realistic network scenarios. In detail, we quantify the impact of random access schemes, as used by IEEE 802.11, on the performance of network coding. In such scenarios, deadlock situations may occur where the delivery process stops and some of the nodes never gather the required packets. To tackle this problem, we propose a proactive mechanism (called proactive network coding) which adapts its transmission schedule according to the decoding status of neighboring nodes. This scheme can detect when nodes need additional packets in order to decode and acts accordingly. We finally investigate the behavior of network coding schemes in multi-rate environments, where we propose a distributed heuristic approach for the selection of data rates.

On MAC Scheduling and Packet Combination Strategies for Practical Random Network Coding

The present paper investigates practical algorithms to efficiently exploit random network coding for data delivery in multi-hop wireless networks. In the past few years, a great deal of work has been carried out to derive analytical results about network coding. However, only recently have researchers started to utilize the theoretical findings in practical settings. Network coding is a new paradigm for data delivery which proved to be very efficient. It is particularly suitable for wireless networks due to the inherent broadcast nature of the channel. Even though previous work dealt with practical schemes exploiting these new techniques, many issues concerning the coexistence of network coding and channel access mechanisms are still unsolved. In addition, it is still unclear how packets should be combined in order to get the highest benefits in terms of throughput, delay, and energy efficiency. Our work presents an accurate investigation of these aspects. In particular, we couple several MAC and scheduling schemes together with different network coding strategies, and compare them via extensive ns2 simulation. Finally, we propose a new timing strategy for the combination of data packets in random network coding.

A Proactive Network Coding Strategy for Pervasive Wireless Networking

In recent years, network coding has proved to be an efficient tool to disseminate data through a network. A number of practical schemes have been proposed to implement network coding also in wireless environments. Most of them are based on reactive and probabilistic random network coding and their effectiveness has been investigated under the assumption of idealized network conditions. However, recent work has shown that the benefits of such strategies decrease when applied in realistic network environments. In this paper, we propose an algorithm to efficiently disseminate data through network coding in realistic wireless networks by using a proactive approach, named ProNC. We develop a distributed and self-adaptable protocol which substantially increases the performance of network coding in practical scenarios and achieves full reliability with both low protocol overhead and low delay. We show the effectiveness of ProNC via ns-2 simulations and compare it with previously proposed schemes.

Challenges and new approaches for efficient data gathering and dissemination in pervasive wireless networks

Motivated by the current trends in wireless technologies, we present challenging scenarios consisting of moving and uncoordinated wireless objects as well as algorithms that are likely to perform well in such environments. Our primary interest is to design network protocols to efficiently build and maintain distributed communication systems based on opportunistic design principles. Such systems should continue to operate well even if communication is sporadic, no end-to-end routes are available, and sources and consumers of information are not known in advance. Also the environment poses many challenges, that are typical for wireless mobile devices, such as wireless channel impairments, the impossibility of having up-to-date and accurate views of the network topology at every device, and limited energy resources. In the second part of the paper, we discuss and propose solutions for data dissemination in such an environment by exploiting network coding techniques. Furthermore, we report first results which reveal that network coding largely outperforms standard solutions which are based on the classical store and forward paradigm.

Phoenix: A Hybrid Cooperative-Network Coding Protocol for Fast Failure Recovery in Ad Hoc Networks

In this paper, we investigate how to apply MIMO_NC in order to increase the efficiency of cooperative communications. MIMO_NC is a recent strategy to combine, in an integrated system, MIMO detection techniques and network coding. MIMO_NC is robust to channel errors, as it can exploit the spatial diversity provided by multiple transmissions of the same information, and throughput effective as it is based on network coding. In this paper we design a cooperative MAC protocol based on MIMO_NC which can outperform classical cooperative schemes. We also prove its effectiveness by means of analytical modelling and simulations in different network configurations.

VoIP Communications in Wireless Ad-hoc Network with Gateways

In this paper, we investigate some of the issues that arise when mobile nodes engage voice connections with remote peers by using a wireless ad hoc network (MANET-cell) to access the distribution core network. We focus on a specific network scenario where all communications are directed to a special node, called gateway, which in turn bridges traffic to and from the core network. We first derive a mathematical expression to estimate the maximum number of sustainable voice sessions in a single-hop cell, with multi-rate terminals. Then, we assess the accuracy of the formula through ns2 simulations, which allow us to determine the voice capacity of the system also in presence of hidden terminals. Hence, we analyze the impact of multi-hop paths on the voice capacity of the system. From this analysis, we propose a new cost metric that we apply to a modified version of the OLSR routing algorithm, named HOLSR. This algorithm has proved to be able to preserve stability in some scenarios that were unstable under other routing algorithms.

On encoding and rate adaptation for MIMO_NC

MIMO_NC is a recently proposed physical layer technique that combines MIMO signal processing and Network Coding. However, it has also been shown that the diversity offered by MIMO_NC cannot be greater than what standard NC offers. In this paper we propose a new encoding strategy for MIMO_NC that improves the diversity order and a rate adaptation technique tailored on MIMO_NC that offers diversity and coding gain over conventional NC.