Julián David Morillo-Pozo

Wireless Multimedia Sensor Networks: Current Trends and Future Directions

Wireless Multimedia Sensor Networks (WMSNs) have emerged and shifted the focus from the typical scalar wireless sensor networks to networks with multimedia devices that are capable to retrieve video, audio, images, as well as scalar sensor data. WMSNs are able to deliver multimedia content due to the availability of inexpensive CMOS cameras and microphones coupled with the significant progress in distributed signal processing and multimedia source coding techniques. In this paper, we outline the design challenges of WMSNs, give a comprehensive discussion of the proposed architectures, algorithms and protocols for the different layers of the communication protocol stack for WMSNs, and evaluate the existing WMSN hardware and testbeds. The paper will give the reader a clear view of the state of the art at all aspects of this research area, and shed the light on its main current challenges and future trends. We also hope it will foster discussions and new research ideas among its researchers.

Review: Security on VANETs: Privacy, misbehaving nodes, false information and secure data aggregation

This article is a position paper on the current security issues in Vehicular Ad hoc Networks (VANETs). VANETs face many interesting research challenges in multiple areas, from privacy and anonymity to the detection and eviction of misbehaving nodes and many others in between. Multiple solutions have been proposed to address those issues. This paper surveys the most relevant while discussing its benefits and drawbacks. The paper explores the newest trends in privacy, anonymity, misbehaving nodes, the dissemination of false information and secure data aggregation, giving a perspective on how we foresee the future of this research area. First, the paper discusses the use of Public Key Infrastructure (PKI) (and certificates revocation), location privacy, anonymity and group signatures for VANETs. Then, it compares several proposals to identify and evict misbehaving and faulty nodes. Finally, the paper explores the differences between syntactic and semantic aggregation techniques, cluster and non-cluster based with fixed and dynamic based areas, while presenting secure as well as probabilistic aggregation schemes.

A Cooperative Vehicular Network Framework

Vehicular Ad Hoc Networks are networks characterized by intermittent connectivity and rapid changes in their topology. This paper addresses car-to-road communications in which vehicles use Access Points (AP) in a Delay Tolerant Network architecture. Results show how the combination of a Delay-Cooperative ARQ mechanism reduces packet losses and in conjunction with a Carry-and-Forward cooperative mechanism improves performance parameters in terms of total file transfer delay and number of AP needed to download files.

A Low Coordination Overhead C-ARQ Protocol with Frame Combining

This paper proposes a low coordination overhead cooperative automatic repeat request (ARQ) scheme with an integrated frame combiner, which exploits space diversity and cooperation between neighbouring nodes. In channels with a strong line of sight (LOS) component and low signal-to- noise ratio (SNR), the maximum achievable throughput of the proposed protocol is many times higher than for other ARQ schemes. For non LOS scenarios, the cooperative ARQ without frame combiner achieves the best efficiency results, and the overhead introduced by the frame combiner mechanisms leads to results which can be even below the classical ARQ mechanism.

Power saving trade-offs in Delay/Disruptive Tolerant Networks

Wireless nodes such as smart-phones in which the WiFi wireless card is continuously on, consume battery energy in just a few hours. Moreover, in many scenarios, an always-on wireless card is useless because there is often no need for transmission and/or reception. This fact is exacerbated in Delay/Disruptive Tolerant Network (DTN) environments, in which nodes exchange Delay Tolerant Objects (DTO) when they meet. Power Saving Management (PSM) techniques enable the lifetime of the nodes to be extended. This paper analyses the trade-offs that appear when wireless nodes periodically turn off the wireless card in order to save battery in DTN environments. The paper shows the conditions in which a node can switch off the battery without impacting the peer-to-peer contact probability, and those in which this contact probability is decreased. For example, it is shown that node lifetime can be doubled while keeping the peer-to-peer contact probability equal to one. But, further increase of the node lifetime quickly decreases peer-to-peer contact probability. Finally, the impact of power savings in DTO dissemination time is also analyzed.

Evaluation of a Cooperative ARQ Protocol for Delay-Tolerant Vehicular Networks

This paper evaluates a Cooperative ARQ protocol to be used in delay-tolerant vehicular networks. The scenario consists in cars downloading information from Access Points along a road. The key difference between proposed Cooperative ARQ protocols is when the cooperation takes place. Simply C-ARQ cooperation occurs in a packet-by-packet basis. In this proposal, that we call DC-ARQ (Delayed Cooperative ARQ), the cooperation is delayed until cars are out of the coverage area of the Access Point. The scheme has been evaluated through simulations. A comparison of DC-ARQ with a baseline case in which no cooperation is used has been performed under different vehicle densities scenarios.

Cooperative forwarding in IEEE 802.11-based MANETs

In this paper we introduce a novel cooperative forwarding mechanism for IEEE 802.11-based MANETs. The mechanism has been adapted to operate together with two well known routing protocols: AODV and LUNAR. We evaluate our proposal by means of a prototype, using pedestrian mobility inside a building. Results show that, in dense MANETs, our cooperative forwarding mechanism is a promising technique to achieve robustness, and with a low cost of overhead.

A protocol stack for cooperative wireless networks

Nowadays, some of the more exciting research areas in networking are based on cooperation between network nodes. Examples of this are ad-hoc or sensor networks, cooperative physical layer techniques known as cooperative diversity, or other new cooperative mechanisms such as Cooperative ARQ. In many scenarios, this cooperation could be further exploited using new mechanisms that fall into the L2-L3 protocols, leading to a cooperative stack. These mechanisms allow an easy use of the resources of adjacent nodes to increase communication capabilities. This combines particularly well with the characteristics of wireless networks thanks to the broadcast advantage inherent in wireless transmission. This paper proposes a novel cooperative relaying scheme that exploits transmitter diversity and performs a fast path repair procedure at L2. All these operations are made transparently to the content of the forwarding tables of the nodes, thanks to the use of a new addressing scheme. This protocol could work together with other cooperative protocols such as Cooperative ARQ, leading to an integrated mechanism for frame relaying. Analytical and simulation results show that cooperative frame relaying clearly improves network resilience.

Impact of the infrastructure in mobile opportunistic networks

Epidemic modeling has been used to analyze many disciplines such as biology, ecology and medicine. In the last years, it also has been applied to networking paradigms such as social networks, virus spreading in Internet and lastly to opportunistic networking in mobile networks. In this paper we revise some of the facts of epidemic modeling in mobile networks and use these models to analyze the impact of adding infrastructure to sparse opportunistic mobile networks. We show how the position in which infrastructure is placed takes an important impact in the dissemination delay.