Daniel F. Macedo

Transmission power control techniques for wireless sensor networks

Communication is usually the most energy-consuming event in Wireless Sensor Networks (WSNs). One way to significantly reduce energy consumption is applying transmission power control (TPC) techniques to dynamically adjust the transmission power. This article presents two new TPC techniques for WSNs. The experimental evaluation compares the performance of the TCP techniques with B-MAC, the standard MAC protocol of the Mica 2 platform. These experiments take into account different distances among nodes, concurrent transmissions and node mobility. The new transmission power control techniques decrease energy consumption by up to 57% over B-MAC while maintaining the reliability of the channel. Under a low mobility scenario, the proposed protocols delivered up to 95% of the packets, showing that such methods are able to cope with node movement. We also show that the contention caused by higher transmission levels might be lower than analytical models suggest, due to the action of the capture effect.

Transmission power control in MAC protocols for wireless sensor networks

Medium access control (MAC) protocols manage energy consumption on the network element during communication, which is the most energy-consuming event on Wireless Sensor Networks (WSNs). One method to mitigate energy consumption is to adjust transmission power. This paper presents two approaches to adjust transmission power in WSNs. The first approach employs dynamic adjustments by exchange of information among nodes, and the second one calculates the ideal transmission power according to signal attenuation in the link. The proposed algorithms were implemented and evaluated with experiments, comparing their results with B-MAC, the standard MAC protocol in the Mica Motes 2 platform. Results show that transmission power control is an effective method to decrease energy consumption, and incurs in a negligible loss in packet delivery rates. For node distances of 5m, the proposed transmission power control techniques decrease energy consumption by 27% over B-MAC.

Protocols, mobility models and tools in opportunistic networks: A survey

Abstract In opportunistic networks, instead of assuming an end-to-end path as in the traditional Internet model, messages are exchanged opportunistically when an encounter happens between two nodes. In the last years, several forwarding algorithms to efficiently decide when to forward messages were proposed. Those protocols are commonly suitable to a specific scenario, which has led to the creation of new subtypes of networks. Two different examples are pocket switched networks – PSN and vehicular networks – VANETs, since those networks have different features like a specific mobility pattern and intermittent connectivity. In this article we present an overview of opportunistic networks, proposing a taxonomy which encompasses those new types of network. We discuss the commonly used tools, simulators, contact traces, mobility models and applications available. Moreover, we analyzed a set of forwarding protocols to map the approach used by the research community to evaluate their proposals in terms of mobility, contacts and traffic pattern, reliability of simulations and practical projects. We show that although researchers are making efforts to use more realistic contact models (e.g., using real traces) the traffic pattern is generally disregarded, using assumptions that may not fit real applications.

Enhancing peer-to-peer content discovery techniques over mobile ad hoc networks

Content dissemination over mobile ad hoc networks (MANETs) is usually performed using peer-to-peer (P2P) networks due to its increased resiliency and efficiency when compared to client-server approaches. P2P networks are usually divided into two types, structured and unstructured, based on their content discovery strategy. Unstructured networks use controlled flooding, while structured networks use distributed indexes. This article evaluates the performance of these two approaches over MANETs and proposes modifications to improve their performance. Results show that unstructured protocols are extremely resilient, however they are not scalable and present high energy consumption and delay. Structured protocols are more energy-efficient, however they have a poor performance in dynamic environments due to the frequent loss of query messages. Based on those observations, we employ selective forwarding to decrease the bandwidth consumption in unstructured networks, and introduce redundant query messages in structured P2P networks to increase their success ratio.

Vehicular networks using the IEEE 802.11p standard

The IEEE 802.11 working group proposed a standard for the physical and medium access control layers of vehicular networks called 802.11p. In this paper we report experimental results obtained from communication between vehicles using 802.11p in a real scenario. The main motivation is the lack of studies in the literature with performance data obtained from off-the-shelf 801.11p devices. Our study characterizes the typical conditions of an 802.11p point-to-point communication. Such a study serves as a reference for more refined simulation models or to motivate enhancements in the PHY/MAC layers. Field tests were carried out varying the vehicles speed between 20 and 60 km/h and the packet length between 150 and 1460 bytes, in order to characterize the range, throughput, latency, jitter and packet delivery rates of 802.11p links. It was observed that communication with vehicles in motion is unstable sometimes. However, it was possible to transfer data at distances over 300 m, with data rates sometimes exceeding 8 Mbit/s.

Evaluation of peer-to-peer network content discovery techniques over mobile ad hoc networks

Both mobile ad hoc networks (MANETs) and peer-to-peer (P2P) networks are decentralized and self-organizing networks with dynamic topology and are responsible for routing queries in a distributed environment. Because MANETs are composed of resource-constrained devices susceptible to faults, whereas P2P networks are fault-tolerant, P2P networks are the ideal data sharing system for MANETs. We have conducted an evaluation of two approaches for P2P content discovery running over a MANET. The first, based on unstructured P2P networks, relies on controlled flooding, while the second, based on structured P2P networks, uses distributed indexing to optimize searches. We use simulations to evaluate the effect of network size, mobility, channel error rates, network workload, and application dynamics in the performance of P2P protocols over MANETs. Results show that unstructured protocols are the most resilient, although at higher energy and delay costs. Structured protocols, conversely, consume less energy and are more appropriate for MANETs where topology is mostly static.

Programmable Networks—From Software-Defined Radio to Software-Defined Networking

Current implementations of Internet systems are very hard to be upgraded. The ossification of existing standards restricts the development of more advanced communication systems. New research initiatives, such as virtualization, software-defined radios, and software-defined networks, allow more flexibility for networks. However, until now, those initiatives have been developed individually. We advocate that the convergence of these overlying and complementary technologies can expand the amount of programmability on the network and support different innovative applications. Hence, this paper surveys the most recent research initiatives on programmable networks. We characterize programmable networks, where programmable devices execute specific code, and the network is separated into three planes: data, control, and management planes. We discuss the modern programmable network architectures, emphasizing their research issues, and, when possible, highlight their practical implementations. We survey the wireless and wired elements on the programmable data plane. Next, on the programmable control plane, we survey the divisor and controller elements. We conclude with final considerations, open issues and future challenges.

A pro-active routing protocol for continuous data dissemination in wireless sensor networks

Wireless sensor networks are ad hoc networks with severe resource constraints. These constraints preclude the use of traditional ad hoc protocols, and demand optimizations that incur in solutions specific to a class of applications. This article presents PROC, a protocol designed for continuous data dissemination networks, that interacts with the application to establish routes, allowing the application to reconfigure PROC on runtime. A performance evaluation in topologies varying from 50 to 200 nodes showed that PROC increases network lifetime around 7% to 12%, and has higher throughput than EAD and TinyOS Beaconing. Furthermore, PROC presents a softer performance degradation when the number of nodes in the network increases.

On the feasibility of WiFi offloading in urban areas: The Paris case study

With the increasing number of users subscribing to mobile Internet such as 3G and 4G networks, the Wireless Internet Services providers (WISP) aim to offer a good service for customers while elevating the number of clients. Several proposals to offload the traffic of 3G networks have been made in the past few years, including the use of femtocells,WiFi offloading and more recently mobile-to-mobile opportunistic offloading. In this paper, we measure the public WiFi hotspots provided by the government and private WiFi access points (AP) scanned during several bus routes in Paris in order to evaluate the feasibility of offloading data traffic through WiFi. We compare the AP positions with the positions of mobile clients provided publicly in Location Sharing Services, such as Foursquare. Our main findings are that, on average, an access point is available up to 60m of range, during 30 seconds, and the already deployed WiFi infrastructure could offload up to 30% of mobile traffic in the scenario analyzed.

Spatial query processing in wireless sensor networks - A survey

Wireless sensor networks (WSN) are particularly useful for obtaining data concerning events limited to a well-defined geographic region, such as a disaster site or a malfunctioning subsection of a factory plant. Such applications typically use spatial queries, which are SQL-like queries where location constraints are imposed on the collected data. Further, spatial queries allow changing the set of nodes (the region of interest) at runtime. This work surveys spatial queries in WSN. Due to the particular energy and resource constraints of WSN, spatial queries are performed by mechanisms having several stages, each of them implemented using localized distributed algorithms. This article categorizes the existing strategies for each stage, in order to ease the understanding of the state of the art. Finally, we analyze the most recent works on spatial query processing, identifying which classes of algorithms are used on each stage.