1,721,164 research outputs found
MAC and Routing in Wireless Ad Hoc and Sensor Networks: a Cross-Layer Approach
No full text"Respecting a network architecture yields better guarantees of reliability, longevity, and modularity, but much better performance can be potentially achieved through wisely chosen violations to that architecture."
In a nutshell, this is the message of a recent paper (see [1] in Chapter 1) outlining pros, cons, consequences and risks of cross-layer design, a currently widely adopted paradigm for wireless networks. The increasing attention and momentum that cross-layer design has recently gained is explained by its potential advantages, namely the network performance improvements that can be achieved, especially under stringent constraints in terms of hardware and computational power. A short definition of cross-layer design identifies this technique as a means of performing information exchange among different layers in the classic ISO/OSI protocol stack model, and of harvesting the potential design opportunities and performance improvements that follow. However, by breaking the modular structure of the ISO/OSI stack, one may encounter two orders of problems: first, unwanted interactions may be introduced; second, the generality of the architecture is lost. While a careful design phase can overcome the first problem, the second one requires stronger efforts. In fact, any cross-layer design is inherently specific to the type of network and scenario it is applied to, and limits the performance improvements to that specific type. Due to this loss of generality, the same protocol hardly offers the same results as applied to different types of networks.
In this Thesis, we will show two relevant examples of successful cross-layer design applied to two very different kinds of wireless networks. The first example deals with ad hoc networks with multiple antennas and MIMO communications. Due to the specific scenario, it can be assumed that nodes have high throughput needs and can accept to, e.g., spend more energy in performing the processing required by MIMO signaling in order to achieve greater communication speed. The analysis of this scenario is focused on the design of a novel PHY-aware MAC protocol for MIMO ad hoc networks and on the analysis and optimization of its performance.
A completely different point of view is required instead to handle wireless sensor networks (WSNs), the second type of wireless network considered in this Thesis. Peculiar to WSNs are the usually low communication speed, processing capabilities and energy supplies. Among others, these constraints do not allow complicated signal processing or the storage of a large amount of information. In turn this requires to limit the buffer of the nodes (the sensors hence have only a limited packet queue) and also to design protocols whose "state" can be summarized and efficiently held in the limited memory of the sensors. In the Thesis, we will provide an in-depth analysis of a geographic MAC/routing protocol for WSNs, and build upon it to yield a complete solution for channel access and packet forwarding. Part of this study is the design of an algorithm to route packets around connectivity holes, where geographic protocols alone fail.
In the appendix, the same cross-layer design concepts are applied to wireless underwater networks, a particular instance of WSNs where communications take place over long delay, low rate acoustic channels, and incur strongly frequency-dependent channel effects. All results (analysis, simulations, comparisons with other solutions) show that cross-layer design is in fact very effective, and offers valuable opportunities to leverage specific features that can lead to performance improvements in each kind of wireless network
The NAUTILUS project: Physical parameters, architectures and network scenarios
No full textThe NAUTILUS (Network Architecture and protocols for Underwater Telerobotics via acoustIc Links in Ubiquitous Sensing, monitoring and explorations) project aims at providing a comprehensive study of the technical issues related to the realization of a complete solution for the network architecture and the communications protocols needed for the tele-operation of underwater robots. When pursuing this goal, the need to implement realistic scenarios for underwater simulations clearly emerges. In this paper, starting from the investigation on the state-of-the-art carried out for the NAUTILUS project,we list the main concepts and parameters that underlie realistic simulations of underwater scenarios. Also, we present and thoroughly discuss the choices made in terms of parameters, network architectures and models for the NAUTILUS project itself. We believe that the information collected in this paper provides a good starting point for the development of a realistic underwater performance evaluation tool
MAC protocols for broadcasting and information retrieval in underwater networks
No full textUnderwater acoustic networks of fixed and autonomous nodes can be a very valuable tool in a number of situations, from environmental monitoring to emergency scenarios
(e.g., ships in distress). In this paper, we compare the performance of some MAC protocols
for underwater networks in typical scenarios. We consider random access protocols, which
provide sufficiently high performance in case of low traffic, and then compare random access
with handshake-based access, which achieves better coordination among nodes, at the price
of greater control overhead. We consider both periodic traffic and event-driven traffic, and
provide insight about which scheme achieves the best performance in terms of relevant network metrics such as throughput, error rate and overhead. In our evaluation, we assume the
network protocols to work over a low-rate FH-BFSK-based physical layer, a simple technique that can be easily implemented, e.g., to work as a common PHY for different modem
hardware
On the Implications of Layered Space-Time Multiuser Detection on the Design of MAC Protocols for Ad Hoc Networks
No full textDSMA: an Access Method for MIMO Ad Hoc Networks Based on Distributed Scheduling
No full textIn this work, we analyze the effects of a distributed transmission coordination scheme that is particularly suited for ad hoc networks with the ability to exploit spatially--multiplexed communications over MIMO links. Following previous work where we discussed the performance of this kind of networks and deployed a fast yet reliable approximation for physical layer behavior, we now employ this knowledge to analyze the performance of a different access scheme, meant to outperform previous results by the use of distributed coordination of transmissions and receptions without adding any further redundancy in communications. Furthermore, we analyze the effect of tuning two parameters on the overall network performance
A RNN-based approach to physical layer authentication in underwater acoustic networks with mobile devices
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TinyNET: A Tiny Network Framework for TinyOS: Description, Implementation and Experimentation
No full textIn this paper we present TinyNET, a modular framework allowing development and quick integration of protocols and applications for Wireless Sensor Networks (WSNs) in TinyOS. The motivation behind TinyNET is two-fold: on one hand it allows to adopt a divide-and-conquer approach in the development of any TinyOS application; on the other hand it provides a flexible administration of network protocols. As a sample development using TinyNET, we consider an environmental monitoring application, and test it over a floor-wide WSN testbed. Data are converge-casted toward a sink node, which gathers all data collected by the sensors. Routing toward the sink is achieved by means of a hop count (HC) based algorithm. Our framework also integrates support for the 6LowPAN standard (providing, e.g., per-sensor queries and pings). Thanks to TinyNET, s these messages will make transparent use of the underlying network protocols. Also, TinyNET transparently manages the network components and related messages, allowing different applications to share the same network stack; furthermore, it translates TinyOS interfaces so that any previously developed application can be easily ported. These features make it possible to have a global vision over any application, as well as to focus on each of its separate components
On the Implications of Layered Space-Time Multiuser Detection on the Design of MAC Protocols for Ad Hoc Networks
No full textIn this paper, we shed some light on the implications that using a recently proposed layered space-time multiuser detection technique has on MAC protocol design for ad hoc networks with multiple antennas. From this point of view, our work relates to both physical layer and network layer studies. In fact, on the one hand physical layer aspects are important to characterize the behavior at the receiver, especially in terms of Bit and Packet Error Rates, but are rarely considered in conjunction with networking scenarios; on the other hand, networking aspects are typically studied using drastically simplified physical layer models that, while allowing easier networking analysis, are often too restrictive or unrealistic. Also, this disconnect between physical and networking layer studies may severely limit the possibilities for cross-layer optimization, which appears to be the right approach for efficient wireless network design. Our paper is then an effort to establish some connection between the "physical" and "network" approaches, highlighting some interesting capabilities that ad hoc networks with multiple antennas are endowed by the use of multiuser detection
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