Gaia Maselli

Cross-layering in mobile ad hoc network design

Mobile ad hoc network researchers face the challenge of achieving full functionality with good performance while linking the new technology to the rest of the Internet. A strict layered design is not flexible enough to cope with the dynamics of manet environments, however, and will prevent performance optimizations. The MobileMan cross-layer architecture offers an alternative to the pure layered approach that promotes stricter local interaction among protocols in a manet node.

Anticollision Protocols for Single-Reader RFID Systems: Temporal Analysis and Optimization

One of the major challenges in the use of Radio Frequency-based Identification (RFID) on a large scale is the ability to read a large number of tags quickly. Central to solving this problem is resolving collisions that occur when multiple tags reply to the query of a reader. To this purpose, several MAC protocols for passive RFID systems have been proposed. These typically build on traditional MAC schemes, such as aloha and tree-based protocols. In this paper, we propose a new performance metric by which to judge these anticollision protocols: time system efficiency. This metric provides a direct measure of the time taken to read a group of tags. We then evaluate a set of well-known RFID MAC protocols in light of this metric. Based on the insights gained, we propose a new anticollision protocol, and show that it significantly outperforms previously proposed mechanisms.

Towards Reliable Forwarding for Ad Hoc Networks

Ad hoc networking is a new paradigm of wireless communications for mobile nodes. Mobile ad hoc networks work properly only if the partecipating nodes cooperate to network protocols. Cooperative algorithms make the system vulnerable to user misbehavior as well as to malicious and selfish misbehavior. Nodes act selfishly to save battery power, by not cooperating to routing-forwarding functions. Lack of cooperation may severely degrade the performance of the ad hoc system. This paper presents a new approach to cope with cooperation misbehavior, focusing on the forwarding function. We present a general framework, based on reliability indices taking into account not only selfish/malicious misbehavior, but also situations of congestion and jammed links. We aim at avoiding unreliable routes and enforcing cooperation, thus increasing network “performability” (performance and reliability).

Dynamic tag estimation for optimizing tree slotted aloha in RFID networks

The emergent commercial use of techniques for Radio Frequency-based IDentification of different items (RFID) requires the investigation and testing of collision resolution mechanisms for the efficient and correct communication between the system reader and the tags labeling the items that need to be identified. Several MAC protocols have been proposed to resolve collisions in RFID networks. A recent solution, named Tree Slotted Aloha (TSA), has been shown to outperform previous ones with respect to the time it takes for identifying all tags, and the total number of bits transmitted to complete the identification process. However, almost half of the time needed by TSA for identifying tags is spent in collisions. This depends on TSA operation and in particular on the way TSA estimates the number of colliding tags. We have observed that in the case of realistically large networks, TSA highly underestimates this number, with non-negligible impact on the protocol performance. In this paper, we propose a Dynamic Tree Slotted Aloha (Dy TSA) protocol that exploits the knowledge acquired during ongoing readings to refine the estimation of the number of colliding tags. In so doing, Dy TSA adapts the length of the following reading cycles to the actual number of tags still requiring identification. Through ns2-based simulations we show that the proposed method is effective for tag identification and results in significantly improved performance over TSA. Specifically, the length of the identification process is up to 20% lower than that of TSA. Furthermore, the amount of transmitted bits needed for identifying all tags decreases up to 30%.

MobileMAN: Mobile Metropolitan Ad hoc Networks

MobileMAN is a project funded by the Future and Emerging Technologies arm of the IST Programme of the the European Commission. This project investigates the potentialities of the Mobile Ad hoc NETworks (MANET’s) paradigm. Specifically, the project aims at defining and developing a metropolitan area, self-organizing, and totally wireless network, called Mobile Metropolitan Ad hoc Network (MobileMAN). The main technical output of this proposal can be summarized as follow. i) Development, validation, implementation and testing of the architecture, and related protocols, for configuring and managing a MobileMAN. ii) Physical implementation of this architecture for lowers layers (i.e., wireless technologies). iii) Integration of applications on top of our self-organized network. iv) Validation of the self-organizing paradigm from the social and economic standpoint.

Performance Analysis of Anti-Collision Protocols for RFID Systems

Recently RFID technology has made its way into end-user applications, enabling automatic item identification without requiring line of sight. In particular passive tags provide a promising, low cost and energy-efficient solution for inventory applications. However, their large-scale adoption strictly depends on the efficiency of the identification process. A major challenge is how to arbitrate channel access so that all tags are able to answer the reader inquiries and identify themselves over time. This paper stems from the observation that a variety of anti- collision protocols for RFIDs have been proposed in the literature. However, a thorough simulation comparison among them and a clear identification of the mechanisms resulting in better end- to-end performance is lacking. The objective of our work has been to fill this gap. This paper presents the results of a detailed ns2-based comparative evaluation of representatives of all the classes of anti-collision protocols so far proposed. Simulation results show that end-to-end performance of the different classes of protocols in terms of metrics such as the time needed for tags identification differ significantly over what previously found by experiments which only focused on the number of reading cycles for tag identification. Our thorough performance evaluation has highlighted that different solutions are to be used in different application scenarios and that decreasing the collisions (rather than idle times) is the way to go to further improve anti-collision protocols performance. I. INTRODUCTION A basic RFID system consists of a reader and a set of tags. The reader inquiries tags that are able to communicate on the radio channel, returning their ID. Tags are typically passive devices, which answer to readers query by back- scattering the received signal. One of the main objectives of a RFID system is the identification of all the tags present in the area covered by the reader. The challenges related to tags identification depend on the reference scenarios, which may include one or more readers, and a variable or stationary set of tags. The coexistence of multiple readers in the same area may cause collisions among readers interfering with each other or with tags. Moreover, collisions may occur among tags simultaneously transmitting to the same reader, indepen- dently of the presence of one or more readers. Collisions are addressed by specific solutions for the multi-reader problem (through frequency allocation mechanisms) and the single- reader problem (through collision arbitration schemes). The other distinguishing factor is given by scenario variability. In case of stationary applications scenarios (i.e., consecutive readings of the same, slightly changed, set of tags), the reader

Throughput-Optimal Cross-Layer Design for Cognitive Radio Ad Hoc Networks

We present a distributed, integrated medium access control, scheduling, routing and congestion/rate control protocol stack for cognitive radio ad hoc networks (CRAHNs) that dynamically exploits the available spectrum resources left unused by primary licensed users, maximizing the throughput of a set of multi-hop flows between peer nodes. Using a network utility maximization (NUM) formulation, we devise a distributed solution consisting of a set of sub-algorithms for the different layers of the protocol stack (MAC, flow scheduling and routing), which result from a natural decomposition of the problem into sub-problems. Specifically, we show that: 1) The NUM optimization problem can be solved via duality theory in a distributed way, and 2) the resulting algorithms can be regarded as the CRAHN protocols. These protocols combine back-pressure scheduling with a CSMA-based random access with exponential backoffs. Our theoretical findings are exploited to provide a practical implementation of our algorithms using a common control channel for node coordination and a wireless spectrum sensor network for spectrum sensing. We evaluate our solutions through ns-2 MIRACLE-based simulations. Our results show that the proposed protocol stack effectively enables multiple flows among cognitive radio nodes to coexist with primary communications. The CRAHN achieves high utilization of the spectrum left unused by the licensed users, while the impact on their communications is limited to an increase of their packet error rate that is below 1 percent.

Improving the performability of data transfer in mobile ad hoc networks

Data transfer in ad hoc environments shows poor network performance due to frequent link breakages and route failures. Selfish and malicious nodes may further deteriorate nodes communication, having a strong impact on transport layer protocols such as TCP, which are highly sensitive to packet losses. Although these misbehaviors have similar effects on the network functioning (i.e. packets are dropped), they are separately addressed by the research community. This paper provides a comprehensive method to improve the performance and reliability (performability) of nodes commu- nication in presence of faults, selfish and malicious behavior. Specifically, we propose and evaluate a novel forwarding policy that is based on multi-path routing and considers nodes reliability and routes length in forwarding decisions. We investigate through simulations how this mechanism improves the performability of TCP data transfers. In particular, we show that the simultaneous use of multiple paths yields higher throughput and continuous network connectivity when compared to single path forwarding. This has been verified in case of both fault conditions and intentional nodes misbehavior. I. INTRODUCTION Mobile ad hoc networking represents a new fron- tier for wireless communications. Its intrinsic extensibility, auto-configuration, ease of maintenance, and infrastructure- independence capabilities make it a prime candidate for be-

Managing heterogeneous sensors and actuators in ubiquitous computing environments

With the increase in the number of sensors and actuators available to ubiquitous computing systems comes the need for architectures that can support the development of intelligent applications and expose the rich control and monitoring capabilities provided by these devices to users. In this work, we present a description of the parameters used to define services provided by sensors and actuators. Using this understanding of the devices that provide sensing and control throughout the environment, we present thedesign of Meditrina, a ubiquitous computing architecture. Meditrina provides clean interfaces for application designers to leverage devices in the environment to support the activities of users in a large variety of scenarios. To demonstrate the power and feasibility of Meditrina, we implemented a prototype, including a room lighting control application. Through the use of the prototype, we show how the architecture facilitates the quick implementation of applications that can react to and affect the environment, even in the face of device failure.

Design of a Flexible Cross-Layer Interface for Ad Hoc Networks

Cross layering has recently emerged as a new trend to cope with performance issues of mobile ad hoc networks. The concept behind this technique is to exploit local information produced by other protocols, so as to enable optimizations and deliver better network performance. However, the need for a new interaction paradigm inside the protocol stack has to face with the legacy aspects of classical architectures (e.g., the Internet), where layer separation allows for easy standardization and deployment. In this paper, we show that cross layering can be achieved maintaining a clean architectural modularity, making protocols exchange information through a vertical interface. Specifically, we present the design of a cross-layer module, and provide a proof of concepts of its “usability” at different layers of the protocol stack, considering two case studies from a design and implementation standpoint.