Ad Hoc Networking for Pervasive Systems

The hardware and software progresses of the last ten years provided the basic elements (wearable computers, several wireless-network technologies, devices for sensing and remote control, etc.) for the realization of pervasive computing and communication systems. In these systems the environment is saturated with computing and communication capabilities, completely integrated with the surrounding environment, aimed at helping the users in the everyday life. In a pervasive computing environment, the infrastructure-based wireless communication model is often not adequate: it takes time to set up the infrastructure network, while the costs associated with installing infrastructure can be quite high. These costs and delays may not be acceptable for dynamic environments where people and/or vehicles need to be temporarily interconnected in areas without a pre-existing communication infrastructure (e.g., inter-vehicular and disaster networks), or where the infrastructure cost is not justified (e.g., in-building networks, specific residential communities networks, etc.). In these cases, infrastructure-less or ad hoc networks provide a more efficient solution

Performance comparison of power saving strategies for mobile Web access

One of the critical issues in mobile Web access is the usage of limited energy resources of mobile computers. Unfortunately, the legacy TCP/IP architecture is very inefficient. This work proposes and analyzes power-saving strategies for mobile Web access. Specifically, in this paper we develop an energy-consumption model for Web transactions and, based on it, we propose and compare four different energy saving strategies: ideal, Indirect-TCP (I-TCP), local and global. The ideal strategy is unfeasible but it is used as a reference bound as it guarantees the lowest energy consumption. The other strategies have been implemented and compared in a real test-bed. The performance comparison is carried out by measuring two main performance figures: the energy spent for downloading a Web page, and the associated transfer-time. Experimental results show that relevant energy saving is achievable and that, among the feasible strategies, the global one gives the best performance: with this strategy we can save (on average) up to 88% of the energy. Furthermore, our results indicate that this power saving is obtained without a significant increase in the transfer-time perceived by the users (on average, 0.2s). Finally, by comparing the feasible strategies, we observe that the global one is much closer to the ideal case than the other strategies. In detail, the global strategy is about twice more efficient than the local one, and eight times more efficient than the I-TCP strategy

Towards Reliable Forwarding for Ad Hoc Networks

Ad hoc networking is a new paradigm of wireless commu- nications 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 sel sh misbehavior. Nodes act sel shly to save battery power, by not cooperating to routing-forwarding functions. Lack of co- operation may severely degrade the performance of the ad hoc system. This paper presents a new approach to cope with cooperation misbehav- ior, focusing on the forwarding function.We present a general framework, based on reliability indices taking into account not only sel sh/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)

Networking Technologies, Services, and Protocols

Mobility and Quality of Services (QoS) are the major issues in today\u27s computer networks research. Projections show that in the next few years we can expect the total number of mobile In ternet users soon to exceed that of fixed-line Internet connec- tions. The QoS perceived by the users is becoming a dominant fact or in the success of Internet-based services. Furthermore, new Internet applications may require the delivery of multimedia data in real time (e.g., streaming stored video and audio), and the information transfer through the Internet is becoming one of the principal paradigms for business, e.g., electronic sales, banking, finance and collaborative work. The aim of this issue is to address the challenges in networking technologies, services and protocols to suppor t mobility, multim edia and Qo

Power-Saving in Wi-Fi Hotspots: an Analytical Study

Wi-Fi hotspots are one of the most promising scenarios for mobile computing. In this scenario, a very limiting factor is the scarcity of mobile-device energetic resources. Both hardware and software architectures of current devices are very ine cient from this standpoint, mainly the networking subsystem. This work analyzes a power-saving network architecture for the mobile-Internet access through Wi-Fi hotspots. Specifically, this solution supports any kind of best-e ort network applications, since it is application-independent. In this paper we derive a complete analytical model of the power-saving system when applied to mobile Web access. Furthermore, we use this model to compare our solution with a well-known approach, i.e., the Indirect-TCP. The comparison is performed by considering two performance gures: the energy saved in downloading a Web page and the related transfer-time. The results show that, in the average, our solution saves up to 78% of the energy. Furthermore, the power-saving system introduces an additional average transfer-time of 0.4 sec, and hence it does not signi cantly a ect the QoS perceived by the users. Finally, we assess the sensitiveness of the power-saving system with respect to Internet key parameters, such as the available throughput and the RTT

Price-based Congestion-Control in Wi-Fi Hot Spots

Wireless networks are now proliferating due to the success of the IEEE 802.11b protocol, also known as "Wi-Fi" (Wireless Fidelity). A Wi-Fi network is characterized by a set of base stations (also called access points) placed throughout the environment and connected to the traditional wired LANs. This technology allows nomadic users a broadband access to the Internet if they are in the transmission range of an access point. A new business model, named Wi-Fi Hot Spots, is now emerging to exploit the potentialities of this technology. A hot spot is a "critical" business area, e.g., airports, stations, hotels, where users can have wireless access by subscribing a contract with the hot spot operator, or with a wireless Internet service provider (WISP). Due to the random access nature of the Wi-Fi technology, if the number of users connected to the same access point increases, the QoS experienced may quickly degrade. This generates complains from the users that, as a consequence, may change their WISP. In order to be competitive, a Wi-Fi hot spot operator needs simple and effective mechanisms to control the congestion therefore guaranteeing the QoS, and (at the same time) maximizing his/her revenues. In this paper we present and evaluate a price-based policy for the access control in a Wi-Fi hot spot. Our policy, named Price-based Congestion Control (PCC), controls the hot spot traffic by dynamically determining the access cost as a function of the current load in the hot spot. We develop a theoretical framework to compute for any load condition the access cost to maintain the hot spot in its optimal operating point, for any load condition. The effectiveness and robustness of the PCC policy has been evaluated by simulating a Wi-Fi hot spot. Both in saturated..

Traffic and Interference Adaptive Scheduling for Internet Traffic in UMTS

We propose a scheduling strategy for radio resources management when transmitting Internet traffic over third-generation systems. More precisely, we consider the UMTS terrestrial radio access network (UTRAN) time division duplex (TDD) mode standardized by ETSI. UTRAN TDD uses a hybrid solution of code and time division multiple access, called TD-CDMA. We present a fair and efficient scheduling algorithm that adapts its behavior to traffic and interference conditions. Specifically, our scheduling algorithm is able to manage the radio resources taking into account both traffic fluctuations, in the uplink and downlink direction, and variations in system interference. The goal of our scheduler is data-throughput maximization for an efficient utilization of available radio resources. The performance of our scheduling algorithm is evaluated via simulation

Optimization of Efficiency and Energy Consumption in p-persistent CSMA-based Wireless LANs

Wireless technologies in the LAN environment are becoming increasingly important. The IEEE 802.11 is the most mature technology for Wireless Local Area Networks (WLANs). The limited bandwidth and the finite battery power of mobile computers represent one of the greatest limitations of current WLANs. In this paper we deeply investigate the efficiency and the energy consumption of MAC protocols that can be described with a p-persistent CSMA model. As already shown in the literature, the IEEE 802.11 protocol performance can be studied using a p-persistent CSMA model [Cal00]. For this class of protocols, in the paper we define an analytical framework to study the theoretical performance bounds from the throughput and the energy consumption standpoint. Specifically, we derive the p values (i.e., the average size of the contention window in the IEEE 802.11 protocol) that maximizes the throughput, $p^C_{opt}$, and minimizes the energy consumption, $p^E_{opt}$. By providing analytical closed formulas for the optimal values, we discuss the trade-off between efficiency and energy consumption. Specifically, we show that power saving and throughput maximization can be jointly achieved. Our analytical formulas indicate that the optimal $p$ values depend on the network configuration, i.e., number of active stations and length of the messages transmitted on the channel