Andrea Baiocchi

Radio resource sharing for ad hoc networking with UWB

Ultra-wideband (UWB) radio is becoming a promising field for new generations digital communication systems. This technique, based mainly on the impulse radio paradigm, offers great flexibility and shows enormous potential in view of a future broadband wireless access. We present the main principles to design a multiaccess scheme based on UWB. The potential of UWB is exploited within a distributed ad hoc wireless system, where we describe the principles for the definition of a medium-access control (MAC) for mobile computing applications and we analyze the main performance results derived from simulations. A general framework for radio resource sharing is outlined for classes of traffic requiring both elastic-dynamic and guaranteed-reserved bandwidth. Then, we discuss the issue of supporting the proposed radio resource sharing scheme by means of a distributed MAC protocol.

Loss performance analysis of an ATM multiplexer loaded with high-speed on-off sources

The performance of an asynchronous transfer mode (ATM) multiplexer whose input consists of the superposition of a multiplicity of homogeneous on-off sources modeled by a two-state Markovian process is studied. The approach is based on the approximation of the actual input process by means of a suitably chosen two-state Markov modulated Poisson process (MMPP), as a simple and effective choice for the representation of superposition arrival streams. To evaluate the cell loss performance, a new matching procedure that leads to accurate results compared to simulation is developed. The application limits of the proposed method are also discussed. The outstanding physical meaning of this procedure permits a deep insight into the multiplexer performance behavior as the source parameters and the multiplexer buffer size are varied. >

The geometric dynamic channel allocation as a practical strategy in mobile networks with bursty user mobility

In this paper we refer to a specific class of Dynamic Channel Allocation (DCA) strategies, namely the interferencefree, timid, not-conditioned class. The main concern of this work is to verify if and to what extent strategies belonging to this class can offer better performance than Fixed Channel Allocation (FCA). The interest in this kind of strategies is motivated by their feasibility with current TDM technologies, the limited amount of information required to carry out channel assignments and their intrinsic stability. In this framework we present a simple, but very attractive DCA strategy, the so-called Geometric DCA (GDCA). A performance evaluation is carried out to compare some representative DCA strategies of the considered class, by using a user mobility model that accounts for the large fluctuations of the number of users in a cell coverage area expected in a microcellular environment. The effect of the non-null propagation time required by the information exchange in the DCA strategies is also taken into account. It emerges that the proposed GDCA allows better performance than more sophisticated strategies already proposed, at the expense of a frequency planning carried out only at network configuration. This is due to the ability of GDCA to exploit the a priori information to maintain a tight geometric packing of used carriers. The reported results also show that DCA strategies in the considered class cope with large and sudden traffic fluctuations remarkably better than the FCA scheme does and that the advantage becomes more evident as the burstiness of the user mobility process (hence of the offered traffic) increases.

On the impact of physical layer awareness on scheduling and resource allocation in broadband multicellular IEEE 802.16 systems [Radio Resource Management and Protocol Engineering for IEEE 802.16]

Multicellular networks based on the IEEE 802.16 standard appear to be very promising candidates to provide end users with broadband wireless access. However, they also pose interesting challenges in terms of radio resource management, where several design choices are not specified in the standard, intentionally left open to implementors. For this reason, we focus in this article on scheduling and resource allocation, and investigate how they could operate in a cross-layer fashion. In particular, we describe the principles of joint scheduling and resource allocation for IEEE 802.16 operating in AMC mode, and discuss the critical role played by physical layer considerations, especially intercell interference estimation and channel state awareness, in the obtained performance. This leads to identifying key open issues and possible general solutions

Stochastic fluid analysis of an ATM multiplexer loaded with heterogeneous ON-OFF sources: an effective computational approach

The authors study the loss performance of an asynchronous transfer mode (ATM) multiplexer, whose input consists of the superposition of a multiplicity of heterogeneous on-off sources. The stochastic fluid flow approach yields the entire buffer occupancy probability distribution in terms of the solution of a linear differential equation system. The focus is on the numerical investigation of the steady-state behavior of models involving very large state spaces. A novel approximate technique is introduced allowing a dramatic reduction of the computational burden, so that the analysis of a large variety of traffic mixes becomes feasible. Many numerical results are presented to support the accuracy of the method. Applications of the analysis method are outlined.<<ETX>>

A distributed beaconless routing protocol for real-time video dissemination in multimedia VANETs

We design a framework for video (and in general high data rate applications) transmission over a VANET.Our framework includes both application and routing layer design.We analyze MAC layer behavior and improve its utilization by solving the Spurious Forwarding problem.We tested our protocols on a real scenario, and considered both QoS and QoE, including MOS experiments in a real car.We grant a high data rate in ad-hoc mode, also for long distance, through our backbone beaconless approach. Vehicular Ad-Hoc Networks (VANETs) will play an important role in Smart Cities and will support the development of not only safety applications, but also car smart video surveillance services. Recent improvements in multimedia over VANETs allow drivers, passengers, and rescue teams to capture, share, and access on-road multimedia services. Vehicles can cooperate with each other to transmit live flows of traffic accidents or disasters and provide drivers, passengers, and rescue teams rich visual information about a monitored area. Since humans will watch the videos, their distribution must be done by considering the provided Quality of Experience (QoE) even in multi-hop, multi-path, and dynamic environments. This article introduces an application framework to handle this kind of services and a routing protocol, the DBD (Distributed Beaconless Dissemination), that enhances the dissemination of live video flows on multimedia highway VANETs. DBD uses a backbone-based approach to create and maintain persistent and high quality routes during the video delivery in opportunistic Vehicle to Vehicle (V2V) scenarios. It also improves the performance of the IEEE 802.11p MAC layer, by solving the Spurious Forwarding (SF) problem, while increasing the packet delivery ratio and reducing the forwarding delay. Performance evaluation results show the benefits of DBD compared to existing works in forwarding videos over VANETs, where main objective and subjective QoE results are measured.

Road Side Unit coverage extension for data dissemination in VANETs

Data dissemination is a key component of Infotainment and safety services in Vehicular Ad Hoc Networks. For infotainment services data dissemination starts from a Road Side Unit (RSU) and propagates to a multiplicity of On Board Units (OBU). A RSU typically can reach with a single hop only a fraction of the interested vehicles. Multi-hop, inter-vehicle communications is necessary to reach vehicles in the whole area that could be interested in the service. For an efficient data dissemination both the number of forwarding vehicles and the number of not covered ones shall be kept down. In this work we study the extension of the RSU coverage area via a simple data dissemination defined for urban scenarios. The proposed forwarding algorithm relies only on information local to the forwarding OBU. We show that in our case studies representing urban structures the protocol guarantees a good RSU coverage extension (in the order of 20 times the transmission area of the RSU) with a very low percentage of vehicles not reached by the disseminated data.

Analysis of the loss probability of the map/g/1/k queue part i: asymptotic theory

Abstract The main result in this paper is the characterization of the asymptotic behavior of the loss probability of the MAP/G/1/K queue for large buffer sizes. It is shown that the loss probability tends to 0 at an exponential rate for mean offered loads less than 1. The decay rate is related to the Perron-Frobenius eigenvalue of the matrix generating function describing the arrivals during a service time. The asymptotic constant can be computed at the expense of a computational effort of the same order as that required for the solution of the infinite buffer MAP/G/1 queue A special class of MAP is defined, namely time-reversible MAPs, for which very detailed asymptotic expressions for the loss probability can be found, regardless of the value of the mean offered load. For time-reversible MAPs it is shown that the decay of the loss probability towards its limiting value for K→∞ is exponential, except for a single special case (mean offered load equal to 1), in which it is linear These theoretical results...

A Layered Architecture for Fair Resource Allocation in Multicellular Multicarrier Systems

We consider a multicell multicarrier system with frequency reuse distance that is equal to one. Allowing all cells to transmit on the whole bandwidth unveils large potential gains in terms of spectral efficiency, in comparison with conventional cellular systems. Such a scenario, however, is often deemed unfeasible because of the strong multiple access interference (MAI) that negatively affects system performance. This paper presents a layered architecture that integrates a packet scheduler with an adaptive resource allocator that was explicitly designed to take care of the MAI. Each cell performs its resource management in a distributed way with no central controller. Iterative resource allocation assigns radio channels to the users to minimize interference. Packet scheduling guarantees that all users get a fair share of resources, regardless of their position in the cell. This scheduler-allocator architecture integrates both goals and is able to self-adapt to any traffic and user configuration. An adaptive distributed load control strategy can reduce the cell load so that the iterative procedure always converges to a stable allocation, regardless of the interference. Numerical results show that the proposed architecture guarantees both high spectral efficiency and throughput fairness among flows.

Optimal design of hybrid FEC/ARQ schemes for TCP over wireless links with Rayleigh fading

In this paper, we investigate interactions between TCP and wireless hybrid FEC/ARQ schemes. The aim is to understand what is the best configuration of the wireless link protocol in order to guarantee TCP performance and channel efficiency. Interactions between TCP and different link layer mechanisms are evaluated by means of an analytic model that reproduces: 1) a Rayleigh fading channel with FEC coding, 2) a generic selective repeat ARQ Protocol, and 3) the TCP behavior in a wired-cum-wireless network scenario. The analytic model is validated-by means of ns-based simulations. The analysis represents a contribution to the optimal design of link layer parameters of wireless networks crossed by TCP/IP traffic. The main findings can be summarized as follows: 1) fully reliable ARQ protocols are the best choice for both TCP performance and wireless link efficiency and 2) optimal values of FEC redundancy degree from the point of view of energy efficiency maximizes TCP performance as well.