M.-G. Di Benedetto

A Survey on MAC Strategies for Cognitive Radio Networks

Dynamic spectrum policies combined with software defined radio are powerful means to improve the overall spectral efficiency allowing the development of new wireless services and technologies. Medium Access Control (MAC) protocols exploit sensing stimuli to build up a spectrum opportunity map (cognitive sensing). Available resources are scheduled (dynamic spectrum allocation), improving coexistence between users that belong to heterogeneous systems (dynamic spectrum sharing). Furthermore, MAC protocols may allow cognitive users to vacate selected channels when their quality becomes unacceptable (dynamic spectrum mobility). The contribution of this survey is threefold. First, we show the fundamental role of the MAC layer and identify its functionalities in a cognitive radio (CR) network. Second, a classification of cognitive MAC protocols is proposed. Third, advantages, drawbacks, and further design challenges of cognitive MAC protocols are discussed.

Modeling and optimization of UWB communication networks through a flexible cost function

The traditional design of communication networks has rarely been able to focus on the optimization of global network properties. Ultra-wideband (UWB) radio is emerging as an attractive physical layer for wireless communication networks offering new opportunities for the principled design and optimization of network properties. We develop a framework for the principled design of UWB wireless networks based on a flexible cost function that can be tailored and scaled to a wide range of networks and applications, ranging from sensor networks to voice and data wireless networks. The function comprises cost terms associated with transmission, connection setup, interference, and quality-of-service. Multihop routing strategies are associated with admissible paths of minimal cost that are computable in linear time. The cost function together with the overall level of requests determine the dynamics of the connections and the equilibrium topology of the network. We report simulation results in the case of simple ring and square lattice networks.

Overview of the IEEE 802.15.4/4a standards for low data rate Wireless Personal Data Networks

The IEEE 802.15.4 standard provides a framework for low data rate communications systems, typically sensor networks. The 802.15.4a revision introduces new options for the physical layer, in order to support higher data rates and accurate ranging capability, enabling new applications based on information on distance and positions of the devices in the network. In this paper the differences among physical layers of 802.15.4 vs. 802.15.4a are briefly reviewed. Next, the MAC layer of 802.15.4 vs. 802.15.4a are reviewed and compared. Device functionalities, network topologies as well as access strategies in both standards are described, and the impact of the new physical layer features on MAC and higher layers are discussed, with particular attention to the ranging scheme adopted in the new revision of the standard.

UWB ad-hoc networks

We propose a new strategy for path selection in a UWB based ad-hoc network which by minimizing a power-dependent global cost function, can potentially lead to an optimal network organization characterized by low emitted power levels and high network performance.

Cut-off in engine control: a hybrid system approach

A novel approach to the control of an automotive engine in the cut-off region is presented. First, a hybrid model which describes the torque generation mechanism and the power-train dynamics is developed. Then, the cut-off control problem is formulated as a hybrid optimization problem, whose solution is obtained by relaxing it to the continuous domain and mapping its solution back into the hybrid domain. A formal analysis as well as simulation results demonstrate the properties and the quality of the control law.

UWB ranging accuracy in high- and low-data-rate applications

The Cramer-Rao lower bound (CRLB) was determined for different ultra-wideband (UWB) signal formats and, in particular, for the two UWB high-data-rate (HDR) signal formats proposed within the IEEE 802.15.3a Task Group, that is, the impulsive direct-sequence UWB (DS-UWB) and the nonimpulsive multiband orthogonal frequency-division multiplexing (MB-OFDM), and an impulsive time hopping (TH) UWB format close to the format for UWB low data rate (LDR) of the forthcoming IEEE 802.15.4a standard. The analysis was carried out for both ideal and multipath channels under power constraints as set by emission masks. Results obtained for HDR formats showed that DS-UWB has better ranging accuracy than does MB-OFDM, thanks to its potentially larger bandwidth and higher frequency of operation. In addition, the degree of multipath strongly affected ranging accuracy, although differently for DS-UWB versus MB-OFDM. When incorporating a correlation receiver structure as well as an Early Late gate synchronizer in the model, ranging performance proved to be related to features of the synchronization sequence. For specific synchronization sequences, in particular, the best ranging accuracy was obtained with MB-OFDM. In the case of LDR, the study analyzed the effect of pulse shape on CRLB. Results showed that a suboptimal choice of the pulse shape reduces the ranging accuracy achievable by TH-UWB signals.

Multiple access design for impulse radio communication systems

We address the problem of designing time hopping codes for impulse radio multiple access communication systems. Time hopping techniques are first reviewed, including a new code that Iacobucci and Di Benedetto (see Proc. International Symposium 3G Infrastructure and Services, Athens, Greece,July 200) proposed for time hopping, and performance in terms of cyclic correlation properties are given. Advantages and disadvantages of different time hopping codes in terms of resource assignment for multiple access communication systems are analyzed and discussed.

Multi user interference in power-unbalanced ultra wide band systems: analysis and verification

Validity of the standard Gaussian approximation (SGA) for modeling multi user interference (MUI) in impulse radio ultra wide band (IR-UWB) systems which do not implement power control is investigated. Analysis focuses on the case of UWB systems adopting binary pulse position modulation (2PPM) with a time hopping (TH) code division multiple access scheme. Theoretical predictions are compared vs. simulation outputs in order to quantify limitations of the SGA hypothesis.

Performance Analysis for a Body Area Network composed of IEEE 802.15.4a devices

Body area networks (BANs) are wearable wireless sensor networks with a high potential for medical and sports applications. BANs appear to be a particularly appealing solution to provide information about the health status of a patient in medical environments such as hospitals or medical centres.This work analyzes the behaviour of a BAN composed of IEEE 802.15.4a ultra wideband (UWB) sensors. A body area network architecture is proposed and investigated by simulation. Performance evaluation takes into account bit error rate as a function of the number of nodes forming the BAN and of the asynchronism level between them.

Computing the differential output rank of a nonlinear system

The main goal of this note is to give a tractable method of computing the differential output rank of a nonlinear control system. As a byproduct, a synthesis is made of diverse algorithms, proposed in the literature, for determining various structural properties of a nonlinear system. In addition, related results on the regular dynamic decoupling problem are given.