arXiv subjects

Umberto Spagnolini

Publications and source records attributed to Umberto Spagnolini.

75 records · Page 5Linked to original sources

arXiv2015

Interference-Cooperation in Multi-User/Multi-Operator Receivers

In a multi-user scenario where users belong to different operators, any interference mitigation method needs unavoidably some degree of cooperation among service providers. In this paper we propose a cooperation strategy based on the exchange of mutual interference among operators, rather than of decoded data, to let every operator to recover an augmented degree of diversity either for channel estimation and multi-user detection. In xDSL scenario where multiple operators share the same cable binder the interference-cooperation (IC) approach outperforms data-exchange methods and preserves to certain degree the privacy of the users as signals can be tailored to prevent each operator to infer parameters (channel and data) of the users from the other operators. The IC method is based on Expectation Maximization estimation shaped to account for the degree of information that each operator can exchange with the others during the two steps of multi-user channel estimation and multi-user detection. Convergence of IC is guaranteed into few iterations and it does not depend on the structure of the interference. IC performance attains those of centralized receivers (i.e., one fusion-center that collects all the received signals from all the users/operators), with some loss when in heavily interfered multi-user channel such as in twisted-pair communications allocated beyond 50-100MHz spectrum.

cs.IT↗

arXiv2012

On the Optimal Scheduling of Independent, Symmetric and Time-Sensitive Tasks

Consider a discrete-time system in which a centralized controller (CC) is tasked with assigning at each time interval (or slot) K resources (or servers) to K out of M>=K nodes. When assigned a server, a node can execute a task. The tasks are independently generated at each node by stochastically symmetric and memoryless random processes and stored in a finite-capacity task queue. Moreover, they are time-sensitive in the sense that within each slot there is a non-zero probability that a task expires before being scheduled. The scheduling problem is tackled with the aim of maximizing the number of tasks completed over time (or the task-throughput) under the assumption that the CC has no direct access to the state of the task queues. The scheduling decisions at the CC are based on the outcomes of previous scheduling commands, and on the known statistical properties of the task generation and expiration processes. Based on a Markovian modeling of the task generation and expiration processes, the CC scheduling problem is formulated as a partially observable Markov decision process (POMDP) that can be cast into the framework of restless multi-armed bandit (RMAB) problems. When the task queues are of capacity one, the optimality of a myopic (or greedy) policy is proved. It is also demonstrated that the MP coincides with the Whittle index policy. For task queues of arbitrary capacity instead, the myopic policy is generally suboptimal, and its performance is compared with an upper bound obtained through a relaxation of the original problem. Overall, the settings in this paper provide a rare example where a RMAB problem can be explicitly solved, and in which the Whittle index policy is proved to be optimal.

math.OC↗

arXiv2011

Medium Access Control Protocols for Wireless Sensor Networks with Energy Harvesting

The design of Medium Access Control (MAC) protocols for wireless sensor networks (WSNs) has been conventionally tackled by assuming battery-powered devices and by adopting the network lifetime as the main performance criterion. While WSNs operated by energy-harvesting (EH) devices are not limited by network lifetime, they pose new design challenges due to the uncertain amount of harvestable energy. Novel design criteria are thus required to capture the trade-offs between the potentially infinite network lifetime and the uncertain energy availability. This paper addresses the analysis and design of WSNs with EH devices by focusing on conventional MAC protocols, namely TDMA, Framed-ALOHA (FA) and Dynamic-FA (DFA), and by accounting for the performance trade-offs and design issues arising due to EH. A novel metric, referred to as delivery probability, is introduced to measure the capability of a MAC protocol to deliver the measure of any sensor in the network to the intended destination (or fusion center, FC). The interplay between delivery efficiency and time efficiency (i.e., the data collection rate at the FC), is investigated analytically using Markov models. Numerical results validate the analysis and emphasize the critical importance of accounting for both delivery probability and time efficiency in the design of EH-WSNs.

cs.IT↗