D2D Data Offloading in Vehicular Environments with Optimal Delivery Time Selection

Within the framework of a Device-to-Device (D2D) data offloading system for cellular networks, we propose a Content Delivery Management System (CDMS) in which the instant for transmitting a content to a requesting node, through a D2D communication, is selected to minimize the energy consumption required for transmission. The proposed system is particularly fit to highly dynamic scenarios, such as vehicular networks, where the network topology changes at a rate which is comparable with the order of magnitude of the delay tolerance. We present an analytical framework able to predict the system performance, in terms of energy consumption, using tools from the theory of point processes, validating it through simulations, and provide a thorough performance evaluation of the proposed CDMS, in terms of energy consumption and spectrum use. Our performance analysis compares the energy consumption and spectrum use obtained with the proposed scheme with the performance of two benchmark systems. The first one is a plain classic cellular scheme, the second is a D2D data offloading scheme (that we proposed in previous works) in which the D2D transmissions are performed as soon as there is a device with the required content within the maximum D2D transmission range..

Distributed Decision Through Self-Synchronizing Sensor Networks in the Presence of Propagation Delays and Asymmetric Channels

In this paper we propose and analyze a distributed algorithm for achieving globally optimal decisions, either estimation or detection, through a self-synchronization mechanism among linearly coupled integrators initialized with local measurements. We model the interaction among the nodes as a directed graph with weights (possibly) dependent on the radio channels and we pose special attention to the effect of the propagation delay occurring in the exchange of data among sensors, as a function of the network geometry. We derive necessary and sufficient conditions for the proposed system to reach a consensus on globally optimal decision statistics. One of the major results proved in this work is that a consensus is reached with exponential convergence speed for any bounded delay condition if and only if the directed graph is quasi-strongly connected. We provide a closed form expression for the global consensus, showing that the effect of delays is, in general, the introduction of a bias in the final decision. Finally, we exploit our closed form expression to devise a double-step consensus mechanism able to provide an unbiased estimate with minimum extra complexity, without the need to know or estimate the channel parameters.Comment: To be published on IEEE Transactions on Signal Processin

Distributed Decision Through Self-Synchronizing Sensor Networks in the Presence of Propagation Delays and Nonreciprocal Channels

In this paper we propose and analyze a distributed algorithm for achieving globally optimal decisions, either estimation or detection, through a self-synchronization mechanism among linearly coupled integrators initialized with local measurements. We model the interaction among the nodes as a directed graph with weights dependent on the radio interface and we pose special attention to the effect of the propagation delays occurring in the exchange of data among sensors, as a function of the network geometry. We derive necessary and sufficient conditions for the proposed system to reach a consensus on globally optimal decision statistics. One of the major results proved in this work is that a consensus is achieved for any bounded delay condition if and only if the directed graph is quasi-strongly connected. We also provide a closed form expression for the global consensus, showing that the effect of delays is, in general, to introduce a bias in the final decision. The closed form expression is also useful to modify the consensus mechanism in order to get rid of the bias with minimum extra complexity.Comment: Conference paper. Journal version submitted to IEEE Transactions on Signal Processing, January 10, 2007. Paper accepted for the publication on the VIII IEEE Workshop on Signal Processing Advances in Wireless Communications, (SPAWC 2007), January 22, 200

Next Generation Opportunistic Networking in Beyond 5G Networks

Beyond 5G networks are expected to support massive traffic through decentralized solutions and advanced networking mechanisms. This paper aims at contributing towards this vision through the integration of device-centric wireless networks, including Device-to-Device (D2D) communications, and the Next Generation of Opportunistic networking (NGO). This integration offers multiple communication modes such as opportunistic cellular and opportunistic D2D-aided communications. Previous studies have demonstrated the potential and benefits of this integration in terms of energy efficiency, spectral efficiency and traffic offloading. We propose an integration of device-centric wireless networks and NGO that is not driven by a precise knowledge of the presence of the links. The proposed technique utilizes a novel concept of graph to model the evolution of the networking conditions and network connectivity. Uncertainties and future conditions are included in the proposed graph model through anticipatory mobile networking to estimate the transmission energy cost of the different communication modes. Based on these estimates, the devices schedule their transmissions using the most efficient communication mode. These decisions are later revisited in real-time using more precise knowledge about the network state. The conducted evaluation shows that the proposed technique significantly reduces the energy consumption (from 60% to 90% depending on the scenario) compared to traditional single-hop cellular communications and performs closely to an ideal “oracle based” system with full knowledge of present and future events. The transmission and computational overheads of the proposed technique show small impact on such energy gains.This work has been partially funded by the Spanish Ministry of Science, Innovation and Universities, AEI, and FEDER funds (TEC2017-88612-R)the Ministry of Science, Innovation and Universities (IJC2018-036862-I)the UMH (‘Ayudas a la Investigación e Innovación de la Universidad Miguel Hernández de Elche 2018’)and by the European Commission under the H2020 REPLICATE (691735), SoBigData (654024) and AUTOWARE (723909) project

Testing Off-the-Shelf Optical Wireless LANs for Smart City Environments

Optical wireless LANs (OWLs) constitute an emerging networking paradigm for indoor scenarios’ fit to different smart cities’ fields of applications. Commercial products employing this technology have been made available on the market in recent years. In this work, we investigate, through a set of indoor communication experiments based on commercially available products, how different environmental and usage modes affect the performance of the system, addressing the presence of multiple users, the position and mobility of the mobile devices, the handover among adjacent cells and the effect of background lighting. Our finding shows that the system is quite robust with respect to the variation of operational conditions. We show that, in most conditions, the links can reliably sustain a stable throughput, achieving at least 50% of the throughput achieved with using the maximum light intensity of the transmitting lamp, while they are affected in a very mild way by factors like position and height of the mobile device, and virtually unaffected by variations in the background light

Wireless Sensor Networks for Spectrum Sensing to Support Opportunistic Spectrum Access Networks: Protocol Design and Fundamental Trade-offs

Supporting secondary users through a collateral network dedicated to spectrum sensing has been recently proposed as a mean to overcome spectrum sensing limitations of secondary devices. Building on this idea, we propose a protocol for a Wireless Sensor Network (WSN) to support secondary devices of an Opportunistic Spectrum Access (OSA) network. We examine the fundamental tradeoff between the statistics of the primary network traffic for which the WSN is able to support the OSA network and the interference range or, equivalently, the transmit power of secondary transmitters. We optimize the parameters of the proposed protocol to achieve the minimum delay for delivering channel availability information to secondary users, thus maximizing the portion of time they can effectively use idle primary channels to send their data. We further provide simulation results to demonstrate the feasibility and effectiveness of our design, and point at possible research directions to improve the proposed system capabilities

On the optimal relay location and power allocation in a virtual array system with minimum overall outage probability

Cooperative communication among terminals allows the achievement of the benefits of MIMO links, such as diversity and multiplexing gains, even with single antenna radio transceivers. In this work we focus on a virtual MIMO link created between a source, cooperating with several relays to form a virtual array, and a destination, equipped with multiple antennas, in a Rayleigh flat-fading scenario. We asses the performance limits of this system, under the non-ergodicity assumption, in terms of outage probability, with the aim to single out the role played by important factors such as the distances between the terminals, power allocation, and time sharing. ©2007 IEEE

Distributed decision in sensor networks based on local coupling through Pulse Position Modulated signals

In this work we propose a physical layer design, based on Pulse Position Modulated (PPM) signals, for a decentralized wireless sensor network implementing an iterative consensus algorithm. The proposed scheme does not require any MAC protocol to avoid or resolve collisions, and is also suitable for a half-duplex implementation. The considered network model assumes only local coupling among the nodes, thus allowing for low transmit power even in large scale networks. Furthermore, we show how to remove the effect of propagation delays, multipath, and non perfect synchronization among the nodes, without requiring any channel parameter estimate. As an example of application, we consider a simple parameter estimation problem, which is instrumental to discuss the fundamental trade-offs arising in the system parameters settings, when both observation noise and coupling noise are considered in the performance analysis. ©2008 IEEE

Optimal Decentralized Estimation Through Self-Synchronizing Networks in the Presence of Propagation Delays

In this paper we focus on a sensor network scheme whose nodes are locally coupled oscillators that evolve in time according to a differential equation, whose parameters depend on the local estimate. The proposed system is capable, by self-synchronization, to reach the network consensus that coincides with the globally optimum maximum likelihood estimate, even though each sensor is only locally coupled with nearby nodes. Our main contribution is to study the effect of propagation delay on both the synchronization capability of the system and the final estimate. We provide delay-independent conditions for the proposed system to synchronize, and we derive closed-form expression of the synchronized state. Interestingly, the effect of propagation delays is simply to introduce a bias on the final estimate, that depends on the network topology and on the values of the delays. The analysis of this bias, suggest us how to design the coupling mechanism in order to alleviate it or even remove it