Marco Di Felice

Search: A routing protocol for mobile cognitive radio ad-hoc networks

Recent research in the emerging field of cognitive radio (CR) has mainly focused on spectrum sensing and sharing, that allow an opportunistic use of the vacant portions of the licensed frequency bands by the CR users. Efficiently leveraging this node channel information in order to provide timely end-to-end delivery over the network is a key concern for CR based routing protocols. In addition, the primary users (PUs) of the licensed band affect the channels to varying extents, depending on the proportion of the transmission power that gets leaked into the adjacent channels. This also effects the geographical region, in which, the channel is rendered unusable for the CR users. In this paper, a geographic forwarding based SpEctrum Aware Routing protocol for Cognitive ad-Hoc networks (SEARCH), is proposed that jointly undertakes path and channel selection to avoid regions of PU activity during route formation. Specifically, the optimal paths found by geographic forwarding on each channel are combined at the destination with an aim to minimize the hop count. By binding the route to regions found free of PU activity, rather than particular CR users, the effect of the PU activity is mitigated. Our proposed approach is thoroughly evaluated through simulation study.

SEARCH: A routing protocol for mobile cognitive radio ad-Hoc networks

Recent research in the emerging field of cognitive radio (CR) has mainly focused on spectrum sensing and sharing, that allow an opportunistic use of the vacant portions of the licensed frequency bands by the CR users. Efficiently leveraging this node channel information in order to provide timely end-to-end delivery over the network is a key concern for CR based routing protocols. In addition, the primary users (PUs) of the licensed band affect the channels to varying extents, depending on the proportion of the transmission power that gets leaked into the adjacent channels. This also effects the geographical region, in which, the channel is rendered unusable for the CR users. In this paper, a geographic forwarding based SpEctrum Aware Routing protocol for Cognitive ad-Hoc networks (SEARCH), is proposed that jointly undertakes path and channel selection to avoid regions of PU activity during route formation. Specifically, the optimal paths found by geographic forwarding on each channel are combined at the destination with an aim to minimize the hop count. By binding the route to regions found free of PU activity, rather than particular CR users, the effect of the PU activity is mitigated. Our proposed approach is thoroughly evaluated through simulation study.

End-to-end protocols for Cognitive Radio Ad Hoc Networks: An evaluation study

Cognitive radio ad hoc networks (CRAHNs) constitute a viable solution to solve the current problems of inefficiency in the spectrum allocation, and to deploy highly reconfigurable and self-organizing wireless networks. Cognitive radio (CR) devices are envisaged to utilize the spectrum in an opportunistic way by dynamically accessing different licensed portions of the spectrum. To this aim, most of the recent research has mainly focused on devising spectrum sensing and sharing algorithms at the link layer, so that CR devices can operate without interfering with the transmissions of other licensed users, also called primary users (PUs). However, it is also important to consider the impact of such schemes on the higher layers of the protocol stack, in order to provide efficient end-to-end data delivery. At present, routing and transport layer protocols constitute an important yet not deeply investigated area of research over CRAHNs. This paper provides three main contributions on the modeling and performance evaluation of end-to-end protocols (e.g. routing and transport layer protocols) for CRAHNs. First, we describe NS2-CRAHN, an extension of the NS-2 simulator, which is designed to support realistic simulation of CRAHNs. NS2-CRAHN contains an accurate yet flexible modeling of the activities of PUs and of the cognitive cycle implemented by each CR user. Second, we analyze the impact of CRAHNs characteristics over the route formation process, by considering different routing metrics and route discovery algorithms. Finally, we study TCP performance over CRAHNs, by considering the impact of three factors on different TCP variants: (i) spectrum sensing cycle, (ii) interference from PUs and (iii) channel heterogeneity. Simulation results highlight the differences of CRAHNs with traditional ad hoc networks and provide useful directions for the design of novel end-to-end protocols for CRAHNs.

Analyzing the potential of cooperative Cognitive Radio technology on inter-vehicle communication

Recent studies demonstrate that Cognitive Radio (CR) technology can increase the spectrum efficiency of wireless systems, provided that the activity of primary users (PUs) must be carefully protected. For this reason, several sensing schemes leverage the cooperation among nodes to increase the accuracy of PU detection. In this paper, we propose to employ the CR principles in the vehicular environment in order to increase the spectrum opportunities for inter-vehicle communication (IVC). We propose a cooperative sensing and spectrum allocation scheme through which vehicles can share information about spectrum availability of TV channels on their path, and dynamically decide the channels to use on each road segment. Moreover, we investigate the role of vehicular mobility in the cooperation process, which might allow a vehicle to know in advance the spectrum availability on future locations along its path. Simulation results confirm the ability of our scheme in providing robust PU detection under fading conditions, and analyze the impact of some vehicular networks characteristics into the operations of CR systems.

Cooperative spectrum management in cognitive Vehicular Ad Hoc Networks

In recent years, Cognitive Radio (CR) technology has received significant attention from the research community as it enables on-demand spectrum utilization, based on the requests of the end-users. An interesting application area of CR technology is Vehicular Ad Hoc Networks (VANETs). In such networks, several innovative services and applications based on inter-vehicular communication have strict requirements in terms of bandwidth and delay, which might not be guaranteed by a fixed spectrum allocation paradigm. In this paper, we propose two key contributions pertaining to CR-VANETs: (i) an experimental study of the spectrum availability and sensing accuracy in a moving vehicle and (ii) a collaborative spectrum management framework (called Cog-V2V), which allows the vehicles to share spectrum information, and to detect spectrum opportunities in the licensed band. As part of this framework, we design a collaborative sensing and decision algorithm, enabling the vehicles to share spectrum information and to know in advance the spectrum availability at future locations along their motion paths. The simulation results, produced through a novel integrated simulation platform for CR networks, reveal significant improvements of Cog-V2V in sensing accuracy and pair-wise communication performance compared to classical fixed spectrum approaches.

Routing and Link Layer Protocol Design for Sensor Networks with Wireless Energy Transfer

Wireless sensor networks are equipped with batteries with limited charge, and are often deployed in conditions that make their retrieval and replacement infeasible. Thus, energy conservation has been a primary consideration for protocol design for such networks. Recent advancements in the transfer of energy wirelessly over large distances, such as through radio frequency electromagnetic (EM) waves and magnetic coupling, may give rise to a new class of networks that allow the sensors to be charged on the field, thereby prolonging the network lifetime. Moreover, wireless charging though EM waves may be undertaken in the same unlicensed band as that used for communication, leading to several unique protocol design challenges for such a network. The contribution of this paper is threefold: First, a set of experiments is undertaken to investigate the effect of distance and location on the energy transfer through EM waves. Second, a new routing metric based on the charging ability of the sensor nodes is proposed. Finally, an optimization framework is developed to determine the optimal charging and transmission cycle for the sensor network, resulting in enhanced lifetime of the network under user-specified end-to-end constraints of throughput and latency.

Modeling and performance evaluation of transmission control protocol over cognitive radio ad hoc networks

Cognitive Radio (CR) technology constitutes a new paradigm to provide additional spectrum utilization opportunities in wireless ad hoc networks. Recent research in this field has mainly focused on devising spectrum sensing and sharing algorithms, to allow an opportunistic usage of licensed portions of the spectrum by Cognitive Radio Users (CRUs). However, it is also important to consider the impact of such schemes on the higher layers of the protocol stack, in order to provide efficient end-to-end data delivery. Since TCP is the de facto transport protocol standard on Internet, it is crucial to estimate its ability in providing stable end-to-end communication over Cognitive Radio Ad Hoc Networks (CRAHNs). The contributions of this paper are twofold. First, we propose an extension of the NS-2 simulator to support realistic simulation of CRAHNs. Our extension allows to model the activities of Primary Users (PUs), and the opportunistic spectrum management by CRUs in the licensed band. Second, we provide an accurate simulation analysis of the TCP performance over CRAHNs, by considering the impact of three factors: (i) spectrum sensing cycle, (ii) interference from PUs and (iii) channel heterogeneity. The simulation results show that the sensing interval and the PU activity play a critical role in deciding the optimal end-to-end performance, and reveals the inadequacy of classical TCP to adapt to variable spectrum conditions.

Group communication on highways

Nowadays, most of the applications proposed for Vehicular Ad Hoc Networks (VANETs) rely on geocasting, i.e. on the possibility to identify the end-points of the communication through their geographic coordinates instead of their network addresses. At the same time, each vehicular application has its own set of Quality-of-Service (QoS) requirements which must be guaranteed by the underlying dissemination protocol. This has lead to a proliferation of geocast protocols proposed in the literature of VANETs, usually based on reactive or proactive approaches. However, most of these solutions are tailored for a specific application (e.g. active-safety applications), and thus might not be suitable for generic deployments of VANETs. In this paper, we propose a Dynamic Backbone Assisted (DBA) MAC protocol as a general solution to support geocast communication on highway scenarios for different classes of vehicular applications. DBA-MAC combines the benefits of proactive and reactive schemes through a cross-layer architecture which includes: (i) a novel distributed clustering algorithm and (ii) a fast information dissemination mechanism. First, DBA-MAC creates and maintains a virtual backbone of vehicles inside the highway scenario. Then, it provides fast dissemination of geocast messages through a combination of contention-free and contention-based forwarding mechanisms at the link layer. We provide a complete and exhaustive evaluation of the DBA-MAC scheme under different application requirements and network load conditions. We propose three metrics for the selection of backbone members which provide different characteristics in terms of delivery delay and ratio, and we analyze their performance with both analytical models and simulation studies. Then, we evaluate the performance of DBA-MAC compared to traditional geocast schemes for three classes of vehicular applications: active-safety applications, traffic-information applications, multimedia streaming (audio/video) applications. The simulation results confirm that DBA-MAC is able to greatly reduce the delivery delay for active-safety applications, and to adequately meet the requirements of multimedia applications for VANETs.

By train or by car? Detecting the user's motion type through smartphone sensors data

Nowadays, the increasing popularity of smartphone devices equipped with multiple sensors (e.g. accelerometer, gyroscope, etc) have opened several possibilities to the deployment of novel and exciting context-aware mobile applications. In this paper, we exploit one of this possibility, by investigating how to detect the user motion type through sensors data collected by a smartphone. Our study combines experimental and analytical contributions, and it is structured in three parts. First, we collected experimental data that demonstrate the existence of specific sensors data patterns associated to each motion type, and we propose methods for data analysis and features extraction. Second, we compare the performance of different supervised algorithms for motion type classification, and we demonstrate that jointly utilizing the multiple sensor inputs of a smartphone (i.e. the accelerometer and the gyroscope) can significantly improve the accuracy of the classifiers. At the same time, we analyze the impact of sampling parameters (e.g. the sampling rate) on the system performance, and the corresponding trade-off between classification accuracy and energy consumption of the device. Third, we integrate the motion type recognition algorithm into an Android application, that allows to associate a specific smartphone configuration to each detected motion type, and to provide this information at system-level to other context-aware Android applications. Experimental results demonstrate the ability of our application in detecting the users motion type with high accuracy, and in mitigating the classification errors caused by random data fluctuations.

Urban-X: Towards distributed channel assignment in cognitive multi-radio mesh networks

Researches about multi-radio mesh networks have mostly focused on channel allocation under internal interference. However, the deployment of WMNs in unlicensed bands of dense urban areas imposes many challenges regarding co-existence with residential access points. In this paper, we propose Urban-X, which is a first attempt towards a new architecture for MultiRadio Cognitive Mesh Networks. We develop a novel channel assignment that reflects channel and residential traffic state of external users to maximize network throughput. We evaluate our approach using an enhancement of the ns-2 simulator. Urban-X demonstrate the feasibility of our approach and show robustness to variation of channel environment and external user traffic.