http://hdl.handle.net/2117/1659 2013-05-21T09:03:57Z http://hdl.handle.net/2117/18413 Title: On demonstrating spectrum selection functionality for opportunistic networks Authors: Raschellà, Alessandro; Umbert Juliana, Anna; Pérez Romero, Jordi; Sallent Roig, José Oriol Abstract: This paper presents a testbed platform to demonstrate and validate spectrum opportunity identification and spectrum selection functionalities in Opportunistic Networks (ONs). The hardware component of the testbed is based on reconfigurable devices able to transmit and receive data at different operating frequencies, which are dynamically configured. The software component has been developed to perform the creation and maintenance of ON radio links, including spectrum opportunity identification and selection decision making as well as all the necessary signaling to support the ON operation. Therefore, the presented platform provides a powerful tool for testing different algorithms in real operational radio environments under various interference conditions, thus enabling to gain deeper insight into the performance of algorithmic solutions, beyond the purely theoretical analyses based on models and/or simulations. Results presented in the paper validate the implementation conducted at the laboratory and illustrate the reconfigurability capabilities of the ON links under different conditions. 2013-03-19T15:38:51Z http://hdl.handle.net/2117/18195 Title: Rate adaptive resource allocation with fairness control for OFDMA networks Authors: Bezerra Rodrigues, Emanuel; Casadevall Palacio, Fernando José Abstract: The use of opportunistic radio resource allocation techniques in order to efficiently manage the resources generates a low fairness among the users in a cellular system due to uneven Quality of Service (QoS) distribution. Some classic rate adaptive policies tried to tackle this problem for OFDMA systems by proposing solutions to maximize capacity, maximize fairness, or find a static trade-off between these two objectives. This work generalizes these classic policies and propose a dynamic fairness/rate adaptive technique based on dynamic sub-carrier assignment and equal power allocation that considers a new fairness constraint in the optimization problem. By means of extensive system-level simulations, it is demonstrated that the proposed technique is able to provide an instantaneous (short-term) fairness control, which provides to the network operator the flexibility to operate on any desired trade-off point. 2013-03-11T19:17:39Z http://hdl.handle.net/2117/18079 Title: Envelope tracking amplification with reduced slew-rate and bandwidth envelopes Authors: Vizarreta Paz, Pedro Pablo; Montoro López, Gabriel; Gilabert Pinal, Pere Lluís; Bertran Albertí, Eduardo; Berenguer Sau, Jordi; Gelonch Bosch, Antonio José; García, José Angel Abstract: This paper presents an Envelope Tracking Pow- er Amplifier whose architecture includes a Hybrid Envelope Amplifier (HEA) and an algorithm to adapt the envelope’s characteristics to the HEA’s limitations. The HEA attempts to combine the high efficiency of a switched amplifier with the wide band capabilities of a linear amplifier. A modified Slew Rate (SR) reduction algorithm cope with the bandwidth and SR limitations of the HEA. On the other hand, the non-linearities introduced by this Envelope Amplifier (EA) and by the dynamic supply are compensated using Digital Pre-Distortion. Results show that these non-linearities are compensable and that the architecture offers higher efficiency figures compared to the conventional linear EA 2013-03-05T18:26:37Z http://hdl.handle.net/2117/16741 Title: Exploiting knowledge management for supporting spectrum selection in cognitive radio networks Authors: Pérez Romero, Jordi; Bouali, Faouzi; Sallent Roig, José Oriol; Agustí Comes, Ramon Abstract: Abstract—In order to increase Cognitive Radio operation efficiency, this paper builds up a new knowledge management functional architecture for supporting spectrum management. It integrates the fittingness factor concept proposed by the authors in a prior work and includes a set of advanced statistics capturing the influence of the radio environment. Then, a Knowledge Manager (KM) exploiting these statistics and observed fittingness factor values has been developed to monitor the time-varying suitability of spectrum resources to support heterogeneous services. Based on estimated suitability levels, a new strategy combining Spectrum Selection (SS) and Spectrum Mobility (SM) functionalities has been proposed. Results have shown that the proposed strategy efficiently exploits the KM support at low loads and the SM functionality at high loads to introduce significant gains (ranging from 85% to 100%) w.r.t. a pure random selection while exhibiting substantial robustness to changes in interference levels. 2012-10-17T11:35:31Z http://hdl.handle.net/2117/16740 Title: A Spectrum selection framework for opportunistic networks Authors: Moessner, Klaus; Pérez Romero, Jordi; Sallent Roig, José Oriol; Bouali, Faouzi; Sarvanko, Heli; Mustonen, Miia; Matinmikko, Marja; Lee, Haeyoung; Vahid, Seiamak Abstract: This paper presents a framework for including cognitive management functionalities in the spectrum selection process for Opportunistic Networks (ONs).The framework is based on a decision making functionality interacting with a knowledge management block that stores and processes information about the spectrum use. Different approaches for spectrum selection are discussed covering specific cases including the capability to aggregate different bands and the possibility to jointly select the spectrum and the network interface. Illustrative results of the proposed framework are presented. 2012-10-17T11:18:51Z http://hdl.handle.net/2117/16176 Title: A radio spectrum measurement platform for spectrum surveying in cognitive radio Authors: López Benítez, Miguel; Casadevall Palacio, Fernando José Abstract: This paper presents a sophisticated radio spectrum measurement platform specifically envisaged and designed for spectrum occupancy surveys in the context of Dynamic Spectrum Access/Cognitive Radio (DSA/CR). The presented tool is a very flexible computer-controlled radio measurement system, which has successfully been used in extensive spectrum measurement campaigns and empirical studies in the context of the DSA/CR technology. An exhaustive and in-depth description of the developed measurement platform is provided, with a special emphasis on implementation details and lessons learned during the development of the tool that may result helpful to other researchers and engineers in the development of similar radio spectrum measurement tools. 2012-07-04T16:25:21Z http://hdl.handle.net/2117/16129 Title: Modeling and simulation of joint time-frequency properties of spectrum usage in cognitive radio Authors: Casadevall Palacio, Fernando José; López Benítez, Miguel; López Pérez, David Orencio; Vasilakos, Athanasios V. Abstract: The development of the Dynamic Spectrum Access/Cogni- tive Radio (DSA/CR) technology can signi cantly bene t from the availability of realistic models able to accurately capture and reproduce the statistical properties of spectrum usage in real wireless communication systems. Relying on eld measurements of real systems, this paper analyzes the joint time-frequency statistical properties of spectrum usage and develops adequate models describing the observed char- acteristics. Based on such models, a sophisticated method is also proposed to generate arti cial spectrum data for simulation or other purposes. The proposed method is able to accurately reproduce the statistical time-frequency characteristics of spectrum usage in real systems. 2012-06-22T15:00:44Z http://hdl.handle.net/2117/16128 Title: Modeling and simulation of time-correlation properties of spectrum use in cognitive radio Authors: López Benítez, Miguel; Casadevall Palacio, Fernando José Abstract: The development of the cognitive radio technology can enormously benefit from the availability of realistic and accurate spectrum occupancy models. Time-dimension models of spectrum use proposed in the literature so far are able to capture and reproduce essential temporal characteristics such as the mean occupancy level (duty cycle) and the statistical distribution of busy/idle-period lengths. However, more sophisticated aspects of spectrum use, such as time-correlation properties, have not been properly addressed yet. In this context, this paper studies and analyzes, based on field measurements of various radio technologies, the time-correlation properties of spectrum use. Appropriate models and simulation techniques are proposed in order to accurately capture and reproduce such features. 2012-06-22T14:52:34Z http://hdl.handle.net/2117/16127 Title: Discrete-time spectrum occupancy model based on Markov chain and duty cycle models Authors: Casadevall Palacio, Fernando José; López Benítez, Miguel Abstract: This paper presents an empirical time-dimension model of spectrum use in the context of dynamic spectrum access. Concretely, a discrete-time two-state Markov chain with novel duty cycle models is proposed as an adequate mean to accurately describe spectrum occupancy in the time domain. The validity and accuracy of the proposed model is assessed and corroborated with extensive empirical data from a multiband spectrum measurement campaign. The obtained results demonstrate that the proposed approach is able to capture and reproduce with significant accuracy the statistical properties of spectrum use observed in real channels of various technologies. 2012-06-22T14:47:06Z http://hdl.handle.net/2117/16126 Title: Statistical prediction of spectrum occupancy perception in dynamic spectrum access networks Authors: Casadevall Palacio, Fernando José; López Benítez, Miguel Abstract: Cognitive radio nodes of a dynamic spectrum access network monitor the spectrum around them in order to detect and opportunistically exploit temporarily unoccupied spectrum gaps. The overall behavior of the whole network depends on the spectrum occupancy perceived by each node at its local environment. An appropriate understanding of the local perception of cognitive radio nodes in various scenarios and locations as well as its dependence on the propagation environment can provide valuable information for the design, dimensioning and performance evaluation of dynamic spectrum access networks. In this context, this work presents a novel and practical approach to predict the spectrum occupancy that would be perceived by cognitive radio nodes in realistic scenarios. Based on such approach, we explore the dependence of the spectrum occupancy perception with the considered scenario and location as well as the impact of particular parameters of the radio environment. 2012-06-22T14:41:35Z http://hdl.handle.net/2117/16094 Title: Control channels for the cooperation of cognitive management systems in opportunistic and composite wireless networks Authors: Stavroulaki, Vera; Tsagkaris, Kostas; Georgakopoulos, Andreas; Demestichas, Panagiotis; Ferrús Ferré, Ramón Antonio; Filo, Marcin Abstract: Opportunistic Networks (ONs) are assumed to be temporary, localized extensions of the infrastructure network that are created under certain circumstances. According to that vision, ONs are coordinated by the radio access network (RAN) operator which governs the overal system behaviour (e.g. ON related policies), provides the neccessary resources (e.g. dedicated specturm bands) and supports users in decision making (e.g. additional knowledge and context information). ONs comprise both nodes of the infrastructure and infrastructure-less devices. For the management and control of operator-governed ONs the introduction of Cognitive Management Systems (CMSs), localized on the terminal and infrastructure side, is proposed. The cooperation of CMS entities will require existence of well-defined control channels. In order to enable the necessary signalling between the CMS entities, Control Channels for the Cooperation of the Cognitive Management Systems (C4 MS) are proposed. 2012-06-18T16:50:04Z http://hdl.handle.net/2117/16093 Title: Distributed channel assignment algorithm based on simulated annealing for uncoordinated OSA-enabled WLANs Authors: Novillo Parales, Francisco Vicente; Ferrús Ferré, Ramón Antonio Abstract: A promising approach to alleviate ISM band congestion problems in highly dense WLAN scenarios consists of exploiting opportunistic spectrum access (OSA) to underutilized bands under a primary-secondary model. This paper develops a distributed channel assignment algorithm valid for uncoordinated WLAN deployments where access points do not follow any specific planning and they could belong to different administrative domains. Unlike existing channel assignment schemes proposed for legacy WLANs, channel assignment mechanisms for OSA-enabled WLAN should address two distinguishing issues: channel prioritization and spectrum heterogeneity. Over such a basis, this paper develops and assesses the performance of a distributed channel assignment algorithm that is able to exploit both channel prioritization and spectrum heterogeneity concepts. In particular, the algorithm is based on a distributed adaptation of the simulated annealing metaheuristic algorithm commonly used in global optimization problems. 2012-06-18T16:32:53Z http://hdl.handle.net/2117/16092 Title: Cognitive control channels for the cooperation of opportunistic and composite wireless networks Authors: Gebert, Jens; Georgakopoulos, Andreas; Stavroulaki, Vera; Tsagkaris, Kostas; Ferrús Ferré, Ramón Antonio; Demestichas, Panagiotis Abstract: Opportunistic networks (ONs) are considered as coordinated extensions of a radio access network infrastructure, which are dynamically and temporarily created in an infrastructure-less manner in order to increase service reachability, improve resource utilization efficiency and facilitate localised service provisioning. The realization of the ON concept relies on the existence of control channels which will provide necessary signalling for the coordination of the ON nodes. Proposed control channels are conceived as an evolution of the already established cognitive pilot channel concept. As a result, new interfaces are discussed in order to convey information from the infrastructure to the terminals and vice versa or between terminals. Finally, the business benefits of the aforementioned approach are provided in order to strengthen the notion of the proposed control channels and consider future expansions. 2012-06-18T16:30:08Z http://hdl.handle.net/2117/15375 Title: Context discovery mechanisms for cognitive radio Authors: Bolea, Liliana; Pérez Romero, Jordi; Agustí Comes, Ramon; Sallent Roig, José Oriol Abstract: This paper addresses the estimation of different context parameters of a primary user network based on signal strength measurements obtained by a sensor network and without any prior knowledge of the antenna types used by primary transmitter or the propagation model. The obtained context information can be stored in a database like a Radio Environment Map (REM) and be used to decide the appropriate configuration of a secondary cognitive radio network. Proposed methodology is based on applying image processing over the set of measurements to identify the existing transmitters in the scenario and their parameters such as position, antenna pattern and propagation model. 2012-02-27T10:42:51Z http://hdl.handle.net/2117/15374 Title: Strengthening radio environment maps with primary-user statistical patterns for enhancing cognitive radio operation Authors: Bouali, Faouzi; Sallent Roig, José Oriol; Pérez Romero, Jordi; Agustí Comes, Ramon Abstract: In order to increase spectrum utilization efficiency, CRs (Cognitive Radios) have been introduced to reuse white spaces left unused by legacy services under the strict constraint of not interfering them. In order to fulfill this constraint while optimising spectrum utilisation, it is important to get knowledge about primary-user activity in order to devise proper strategies for secondary-user operation. In this context, this paper proposes to strengthen Radio Environment Maps (REM) with statistical patterns of primary systems that capture among others temporal dependence structures between activity (ON) and inactivity (OFF) periods. Convergence times for the different statistics are analysed. Then, a set of novel spectrum selection criteria exploiting these statistics are proposed and assessed to benchmark the usefulness of primary statistical patterns retained in the REM. Results show that significant performance gains can be achieved in terms of a reduction in the number of required spectrum hand-overs. 2012-02-27T10:35:54Z