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    Title: Time-Knocking: a novel addressing mechanism for wake-up receivers Authors: Oller Bosch, Joaquim; Seyfettin Demirkol, Ilker; Paradells Aspas, Josep; Casademont Serra, Jordi; Heinzelman, Wendi Abstract: Wake-up radios present a promising alternative to traditional duty-cycle approaches, by reducing overhearing and by eliminating idle listening completely. However, energy-efficient operation of the wake-up mechanism is required for the success of such systems. In particular, addressing is an important component of the wake-up procedure that can consume a significant portion of the energy required. Hence, in this paper we propose a novel energy-efficient scheme for addressing. The proposed method is called Time-Knocking (TicK), since it utilizes the time duration of the MicroController Unit (MCU) sleeping to encode an address. In this paper, it is shown through mathematical analysis that TicK is much more energy efficient compared to the two common addressing mechanisms: MCU-decoding and correlator-based addressing. For realistic performance evaluations, physical measurements are performed to extract the parameter values of each method or the parameter values from well-documented off-the-shelf devices are used. TicK enables significant energy savings, especially in environments where false addressing initiations are frequent due to interference or where multiple nodes are addressed frequently.

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    Title: Design, development and performance evaluation of a low-cost, Low-power wake-up radio system for WSN Authors: Oller Bosch, Joaquim; Seyfettin Demirkol, Ilker; Casademont Serra, Jordi; Paradells Aspas, Josep Abstract: Energy-efficient operation is a challenge for wireless sensor networks (WSNs). A common method employed for this purpose is duty-cycled operation, which extends battery lifetime yet incurs several types of energy wastes and challenges. A promising alternative to duty-cycled operation is the use of wake-up radio (WuR), where the main microcontroller unit (MCU) and transceiver, that is, the two most energy-consuming elements, are kept in energy-saving mode until a special signal from another node is received by an attached, secondary, ultra-low power receiver. Next, this so-called wake-up receiver generates an interrupt to activate the receiver node's MCU and, consequently, the main radio. This article presents a complete wake-up radio design that targets simplicity in design for the monetary cost and flexibility concerns, along with a good operation range and very low power consumption. Both the transmitter (WuTx) and the receiver (WuRx) designs are presented with the accompanying physical experiments for several design alternatives. Detailed analysis of the end system is provided in terms of both operational distance (more than 10 m) and current consumption (less than 1 µA). As a reference, a commercial WuR system is analyzed and compared to the presented system by expressing the trade-offs and advantages of both systems. © 2013 ACM.

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    Title: Energy efficient wireless networking of sensor nodes Authors: Seyfettin Demirkol, Ilker; Paradells Aspas, Josep; Oller Bosch, Joaquim; Casademont Serra, Jordi; Calveras Augé, Anna M.; Catalán Cid, María Luisa Abstract: Wireless sensor networks have paved the way to a new era in user applications, where information can be sensed, processed, and distributed from remote environments with minimal or no human interaction. As the sensor nodes in these networks are often battery-operated and communicate wirelessly, they are constrained by limited resources such as bandwidth, processing speed and especially by energy. Therefore, depending on the user application, different challenges are encountered for the realization of wireless sensor networks. In this paper, we will present several reallife applications along with the challenges encountered and benefits provided by the networking of the sensors for these applications.

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    Title: Congestion control in reliable CoAP communication Authors: Betzler, August; Gómez Montenegro, Carlos; Seyfettin Demirkol, Ilker; Paradells Aspas, Josep Abstract: The development of IPv6 stacks for wireless constrained devices that have limited hardware resources has paved the way for many new areas of applications and protocols. The Constrained Application Protocol (CoAP) has been designed by the IETF to enable the manipulation of resources for constrained devices that are capable of connecting to the Internet. Due to the limited radio channel capacities and hardware resources, congestion is a common phenomenon in networks of constrained devices. CoAP implements a basic congestion control mechanism for the transmission of reliable messages. Alternative CoAP congestion control approaches are a recent topic of interest in the IETF CoRE Working Group. New Internet-Drafts discuss the limitations of the default congestion control mechanisms and propose alternative ones, yet, there have been no studies in the literature that compare the original approach to the alternative ones. In this paper, we target this crucial study and perform evaluations that show how the default and alternative congestion control mechanisms compare to each other. We use the Cooja simulation environment, which is part of the Contiki development toolset, to simulate CoAP within a complete protocol stack that uses IETF protocols for constrained networks. Through simulations of different network topologies and varying traffic loads, we demonstrate how the advanced mechanisms proposed in the drafts perform relative to the basic congestion control mechanism.

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    Title: Wake-up radio as an energy-efficient alternative to conventional wireless sensor networks MAC protocols Authors: Oller Bosch, Joaquim; Seyfettin Demirkol, Ilker; Casademont Serra, Jordi; Paradells Aspas, Josep; Gamm, Gerd Ulrich; Reindl, Leonhard Abstract: The use of duty-cycling in Medium Access Control (MAC) protocols effectively helps improving the energy efficiency of wireless networks. However, while the benefits of these protocols are unquestionable, most of them still suffer from overhearing and idle listening, two issues that prevent duty-cycled systems from achieving optimum energy usage, which is a crucial aspect in specific types of wireless networks such as Wireless Sensor Networks (WSN).Wake-up Radio (WuR) systems have been employed recently to overcome these issues. Under this approach, the nodes' MicroController Unit (MCU) and main radio transceiver are completely switched off and only activated when a secondary, extremely low-power receiver in the node is triggered by a particular wireless transmission. Wake-up Radio systems allow for drastic energy savings since receiver nodes are only activated on-demand, maximizing their battery lifetimes. In this paper, we have modeled and simulated a real, recent and promising WuR hardware platform based on its time and energy consumption characterization. By comparing such WuR approach to B-MAC and IEEE 802.15.4, two well-known and widely employed MAC protocols, we show it effectively out-performs the conventional WSN MAC approaches in terms of energy efficiency. To the best of authors' knowledge, this is the first study to include a comparative analysis for multi-hop networks based on a real WuR platform, which shows WuR systems represent an energy-efficient solution that also provides a good tradeoff between latency, packet delivery ratio and applicability..

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    Título: A new class of codes for fingerprinting schemes Autor: Fernández Muñoz, Marcel; Soriano Ibáñez, Miguel; Cotrina Navau, Josep Resumen: In this paper we discuss the problem of collusion secure fingerprinting. In the first part of our contribution we prove the existence of equidistant codes that can be used as fingerprinting codes. Then we show that by giving algebraic structure to the equidistant code, the tracing process can be accomplished by passing a modified version of the Viterbi algorithm through the trellis representing the code.

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    Título: A note about the traceability properties of linear codes Autor: Fernández Muñoz, Marcel; Cotrina Navau, Josep; Soriano Ibáñez, Miguel; Domingo, Neus Resumen: We characterize the traceability properties of linear codes. It is well known that any code of length n and minimum distance d is a c-TA code if c 2¿

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    Título: Tracing traitors by guessing secrets. The q-ary case Autor: Fernández Muñoz, Marcel; Soriano Ibáñez, Miguel; Cotrina Navau, Josep Resumen: In this paper we present, by solving a variant of the guessing secrets problem defined by Chung, Graham and Leighton [3], a sequential traitor tracing scheme equipped with an efficient identification algorithm. Sequential traitor tracing schemes are used to detect piracy in multimedia content broadcast systems, where the traitors illegally rebroadcast the content they receive to unauthorized users.

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    Título: Analytical model of large data transactions in CoAP networks Autor: Ludovici, Alessandro; Di Marco, Piergiuseppe; Calveras Augé, Anna M.; Johansson, Karl H. Resumen: We propose a novel analytical model to study fragmentation methods in wireless sensor networks adopting the Constrained Application Protocol (CoAP) and the IEEE 802.15.4 standard for medium access control (MAC). The blockwise transfer technique proposed in CoAP and the 6LoWPAN fragmentation are included in the analysis. The two techniques are compared in terms of reliability and delay, depending on the traffic, the number of nodes and the parameters of the IEEE 802.15.4 MAC. The results are validated trough Monte Carlo simulations. To the best of our knowledge this is the first study that evaluates and compares analytically the performance of CoAP blockwise transfer and 6LoWPAN fragmentation. A major contribution is the possibility to understand the behavior of both techniques with different network conditions. Our results show that 6LoWPAN fragmentation is preferable for delay-constrained applications. For highly congested networks, the blockwise transfer slightly outperforms 6LoWPAN fragmentation in terms of reliability.

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    Título: Infrastructureless smart cities. Use cases and performance Autor: Paradells Aspas, Josep; Gómez Montenegro, Carlos; Seyfettin Demirkol, Ilker; Oller Bosch, Joaquim; Catalan Cid, Maria Luisa Resumen: Smart cities are a hot topic nowadays for several reasons. For city managers and citizens a smart city is a concept that should allow providing better services and/or with more efficiency. For technicians a smart city represents one of the large-scale deployments of equipment for data capturing, storage and processing. For Internet researchers a smart city can become the first massive installments of the Internet of Things concept. Smart cities are commonly implemented in several parts: the data acquisition and actuation, the aggregation networks that connect sensors/actuators with the general purpose network, the platform where data is stored and processed and the application that use the information for informing the city managers and citizens. The most costly parts of a smart city are the sensor/actuator and the aggregation network. This cost is due mainly due to the deployment and maintenance of the equipment on the city street. This paper describes the different alternatives for building the aggregation networks and provides a novel approach to facilitate the deployment of a smart city. This new solution has been tested in a real scenario achieving satisfactory results. © 2014 IEEE.

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    Título: A proxy design to leverage the interconnection of CoAP wireless sensor networks with web applications Autor: Ludovici, Alessandro; Calveras Augé, Anna M. Resumen: In this paper, we present the design of a Constrained Application Protocol (CoAP) proxy able to interconnect Web applications based on Hypertext Transfer Protocol (HTTP) and WebSocket with CoAP based Wireless Sensor Networks. Sensor networks are commonly used to monitor and control physical objects or environments. Smart Cities represent applications of such a nature. Wireless Sensor Networks gather data from their surroundings and send them to a remote application. This data flow may be short or long lived. The traditional HTTP long-polling used by Web applications may not be adequate in long-term communications. To overcome this problem, we include the WebSocket protocol in the design of the CoAP proxy. We evaluate the performance of the CoAP proxy in terms of latency and memory consumption. The tests consider long and short-lived communications. In both cases, we evaluate the performance obtained by the CoAP proxy according to the use of WebSocket and HTTP long-polling.

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    Título: IEEE 802.11-enabled wake-up radio system: design and performance evaluation Autor: Oller Bosch, Joaquim; García Villegas, Eduard; López Aguilera, M. Elena; Seyfettin Demirkol, Ilker; Casademont Serra, Jordi; Paradells Aspas, Josep; Gamm, Gerd Ulrich; Reindl, Leonhard Michael Resumen: Today, the vast majority of personal communication devices, such as laptops, smartphones, and logically wireless fidelity (Wi-Fi) access points feature IEEE 802.11 chipsets. In turn, wake-up radio (WuR) systems are used to reduce the significant energy waste that wireless devices cause during their idle communication mode. A novel WuR system is introduced that enables any IEEE 802.11-enabled device to be used as a WuR transmitter without requiring any hardware modification. The corresponding developed WuR receiver achieves a remarkably low power consumption of 10.8 µW and operates in the Wi-Fi 2.4 GHz band. By means of thorough physical tests, it is shown that the proposed IEEE 802.11-based WuR system enables important energy savings.

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    Título: Networking solutions for connecting bluetooth low energy enabled machines to the internet of things Autor: Nieminen, Johanna; Gómez Montenegro, Carlos; Isomaki, Markus; Savolainen, Teemu; Patil, Basavaraj; Shelby, Zach; Oller Bosch, Joaquim Resumen: The next wave driving the expansion of the Internet will come from the Internet of Things. Bluetooth LE is a rapidly emerging ultra-low-power radio technology expected to be incorporated in billions of IoT devices in the next few years. Consequently, it is particularly important to specify Internet connectivity solutions for Bluetooth LE. In this article we present such solutions based on the ongoing standardization work in the IETF and Bluetooth Special Interest Group. We prove the feasibility of a complete IP-based protocol stack on constrained devices and illustrate its performance, highlighting key trade-offs. In addition, we discuss gateway operation covering global IPv6 connectivity and proxy-cache functionality.

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    Título: Modeling the network convergence time in RPL in error-prone, IEEE 802.15.4 chain topology multihop networks Autor: Kermajani, Hamidreza; Gómez Montenegro, Carlos Resumen: This paper presents an analytical model for estimating the network convergence time of IPv6 Routing Protocol for Low-power and Lossy Networks (RPL) in a static chain topology network of IEEE 802.15.4 nodes, in the presence of bit errors. The model presented is validated by extensive simulation results. We show that performance degradation may be noticed by a user for BER values around or greater than 8·10

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    Título: Token-MAC: A fair MAC protocol for passive RFID systems Autor: Chen, Li; Seyfettin Demirkol, Ilker; Heinzelman, Wendi Resumen: Passive RFID systems used for inventory management and asset tracking typically utilize contention-based MAC protocols, such as the standard C1G2 protocol. Although the C1G2 protocol has the advantage that it is easy to implement, it suffers from unfairness and relatively low throughput when the number of tags in the network increases. This paper proposes a token-based MAC protocol called Token-MAC for passive RFID systems, which aims a) to provide a fair chance for tags in the network to access the medium without requiring synchronization of the tags, b) to increase the overall throughput, i.e., the tag rate, and c) to enable a high number of tags to be read under limited tag read time availability, which is an especially important challenge for mobile applications. We implement Token-MAC as well as C1G2 and a TDMA-based protocol using Intel WISP passive RFID tags and perform experiments. Additionally, based on our experimental results, we develop energy harvesting and communication models for tags that we then use in simulations of the three protocols. Our experimental and simulation results all show that Token-MAC can achieve a higher tag rate and better fairness than C1G2, and it can provide better performance over a longer range compared with the TDMA-based protocol. It is also shown that Token-MAC achieves much lower tag detection delay, especially for high numbers of tags. Token-MAC is, therefore, a promising solution for passive RFID systems.

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    Título: On the network convergence process in RPL over IEEE 802.15.4 multihop networks: improvement and trade-offs Autor: Kermajani, Hamidreza; Gómez Montenegro, Carlos Resumen: The IPv6 Routing Protocol for Low-power and Lossy Networks (RPL) has been recently developed by the Internet Engineering Task Force (IETF). Given its crucial role in enabling the Internet of Things, a significant amount of research effort has already been devoted to RPL. However, the RPL network convergence process has not yet been investigated in detail. In this paper we study the influence of the main RPL parameters and mechanisms on the network convergence process of this protocol in IEEE 802.15.4 multihop networks. We also propose and evaluate a mechanism that leverages an option available in RPL for accelerating the network convergence process. We carry out extensive simulations for a wide range of conditions, considering different network scenarios in terms of size and density. Results show that network convergence performance depends dramatically on the use and adequate configuration of key RPL parameters and mechanisms. The findings and contributions of this work provide a RPL configuration guideline for network convergence performance tuning, as well as a characterization of the related performance trade-offs.

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    Título: A holistic approach to ZigBee performance enhancement for home automation networks Autor: Betzler, August; Gómez Montenegro, Carlos; Seyfettin Demirkol, Ilker; Paradells Aspas, Josep Resumen: Wireless home automation networks are gaining importance for smart homes. In this ambit, ZigBee networks play an important role. The ZigBee specification defines a default set of protocol stack parameters and mechanisms that is further refined by the ZigBee Home Automation application profile. In a holistic approach, we analyze how the network performance is affected with the tuning of parameters and mechanisms across multiple layers of the ZigBee protocol stack and investigate possible performance gains by implementing and testing alternative settings. The evaluations are carried out in a testbed of 57 TelosB motes. The results show that considerable performance improvements can be achieved by using alternative protocol stack configurations. From these results, we derive two improved protocol stack configurations for ZigBee wireless home automation networks that are validated in various network scenarios. In our experiments, these improved configurations yield a relative packet delivery ratio increase of up to 33.6%, a delay decrease of up to 66.6% and an improvement of the energy efficiency for battery powered devices of up to 48.7%, obtainable without incurring any overhead to the network.

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    Título: Uso de métodos ágiles y PBL en una asignatura de ingeniería del software del grado de ingeniería telemática: gestión de proyectos de ingeniería del software en un entorno docente Autor: Oller Arcas, Antonio; Gallardo Gómez, Antonia; García Villegas, Eduard; Valero García, Miguel Resumen: Actualmente, empresas como Amazon o Google aplican un método llamado Scrum para agilizar el proceso de desarrollo de sus proyectos software y mejorar la calidad de los resultados. Por otro lado, en el entorno docente, la metodología del aprendizaje basado en proyectos o PBL se afianza cada día más porque, además de potenciar la motivación de los estudiantes, facilita el desarrollo de competencias transversales. Este documento describe cómo se aplica Scrum en una asignatura que sigue los conceptos de PBL y presenta los primeros resultados obtenidos. Dichos resultados apuntan a que Scrum aporta beneficios a PBL.

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    Enhanced multiclass SVM with thresholding fusion for speech-based emotion classification Yang, Na; Yuan, Jianbo; Zhou, Yun; Seyfettin Demirkol, Ilker; Duan, Zhiyao; Heinzelman, Wendi; Sturge Apple, Melissa L. As an essential approach to understanding human interactions, emotion classification is a vital component of behavioral studies as well as being important in the design of context-aware systems. Recent studies have shown that speech contains rich information about emotion, and numerous speech-based emotion classification methods have been proposed. However, the classification performance is still short of what is desired for the algorithms to be used in real systems. We present an emotion classification system using several one-against-all support vector machines with a thresholding fusion mechanism to combine the individual outputs, which provides the functionality to effectively increase the emotion classification accuracy at the expense of rejecting some samples as unclassified. Results show that the proposed system outperforms three state-of-the-art methods and that the thresholding fusion mechanism can effectively improve the emotion classification, which is important for applications that require very high accuracy but do not require that all samples be classified. We evaluate the system performance for several challenging scenarios including speaker-independent tests, tests on noisy speech signals, and tests using non-professional acted recordings, in order to demonstrate the performance of the system and the effectiveness of the thresholding fusion mechanism in real scenarios.

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    Throughput and range characterization of IEEE 802.11ah Baños González, Víctor Hugo; Afaqui, Muhammad Shahwaiz; López, Elena; García Villegas, Eduard © 2017 IEEE. The most essential part of Internet of Things (IoT) infrastructure is the wireless communication system that acts as a bridge for the delivery of data and control messages. However, the existing wireless technologies lack the ability to support a huge amount of data exchange from many battery driven devices spread over a wide area. In order to support the IoT paradigm, the IEEE 802.11 standard committee is in process of introducing a new standard, called IEEE 802.11ah. This is one of the most promising and appealing standards, which aims to bridge the gap between traditional mobile networks and the demands of the IoT. In this paper, we first discuss the main PHY and MAC layer amendments proposed for IEEE 802.11ah. Furthermore, we investigate the operability of IEEE 802.11ah as a backhaul link to connect devices over a long range. Additionally, we compare the aforementioned standard with previous notable IEEE 802.11 amendments (i.e. IEEE 802.11n and IEEE 802.11ac) in terms of throughput (with and without frame aggregation) by utilizing the most robust modulation schemes. The results show an improved performance of IEEE 802.11ah (in terms of power received at long range while experiencing different packet error rates) as compared to previous IEEE 802.11 standards.

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