C. Lopez-Bravo

Bio: C. Lopez-Bravo is an academic researcher from University of Vigo. The author has contributed to research in topics: Packet switching & Network packet. The author has an hindex of 5, co-authored 31 publications receiving 160 citations. Previous affiliations of C. Lopez-Bravo include Polytechnic University of Puerto Rico & Universidad Politécnica de Cartagena.

Experiences inside the Ubiquitous Oulu Smart City

Abstract: The UrBan Interactions (UBI) research program, coordinated by the University of Oulu, has created a middleware layer on top of the panOULU wireless network and opened it up to ubiquitous-computing researchers, offering opportunities to enhance and facilitate communication between citizens and the government.

Practical Scalability of Wavelength Routing Switches

Abstract: Packet switches with optical fabrics can potentially scale to higher capacities. It is also potentially possible to improve their reliability, and reduce both their footprint and power consumption. A well-known alternative for implementing hardwired switches is Arrayed Waveguide Grating (AWG). Ideally, AWG insertion losses do not depend on the number of input-output ports, meaning that scalability is theoretically infinite. However, accurate second-order assessment has demonstrated that in-band crosstalk exponentially increases the power penalty, limiting the realistic useful size of AWG commercial devices to about 10-15 ports (13-18 dB) [1]. On the other hand, the in-band crosstalk at AWG outputs depends on the connection pattern set by the scheduling algorithm and this port count limitation is calculated for worst-case scenarios. In this paper, we show that distributed schedulers with predetermined connection patterns can be used to avoid these harmful arrangements. We also show that the probability of worst-case patterns is very low, allowing us to set a more realistic port limit for general centralized schedulers and very small losses. With these results, we calculate more realistic port count limits for both scheduler types.

On the behavior of PHM distributed schedulers for input buffered packet switches

Abstract: iSLIP and parallel hierarchical matching (PHM) are distributed maximal size matching schedulers for input-buffered switches. Previous research has analyzed the hardware cost of those schedulers and their performance after a small number of iterations. In this paper, we formulate an upper bound for the number of iterations required by PHM to converge. Then, we compare the number of iterations required by iSLIP and PHM to achieve a maximal throughput under uniform Bernoulli traffic, by means of simulation. Finally, we obtain the corresponding delay performances, which are similar. The results suggest that PHM has both the advantages of previous hierarchical matching algorithms (low hardware complexity) and iSLIP (low number of iterations).

On the Implementation of a Multi-Reader Radio Frequency Identification (RFID) Architecture

Abstract: Radio Frequency Identification (RFID) systems are one of the enabling technologies for the ubiquitous computing paradigm. At the moment, the EPCglobal organization leads the development of industry-driven standards for this field and has settled the EPC "Gen 2" as a reference standard. In this paper, we analyze the anti-collision procedure of EPC "Gen 2" to find the time needed to identify a population of tags, by means of the finite Markov-chain of the system. In addition, a UHF multi-reader prototype based on time division multiple access (TDMA) scheme is evaluated in this work. In this TDMA scheme, the reader time-slot duration is allocated according to the computations obtained from our analytical study. The main conclusions derived from this implementation are summarized in this work.

Fast Decision Algorithms for Efficient Access Point Assignment in SDN-Controlled Wireless Access Networks

Abstract: Global optimization of access point (AP) assignment to user terminals requires efficient monitoring of user behavior, fast decision algorithms, efficient control signaling, and fast AP reassignment mechanisms. In this scenario, software defined networking (SDN) technology may be suitable for network monitoring, signaling, and control. We recently proposed embedding virtual switches in user terminals for direct management by an SDN controller, further contributing to SDN-oriented access network optimization. However, since users may restrict terminal-side traffic monitoring for privacy reasons (a common assumption by previous authors), we infer user traffic classes at the APs. On the other hand, since handovers will be more frequent in dense small-cell networks (e.g., mmWave-based 5G deployments will require dense network topologies with inter-site distances of ~150–200 m), the delay to take assignment decisions should be minimal. To this end, we propose taking fast decisions based exclusively on extremely simple network-side application flow-type predictions based on past user behavior. Using real data we show that a centralized allocation algorithm based on those predictions achieves network utilization levels that approximate those of optimal allocations. We also test a distributed version of this algorithm. Finally, we quantify the elapsed time since a user traffic event takes place until its terminal is assigned an AP, when needed.

What makes a city smart? Identifying core components and proposing an integrative and comprehensive conceptualization

Abstract: This study represents two critical steps forward in the area of smart city research and practice The first is in the form of the development of a comprehensive conceptualization of smart city as a resource for researchers and government practition- ers; the second is in the form of the creation of a bridge between smart cities research and practice expertise City governments increasingly need innovative arrangements to solve a variety of technical, physical, and social problems "Smart city" could be used to represent efforts that in many ways describe a vision of a city, but there is little clarity about this new concept This paper proposes a comprehensive conceptualization of smart city, including its main components and several specific elements Academic literature is used to create a robust framework, while a review of practical tools is used to identify specific elements or aspects not treated in the academic studies, but essential to create an integrative and comprehensive conceptualization of smart city The paper also provides policy implications and suggests areas for future research in this topic

Privacy in the Smart City—Applications, Technologies, Challenges, and Solutions

Abstract: Many modern cities strive to integrate information technology into every aspect of city life to create so-called smart cities. Smart cities rely on a large number of application areas and technologies to realize complex interactions between citizens, third parties, and city departments. This overwhelming complexity is one reason why holistic privacy protection only rarely enters the picture. A lack of privacy can result in discrimination and social sorting, creating a fundamentally unequal society. To prevent this, we believe that a better understanding of smart cities and their privacy implications is needed. We therefore systematize the application areas, enabling technologies, privacy types, attackers, and data sources for the attacks, giving structure to the fuzzy term “smart city.” Based on our taxonomies, we describe existing privacy-enhancing technologies, review the state of the art in real cities around the world, and discuss promising future research directions. Our survey can serve as a reference guide, contributing to the development of privacy-friendly smart cities.

A Fully Integrated 900-MHz Passive RFID Transponder Front End With Novel Zero-Threshold RF–DC Rectifier

Abstract: This paper presents a fully integrated CMOS analog front end for a passive 900-MHz radio-frequency identification (RFID) transponder. The power supply in this front end is generated from the received RF electromagnetic energy by using an RF-dc voltage rectifier. In order to improve the compatibility with standard CMOS technology, Schottky diodes in conventional RF-dc rectifiers are replaced by diode-connected MOS transistors with zero threshold. Meanwhile, theoretical analyses for the proposed rectifier are provided and verified by both simulation and measurement results. The design considerations of the pulsewidth-modulation (PWM) demodulator and the backscatter modulator in the front end are also discussed for low-power applications. The proposed front end is implemented in a 0.35-mum 2P4M CMOS technology. The whole chip occupies a die area of 490 times 780 mum2 and consumes only 2.1 muW in reading mode under a self-generated 1.5-V supply voltage. The measurement results show that the proposed rectifier can properly operate with a -14.7-dBm input RF power at a power conversion efficiency of 13.0%. In the proposed RFID applications, this sensitivity corresponds to 10.88-m communication distance at 4-W equivalent isotropically radiated power from a reader base station.