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Assessment Activities in MOOCs
No full textThis chapter analyzes the different implications of the new MOOC paradigm in assessment activities, emphasizing the differences with respect to other non MOOC educational technology environments and giving an insight about the redesign of assessment activities for MOOCs. The chapter also compares the different assessment activities that are available in some of the most used MOOC platforms at present. In addition, the process of design of MOOC assessment activities is analyzed. Specific examples are given about how to design and create different types of assessment activities. The Genghis authoring tool as a solution for the creation of some types of exercises in the Khan Academy platform is presented. Finally, there is an analysis of the learning analytics features related to assessment activities that are present in MOOCs. Moreover, some guidelines are provided about how to interpret and take advantage of this information.TRUEpu
Architectures for intelligent vehicles
No full textArchitectures decompose complex engineering problems into smaller, more manageable pieces, the modules of the architecture. The objective is to engineer, implement, and test the modules separately. If the modules have well-defined interfaces and implement well-defined services, it is possible to modify some of the modules, without modifying them all. As intelligent vehicles evolve, because of better sensors, better control mechanisms, and new applications, most of the modules in the previous implementation can be reused, rather than requiring an entirely new implementation.
The modules in the architecture also isolate operations that require specialized knowledge. In intelligent vehicles, some operations require knowledge of the physics of motion of the vehicle, the stability of different control mechanisms, or the limitations of different sensing mechanisms. By performing operations that require specialized knowledge in independent modules, experts on a topic can implement the appropriate modules without requiring any one person to be expert in everything.
The architectures that are being designed for intelligent vehicles are changing from simple interconnections of modules to layered architectures, similar to those used in communications networks. A layered architecture has successfully allowed the Internet to evolve over the past 50 years.
Intelligent vehicles are more complex than communications networks. They interact with the physical world in many ways, and collaborative maneuvers are time critical. An architecture that satisfies the new requirements, while preserving the characteristics of traditional architectures, is described.TRUEpu
Modelling D2D Communications in Cellular Access Networks via Coupled Processors
Get PDFThis paper presents a first fully analytical approach to performance evaluation of D2D communication systems, which does not assume the system to be in saturated conditions. We adopt a Coupled Processors model to describe a cellular scenario with D2D users sharing radio resources with cellular users, i.e., adopting in-band underlay D2D schemes. We derive sufficient conditions for stability of such system, characterizing the effect of D2D transmissions on cellular user performance. Moreover, we present a computationally feasible method for the determination of a proportionally fair allocation of resources. We show that, in non-saturated networks, such an allocation sensibly improves the one derived under the assumption of saturation. Our results show the importance of accurately modelling the interdependence in users performance in the design and evaluation of a D2D cellular system.TRUEpu
Efficient Networking in Millimeter Wave Bands
No full textState-of-the-art wireless communication already operates close to Shannon capacity and one of the most promising options to further increase data rates is to increase the communication bandwidth. Very high bandwidth channels are only available in the extremely high frequency part of the radio spectrum, the millimeter wave band (mm-wave). Upcoming communication technologies, such as IEEE 802.11ad, are already starting to exploit this part of the radio spectrum to achieve data rates of several GBit/s. However, communication at such high frequencies also suffers from high attenuation and signal absorption, often restricting communication to line-of-sight (LOS) scenarios and requiring the use of highly directional antennas. This in turn requires a radical rethinking of wireless network design. On the one hand side, such channels experience little interference, allowing for a high degree of spatial reuse and potentially simpler MAC and interference management mechanisms. On the other hand, such an environment is extremely dynamic and channels may appear and disappear over very short time intervals, in particular for mobile devices. This talk will highlight some of the challenges of and possible approaches for networking in the mm-wave band.TRUEpu
Deep Inspection of the Noise in WiFi Time-of-Flight Echo Techniques
Get PDFTime-of-flight (ToF) echo techniques have been proposed to estimate the distance between a local and a target station using regular WiFi radio devices. As of today, there is little understanding of the noise sources from ToF measurements. We conduct extensive experimental tests based on a customized WiFi echo technique implementation residing in the core of the 802.11 MAC processor and a high-resolution signal analysis of the WiFi traffic captured with a wideband oscilloscope. We discern the root of the error components in WiFi echo technique measurements and statistically characterize the offset noise added by the target station. Our measurements provide key insights to model the sources of noise and guidance for the design of robust distance estimators.TRUEpu
Empirical comparison of power-efficient virtual machine assignment algorithms
Get PDFhttp://dx.doi.org/10.1109/SustainIT.2015.7101361The advent of cloud computing has changed the way many companies do computation, allowing them to outsource it to the cloud. This has given origin to a new kind of business, the cloud providers, which run large datacenters. In order to be competitive, cloud providers must keep the energy consumed by the datacenter low. One way to achieve this is with smart task assignment algorithms, which decide where tasks are to be placed upon their arrival. In this paper we compare the performance of multiple task assignment algorithms for saving energy. We assume tasks are in fact virtual machines that have to be assigned to physical machines, and we assume that the physical machines have a power consumption that increases superlinearly with the load. Then, we propose an assignment algorithm VMA2 and compare its performance with other state-of-the-art assignment algorithms, both theoretical or already deployed in real cloud computing platforms. VMA2 leads to low energy consumption. It outperforms the other algorithms in most situations, proving itself to be an effective assignment algorithm for cloud computing platforms.TRUEpu
Low-Cost, Flexible and Open Platform for Visible Light Communication Networks
Get PDFBuilt around a cost-effective embedded Linux system, OpenVLC1.0 is an open source, flexible, software-defined, and low-cost platform for research in Visible Light Communication (VLC) Networks. OpenVLC1.0 consists of simple electronic hardware for optical transmission and reception, and of software implementation that runs the MAC layer, part of the PHY layer, and offers an interface to Internet protocols. We have designed and developed a printed circuit board (OpenVLC1.0 cape) that implements a flexible optical front-end. Researchers can plug the cape into the main Beaglebone board and swiftly build and prototype innovative PHY and MAC protocols using the software implementation (OpenVLC1.0 driver). In this work, we provide preliminary measurement results that demonstrate the flexibility of the platform in a few but yet representative scenarios.TRUEpu
Cost-Effective Multi-Mode Offloading with peer-assisted communications
Get PDFData offloading through WiFi networks has been identified as a promising solution to cellular network congestion caused by the ongoing explosive growth in mobile data traffic. In this paper, we propose Cost-Effective Multi-Mode Offloading (CEMMO) that enhances offloading with multi-hop peer-assisted communications regardless of content and popularity. CEMMO enables three modes of communication: cellular delivery, delay-tolerant offloading, and peer-assisted offloading. Exploiting user knowledge on mobility and WiFi connectivity, CEMMO assists the cellular operator in selecting the best out of its three modes in order to reduce the overall cost in terms of financial settlement, energy consumption, and user satisfaction. Our simulations with a realistic mobility and connectivity prediction model based on a Markov process show that CEMMO offloads up to 59% of the mobile data traffic and reduces transfer cost per MB up to 16% over delay-tolerant offloading. This paper also discusses practical issues in CEMMO adoption.pu
CMCD: Multipath Detection for Mobile GNSS Receivers
Get PDFIn recent years, the rising demand for high precision
localization has challenged the use of GNSS particularly
in automotive applications. This is especially the case in
urban scenarios where the most crucial GNSS disturbance
is multipath – the reception of reflected signals. This work
addresses the detection of multipath errors in pseudorange
measurements for the special case of a moving receiver
without the need for redundant observations or motion sensors.
Our proposed detection scheme is based on a combined
observable we call CMCD (Code-Minus-Carrier
Deltarange). It is defined as the difference between
code- and carrier-derived deltaranges and approximately
resolves to the derivatives of the receiver noise and the code multipath error. The CMCD-based detection algorithm
exploits the fact that the CMCD observable is equal to the
receiver noise process for multipath-free environments.
Simulations of a two ray multipath model show that the
code multipath error can be described as a broadband
noise process in case of a moving receiver and an abrasive
reflection surface. This additional noise process causes
changes in the statistical properties of CMCD and hence
indicate multipath occurrences. A statistical test is used to detect these changes.
With a test drive under heavy mutlipath conditions the
detection performance was evaluated and the suitability of
CMCD-based multipath detection was shown. The results
indicate a correlation between multipath detections and high
ranging errors. In addition, the horizontal position error
with a set of 4 satellites was evaluated. In cases of at least one multipath-affected pseudorange a resulting position error of around 15 m (CEP95) and above was observed. With measurements detected as multipath-free the resulting error was around 5 m (CEP95).TRUEpu
