Carlos Turro

A fast design model for indoor radio coverage in the 2.4 GHz wireless LAN

In this paper, an empiric radio coverage model for indoor wireless LAN is presented. This model has been tried out in a vast series of large extension buildings obtaining successful results. The objective of the model is to facilitate the radio design work of a wireless LAN by means of straightforward calculations, because the use of statistical methods is very time consuming, and difficult to put in practice at most situations. Our model is based on a derivation of the free field propagation equation taking into account the building structure and its materials and it has been tested on a large scale design of a WLAN network of over 400 access points. Finally, the paper includes the guidelines to setup a home, building, university campus, or city wireless LAN easily in three simple steps.

IEEE 802.11a/b/g/n Indoor Coverage and Performance Comparison

There are several IEEE 802.11 variants to interconnect several wireless devices. Usually, a variant is chosen based on their bandwidth and their coverage area. However, sometimes, there are special cases where the best technology is not the newest one. E.g., in the case where devices are going to transmit at a maximum of 1 Mbps, any choice is acceptable. In this paper, we are going to compare IEEE 802.11a/b/g/n in indoor environments in order to know which technology is better. This comparison will be taken in terms of RSSI, coverage area, and measuring the interferences between channels. This study will help the researchers to choose the best technology depending of their deploying case and we will see that the best technologies for in indoors are IEEE 802.11b and IEEE 802.11n.

IEEE 802.11a/b/g/n short scale indoor wireless sensor placement

Wireless signals present particular behaviour in indoor environments. Walls, roofs and floors generate reflections and refractions that conduce to constructive and destructive interferences due to the multipath effect. In this paper, we perform an analytical study based on the signal strength generated by an access point (AP) inside a building. The evolution of the signal strength allows us to move away the sensors from the AP without reducing the signal level and link quality. We study the IEEE 802.11 technology. These results are compared with the theoretical distribution channels to know what should be followed to avoid interferences. Finally, taking as a reference the measures provided, we develop a method for estimating indoor signal strength that will help us determine the best position for wireless sensors. Our method will allow saving 15% of sensors. The reduction in the number of sensors provides us economic and energy savings, allowing us to prolong the network lifetime.

Video Learning Objects Creation with Polimedia

In this paper we present Polimedia as an alternate way of producing video learning objects instead of lecture recording. We are using heavily this technology with a teacher support program involving more than two hundred teachers and in this time we have produced more than two thousand Polimedia learning objects and we have also disseminated this technology with several universities. We present also results of using this technology together the support program.

Evaluating Intelligent Interfaces for Post-Editing Automatic Transcriptions of Online Video Lectures.

Video lectures are fast becoming an everyday educational resource in higher education. They are being incorporated into existing university curricula around the world, while also emerging as a key component of the open education movement. In 2007, the Universitat Politècnica de València (UPV) implemented its poliMedia lecture capture system for the creation and publication of quality educational video content and now has a collection of over 10,000 video objects. In 2011, it embarked on the EU-subsidised transLectures project to add automatic subtitles to these videos in both Spanish and other languages. By doing so, it allows access to their educational content by non-native speakers and the deaf and hard-of-hearing, as well as enabling advanced repository management functions. In this paper, following a short introduction to poliMedia, transLectures and Docència en Xarxa (Teaching Online), the UPV’s action plan to boost the use of digital resources at the university, we will discuss the three-stage evaluation process carried out with the collaboration of UPV lecturers to find the best interaction protocol for the task of post-editing automatic subtitles.

IP Telephony Development and Performance over IEEE 802.11g WLAN

With the adoption of the Wireless LAN technology as one of the main ways to access the enterprise network, IP services have found another place where they can be implemented. In this paper we will show the test and performance used to develop the IP telephony network over the 802.11g wireless LAN of the Polytechnic University of Valencia. In order to make these measurements, we have used the Open Source PBX & Telephony Platform: Asterisk and SmartPhones. We will show the results obtained about the delay, the jitter and the number of lost packets when the SmartPhones are in the same wireless cell and when they are roaming. Finally, we will calculate the amount of IP phones that can be working in a single access point and the bandwidth wasted in different cases. This work can be used to design VoIP and IP telephony wireless networks and to design wireless IP phones relocation algorithms.

Multicast TV over WLAN in a University Campus Network

One of the multimedia services offered by the campus network of the Polytechnic University of Valencia is TV over IP. This service works well in the devices connected directly to the wired network but we have detected some problems when the receivers access to the campus network through wireless IEEE 802.11, especially when devices roam across the Campus. In this paper we propose and evaluate a server-based solution to minimize the packet loss and reduce the lack of service when the mobile devices roam from an Access Point to another Access Point in the wireless network. This solution uses a location system to modify the behaviour of standard multicasting protocols in order to get a near-seamless multicast WiFi roaming.

Efficiency and usability study of innovative computer-aided transcription strategies for video lecture repositories

Real-life evaluation of automatic transcriptions in a large videolecture repository.Three different evaluation protocols are compared to minimise user supervision time.Discovered dependencies between transcription quality and time expended in supervision.Attained up to 70% of time reduction with supervisions compared with transcribe from scratch.Lecturers valued simplicity over other sophisticated but more-efficient protocols. Video lectures are widely used in education to support and complement face-to-face lectures. However, the utility of these audiovisual assets could be further improved by adding subtitles that can be exploited to incorporate added-value functionalities such as searchability, accessibility, translatability, note-taking, and discovery of content-related videos, among others. Today, automatic subtitles are prone to error, and need to be reviewed and post-edited in order to ensure that what students see on-screen are of an acceptable quality. This work investigates different user interface design strategies for this post-editing task to discover the best way to incorporate automatic transcription technologies into large educational video repositories. Our three-phase study involved lecturers from the Universitat Politecnica de Valencia (UPV) with videos available on the poliMedia video lecture repository, which is currently over 10,000 video objects. Simply by conventional post-editing automatic transcriptions users almost reduced to half the time that would require to generate the transcription from scratch. As expected, this study revealed that the time spent by lecturers reviewing automatic transcriptions correlated directly with the accuracy of said transcriptions. However, it is also shown that the average time required to perform each individual editing operation could be precisely derived and could be applied in the definition of a user model. In addition, the second phase of this study presents a transcription review strategy based on confidence measures (CM) and compares it to the conventional post-editing strategy. Finally, a third strategy resulting from the combination of that based on CM with massive adaptation techniques for automatic speech recognition (ASR), achieved to improve the transcription review efficiency in comparison with the two aforementioned strategies.

A stereoscopic video transmission algorithm for an IPTV network based on empirical data

IPTV service is one of the topics where industry and academia are providing more efforts with the purpose of enhancing the systems in existence. One of the potentially biggest advantages of IPTV is the existence of a return channel from the customer to the IPTV service provider, which makes this technology the upcoming TV distribution system. The next big step is to serve stereoscopic video over IP networks. In this paper, we evaluate the stereoscopic video transmission over IP by taking measurements of the bandwidth, delay and jitter. These measurements are useful to test the QoS and QoE of the ITPV service and to demonstrate the need for high-performance stereoscopic compression codecs. Then, we study the performance of four free codecs in order to propose an algorithm to perform the appropriate decisions to transmit stereoscopic video in the IPTV network properly. The algorithm is based on the empirical data obtained from our test and on some analytical considerations. Finally, we show the impact on the network given by the algorithm, and we compare the QoS parameters when each codec is chosen. Copyright

A User-Balanced System for IP Telephony in WLANs

Wireless IP telephony is becoming very popular between the users of large wireless local area networks (WLANs). This increment has been mainly caused because it allows cost savings. Although, large WLANs use to provide high availability and redundancy, WLANs lack on the available throughput when there are many IP telephony users. In this paper we present a system that reallocates IP telephony devices when the system detects that an AP is overloaded. The algorithm and the frames used for our proposal are described. Measurements taken show how the bandwidth consumed is transferred from an access point to another when our proposal is running. Finally, we show the time needed to re-associate remainder users.