Simão Cardeal

Bio: Simão Cardeal is an academic researcher from Portugal Telecom. The author has contributed to research in topics: Voice over IP & Fourier series. The author has an hindex of 3, co-authored 8 publications receiving 28 citations. Previous affiliations of Simão Cardeal include University of Trás-os-Montes and Alto Douro.

Quality model for monitoring QoE in VoIP services

Abstract: This paper presents a no-reference model for monitoring the voice quality experienced by users in VoIP services. The proposed model is based on the E-Model, which is adapted from Recommendation ITU-T G.107 for this purpose. A calibration function was determined for relevant codecs under different packet loss conditions. Extensive field testing was carried out to validate the proposed model at PT Inovacao Labs (Portugal). The results show that the mean opinion score (MOS) obtained from the proposed model match class C2 of conformance tests defined in ITU-T Recommendation P.564. The QoE model described in this paper was implemented in a VoIP QoE probe and is currently fully operational at Portugal Telecom.

Teaching Fourier Series Expansions in Undergraduate Education with the Help of the FouSE Android Application

Abstract: This paper discusses the teaching of Fourier Series concepts in undergraduate Electrical Engineering education with the help of an Android application, especially developed to that end. In order to better understand the links and implications, some of the basic Fourier series theory is briefly reviewed. The Android application has an easy-to-use, friendly interface, conceived to help undergraduate students test and assess the Fourier series expansions on a typical set of signals. The application also allows the students to control the total approximation error and the number of terms/harmonics used in the expansions. It has been found a very useful learning resource in the Fourier series context.

ArQoS®: System to monitor QoS/QoE in VoIP

Abstract: The evolution of telecommunications technology from circuit to packet switching, in which the Internet is the great paradigm, offers nowadays more flexibility in services and higher efficiency in the transport infrastructure that was not experienced before. As consequence, several new services have emerged. Among them, Voice over IP (VoIP) is, indubitably, one of the most popular, mainly because it allows anyone to make low cost voice calls, making it a very attractive service. This is perhaps one of the main factors responsible for the fast development of VoIP technology. However, IP networks were not designed for services with real time requirements and factors like delay, jitter, codec distortions and packet loss lead to degradations that directly influence de VoIP user experience. The quality experienced by these users is highly dependent on network conditions and also on the subjective experience perceived by them. Thus, new challenges have brought with this evolution of telecommunications networks. In order to meet the assigned Service Level Agreement (SLA's), service providers around the world need to monitor and guarantee the agreed Quality of Service (QoS) to its customers. Consequently, an emergent way to measure QoS arises in the field of the telecommunications sector: the Quality of Experience (QoE) assessment and monitor that takes into account that subjective experience. Thus, a new challenging need arises: the development of systems and methods for assessing quality of experience, such that, network operators and service providers can actually know how users evaluate the quality of the service provided to them. In this paper, a system for assessing QoS/QoE is described: the ArQoS®. This is an integrated system provided by Portugal Telecom Inovacao (PTIn) which implements QoE assessment methods to assess the networks performance and their telecommunications services. Beyond the existing methods already supported by the system, a novel QoE monitor for VoIP services was recently integrated as a result of fundamental research carried out at PTIn Labs. The ArQoS® is a probing system based on different types of probes, actually comprising two systems operating in two different modes: the active system (intrusive mode) and the passive system (non-intrusive mode). The ArQoS® active system is based on intrusive probing and is intended to generate test calls on different types of networks (fixed/mobile/IP), simulating typical user's activity. It is possible to create interactive or scheduled tests with a custom task pool. The system gathers QoS network parameters (KPI and KQI), and evaluates the functional aspects of its associated network services, according to the related ETSI/ITU-T/IETF/3GPP standards and recommendations. The ArQoS® passive system is designed to analyse VoIP traffic, including signaling (SIP, Megaco, Radius, Diameter) and media stream (RTP) protocols. Passive probes analyse multi parallel RTP voice traffic without any interference in the communication. These probes can be setup close to any element of the VoIP network, such as VoIP clients, Media Gateways or in the core of the network. Collected data is gathered, analysed and processed automatically at the server management system, providing many QoS/QoE statistics. The user system manager can also use the system to trace a VoIP call in every probing point and in every protocol involved, allowing the end user to troubleshoot any possible problem. The ArQoS® passive probes are deployed in the Portugal Telecom VoIP Network core. A general diagram of the application scenario is depicted in Fig.1. All VoIP traffic converges in a Softswitch that controls all VoIP network. The connection to PSTN and Mobile networks is performed by a Media Gateway. The Session Border Controller (SBC) interconnects networks of different service providers, implements security functions and manages QoS guarantees, among other functions. The ArQoS® probes analyse the entire flow that converges to the Softswitch, and monitor all signaling traffic. The RTP traffic is analysed in the Media Gateway checking the performance of transmission network. In SBC, the quality of interoperability between operators is analysed. Fig. 2 presents a block diagram of ArQoS® VoIP QoE monitor, which was developed and integrated in the ArQoS® passive probes. The voice RTP packets are captured and processed by the probe, and then the Jitter Buffer Emulator accurately predicts which packets are lost or discarded. In the Gilbert Model module, the packet loss distribution is calculated. This distribution and other network metrics are inputs for ArQoS® Speech Assessment Model, which implements the novel QoE monitoring model based on the E-Model. This model is described in detail in the paper “Quality model for monitoring QoE in VoIP services” from the same authors at EUROCON'2011. Using this enhanced QoE model, the ArQoS® passive system provides now better estimates of voice quality, than the standard E-Model. Table 1 shows that the correlation factor of estimated quality is higher and the RMSE is lower than the standard E-Model. Thus, the novel QoE monitoring system allows the translation of pure QoS metrics such as packet loss rate and jitter to a perceptual QoE metric: the Mean Opinion Score (MOS). Overall the integration of this novel QoE monitoring model in the ArQoS® system has improved its technical characteristics and proved to be a successful case of technology transfer between academic institutions and the industry.

Teaching of Fourier series expansions in undergraduate education

Abstract: Here we discuss the teaching of Fourier series concepts in connection with undergraduate Electrical Engineering education. We briefly review some of the basic Fourier series theory, and present an Android application that has been found useful in this context. As expected, the application has an easy-to-use, friendly interface, and can be viewed as a tool to help undergraduate students test and assess the Fourier series expansions on a typical set of signals, whose analytical Fourier series coefficients were found during the theoretical lectures. Additionally, students can also control the total approximation error and the number of terms/harmonics used in the expansion. It seems that our students prefer this Android application to the traditional applet fashioned web-based applications.

Quality Evaluation Methods to Improve Enterprise VoIP Communications

Abstract: In the last few years there has been a dramatic development in voice communications technology with a significant move towards Voice over the Internet Protocol (VoIP). Since the Internet was primarily designed as a besteffort technology, good quality conversation and intelligibility are not guaranteed. In this paper we address quality evaluation of voice communications in the context of modern enterprises using VoIP as an emerging technology with impact in their activity. Relevant factors for service providers and enterprises using VoIP technology are described, such as those related to measurement of intelligibility and evaluation of overall voice communications quality. Also, the most relevant voice quality evaluation methods recommended by the ITU-T are described along with the main features that can be used to improve voice communications. Fundamental concepts are presented, such as intrusive, non intrusive, objective, subjective and parametric methods. Mastering the concepts of such emerging technology, has recently lead to research and development of a model-based voice quality monitor for VoIP services. After its successful implementation, it is now fully operational in a Portuguese telecom operator.

Going mobile

Abstract: P h o t o g r a P h b y b r U C e a L d e r s o n Mobile devices are quickly becoming ubiquitous around the world and the resulting usage of the “Mobile Internet” is rapidly increasing, as is the need for Web sites that serve up content on the small screen efficiently and effectively. Organizations that ignore this trend will miss opportunities to capture and keep users engaged. Gartner Inc. predicts that mobile phones will overtake PCs as the most common Web access device worldwide by 2013 (http://www.gartner.com/ it/page.jsp?id=1278413). Communications’ site will be making changes to better accommodate mobile users of portable platforms like smartphones, tablet PCs, and e-readers.

Application of Quality of Experience in Networked Services: Review, Trend & Perspectives

Abstract: Over the last decade, there has been an exponential growth of services over the Internet. Services such as online gaming are gaining popularity, whereas, Voice over Internet (VoIP) has been well established. Storage, management and processing of data have moved away from the devices to the cloud. Quality of experience (QoE) defined as the user’s perception of service quality is utilized in different technologies, services and products for improving end user satisfaction and provides quality of service (QoS) according to their demands. In this paper, we describe the utilization of QoE in different technologies, services and products for improving end user satisfaction. Specifically, we present the latest developments in QoE in multimedia services, network management, VoIP, web development, games and cloud computing. Finally, we discuss the current research, solutions and present open issues of future research in QoE.

Analysis of the quality of experience of a commercial voice-over-IP service

Abstract: Voice-over-IP (VoIP) services, enabling users to make cheap phone calls using the Internet, are becoming increasingly popular, not only on desktop computers but also on mobile devices such as smartphones that are connected through mobile networks. Users' perception of the level of quality plays a key role in making a VoIP service to succeed or to fail. This paper demonstrates the influence of technical parameters (such as the audio codec, type of data network, and handovers during the call), device characteristics (such as the platform, manufacturer, model, and operating system), and application aspects (such as the software version and configuration) on the subjective quality of a commercial VoIP service. The relative influence of all these parameters is determined and a decision tree combines these results in order to assess the subjective quality. Combining a large number of objective parameters in a decision tree to determine the user's subjective evaluation of the quality of a VoIP call is a novel and complex procedure. The subjective quality, in turn, has an influence on the duration of the call, and as a result an influence on the usage behavior of the service. The users' assessment of the service quality is not evaluated by merely taking a snapshot of the perceived quality at one moment in time but rather by analyzing the perceived quality over a longer period of time during service usage, which has not been done up to now. Analyzing the VoIP service using a regression analysis over a period of 120 days showed that the perceived quality decreases slightly when the user utilizes the service more often and gets more familiar with it.

Quality assessment and usage behavior of a mobile voice-over-IP service

Abstract: Voice-over-IP (VoIP) services offer users a cheap alternative to the traditional mobile operators to make voice calls. Due to the increased capabilities and connectivity of mobile devices, these VoIP services are becoming increasingly popular on the mobile platform. Understanding the user's usage behavior and quality assessment of the VoIP service plays a key role in optimizing the Quality of Experience (QoE) and making the service to succeed or to fail. By analyzing the usage and quality assessments of a commercial VoIP service, this paper identifies device characteristics, context parameters, and user aspects that influence the usage behavior and experience during VoIP calls. Whereas multimedia services are traditionally evaluated by monitoring usage and quality for a limited number of test subjects and during a limited evaluation period, this study analyzes the service usage and quality assessments of more than thousand users over a period of 120 days. This allows to analyze evolutions in the usage behavior and perceived quality over time, which has not been done up to now for a widely-used, mobile, multimedia service. The results show a significant evolution over time of the number of calls, the call duration, and the quality assessment. The time of the call, the used network, and handovers during the call showed to have a significant influence on the users' quality assessments.