Conference Papers

QoE assessment of HTTP adaptive video streaming

Salvador A., Nogueira J., Sargento S.

Lecture Notes of the Institute for Computer Sciences, Social-Informatics and Telecommunications Engineering, LNICST

2015

Abstract:

Quality of Experience (QoE) is a crucial characteristic of any multimedia service and must be accounted for during the service development and planning stages. Nonetheless, given its subjective nature, it is extremely difficult to use analytical methods to estimate the average Mean Opinion Score (MOS). Traditional progressive multimedia streaming is a well researched topic with respect to QoE, however, modern streaming services relying on advanced adaptive video streaming technologies, with specific characteristics, have yet to have an all-encompassing method for QoE estimation, as research work tend to focus on only one, or a small subset, of the technology’s aspects, such as the impact of buffering events, bit-rate change frequency, or initial playout delay. This paper proposes a model for determining the QoE estimate of a playback session of HTTP adaptive video streaming, encompassing its complete range of characteristics. Several key-metrics are extracted throughout the playback session, and then analyzed by an analytical method able to predict the consumers’ QoE. A subjective QoE survey is conducted according to industry’s best practices and recommendations in order to validate the proposed models. The obtained results show that both subjective and objective estimations produce similar results, hence validating the proposed model.

QoE Driven Server Selection for VoD in the Cloud

Wang C., Kim H., Morla R.

Proceedings - 2015 IEEE 8th International Conference on Cloud Computing, CLOUD 2015

2015

Abstract:

In commercial Video-on-Demand (VoD) systems, user’s Quality of Experience (QoE) is the key factor for user satisfaction. In order to improve user’s QoE, VoD providers replicate popular videos in geo-distributed Cloud and deploy cache servers close to users. Generally, the VoD provider selects a server for the user request according to the user’s location. Usually geographically closely located servers would provide lower network delay. However, the performance of VoD servers deployed in cloud virtual machines (VM) depends not only on the network delay but also resource contention due to other VMs and highly dynamic user demands. Thus, QoE offered by the server varies greatly over time as user demands and network traffic fluctuate regardless of the location. Selecting a server close to users sometimes reduces the network delay but cannot guarantee QoE in general. We believe that end users have the best perception of server performance in terms of their QoE rather than the servers themselves. What user perceives incorporate performance of all elements, such as network delay and server response time in VoD service. We propose VoD server selection schemes that dynamically select servers according to user’s QoE feedback. We integrate our server selection schemes with Dynamic Adaptive Streaming over HTTP (DASH) clients and evaluate our system both in simulation and in Google Cloud. Results show our system improves user QoE up to 20% compared to existing solutions.

Quality of experience optimized scheduling in multi-service wireless mesh networks

Reis A.B., Chakareski J., Kassler A., Sargento S.

Proceedings - International Conference on Image Processing, ICIP

2010

Abstract:

A growing trend has emerged in network architecture research to switch focus from Quality of Service (QoS) to Quality of Experience (QoE) optimization. In this paper, we first present QoE models that characterize user satisfaction of video, audio, and data services over wireless networks. We then develop a novel packet scheduling algorithm for multi-hop wireless networks that jointly optimizes the delivery of multiple video, audio, and data flows according to the QoE metrics. We formulate a multidimensional optimization problem that minimizes the overall distortion across all flows for the given network resources on wireless links. Fairness constraints over the flows are also considered as part of the optimization. Our experimental results, obtained with the NS-2 IEEE 802.16 MESH-mode simulator, show that distortion-aware scheduling can significantly increase the perceived quality of different wireless services under bandwidth constraints. Additionally, improved fairness across the competing flows is demonstrated relative to conventional scheduling techniques.

Real-world evaluation of IEEE 802.11p for vehicular networks

Neves F., Cardote A., Sargento S.

Proceedings of the Annual International Conference on Mobile Computing and Networking, MOBICOM

2011

Abstract:

This paper presents a set of experiments, performed using an IEEE 802.11p physical layer implementation based on the open-source ath5k driver, in both line of sight (LOS) and non-line of sight (NLOS) conditions. The results are compared against theoretical models and simulation of the same scenarios with proper propagation and channel models. The communication range in LOS can reach values larger than 1Km, while in NLOS scenarios, this communication range is decreased to the order of hundreds of meters.

Recovery of acronyms, out-of-lattice words and pronunciations from parallel multilingual speech

Miranda J., Neto J.P., Black A.W.

2012 IEEE Workshop on Spoken Language Technology, SLT 2012 - Proceedings

2012

Abstract:

In this work we present a set of techniques which explore information from multiple, different language versions of the same speech, to improve Automatic Speech Recognition (ASR) performance. Using this redundant information we are able to recover acronyms, words that cannot be found in the multiple hypotheses produced by the ASR systems, and pronunciations absent from their pronunciation dictionaries. When used together, the three techniques yield a relative improvement of 5.0% over the WER of our baseline system, and 24.8% relative when compared with standard speech recognition, in an Europarl Committee dataset with three different languages (Portuguese, Spanish and English). One full iteration of the system has a parallel Real Time Factor (RTF) of 3.08 and a sequential RTF of 6.44.

Reductions and abstractions for formal verification of distributed round-based algorithms

Barbosa R., Fonseca A., Araújo F.

Software Quality Journal

2021

Abstract:

Model checking has advanced over the last decades to become an effective formal technique for verifying distributed and concurrent systems. As computers grew in memory and processing capacity, it became possible to exhaustively verify systems with billions of states, making it practical to model and verify real-world protocols and algorithms. However, writing a model is a manual task that potentially introduces defects which the model checker tool finds to fulfill the formal specification (e.g., an incorrect model that fulfills an incomplete specification). Furthermore, this kind of formal verification technique is limited by the well-known state-space explosion problem. This paper aims to provide a set of generic template models, appropriate for distributed round-based algorithms, to be used to focus modeling effort on algorithm-specific details. To mitigate state-space explosion, the paper proposes two reduction techniques, named partition symmetry reduction and message order reduction, that exploit symmetries in the state space to avoid expanding equivalent states. The reusable framework for verifying round-based algorithms and the two proposed reduction techniques provide the means for reducing by orders of magnitude the number of states required to analyze common distributed algorithms.

REINVENT: Accessing vehicular networks in mobile applications

Oliveira F., Sargento S., Fernandes J.M., Cardote A.

Proceedings - International Symposium on Computers and Communications

2014

Abstract:

This paper proposes REINVENT, a software architectural solution to decouple the specificities of using vehicular network communication resources in Android smartphone applications. REINVENT provides a REST based message passing interface based on Android’s content provider to abstract vehicular network communication services. Using REINVENT, Android applications can use transparently the communication resources avoiding network transport layer details. REINVENT was tested in both laboratory and real world scenarios in the road with WAVE/IEEE 802.11p technology, to assess its usefulness in two Android applications, (VNChat and iThere). The real experiments also assess how REINVENT supports a mobile application to log relevant parameters in typical vehicular networks testing in different network scenarios.

Reiterated homogenization in BV via multiscale convergence

Ferreira R., Fonseca I.

SIAM Journal on Mathematical Analysis

2012

Abstract:

Multiple-scale homogenization problems are treated in the space $BV$ of functions of bounded variation, using the notion of multiple-scale convergence developed in [R. Ferreira and I. Fonseca, J. Convex Anal., to appear]. In the case of one microscale, Amar’s result [Asymptot. Anal., 16 (1998), pp. 65–84] is recovered under more general conditions; for two or more microscales, new results are obtained.

Reliable THz Communications for Outdoor based Applications- Use Cases and Methods

Singh R., Sicker D.

Preprint. To appear in IEEE CCNC 2020.

2019

Abstract:

Future (beyond 5G) wireless networks will demand high throughput and low latency and would benefit from greenfield, contiguous, and wider bandwidth, all of which THz spectrum can provide. Although THz has been envisioned to be deployed in an indoor setting, with proper enforcement and planning, we can draw a limited number of use cases for outdoor THz communication. THz can provide high capacity and ultra-high throughput but at the cost of high path loss and sensitivity to device orientation/mobility.. We identify scenarios where the use of the THz spectrum for an outdoor setting is justified and their critical operating parameters. We further categorize the applications based on the relative mobility between the access point (AP) and user equipment (UE). We present an approach for deploying THz on an outdoor framework by presenting preliminary technical parameter analysis for scenarios, like wireless backhaul, high-speed kiosks, and the aerial base station (ABS). Our preliminary analysis shows that the application for each of these scenarios is limited based on multiple parameters, such as distance, device mobility, device orientation, user geometry, antenna gain, and environment settings, which requires separate consideration and optimization