Vitor Bernardo

VoIP over WiMAX: Quality of experience evaluation

VoIP applications are being widely used in todays networks challenging their capabilities to provide a good quality of experience level to the users. In particular, new wireless broadband technologies, such as WiMAX, are being deployed and need to be evaluated to check the performance levels of VoIP services. The work presented in this paper is a unique contribution assessing the VoIP sessions quality on a real WiMAX test-bed, using UDP/RTP and DCCP transport protocols. VoIP quality is measured according the quality perceived by the end users as well as through conventional network parameters, such as one-way delay and packet loss. The results put in evidence a good quality for VoIP services with 60 simultaneous users in a WiMAX link with resources pre-provisioned. Moreover, in the scenarios tested, DCCP has not shown enhanced performance when compared with UDP/RTP, despite the congestion control mechanisms natively supported.

A methodology for assessing video transmission energy consumption and quality

Video traffic has been growing significantly and it is expected to be a large share of the future Internet traffic, within an increasingly mobile environment with scarce resources. In this context, new challenges arise, and energy-efficiency is becoming a key factor for the successful deployment of mobile networks. The development and validation of mechanisms for energy-efficient video transmission require the measurement of the energy consumption needed for video transmission, considering also the end-user Quality of Experience. This issue is of utmost importance, as users will tailor their application and network usage behaviors based on the perceived quality of the services and on the capabilities of their devices. In this work, an integrated empirical methodology to assess the video transmission energy consumption and quality is proposed. The developed methodology was validated on two distinct testbeds, one with IEEE 802.11 and the other with IEEE 802.16e. Results showed that the proposed methodology enables an accurate assessment of energy consumption with different technologies, while measuring the end-user Quality of Experience. Another contribution of the proposed methodology is the capability to gather data to support the creation and validation of realistic simulation models.

VoIP performance over mobile WiMAX: An urban deployment analysis

The significant growing of Voice over IP (VoIP) ready mobile devices raises new challenges in the deployment of novel broadband wireless access networks (BWA), such as WiMAX or Long Term Evolution (LTE). Due to voice service importance for the mobile market, the empirical assessment of voice traffic performance and quality is crucial for a successful deployment. In this work, the Mobile WiMAX (IEEE 802.16e) capabilities to support VoIP traffic under different scenarios and employing distinct Quality of Service (QoS) service classes were performed. Additionally, the paper characterizes the heterogeneity access conditions within a city, by analyzing both Line of Sight (LOS) and Non-Line of Sight (NLOS) conditions. By examining the end-user perceived quality (Quality of Experience) and the network QoS related parameters, the attained results shown the impact of the correct WiMAX QoS service classes management on the number of well served VoIP users.

Multi-client video streaming over wirelessMAN-OFDMA

Wireless Interoperability for Microwave Access (WiMAX) is a prime contender in the Broadband Wireless Access (BWA) market due to its next generation network architecture, low patent portfolio load considerations, support for Quality of Service (QoS), and last but not least, high capacities. Although until recently there has been a lot of interest in the mobility support of the technology, with the recent push for the Third Generation Partnership Projects (3GPP) Long Term Evolution (LTE), vendors are advancing WiMAX (in particular with the Wireless Metropolitan Area Network - Orthogonal Frequency Division Multiple Access (WirelessMAN-OFDMA) air interface specified by the IEEE 802.16 working group) as a fixed broadband replacement. For this market segment, Audio/Video (A/V) delivery is expected to be a key service offering. In this paper, we perform a detailed empirical evaluation using a state-of-the-art WiMAX testbed with multiple video flows directed at several Customer Premises Equipment (CPE) devices simultaneously. We employ the Evalvid framework and develop a methodology for its use in multi-client evaluations. We report our results for Variable Bit Rate (VBR) and Constant Bit Rate (CBR) video streams and draw conclusions.

An Overview of Energy Consumption in IEEE 802.11 Access Networks

Nowadays users are expecting to have some type of Internet access, independently of the place where they are. This is indeed supported by the fact that wireless access networks are becoming available almost everywhere through different types of service providers. In this context, new applications have emerged with demanding requirements from the network, but also from the end-user device capabilities. Energy is the most prominent limitation of end user satisfaction within the anytime and anywhere connectivity paradigm. Since IEEE 802.11 is one of the most widely used wireless access technologies, this work provides insights on the study of its energy consumption properties, laying the grounds for further improvements towards enhanced battery lifetime. Experimental energy assessment results demonstrate the efficacy of power saving mechanisms and the relevance of wireless devices’ state management.

Enhancing IEEE 802.11 Energy Efficiency for Continuous Media Applications

This paper proposes the Optimized Power save Algorithm for continuous Media Applications OPAMA to improve end-user device energy efficiency. OPAMA enhances the standard legacy Power Save Mode PSM of IEEE 802.11 by taking into consideration application specific requirements combined with data aggregation techniques. By establishing a balanced cost/benefit tradeoff between performance and energy consumption, OPAMA is able to improve energy efficiency, while keeping the end-user experience at a desired level. OPAMA was assessed in the OMNeT++ simulator using real traces of variable bitrate video streaming applications. The results showed the capability to enhance energy efficiency, achieving savings up to 44% when compared with the IEEE 802.11 legacy PSM.

HyPath: An Approach for Hybrid On-Path Off-Path End-to-End Signaling

In a multi-domain Internet that offers quality of service guaranties, there is the need of signaling among the domain entities that are responsible for the management of quality of service. Because different domains have different network protocols and topologies, there is no solution that is able to signal these entities using an off-path approach and, in particular, that is able to interwork with the on-path signaling mechanisms. The HyPath approach extends the NSIS framework and its interactions with the local routing protocols to achieve off- path signaling in these hybrid environments. This document presents HyPath and its evaluation on a test-bed, showing that the mechanisms proposed have the potential to perform off-path signaling without introducing an excessive overhead in the network.

Towards End-User Driven Power Saving Control in Android devices

During the last decade mobile communications increasingly became part of people’s daily routine. Such usage raises new challenges regarding devices’ battery lifetime management when using most popular wireless access technologies, such as IEEE 802.11. This paper investigates the energy/delay trade-off of using an end-user driven power saving approach, when compared with the standard IEEE 802.11 power saving algorithms. The assessment was conducted in a real testbed using an Android mobile phone and high-precision energy measurement hardware. The results show clear energy benefits of employing user-driven power saving techniques, when compared with other standard approaches.

Evaluating the trade-off between energy efficiency and QoE in wireless mesh networks

The increasing usage of wireless networks creates new challenges for wireless access providers. On the one hand, providers want to satisfy the user demands but on the other hand, they try to reduce the operational costs by decreasing the energy consumption. In this paper, we evaluate the trade-off between energy efficiency and quality of experience for a wireless mesh testbed. The results show that by intelligent service control, resources can be better utilized and energy can be saved by reducing the number of active network components. However, care has to be taken because the channel bandwidth varies in wireless networks. In the second part of the paper, we analyze the trade-off between energy efficiency and quality of experience at the end user. The results reveal that a providers service control measures do not only reduce the operational costs of the network but also bring a second benefit: they help maximize the battery lifetime of the end-user device.