Cross-layer Perceptual ARQ for Video Communications over 802.11e Wireless Networks

This work presents an application-level perceptual ARQ algorithm for video streaming over 802.11e wireless networks. A simple and effective formula is proposed to combine the perceptual and temporal importance of each packet into a single priority value, which is then used to drive the packet-selection process at each retransmission opportunity. Compared to the standard 802.11 MAC-layer ARQ scheme, the proposed technique delivers higher perceptual quality because it can retransmit only the most perceptually important packets reducing retransmission bandwidth waste. Video streaming of H.264 test sequences has been simulated with ns in a realistic 802.11e home scenario, in which the various kinds of traffic flows have been assigned to different 802.11e access categories according to the Wi-Fi alliance WMM specification. Extensive simulations show that the proposed method consistently outperforms the standard link-layer 802.11 retransmission scheme, delivering PSNR gains up to 12 dB while achieving low transmission delay and limited impact on concurrent traffic. Moreover, comparisons with a MAC-level ARQ scheme which adapts the retry limit to the type of frame contained in packets and with an application-level deadline-based priority retransmission scheme show that the PSNR gain offered by the proposed algorithm is significant, up to 5 dB. Additional results obtained in a scenario in which the transmission relies on an intermediate node (i.e., the access point) further confirms the consistency of the perceptual ARQ performance. Finally, results obtained by varying network conditions such as congestion and channel noise levels show the consistency of the improvements achieved by the proposed algorithm

QoS in LEO satellite networks with multipacket reception

Dissertação apresentada para obtenção do Grau de Mestre em Engenharia Electrotécnica e de Computadores, pela Universidade Nova de Lisboa, Faculdade de Ciências e TecnologiaLow Earth Orbit (LEO) satellite networks can improve terrestrial wireless networks to allow global broadband services for Mobile Terminals (MT), regardless of the users' location. In this context, hybrid telecommunication systems combining satellites with Long Term Evolution (LTE) networks, like the LightSquared technology, are intended to provide ubiquitous high-speed services. This dissertation analyses the performance of a random access protocol that uses Hybrid Network-assisted Diversity Multiple Access (H-NDMA), for a LEO satellite system network, named by Satellite Random NDMA (SR-NDMA). The protocol also considers a Single Carrier-Frequency Domain Equalization (SC-FDE) scheme for the uplink transmission and a Multipacket Reception (MPR) receiver. In this scenario, the transmission of data packets between MTs and the Base Station (BS) is made through random access and schedule access slots, organized into super-frames with the duration of a Round Trip Time (RTT). A SR-NDMA simulator is implemented to measure the system performance in matters of throughput, energy consumption, system delay and also the protocol capacity to meet Quality of Service (QoS) requirements. A set of simulations tests were made with a random Poisson process tra c generation to validate the analytical model. The capacity to ful l the QoS requirements of a real-time tra c class was also tested.FCT/MEC: MPSat - PTDC/EEA-TEL/099074/2008, OPPORTUNISTIC CR - PTDC/EEA-TEL/115981/2009, Femtocells - PTDC/EEA-TEL/120666/2010 e ADIN - PTDC/EEI-TEL/2990/201

Video QoS/QoE over IEEE802.11n/ac: A Contemporary Survey

The demand for video applications over wireless networks has tremendously increased, and IEEE 802.11 standards have provided higher support for video transmission. However, providing Quality of Service (QoS) and Quality of Experience (QoE) for video over WLAN is still a challenge due to the error sensitivity of compressed video and dynamic channels. This thesis presents a contemporary survey study on video QoS/QoE over WLAN issues and solutions. The objective of the study is to provide an overview of the issues by conducting a background study on the video codecs and their features and characteristics, followed by studying QoS and QoE support in IEEE 802.11 standards. Since IEEE 802.11n is the current standard that is mostly deployed worldwide and IEEE 802.11ac is the upcoming standard, this survey study aims to investigate the most recent video QoS/QoE solutions based on these two standards. The solutions are divided into two broad categories, academic solutions, and vendor solutions. Academic solutions are mostly based on three main layers, namely Application, Media Access Control (MAC) and Physical (PHY) which are further divided into two major categories, single-layer solutions, and cross-layer solutions. Single-layer solutions are those which focus on a single layer to enhance the video transmission performance over WLAN. Cross-layer solutions involve two or more layers to provide a single QoS solution for video over WLAN. This thesis has also presented and technically analyzed QoS solutions by three popular vendors. This thesis concludes that single-layer solutions are not directly related to video QoS/QoE, and cross-layer solutions are performing better than single-layer solutions, but they are much more complicated and not easy to be implemented. Most vendors rely on their network infrastructure to provide QoS for multimedia applications. They have their techniques and mechanisms, but the concept of providing QoS/QoE for video is almost the same because they are using the same standards and rely on Wi-Fi Multimedia (WMM) to provide QoS