Saviour Zammit

A Survey of Multicasting over Wireless Access Networks

In this paper a survey of the research effort invested in the analysis of multicasting over wireless access networks from the late nineties onwards is presented. The analysis is dedicated although not limited to video multicasting both of live events and pre-stored video streaming. This investigation was not limited to a particular access network but focused on infrastructure topologies, including ad-hoc networks only when the latter was used to aid the former, which is a method frequently used in cooperative networking. We were interested in proposals aiming to decrease the packet error rate, in order to overcome the bursty error-prone wireless medium, since multicasting cannot simply receive feedback from the users as these will reply simultaneously causing a collision at the source. Hence, in this survey a review is presented showing how researchers proposed to solve this constraint using both modified unicast data transmission and also error correction techniques at various levels of the network protocol stack. However, a survey of multicasting over IEEE 802.16 and 3G radio access networks shows that reliability and resilience was not the only interest in which researchers have shown. There was in fact significant work dedicated to resource allocation as shall also be presented hereafter.

Performance improvement of long distance MIMO links using cross polarized antennas

The hype with respect to MIMO systems is due to the theoretical analysis which have been reported, stating that such systems may increase the channel capacity by a factor equivalent to the smallest value between Nt and Nr, where Nt and Nr are the number of transmit and receive antennas respectively. Moreover, an improvement in the range may be observed if the number of antennas is increased at both the transmitter and the receiver, without demanding more transmit power. However, point-to-point long distance MIMO links are limited by the “keyhole” effect which results in a degenerate channel.

Infrastructure-dependent wireless multicast - improving the code rate

This paper shows how a novel infrastructure which makes use of the multiple antennas available on IEEE 802.11n Access Points can be combined with block erasure coding to multicast video with no packet loss. This paper also shows that this can be obtained while maintaining an efficient code rate, which is better than 1) packet repetition on the new infrastructure, 2) Block erasure coding on the legacy infrastructure and 3) Leader-Based Protocols used on the legacy infrastructure. This study employs physical layer data rates of 52Mbps, 58.5Mbps and 65Mbps. Hence the infrastructure proposed solves also the “Performance Anomaly Problem” which results with legacy multicast that transmits the data using the most robust modulation and coding scheme.

Mobile gaming on a virtualized infrastructure

This paper describes the design, implementation and testing of a prototype system that processes and manages games on a remote server and played on a mobile device. The game application is executed on the remote server and video-streamed to a mobile device over WiFi. The mobile keyboard input is relayed to the server to control the game. The prototype test-bed includes a virtualization based infrastructure and the necessary software for both the virtual game server and the mobile device. Performance tests are carried out on this prototype test-bed and the results are evaluated.

An analytical method of assessment of RemoteFX as a cloud gaming platform

This paper describes a cloud computing platform that executes graphics intensive programs, such as computer games, with the support of a GPU to render the graphics, and stream the ensuing video to a mobile device over bandwidth constrained channels. Controls on the mobile device allow the user to interact with the game remotely. Initial results based on a Microsoft Windows platform using the Hypervisor in Windows Server 2012, with RemoteFX are reported.

Objective video quality metrics for HDTV services: A survey

The exponential growth of video traffic is expected to reach 62% of the global Internet traffic by the end of 2015 [1]. This presents as a significant challenge for the television service providers who need to employ networking technologies to monitor specific Quality of Service (QoS) parameters such as packet loss rate, jitter and delay, to ensure an acceptable level of quality. However, recent research has demonstrated that the quality experienced by the end-user does not correlate to the QoS parameters employed by most service providers [2]. This paper investigates the correlation between the QoS parameters and the quality perceived by the end. user. These results indicate that although the QoS parameters may sometimes achieve high correlation with respect to the quality perceived by the viewer, they still have large variances. This suggests that the QoS parameters are not enough to quantify the subjective quality with a high level of confidence. This work further compares a number of existing objective video quality metrics. The results presented in this paper show that the Full-Reference Motion based Video Integrity Evaluation (MOVIE) metric and the Spatio-Temporal Reduced Reference Entropic Differences (STRRED) metric achieve excellent correlation with the subjective scores. This research also demonstrates that the STRRED metric and its derivatives have several advantages over the MOVIE metric since less information needs to be transmitted and it is less computationally intensive.

Effect of human movement on the body coupled communications channel in body area networks

Body Coupled Communication (BCC) systems use the human body as the medium through which a signal is transmitted to connect devices placed in, on or in close proximity to the human body. To enable good BCC system design, the BCC channel has to be very well understood. This study focuses on understanding the effect of human body movement on the BCC channel. First some experiments were carried out to measure how the signal properties vary as a person moves. Two types of movements were investigated; sideways arm movement and marching on the spot. After that, the results obtained were used to derive a model for the behaviour of the BCC channel under moving body conditions. It was found that different body movements result in significantly different BCC channel behaviour. The type and speed of movement was found to affect the channel properties. It was found that the sideways arm movement is accurately modelled by a Log-normal distribution whilst the marching-on-the-spot movement is modelled by a Generalized Extreme Value distribution.

Infrastructure dependent wireless multicast - The effect of spatial diversity and error correction

The use of multiple Access Points (APs) with one AP placed at the middle of a coverage area and the remaining placed at the edge may reduce the Packet Error Rate (PER) experienced by a group of multicast receivers. This paper shows that Spatial Diversity can augment the channel quality experienced especially by those nodes which are located farther from the Master AP, i.e. the AP at the middle, however this study also demonstrates the need for error correction scheme. The aim of this analysis is to propose a means of enhancing the infrastructure end of an IEEE 802.11n Wireless Local Area Network (WLAN), such that multicast data can be delivered reliably in order to guarantee that the received video has an adequate Peak Signal to Noise Ratio (PSNR), but with the constraint that the Medium Access Control (MAC) and the Physical (PHY) layer of the receivers are not modified, hence a legacy IEEE 802.11n node may join the multicast group and experience good Quality of Service.

An analytical study of infrastructure-dependent wireless multicast over IEEE 802.11n WLAN

Infrastructure-Dependent Wireless Multicast (IDWM) is a technique where transmit sources are placed at the edge of the coverage area, to combat the attenuation that the multicast signal from the source in the middle of the coverage area experiences. In this paper, the concept of IDWM is studied using a semi-analytical approach considering an IEEE 802.11n wireless local area network (WLAN) by placing the antennas at opposite ends of a sector of the coverage area simulated. The study shows how the Packet Error Rate (PER) of those nodes, which are located at a larger distance from the original source experiences a decrease. Besides this advantage, the IDWM is also beneficial because it does not require any changes at the receivers and hence can be easily implemented in already existing WLANS.

Robust wireless video multicast using distributed antennas-based IEEE 802.11n infrastructure

Wireless Video Multicast is prone to suffer from frequent packet losses, resulting from the fact that the IEEE 802.11 standard does not use any mechanisms such as Acknowledgements and retransmissions, to combat the errors that are common in the dynamic wireless medium. However this paper shows that the infrastructure can be adapted to reduce the wireless errors, by using spatial diversity and spatial expansion to combat the wireless mediums random nature. This is obtained by adding a number of antennas placed equidistantly at the edge of the coverage area, using the same total transmit power that would be used with one transmit antenna. Moreover, this paper shows that since the IEEE 802.11n, the standard which facilitates the use of multiple antennas, states that the maximum number of antennas at any transceiver is four, two Access Points can be used to transmit the same data packet in orthogonal time slots to transmit good quality H.264 video resulting in all nodes experiencing an average Peak Signal to Noise Ratio greater than 36dB for MCS-5 and MCS-6 for a coverage area having radius of 60m. Since only two time slots are used, these results are obtained with a ½ code rate which is an improvement to the code rate used in current cooperative schemes.