Berna Bulut

Cross-layer design of raptor codes for video multicast over 802.11n MIMO channels

This paper explores the benefits of application layer forward error correction (AL-FEC) based on Raptor codes for high quality video multicasting over 802.11n multiple-input multiple-output (MIMO) channels. A cross-layer Wi-Fi simulator in combination with a state-of-the-art ray tracing propagation tool was used to analyse the performance of spatial multiplexing (SM) and space time block coding (STBC) MIMO techniques under different channel conditions. Simulation results showed that with the use of Raptor code AL-FEC, the operation range of the SM system was increased, i.e., the outage probability was driven to zero even though the MIMO channels were highly correlated. Furthermore, the spectral efficiency was also increased since the SNR gain can be increased up to 10 dB depending on the channel conditions. This results in a higher MCS mode to be selected for the transmission of data. We also presented a MIMO switching algorithm which implements Raptor codes as a means to improve the SM performance and then we evaluated the system under realistic wireless channel conditions.

Carousel-based wireless multicast transmission over WLANs employing raptor codes

Data carousels are a traditional way of providing reliable multicast transmission without the need for per-user feedback channels. Application Layer Forward Error Correction (AL-FEC) codes (in the form of Reed-Solomon codes) have previously been used to improve the performance of data carousels. However, until now, their joint design has only been investigated analytically with unrealistic random packet loss values. In this paper we investigate the joint design of an AL-FEC enhanced data carousel for use in an outdoor 802.11 multicast wireless LAN. We use an advanced end-to-end system level simulator to determine the optimal design parameters. Furthermore, we extend previous research in this area by combining data carousels with AL-FEC based on fountain codes. Our simulation results show that this new approach is more efficient than traditional Reed-Solomon block codes. More specifically, average download times are reduced, percentages of satisfied users are increased and valuable network resources are more efficiently utilized.

Multicast Wi-Fi Raptor-enabled data carousel design: simulation and practical implementation

Multicast is an efficient way of transmitting the same set of data to multiple interested users. Unlike the 3rd Generation Partnership Project (3GPP) cellular standards, for Wi-Fi, there is no standardised solution for reliable multicast data transmission. Multicast packets are delivered to multiple users as a broadcast service without support for automatic repeat request. Hence, multicast transmission often results in high packet loss. In order to improve the reliability of multicast delivery, a fixed low-speed (robust) transmission mode can be used. However, this results in the inefficient use of scarce and valuable radio bandwidth. This paper presents a reliable and efficient Wi-Fi multicast delivery solution for use in challenging outdoor environments. An application layer forward error correction (AL-FEC)-enabled data carousel is proposed to enhance reliability. For multicast transmission, we demonstrate that limitations in the Wi-Fi clients are a major source of packet loss, even in ideal channel conditions. Client limitations (particularly data rate limitations) were found to vary as a function of modulation and coding mode, Raptor code parameters and multicast server rate. Our initial Raptor-enabled carousel designs are based on computer simulations and lab-based trials. Analysis is then extended to field trials using a practical implementation of the recommended design. These trials were performed in central Bristol with parameters such as received signal level, packet loss traces and file download times recorded at the clients. Finally, we compare our site-specific simulated results against real-world measurements.

A raptor enabled data carousel for enhanced file delivery and QoS in 802.11 multicast networks

802.11 WLANs do not provide any standardized solution for reliable data multicast. Multicast packets are delivered to multiple clients as a simple broadcast service without support for Automatic Repeat Request. Hence, a fixed low speed (robust) transmission mode is generally used to improve the reliability of multicast files. However, this results in the inefficient use of bandwidth. This paper details a reliable and efficient Wi-Fi multicast delivery solution for use in challenging outdoor environments. We propose an Application Layer Forward Error Correction enabled data carousel for reliable multicast transmission over standard 802.11 WLANs. To quantify the benefits of the proposed system, results are reported from a cross-layer simulator combining novel outdoor ray-tracing, a Physical layer abstraction simulator (to rapidly quantify the radio performance), a RaptorQ enabled multicast data carousel simulator and an optimal access point deployment tool. The simulation results demonstrate that RaptorQ enabled carousels (compared to standard carousels) significantly reduce the average response time and increase the percentage of satisfied users in a multicast network.

Performance Evaluation of Multicast Video Distribution Using LTE-A in Vehicular Environments

Application Layer Forward Error Correction (AL-FEC) based on Raptor codes has been employed in Multimedia Broadcast/Multicast Services (MBMS) to improve reliability. This paper considers a cross-layer system based on the latest Raptor Q codes for transmitting high data rate video. Multiple Input Multiple Output (MIMO) channels in a realistic outdoor environment for a user moving at 50kmph in an LTE-A system is considered. A link adaptation model with optimized cross-layer parameters is proposed under different channel conditions and quality of service requirements. The system investigates throughput performance for Spatial Time Block Coding (STBC) and Spatial Multiplexing (SM) MIMO with and without raptor codes. Improvements of up to 4dB SNR are seen by using raptor codes with SM depending upon the channel conditions and chosen Modulation and Coding Scheme (MCS). Results also show that at low SNR and low spatial correlation, the performance of AL-FEC with SM is better than STBC even when the user is moving at high speeds.

An Adaptive Raptor Enabled Data Carousel for File Delivery in 802.11 Multicast Networks

WLANs currently do not provide a robust solution for reliable data multicast. Multicast packets are delivered to multiple users as a simple broadcast service without support for Automatic Repeat Request. Hence, a fixed low speed transmission mode is generally used to improve the reliability of multicast files. However, this results in the inefficient use of bandwidth. This paper proposes a reliable and efficient Wi-Fi multicast delivery solution for use in challenging outdoor environments. We proposed an adaptive Application Layer Forward Error Correction (AL-FEC) enabled data carousel for reliable multicast transmission over standard 802.11 WLANs. To quantify the benefits of the proposed system, results are presented from a cross-layer simulator combining novel outdoor ray-tracing, a physical layer abstraction simulator and a RaptorQ enabled multicast data carousel simulator. The simulation results demonstrate that adaptive FEC carousels significantly reduce the average download time, increase the percentage of satisfied users and bandwidth efficiency in a multicast network.