Victoria Sgardoni

Raptor Code-Aware Link Adaptation for Spectrally Efficient Unicast Video Streaming over Mobile Broadband Networks

This paper proposes novel Raptor-aware link adaptation (LA) when application layer Forward Error Correction (AL-FEC) with Raptor codes is used for live, high quality, video unicast over mobile broadband networks. The use of Raptor code AL-FEC is taken into account for the adaptation of the modulation and coding scheme (MCS) used in the physical layer. A cross-layer optimization approach is used to select the Raptor code parameters and the MCS mode jointly, in order to maximize transmission efficiency. The proposed methodology takes into consideration the channel resources required to accommodate the Raptor overheads. Simulation results show that packet loss is eliminated and the amount of radio resource required is reduced significantly. Automatic repeat request (ARQ) based unicast systems require up to 115.6 percent more channel resources, by comparison to the proposed Raptor-aware LA system without retransmissions. Furthermore, the Raptor-aware LA system can enhance the link budget by up to 4 dB, increasing coverage in LoS locations, and can improve total goodput by 46.7 percent compared to an ARQ-based system.

Frame Delay and Loss Analysis for Video Transmission over time-correlated 802.11A/G channels

This paper presents simulation results for the transmission of unicast MAC frames over 802.11a/g. Fading channel models at various Doppler frequencies are developed to generate time- correlated SNR waveforms. These are then used together with a bit accurate MAC/PHY simulator to estimate the frame loss rate, the transmission delay, and the jitter for a steady flow of transmit frames. Time correlated channels are required to correctly simulate the bursty nature of packet loss in a wireless channel. The Doppler spread is shown to have a strong effect on the performance of the ARQ mechanism in the MAC layer. Delay is computed as the sum of the transmission delay and the accumulated queuing delay in the MAC buffer. Delay and frame loss are compared for time correlated and time uncorrelated fading channels. Compared to the slow fading case, in a fast fading channel fewer retransmissions are required and the end-to-end delay is significantly reduced. When channel conditions are poor the simulated delay and frame loss rate are seriously underestimated when time uncorrelated fading is assumed. To analyze the performance of video codecs, we show that a time correlated channel model must be combined with a dedicated 802.11a/g MAC/PHY simulation.

Robust video broadcasting over 802.11a/g in time-correlated fading channels

In order to deliver video streams efficiently over WiFi to many thousands of consumer handheld devices, broadcast protocols must be employed. In this mode of operation the received video quality can deteriorate rapidly as a result of high application layer packet loss which occurs because MAC frame retransmission cannot be used. In this paper we develop a robust video delivery solution for broadcast transmission over 802.11a/g. Using a cross-layer WiFi simulator in combination with an accurate time-correlated fading channel, the received video quality is evaluated for broadcast H.264 video sequences. Application layer cross-packet forward error correction is then used together with error concealment at the video client. Furthermore, the application of an external packet interleaver is considered. Combining a block size of two hundred packets (which introduces a 4.8 second delay) and an application layer FEC code rate of 0.75 our results demonstrate that video can be successfully broadcast over WiFi to many thousands of handheld terminals at large-scale spectator events.

Spectrum efficient cross-layer adaptation of Raptor codes for video multicasting over mobile broadband networks

This paper explores the use of rateless application layer Forward Error Correction (AL-FEC) based on Raptor codes in a spectrally efficient way for real-time video multicasting over mobile broadband networks. The link between channel errors at the PHY, MAC and application layers and the required Raptor code parameters for quasi-error free video transmission is investigated. Low Raptor code rates are shown to place high demands on the limited bandwidth of a wireless channel. The selection of Modulation and Coding Scheme (MCS) is extended to take into account the channel resources required to accommodate the additional Raptor overheads. A cross-layer optimization approach and a novel metric are proposed to select the Raptor code parameters and the MCS mode jointly to maximize wireless transmission efficiency. Simulation results show that 166% more bandwidth is required by a non-Raptor enabled multicast WiMAX system, assuming a Mobile Station (MS) speed of 10?km/h, in comparison to the optimized Raptor AL-FEC multicast WiMAX system. Results show that more bandwidth is required at lower MS speeds. Furthermore, the optimized Raptor AL-FEC system is shown to eliminate packet loss, to enhance the link budget by up to 6?dB, which quadruples multicast coverage in LoS locations, and to increase the total goodput by 67%, in comparison to a non-Raptor enabled multicast WiMAX system.

ARQ-Aware Scheduling and Link Adaptation for Video Transmission over Mobile Broadband Networks

This paper studies the effect of ARQ retransmissions on packet error rate, delay, and jitter at the application layer for a realtime video transmission at 1.03Mbps over a mobile broadband network. The effect of time-correlated channel errors for various Mobile Station (MS) velocities is evaluated. In the context of mobile WiMAX, the role of the ARQ Retry Timeout parameter and the maximum number of ARQ retransmissions is taken into account. ARQ-aware and channel-aware scheduling is assumed in order to allocate adequate resources according to the level of packet error rate and the number of ARQ retransmissions required. A novel metric, namely, goodput per frame, is proposed as a measure of transmission efficiency. Results show that to attain quasi error free transmission and low jitter (for real-time video QoS), only QPSK 1/2 can be used at mean channel SNR values between 12dB and 16dB, while 16QAM 1/2 can be used below 20dB at walking speeds. However, these modes are shown to result in low transmission efficiency, attaining, for example, a total goodput of 3Mbps at an SNR of 14dB, for a block lifetime of 90ms. It is shown that ARQ retransmissions are more effective at higher MS speeds.

Mobile WiMAX video quality and transmission efficiency

This paper explores rules and defines cross layer parameters that enhance the received video quality per unit bandwidth while observing strict video QoS for unicast video transmission over mobile WiMAX. Channel capacity and goodput are estimated using a detailed MAC/PHY simulator. The simulator supports link adaptation of the PHY layer Modulation and Coding Scheme (MCS) alongside MAC layer Automatic Repeat Request (ARQ). A new performance indicator, PSNR per Hz, is defined to capture the video PSNR attained for a given effective bandwidth. For the 3GPP urban micro channel, MCS and MAC layer block lifetime are jointly determined as a function of average channel SNR in order to enhance video PSNR and goodput. At low SNR higher level QAM is inefficient (as a result of excessive MAC layer ARQ or high packet error rate) for video transfer. Results show that video efficiency improves for block lifetimes up to 100ms, since the greater use of ARQ enables more spectrally efficient MCS modes to be applied.

5G systems: The mmMAGIC project perspective on use cases and challenges between 6–100 GHz

mmMAGIC (Millimetre-Wave Based Mobile Radio Access Network for Fifth Generation Integrated Communications) is an EU funded 5G-PPP project, whose overall objective is to design and pre-develop a mobile radio access technology (RAT) operating in the 6–100 GHz range, capable of impacting standards and other relevant fora. The focus of the project is on extreme Mobile Broadband, which is expected to drive the 5G requirements for massive increase in capacity and data-rates. This paper elaborates on some 5G key research areas such as: identification of the most compelling use-cases and Key Performance Indicators (KPIs) for future 5G systems, advantages and challenges of millimeter-wave (mmWave) technologies, channel measurements and channel modeling, network architecture; and the design of a new mobile radio interface including multi-node and multi-antenna transceiver architecture.

Frame Delay, Loss Rate and Throughput Analysis for Video Applications over time correlated 802.11a/g channels

This paper presents simulation results for the transmission of unicast MAC frames over 802.11a/g. Fading channel models at various Doppler spreads are developed to generate time-correlated SNR waveforms. These are used in a bit accurate MAC/PHY simulator to estimate frame loss rate, transmission delay, jitter and throughput for a steady flow of transmit frames. Time-correlated channels are required to correctly simulate the bursty nature of packet loss in a wireless channel. The Doppler spread is shown to have a strong effect on the performance of 802.11 ARQ at the MAC layer. Compared to the slow fading case, in a fast fading channel fewer MAC layer retransmissions are required and the end-to-end delay is significantly reduced. Under poor channel conditions the simulated delay and frame loss rate are seriously underestimated if time-uncorrelated fading is assumed.

IEEE International Conference on Signal Processing and Communications, 2007, ICSPC 2007

This paper presents simulation results for the transmission of unicast MAC frames over 802.11a/g. Fading channel models at various Doppler spreads are developed to generate time-correlated SNR waveforms. These are used in a bit accurate MAC/PHY simulator to estimate frame loss rate, transmission delay, jitter and throughput for a steady flow of transmit frames. Time-correlated channels are required to correctly simulate the bursty nature of packet loss in a wireless channel. The Doppler spread is shown to have a strong effect on the performance of 802.11 ARQ at the MAC layer. Compared to the slow fading case, in a fast fading channel fewer MAC layer retransmissions are required and the end-to-end delay is significantly reduced. Under poor channel conditions the simulated delay and frame loss rate are seriously underestimated if time-uncorrelated fading is assumed.