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 real-time video transmission at 1.03 Mbps 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 12 dB and 16 dB, while 16QAM 1/2 can be used below 20 dB at walking speeds. However, these modes are shown to result in low transmission efficiency, attaining, for example, a total goodput of 3 Mbps at an SNR of 14 dB, for a block lifetime of 90 ms. It is shown that ARQ retransmissions are more effective at higher MS speeds

Enhanced wireless video transmission using a cross-layer design

The increasing demand for video services over wireless LANs and mobile broad- band networks and the challenges wireless video transmission is facing, drives the need to improve the support for video services over these networks. The aim of this thesis is to design and quantify the benefits of new methods that optimise end-to-end wireless video delivery via generic cross-layer design. These new ar- chitectures encourage complex interactions between the PRY/MAC layers of the wireless system and the application layer of the video services. Wireless networks are fundamentally error-prone due to the time varying nature of the radio channel while video services are typically intolerant to data loss. To improve data reliab- ility wireless networks offer forward error correction (FEC), such as the recently proposed application layer FEC based on Raptor codes, and ARQ packet retrans- mission at the PRY and MAC layers respectively. The performance of the WiFi ARQ mechanism is studied in terms of packet loss and packet delay, using time-correlated packet errors generated from a time- varying channel model. It is shown that prior simulations assuming uncorrelated errors seriously under predict the packet loss rate and latency resulting from ARQ retransmissions. The work in this thesis then focuses on the transmission of video over a mobile WiMAX network. The ARQ mechanism of mobile WiMAX is studied in terms of packet loss rate and latency. The properties and benefits of Raptor codes are then explored. In particular, interactions between the mobile WiMAX Modulation and Coding Scheme, the Raptor block size and the Raptor code rate are explored (for various Doppler spreads) via Monte Carlo simulation. This thesis proposes a novel cross-layer design with tight coupling between formats and packets across the OSI layers. A new methodology based on "Raptor- aware" link adaptation is proposed to select the optimum pairs of MCS mode and Raptor code rate in order to maximise transmission efficiency while maintaining a required level of PER at the application layer. Simulation results show that the proposed methodology significantly reduces the required radio resources, whilst offering error free communication to the video layer. To achieve these gains it is shown that MAC SDUs with missing ARQ blocks must be delivered to the higher layers. This can be achieved with the introduction of a permeable layer into the standard OSI model. Simulations show that to achieve the same level of video performance a standard mobile WiMAX system (at low mobile speeds) requires 118% more bandwidth at an SNR of 18dB, dropping to 40% at 16dB SNR. The proposed design also offers an SNR gain of 4dB which can extend the range of video services (particularly useful for multicast transmissions).EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Robust Multicast Delivery for WLANs: Transforming Theory into Practice

AbstractMulticast is an efficient way of transmitting the same set of data to multiple interested users. WLANs do not provide any standardized solution for reliable data multicast. Multicast packets are delivered to multiple users as a simple broadcast service without support for Automatic Repeat Request. Hence, multicast transmission results in higher packet error rates. In order to improve the reliability of multicast delivery, a fixed low speed (robust) transmission mode is generally required. However, this results in the inefficient use of scarce and valuable bandwidth. This paper presents a reliable and efficient Wi-Fi multicast delivery solution for challenging outdoor applications. An Application Layer Forward Error Correction enabled data carousel is proposed for reliable multicast transmission over standard IEEE 802.11 WLANs. Field trials have been conducted to demonstrate and quantify system performance. Results show that the proposed system enhances user quality of experience while time efficiently utilising available bandwidth. The proposed interleaved carousel that is Raptor code enabled, attains 74.5% less download time than the traditional carousel, because of randomisation of errors and the protection of Raptor AL-FEC. 90% of users are able to download successfully a video file of 2.8MB within 12sec, with multicasting using the Modulation and Coding Scheme (MCS) at 26Mb/s. Higher MCS modes become viable by exploiting the rateless properties of RaptorQ codes to radically enhance the reliably of multicast transmissions