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Title: Enhanced wireless video transmission using a cross-layer design
Author: Sgardoni, Victoria
ISNI:       0000 0004 2741 3892
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2012
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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).
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available