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Title: Cross-layer design and evaluation of raptor codes for reliable and efficient multimedia content transmission over WLANs
Author: Bulut, Berna
ISNI:       0000 0004 5916 8641
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2015
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The demand for multimedia applications is increasing and existing point-to-point data communication systems cannot meet the requirements for high data rate multimedia transmission. This leads to the introduction of more spectrally efficient point-to-multipoint services. However, efficiently transmitting large data to a heterogeneous and large receiver population over unreliable wireless channels requires sophisticated multi cast techniques. The aim of this thesis is to design and quantify the benefits of application layer solutions that provide end-to-end reliability for multicast WLAN transmission. To this end, a cross-layer design based on the latest RaptorQ (RQ) codes for transmitting high data rate video over the multiple input multiple output (MIMO) channels in realistic outdoor environments is presented. RQ code performance is investigated for spatial multiplexing (SM) systems. A detailed crosslayer simulator is used to define the optimum system parameters under different MIMO channel conditions. The channels are generated using a state-of-the-art 3D ray tracing tool and are used to evaluate performance in realistic outdoor environments. It is shown that with the use of Raptor codes there can be up to 10 dB improvement in the required signal to noise ratio (SNR) depending on the correlation between the MIMO channels. An adaptive MIMO technique is proposed that considers Raptor code application layer forward error correction (AL-FEC) in SM as a means to enhance reliability and transmission efficiency. The benefits of the proposed system are highlighted using a site specific case study. This thesis proposes a FEC carousel model based on Raptor codes for wireless multicast transmission over WLANs. Different carousel models, namely sequential and interleaved models, are designed and evaluated in realistic environments. It is shown that the interleaved carousel model provides a lower download time and superior coverage as compared to the sequential model. A complete system design methodology that enables the trade-off between user coverage, AP density and data download time to be managed in a complex real-world environment is presented. Furthermore, the proposed multicast carousel system is validated via experimental measurements. This thesis presents the first detailed analysis on the implementation ofRQ codes and data carousels in a practical Wi-Fi based server/client system. It is shown that system performance is mostly dominated by hardware and software limitations on constrained host platforms where the incoming packet rate exceeds the device's ability to consume the traffic. RQ parameters are evaluated through measurements. It is recommended to choose Raptor source block length K ::; 200 and symbol size T;::: 1000 bytes in order to provide a better quality of experience. Finaliy, an adaptive FEC carousel system, which provides reliable and scalable multicast transmissions over the IEEE 802.11 WLANs, based on Raptor codes is proposed. It is shown that the adaptive system significantly reduces the average download time, increases the percentage of satisfied users and effectively utilises the valuable radio and network resources in a multicast network with suitable design parameters.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available