Title:
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Cross-layer design and evaluation of raptor codes for reliable and efficient multimedia content transmission over
WLANs
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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.
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