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UBC Theses and Dissertations

Statistical quality-of-service aware adaptive transmission for free space optical communication systems Hassan, Md. Zoheb


Despite the growing attention for free space optical (FSO) networks, state-of-the-art literature lacks appropriate adaptive transmission (AT) schemes that can exploit the stochastic propagation channel of the FSO networks and guarantee delay quality-of-service (QoS) in the link-layer. Specifically, weather-induced channel impairments not only affect the error-rate or outage probability but also increase the end-to-end queueing-delay of the FSO network. This dissertation aims to improve QoS-aware throughput of the terrestrial FSO communication systems by designing innovative AT schemes. The key goal of the developed AT schemes is to maximize the supportable arrival rate while ensuring the QoS in terms of certain delay-bound violation probability constraints. We first analyze the effective capacity (EC) of terrestrial FSO communication systems. We derive accurate closed-form expressions of the achievable EC by considering several FSO channel impairments. Through asymptotic analysis, we reveal insights on the EC increment. Next, we present delay-QoS aware discrete-rate AT schemes for FSO communication systems with parallel optical beams and average/peak transmit power constraints. Our results suggest that to improve the delay-throughput trade-off, only suitable optical channels need to be activated. Simulation results demonstrate that joint adaptation of transmission parameters of the active optical beams improve throughput of the FSO communication systems in the strict statistical-QoS constraints. Subsequently, we develop AT schemes for FSO backhaul/fronthaul networks. We first study AT schemes for buffer-aided parallel decode-and-forward relaying assisted hybrid radio-frequency (RF)/FSO backhaul networks. Two different hybrid RF/FSO system configurations are considered, and AT schemes for both configurations are developed. These schemes maximize the arrival rate subject to the total queue-occupancy constraint. Next, we develop delay-QoS aware joint power allocation and relaying link selection for amplify-and-forward relay assisted uplink FSO fronthaul networks. Finally, we investigate joint FSO fronthaul and millimeter-wave access link optimization for the downlink cloud small cell network subject to end-to-end queue-length-bound violation probability constraints. Extensive simulations are performed to evaluate the performance of the proposed AT schemes by considering several FSO channel impairments and statistical-QoS requirements. Simulation results demonstrate that our proposed AT schemes substantially improve the statistical-QoS aware arrival rate in the FSO backhaul/fronthaul networks.

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