Date of Award

4-4-2017

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Systems Engineering

First Advisor

Seshadri Mohan

Abstract

The Free Space Optical Networks are characterized by dynamic performance of optical wireless links as well as the atmospheric conditions and the mobility of free space optical nodes. In this dissertation, we focus on how to enhance the performance of free space optical network due to the mobility of free space optical nodes. The objective is to define and evaluate algorithms to establish continuous free space optical links in a stratospheric balloon mesh network. The main resource is the optical transceiver, which can be tuned to only one wavelength. Considering the constraint of single wavelength per transceiver, the wavelengths must be assigned in an optimized manner to utilize the scarce resources efficiently. Such optimization of the network requires an efficient configuration of logical topology of free space optical network for every change in physical topology. The physical topology can be only controlled up to a certain extent by tracking information of each node in the network and using pointing, acquisition and tracking (PAT) methods. The logical topology control requires more complex and in-depth analysis to exploit the use of optimization tools. The free space optical network topology is reconfigured and controlled to build an optimized physical and logical topology. The metrics of optimization problem are traffic load, distance and mobility of each balloon in the network. We solve tracking and logical topology reconfiguration method for non-stationary free space optical networks. The proposed methodology is aimed to solve two major aspects of non-stationary free space optical networks, Tracking the mobile FSO nodes and Reconfiguration of the logical topology of non-stationary free space optical networks. We simulate two different scenarios of the non-stationary free space optical networks to evaluate our proposed methodology. We consider non-stationary free space optical networks as a network of high altitude stratospheric balloons with free space optical systems attached to their payloads. The tracking of free space optical balloon is required to update the steering system of FSO transceiver to keep the pointing axis of each transceiver in line of sight to the corresponding balloon. A state estimation method is adopted to formulate the tracking problem using stratospheric balloon dynamics at high altitude. We introduce physical topology (distance and orientation) bounds (upper and lower) to the Mixed Integer Linear Programming logical topology reconfiguration. We use Matlab to evaluate tracking algorithm and to solve the Mixed Integer Linear Programming. OMNeT++ is used for non-stationary routing network simulation to evaluate Mixed Integer Linear Programming generated logical topologies. The simulation results show about 70% reduction in congestion by introducing tracking and applying Mixed Integer Linear Programming generated logical topologies.

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