Abstract
For the first topic of this thesis, we propose a software-defined network (SDN) controlling FBG-based optical sensing system with mesh topology. In this system, we use a multiple sensing regions scheme supervised by many SDN controllers. Each SDN controller can know the whole network information of every sensing region by exchanging messages with other controllers. Every regular sensing procedure is automatically executed based on the built-in routing table in central office (CO). SDN controller will only participate in and update the sensing procedures based on software algorithms when abnormal occasions occur, such as link failures. This multiple sensing regions scheme is an effective solution to issues of remote nodes controlling and sensing network survivability enhancement. We apply Mininet and Floodlight as simulation platforms to simulate the data plane and control plane respectively. The numerical simulations, including evaluations of the available light path ratio, the sensing signal power loss, and the network survivability, are conducted based on different sensing regions schemes and link failures. As a result, by taking the advantages of the SDN scheme, our demonstration can not only enhance the performance of sensing procedures and the tolerance of link failures, but also offer an effective solution of the network controlling issues. For the second topic of this thesis, we propose a low complexity I/Q imbalance estimation algorithm and iterative compensation scheme for orthogonal frequency division multiplexing (OFDM) system. The I/Q imbalance parameters can be estimated by simple training symbols. Instead of other complex nonlinear calculations, this estimation algorithm only applies simple linear operations, including division and subtraction, to obtain the estimated I/Q imbalance amplitude and phase factors. These compensations are designed as an iterative procedure by compensating imbalances from receiver and transmitter alternatively. With such a design, the distorted I/Q imbalance signals can be greatly improved, such that performance can be approaching to that of undistorted signals. This proposed estimation and compensation scheme is demonstrated by numerical simulations under various I/Q imbalance conditions.