Enhanced Simulation Tools for Analyzing Signal Processing Techniques in the Optical Transmission Path

Introduction

For new multimedia broadband services and advanced modern applications provisioned in 5G networks to both residential and business customers, a reliable and safety transmission medium - the optical fiber - must be necessarily used in a certain form. One of the prominent technologies is the broadband optical network. In advanced forms of broadband optical networks, active elements should be considered for including in optical network terminals. Architectures of broadband optical networks must be reliable and cost effective; therefore, no switching and control elements in the optical distribution network are preferable against active ones. Moreover, optical network terminals on the subscriber side must be cheap and simple. The optical line terminal on the central office side can be more sophisticated because it represents the main managing equipment of broadband optical networks.

The broadband optical network is a bi-directional multipoint-to-multipoint system that contains passive (optical fibers, passive optical splitters, couplers, connectors) optical elements in a distribution part and active (optical line and network terminals) optical elements placed in end terminating points of the access, metropolitan and long-distance network. The transmission path between optical transmitters and receivers is presented by single-mode optical fibers. It can be divided into the three main parts:

• 1.

  A transmitting part is responsible for generating optical signals using the laser and for modulating generated signals according to relevant input data into a form suitable for transmitting in the environment of the optical fiber.

• 2.

  A transmission channel represents the optical transmission medium with linear and nonlinear effects with negative influences on transmitted signals. A main attention is focused on the attenuation, various types of the dispersion and different nonlinearities. Because these negative influences expressively interfere into the communication and represent its main limiting factors, they present a critical part of the simulation model and, therefore, it is necessary exactly to recognize and express their characteristics by correct transmission parameters.

• 3.

  A receiving part is responsible for demodulating received optical signals and for calculating of the bit error rate. Moreover, graphical presentations (eye diagrams, signal constellation diagrams) of optical signals in any part of the optical transmission path can be utilized.

Nowadays, an interest in the signal transmission through optical fibers rapidly increases due to demand of 5G networks. Constructing new optical transmission paths can be time consuming, expensive and sometimes not available solution. In the electric domain, utilizing new advanced signal processing can lead to increasing of the transmission capacity. Such solutions can be easily integrated. With increasing of modulation rates, linear and nonlinear influences in the optical transmission medium on transmitted optical signals are growing and by this way additional bit errors in information signals are generating. Therefore, it is important to design and analyze advancements in the optical domain with respect to the optical transmission medium. The simulation gives transmission boundaries of each designed advanced signal processing techniques for the optical transmission path and allows comparing all the solutions before their deployment and implementation into real optical transmission systems. The simulation allows increasing the data rate and the transmission range of deployed optical transmission systems using advanced signal processing techniques and allows designing a new optical transmission system with different optical fibers. Due to increased demands for transmission rates in the optical transmission medium, it is very important to avoid expensive practical demonstration and testing. Therefore, simulation platforms are increasing their role. However, it is important to search for a simulation platform that will be able to accurately describe behavior and limitations of the optical transmission system under various working conditions. After becoming acquainted with several various commercial simulation software products, we decided for designing and creating our own simulation platform based on the Matlab Simulink programming environment.