Design Issues of Digital and Analog Chaotic RoF Link Using Chaos Message Masking

Danish Ali Mazhar,Farhan Qamar,Muhammad Khawar Islam,Syed Zafar Ali Shah

doi:10.1109/access.2019.2957255

Abstract

This work presents the joint use of Radio Over Fiber and optical chaos to investigate the secure ROF link. Merging the two technologies, optical chaos for physical layer communication security and Radio over Fiber creates new design issues which have been identified and studied in detail in this paper for both analog Radio Frequency/Intermediate Frequency and digitized data. A semiconductor laser diode is driven into chaotic region using direct modulation scheme and RoF signal is added by chaos message masking scheme. The chaotically masked signal is transmitted over an optical communication link to investigate the propagation issues and synchronization of chaos at the receiver. The transmitted chaos is synchronized at the receiver to unmask the signal by using subtraction rule. To investigate the performance of chaotic communication system for Radio over Fiber transmission, the figure of merits like Bit error rate, Quality factor, Eye Opening Penalty and Root-mean-squared phase jitter are studied for digital data and Signal to Noise ratio and Total Harmonic Distortion are studied for analog waveform to address the effects of link length and data rate/message bandwidth.

Highlights

The three biggest discoveries of 21st century are theory of Relativity, Quantum Mechanics and Chaos Theory
The chaos generated by direct modulation of semiconductor laser is shown in Fig. 3(a) without any message added while Fig.3(b) shows the amplitude modulated Radio Frequency (RF) signal
The message signal is added by chaos message masking and it can be observed that message power is kept so less as compared to chaos that it is not visible in time domain and frequency domain as shown in Fig. 3(c) and (d) respectively

Summary

Introduction

The three biggest discoveries of 21st century are theory of Relativity, Quantum Mechanics and Chaos Theory. While sensitive dependence on initial conditions was first encountered by Henri Poincare during study of three body problem, the formal discovery of chaos was done by Lorenz in 1960s during computer simulation of weather dynamical model constituting three nonlinear coupled differential equations. The chaos is governed by two trajectories nearby in phase space diverge exponentially away with time as measured by Lyapunov exponent calculation. This divergence in chaotic dynamics leads to unpredictability of waveform which can be used for applications like random number generation and to hide message signal in secure communication. Two chaotic systems starting at same time would produce completely different outputs due to inability to ensure exactly same initial conditions was the

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