Orthogonal frequency division multiplexing for optical access networks

Orthogonal Frequency Division Multiplexing (OFDM) is a modulation scheme with numerous advantages that has for years been employed as the leading physical interface in many wired and wireless communication systems. Recently, with advancements made in digital signal processing, there has been a surge of interest in applying OFDM techniques for optical communications. This thesis presents extensive research on optical OFDM and how it is being applied in access networks. With the aid of theoretical analysis, simulations and experiments, it is shown that the system performance of direct-detection optical OFDM (DD-OOFDM) in the presence of MZM non-linear distortion can be improved by proper biasing and selection of appropriate drive to the MZM. Investigations are conducted to illustrate how a variation in the number of subcarriers and the modulation format influences the sensitivity of the DD-OOFDM system to the MZM non-linear distortion. The possibility of improving the spectral efficiency by reduction of the width of the guard band is also investigated. This thesis also looks into the radio-over-fibre (RoF) transmission of Multiband OFDM UWB as a transparent and low-cost solution for distributing multi-Gbit/s data to end-users in FTTH networks. Due to relaxed regulatory requirements and the wide bandwidth available, UWB operation in the 60-GHz band is also considered for this FTTH application scenario. Four techniques for enabling MB-OFDM UWB RoF operation in the 60-GHz band are experimentally demonstrated. The impacts of various parameters on the performance of the techniques as well as the limitations imposed by fibre distribution are illustrated. Finally, a digital pre-distorter is proposed for compensating for the MZM non-linearity. Experimental demonstration of this digital pre-distortion in an UWB over fibre transmission system shows an increased tolerance to the amplitude of the driving OFDM signal as well as an increase in the optimum modulation index of the OFDM signal

Noise Resistant Spreading OOFDM Design for Suppressing PAPR of High Data Rate Wireless Optical Communication System

In this paper, we present a novel noise resistent diagonal iteration-based carrier interferometry (DICI) codes for spreading optical orthogonal frequency-division multiplexing (OOFDM) symbols, and thereby suppressing the peak to average power ratio (PAPR) for high data rate OOFDM based systems. Considering that the high date rate transmission requires the subcarrier number to be large, and that the large subcarrier number may induce smaller intervals between the symbols and higher PAPR and thus leading to the performance degradation, we propose to use DICI codes to enlarge the intervals and suppress the noises including the signal- dependent noises in intensity modulated system and the phase noises in coherent modulated systems to improve the performances. More explicitly, we perform the diagonal iteration on the carrier interferometry (CI) codes by calculating the Kronecker product of identity matrix and CI code matrix, thus the matrix extension is achieved by the DICI codes. Moreover, we prove that the presented DICI codes are orthogonal and invertible. Simulations are performed and the results demonstrate the outstanding bit error rate (BER) and PAPR performances of the proposed DICI-aided spreading OOFDM systems

Noise Resistant Spreading OOFDM Design for Suppressing PAPR of High Data Rate Wireless Optical Communication System

In this paper, we present a novel noise resistent diagonal iteration-based carrier interferometry (DICI) codes for spreading optical orthogonal frequency-division multiplexing (OOFDM) symbols, and thereby suppressing the peak to average power ratio (PAPR) for high data rate OOFDM based systems. Considering that the high date rate transmission requires the subcarrier number to be large, and that the large subcarrier number may induce smaller intervals between the symbols and higher PAPR and thus leading to the performance degradation, we propose to use DICI codes to enlarge the intervals and suppress the noises including the signal- dependent noises in intensity modulated system and the phase noises in coherent modulated systems to improve the performances. More explicitly, we perform the diagonal iteration on the carrier interferometry (CI) codes by calculating the Kronecker product of identity matrix and CI code matrix, thus the matrix extension is achieved by the DICI codes. Moreover, we prove that the presented DICI codes are orthogonal and invertible. Simulations are performed and the results demonstrate the outstanding bit error rate (BER) and PAPR performances of the proposed DICI-aided spreading OOFDM systems