Performance analysis of coherent OFDM-PON in future optical access networks

Abstract

The need to have ever increasing transmission rates makes optical communications the technology to adopt, being the only technology that currently allows transmission of data in the Tb/s region. However, with passive optical networks NG-PON2 it is possible to achieve speeds of 40 Gb/s downstream and 10 Gb/s upstream but, due to the constant increasing of demanding services and applications, there is an incessant investigation in order to suppress these future needs. OFDM has been used successfully in numerous applications, such as digital audio/video transmission, wireless communication systems, among others. It is a very viable solution that has in its favor a low interference between symbols and a good spectral efficiency, besides passing the complexity of the transmitters and receivers from analog domain to the digital domain. This dissertation studies OFDM technology, describing all processes from generation, modulation, transmission and reception of the signal. It is performed an exhaustive simulation study using a 40 Gb/s bit rate and advanced modulation techniques, such as QPSK and 16QAM. It's also studied the impact that direct and coherent detection techniques have on the system, as well as the effect that the optical channel length has on the transmitted signal. This dissertation aims to demonstrate that OFDM is a viable technology and a true alternative to be used in future optical access networks.The need to have ever increasing transmission rates makes optical communications the technology to adopt, being the only technology that currently allows transmission of data in the Tb/s region. However, with passive optical networks NG-PON2 it is possible to achieve speeds of 40 Gb/s downstream and 10 Gb/s upstream but, due to the constant increasing of demanding services and applications, there is an incessant investigation in order to suppress these future needs. OFDM has been used successfully in numerous applications, such as digital audio/video transmission, wireless communication systems, among others. It is a very viable solution that has in its favor a low interference between symbols and a good spectral efficiency, besides passing the complexity of the transmitters and receivers from analog domain to the digital domain. This dissertation studies OFDM technology, describing all processes from generation, modulation, transmission and reception of the signal. It is performed an exhaustive simulation study using a 40 Gb/s bit rate and advanced modulation techniques, such as QPSK and 16QAM. It's also studied the impact that direct and coherent detection techniques have on the system, as well as the effect that the optical channel length has on the transmitted signal. This dissertation aims to demonstrate that OFDM is a viable technology and a true alternative to be used in future optical access networks.

A necessidade de aumentar cada vez mais os ritmos de transmiss~ao fazem das comunicações oticas a tecnologia a adotar, sendo esta a única tecnologia que, atualmente, permite transmissão de dados na região dos Tb/s. Todavia, com as redes óticas passivas NG-PON2 é possível obter velocidades de 40 Gb/s downstream e 10 Gb/s upstream mas, devido ao constante aumento de serviços e aplicativos cada vez mais exigentes, é espectável que seja insuficiente para suprimir necessidades futuras, havendo uma incessante investigação de forma a colmatar essas esse defice. Orthogonal frequency division multiplexing (OFDM) tem vindo a ser utilizado com sucesso em in umeras aplicações, tais como transmissão áudio/vídeo digital, sistemas de comunicação wireless, entre outras. É uma solução bastante viável que tem a seu favor uma baixa interferência entre símbolos e uma boa eficiência espectral, alem de passar a complexidade dos transmissores e recetores do dominio analógico para o domínio digital. Nesta dissertação é estudada a tecnologia OFDM, descrevendo todo processo desde geração, modulação, transmissão e recepção do sinal. Foi tamb em feito um estudo de simulação exaustivo usando um bit rate de 40 Gb/s e técnicas de modulação avançadas, sendo estas QPSK e 16QAM. Foi também estudado o impacto que as técnicas de detecção direta e coerente têm no sistema, assim como o efeito que o comprimento do canal ótico tem no sinal transmitido. Esta dissertação visa demonstrar que OFDM é uma tecnologia viável e uma verdadeiras alternativa a ser usada em futuras redes óticas de acesso.