Transmissão de sinais OFDM com envoltória constante em sistemas ópticos com detecção coerente

• Autor(a) principal: Pereira, Esequiel da Veiga
• Data de Publicação: 2017
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: Repositório Institucional da Universidade Federal do Espírito Santo (riUfes)
• Texto Completo: http://repositorio.ufes.br/handle/10/9721
• topic: Relação entre potência de pico e potência média (PAPR); Constante envelope; Engenharia Elétrica; Fibras ópticas; Multiplexação ortogonal por divisão de frequência; Teoria da codificação; 621.3

To keep pace with the ever-increasing demand for channel capacity of optical back bone networks, investigation of modulation formats supporting huge transmission capacity are gained special interest. Coherent optical orthogonal frequency division multiplexing (COOFDM) is one of the candidates for upgrading the conventional photonic systems. Because of the compact optical spectrum, CO-OFDM signals are scarcely influenced by linear degradation such as group velocity dispersion (GVD) and polarization mode dispersion (PMD). However, the large peak to average power ratio (PAPR) makes them vulnerable to fiber nonlinearity and degrades their transmission performance. A low PAPR coherent-detection optical OFDM system has been proposed and discussed to increase tolerance towards Mach-Zehnder modulator and fiber nonlinearities. Based on constant envelope signals (PAPR = 3 dB) obtained after electrical phase modulation, the denominated CO-CE-OFDM scheme outperforms conventional optical coherent-detection OFDM systems, in some specific circumstances. Simulations results after propagations through 1200 km of standard single mode fiber (SSMF) shows that when the transmission is done in a linear regime (low optical power at fiber input), in some situations CO-CE-ODFM outperforms conventional coherent detection. For example, for a 100 / rate, mapping levels of 16 QAM and optical modulation index (OMI) equal to 2.5, the proposed system with electric phase modulation index (2ℎ ) equal to 3 exhibited optical signal-to-noise ratio (OSNR) gains greater than 12 dB, for a bit error rate of 10−3. In the nonlinear regime, due to the increase in optical power, even for low OMI values and high optical signal-to-noise ratio, CO-CE-OFDM presented performance gains of approximately 26 dB over the conventional CO OFDM, when the optical input power is 10 dBm. For high OMI values, this performance gain is about 12 dB, for 16 QAM and 100 Gb/s rate. In addition, an analytical model is presented, which allows evaluating, in a fast and at low computational cost, the performance of the system against the variation of the optical signal-to-noise ratio. Despite the performance gain presented, CO-CE-OFDM shows spectral widening, which can be a problem in multichannel systems