Performance evaluation of (D)APSK modulated coherent optical OFDM system
Performance of amplitude and phase shift keying (APSK) modulated coherent optical orthogonal frequency division multiplexing (CO-OFDM) with and without differential encoding is investigated. Numerical simulations based on 40Gbit/s single-channel and 5*40Gbit/s wavelength division multiplexing transmission are performed, and the impacts of amplified spontaneous emission noise, laser linewidth, chromatic dispersion, and fiber nonlinearity on the system performance are analyzed. The results show that compared with conventional 16 quadrature amplitude modulation (QAM) modulated optical OFDM signal, although 16(D)APSK modulated optical OFDM signal has a lower tolerance towards amplified spontaneous emission (ASE) noise, it has a higher tolerance towards fiber nonlinearity such as self-phase modulation (SPM) and cross-phase modulation (XPM): the optimal launch power and the corresponding Q2 factor of 16(D)APSK modulated OFDM signal are respectively 2dB and 0.5dB higher than 16QAM modulated optical OFDM signal after 640km transmission, both in single-channel and WDM CO-OFDM systems. Although the accumulated CD decreases the peak-to-average power ratio (PAPR) during transmission, 16(D)APSK modulated OFDM signal will still remain an advantage compared with 16QAM modulated OFDM signal up to 1000km single-channel transmission, meanwhile relaxing the needs for training symbols and pilot subcarriers and consequently increase the spectral efficiency.
amplitude and phase shift keying (apsk) fiber nonlinearity quadrature amplitude modulation (qam) orthogonal frequency-division multiplexing (ofdm)