Performance analysis of next generation OFDM based optical access networks using multi-level modulation under various system impairments

Passive optical network based on orthogonal frequency division multiplexing (OFDM-PON) is a promising candidate for 10 Gb/s and 40 Gb/s or even higher optical access network due to its greater resistance to fiber dispersion. High spectral efficiency is also achieved due to the orthogonality among all sub-carriers which overlap in the frequency domain. In this paper, without optical dispersion compensation, the performance of 10 Gb/s and 40 Gb/s OFDM-PON using multi-level modulation scheme under various system impairments is analytically analyzed and compared for their transmission distance, transmission capacity, bandwidth efficiency and BER for coherent optical orthogonal frequency division multiplexing (CO-OFDM) system. Analytical result show that at BER of 10^-3 which is the limit of forward error correction (FEC), and using 16-QAM, an optical budget (downstream) of 49.2 dB and 47 dB is obtained for 10 Gb/s and 40 Gb/s respectively. For 64-QAM the corresponding values are 47.7 dB and 45.2 dB. It implies that there is 2.2 dB degradation in optical budget if the bit rate is increased from 10 Gb/s to 40 Gb/s for 16-QAM and 2.6 dB degradation for 64-QAM. On the other hand, higher order modulation gives better bandwidth efficiency than lower order modulation. Thus, in designing optical access network, the transmission capacity, transmission distance, BER and implementation complexity of the equipment must be comprehensively considered.