Performance Analysis of Different Modulation Schemes for Coherent Optical OFDM System
Without optical dispersion compensation, the performances of different modulation schemes are analyzed and comparison of their transmission distance, transmission capacity, band width efficiency and their resistance to BER are made in Coherent optical orthogonal frequency division multiplexing (CO-OFDM) system in this paper. Then some simulation results are given using Matlab software. Simulation results show that: in the same conditions, the relationship of transmission capacity, transmission distance and bit error rate of the system is contradictory. The anti-BER ability of 2PSK is best, but its bandwidth efficiency is lower than other modulation methods. The bandwidth efficiency of 4QAM is as twice as the 2PSK, and the BER of the system is smaller than 10-3 and the required OSNR is about 9dB. When the OSNR is 12dB, the transmission distance is up to 1600km. Although the bandwidth efficiency of 8QAM is higher than other two kinds of modulation methods, its performance of anti-BER is relatively poor. Therefore, we should choose the specific scheme modulation depending on the actual needs of the system when we design communication.