With the wide application of repeatless optical fiber transmission system, its complexity and cost become factors to be considered. A simplified transmission system without relay is proposed, in which Stokes vector direct detection(SV-DD) is used instead of coherent receiver. The performance of 128 Gb/s 16QAM signal transmission system with single wave and three wave multiplexing is simulated. The simulation results show that the system can demodulate the signal well, and the performance of forward and backward Raman pump is better when the power is 0.6 W and 0.8 W, and it can withstand the residual dispersion of about 400 ps · nm-1.