In this letter, we numerically investigate noise suppression using self-phase-modulation (SPM) in transmission optical fiber and degenerate phase-sensitive optical amplifier (PSA). It is clarified that the optimum fiber input signal power for SPM and phase shift for amplitude noise suppression of 10Gbit/s binary-phase-shift keyed (BPSK) signals. Then, 10-Gbit/s BPSK signal transmission on multi-relay systems is evaluated. When the fiber input optical power is 5mW, the signal-to-noise ratio (SNR) of PSA output is larger than 20dB on 200-relays while SNR of the conventional PSA output is 15dB after 63-relays.