The optical relaying networks (ORN) on free-space optical (FSO) communications give beneficial prospect in the development to reach the last mile users in the order of tenth kilometer. However, the ORN on FSO that is configured in many nodes of transmission has a major drawback. This major problem is risen by the induce of turbulence effects in every node that degrades the performance of system. In this work, the reception of signal by the receiver system in the ORN on FSO is investigated. We propose a method of noise filtering in the output of photodetector in order to enhance the performance of system. The proposed method is intended to enhance the performance for application of wavelength division multiplexing signal on the ORN on FSO. Four types of filters are investigated which are Gaussian-, Butterworth-, Bessel- and Chebyshev-filter. Two modulation formats of signal also implemented which are non-return to zero and return to zero. From the results of simulation, noise filtering through low-pass filter in the output of photodetector has the capability to improve the performance of bit-error-rate (BER) in the range value of 10-1 to 10-3 in comparison with non-filtering setup.