aspg-33-2142-1792222675 20261017073755 American Scientific Publishing Group admin@americaspg.com American Scientific Publishing Group Galoitica: Journal of Mathematical Structures and Applications GJMSA 2834-5568 2023 8 2 Sandy Montajab Hazzouri Faculty of Informatics Engineering , Albaath University, Syria This paper presents Improving performance of 112 Gbit/s optical coherent communications systems using digital signal processing techniques to compensate linear impairments that are exposed to the signal during its propagation in optical fiber. In this paper, different multi-level modulation formats (DP-QPSK, DP 8PSK, DP- 16PSK and DP-16-QAM) were compared for the same data rate at different distances from the transmitter without amplification. the comparison was done by measuring bit error rate value. We used digital signal processing techniques for linear effects compensation. Where chromatic dispersion was compensated using a simple digital filter, and Polarization mod dispersion was realized by applying the constant-modulus algorithm (CMA). The phase and frequency mismatch between the transmitter and the local oscillator in the receiver was compensated using the modified Viterbi-Viterbi algorithm. We used the Optical simulator Opti-system , which was linked with MATLAB R2011 in order to implementation DSP algorithms and analyze obtained results. 2023 16 28 2142 https://creativecommons.org/licenses/by/4.0/ 10.54216/GJMSA.080202 https://americaspg.com/journal/33/article/2142 https://americaspg.com/storage/31696792849.pdf