In this paper, the performance of downlink design utilizing the free space optic (FSO) is presented. The permissible BER of 10-58 is achieved when the system utilized 40 cm aperture diameter. The highest system sensitivity will lead to less error and enable more transmission output. The result revealed, at a bit rate 155Mbps and effective received power -27.5 dBm, FSO downlink system at bit rate 155 Mbps improved by 13% as compared to 1.5 Gbps and 2.5 Gbps in single transmission line. It is truly shown that, the FSO system utilized 155 Mbp/s with 40 cm aperture diameter shown good performance of a reliable FSO downlink system.
