In the B-ISDN using satellite between geo-satellites and earth stations, the laser having high security and broad band width has to be used as a carrier for transmitting massive information of visual, vocal, and high rate data. In this paper, by computer simulation we analyzed the number of optical detector array of optical satellite communication downlink in case of using channel coding and no channel coding for BISDN between geo-satelites and earth stations under clear weather condition. It was supposed that 1 watt semiconductor laser was used and as modulation method, the binary FSK was used. The data rate of 10Gbps was used for B-ISDN. Also, hardly affected by atmospheric absorption 1.55$mu$m wave-length was used to reduce influence of dispersion and chirp generated at a high speed transmission. We analyzed the received power, SNR and BER. The number of optical detector array was determined to satisfy for the BER less than 10$^{-7}$. Also, we ananlyzed the possibility of reducting the number of optical detector array in case of using channel coding. the number of optical detector array is one in the region where the elevation nangle is between 38$^{circ}$ and 90$^{circ}$ and two where the elevation angle is between 33$^{circ}$ and 37$^{circ}$ and three where the elevation angle is between 30$^{circ}$ and 32$^{circ}$ and increases per one as the elevation angle decreases per 1.deg.. So in the region where the elevation angle is 25$^{circ}$, the number of optical detector arrays is eight. In case of using channel coding, the number of optical detector arrays decreases to five in the region where the elevation angle is 25$^{circ}$. Therefore, we remaark the advantage of the channelcoding to decrease the size of received antenna and the number ob optical detector arrays.