Tham khảo tài liệu 'advances in satellite communications part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Theoretical Analysis of Effects of Atmospheric Turbulence on Bit Error Rate for Satellite Communications in Ka-band 49 beam spot size at the plain of the receiving antenna becomes smaller as W0 increases. The displacement of the arrived beam axis due to spot dancing makes the received intensity decrease considerably faster as the beam spot size becomes smaller. Therefore the average intensity affected by atmospheric turbulence decreases at the center of the receiving antenna and the profile is spread as W0 increases as shown in Figs. 14 to 17. This is why BER in the uplink increases as an aperture radius of the ground station s antenna becomes larger. From these results we find that the increase in the transmitting power is better than the increase in the aperture radius of the ground station s antenna in order to satisfy the required EIRP from the point of view of the decrease in an influence of atmospheric turbulence on BER in the uplink. Downlink For the downlink we can obtain BER derived from the average received power given by 53 PEP 1erfc A SP T EIRP 1 G T 2 1 kB 2kzL 2 67 Fig. 18 shows the BER as a function of kae under the condition that EIRP and G T keep constant where the noise power density No changes in inverse proportion to the square of kae in 63 . It is found that the BER affected by atmospheric turbulence increases as kae becomes larger. Fig. 19 shows the BER for various aperture radius of the receiving antenna as a function of Eb No obtained by 65 . It is shown that BER increases as ae becomes larger as well as Fig. 18. From results of the DOC in Fig. 9 it is found that the spatial coherence radius becomes smaller relative to a radius of the receiving antenna and then the spatial coherence Fig. 18. BER derived from the average received power in the downlink as a function of kae when the G T of the receiver system keeps constant. 50 Advances in Satellite Communications Fig. 19. BER derived from the average received power in the downlink for .
