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View File - University of Engineering and Technology, Taxila

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FIGURE 4.10 Cross-link E b =N 0 vs. antenna diameter. Parameters used:f ¼ 14.5 GHz, Z ¼ 65%, r b ¼ 50 Mb=sec, d c ¼ 9598 km, T e ¼ 1000 K.To ensure that pointing error is maintained to the barest minimum, aform <strong>of</strong> automatic tracking (simply autotracking) system should be installed atthe receiver. The function <strong>of</strong> the autotracking system is to track the arrival <strong>of</strong>the transmitter beam <strong>and</strong> point it back at the receiver antenna. The curvesshown by Fig. 4.10 are instrumental in determining the trade<strong>of</strong>f betweendesigning <strong>and</strong> installing on the satellite an automatic tracking system or simplyallowing an open-loop mispointing.4.2.2 Modelling Interference Plus NoiseFor brevity, the interference is modelled as additive interfering signals on theuplink with respective powers, say I u1 ; I u2 ; ...; I uk within the b<strong>and</strong>width <strong>of</strong> thedesired carrier. Therefore, the total uplink interference plus noise power can bewritten asN IU ¼ N u þ PkI uii¼1The uplink carrier-to-noise plus interference ratio can be written as C¼C þ Pk C uNUINu i¼1 I ui¼C N uþ C Iuð4:38Þð4:39ÞCopyright © 2002 by Marcel Dekker, Inc. All Rights Reserved.

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