enna on the ground? Answer L =32.4+20*log(36000)+20*log(4000) =195.5dB This means the signal power diminishes by a factor of nearly 1020 as it travels the distance between this satellite and the earth station. Broadband Telecommunications Technologies and Management Without powerful antennas, a signal transmitted to/from a satellite will be received at a power significantly lower than noise power, and cannot therefore support reliable, high quality communications. The path loss is therefore compensated through boosting of signal power on both transmitter and receiver sides through powerful antennas on both the satellite and earth station. The required antenna gain is found through a link budget calculation process as described in Chapter 4. Example 11.2 For a geostationary Earth orbit (GEO) satellite communication system, the downlink transmit signal power P = 40 W or 46 dBm; the satellite transmitter antenna gain, G = 15 dB; the earth station antenna gain, G, = 30 dB. If frequency of operation is 12 GHz, and noise power level at the receiver N = - 120 dBm: What is the EIRP? What is the path loss? What is the received SNR? Answer EIRP = :P,+G,=61 dBm Path loss = 32.4 + 201og(36 000) + 201og(12 000) = 205 dB Received signal power: P = + G - L = 61 + 30 - 205 = -114 dBm Received SNR = P, - N, = -114 (-120) = 6 dB Earth Orbits Earth orbits are classified based on their distance (altitude) from the Earth. As articulated by Arthur C. Clarke, at a specific altitude, the orbital period exactly equals the time it takes for the Earth to rotate once around its axis or approximately 24 h. A satellite at such an altitude and orbiting within the equatorial plane appears stationary to an observer on the ground. This is known as the GEO and satellites orbiting here are called GEO satellites. Satellite Communications Distance from the 35 786 Earth's surface (km) Figure 11.7 Earth orbits The GEO satellite's altitude for the length of a sidereal2 day of 86 164 S is calculated to be equal to 42164 km from the centre of the Earth or