at sends signals to an Earth station as shown. What is the received power to noise ratio at the Earth station receiver for the fol- lowing parameters? Transmit Signal power = P = 40 W: =46 dBm Satellite transmitter antenna gain = G = 15 dB Earth station receiver antenna gain = G,=30 dB Path loss = L = 196 dB Noise level at the receiver N,=-120 dBm Answer The received signal power P, is: P,=P,+G,+G,-L=46+30+15-196 - - = -105 dBm The received SNR is: Received SNR=P,-N,=-105-(-120)=15dB = - Information Theory Example 4.6 Calculate the power link budget for a device 1 km from a base station for the following parameters: Transmit signal power=P,=33 dBm = Transmitter antenna gain=G,=7 dB Mobile device antenna gain=G,=1 dB Noise level at the receiver N.=-111 dBm Required receiver SNR,=7 dB Path loss at 1 km=L=138 dB Answer Receiver SNR at 1 km: SNR at 1 km = -G, + G, - N-L=33+7+1-(-111)-138=14 dB Link budget = SNR at 1 km - required SNR,=14-7=7dB This means that an extra 7 dB signal loss may be tolerated before telecommunication performance is degraded. Case Study 4.1: Voyager Mission Two Voyager space probes were launched in 1977 by the National Aeronautics and Space Administration (NASA) agency of the United States government to explore Jupiter, Saturn, Uranus and Neptune and continue on to explore the interstellar space beyond the solar system. Their mission was to examine the atmospheric, magnetic and spectral properties of outer solar system planets, and communicate the collected information back to Earth. Clearly a telecommunications system needed to be designed that ensured such information could be correctly transmitted back to Earth. The power systems on-board the crafts are designed to last many years and support telecommunications over the long distances to the Earth. Indeed, the probes sent valuable information on the structure of the outer planets, and have now left the solar system while continuing to send back important information. For example, as one probe crossed into interstellar space it observed tha