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The RF link between the satellite and the Martian surface is the most challenging link. Low transmit power is especially important for the ground terminal. It is not realistic that large solar cell must be carried around just to use the radio. The solution to this problem is to use phased array antenna's both on the planet's surface and on the satellite. Though these are expensive, the cost will be recovered in the much less RF power required to establish a reliable link. FDMA is used because it provides the best noise performance. This table lists the frequencies of each channel. Because FDMA is being used, there must be an output back of the transmitter of 5 dB [4]. A root raised cosine pulse shape is used with a role off of 0.3. A 15% guard band is also used between each channel. See the spread sheet for the channel spacing calculation.
Satellite to Surface Link Budget
A total of 100 watts is transmitted from the satellite. The satellite's antenna is a phased array capable of achieving a gain of 20 dBi. The Earth terminal has a phased array with a 10 dBi gain. A sophisticated search and track algorithm will need to be developed to allow the satellite and terminal to effectively find and track each other's movements. This will make it very easy for the terminal operator, as he will not have to manually point the antenna. This link has an extra 10.58 dB which will compensate for any Mars atmospheric phenomenon.
Surface to Satellite Link Budget
The surface terminal will only need to transmit 20 watts to communicate with the satellites. There is an extra link margin of 5.62 dB to compensate for any Mars atmospheric phenomenon. If there are larger unknown atmospheric effects, then the terminal transmit power can be increased. The satellite has plenty of link margin so it will not have to be upgraded, which would be very hard to do.
Satellite Transceiver Design
Terminal Transceiver Design
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