Calculation of the link margin is given in the table below.

Two antennas are included in the proposed system; one for the uplink band and one for the downlink. Each requires approximately 5 GHz of bandwidth.
The antennas’ diameters are small because of size and weight constraints. Noise temperatures on the order of 200 K are predicted since the antenna’s main beam is always pointing towards the (relatively) warm earth.
Downlink transmit power is constrained by hardware capabilities and power limitations onboard the spacecraft; we suggest 3 Watts of RF output power as a good compromise.
The earth station’s antenna diameter may be much larger and transmit power may be much greater thanks to the relaxed power and space constraints. Additionally, its antenna’s noise temperature is much lower since it is pointing towards space.
Finally, a downlink margin of 36 dB and an uplink margin of 49.6 dB are achieved at 10 Mbps raw data rate by carefully balancing system parameters.

Reference
[1] Pratt, T., Bostian, C., Allnutt J., Satellite Communications, 2nd Edition, John Wiley & Sons, Inc., 2003.