For a system gain of 120 dB a minimum input CN of 30 dB and

For a system gain of 120 dB, a minimum input C/N of 30 dB, and an input noise power of -115 dBm, determine the minimum transmit power (Pt).

The book is saying the answer is -85 dBm. I\'m not getting that answer for Pt, I am getting 35 dBm. Please help. Is the book wrong or am I wrong?

Thank you.

Solution

Cmin (dBm) = (C/N)i + Ni

                   = 30-145= -115db= -85dbm

Pt (dBm) = Cmin + Gs

                 = -85+150= 65dbm