The Channel from a Space Probe to Earth Has a Bandwidth

Essay

The channel from a space probe to earth has a bandwidth $B = 10 ^ { 6 }$ Hz.The channel capacity when the probe is $10 ^ { 3 }$ km from earth is $C = 10 ^ { 7 }$ bps = 10 Mbps.Using the inverse square law to describe the signal power loss, the capacity when the probe is at $2 \times 10 ^ { 3 }$ km from earth equals _____ Mbps.Assume that the noise power is constant.