Repeaters in Relativistic Communications

The communication efficiency between a transmitter and a receiver is affected by motion and the presence of gravitational fields. We study the effect of regenerating the signal in intermediate repeaters in different relativistic scenarios where relativistic effects on communication can become relevant, like ships moving at relativistic speeds or in the proximity of black holes. Without any repeater, a ship leaving the solar system at relativistic speed would be more difficult to contact than the same ship, in the same location, but at rest with respect to the other side of communication on Earth. We show the optimal frames for the repeaters in this and other scenarios and compare the result to communication with nonrelativistic repeaters.