The basic idea behind CSMA/CD is that a station needs to be able to receive while
transmitting to detect a collision. When there is no collision, the station receives one
signal: its own signal. When there is a collision, the station receives two signals: its own
signal and the signal transmitted by a second station. To distinguish between these two
cases, the received signals in these two cases must be significantly different. In other
words, the signal from the second station needs to add a significant amount of energy to
the one created by the first station.