Near–far problem

In a loud, crowded bar, it would be impossible to hear the same voice level, and the only solution (for that distance) is for both you and your friend to speak louder.

Of course, this increases the overall noise level in the bar, and every other patron has to talk louder too (this is equivalent to power control runaway).

Taking this analogy back to wireless communications, the far transmitter would have to drastically increase transmission power which simply may not be possible.

In CDMA systems and similar cellular phone-like networks, the problem is commonly solved by dynamic output power adjustment of the transmitters.

This process continues, and eventually distant transmitters lose their ability to maintain a usable SNR and drop from the network.