Turning up the transmitter power is a good way to insure that more cellphones,
farther away, can hear the base station. But it doesn't to anything to help the
base station hear the cellphones that are farther away. The only way to increase
the coverage range reciprocally is to do something with the antenna. But that's a
catch-22 . . . a higher-gain antenna has a narrower beam-width. So it works farther
out, but only through a narrower 'window' of directions.