You can increase the range of a single AP by relocating the AP to avoid obstacles, adjusting the AP's transmission power output, adding a signal booster, or adding a higher-gain directional antenna. See these tips for information on signal boosters and directional antennas.
Free space path loss refers to the way in which signal strength diminishes as a radio wave propagates through the air. The signal beam spreads out as it moves, dispersing power across a wider wave front. This is why loss increases with distance between the transmitter and receiver. You can't really change these physics, but keeping transmitters and receivers close together reduces free space path loss - for example, growing your WLAN coverage by adding APs vs. extending the range of a single AP.
This was first published in July 2003