1. Install an external Wi-Fi antenna
on the laptop (if possible). For this option to be feasible, the laptop must support add-on antennas. Look for a special jack similar in appearance to a headphone or microphone jack. Sometimes these are called "SMA jacks." Consult the laptop product documentation for details.
Hiro H50193 Wireless USB Network Adapter and External Antenna - High-Gain, OMNI Direction, 2dBi at TigerDirect.com
2. Use a USB wireless network adapter with external antenna
. USB Wi-Fi adapters hook onto the back or side of a laptop with a short USB cable. The external antenna on these adapters improves signal range, and the antenna can be adjusted/pointed for fine tuning. To use this option, the laptop must have an open USB port available. Additionally, other network adapter(s) on the laptop should be disabled to prevent interference.
F5D7050 Belkin Wireless G USB Adapter
3. Check transmission power settings
. Some network adapters support adjusting their transmission power. If available, this setting can be adjusted through the adapter's driver interface program, along with the other settings for wireless profiles and Wi-Fi channel number. The transmission power should be set to "maximum" or "100%" to ensure the strongest signal possible. Note that if a laptop is being run in a power saving mode, this setting may automatically be lowered and decrease the adapter's range and signal strength.