The first thing to consider is whether you should improve the access point or client end of the connection. The natural inclination is to focus on the AP, especially when your wireless network includes more than one client. There are basically three ways to go:
1) Boosting Transmit Power
2) Upgrading Antennas
3) Buying new gear
Boosting transmit power is the least preferable way to go, because this "fix" is only one-way. Since wireless LANs require two-way communication between AP and client, you may not see any performance improvement by making the signal stronger at only one end of the connection. The other negative of this approach—higher visibility of your WLAN—is described in the sidebar below.
Be Careful What You Wish For...
As with many things in life, WLAN performance improvement is not a case of "if a little is good, more is better"! Giving your WLAN too much of a boost can bring you the problem of unwanted visitors flocking to your nice strong signal, especially in high-density areas such as apartment buildings, dorms, dense neighborhoods, etc.
If you don't want to provide wireless Internet service (or access to your LAN) to the neighborhood, keep the following in mind:
Focus on client-based improvements - Although a stronger client signal still exposes your data to being "sniffed", you won't be providing free access to your Internet connection and other LAN clients.
Aim your signal - Use a directional antenna on your AP, pointed at the area that you want to cover. Also move the AP away from outside walls. Both techniques can minimize signal "leakage" to unwanted areas. Make sure you pay attention to the vertical signal path when choosing and installing your directional antenna, too!
Cover the Security basics
- Use WPA2 with a strong key.
- Change your AP's default password and use a new strong one.
- Change your ESSID to one that doesn't give away your location or identity.
- Shut off the AP when you are not around (use an old-fashioned lamp timer if you tend to be forgetful).
- Enable MAC address filtering to limit access to only known clients. Yes, MAC addresses can be spoofed, but every bit helps.
None of these steps will guarantee you won't get uninvited guests, but they'll probably make "doorknob rattlers" go and find easier prey.
NOTE: If you need absolute security for your wireless data, use a VPN or SSL-based connection.
If you still want to try boosting power, the easiest approach is to load your wireless router with an alternative firmware such as DD-WRT, OpenWrt or others. If you do this, read the documentation carefully and make sure that your router is supported before you try to flash it, or you may "brick" it.
If you're going to try the centralized approach, a good choice is to use a higher-gain antenna— if your AP's antennas are attached via connectors. If your antennas are hard-wired, you'll either need to choose another method, buy a new AP, or try using the information in the sidebar below to add parabolic reflectors to your existing antennas.
You can add parabolic reflectors to most any dipole antenna used on wireless access points and routers. These are completely passive, don't violate your product's warranty and can add 10 or so dBi of gain.
Michael Erskine's website is a little tricky to navigate, but well worth the exploration. He has a number of designs that you can print out and make from cardboard and tinfoil and slip right over your AP's antenna(s).