I tried just about every 'solution' to the Wi-Fi dropping problem in OXS Lion but whilst they didn't work for me, they did for others and so it is worth trying these first - you never know, you might be the lucky one.
Solutions That Have Worked For Others
- Resetting the PRAM and NVRAM
This can be done by simply holding down the Command, Option, P, and R keys whilst turning the computer on. Hold down these keys until the computer restarts. More information on how to do this can be found here. Most people though say that this has no effect but as it's completely safe to do it's worth a try.
- Resetting the SMC
For some this simple fix did cure the problem, for a lot though it did not. Resetting the SMC couldn't be simpler. Just turn the computer off and disconnect the power lead for 15 seconds. More information can be found here
- Add a new network location.
For some people this solution did seem to work but it also does seem to be a temporary fix in that it may work for a few days or weeks but then it starts dropping the Wi-Fi again. To do this go to System Preferences and the Network panel. Click on the Location pull down menu and select Edit Location. Click on the + symbol to add a new network location and then give it a unique name before clicking Done. Back in the Network panel select your new location and click on the Advanced button and then click on the TCP/IP tab. Click on the Renew DHCP Lease button and wait for the IP address to populate. Once this has happened, click OK.
- Move Wi-Fi to the top of the List in Network Preferences
This generally doesn't seem to make a difference but it may be worth trying. Go to System Preferences and Network where you will see a list of all your network services on the left, namely Wi-Fi, Ethernet, Bluetooth Pan and Firewire. Simply select Wi-Fi and move it to the top of the list.
- Delete the Wi-Fi connection and add it again.
This has seemed to work for some but generally it seems to fix it for a while before it returns. You can do this just by clicking on the minus symbol in Wi-Fi Network settings before adding them again via the Plus symbol.
- Add an additional DNS entry.
I must admit this was not one that I have tried myself as I couldn't really understand how this would make a difference but some people claim it does whilst many others say it doesn't. Most people seem to add 184.108.40.206 for Google's public DNS. This is done by selecting your Wi-Fi connection in the Network panel of System Preferences, clicking on the Advanced button and then the DNS tab.
- Installing or re-installing OSX Lion 10.7.3 Client Combo
A lot of users have said that re-installing this download, rather than just applying the 10.7.3 update fixed their problem. Initially it did seem to work for me in that my Wi-Fi connection remained stable for a couple of days but then it went back to dropping constantly. You can download the update here.
- Install Apple's Wi-Fi fix update.
Apple really seemed to take their time in releasing a fix for this bug and when they did, for some it was the answer to their prayers. For others it was yet another cause for false hope. When I installed it, it did seem to work and I had a stable connection for days but then I noticed that whenever I switched profiles the problem would return again until I re-installed the update. Close but no cigar. You can download the Wi-Fi update for the iMac here.
As I say, none of these things seem to work and in doing a lot of searching on the Internet I noticed that most users who were affected, certainly it seemed the majority who were still affected after trying the solutions above, did not use the Airport Extreme Basestations. In other words if you had an Airport Extreme Basestation your Wi-Fi always seemed to be nice and stable. There was no way I was going to go out and spend a small fortune on an Airport Extreme when there was no good reason why I shouldn't be able to use my iMac with any router. This got me thinking. I had just bought a new 27" 3.1Ghz Quad Core iMac to replace my much older 20" Dual Core 2006 model that couldn't really run OSX Lion but never had a problem with Wi-Fi at all. So what were the differences between the two machines, other than one was a hell of a lot faster? The new iMac comes with bluetooth keyboard and mouse whereas my old iMac used a USB one. Could there be interference between bluetooth and the Wi-Fi?
The Solution That Worked For Me
I don't honestly know if this is the problem all I can say is that I then logged onto my router and went to it's Wireless settings page. The channel it was set to was Auto. I changed this to Channel 11 and, so far, I can't now get my Wi-Fi to drop at all. I have deliberately put my iMac into Sleep, tried Switching Profiles, rebooting etc etc and each and every time the Wi-Fi works perfectly. So far it's been absolutely constant for 3 weeks. I won't say that it's definitely cured but this is without doubt the longest it has remained stable for.