WI-FI connection drops down constantly after upgrading Mac OS X Lion v.10.7

I have an imac fall 2009 21.5" at home. I have been a big fan of apple. I have very recently upgraded my imac with the Mac OS X lion update. After this update I am having problems related to the WIFI connection. I have noticed that after this update, my WIFI connection is dropping down constantly. I have to turn off the WIFI every minute. I have tried connecting but I did not find any success. I want to know that how I can fix this problem. Any suggestions regarding this would be highly appreciated.

I would like to ask you few questions before I start to provide solution. So my questions are below,
• What is the strength of the signal of the wireless network that you see? I hope you know what I am saying. If you don’t know to check it then I would say that. Press the option key and click on the WIFI menu extra and you will come to know the strength of the signal. A good signal is between -40 and -70. If the signal is lower than -70 then also there is no issue and it will work.
• Tell me that do you get IP address when you connect?
• When connection of WIFI drops down does the Wi-Fi Menu Extra grey out?
• Can you ping your wireless router?

Well I am facing the same issue with me. Actually my WI-FI is working fine for me but I have seen that there has been connection dropping down 3 or 4 times. My friend is also having the same problem. I don’t know why this is happening.

I think you can try out this method but I am not sure whether it will fix the issue or not. There is no harm in trying it. I also used to face the WI-FI drop down problem. There is an applescript below; it is saved as application with stay open ticked.
try
repeat
do shell script "ping -c 1 <replace with ip address of router>"
delay 5
end repeat
end try

I would suggest you to try to run the following command in the terminal,
sudo /usr/libexec/airportd debug +alluserland +alldriver +allvendor
sudo /usr/libexec/airportd logger
After this, try to reproduce the issue where the machine drops WI-FI. Copy and paste the output in the Terminal app. here.

I would like to know that what are the Energy Saver settings on your Mac? Does increasing the Sleep time help?

I think you should do some changes in the WI-FI settings. I would suggest you to a blank Network Preferences window:
• Remove the Wi-Fi connection and Bluetooth DUN from Network Preferences
• Create a new location in Network Preferences & removed the "Automatic" entry
• Add a new Wi-Fi connection
• Set DNS address settings to 8.8.8.8 (Google public DNS), and 8.8.1.1
• Set Service Order to Wi-Fi at the top of the list
• Reboot the router & Mac-book
I hope this helps.

I would say that try to reset the SMC. For this try to follow the following steps and after them you should try to connect the WI-FI,
• Press Command + Option + Escape to force quit any application that is not responding.
• Put your Mac to sleep by choosing the Apple menu from the upper-left menu bar and then choosing Sleep. Wake the computer after it has gone to sleep.
• Restart your Mac by choosing the Apple menu from the upper-left menu bar and then choosing Restart.
• Shut down your Mac by choosing the Apple menu from the upper-left menu bar and then choosing Shut Down.

I think this issue is because of driver installed. If it is occurring while using the recovery option then definitely it is a driver problem. I also have a Mac book Pro 15" Mid 2010. When I try to boot to new lion recovery partition, I am not able to access WI-FI network. I tried SMC reset, PRAM reset but I couldn’t find any help. I also tired to reboot my Airport Express and Time Machine and changed the channel settings on each.

I would suggest you to go for trying,
• Resetting SMC.
• Removing Bluetooth PAN.
• Removing and re-adding network settings.
• Fixing IP.
• Adding extra DNS servers.
• Deleting lists and re-setting up network.
• Moving order of services to promote Wi-Fi.
• Switching off Time Machine.
• Fixing Location / Adding new location.
• Removing all preferred networks.
• Turning round three times while saying the name of the Scottish Play.

I would suggest you to try out these tips; they are basic but work in some cases:
• Try to Turn wireless on & off
• Reboot the Mac
• Reset the Router
There is advanced WI-FI troubleshooting tips that you can find on the website.