Step 1: Do you have iTunes 10.5 installed. Please check either your Apple device iPhone, iPad or iPod Touch is connected to your Wi-Fi network and also running the latest iOS 5.( If you still did not upgraded your device to iOS 5 here is the process How to update or get iOS 5)
Step 3: Wait few seconds, So your computer recognize your device, Now after it has been recognized, Click on it in the left column then select the option Summary in the header bar
Step 5: Now click in side the box to turn it on just like the above image.
Step 6: Now click Apply.
And now you are connected with the Wi-Fi sync using the iTunes 10.5 and iOS 5. Now as far as your iTunes is turn on your computer, and as soon as you will plug your iPhone, ipad, ipod touch into the power outlet, it should appear in iTunes and sync over Wi-Fi.
But remember, it has to be plugged into the power for working with the Wi-Fi sync, so you are really just cutting the cord to the computer to the wall
If you want to install a Wi-Fi sync using manually process, you can do this from your iOS device and you do not need to be plugged into the power outlet.
How to setup IOS Wi-Fi sync manually for windows
Step 1: Go to Settings
Step 2: Select General
Step 4: Click on Sync Now
Now you are done, now your iPhone or iPod or iPad touch or iPad are connected Wi-Fi sync without any cable. Just as simple it is connected with your computer without cable anyway.