1. Tap the "All Apps" option in the top right corner of the home screen.
2. Tap "Settings," "Wireless & networks" and then "Wi-Fi."
3. Tap the menu icon, then "Advanced."
4. Tap "Keep Wi-Fi during sleep" to place a check in the box beside it.
Android 3.0
1. Tap the time in the lower right corner of the home screen and tap "Settings."
2. Tap "Wireless & networks," then "Wi-Fi settings."
3. Tap "Wi-Fi disconnect policy."
4. Tap "Never."
Android 2.3
1. Press the "Menu" button on the home screen, and tap "Settings."
2. Tap "Wireless & networks."
3. Press the "Menu" button, then "Advanced."
4. Tap "Wi-Fi sleep policy."
5. Tap "Never."