Hey there Chantima,
It sounds like you are now able to join the wireless network but the connection drops periodically. I want to recommend the troubleshooting steps in the article named:
iOS: Troubleshooting Wi-Fi networks and connections
Follow these steps to troubleshoot the above issues:
- Be sure you're in range of your Wi-Fi router (access point).
- Tap Settings > Wi-Fi and turn Wi-Fi off and on. If your Wi-Fi setting is dimmed, follow these steps.
- Confirm that your Wi-Fi router and cable or DSL modem are connected to power, turned on, and connected to the Internet. If not, refer to your network administrator or Internet service provider (ISP) for assistance.
- Restart your iOS device.
- Tap Settings > Wi-Fi and locate the Wi-Fi network to which you're connected.
- Tap and Forget this Network.
- Try to connect to your desired Wi-Fi network.
Note: You may need to enter your Wi-Fi password again if your network requires one.
- Turn your Wi-Fi router off and on2. If your ISP also provides cable or phone service, check with them before attempting this step to avoid interruption of service.
- Update your device to the latest version of software.
- Update your Wi-Fi router to the latest firmware2. For AirPort Base Stations, install updates using the AirPort Utility.
And this section from near the bottom if you need it:
- Move closer to the Wi-Fi router (access point).
- Check for sources of potential interference.
- Remove any case, stand, or other accessories from your iOS device and see if signal strength improves.
- Reset network settings by tapping Settings > General > Reset > Reset Network Settings. Note: This will reset all network settings including
- previously connected Wi-Fi networks and passwords
- recently used Bluetooth accessories
- VPN and APN settings
Also here is an article outlining the recommended wifi settings for iOS devices.
iOS and OS X: Recommended settings for Wi-Fi routers and access points
Thank you for using Apple Support Communities.
We already tried forget the network without out rebooting it first.
The wifi signal is very strong. the device can authenticate with WPA2/PSK fine without any signal dropping, only with 802.1x where the signal is intermittently dropped.
Will give it a try and let you know.
Thanks for your help.