Windows Internet Share through WIFI ad hoc

Open the Network and Sharing Center from windows control panel

Make sure the "Network discovery" is on on the active Internet connection and click "Manage wireless network" on the top left of the window.

Click "Add" button in the "Manage Wireless Network" window and then select "Create an ad hoc network" in the popped window

Press "Next" button and input the network name and at least 8 characters for password in then next pop up window, then press "Next".After waiting windows create the ad hoc press "Close" button to finish the ad hoc network creatation

Go back to "Network Connection" window either by click "Manage Network Connection" on the top left of "Network and Sharing Center" or execute ncpa.cpl in the DOS command line.

Right click the active Internet connection and go to "sharing" tab

Tick "Allow other network users to connect through this computer's Internet connection" and "Establish a dial-up connection whenever a computer on my network attempts to access the Internet".

Select the network connection which you want to share Internet through in the "Select a private network connection" drop down menu. In this case select "Wireless Network Connection". Finally press "ok" button. 

Now connect other devices to this ad hoc and use DHCP for IP and DNS address to connect to Internet