Device page variants are not working properly in oracle webcenter portal

Question

       I am working on oracle webcenter 11.1.1.8.0 and designing page layouts for android and ios tablets. For designing the page layouts i followed the follwing steps.

To create a page variant for a device group:
1. In the portal editor or portal administration, open the portal page in edit mode.
2. In the selection pane, select the page for which you want to create a page variant.
3. Click the Add icon, and select New Page Variant.
4.Select the Device Group and Page Content and Style.
       ■ To copy the content and style from the base page, select the Copy Base Page Content and Style check box.
       ■ To create a page variant with different content and style than the base page, de select the check box, and select the required page style.
5.Click Create.

If i follow the above steps, it is working in webcenter tablet previews but in real tablet the default page is rendered rather than displaying of tablet page layout. I enabled all device groups for that portal. Please suggest me to resolve this issue.

Thanks,
mintu