Wi-Fi going down after 30 min of inactivity is a documented behavior. Cellular network is always active, unless turned off by the user. So if it goes down for a while it should  get back online automatically when possible even if there was no user activity.

iphone 3G data network timeout?
what am i doing wrong 

user.ps1
    $user = "sp2010\systemsacct"
    $site = $gc | Get-SPSite sp2010
    $site | Get-SPWeb -Limit All | Get-SPUserEffectivePermissions $user   Out-GridView -Title "Web Permissions for $user"

