Hi, I just bought a XPS12 and am having the same issues with the wifi. This is what I done, I went into the hardware manager and did 3 things.
1. I opened the properties manager for the 6235 Intel card, clicked change settings, changed the roaming aggressiveness from medium to high.
2. Then in the same properties manager for the card, I went to the power management pane and un checked allow this device to wake up the computer
3. the same power management pane, I then unchecked allow computer to turn this device off to save power
My computer was usually dropping out the wifi about every 30 minutes or so before, and has stayed active for the last for hours without any issues so far.
I did notice the bandwidth went from 38-39 mbps to a whopping 68-72 mbps. Funny, my signal strength is staying full scale more than 90% of the time. I'm hopeing this solves the issue.