Thanks for writing to us.
Was there any software update recently on the machine?
Do you mean the issue doesn't happen when its running on charger?
Please update the wireless drivers and BIOS and disable any power management option in device manager under wireless card properties.
drivers can be found on support.euro.dell.com--enter the tag#--submit--drivers and downloads--select your operating system--install as suggested.
Do provide us your system tag#, email address and name via private message,by clicking on my name in blue and then select send a private message