XPS 13 DE Poor WiFi Signal.

If you're using the latest driver version (you don't tell what version you use), then it is not a driver problem, but probably you router's settings.

Latest version (the one you should install if you didn't have it already) is 6.30.223.271 

http://en.community.dell.com/techcenter/os-applications/f/4613/t/19655021 

Then you should check what frequency range your laptop uses. If moving closer to the router helps, then I assume it uses 5Ghz network (that is blocked more easily by walls and other obstacles), while your other devices use 2.4Ghz range.So easiest way to check whether things improve is to disable the 5Ghz mode in your router and check again. (you can also assign two different SSIDs to allow easier switching between the two/specify the access point's mac-hardware in your laptop's network configuration to explicitly choose one of the two modes).

If you're already in 2.4Ghz mode, make sure that you did enable WMM in your router's settings.

http://en.community.dell.com/techcenter/os-applications/f/4613/p/19628926/20812387#20812387

The broadcom wireless absolutely requires that, while other devices don't seem to care.

With the current driver, I don't have any problem connecting to N or AC routers, in either 2.4Ghz or 5Ghz.

Thanks for the detailed answer.

It looks like the drivers are not (yet?) in Ubuntu 15.04. I just tried.

Broadcom's readme is poor - it doesn't even list the major bugfix (namely allowing channels 12 and 13) - so if you have early 2015 Dell XPS 13 with the Broadcom card, the driver will support it (I have same ID)

Just saw that dell didn't update their driver package for the XPS. http://www.dell.com/support/home/uk/en/rc1050266/Drivers/DriversDetails?driverId=M5R51 so I suggest to contact Dell Support and ask for the updated driver installation files and ask them to provide an updated driver package.

(I'm not using Ubuntu, so I asked my distribution to provide and update)

You should also be able to use the packages from ubuntu's development version, as it is a dkms module it will be compiled to fit your system anyway.

so go to https://launchpad.net/ubuntu/+source/broadcom-sta/6.30.223.271-2 and download & install the binary packages for the common and dkms variant, uninstall the currently installed version (but make sure to download the packages first or have a ethernet connection available as fallback, so you can reinstall the 14.10 version again in case the new drivers unexpectedly won't work)

Updating to 15.10 is also highly recommended, although for other reasons (mainy much improved touchpad support) but as you said no help with the wlan driver.

Thanks!

Indeed, installing broadcom-sta-dkms 6.30.223.271-2 seems to have solved the issue.

(I am using already on 15.10.)