Installing "firmware-b43-installer" offline

You need to install firmware-b43-installer.

If you do not have an alternative internet connection, do it this way.

If you installed bcmwl-kernel-source, then remove it.

    sudo apt-get purge bcmwl-kernel-source

1. Download these files

http://mirrors.kernel.org/ubuntu/pool/main/b/b43-fwcutter/b43-fwcutter_015-9_amd64.deb http://www.lwfinger.com/b43-firmware/broadcom-wl-5.100.138.tar.bz2

2. Copy them to your Ubuntu Home folder.

3. Run in terminal

   sudo dpkg -i b43-fwcutter_015-9_amd64.deb
   tar xfvj broadcom-wl-5.100.138.tar.bz2
   sudo b43-fwcutter -w /lib/firmware broadcom-wl-5.100.138/linux/wl_apsta.o
   

4. Reboot or run:

   sudo modprobe b43
   

Note: For 32-bit systems download http://mirrors.kernel.org/ubuntu/pool/main/b/b43-fwcutter/b43-fwcutter_019-2_i386.deb instead of amd64 and update the file name in the dpkg command.

For Ubuntu 16.04 http://mirrors.kernel.org/ubuntu/pool/main/b/b43-fwcutter/b43-fwcutter_019-2_amd64.deb should be installed or the i386 alternative.

If you are having trouble finding another computer, an Android phone can be used as a USB modem. You can connect the phone and choose "USB modem" in settings.