I tried everything from this tutorial Installing Broadcom Wireless Drivers without any success. bcmwl-kernel-source simply leaves my wifi adapter undetected and firmware-b43-installer makes adapter see the wireless networks but it cannot connect to any one of them. I tried perhaps every advice I could find on Google. It doesn't work.
When I booted from liveusb before I installed 18.04 there were similar issues with wifi - it was working only in 2 in 3 attempts and I had to reboot again for it to connect. After I installed 18.04 wifi worked for 6 hours, then I suspended my PC and then no wifi and no hope…
lspci -vv -s 06:00.0
06:00.0 Network controller: Broadcom Inc. and subsidiaries BCM43602
802.11ac Wireless LAN SoC (rev 01)
Subsystem: Apple Inc. BCM43602 802.11ac Wireless LAN SoC
Control: I/O- Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx+
Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
Latency: 0, Cache Line Size: 64 bytes
Interrupt: pin A routed to IRQ 151
Region 0: Memory at ef400000 (64-bit, non-prefetchable) [size=32K]
Region 2: Memory at ef000000 (64-bit, non-prefetchable) [size=4M]
Capabilities: <access denied>
Kernel driver in use: brcmfmac
Kernel modules: brcmfmac
brijabasi@brijabasi:~$ dmesg | grep brcm
dmesg | grep brcm
[ 7.123837] usbcore: registered new interface driver brcmfmac
[ 7.123857] brcmfmac 0000:06:00.0: enabling device (0000 -> 0002)
[ 7.236303] brcmfmac: brcmf_fw_map_chip_to_name: using brcm/brcmfmac43602-pcie.bin for chip 0x00aa52(43602) rev 0x000001
[ 7.258514] brcmfmac 0000:06:00.0: Direct firmware load for brcm/brcmfmac43602-pcie.txt failed with error -2
[ 7.769594] brcmfmac 0000:06:00.0: Direct firmware load for brcm/brcmfmac43602-pcie.clm_blob failed with error -2
[ 7.769595] brcmfmac: brcmf_c_process_clm_blob: no clm_blob available(err=-2), device may have limited channels available
[ 7.769912] brcmfmac: brcmf_c_preinit_dcmds: Firmware version = wl0: Nov 10 2015 06:38:10 version 7.35.177.61 (r598657) FWID 01-ea662a8c
[ 7.784315] brcmfmac 0000:06:00.0 wlp6s0: renamed from wlan0
[ 536.941863] brcmfmac: brcmf_inetaddr_changed: fail to get arp ip table err:-23
[ 673.754656] brcmfmac: brcmf_inetaddr_changed: fail to get arp ip table err:-23
[ 1278.675425] brcmfmac: brcmf_inetaddr_changed: fail to get arp ip table err:-23
[ 1281.059160] brcmfmac: brcmf_inetaddr_changed: fail to get arp ip table err:-23
[ 1290.105414] brcmfmac: brcmf_inetaddr_changed: fail to get arp ip table err:-23
[ 1349.739849] brcmfmac: brcmf_inetaddr_changed: fail to get arp ip table err:-23
[ 4758.587063] usbcore: deregistering interface driver brcmfmac
[ 4758.602770] brcmfmac: brcmf_cfg80211_get_tx_power: error (-5)
[ 4759.130748] brcmfmac: brcmf_fil_cmd_data: bus is down. we have nothing to do.
[ 4759.130836] brcmfmac: brcmf_fil_cmd_data: bus is down. we have nothing to do.
[ 4759.131277] brcmfmac: brcmf_fil_cmd_data: bus is down. we have nothing to do.
[ 4759.131286] brcmfmac: brcmf_cfg80211_get_channel: chanspec failed (-5)
[ 5109.901277] usbcore: registered new interface driver brcmfmac
[ 5110.009905] brcmfmac: brcmf_fw_map_chip_to_name: using brcm/brcmfmac43602-pcie.bin for chip 0x00aa52(43602) rev 0x000001
[ 5110.010524] brcmfmac 0000:06:00.0: Direct firmware load for brcm/brcmfmac43602-pcie.txt failed with error -2
[ 5110.516145] brcmfmac 0000:06:00.0: Direct firmware load for brcm/brcmfmac43602-pcie.clm_blob failed with error -2
[ 5110.516152] brcmfmac: brcmf_c_process_clm_blob: no clm_blob available(err=-2), device may have limited channels available
[ 5110.516550] brcmfmac: brcmf_c_preinit_dcmds: Firmware version = wl0: Nov 10 2015 06:38:10 version 7.35.177.61 (r598657) FWID 01-ea662a8c
[ 5110.543498] brcmfmac 0000:06:00.0 wlp6s0: renamed from wlan0
[ 6861.767619] brcmfmac: brcmf_inetaddr_changed: fail to get arp ip table err:-23
[ 7053.761865] brcmfmac: brcmf_inetaddr_changed: fail to get arp ip table err:-23
[ 7056.639410] brcmfmac: brcmf_inetaddr_changed: fail to get arp ip table err:-23
[ 7114.670792] brcmfmac: brcmf_inetaddr_changed: fail to get arp ip table err:-23
[ 7181.562020] brcmfmac: brcmf_inetaddr_changed: fail to get arp ip table err:-23
have you tried updating your kernel? the latest mainline build, 4.18-rc8, can be downloaded here: http://kernel.ubuntu.com/~kernel-ppa/mainline/v4.18-rc8/. (Instructions can be found here: https://www.tecmint.com/upgrade-kernel-in-ubuntu/)
if a simple upgrade doesn't work, you may have to patch and compile the latest kernel from source. (Instructions for that can be found here: How to apply kernel patches).