I am at my wit's end. I have a Dell Vostro 1700 laptop, maybe six or seven years old. It has an internal Broadcom 4321 wireless adapter, that I got running using the legacy B43 installer. Download speeds with this adapter stink. Ookla Speedtest gives me less than 1Mbs down, but nearly 6Mbs up (that just ain't right). The Broadcom yielded approximately the same values when I had Win 10 running (poorly) on this machine. While the laptop was still running Win 10, I bought the ASUS USB-AC51 wireless adapter. After getting drivers for it, download speeds increased by a factor of 30. So, that tells me that there's no hardware impediment to using the AC51.
I have tried everything from the top 3 or 4 search results for installing the AC51 on Ubuntu 16.04, to no avail.
sudo lshw -C network gives me this:
*-network
description: Wireless interface
product: BCM4321 802.11a/b/g/n
vendor: Broadcom Corporation
physical id: 0
bus info: pci@0000:0c:00.0
logical name: wlp12s0
version: 03
serial: 00:1d:d9:45:70:f8
width: 64 bits
clock: 33MHz
capabilities: pm msi pciexpress bus_master cap_list ethernet physical wireless
configuration: broadcast=yes driver=wl0 driverversion=6.30.223.248 (r487574) ip=10.60.33.250 latency=0 multicast=yes wireless=IEEE 802.11abg
resources: irq:17 memory:f9ffc000-f9ffffff memory:f0000000-f00fffff
*-network
description: Ethernet interface
product: BCM4401-B0 100Base-TX
vendor: Broadcom Corporation
physical id: 0
bus info: pci@0000:03:00.0
logical name: eth0
version: 02
serial: 00:19:b9:82:04:5b
size: 10Mbit/s
capacity: 100Mbit/s
width: 32 bits
clock: 33MHz
capabilities: pm bus_master cap_list ethernet physical mii 10bt 10bt-fd 100bt 100bt-fd autonegotiation
configuration: autonegotiation=on broadcast=yes driver=b44 driverversion=2.0 duplex=half latency=64 link=no multicast=yes port=twisted pair speed=10Mbit/s
resources: irq:17 memory:f9bfe000-f9bfffff
*-network DISABLED
description: Wireless interface
physical id: 1
logical name: ra0
capabilities: ethernet physical wireless
configuration: broadcast=yes driver=RALINK WLAN multicast=yes wireless=Ralink STA
lsusb gives me this:
Bus 002 Device 003: ID 04e8:6860 Samsung Electronics Co., Ltd Galaxy (MTP)
Bus 002 Device 002: ID 0b05:17d1 ASUSTek Computer, Inc. AC51 802.11a/b/g/n/ac Wireless Adapter [Mediatek MT7610/Ralink RT2870]
Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 007 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 006 Device 002: ID 1532:0034 Razer USA, Ltd
Bus 006 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 005 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 004 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 003 Device 005: ID 0a5c:4503 Broadcom Corp. Mouse (Boot Interface Subclass)
Bus 003 Device 004: ID 0a5c:4502 Broadcom Corp. Keyboard (Boot Interface Subclass)
Bus 003 Device 003: ID 413c:8126 Dell Computer Corp. Wireless 355 Bluetooth
Bus 003 Device 002: ID 0a5c:4500 Broadcom Corp. BCM2046B1 USB 2.0 Hub (part of BCM2046 Bluetooth)
Bus 003 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
So, lsusb sees the AC-51, but the adapter doesn't light up, even after compiling and installing the driver from MT7612U_DPO_LinuxSTA_3.0.0.1_20140718, doing a make clean when that didn't work, then installing the driver from RTL8812AU_linux_v4.3.20_16317_20160108.
lshw sees the internal Broadcom wireless adapter, but also a disabled wireless adapter that it doesn't identify. I'm guessing this is the AC-51.
P.S. As soon as I can login, I'll post output from the wireless troubleshooting script to DropBox.