Hello, this is my first topic/reply ever here and I need some help.
I have a TP-link TL-WN751ND wireless card, and my internet connection speed is 30 Mbits (Download). I use Ubuntu MATE 16.04.1 x64 for a while now, with an XP as a dual boot system. Problem is, that with MATE my download speed at speedtest.net is only between 12 and 18 Mbits (even with different servers), while under XP I get my full 30 Mbits. So this is probably a driver related issue.
In terminal lspci command shows, that my chip is a “Qualcomm Atheros AR9227 Wireless Network Adapter (rev 01)”, and since there is no official ubuntu support at this company, my driver is ath9k.
Nothing worked so far in this case, even the nohwcrypt=-1 method in ath9k.conf. Power saving mode is off also. I would like to have my full 30 Mbits of download speed with Ubuntu MATE.
Thank you for the replies in advance! 
Have you installed Additional Drivers and the Firmware package in Ubuntu MATE Welcome?
I am regularly checking the welcome screen’s options for additional drivers and firmwares and installing them as soon as possible. I have only one option on additional driver screen called processor microcode firmware for Intel CPU-s.
I install almost every updates instantly (even software boutique’s updates), but what needs to be mentioned, that the problem (mentioned in the first post ) occurs even with the x86 version, and with the livecd-s, also.
Theoretically my hardware is supported, but i don’t know now, what more I have to do. 
Are you sure it’s =-1 and not =1?
Sorry, my mistake, in the modprobe.d directory I have created an ath9k.conf file before, and there is this line:
options ath9k nohwcrypt=1
So the value is 1, but it does nothing. I followed the instructions written here, when creating the file (right column).
It seems like you get different instructions depending on who you read.
echo "options ath9k nohwcrypt=1" | sudo tee /etc/modprobe.d/ath9k.conf
sudo modprobe -rfv ath9k
sudo modprobe -v ath9k
Change the conf, reload the kernel module. I can’t remember how much is cached and how much is read fresh on boot.
edit
“We highly recommend to change it (in your router) to pure WPA2-PSK with AES. No mixed mode, no TKIP. Change the setting > Save it > Reboot both the router and laptop and see if there is further performance improvement.” says a forum somewhere.
Okay I pasted the command lines into the terminal one by one. The conf is still the same. Then I deleted the original conf, pasted the lines again, but the new conf is still the same, it has only one line:
options ath9k nohwcrypt=1
Then in the router settings I had “WPA or WPA2 Personal” setting, now I changed it to “WPA2-Personal” setting. Further options are WPA2-Enterprise, but I dont know what’s the difference between Personal and Enterprise. Did I anything wrong so far?
Encyption type was AES, so I did not change that. I rebooted router and PC, and these are the results:
1st: with the server of my ISP, x64 ubuntu
2nd: with another server, x86 XP
3rd: same server as 2nd, x64 ubuntu, best result so far, but notice the differences in ping
4th: 1 minute after the 3rd, and I did not change a thing…
It’s very hectic with the ath9k driver. Okay it’s usable, but still.