How do I fix the low speed of Qualcomm Atheros AR9285 Wireless Network Adapter’s ap0 in Debian?

Unlike Windows, I discovered that the speed of my Access Point is too slow about 50-70KB on Debian unlike Windows it is about 1.3MB which is the original full download speed of my connection.

Here are the interfaces I have:

PHY     Interface       Driver          Chipset

 phy0    ap0             ath9k           Qualcomm Atheros AR9285 Wireless Network Adapter (PCI-Express) (rev 01)
 phy0    wlan0           ath9k           Qualcomm Atheros AR9285 Wireless Network Adapter (PCI-Express) (rev 01)
 phy1    wlan1           rt2800usb       Ralink Technology, Corp. RT2870/RT30

Unlike Windows, since I cannot use Ralink Technology, Corp. RT2870/RT3070 as AP and STA in the same time, I used Qualcomm Atheros AR9285 Wireless Network Adapter (PCI-Express) (rev 01) yet It is slow.

How do I tweak the speed?