Unable to change default bitrate of wireless network interface

Question

I am trying to change the bitrate of my wireless nic (AR9565 driver: ath9k_htc) for experimentation purposes. I am running Ubuntu 14.04 LTS and my card details are as follows:

wlan0     IEEE 802.11abgn  ESSID:"FACULTY-STAFF-N"  
             Mode:Managed  Frequency:5.24 GHz  Access Point: C4:0A:CB:2D:75:5A   
             Bit Rate=240 Mb/s   Tx-Power=17 dBm   
             Retry short limit:7   RTS thr:off   Fragment thr:off
             Power Management:off
             Link Quality=38/70  Signal level=-72 dBm  
             Rx invalid nwid:0  Rx invalid crypt:0  Rx invalid frag:0
             Tx excessive retries:2  Invalid misc:0   Missed beacon:0

To fix the bitrate (9Mbps in this case, but I checked multiple bit rates), I use these commands:

sudo iw dev wlan0 set bitrates legacy-5 9

OR

sudo iwconfig wlan0 rate 9M

I check the maximum bit rate used by wlan0 by iw dev wlan0 link; iwconfig wlan0 and I check the current bitrate used by interface through glances. However, none of these commands seem to have any effect on the bit rate.

This is the information on running iw dev wlan0 link:

Connected to c4:0a:cb:2d:75:55 (on wlan0)
SSID: FACULTY-STAFF-N
freq: 2462
RX: 420678 bytes (1949 packets)
TX: 144065 bytes (850 packets)
signal: -57 dBm
tx bitrate: 130.0 MBit/s MCS 14 short GI

bss flags:  short-preamble short-slot-time
dtim period:    1
beacon int: 102

The accepted answer to the related question asked here requires me to bring down the interface before I change the rates. However, doing so I encounter the following error:

Error for wireless request "Set Bit Rate" (8B20) :
SET failed on device wlan0 ; Network is down

Also I tried iw list. This command does not return all available rates but returns the current rate.

Solution

I will be assuming that the WiFi card is called wlan0. I will divide the answer in two parts:

1. Fixing the Error

Run sudo ifconfig wlan0 up to start the network, because you are getting error : SET failed on device wlan0 ; Network is down

2. How to change the bitrate properly

Run iwlist wlan0 bitrate first to check what bit rates are supported and the current bitrate is.

Then, iwconfig wlan0 bitrate 24M

Comments

[Tanya Shreedhar]

My wireless chipset is AR9565 (driver: ath9k_htc). I checked for multiple bit rates. Also I tried iw list. This command does not return all available rates but returns the current rate.

[Tanya Shreedhar]

I have also used different laptops, another one using Atheros AR9485.

[Alex Stragies]

did you check the available bit rates on the AP side too?. Do they include the bit-rates you tried?. For future reference: Add new information (like "I tried another device, AR9485") to the Question, not into comments. If the new information is in response to a commenter asking for it, perhaps flag it as helpful, and then -after adding the new info- flag the comment asking for it as "obsolete". That way the comment section can be kept on-topic, up2date and "clean".

[Rolf]

I'm having weird behavior as well. If I use iwconfig, then the rate will be set to either 1 or 11 and I cannot get it back to anything faster without resetting the adapter. If I use iw, any changes seem to affect only tx. Rx keeps switching wildly across modulations, free like the wind.