Krdytkyu

I'm trying to reduce the connection bit rate on my Atheros TP-Link TL-WN821N v3 usb wifi adapter due to frequent instability issues (reported connection speed goes down to 1Mb/s and I have to physically reconnect the adapter to regain a connection). I know this is a common problem with this device, and I have tried everything I can think of to fix it, including using drivers from linux-backports; compiling and installing a custom firmware (following instructions on https://wiki.debian.org/ath9k_htc#fw-free) and (as a last resort) using ndiswrapper.

When using ndiswrapper, the wifi adapter is stable and operates in g mode at 54Mb/s (whilst when using the default ath9k_htc module, the adapter connects in n mode and the bit rate fluctuates constantly). Unfortunately, with this setup I have to run my processor using only one core, since using SMP with ndiswrapper causes a kernel oops on my system.

So I want to lock my bit rate to 54Mb/s (or less, if need be) for connection stability, using the ath9k_htc module.

I've tried 'sudo iwconfig wlan0 rate 54M'; the command runs with no error but when I check the bit rate with 'sudo iwlist wlan0 bitrate' the command returns:

wlan0 unknown bit-rate information. 

          Current Bit Rate:78 Mb/s

Any ideas? Here's some info (hopefully relevant) on my setup:

Xubuntu (12.04.3) 64bit (kernel 3.2.0-55.85-generic) using Network Manager. My Router is from Virgin Media, the VMDG480.

lshw -C network :



  *-network               

       description: Wireless interface 

       physical id: 1 

       bus info: usb@1:4 

       logical name: wlan0 

       serial: 74:ea:3a:8f:16:b6 

       capabilities: ethernet physical wireless 

       configuration: broadcast=yes driver=ath9k_htc driverversion=3.2.0-55 firmware=1.3 ip=192.168.0.9 link=yes multicast=yes wireless=IEEE 802.11bgn

lsusb -v:



Bus 001 Device 003: ID 0cf3:7015 Atheros Communications, Inc. TP-Link TL-WN821N v3 802.11n [Atheros AR7010+AR9287] 

Device Descriptor: 

  bLength                18 

  bDescriptorType         1 

  bcdUSB               2.00 

  bDeviceClass          255 Vendor Specific Class 

  bDeviceSubClass       255 Vendor Specific Subclass 

  bDeviceProtocol       255 Vendor Specific Protocol 

  bMaxPacketSize0        64 

  idVendor           0x0cf3 Atheros Communications, Inc. 

  idProduct          0x7015 TP-Link TL-WN821N v3 802.11n [Atheros AR7010+AR9287] 

  bcdDevice            2.02 

  iManufacturer          16 ATHEROS 

  iProduct               32 UB95 

  iSerial                48 12345 

  bNumConfigurations      1 

  Configuration Descriptor: 

    bLength                 9 

    bDescriptorType         2 

    wTotalLength           60 

    bNumInterfaces          1 

    bConfigurationValue     1 

    iConfiguration          0 

    bmAttributes         0x80 

      (Bus Powered) 

    MaxPower              500mA 

    Interface Descriptor: 

      bLength                 9 

      bDescriptorType         4 

      bInterfaceNumber        0 

      bAlternateSetting       0 

      bNumEndpoints           6 

      bInterfaceClass       255 Vendor Specific Class 

      bInterfaceSubClass      0 

      bInterfaceProtocol      0 

      iInterface              0 

      Endpoint Descriptor: 

        bLength                 7 

        bDescriptorType         5 

        bEndpointAddress     0x01  EP 1 OUT 

        bmAttributes            2 

          Transfer Type            Bulk 

          Synch Type               None 

          Usage Type               Data 

        wMaxPacketSize     0x0200  1x 512 bytes 

        bInterval               0 

      Endpoint Descriptor: 

        bLength                 7 

        bDescriptorType         5 

        bEndpointAddress     0x82  EP 2 IN 

        bmAttributes            2 

          Transfer Type            Bulk 

          Synch Type               None 

          Usage Type               Data 

        wMaxPacketSize     0x0200  1x 512 bytes 

        bInterval               0 

      Endpoint Descriptor: 

        bLength                 7 

        bDescriptorType         5 

        bEndpointAddress     0x83  EP 3 IN 

        bmAttributes            3 

          Transfer Type            Interrupt 

          Synch Type               None 

          Usage Type               Data 

        wMaxPacketSize     0x0040  1x 64 bytes 

        bInterval               1 

      Endpoint Descriptor: 

        bLength                 7 

        bDescriptorType         5 

        bEndpointAddress     0x04  EP 4 OUT 

        bmAttributes            3 

          Transfer Type            Interrupt 

          Synch Type               None 

          Usage Type               Data 

        wMaxPacketSize     0x0040  1x 64 bytes 

        bInterval               1 

      Endpoint Descriptor: 

        bLength                 7 

        bDescriptorType         5 

        bEndpointAddress     0x05  EP 5 OUT 

        bmAttributes            2 

          Transfer Type            Bulk 

          Synch Type               None 

          Usage Type               Data 

        wMaxPacketSize     0x0200  1x 512 bytes 

        bInterval               0 

      Endpoint Descriptor: 

        bLength                 7 

        bDescriptorType         5 

        bEndpointAddress     0x06  EP 6 OUT 

        bmAttributes            2 

          Transfer Type            Bulk 

          Synch Type               None 

          Usage Type               Data 

        wMaxPacketSize     0x0200  1x 512 bytes 

        bInterval               0 

Device Qualifier (for other device speed): 

  bLength                10 

  bDescriptorType         6 

  bcdUSB               2.00 

  bDeviceClass          255 Vendor Specific Class 

  bDeviceSubClass       255 Vendor Specific Subclass 

  bDeviceProtocol       255 Vendor Specific Protocol 

  bMaxPacketSize0        64 

  bNumConfigurations      1 

Device Status:     0x0000 

  (Bus Powered)

iwlist wlan0 scanning:



wlan0     Scan completed : 

          Cell 01 - Address: C4:3D:C7:3A:1F:5D 

                    Channel:1 

                    Frequency:2.412 GHz (Channel 1) 

                    Quality=37/70  Signal level=-73 dBm  

                    Encryption key:on 

                    ESSID:"my essid" 

                    Bit Rates:1 Mb/s; 2 Mb/s; 5.5 Mb/s; 11 Mb/s; 18 Mb/s 

                              24 Mb/s; 36 Mb/s; 54 Mb/s 

                    Bit Rates:6 Mb/s; 9 Mb/s; 12 Mb/s; 48 Mb/s 

                    Mode:Master 

                    Extra:tsf=00000070cca77186 

                    Extra: Last beacon: 5588ms ago 

                    IE: Unknown: 0007756E69636F726E 

                    IE: Unknown: 010882848B962430486C 

                    IE: Unknown: 030101 

                    IE: Unknown: 2A0100 

                    IE: Unknown: 2F0100 

                    IE: IEEE 802.11i/WPA2 Version 1 

                        Group Cipher : TKIP 

                        Pairwise Ciphers (2) : CCMP TKIP 

                        Authentication Suites (1) : PSK 

                    IE: Unknown: 32040C121860 

                    IE: Unknown: 2D1AFC181BFFFF000000000000000000000000000000000000000000 

                    IE: Unknown: 3D1601080400000000000000000000000000000000000000 

                    IE: Unknown: DD7E0050F204104A0001101044000102103B00010310470010F99C335D7BAC57FB00137DFA79600220102100074E657467656172102300074E6574676561721024000631323334353610420007303030303030311054000800060050F20400011011000743473331303144100800022008103C0001011049000600372A000120 

                    IE: Unknown: DD090010180203F02C0000 

                    IE: WPA Version 1 

                        Group Cipher : TKIP 

                        Pairwise Ciphers (2) : CCMP TKIP 

                        Authentication Suites (1) : PSK 

                    IE: Unknown: DD180050F2020101800003A4000027A4000042435E0062322F00

iwconfig:



lo        no wireless extensions. 



wlan0     IEEE 802.11bgn  ESSID:"my essid"  

          Mode:Managed  Frequency:2.412 GHz  Access Point: C4:3D:C7:3A:1F:5D   

          Bit Rate=78 Mb/s   Tx-Power=20 dBm   

          Retry  long limit:7   RTS thr:off   Fragment thr:off 

          Power Management:off 

          Link Quality=36/70  Signal level=-74 dBm  

          Rx invalid nwid:0  Rx invalid crypt:0  Rx invalid frag:0 

          Tx excessive retries:0  Invalid misc:0   Missed beacon:0,

I don't have this hardware so I am unable to test, however, it appears that the rate is decided by the firmware. There's patched firmware here that should work with kernel 3.2.0-55.85-generic and perhaps later kernels as well.

Quoting befinitiv

You find a pre-compiled firmware that uses MCS3 (26mbit/s) as an injection rate under patches/AR9271/firmware/htc_9271.fw. Copy this file to /lib/firmware and re-insert the card to use the modified firmware. If you want to compile the firmware with a different injection rate you can take look at the patch that I supplied. The easiest way is to replace the first line in the list with a copy of the wanted injection rate. Instructions for compiling the firmware for Linux are given in the firmware repo.

After installing the firmware, simply re-plug the USB Adapter to use it.

Sources:

https://befinitiv.wordpress.com/2015/02/22/finding-the-right-wifi-dongle-and-patching-its-kernel-driver-and-firmware/

https://github.com/qca/open-ath9k-htc-firmware/blob/master/README

Edit: As @pandalion98 points out in this comment the patch under discussion can be found here.

Use iw instead:

iw wlan0 set bitrates legacy-2.4 9

before establishing the connection