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Version 26 (modified by Tim Harvey, 7 years ago) ( diff )
added note about WLE1216v5-20 not supporting VHT160

802.11 WiFi

This information has been tested and created for use on the Gateworks Single Board Computers (SBCs), specifically the Ventana family that utilizes the Freescale i.MX6 processors.

Gateworks SBCs can be viewed at the following link: http://www.gateworks.com

For information on various wireless technologies see the following pages:

802.11 WiFi

Gateworks has had extensive experience with wireless radio's. This list includes miniPCI and miniPCIe, specifically with the Atheros wireless chipsets which happen to be one of the most common chipset's used under Linux in the industrial world.

Out of box, our BSP's include the latest wireless drivers available. This allows our customers to get the latest and greatest support right away.

Common Wireless Radio Hardware

Gateworks re-sells some of the more popular radios in our on-line store and has tested several others:

Wireless 802.11AC
- Using ath10k Driver:
  - MiniPCIe Compex WLE1216V5-20 - Highest Throughput
    - 802.11b/g/a/c wave2
    - 4x4 MU-MIMO
    - 4 spatial streams (4SS) at 80MHz
    - 2 spatial streams (2SS) at 80+80MHz (unclear if this is supported by driver/firmware/hostapd yet)
    - Note that this card does not support VHT160 even though its EEPROM states it does
    - single-band: 5
    - tested on Newport GW630x with 4.14 kernel:
      - requires updated board-2.bin file from CT in /lib/firmware/ath10k/QCA9984/hw1.0/board-2.bin
    - Datasheet
  - MiniPCIe Compex WLE900VX 7AA - Standard Recommended Radio
    - Pre-Certified with FCC
    - 802.11b/g/a/c
    - dual-band: 2.4, 5
    - 3x3 MIMO
    - Datasheet
  - MiniPCIe Compex WLE900N5
    - 802.11a/c
    - single-band: 5
    - 3x3 MIMO
  - MiniPCIe Unex DAXA-O1
    - 802.11n/a/c
    - dual-band: 2.4, 5
    - 3x3 MIMO
    - Datasheet
  - MiniPCIe Doodle Labs ACE-DB-3 Radio
    - 802.11b/g/a/c
    - tri-band: 2.4, 5, 4.9
    - 3x3 MIMO
    - Datasheet
- Using Intel iwlwifi Driver:
  - MiniPCIe Intel 7260
    - 802.11 ac/a/b/g/n
    - dual-band: 2.4, 5
    - 2x2 MIMO
    - Other Specifications
    - Note: This card cannot emit radiation in the 5GHz range, i.e. AP mode does not work in 5GHz

Wireless 802.11N
- MiniPCIe Unex DHXA-225 - Very common, cost effective
- MiniPCIe Ubiquiti SR71E
- MiniPCIe Compex WLE350NX - EOL, not recommended for new design

Wireless 802.11B/G
- miniPCIe Ubiquiti XR2

Some additional radio vendors:

Doodle Labs - High powered WiFi radios http://doodlelabs.com/
Compex - High powered WiFi radios http://www.compex.com.sg/
Unex - High powered WiFi radios http://www.unex.com.tw/wi-fi
Silex - WiFi radios http://www.silexamerica.com/
Ubiquiti - High powered WiFi 802.11abg radios http://www.ubnt.com/

Doodlelabs Prism-FES (Front End Subsystems)

Doodlelabs creates frequency shifting modules to allow frequencies between 700MHz - 6.5GHz, while using standard linux drivers. These systems are comprised of one ath9k/ath10k radio with a FES module on each chain. The below picture will help visualize this:

In this system, a radio has two separate FES modules per chain. From the factory, Doodlelabs calibrates each chain on a specific radio to a particular FES module. This means that a radio with 2 chains is specifically paired with two FES modules. You can find which FES modules are paired with what radio by comparing serial numbers (Hint: all components in the system have the same serial). It's very highly recommended by Doodlelabs that nothing is mixed and matched.

Radio's configured to be used in a Prism-FES all have EEPROM values programmed in to only allow a maximum of 10dBm output (per chain). Anything higher will damage the frequency translator. For this reason, Prism-FES's that are using ath10k are recommended to stay away from using the STA firmware (999.999.0.636) as we found that this firmware does not honor the EEPROM settings and configures the radio to output much higher than 10dBm.

Part Numbering Scheme

Before we break this down further, the following terminology used by Doodlelabs is required:

Grade Breakdown:

Military Grade - This is their Industrial grade option. This grade has extended temp of -40C - +85C. This grade also has antenna port protection, and is built to a higher standard than their other radio's.
Enterprise - This is their Indoor Commercial grade option. This grade has a temperature range of 0C - +60C and has no antenna port protection.
Outdoors - This is their Outdoor Commercial grade option. This grade has a temperature range of -40C - +40C and has antenna port protection.

The model number NM-770-2F is broken down into three sections: NM, 770, 2F

NM - The 'N' refers to this being an 80211N radio. If this were 'ACM', for example, that would mean the radio is a 80211AC radio. The last character of the first section refers to the grade the radio is. In this case, the 'M' stands for Military, or rugged, grade.
770 - This number refers to the middle frequency of the frequency range that the card supports. In this case, the card supports 746~798, the midpoint center frequency resulting in 770. If there is no number, and instead has either 'DB' or 'TB', that only means "Dual-Band" and "Tri-Band", respectively. When DB is specified, that refers to both the 2.4GHz and 5.8GHz range. TB refers to DB, but also includes the 4.9GHz frequency range.
2F - The number '2' refers to the number of chains the radio has. In this case, there are two chains on this radio. A '3' would indicate three chains. The 'F' alludes to the fact that each chain get's frequency shifted through the frequency shifting module. This means that you're always going to have a FES module per chain.

So in conclusion, the NM-770-2F system includes a 80211N radio with two chains, each getting frequency shifted by a FES module to the 770MHz range.

Licensed vs Unlicensed

In the US, the difference between Licensed and Unlicensed comes down to how the FCC regulates the frequency spectrum. In general, Doodlelabs refers to 'unlicensed' radio's the 2.4GHz and 5GHz range frequencies. All other frequencies fall under being 'licensed'.

Frequency Shifting/Power Level Mappings

Coming Soon.

References

Gateworks BSP Support

Gateworks supports multiple Board Support Packages. The following table shows details on WiFi support for each:

BSP	Product Families	Drivers	Modes
OpenWrt	All	ath5k/ath9k/ath10k	AP / client
Yocto	Ventana	ath5k/ath9k/ath10k	AP / client
Android	Ventana	ath5k/ath9k	AP / client
ubuntu	Ventana, Newport	ath9k/ath10k	AP / client

If you are looking for additional support please contact support@…

OpenWrt Wireless Configuration

OpenWrt uses the standard Linux wireless utilities but configured and launched through its own configuration system.

For more info on configuring Wireless for OpenWrt see:

OpenWrt Wireless Configuration

Yocto Wireless Configuration

Yocto uses the standard Linux utilities, init scripts, and conf files.

For more info on configuring Wireless for Yocto see:

Yocto Wireless Configuration

Android Wireless Configuration

Android uses the standard Linux utilities but wraps them around a Network Daemon that performs configuration and management.

For more info on configuring Wireless for Android see:

Android Wireless Configuration

Ubuntu Wireless Configuration

Ubuntu uses the standard Linux utilities, init scripts, and conf files.

For more info on configuring Wireless for Ubuntu see:

Ubuntu Wireless Configuration

Wireless Configuration (Standard Linux)

There are several tools and applications that are used by Linux to configure wireless devices:

iw
hostapd
wpa_supplicant

For more info on configuring Wireless for Yocto see:

Yocto Wireless Configuration

iw

The 'iw' tool is the modern tool (which replaces the older set of WIRELESS_EXTENSION tools such as iwconfig, iwpriv, iwlist, etc) for configuration of wireless drivers.

The full documentation is here but some common commands we find useful are:

list devices:

iw dev ;# 'iw dev wlan0 info' for each dev
iw phy ;# 'iw phy phy0 info' for each dev

list device info:

iw dev wlan0 info ;# basic info: ifname, mode, mac (same as iw wlan0 info)
iw phy phy0 info ;# detailed info: antennas, supported modes, bands, freqs (same as iw phy0 info)
iw dev wlan0 link # info about link

antenna info:

iw phy phy0 | grep Antenna ;# get Antenna bitmasks
iw phy phy0 set antenna_gain <gainindbm>
iw phy phy0 set antenna <bitmap> | all <txbitmap> <rxbitmap> ;# set allowed antennas

TX power info:

iw dev wlan0 set txpower <auto|fixed|limit> [<txpowermbm>]
iw phy phy0 set txpower <auto|fixed|limit> [<txpowermbm>]
iw phy phy0 set distance <distance meters> ;# set appropriate coverage class (0-114750)
iw phy phy0 set coverage <coverage class> ;# set coverage class (1 for every 3us of air prop time 0-255)

channel:

iw dev wlan0 set channel <channel> [HT20|HT40+|HT40-]  ;# or iw phy
iw dev wlan0 set freq <freq> [HT20|HT40+|HT40-]  ;# or iw phy
iw dev wlan0 set freq <control freq> [20|40|80|80+80|160] [<center freq>] [<center freq2>]
iw phy phy0 set freq <freq> [HT20|HT40+|HT40-]

4-addr header parsing (WDS):
```
iw dev wlan0 set 4addr <on|off>
```

interface mode:

iw dev wlan0 set type <managed|ibss|monitor|mesh|wds>

rate masks (when fixed mask set you won't see T,p,P change in rc_stats but will see the stats change)
```
iw dev set bitrates ;# clear masks
iw dev wlan0 set bitrates ht-mcs-5 19 ;# set MCS-19
```

interface creation:

iw phy phy0 interface add <name> type <type>
iw phy phy0 interface add mon0 type monitor
iw dev <name> del ;# delete interface

turn off powersave mode:

# May increase wireless performance depending on radio
iw dev wlan0 set power_save off

Notes:

most commands allow specification of a network device (ie wlan0) or a phy (ie phy0)
most 'set' commands will show current settings if a value isn't specified
'iw wlan0 ...' is short for 'iw dev wlan0 ...' and 'iw phy0 ...' is short for 'iw phy phy0 ...'

References:

http://wireless.kernel.org/en/users/Documentation/iw
source:
- release tarballs: https://www.kernel.org/pub/software/network/iw/
- git http://git.kernel.org/cgit/linux/kernel/git/jberg/iw.git (tagged per kernel release)

hostapd

The hostapd application is the userspace application that configures and manages wireless drivers in Access Point (AP) mode.

References:

http://hostap.epitest.fi/hostapd/
http://wireless.kernel.org/en/users/Documentation/hostapd
source:
- stable release tarballs: http://w1.fi/hostapd/
- git http://w1.fi/cgit/hostap/ (cgit: http://hostap.epitest.fi/cgit/hostap/)

Access Point Configuration (AP)

By default the Yocto BSP is configured to enable a Wireless Access Point.

The 'hostap-daemon' package provides the hostapd application which configures the radio for AP mode using configuration from /etc/hostapd.conf.

You will need to configure /etc/hostapd.conf to specify important details such as:

interface
driver type (the default is nl80211 which is used for all modern mac80211 drivers)
bridge config
ssid
channel
encryption

The default /etc/hostapd.conf file contains detailed documentation and you can find more info here. However, because every wireless cards' capabilities are vastly different from one another, Gateworks has written a script to help ascertain a proper hostapd.conf file. Though not 100% of the functionality mentioned in the hostapd documentation is supported, it does help the user create a hostapd.conf file specific to their wireless card.

This bash script, named hostapd-conf, is included in our latest Yocto 1.8/Master branches. To read over the script, please click here.

Usage is as follows:

root@ventana:~# ./hostapd-conf
hostapd-conf [OPTIONS] <iface> <ssid> <channel> [<htmode>] [<passphrase>]

Options:
 --help           - This help
 --br-name <name> - Name of bridge
 --wds <0|1>      - Enable WDS
 --version        - Print this version: v1.0

Example:
 Print channel information for wlan0 and exit:
  hostapd-conf wlan0

 State wlan0 SSID is 'myssid', on channel 6 with WPA2 passphrase "nowayinside":
  hostapd-conf wlan0 myssid 6 nowayinside

 State wlan0 is in named bridge br0, enable WDS, SSID 'myssid', channel 6,
 in HT20(802.11n), with WPA2 passphrase "nowayinside":
  hostapd-conf --br-name=br0 --wds=1 wlan0 myssid 6 HT20 nowayinside

Below are some usage cases for this script. In these examples, a WLE900VX radio was used. Note, any information that isn't apparent in the below script may be found via the iw phy phy<n> info command.

Step 0 : Scan Available Options

To view all channels/frequencies and HT modes that can emit radiation on a specified interface, indicate just the interface:

root@ventana:~# ./hostapd-conf wlan0
ERROR: SSID is empty

Available Channel Information on phy0
=====================================
Band 1:
Channel  Freq  Allowed HT Modes
0        0000  HT20 HT40 HT40+ HT40-
1        2412  HT20 HT40 HT40+
2        2417  HT20 HT40 HT40+
3        2422  HT20 HT40 HT40+
4        2427  HT20 HT40 HT40+
5        2432  HT20 HT40 HT40+ HT40-
6        2437  HT20 HT40 HT40+ HT40-
7        2442  HT20 HT40 HT40+ HT40-
8        2447  HT20 HT40 HT40+ HT40-
9        2452  HT20 HT40 HT40+ HT40-
10       2457  HT20 HT40 HT40-
11       2462  HT20 HT40 HT40-

Band 2:
Channel  Freq  Allowed HT Modes
0        0000  HT20 HT40 HT40+ HT40- VHT20 VHT40 VHT80
36       5180  HT20 HT40 HT40+ VHT20 VHT40 VHT80
40       5200  HT20 HT40 HT40- VHT20 VHT40 VHT80
44       5220  HT20 HT40 HT40+ VHT20 VHT40 VHT80
48       5240  HT20 HT40 HT40- VHT20 VHT40 VHT80
149      5745  HT20 HT40 HT40+ VHT20 VHT40 VHT80
153      5765  HT20 HT40 HT40- VHT20 VHT40 VHT80
157      5785  HT20 HT40 HT40+ VHT20 VHT40 VHT80
161      5805  HT20 HT40 HT40- VHT20 VHT40 VHT80
165      5825  HT20 HT40 HT40+ VHT20 VHT40 VHT80

Step 1 : Configure Access Point

2.4GHz 802.11g

To create a hostapd.conf file in the 2.4GHz range, using 802.11g technology:

root@ventana:~# ./hostapd-conf wlan0 test-ssid 6
Settings:
 IFACE:   wlan0
 PHY:     phy0
 SSID:    test-ssid
 CHANNEL: 6
 FREQ:    2437
 BANDS:   1 2
 HWMODE:  g

Written to hostapd-phy0.conf
root@ventana:~# cat hostapd-phy0.conf
# For more options, please visit the following:
#  http://linuxwireless.org/en/users/Documentation/hostapd/
driver=nl80211
logger_syslog=-1
logger_syslog_level=2
logger_stdout=-1
logger_stdout_level=2
# a=5GHz, g=2.4GHz
hw_mode=g
# channel=0 turns on ACS survey
channel=6
# Please take the following into consideration:
# Country code (ISO/IEC 3166-1). Used to set regulatory domain.
# Set as needed to indicate country in which device is operating.
# This can limit available channels and transmit power.
#country_code=US
# Enable IEEE 802.11d. This advertises the country_code and the set of allowed
# channels and transmit power levels based on the regulatory limits. The
# country_code setting must be configured with the correct country for
# IEEE 802.11d functions.
# (default: 0 = disabled)
#ieee80211d=1
# Enable IEEE 802.11h. This enables radar detection and DFS support if
# available. DFS support is required on outdoor 5 GHz channels in most countries
# of the world. This can be used only with ieee80211d=1.
# (default: 0 = disabled)
#ieee80211h=1
interface=wlan0
ctrl_interface=/var/run/hostapd
ctrl_interface_group=0
disassoc_low_ack=1
preamble=1
wmm_enabled=1
macaddr_acl=0
auth_algs=1
ignore_broadcast_ssid=0
ssid=test-ssid
ieee80211n=0
ieee80211ac=0

5.8GHz 802.11ac

To create a hostapd.conf file in the 5GHz range, using 802.11ac technology, plus WPA2 encryption:

root@ventana:~# ./hostapd-conf wlan0 test-ssid 157 VHT80 nowayinside
Settings:
 IFACE:      wlan0
 PHY:        phy0
 SSID:       test-ssid
 CHANNEL:    157
 FREQ:       5785
 BANDS:      1 2
 HWMODE:     a
 HTMODE:     VHT80
 PASSPHRASE: nowayinside

Written to hostapd-phy0.conf
root@ventana:~# cat hostapd-phy0.conf
# For more options, please visit the following:
#  http://linuxwireless.org/en/users/Documentation/hostapd/
driver=nl80211
logger_syslog=-1
logger_syslog_level=2
logger_stdout=-1
logger_stdout_level=2
# a=5GHz, g=2.4GHz
hw_mode=a
# channel=0 turns on ACS survey
channel=157
# Please take the following into consideration:
# Country code (ISO/IEC 3166-1). Used to set regulatory domain.
# Set as needed to indicate country in which device is operating.
# This can limit available channels and transmit power.
#country_code=US
# Enable IEEE 802.11d. This advertises the country_code and the set of allowed
# channels and transmit power levels based on the regulatory limits. The
# country_code setting must be configured with the correct country for
# IEEE 802.11d functions.
# (default: 0 = disabled)
#ieee80211d=1
# Enable IEEE 802.11h. This enables radar detection and DFS support if
# available. DFS support is required on outdoor 5 GHz channels in most countries
# of the world. This can be used only with ieee80211d=1.
# (default: 0 = disabled)
#ieee80211h=1
interface=wlan0
ctrl_interface=/var/run/hostapd
ctrl_interface_group=0
disassoc_low_ack=1
preamble=1
wmm_enabled=1
macaddr_acl=0
auth_algs=1
ignore_broadcast_ssid=0
# Put a 3 here if you want both WPA/WPA2
wpa=2
wpa_passphrase=nowayinside
wpa_key_mgmt=WPA-PSK
wpa_pairwise=TKIP
rsn_pairwise=CCMP
ssid=test-ssid
ieee80211n=1
ht_capab=[HT40+][LDPC][SHORT-GI-20][SHORT-GI-40][TX-STBC][RX-STBC1][DSSS_CCK-40]
ieee80211ac=1
vht_oper_chwidth=1
vht_oper_centr_freq_seg0_idx=155
vht_capab=[RXLDPC][SHORT-GI-80][TX-STBC-2BY1][RX-ANTENNA-PATTERN][TX-ANTENNA-PATTERN][RX-STBC1][MAX-MPDU-11454][MAX-A-MPDU-LEN-EXP7]

Step 2 : Copy Access Point Configuration

After the hostapd-<phy>.conf file has been created and any edits have been made (if any), you may either:

Copy the hostapd-phy.conf file over /etc/hostapd.conf and restart hostapd, noting that /etc/network/interfaces isn't configuring the wlan interface automatically (e.g. make sure no auto wlan0 exists in /etc/network/interfaces)
```
mv /etc/hostapd.conf /etc/hostapd.conf.bak # Backup original hostapd.conf file
cp hostapd-phy0.conf /etc/hostapd.conf
/etc/init.d/hostapd restart
```

Run hostapd using this new conf file, knowing that the settings won't persist over a new boot:

root@ventana:~# /etc/init.d/hostapd stop
root@ventana:~# hostapd -B hostapd-phy0.conf
Configuration file: hostapd-phy0.conf
[ 1825.468968] IPv6: ADDRCONF(NETDEV_UP): wlan0: link is not ready
wlan0: interface state UNINITIALIZED->HT_SCAN
[ 1825.636135] IPv6: ADDRCONF(NETDEV_CHANGE): wlan0: link becomes ready

At this point your wlan0 interface should be up and authenticating with WiFi clients and the next step is to configure IP networking (below).

Routed Access Point

A routed Access Point is used when you want the wireless network to have its own DHCP server and network. In this case traffic is routed across the WAN (Wide Area Network) interface (ie eth0) and WLAN (Wireless Local Area Network) interface (ie wlan0). This is the typical configuration for a wireless access point.

For this you need:

the WAN (Wide Area Network) interface (ie eth0) should have an IP configuration from the WAN segment from the upstream Internet provider
the WLAN network interface (ie wlan0) should be assigned a static address on a private network
A DHCP server (ie dnsmasq) configured to serve a private IP address range on the WLAN network interface (ie wlan0)
Network Address Translation (NAT) routing configuration using Linux iptables and Linux kernel netfilter support
ip forwarding enabled in kernel

Configuration:

configure your WAN and WLAN interfaces in /etc/network/interfaces. Here we will use eth0 as our WAN configured to obtain IP configuration via DHCP from the upstream provider and wlan0 as our WLAN configured with a DHCP server for a private subnet on the 10.0.0/24 network:

cat << EOF > /etc/network/interfaces
# WAN interface
auto eth0
iface eth0 inet dhcp

# WLAN interface
auto wlan0
iface wlan0 inet static
        address 10.0.0.1
        netmask 255.255.255.0

# NAT configuration via iptables
post-up iptables-restore < /etc/iptables.ipv4.nat
EOF

configure dnsmasq. Here we will configure it to serve addresses on the 10.0.0/24 network with a pool of 190 addresses from .10 to .200 with a 2hour lease:
```
cat << EOF > /etc/dnsmasq.conf
interface=wlan0
dhcp-range=10.0.0.10,10.0.0.200,2h
EOF
```

configure Linux NAT routing. We will do this for the current boot and use that configuration to store hooks for subsequent reboots:

# enable forwarding on bootup
echo net.ipv4.ip_forward=1 >> /etc/sysctl.conf

# configure NAT via iptables and then save its config to the restore script
iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
iptables -A FORWARD -i eth0 -o wlan0 -m state --state RELATED,ESTABLISHED -j ACCEPT
iptables -A FORWARD -i wlan0 -o eth0 -j ACCEPT
iptables-save > /etc/iptables.ipv4.nat
chmod +x /etc/iptables.ipv4.nat

restart networking and enable forwarding (or sync and reboot at this point instead):
```
/etc/init.d/networking restart
echo 1 > /proc/sys/net/ipv4/ip_forward
```

Bridged Access Point

A bridged Access Point is used to provide an a Wireless Access Point on a LAN that already has a DHCP server and creates a bridge between the LAN interface and the WIFI interface such that wireless client DHCP requests will be bridged to the LAN and answered from there.

For this you need:

bridge-utils package
CONFIG_BRIDGE support in kernel (default in our Yocto kernel)
ip forwarding enabled in kernel

create a bridge between your wifi interface and your lan interface. For example, assuming wlan0 and eth0:
```
# create a bride and add interfaces to it
brctl addbr br0
brctl addif br0 eth0
brctl addif br0 wlan0
# bring it up
ifconfig br0 up
# use DHCP to assign IP info
udhcpc -i br0
```
- Note that you can use /etc/network/interfaces to bring up and configure the bridge, but if you are using a fairly limited ifup/ifdown (like busybox) you will probably need to create the bridge first (ie in an init script prior to networking coming up)

enable IP forwarding:

echo 1 > /proc/sys/net/ipv4/ip_forward

you can enable IP forwarding on bootup with:

echo net.ipv4.ip_forward=1 >> /etc/sysctl.conf

Note that if your intention is to also create a wireless client bridge where a wireless client connection is bridging its wireless to a local Ethernet network you will need to enable WDS/4-addr header parsing on both the Access Point and the Client. To do this on the Access Point, add the following to /etc/hostapd.conf:

wds_sta=1

Alternatively, if using the hostapd-conf script, an option exists to enable this feature via --wds=1.

Troubleshooting

If encountering bad TCP performance with MIMO cards (typically ath10k):

see TCP Congestion Control
see TCP Small Queues

If encountering issues:

hostapd-conf was written for and takes advantage of the bash shell, make sure you aren't running it with another shell program (ie Ubuntu's default "dash" shell)
ensure both hostapd and wpa_supplicant are not both trying to manage the interface (ie you have it configured for both AP and Client mode)
ensure your client can see the AP (ie iw dev wlan0 scan for a Linux client, or use a wireless scanner such as 'Wifi Analyzer' on an Android device)
For client mode ensure the kernel shows that you are associated with the AP. You should see wlan0: associated in the kernel messages
check your encryption settings
if you can ping between the AP and the client directly but not get through them:
- check your routing configuration (ie via route -n on Linux) and make sure you have a proper gateway
- if trying to bridge wireless to ethernet networks ensure 'both' the AP and the Client have 4addr header parsing enabled
if DNS resolution is not occurring first make sure you can ping the nameserver by IP

wpa-supplicant

The wpa-supplicant application is the userspace application that configures and manages wireless drivers in Station (STA) mode.

References:

http://hostap.epitest.fi/wpa_supplicant/
http://wireless.kernel.org/en/users/Documentation/wpa_supplicant
source:
- stable release tarballs: http://w1.fi/hostapd/
- git git://w1.fi/srv/git/hostap.git (cgit: http://hostap.epitest.fi/cgit/hostap/)

Linux Kernel Drivers

There are various linux kernel drivers such as madwifi, ath5k, ath9k, ath10k, iwlwifi, to name a few. The below few sections will talk at length about several of them.

Atheros AR5xxx 802.11abg cards (ath5k)

There are two driver options for the Atheros AR5xxx based 802.11abg cards:

madwifi driver - development of this driver has ceased but it still has been known to outperform the fully opensource ath5k replacement and has some additional features that are not (and will not be) in ath5k
ath5k - mac80211 driver - driver should be stable, but does not get much attention anymore as most users have moved on to 802.11n or 802.11ac devices
- see ath5k for more info

Theoretical max throughput rate of 802.11abg is 54mbps. Typical performance is around 30mbps (TCP)

Atheros AR9xxx 802.11abgn cards (ath9k)

The linux-wireless 'ath9k' driver supports the Atheros AR9xxx based 802.11n cads.

The 802.11n standard released in 2009 introduces some additions on top of the 802.11a standard:

widening the channel bandwidth (up to 40MHz)
Multiple Input(rx) Multiple Output(tx) streams (MIMO) up to 4
64-QAM modulation

Current popular hardware available supports up to 3x3 MIMO and up to 40MHz channel bandwidths using HT40+/HT40- which can 'theoretically yield' 300mbps of throughput. Actual results will vary based on CPU and bus bottlenecks, driver performance, and RF characteristics.

We regularly obtain throughputs around 150mbps.

See ath9k for more info

Atheros AR10xx 802.11ac cards (ath10k)

The linux-wireless 'ath10k' driver supports the Atheros AR10xx based 802.11ac cards.

The 802.11ac standard which was developed from 2011 through 2013 and approved in Jan 2014, introduces some additions on top of the 802.11n standards:

widening the channel bandwidth (up to 160MHz)
increased MIMO spatial streams (up to 8 vs 4 in 802.11n)
multi-user MIMO (aka MU-MIMO)
high-density modulation (up to 256-QAM vs 64-QAM for 802.11n)

Current popular hardware available supports up to 4x4 MU-MIMO and up to 160MHz channel bandwidths using VHT160 which can theoretically yield >2.0gbps of throughput. Some cards also support VHT80+80 which functions similarly to VHT160 but is composed to two 80MHz channels that do not need to be contiguous, which can help with band selection. Actual results will vary based on CPU and bus bottlenecks, driver performance, and RF characteristics.

ath10k notes:

10.1.467.2-1
- What we ship with
- Focuses as AP in which DFS works. STA mode works, but not well tested. No AdHoc or P2P support
- Works in wireless bridge with upstream ath10k patches. These patches are in our 14.08 Branch (as well as trunk) of OpenWrt.
999.999.0.636
- Supports both AP and STA, AdHoc, and P2P. Has issues with DFS and cannot be configured an an AP in a wireless bridge
- Has less than half the performance than the 10.1.467.2-1 firmware. This was a primary reason for not choosing this firmware as our default shipped firmware.
- Monitor mode is not supported (crashes the firmware).
- TX Power inconsistent

Verifying / Checking Firmware Version

To check which version of ath10k firmware is being used on the Single board computer, use the dmesg and grep command:

root@OpenWrt:/# dmesg | grep ath10k
[   10.934967] ath10k: qca988x hw2.0 (0x4100016c, 0x043202ff) fw 10.1.467.2-1
root@OpenWrt:/#

Alternative Firmware instructions

To select between default and custom firmware you must rename or re-link it using the existing filenames in the driver directory. The driver will not use your custom firmware unless it has a name it's familiar with. This can vary depending on the chipset firmware you are intending to use as well as the BSP

Some examples:

link CT's QCA988x firmware on OpenWrt 16.02:

$ cd /lib/firmware/ath10k/QCA988X/hw2.0/
$ ln -sf firmware-2-ct-full-community-beta.bin firmware-2.bin
$ # Reboot board

Replace stock QCA9984 (to support Wave2 cards such as the WLE1216) firmware with CT's:

# Download Candelatech's firmware.bin and board.bin files
wget http://www.candelatech.com/downloads/ath10k-9984-10-4/board-2-ct.bin
wget http://www.candelatech.com/downloads/ath10k-9984-10-4/firmware-5-ct-full-community.bin

# Back up old files
cp /lib/firmware/ath10k/QCA9984/hw1.0/board-2.bin /lib/firmware/ath10k/QCA9984/hw1.0/board-2.bin_old
cp /lib/firmware/ath10k/QCA9984/hw1.0/firmware-5.bin /lib/firmware/ath10k/QCA9984/hw1.0/firmware-5.bin_old

# Drop in Candelatech files
mv board-2-ct.bin /lib/firmware/ath10k/QCA9984/hw1.0/board-2.bin
mv firmware-5-ct-full-community.bin /lib/firmware/ath10k/QCA9984/hw1.0/firmware-5.bin

That's it! You can use this method to link any firmware, so long as it's called firmware-2.bin (and if using the latest ath10k drivers, firmware-3.bin).

Candelatech

Candelatech licenses the source code for the ath0k firmware from QCA and has been actively developing it to provide enhancements and bugfixes that are not necessarily limitted to QCA's stock firmware priorities. One such enhancement is that they add IBSS/adhoc support.

Candelatech also has a web page for custom firmware files that may be required for certain radio's such as the WLE1216V5-20 wave 2 radio.

You may need this firmware if the ath10k driver and QCAXXXX firmware combination does not properly probe your device and create an interface. This would appear in your system log as:

root@xenial-newport:~# dmesg | grep ath10k
[    2.362523] ath10k_pci 0000:02:00.0: Direct firmware load for ath10k/QCA9984/hw1.0/board-pci-168c:003e:11ad:0804.bin failed with error -2
[    2.362527] ath10k_pci 0000:02:00.0: failed to load spec board file, falling back to generic: -2
[    2.362536] ath10k_pci 0000:02:00.0: Direct firmware load for ath10k/QCA9984/hw1.0/board.bin failed with error -2
[    2.362538] ath10k_pci 0000:02:00.0: failed to fetch generic board data: -2
[    2.362540] ath10k_pci 0000:02:00.0: failed to fetch board file: -2
[    2.362541] ath10k_pci 0000:02:00.0: could not fetch firmware files (-2)
[    2.362543] ath10k_pci 0000:02:00.0: could not probe fw (-2)

If this is the case, you can use CT's firmware as follows:

# Download Candelatech's firmware.bin and board.bin files
wget http://www.candelatech.com/downloads/ath10k-9984-10-4/board-2-ct.bin
wget http://www.candelatech.com/downloads/ath10k-9984-10-4/firmware-5-ct-full-community.bin

# Back up old files
cp /lib/firmware/ath10k/QCA9984/hw1.0/board-2.bin /lib/firmware/ath10k/QCA9984/hw1.0/board-2.bin_old
cp /lib/firmware/ath10k/QCA9984/hw1.0/firmware-5.bin /lib/firmware/ath10k/QCA9984/hw1.0/firmware-5.bin_old

# Drop in Candelatech files
mv board-2-ct.bin /lib/firmware/ath10k/QCA9984/hw1.0/board-2.bin
mv firmware-5-ct-full-community.bin /lib/firmware/ath10k/QCA9984/hw1.0/firmware-5.bin

Note that this example was done for the WLE1216V5-20 wave 2 radio using a QCA9984 chipset. You may need to change your wget and /usr/lib/firmware/... targets accordingly.
Note that if you want to use the stock firmware you can just replace the board-2.bin file with CT's until the stock firmware supports the Wave2 cards properly.

Finally, to see what's current in ath10k, see here for more info

Wireless Testing

First, some testing vocabulary:

Symbol Legend
Key Meaning
AP Access Point
STA Station
<---> Ethernet Connection
<- -> Wireless Connection
(S) iperf server ⁽¹⁾
(C) iperf client ⁽²⁾
X Doesn't Work
NA Didn't Test

_{1. TCP server run with: iperf -s -w3M; UDP server run with: iperf -su}
_{2. TCP client run with: iperf -c $IP -i1 -t25 -w3M; UDP client run with: iperf -u -c $IP -i1 -t25 -b999M}

Infrastructure mode means the following:

1. Testing between AP and STA
(S)     (C)
AP<- ->STA

2. Testing between WAN and STA (Our standard infrastructure mode test)
(S)             (C)
PC-A<--->AP<- ->STA

Wireless Bridging means the following:

(S)                     (C)
PC-A<--->AP<- ->STA<--->PC-B

AdHoc means the following:

1. No Bridge
(S)       (C)
NODE1<- ->NODE2 (Our standard !AdHoc test)

2. With Bridge (Requires special software)
(S)                          (C)
PC-A<--->NODE1<- ->NODE2<--->PC-B

Below is an example setup of how we test and with what hardware:

No image "wirelesssetup.png" attached to wireless/wifi

_{1. 60dB Attenuators on each chain}
_{2. Directional Coupler (Krytar 1850 shown)}
_{3. Power Sensor (Agilent 8481A shown)}
_{4. Power Meter (HP E4418A shown)}

The image above shows our testing setup. In general, to test TX Power, we use a Power Meter + Power Sensor + Directional Coupler. Further, when people talk about performance, they typically are talking about throughput from AP<- ->STA. When we talk about performance, we spell out specifically which network topology we are testing, who is generating/sending packets, and who is receiving. This should make it very clear where performance numbers came from and how you can compare against them.

Performance

We define performance as the rate at which data can travel at. This essentially means looking at throughput numbers via performance tools such as iperf. One of the ways we stress test our product is by running it through conditions that our customers might use. Since we also support a wide variety of wireless cards, we test a whole lot. The below sections will talk about how to tune a product to get the best performance and talk about the numbers we've gotten for each card we've tested.

Performance Tuning

There are many characteristics that factor into performance (throughput):

Radio factors:
- use wider channel bandwidths for the highest bandwidth (ie HT40 for 802.11n or VHT80/VHT160 for 802.11ac)
- RF characteristics (look at the driver's rate control statistics to ensure you are achieving the expected modulation rate. Modulation rates are dynamic and achieving the best one will result in the highest bandwidth)
CPU factors:
- CPU performance bottleneck (which can be verified by watching output of 'top' while doing performance tests) can vary greatly based on SMP configuration, IRQ configuration, kernel netfilter modules, userspace services, and CPU cache configuration:
TCP Congestion control (affecting TCP performance)
- see TCP Congestion Control
- see TCP Small Queues

Additional References:

see Wireless Tuning for more information
see Multi-core Processing for more information

Performance Comparison (Measured Data Rates)

Below are our results with the following firmware modifications:

Firewall was turned off

802.11AC (ath10k|iwlwifi)

This table contains some throughput numbers (in Mbits/s) seen during testing.

Radio	Chipset	Platform	OS Used	Infrastructure Results²		Wireless Bridge Results³		AdHoc Results⁴
				TCP	UDP	TCP	UDP	TCP	UDP
3x3 ACE-DB-3	QCA9880	GW5400 (Ventana)	OpenWrt (14.08 BSP)	NA	NA	271	380	4	9
			Yocto 1.6 (backports 20140808)	NA	NA	NA	NA	NA	NA

3x3 WLE900VX	QCA9880	GW5400 (Ventana)	OpenWrt (14.08 BSP)	NA	NA	228	495	NA	NA
			Yocto 1.6 (backports 20140808)	NA	NA	NA	NA	NA	NA
		GW6300 (Newport)	Ubuntu (16.02 Xenial)	NA	NA	330	677	NA	NA

3x3 DAXA-O1	QCA9880	GW5400 (Ventana)	OpenWrt (14.08 BSP)	NA	NA	240	463	13¹	NA
			Yocto 1.6 (backports 20140808)	NA	NA	NA	NA	NA	NA

4x4 WLE1216V5-20	QCA9984	GW6300 (Newport)	Ubuntu (16.02 Xenial)	NA	NA	800¹	718¹	NA	NA

_{1. Best performing in this category}
_{2. Infrastructure tested by generating packets on PC-A and sourcing them on the STA. See the wireless testing section for more details}
_{3. Wireless bridging works only with the 10.1.467.2-1 firmware with upstream patches}
_{4. AdHoc works only with the 999.999.0.636 firmware and since there isn't wireless bridging, this number is based on NODE to NODE}

802.11N (ath9k)

Radio	Platform	OS Used	Infrastructure Results³		Wireless Bridge Results		AdHoc Results⁴
			TCP	UDP	TCP	UDP	TCP	UDP
1x1 GTM671WFSd	GW2387 (Laguna)	OpenWrt (13.06 BSP)	NA	NA	21	29	NA	NA
(miniPCIe)	GW2388-4 (Laguna)	OpenWrt (14.08 BSP)	NA	NA	NA	NA	NA	NA
	GW5400 (Ventana)	OpenWrt (14.08 BSP)	NA	NA	50	65	NA	NA

2x2 SR71-15	GW2388-4 (Laguna)	OpenWrt (13.06 BSP)	NA	NA	110	161	NA	NA
(miniPCI)		OpenWrt (14.08 BSP)	NA	NA	101	151	NA	NA
	GW5400 (Ventana)	OpenWrt (14.08 BSP)	NA	NA	92	112	NA	NA

2x2 WLM200N5-26	GW2388-4 (Laguna)	OpenWrt (13.06 BSP)	NA	NA	102	141	NA	NA
(miniPCI)		OpenWrt (14.08 BSP)	NA	NA	108	151	NA	NA
	GW5400 (Ventana)	OpenWrt (14.08 BSP)	NA	NA	88	106	NA	NA

2x2 SR71e	GW2388-4 (Laguna)	OpenWrt (13.06 BSP)	NA	NA	122	147	NA	NA
(miniPCIe)		OpenWrt (14.08 BSP)	NA	NA	102	151	NA	NA
	GW5400 (Ventana)	OpenWrt (14.08 BSP)	NA	NA	190²	245²	NA	NA

3x3 HNMA-H5	GW2388-4 (Laguna)	OpenWrt (13.06 BSP)	NA	NA	108	156	NA	NA
(miniPCI)		OpenWrt (14.08 BSP)	NA	NA	115	151	NA	NA
	GW5400 (Ventana)	OpenWrt (14.08 BSP)	NA	NA	111	119	NA	NA

3x3 WLE300NX	GW2387 (Laguna)	OpenWrt (12.10 BSP)	NA	NA	82.6	145	NA	NA
(miniPCIe)	GW2388-4 (Laguna)	OpenWrt (13.06 BSP)	NA	NA	100	138	NA	NA
		OpenWrt (14.08 BSP)	NA	NA	107	140	NA	NA
	GW5400 (Ventana)	OpenWrt (14.08 BSP)	NA	NA	240	367¹	NA	NA

3x3 WLE350N5-25	GW2388-4 (Laguna)	OpenWrt (13.06 BSP)	NA	NA	153	178	NA	NA
(miniPCIe)		OpenWrt (14.08 BSP)	NA	NA	150	181	NA	NA
	GW5400 (Ventana)	OpenWrt (14.08 BSP)	NA	NA	243¹	355	NA	NA

_{1. Best performing in this category (802.11n)}
_{2. Best performing in this sub-category (802.11n, number of chains, form-factor)}
_{3. Infrastructure tested by generating packets on PC-A and sourcing them on the STA. See the wireless testing section for more details}
_{4. AdHoc testing is based on NODE to NODE}

802.11ABG (ath5k|madwifi)

Radio	Platform	OS Used	Infrastructure Results²		Wireless Bridge Results		AdHoc Results
			TCP	UDP	TCP	UDP	TCP	UDP
CM9	GW2388-4 (Laguna)	OpenWrt (12.10BSP) + madwifi	NA	NA	10.4	11.5	NA	NA
		OpenWrt (12.10BSP) + ath5k	NA	NA	30.1¹	32.4¹	NA	NA

_{1. Best performing in this category}
_{2. Infrastructure tested by generating packets on PC-A and sourcing them on the STA. See the wireless testing section for more details}

WiFi Terminology and Concepts

TCP Congestion Control

Starting in Linux 2.6.7 (and back-ported to 2.4.27), Linux includes alternative congestion control algorithms beside the traditional 'reno' algorithm. 2.6.13 added support for plug-able congestion control algorithms set using sysctl variable net.ipv4.tcp_congestion_control which is set to bic/cubic or reno by default depending on kernel versions.

The Internet has predominantly used loss-based congestion control (largely Reno or CUBIC) since the 1980s, relying on packet loss as the signal to slow down. While this worked well for many years, loss-based congestion control is unfortunately out-dated in today's networks. On today's Internet, loss-based congestion control causes the infamous bufferbloat problem, often causing seconds of needless queuing delay, since it fills the bloated buffers in many last-mile links. On today's high-speed long-haul links using commodity switches with shallow buffers, loss-based congestion control has abysmal throughput because it over-reacts to losses caused by transient traffic bursts.

TCP congestion control algorithms can be configured in the Kenrel under 'Networking support (NET) -> Networking options -> TCP/IP networking (INET) -> TCP: advanced congestion control (TCP_CONG_ADVANCED). The default is typically CONFIG_TCP_CONG_CUBIC which builds in CUBIC (default) and Reno. A more modern algorithm called BBR was introduced more recently.

You can select between multiple TCP congestion control algorithms via userspace sysctl:

cat /proc/sys/net/ipv4/tcp_available_congestion_control # see available algos
sysctl net.ipv4.tcp_congestion_control=reno # select Reno

References:

TCP Small Queues (TSQ)

TCP Small Queues (TSQ) performs local flow control, limiting the amount of data in the queues on the sending host. Like TSO autosizing, TSQ has its own balancing act, keeping the queues small to reduce latency and head-of-line blocking (HoLB), while keeping the queues just large enough to ensure the queues on the sending host.

The kernel TSQ logic allows up to 1ms of bytes to be queued into qdisc and driver queues. However, Wifi aggregation (multiple streams) needs a bigger budget to allow bigger rates to be discovered by various TCP Congestion Control algos.

A patch has made it into the 4.15 kernel that allows wifi drivers to adjust this value as needed but drivers need to be updated to add this functionality.

Gateworks has a patch in the Newport kernel that allows userspace to change the default 1ms buffering time manually with sysctl. Increasing the buffering to something between 1ms and 9ms shows significant throughput increases for MIMO cards. For example:

sysctl net.ipv4.tcp_tsq_limit_output_interval=5 # use 5ms of buffering in TSQ logic

References:

mac80211

mac80211 refers to the Linux kernel 802.11 MAC layer software stack written for !SoftMAC radios. For many years all radio drivers utilize this layer and those drivers are referred to as 'mac80211 drivers'. An exception to this would be the popular 'madwifi' driver used for Atheros AR5XXX based 802.11abg radios (the mac80211 driver alternative to madwifi is the ath5k driver).

References:

http://wireless.kernel.org/en/developers/Documentation/mac80211

Regulatory Domain

Different regulatory domain's exist around the world that are regulated by various bodies - examples include the FCC for North Ameriaca, and ETSI for many European countries. Modern Linux mac80211 based drivers use the crda (Central Regulatory Domain Agent) userspace agent for regulatory domain rule database and checking. It is comprised of a database of regulatory domain rules.

Alternatively mac80211 can be configured at compile-time with CONFIG_CFG80211_INTERNAL_REGDB to use an internal regdb based on net/wireless/db.txt which can be easier to udpate if need be for your application (providing you are making changes that are legal in the regulatory domain you will be operating in). One example of where this would be useful is if you are licensed to operate in the US Public Safety band, which crda has no support for.

Notes:

OpenWrt uses this option
If you enable CONFIG_CFG80211_INTERNAL_REGDB and fail to overwrite the default net/wireless/db.txt a default domain will be used which sets the 'no IR' flag on all channels (meaning you can not transmit)

References:

Automatic Channel Selection (ACS)

The Automatic Channel Selection (ACS) feature is useful if you want the operating channel to be selected based on usage in your area. A specification exists on how this is done.

Notes:

a modern hostapd (2013-11-21) must be used and built with CONFIG_ACS
specify channel=0 or channel=acs_survey in hostapd.conf

References:

http://wireless.kernel.org/en/users/Documentation/acs

Dynamic Frequency Selection (DFS)

Dynamic Frequency Selection (DFS) is a specification required by certain regulatory domains on specific channels in order to eliminate conflicts with weather and government/military radar equipment. For this reason it is sometimes know as 'radar detection' (which is likely a better description of it). This is often required for channels on the 5.8GHz band and there are specific rules for how and if a radio can transmit on these channels.

Because DFS is complex many small office and home office AP's as well as some enterprise AP's don't allow operation at all on DFS channels in the 5GHz band and many client devices are not certified for DFS operation.

Notes:

a modern hostapd (2013-11-21) must be used
not supporting DFS limits the channels that can be used:
- In the US (FCC regulatory domain) there are 4 channels in the 5.8GHz band that do not require DFS and 4 that do

The ath9k as well as ath10k (and possibly others) fully support ETSI DFS and FCC DFS requirements according to reports on the linux-wireless maillist and various radio certifications.

References:

http://wireless.kernel.org/en/developers/DFS

Antenna Selection

MIMO (Multiple-In Multiple-Out) radios (802.11n and 802.11ac) have multiple transmit and multiple receive antennas (also known as 'chains'). On some devices/drivers you can configure which are used for tx as well as rx using the 'set antenna' command:

iw phy0 info | grep Antenna # show available Antennas
iw phy0 set antenna 1 2 # set tx for antenna1, rx for antenna 2
iw phy0 set antenna 1 3 # set tx for antenna1, rx for antenna 2 and 3

the values are a bitmask (ie 1 for antenna1, 2 for antenna2, 4 for antenna 3, 3 for antenna 1&2, 6 for antenna 2&3 etc)
typically the interface needs to be in a down state (ifconfig wlan0 down) in order to set the antenna selection bitmasks
not all drivers support this

Guard band Interval (GI)

The guard band interval describes how long you wait in between packets before transmission. For 802.11 OFDM this is 800ns hjwever 802.11n (also supported in 802.11ac) introduced a 400ns option to increase data-rates. This new 400ns GI is referred to as a 'short' GI and the original 800ns is referred to as a 'long' GI.

Notes:

The rate control algorithm may decide between short GI and long GI based on statistics and alternate this over time

Channel Width

Channel Width refers to the bandwidth per channel and varies per 802.11 mode:

802.11b - defines 20MHz channel width (this allows for 3 non-overlapping channels out of the 11 channels defined in the 2.4GHz band)
802.11n - added the capability of 40MHz channels referred to as 'HT' or High Throughput channels. When using 40MHz HT channels you must specify HT40- to use the current channel specified frequency and the 20MHz below it, and HT40+ to use the current channel specified frequency and the 20MHz above it
802.11ac - added the capability of 80MHz and 160MHz channels referred to as 'VHT' or Very High Throughput channels
- Wave 2 - added an 80+80MHz configuration that could be set for two non contiguous bands to minimize interference

Some drivers also support 'half' channel bandwidth (10MHz) and/or 'quarter' channel bandwidth (5Mhz) which is useful if you don't need the bandwidth provided by standard (20MHz) channels or HT/VHT channels and instead want more channel separation.

Note that as you increase the channel width, you increase channel overlap and decrease separation.

Modulation Rates

Various 802.11 specifications allow for varying modulation schemes which trade off error resilience, throughput, and effective distance. Each transmission can vary the modulation scheme and A 'rate control algorithm' has the ability to change this dynamically for each node being transmitted to based on different statistics.

Modulation Schemes:

802.11b - allowed for 1M, 2M, 5.5M, 11M CCK modulation rates
802.11g - added additional OFDM modulation schemes to allow for 6M, 9M, 12M, 18M, 24M, 36M, 48M, and 54M modulation rates
802.11n - added additional modulation schemes to allow several more rates and introduced the concept of a Modulation and Coding Scheme (MCS) index to describe them
802.11ac - added 2 additional MCS indexes for new 256-QAM modulation schemes
- Wave 2 - Improved on the original Wave 1 release by adding MU-MIMO and an optional 4th spatial stream, see this Cisco FAQ for more information

Notes:

you can use the 'iw dev wlan0 set bitrates' command to set bitmasks to indicate which modulation rates to allow
there is not a standard mac80211 way to determine what modulation rate is being used, or what the rate control algorithm is doing
some devices/drivers use the mac80211 rate control algorithms (there are 2 to choose from at compile time) and others use algorithms baked into device firmware
Modulation Table Online

Adhoc mode (IBSS)

Though not part of the 802.11 spec (was part of the 802.11 draft), a popular mode is referred to as 'adhoc' mode or 'IBSS' mode. In this mode there is no authentication/de-authentication and no concept of an Access Point. Instead a 'network' is defined by the 'BSSID' used by the nodes. Network discovery is performed by listening to beacons and beacon transmission is shared by nodes in a BSSID (each node has a beacon timer with a random backoff interval which is reset when a beacon matching the nodes network is received which tends to share the beacon transmission load). A scheme was defined so that nodes would join a network if a beacon is received matching the nodes network configuration and BSSID's would 'merge' depending on timestamps however this is not implemented consistently and can cause issues such as merge storms across various drivers/chipsets. Because of this often adhoc networks will define a BSSID instead.

Because adhoc mode is not in the 802.11 spec and is not as popular as infrastructure mode (AP/STA) it isn't always as stable as infrastructure mode.

While not required, Adhoc networking is often used as the underlying connection mode for layer2 (MAC layer) and layer3 (IP layer) MESH networks such as olsrd.

When using adhoc mode, you do not need hostapd or wpa_supplicant and the iw tool can be used to join/leave adhoc network:

iw phy phy0 interface add wlan0 type ibss # create an interface on phy0 called wlan0 configured for adhoc mode
iw dev wlan0 ibss join myssid 5180 # join the 'myssid' network, on 5180MHz (20MHz) and rely on IBSS discovery and merging
iw dev wlan0 ibss leave # leave the adhoc network

Some other useful commands for adhoc nodes:

iw dev wlan0 set type ibss # change an existing wlan0 device to ibss mode (if must be down)
iw dev wlan0 ibss join myssid 5180 0a:0b:0c:0d:0e:0f # join the 'myssid' network, on 5180MHz (20MHz) with fixed bssid
iw dev wlan0 ibss join myssid 5180 HT40- 0a:0b:0c:0d:0e:0f # join the 'myssid' network, on 5180MHz (40MHz using 5180 and the ch below) with fixed bssid

Frame Aggregation

As data rates increase the overhead of management and headers starts to create bandwidth bottlenecks. The 802.11n specification introduced the concept of Frame Aggregation to combat this. Two types of aggregation was introduced: A-MPDU and A-MSDU.

This does not need to be enabled and should be used automatically by the driver if the card has the capability.

References:

http://en.m.wikipedia.org/wiki/Frame_aggregation

Quality of Service

The 802.11e specification added various aspects to 802.11 to create the concept of multiple data queues with different priorities in order to create a quality of service.

References:

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Symbol Legend
Key	Meaning
AP	Access Point
STA	Station
<--->	Ethernet Connection
<- ->	Wireless Connection
(S)	iperf server ⁽¹⁾
(C)	iperf client ⁽²⁾
X	Doesn't Work
NA	Didn't Test

Context Navigation

802.11 WiFi

Common Wireless Radio Hardware

​Doodlelabs Prism-FES (Front End Subsystems)

Part Numbering Scheme

Licensed vs Unlicensed

Frequency Shifting/Power Level Mappings

References

Gateworks BSP Support

OpenWrt Wireless Configuration

Yocto Wireless Configuration

Android Wireless Configuration

Ubuntu Wireless Configuration

Wireless Configuration (Standard Linux)

iw

hostapd

Access Point Configuration (AP)

Step 0 : Scan Available Options

Step 1 : Configure Access Point

Step 2 : Copy Access Point Configuration

Routed Access Point

Bridged Access Point

Troubleshooting

wpa-supplicant

Linux Kernel Drivers

Atheros AR5xxx 802.11abg cards (ath5k)

Atheros AR9xxx 802.11abgn cards (ath9k)

Atheros AR10xx 802.11ac cards (ath10k)

Verifying / Checking Firmware Version

Alternative Firmware instructions

Candelatech

Wireless Testing

Performance

Performance Tuning

Performance Comparison (Measured Data Rates)

802.11AC (ath10k|iwlwifi)

802.11N (ath9k)

802.11ABG (ath5k|madwifi)

WiFi Terminology and Concepts

TCP Congestion Control

TCP Small Queues (TSQ)

mac80211

Regulatory Domain

Automatic Channel Selection (ACS)

Dynamic Frequency Selection (DFS)

Antenna Selection

Guard band Interval (GI)

Channel Width

Modulation Rates

Adhoc mode (IBSS)

Frame Aggregation

Quality of Service

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Doodlelabs Prism-FES (Front End Subsystems)