QCA wireless settings

From DD-WRT Wiki

Revision as of 08:42, 29 July 2010 by Tatsuya46 (Talk | contribs)
Jump to: navigation, search



This page shows the contents and descriptions of advanced wireless settings for Atheros based Routers. If you are a Broadcom user, please refer to this page for Broadcom advanced wireless settings.

Advanced Settings

Regulatory Domain

This determines the channels available in the list for both bands (if you have a dual band router) and the maximum EIRP "legally" allowed by the FCC for the chosen country. EIRP is TX power plus antenna gain, an example.

20dBm TX power and 2dBi antenna gain has an EIRP of 22dBm. 22dBm TX power and 0dBi antenna gain also has an EIRP of 22dBm.

Maximum EIRP varies by nation and your max TX power will be capped by the regulatory domain if you have a powerful radio. For example, Canada's max EIRP is 36dBm, with Canada selected and antenna gain at 0dBi. The radios will never go above 36dBm.

TX Power

Transmit power (TX) is the amount of "current" or "juice" going to the antennas, it is NOT the output power FROM the antennas, as that is EIRP. Usually more TX power is better as it allows clients further away to "hear" your AP. Assuming the clients also have near equal TX power so the AP can "hear" them back. If TX power is increased too much excess noise can develop and reduce throughput or even rage, but with Atheros this does not seem to be much of a problem as most Atheros radios work very well at their max TX power. Maximum TX power is controlled by the radios, regulatory domain, wireless channel used, and wireless channel width. The default value for most routers currently is 20dBm.

Antenna Gain

Antenna gain is amount of "gain" or "boost" of signal that the antenna provides. Its a bit complicated but remember this, antennas are not amplifiers. They do not magnify the signal, but instead "focus" the signal in certain directions, yes even omni directional antennas do it. The higher the gain the better as it increases EIRP which somewhat helps extend range and significantly helps sensitivity. With high sensitivity, the AP is able to hear "faint" clients, clients that may have a low TX power or are just simply very far away. Set this to the correct value of the antennas used on your router, it does do a difference, small, but its there.

Protection Mode

Available Settings: None, CTS, RTS/CTS

This setting controls whether the clear to send/request to send mechanism is enabled or disabled. When enabled, a RTS/CTS handshake must be completed before data can be transmitted. Sometimes helpful in noisy environments it ensures all clients "take turns" communicating with each other or the AP, if disabled sometimes packet collisions can occur causing a drop in throughput due to retransmission overhead. This is a setting to experiment with if you have high TX/RX packet errors especially in a short time. Most users should leave this set to none for max throughput, enabling RTS/CTS when not needed generates more overhead, most people should not need to enable this on the AP as the AP can already see all the clients connected to it. It is more beneficial to be enabled on the clients' NIC card in an Ad-Hoc environment, and only the more expensive NIC cards offer this feature.

RTS Threshold

Only valid if RTS/CTS is enabled, this setting sets the maximum packet size before it is fragmented into smaller packets, if you still have high TX/RX errors with RTS/CTS enabled and RTS Threshold at it's default, try lowering it by 10. Lowering it too much can further create overhead and reduce throughput. Leaving this on the default setting 2346 essentially disables the RTS feature and only leaves CTS enabled as most packets don't exceed 2346 bytes.

Transmission Minimum & Maximum Rate

Available Settings (B-Only): Auto, 1 Mbps, 2 Mbps, 5.5 Mbps, 11 Mbps

Available Settings (G-Only HT20): Auto, 6 Mbps, 9 Mbps, 12 Mbps, 18 Mbps, 24 Mbps, 36 Mbps, 48 Mbps, 54 Mbps

Available Settings (G-Only HT40): Auto, 12 Mbps, 18 Mbps, 24 Mbps, 36 Mbps, 48 Mbps, 72 Mbps, 96 Mbps, 108 Mbps

Available Settings (BG-Mixed ): Auto, 1 Mbps, 2 Mbps, 5.5 Mbps, 6 Mbps, 9 Mbps, 11 Mbps, 12 Mbps, 18 Mbps, 24 Mbps, 36 Mbps, 48 Mbps, 54 Mbps

Available Settings (NG-Mixed HT20 or 40): Auto, 1 Mbps, 2 Mbps, 5.5 Mbps, 11 Mbps

Available Settings (N-Only 2.4GHz HT20 or 40): Auto, 1 Mbps, 2 Mbps, 5.5 Mbps, 11 Mbps

Available Settings (Mixed HT20): Auto, 1 Mbps, 2 Mbps, 5.5 Mbps, 6 Mbps, 9 Mbps, 11 Mbps, 12 Mbps, 18 Mbps, 24 Mbps, 36 Mbps, 48 Mbps, 54 Mbps

Available Settings (Mixed HT40): Auto, 12 Mbps, 18 Mbps, 24 Mbps, 36 Mbps, 48 Mbps, 54 Mbps, 72 Mbps, 96 Mbps, 108 Mbps

This setting controls the minimum and maximum theoretical rates for connected clients, on certain wireless network modes such as NG-Mixed this setting does not work properly, if at all. It is recommended to leave this setting on Auto.

Short Preamble

Available Settings: Enable, Disable

If you have 802.11b clients in your network try enabling this, if they have problems connecting or with performance then leave it disabled. Preamble is at the head or front of the PLCP which devices need in order to start transferring data. The long preamble ensure compatibility with legacy 802.11b devices but can slightly reduce throughput at high data rates. The support for short preamble which is reducing the header's size by 50%, down to 9 bytes, is optional for 802.11b. 802.11g and newer all support short preamble, so if you do not have and 802.11b devices in your network you can enable this for a small throughput increase.

TX & RX Antenna Chains

Available Settings:1+2, 1+3, 1+2+3

This setting is critical to proper, smooth, fast Wi-Fi performance. 2x2 routers will either have TX/RX chains at 1+2/1+2, 1+3/1+3, 1+2/1+3, or 1+3/1+2. This can take some time to find the proper setting but its worth it, you can more easily find the correct setting by using a 802.11n draft 2.0 client thats capable of 300 Mbps link. Note the TX/RX link rates on the wireless status page, when set incorrectly one or both of the rates will drop to a much lower speed such as 200, 170, 81 etc. This is best done with the client less than 10 feet from the AP with clear line of sight. Some routers with chains set incorrectly such as D-Link DIR-615 C1, will deny connections to clients, heavily reduce throughput, and other errors. Searching the FCC ID of your router will aid in setting the correct chain settings. Some popular router such as the Netgear WNDR3700 and D-Link DIR-825 B1/B2 require both chains set at 1+2 for proper Wi-Fi performance. Default is not always right!

AP Isolation

Available Settings: Enable, Disable

AP Isolation allows clients connected to the same AP to communicate with each other or not, very much like Ad-Hoc mode. If you run a Wi-Fi hotspot its recommended you enable this for privacy reasons. If you want files to be shared from client to client in your home network, AP isolation must be disabled. This setting does not influence Wi-Fi throughput.

Radar Detection

Available Settings: Enable, Disable




Sensitivity Range (ACK Timing)

Available Settings: 0 - 999999

ACK timing is also a throughput controller, too high and your devices will literally be "waiting" too long and time will be passing with them at idle. Too low and active transmissions could be cut off causing retransmissions which create overhead, that lowers throughput. The AP sends a packet and all clients must wait for XXX time, where XXX is the ACK timing, the client then receives that packet and responds to the AP with an ACK(nowledgement), AP sees the AP then finally everyone is free to transmit. For Atheros routers 0 will not disable ACK timing, but set it into auto mode. This setting is not recommended unless you know what you are doing as auto takes a few real world seconds to adjust to, causing a latency spike everytime.

Most users want this between 1000 - 1500, the distance used is meters and needs to be doubled the distance of the furthest client from the AP (plus some headroom). Doubled because the signal travels to the client and back, double the distance. Reducing ACK from default 2000 to even 1500 causes a throughput increase of 0.7 Mbps - 1.1 Mbps and range won't be affected as most routers don't even get 1000m range in a residential area.

Long distance links, such as 2km or more will need to increase this setting accordingly. 2000m for 2km, 3000m for 3km, and so on.

Max Associated Clients

Available Settings: 1 - 256

Determines the maximum number of clients that can be connected to the AP at any given time. Hotspot users will find this very handy.

MTik Compatibility

Available Settings: Enable, Disable


Network Configuration

Available Settings: Unbridged, Bridged

This setting controls if the wireless interface is "bridged" with the LAN ports. Bridged meaning a client on the wireless interface and a client on the Ethernet LAN interface are on the same network on the same subnet. Unbridged allows you to "separate" the WLAN (wireless LAN) by giving it its own subnet and even its own DHCP server.