Channel selection is very important. The wrong channel on your wireless router can cause you to pull you hair out thinking what can be wrong with the wireless setup. Interference is a real threat in case of a Wi-Fi network. Selecting the correct channel can asave you hours of grief.
The table below lists the ETSI specified frequencies and corresponding channel for European operation of Direct Sequence Spread Spectrum:
Channel No. European Frequencies
1 2401 – 2423 MHz
2 2406 – 2428 MHz
3 2411 – 2433 MHz
4 2416 – 2438 MHz
5 2421 – 2443 MHz
6 2426 – 2448 MHz
7 2431 – 2453 MHz
8 2436 – 2458 MHz
9 2441 – 2463 MHz
10 2446 – 2468 MHz
11 2451 – 2473 MHz
12 2456 – 2478 MHz
13 2461 – 2483 MHz
Each Channel is 22 MHz wide and uses a 1 MHz carrier frequency. As you can see from the diagram, the channels are spaced at 5 MHz intervals. e.g. Channel 1 operates from 2401-2.423 GHz/ Out of the 13 Channels available in most European countries under the ETSI standard in the 2.4 GHz ISM band (which covers 802.11b and 802.11g) only 3 channels at any one time are unique.
1, 7, 13 (preferred) do not cross over at all against each others frequencies, and for this reason we tend to use these most as the preferred channels for transmissions.
Channels 2, 3, 4, 5, 6, 8, 9, 10, 11, 12 all overlap into other channels beside themselves, and this can cause interference to any other transmission signal.
Note: 1, 6, 11 are also unique, however for ETSI and this guide we will use 1, 7, 13 as they are the furthest apart as well.
When setting up your wireless network you should take into consideration other wireless Cells active in your area, and change SSID and Channels to accommodate you and your neighbours. Furthermore there are also a few things to tweak your wireless router to get the best out of the signal without loosing connection.
Position the Router in the highest place possible. Don’t put it in the basement this will affect wireless signal strength.
Keep it away from large metal objects such as filing cabinets.
Try to keep the AP’s away from operating microwave ovens and 2.4GHz cordless phones. In addition, if you use 2.4 GHz phones and experience interference, try using a different channel on the phone.
If one of the Wireless computers can obtain an IP address but can not ping, then set the “RTS Threshold” to something lower. (no lower than 2304 though)
Adjusting the “Beacon Interval” can help association problems. If there is a wireless adapter that is able to see the access point, but is unable to get locked, try adjusting the “Beacon Interval” to 50 Adjusting the “Fragmentation Threshold” can help association problems.
If there is a wireless adapter that is able to see the access point, but is unable to get locked, try adjusting the “Fragmentation Threshold” to something lower. (no lower than 2304 though)
If you have just one or two clients enabling frameburst will help.
Adding a Directional Antenna to your wireless PC’s will help in reception.
You can adjust the signal strength output of the routers. The default for most routers is 18mW. You can increase this drastically with upto a max of 100mW. Putting the transmission rate beyond 100mW is illegal in ETSI/FCC standards. Also Heat is an issue of the radio chip set when putting the power up to 251mW, and the signal gets “dirty” and channels either side of the one you have slect can be affected.
One other thing: The signal strength maybe adequate but the reception is the problem. You can sometimes gain better signal strength by adding a reflector than adding any bigger antennas.
Here are is a short list on common causes of interference:
WINDOW IN BRICK WALL = 2dB METAL FRAME
GLASS WALL INTO BUILDING = 6dB
OFFICE WALL = 6dB
METAL DOOR IN OFFICE WALL = 6dB
CINDER WALL = 4dB
METAL DOOR IN BRICK WALL = 12.4dB
BRICK WALL NEXT TO METAL DOOR = 3dB