Wireless can seem like a mystery, but that’s mostly because it’s invisible. Slow speeds and connectivity issues can be caused by a number of different unseen variables. Some of which cannot be overcome by simply buying new WiFi equipment. Below are some common wireless problems that can be discovered and remedied by using inSSIDer Office.
This concept is obvious, especially since all of us carry mobile phones in our pockets—you’ve got to have signal coverage in order to pass data over the wireless network. In WiFi, of course this is no different, if there is no signal or very weak signal at the location you need, connectivity is impossible.
What to do: Measure signal strength with inSSIDer Office in the areas you need connectivity. A good rule of thumb is that you at least need -80 dBm for any sort of usable connection. For applications like Voice-Over WiFi, vendors recommend -67 dBm as a minimum. Relocating or adding wireless access points should be considered.
Low Signal Strength
As signal strength diminishes, it becomes more difficult for wireless packets to make it to and from wireless stations. In order to keep communication going, WiFi has mechanisms built into it that simplifies the modulation so it’s more robust while dealing with weak transmissions. Although these modulation methods keep devices connected to the network and passing data, it absolutely slows down speeds as the simpler modulations trade throughput for robustness. Low signal strength = a low connected rate which creates low throughput over WiFi.
Two things cause a low signal strength condition: distance and physical obstacles such as walls and doors. Different physical obstacles (and the material that they’re made out of) cause different amounts of loss. Below are some examples:
Dry Wall: 3 dB
Hollow Wood Door: 4 dB
Brick Walls: 6 dB
Concrete: 8 dB
Refrigerator: 19 dB
Left: WiFi signals in free space. Right: WiFi signals going through objects and building materials.
(Keep in mind that like the Richter Scale, the dB scale is not linear, but rather logarithmic. E.g. a 3 dB drop in signal equates to a 50% drop in power.)
What to do: Again, access point location is key here. Place access points in a central place where signal will not be blocked. Places like inside server closets, or on steel shelving negatively affects signal and therefore speed. Move or add access points so they are in the open and out of the way from high-loss materials. Use inSSIDer Office to check signal strength in key areas.
Co-Channel “interference”: The more WiFi networks and devices that share a channel, the slower the speed for everyone. The reason behind this is that WiFi devices on the same channel can only talk one at a time. Each WiFi device “waits it’s turn” to communicate as WiFi technology has mechanisms in place to coordinate which station can transmit packets at what time. This cooperation is done between the devices in your network, as well as between your WLAN and your neighbors’ WLAN that share your channel. The more contention for ‘airtime’, the fewer the time slots to go around for every device and slower speeds results for everyone.
Adjacent channel interference: neighboring wireless LANs that are not on the same channel, but rather on an overlapping channel cause speed issues for 2.4 GHz networks. Unlike networks that share the same channel, adjacent channel networks cannot communicate with each other a transmission cooperation scheme and inevitably stations end up transmitting at the same time in which packet collisions occur. When wireless packets collide, the intended receivers get garbled, unreadable packets that have to be sent again for the transmission to complete. In relative terms, this is why adjacent channel interference is worse than co-channel interference--no cooperation and packet “timing” is in place and packet collisions slow down network speeds for everyone.
What to do: Use inSSIDer for Office to pick channels that have the fewest co-channel and overlapping networks. Remember, adjacent (overlapping) channel interference is worse than co-channel interference.
Even more detrimental to speed and connection than co-channel and adjacent channel interference from neighboring WLANs is interference from non-WiFi devices. Typical interfering devices include:
Wireless Audio Systems
Wireless Security Systems
...and hundreds of other devices
Why these devices are especially damaging to WiFi connectivity and speed is because these do not “speak the same language” of WiFi. That is, because WiFi and these devices share the same frequencies, and these technologies do not understand each other WiFi packets end up garbled at the receiver. Plus, a lot of non-WiFi devices use analog signals that are very constant and loud making them especially damaging. If you have excellent signal strength, and there are few other WiFi networks around and still experience dropped signals, non-WiFi interference just may be the culprit.
What to do: Use inSSIDer Office’s spectrum graphs to look for raw RF interference. If bright colors are found on your operating frequencies, avoid it by switching channels on your wireless access point.