* Getting Wi-Fi clients to see and hear each other
If your Wi-Fi performance is degrading, one contributor could be multiple client devices that are all within range of a common access point but too far away from each other to detect the others’ presence.
Having a very dense AP deployment tends to help this situation, because the overlapping “circles” of coverage are smaller, which means their diameter (or distance between client nodes) shrinks, and nodes are more likely to sense one another. If using the 2.4GHz band, though, your circles can only be so small before the three nonoverlapping channels will interfere with their nearest neighbors in the same band.
Some of the RF management products – whether embedded in your WLAN system or in the form of a third-party overlay system – will help you detect a hidden-node situation.
Once the situation is detected, one option is to increase the power levels in the client nodes, so they are more likely to see one another. This won’t help, however, if there is something in the way – such as a cement or steel wall – obstructing the devices’ signals. This, of course, is something to account for in your upfront site survey.
You might also consider replacing directional antennas with omnidirectional antennas. This will let the antennas sense in 180 degrees, delivering a greater chance of the client’s picking up another’s signals. Doing so has to jibe with your security strategy; you may not wish to have WLAN signals spilling outside of the building’s walls in all directions.
Note that the 802.11 request to send/clear to send (RTS/CTS) protocols help. These protocols send some clients permission to transmit while asking others to wait a time period, in an attempt to coordinate transmissions. However, given the dynamic nature of wireless networks, and as the number of clients increases, this isn’t foolproof.
The 802.11e QoS standard, meanwhile, now also contains protocols for call admission control, a stronger traffic coordination function aimed primarily at giving VoIP QoS. It’s possible that this mechanism can be used for further coordinating client-to-AP transmissions for other traffic, as well.
