Advice for setting up a WLAN
I need help setting up a WLAN. I want to cover an area of over 3 square kilometers with wireless. I am planning to do this using 2.4 GHz omni-directional wireless antenna(s). Would a wireless enabled laptop be able to establish two-way communication to the Internet, through an access point that covers such a large area? Or, if I were to place a number of access points within that coverage area, could I use these to establish a number of separately managed small WLANs, to offer services like wireless printing for the clients of each network? Would there be interference between distribution of wireless signal from a central source to the APs, and wireless signal from each AP to the clients?

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It's highly unlikely that a single 802.11g/b AP, outfitted with an omni-directional antenna, will provide adequate signal strength coverage to clients distributed across a 3 square kilometer area. You may very well pick up weak/intermittent signals that far away in open space, but your clients will need a consistently strong signal to browse the Internet, etc... You are probably better off positioning APs in strategic locations throughout your intended coverage area, taking into account client locations, physical obstacles, and channel overlap with adjacent APs.

From your question, I assume that you want to use wireless bridging to backhaul traffic from distributed APs to a central point of Internet access. To avoid cross-channel interference between distributed WLANs and backhaul connections, you'll need to assign non-overlapping channels (e.g., 1, 6, 11 for 802.11b/g). Because you'll also need to avoid interference between distributed WLANs, you may want to consider using 802.11a for your backhaul connections. By using 802.11a, you'll have more non-overlapping channels to choose from, and your backhaul connections will be better insulated from overhead activity (e.g., clients probes/responses) generated by your distributed WLANs. Alternatively, you could use another kind of backhaul network - for example, a wireless mesh interconnecting your distributed APs, or wired backhaul connections. Mesh networking is becoming increasingly popular in municipal wireless networks -- for example, see BelAir Networks, Strix Systems, and Tropos.

This was first published in May 2005