WLAN Design
Load and coverage

There will be pools of coverage at each data rate. If the customer wants to provide a certain area with coverage at a specific data rate, multiple site surveys may be necessary. Each data rate must be surveyed to find out where the coverage pool is for each data rate.

In order to determine where to place the APs, it is important to find out how much throughput the users will require. Bandwidth requirements for wireless connectivity will potentially determine the number of APs that need to be used. If a constant speed is required and that speed is fairly high, such as 11 Mbps, then the coverage will be fairly low and a high number of APs will be required.

In many situations, AP coverage will be the driving factor over bandwidth and autorate negotiation of bandwidth can be used. With autorate negotiation, the client picks the best speed at its current distance, so as the client moves from a close proximity to the AP, it uses a high bandwidth such as 11 Mbps. As the client moves outward from the AP and the distance increases, the bandwidth is reduced to allow for the best possible signal quality.

The load on an access point or the total number of potential clients should be considered in any design. One problem with WLANs is that the number of potential clients can be unknown, since the freedom of wireless allows any number of people to converge within an area. The maximum number of clients as dictated by the address table in the access point is 2048. This maximum is not practical, because WLANs are a shared infrastructure, which is similar to hubs in a wired network.

Each individual user has less overall bandwidth available as more clients are added to an AP. This might be acceptable for variable bandwidth applications. However, for many applications, especially with modern data-intensive graphical environments, this may not be adequate. Distributing the clients among more access points, particularly in congested areas, easily solves this problem. This serves to distribute the load, via overlapping coverage between APs. Make sure that each AP is communicating on its own unique channel to prevent interference with each other. If only two APs are going to have overlapping coverage, then any two different channels can be used between one and 11. When using the 11 channel implementation used in the US, the maximum number of APs that can be used concurrently is three. This is because only three channels do not overlap with each other, which are channels one, six, and 11 as shown in Figure . If additional bandwidth is required, 802.11g can be utilized. If the 2.4 GHz band is crowded by other devices, 802.11a provides another high speed option.

In some environments, bandwidth and AP load are strong design factors for a WLAN implementation. One way to ensure that a small area of users access a selected AP, is to manipulate the power settings on the AP to adjust the size of the cell. This adjustment will create cells that cover specific areas.