Survey
Channel selection, data rates, and overlap

When surveying, remember that there are only three nonoverlapping channels for 802.11b . In order to maximize the data rate, use these channels. The use of nonoverlapping channels ensures that the APs will not interfere with each other.

When designing the WLAN, survey using the channel on which the AP is intended to operate. A test for interference is required as part of the survey. If every AP is surveyed using the same channel, and not the actual channel the AP will be using, there is no certainty that no interference exists on the channel that the AP will actually be using. After determining the minimum data rate the customer will be using, survey at that data rate .

The chosen data rate will drastically affect the results of the site survey. In the example in Figure , the same warehouse is surveyed at two different data rates. If six APs are required to cover the facility at 2 Mbps, twelve APs might be required at 5.5 Mbps.

It is important to know what the customer needs. If a survey is completed at the wrong data rate and the customer installs the WLAN, the connection may only work in certain areas, or it may not work at all.

If there is too much overlap, the wireless engineer may encounter a situation where an additional AP would provide too much coverage, but the current number of APs provides too little coverage . The engineer can solve this in a number of ways. The first option is to use a different antenna to obtain more coverage from the APs. The second option is to use smaller antennas and add more APs. Another possibility is to change the power levels on one or more of the APs to change the size of the coverage cells. The final option is to use a combination of these options to obtain the necessary coverage.

This process is one of trial and error. Therefore, experience plays a vital role. Site surveys are often like puzzles. Sometimes individuals are so sure that they have discovered the best solution that they fail to see other possible solutions. Whenever possible, ask other wireless engineers about their surveys. Creative solutions may be found that can be implemented in future designs.

Sometimes an engineer will survey a few APs, only to discover that the proposed plan will not work. Instead of starting the process over, an engineer may try a series of options to find the last piece of the puzzle.

Sometimes site survey problems are due to frustration or laziness. An engineer might become focused on one solution to avoid having to start the survey over again. In this situation, it is best to take a break from work. This is a good time to go for a cup of coffee, check voicemail, or take a lunch break. The best solution will often present itself after this type of a break. If not, it may be necessary to start over. There may be trouble spots that had been overlooked the first time. When completing the survey the second time, these trouble spots will be evident and can be factored in when planning the new layout of the APs. It is always better to start the survey over and design the WLAN properly than to try and force a solution or use a solution that may not provide the best coverage.