Surveying with the AirMagnet Tool
Chapter 10, you learned about the AirMagnet Surveyor tool. The recommended technique for use of the AirMagnet Surveyor tool is very similar to the inside-out survey methodology. The AirMagnet Surveyor tool measures all the critical values for determining cell boundary locations and provides graphical assistance for collecting and documenting the survey results. After you create a new project (as discussed in Chapter 10), import the floor or building plan graphics file and specify the scaleyou are ready to start collecting data. To begin the data collection in active mode, select a starting position near the perimeter of the area to be covered and physically stand there with the survey tool. Click on this location in the AirMagnet tool to indicate the starting point on the floor plan map. A small stick man will appear at this spot. Begin the walkabout by moving at a smooth pace to the next check-point in the path; stop briefly to click this spot and then continue. The more locations that are used to collect data, the more accurate the survey data will be. It is also important to move at a uniform pace so that the collected data is similar for all parts of the facility. The Survey tool control area displays various real-time data as the walkabout proceeds, which is used to monitor the instantaneous state of the link. The signal-strength, noise-level, link-speed, and packet-loss statistics all display. You can use these indicators to monitor the signal conditions from the test AP and make decisions about the coverage boundary for a given service level specification. If each AP cell of coverage is specified to support a minimum link rate of 5.5 Mbps (for 802.11b), for example, the coverage boundary can be found by walking to points where the Speed indicator crosses from 5.5 Mbps to 2.0 Mbps. Then move back into the solid 5.5-Mbps area to determine the edge of the cell where the performance is stable and record that location. As recommended previously, the initial configuration of the active mode survey tool should set the packet size to most closely resemble the data payload of the real WLAN applications. The next step is to place icons representing the test AP or existing APs in a network. A drop-and-drag tool enables you to easily add the graphics display. The view in Figure 11-15 shows this simple process. First click the Add AP Icon button on the graphics toolbar on the right side of the screen. The dialog box displays, enabling you to add a name. Then drag the AP icon to the appropriate location on the floor plan. Figure 11-15. Adding AP Locations to a Floor MapIf you select the display mode toggle button on the lower toolbar, Surveyor will display data collected from the survey. Two new panels appear in this mode: the Filter area in the center-left panel and the map zoom box in the lower left. First, choose one or more survey data sets to display by clicking the appropriate check-box(es) in the data catalog area in the upper left of the screen. Then choose the display parameter for the data sets, by making a selection from the drop-down menu in the upper-right corner of the floor plan display area. You have the following choices: Signal Noise Speed S/N ratio
Finally, enable appropriate filters to the data. The survey data will then display as color-coded zones tied to the legend shown. For signal level, shown in Figure 11-16, colors represent 10-dBm levels. Figure 11-16. Displaying Survey Results |