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Steps in the Site Survey Process

RF engineering for specific sites is not an exact science, and therefore neither is the practice of doing site surveys. There are many, many ways to perform a site survey, and of all these different methods many are just fine. Because one engineer prefers method one but another engineer prefers method two does not necessarily make one method better or more correct than the other. However, both methods should provide similar resultsthat is, adequate coverage and performance.

The general steps (some of which have been discussed in various chapters in this book already) that should be part of a site survey include the following:

These are general steps, and each one builds on the other to complete a quality survey. Skipping any of these steps can make for problems during the installation or the actual implementation of the WLAN. Several topics have been discussed previously, and in this chapter details of the remaining topics are covered.

Obtain a Floor Plan or Facility Blueprint

You have learned about obtaining a floor plan or facility blueprint in Chapter 6, "Preparing for a Site Survey," and more details are included in Chapter 13, "Preparing the Proper Documentation," so the discussion of such is kept brief here.

Many survey tools, such as the AirMagnet Surveyor and Cisco Wireless LAN Solution Engine (WLSE), enable you to import many types of standard graphic formats such as JPEG and BMP files. This makes importing easy. If a drawing is not available, you should generate one, even if it is somewhat simplistic.

Make this drawing available in a printed version so that the engineer can easily make notes throughout the survey. Without this capability, it will be difficult to capture all the necessary information needed.

Inspect the Facility

When possible, personally visit the site before the survey begins. On-site visits enable you to understand the working conditions under which the WLAN will be used and the conditions under which you will perform the survey. A site visit will also help you determine which types of antennas might be used in a facility, determine whether any particular pieces of equipment might be needed for the survey, and give you a chance to inspect the overall site for unusual issues or concerns that could inhibit the completion of the survey.

This is the time that safety issues should be analyzed, and determinations made as to whether safety equipment or special clothing is required. It also gives you the chance to meet the on-site personnel and learn of any issues or concerns they have regarding your survey work.

Identify User Areas on the Diagram

User density should have already been specified in the initial WLAN design. Understanding the location of the userswhere they gather in numbers and where the WLAN is not neededis critical. These parameters should be well defined on the facility diagram. Make note of areas such as lunch rooms, conference areas, informal gathering areas, and even outdoor areas where users gather in numbers.

Another portion of this documentation task is to identify areas that have the common characteristics for physical user areas and density. For example, cubical areas tend to be similar in physical size and distribution in the same facility, making these areas very similar for user density. Similarly, conference rooms, meeting rooms, and so on, if similar in physical size, can be considered as like areas. Note any areas where the contents, applications to be used, number of users, and geographic location of users are similar. This helps when performing the user-density testing and is vital for using assisted site survey tools. The different types of areas might have different requirements for cell size and bandwidth.

Another task here is to identify areas where users require a constant connection while roaming from one point to another. In most cases, laptops are not used when physically in motion and represent a very small issue here. However, voice over IP (VoIP) phones, PDAs, bar code scanners, and other similar devices are commonly used while moving through some facilities, and you need to consider their requirement for constant connection.

Identify Potential Problems Areas on the Diagram

One of the first steps in a survey is a walk through the facility, which is needed to search for potential problem areas. From the diagram itself, you often can identify building-structure items such as elevators shafts, stairwells, and fire doors. These items tend to cause RF shadow areas and dead spots. If coverage is needed in these areas (as may be desired for seamless roaming with voice, for instance), take special care to place APs strategically for coverage.

Also note other wireless equipment or devices in the facility that might cause interference. This information can help you reduce problems that might occur if you place APs too close to these devices or systems (or prevent placement on the opposite side or a wall, hidden to the eye, but not the RF).

It is also a good idea to note items that might have RF reflections, which in turn might cause multipath signals, such as large metal doors, metal cabinets, or, as commonly found in many warehouses, secure areas that use a metal meshing as the walls. (See Figure 11-1.) This notation helps explain why an AP is placed in a particular location, or why a particular type of antenna is used.

Tip

While noting potential problems, be aware of things that can change in the environment. For instance, large metal doors might be open at the time you perform the survey, but might be closed at other times. Normally you want to perform a survey with all doors closed, even if they are usually kept open. In general, it is better to have a little extra overlapping coverage via open doors than to have closed doors blocking the RF signal and causing dead spots.

Identify AP Locations and Antenna Types

Identifying AP locations and the antennas to be used is the heart of any site survey project. Exactly how you identify these particulars will vary from one type of survey to another and from one site survey tool to another, but the overall results (that is, coverage and user performance) should be similar.

As you perform a survey, you need to have a good understanding of RF issues in the site, such as RF signal attenuation and how to identify RF interference. This knowledge will assist in identifying problem areas in the site. To determine where to place the AP and what antenna to use, a walkabout is performed and RF measurements are taken. These measurements are used to determine the RF coverage, identifying the edges of the APs' cell boundaries. This step also helps to identify the overlap needed between cells to ensure continuous RF coverage with no dead spots. Each of these topics is discussed in detail in the following section (and the differences between manual and automated/assisted survey methods are noted).

RF Issues in the Site

As discussed in Chapter 2, "Understanding RF Fundamentals," one of the first issues to be understood regarding WLAN site surveys is that distance between the AP and client affects WLAN bandwidth and therefore capacity. Unfortunately, when deploying any radio system, including WLANs, the laws of physics apply. RF signals propagating through the air are subject to attenuation, losing signal strength while encountering obstacles, both natural (including the atmosphere) and manmade.

To effectively deploy a WLAN, technicians must understand the causes of RF attenuation and what applicable countermeasures are available. This knowledge is extremely important to the site survey engineer as well.

As a rule, as the distance between a client and an AP increases, the signal strength decreases. And at some point the bandwidth has to decrease to maintain the connection. The actual attenuation will vary widely, and without testing and verification it is impossible to determine exactly the overall effect of all the objects in most sites.

As described in Chapter 2, as the frequency increases, the amount of attenuation produced by the atmosphere increases, reducing range. Unlike outdoor line-of-sight applications based on straightforward path-loss calculations, attenuation for indoor systems is much more difficult to calculate. The main reasons for this difficulty are the multipath signals that occur in most indoor sites and the different attenuation effects created by the various materials found indoors.

The algorithms used to estimate path loss are very complex and are used in the theoretical site survey tools. These algorithms differ from indoor to outdoor, and the attenuation of RF signals also vary. In Figure 11-2, notice that at distances up to 50 feet attenuation is very similar. Beyond this distance, however, the path loss indoors increases much faster. Even so, you can estimate that indoors approximately 100 dB of attenuation occurs over distances of 150 to 200 feet for 2.4-GHz signals. Remember, however, that attenuation is not linear and it increases exponentially as range increases.

Typical obstacles found indoors, such as walls, doors, and office furnishings, offer fairly consistent levels of attenuation. Some standard items can be estimated for attenuation, as shown in Table 11-1.

Some obstacles in the site might offer such a high level of RF attenuation that little or no RF penetrates it. Such a scenario usually results in an area with a high concentration of metallic content, such as steel floor pans, steel reinforced walls, metal mesh behind the stucco walls, elevators shafts, and so on. However, a high concentration of paper, cardboard, or other materials that contain a high level of moisture can causes serious problems for RF penetration, especially at 2.4 GHz. Even some types of tinted glass or energy-efficient glass can cause a high level of attenuation or RF shadows.

When performing a walkabout survey, note areas where the signal drops off rapidly. This generally indicates some type of RF shadow effect and might require a different placement of the AP and antenna so that the area has adequate RF coverage. In some cases, you might need to actually add an AP if the area is totally blocked (such as an x-ray room, metal-walled freezer area, or steel-reinforced section of a building).

Identifying these areas is critical for full coverage and for proper roaming with devices such as wireless phones. Site surveys techniques that do not use a client walkabout to assist in the survey often do not identify areas that will exhibit poor roaming. A totally automated survey just cannot guarantee there are no RF shadows and dead spots associated with shadow effects.

One possible problem mentioned earlier is fire or hazard doors. These are doors that must remain open during normal business hours, but close automatically to restrict the spread of a fire or other hazard. Although many sites do not anticipate using the WLAN during such an emergency, some sites might want to use voice or even PDAs to assess the hazard problem. Surveying with the doors open will likely lead to dead spots when the doors are closed. Obtain permission (and use signage to indicate work is in progress) to close the doors if the survey is being performed during business hours.

While moving throughout the facility during the survey process, you will find that the signal levels vary in strength. However, the amount of variation should not be pronounced over small movements. Because RF is an analog signal with many influences on its strength and propagation, the overall level will be somewhat linear over small movements, unless acted upon by an obstacle. Dramatic variations that occur when moving only short distances (inches and feet) can indicate a high level of multipath interference. For such areas, there are several possible solutions:

Use diversity antennas (recommended in any case)

Verify diversity is set to on in the AP

Move the AP (actually the antennas) farther away from any metal structures

Use a more directional antenna

Detecting Interference

As discussed in Chapter 6, the pre-site survey form should have a place to identify any known RF systems that are used on the site. However, not all sites will have a single document or even someone who knows all of the RF equipment that is in use. Most enterprise WLAN equipment has the capability to look for other WLAN devices (usually referred to as rogue AP detection), and some can even report other interfering signals. The spectrum analyzer. Spectrum analyzers enable you to view the entire spectrum, looking for signals that might not only be within the frequency range of the intended WLAN system, but could be near or at a frequency that could cause interference.

It is vital to the quality of interference detection to become proficient with a spectrum analyzer. To locate any possible interference from some non-802.11 transmitter (see the "Interference from Non-802.11 Equipment" sidebar), use a higher-gain antenna on the analyzer, a peak hold function to capture any signals that are on line for a short period of time, and proper resolution and video bandwidth settings.

Existing WLAN devices represent another common source of interference. If the existing device uses a separate band (900 MHz, for instance), then this should not cause an issue. However, it is still recommended to keep some minimum distance between any two RF devices (minimum of 3 feet, or about 1 meter) even if they are on different bands.

When installing a system in the same facility that has competing RF on the same band, exercise extreme caution during the installation to keep interaction to a minimum. For example, when adding an 802.11b or 802.11g system to a site that has an existing frequency-hopping (FH) system, maintain a minimum of 10 feet (3 meters) between the 802.11b or 802.11g and the FH system RF components.

Another common issue with regard to interference is the rogue AP (that is, the AP that some employee has brought in and put into the network without the consent of the IT staff). This type of AP can cause several issues, with the number one being security (because rogue APs typically do not conform to the IT security requirements).

The second issue is interference with the properly installed WLAN. If not identified before the walkabout portion of the survey begins, it can cause missed packets and higher noise-floor readings, which in turn might trigger the need for another AP in that location. These devices should be "sought and destroyed" before starting a survey.

Some WLANs systems offer rogue AP detection utilities, but require the WLAN to be fully installed and operational before they can be used. Therefore these utilities are more for maintaining a WLAN and identifying rogue APs in an operation WLAN and not for use as part of a site survey.

You might feel like there is far too much to think about regarding interference, but that is not necessarily the case. Although 2.4 GHz does have many more possibilities of interference (because of more devices on the market), in reality you will have few interference problems with a WLAN when surveyed and installed correctly.

The Walkabout Test

The walkabout is one step in performing any site survey and completing any WLAN design. Although the process is nothing more than actually walking through a facility, taking measurements, and verifying coverage levels, it is a vital step that must not be overlooked, and it must be done logically. During the walkabout, you verify the signal attenuation of objects, define cell boundaries, identify noise-floor problems, and verify communication between a client and an AP at the appropriate data rate, all of which help to determine where to place an AP and what type of antenna to use. As stressed throughout this book, skipping the walkabout test will result in a WLAN with one of two problems: dead spots or a highly overengineered, and therefore highly expensive, WLAN. A proper walkabout mixed with other survey techniques and appropriate design is the only way to guarantee the best performance, efficiency, and economy. But how is this vital step completed? Take a look at the steps to identify the boundaries of a wireless cell, as well as to verify the proper overlap of coverage between cells.

Defining the Cell Boundaries

When you start to do either a user-density test (discussed later in the section "Performing a User-Density Test") or a manual survey, you need definitions for the cell boundariesthat is, what constitutes the edge or limitation of the cell. To establish the cell boundaries, you first need to define the following parameters:

Chapter 10, "Using Site Survey Tools," one of the parameters that needs to be set correctly is the packet size. Packet size is dependent upon the applications that will be used in the site. This should be set to the largest packet that will be used. If the system will be used for standard Ethernet access, the packets size should be set to 1400 bytes (or as high as 1518 depending on the limitations of the site survey tools).

Data rate The AP should be set to the minimum data rate permitted in the design.

Transmitter power TX power needs to be set to either the maximum transmitter level of AP (if you are using the same AP model for the survey as for the installation) or to the maximum level of the AP intended for deployment.

So now that you have set the appropriate parameters in the AP for performing the RF tests, it is time to place the AP in a location in the site and take some measurements. Before proceeding, however, you need to define the measurements and RF test results that will determine the cell boundaries.

As mentioned in Chapter 10, you use three major items to determine whether the signal is adequate for proper WLAN performance:

Signal strength

Noise level

Packet retry counts

Together these three can provide not only a good indication of cell boundaries, but also assist the survey engineer to understand why communication issues exist at certain points.

As the client is moving away from an AP, the signal level will be getting lower overall. There will be some fluctuations because of multipath signals, but in overall scope the signal level should gradually decrease. To determine the edge of the coverage for a data network, refer to the values listed in receiver sensitivity) indicates the absolute minimum performance of the receiver at the given data rate. This particular table contains the values for the Cisco Aironet 802.11a/b/g combo card. These values should be set according to the equipment that will be used (the worst-case device). Notice that the minimum recommended RX threshold is 10 dB greater (less negative) than the RX threshold. This provides a 10-dB margin for fluctuations produced by multipath, body movement, body shadows, and so on.

As you understand by now, signal strength alone is not adequate to determine coverage. The table also defines the absolute minimum S/N values for the device to receive and decode a signal properly. Again in this case the values are for the Cisco Aironet 802.11a/b/g combo card, but they are similar to most other devices for the 2.4-GHz band. Next to this column is a recommended minimum S/N value. It is also easy to see that this has the same 10-dB ratio when compared to the minimum S/N value.

Now that you have defined the signal parameters, the final step is to look at overall communications link quality. That is determined by the packet performance. The minimum loss of packets should never exceed 10 percent. Although 10 percent might sound high to engineers who have been working in a wired network world, for RF it is normal to have a few percentage points of lost packets. That is the nature of RF. And at 10 percent for the edges of the cell, the retry mechanism for the data retry protocol will ensure there is no noticeable performance impact to the user in a data environment.

If the packet loss is higher than 10 percent, and the signal strength is also high, verify the noise floor and S/N values. A high noise floor can cause loss of packets. If the noise floor increases, the minimum signal level will also need to increase. Watch for large fluctuations in packet loss and signal strength, indicating an area where multipath is very likely.

Notice that Table 11-2 is for data communications. Wireless voice is a whole different beast than data and requires different minimum recommended values for cell boundaries. If the WLAN system is going to be using voice, overall cell boundaries need to be a bit stronger. Table 11-3 shows some changes to the recommended values.

In Table 11-3, notice that the margin for the recommended minimum signal level and S/N values has increased to 15 dB. This is due to the nature of voice, and the critical necessity for maximum performance in packet transfer. Missed packets in voice are immediately noticeable to the user's ear. Therefore, not only has the minimum recommended value been increased, the maximum packet loss has been reduced to a much lower limit.

Finally, notice that the data rates below 5.5 Mbps are missing. Although it is recommended in most voice applications to maintain an 11-Mbps or higher data rate, a few vendors of wireless voice products do suggest allowable usage of data rates as low as 5.5 Mbps, but nothing lower.

Figure 11-3 shows the defined cell boundaries.

For different devices or different bands, these signal level and S/N values will change. It is important to understand the devices' technical specifications so the criteria can be defined. Using the same Cisco Aironet 802.15 a/g combo card, and looking at the 5-GHz performance as shown in Table 11-4, it is easy to see the differences from the 2.4-GHz band shown in Table 11-3. Although the overall margins have been kept consistent (for the data networks), the overall levels have changed because of differences in the radio capabilities.

Using the parameters defined in Tables 11-2, 11-3, and 11-4, you can define or verify the boundaries of a cell. In defining a cell, however, you must determine where one cell ends and another begins. To put it another way, how much overlapping coverage should occur between cells, and how do you verify that? The next section addresses these issues.

Overlapping Cell Coverage

Just as important as cell boundaries is the concept of overlapping cell coverage. Excessive overlap of coverage can result in some channel interference, unnecessary AP-to-AP roaming (by client devices that have a limited roaming algorithm), and added expense because of more APs being required.

A typical overlap in coverage is set to about 10 percent to 15 percent of the overall cell coverage area. Some engineers try to place a minimum signal level for both APs. Suggesting that the cell boundary of AP 1 is at 72 dBm (for some given data rate) and the signal level of the other AP at that point is 57 dBm seems to indicate some amount of overlap. However, this can be difficult to correlate to a percentage of overlap. Because signal levels vary from site to site, the signal strength of adjacent cells is very much dependent on the contents of the site.

Using a site map, as shown in Figure 11-4, with correct dimensions, you can define what the 10 percent or 15 percent overlap is. When performing the final walkabout, verify not only cell boundaries, but also that cell overlap is within the acceptable range.

To summarize, cell boundaries for a 2.4-GHz 11-Mbps cell for data use only (using the data for the Cisco Aironet 802.11a/b/g card) can be determined by the following parameters:

At the edge of the coverage area, the lowest signal strength should be 72 dBm or higher.

At the edge of the cell, the minimum S/N should be 20 dB.

Packet loss should be no more that 10 percent.

Overlapping overage should be defined by the site map, and verification should be made that the adjacent AP can be heard with values greater that the minimum recommended thresholds.

Also it is important to remember that the client settings used in this cell boundary test process should match the actual network application scenario, as well as emulate the RF performance of the worst-case client that will be used in the WLAN system.

Performing a Manual Survey

The manual site survey is still by far the most popular and the most accurate, but it is also the most time-consuming and work intensive (but then again you don't get quality work without a little effort!). There are many ways to get started with a manual survey, but one that is very common is the "outside-in" survey method. This is where you start at the outside of the area and work toward the center. It is logical and accurate and provides for a very smooth workflow.

It is recommended that an analysis of the ambient RF environment be performed. After that, set the test AP on a channel that has no activity in the desired area.

Consider, for example, a typical retail site. In such, maximum range is needed, because there are only a minimum number of users; user density is not an issue. To start, an AP is placed near a corner of the facility, as shown by reference point A in Figure 11-5. Next, using the parameters defined for cell boundaries, perform a survey and determine where the edge of the coverage is. Mark this on your site plan for a temporary AP location, as shown in Figure 11-5.

You might wonder why the AP is placed in the corner. Well, 75 percent of the signal is outside the facility, and that is what we do not want! However, this is not where the AP will get installed; this is just for a starting point. Here the AP is located in the corner along with a standard antenna (in this case, placed at ceiling level with a 5.2-dBi omni antenna hanging down from the ceiling).

On the site map, locate the approximate center of the coverage arc, as shown by reference point B in Figure 11-5. This will be the new location of the AP for testing. The rationale here is that if the client can communicate from point B to the AP at point A, they should still be able to communicate when the devices are reversed (with the AP at point B and the client at point A). And a minimum amount of signal will extend beyond point A outside the facility, but there will be adequate coverage at point A. Just guessing where point B needs to be based on the site map could result in more energy outside the facility than necessary (or desired), or not enough signal to reach the inside corner, resulting in a dead spot.

Figure 11-6 shows the revised location of the AP with the associated coverage area. Notice the corner of the facility is fully covered as well.

Repeat the same effort for points C, E, and G, as shown in Figure 11-7. After you complete this step, you might need to fill in the center areas if there is still more coverage needed. Because the number of users were defined to be higher in the stockroom, the two area APs (F and H) were slid back slightly to provide adequate overlap and to provide more signal into the storeroom (which results in fewer main store users on these APs because less area of the main store is covered by these APs).

Knowing the average coverage ranges, you can make an estimated guess as to where to place the next AP. In Figure 11-8, point J is selected and its overall coverage tested and noted. In this case, it provides more than enough overlap to the adjacent cells. Take care to verify that it does not overlap with enough cells so that it could interfere with some other cell on the same channel. If this is the case, reducing the power level on this AP (or moving to a smaller antenna) should be considered. Next place an AP at point K and test to complete the site coverage.

Retail stores are typically one of the easiest sites to survey because of their physical nature and contents. So what happens when things get a bit more congested, less open, and coverage requirements and user densities vary? That just takes a little more work. You can use the same scheme throughout the facility. In some cases, however, it requires a little different logic. This can be a more linear movement, starting at one point and moving across the facility as you might do in a warehouse, or just working one section at a time (for a health-care or education facility wing, for example).

Now look at a large do-it-yourself home-improvement warehouse. This type of facility has tall racking that extends up to near the ceiling and runs in long rows. Using an omni-directional antenna to cover something like this is usually not a feasible solution. The use of some type of directional antenna is more common and provides a fairly easy installation by placement along the walls. As shown in patch antenna is placed at one end of the building, with the energy directed down the aisle. The coverage is then tested to see how much coverage is obtained, and exactly how well the RF extends down the aisles.

In this particular case, notice that one AP and a patch antenna provides about 3 to 4 rows of coverage, a little more than 50 percent of the way down the building. Placing another AP several rows over, as shown in Figure 11-10, would provide verification of coverage for adjacent aisles. Using this test, you could analyze that placing APs in the locations shown in Figure 11-10 would provide coverage for the entire facility.

However, it might be worthwhile to test another alternative before deciding on the final approach. Exchanging the patch antenna (8.5 dBi) for a higher-gain (13.5 dBi) Yagi antenna might provide enough range to fully reach down the aisles. This might eliminate the need to place APs at the back of the facility. Because the higher-gain antennas have a narrower beam width, however, they will likely not cover as many rows, requiring more APs along the front of the facility. In the long run, if the number of APs ends up being identical, it might be easier to install and require fewer cable runs to have all the APs on a single wall. This, in the long run, can be less expensive to install. Figure 11-11 shows the coverage obtained with Yagi antennas.

For certain types of facilities (education and health care, for example), you confront several issues. The first is the exposure of the products, or the physical security. In most of these cases, the AP and antenna have to be secured either out of sight or with some type of locking mechanism. Therefore, antennas such as Yagis or omnidirectional, which hang down from the ceiling, are typically not an option. This requires some thought as to possible antenna types and placements.

In some schools, the determination has been made to place one AP in every classroom. This gets quite expensive, but provides the overall best bandwidth performance. Such installations use a very low 1-mW power setting, and some even go beyond that and install an attenuator on every antenna, reducing not only the transmitter power, but also the ability to hear distance clients. Failing to reduce the overall radiated power would create far too much overlap between APs on the same channel.

The IEEE 802.11d specification enables the client to change the frequency of operation and the power levels, based on information received from the AP. This is primarily done to provide a client that can roam from one regulatory domain to another. In some cases, a few WLAN products enable the client to match exactly the power settings of the AP.

For health-care facilities, in some areas the required bandwidth varies drastically. For normal hallways and patient rooms, where the network is used for patient records or perhaps bar code scanning of medicines, bandwidth and redundancy are not critical to patient life and death. In most cases, the WLAN is a requirement for normal operation; if there is a location where the WLAN has failed, however, the user could revert back to the old paper and pen method. If the WLAN goes down, it only affects the overall efficiency of the work that is being done. However, in cardiac care units (CCU) or intensive care units (ICU), where the WLAN is used in the monitoring of the patients' vitals, this is very different. The WLAN is used as a life-monitoring system, and it must be up at all times. In these situations, there should be enough overlap of APs to provide absolute redundancy of coverage. (See Figure 11-12.) In these cases, some overlap of the same-channel cells might be necessary. There should be no area where a client cannot hear at least two different APs.

Another way to ensure redundancy is to use APs that perform hot standby. In a hot standby setup, two APs are mounted at each location. One AP is in standby mode and monitors the other AP. If a problem occurs, the standby unit takes over.

When trying to survey something such as a hospital wing or office building with long hallways and identical offices, your best bet is not the use of omnidirectional antennas. In many cases, low-gain patch antennas might work well. In the case of the five floors depicted in radiation, however, it did cover some of the floors above and below, so alternating ends of hallways allowed enough coverage to "bleed over" so that full coverage was obtained. In this case, a Yagi might have worked, but the aesthetics of the Yagi were not conducive to the facility.

While surveying, you need to consider another dimension: vertical. RF is three-dimensional in that it radiates in all directions. Facilities that are more than a single floor need special attention. In these situations, it is important to survey on floors above and below to verify where coverage comes into play. You can reduce undesired floor-to-floor coverage by using specific antennas. However, be sure to rotate channels of APs so that the same channel is not used directly above or below an AP on the same channel. (See Figure 11-14.)

Documenting the Site Survey

As you complete every cell, stop and document the coverage area, AP location, and antenna type. You can use this information for notes for the final documentation (discussed in Chapter 13); this information also proves useful as you move to the next cell area to survey, helping you judge well where to place the AP to start the survey process for the next area. This is also a good time to make any notes about issues or possible problems that you discovered but were not included in the pre-site survey documentation.